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Acknowledgements
1 wish to lhank the many firms, organisations and individuals who have providedme with assistance and malcrial during the writing of lhis book.
For guidance provided in their specialist areas I would like (0 thankMe W. Cole, Welding Manager and Mr I. Waugh, Ship Manager, both of SwanHunter Shipbuilders.
To the firm of Swan Hunter Shipbuilders, now a member of British Shipbuilders, I wish 10 extend my thanks for their permission to use drawings andinformation based on their current shipbuilding practices.
The following firms and organisations contributed drawings and informationfor various sections of this hook, for which I thank them:
AGA Welding LtdAustin and Pickergill LtdBlohm and Voss, A.G.DOC CUlling MachinesBrown Brothers & Co. LtdCammcll Laird ShipbuildersCape Boards and Panels LtdClarke Chapman LtdDookin and Co. LtdF.A. Hughes and Co. LtdFlakt Ltd (S.F. Review)Glacier Metal Co. LtdHempel's Marine PaintsHugh Smith (Glasgow) LtdInternational Maritime OrganisatonUoyd's Register of Shipping
MacGregor Centrex LtdMoss Rosenberg Verft, AS.Odense Steel Shipyard ltdPhilips Welding IndustriesPhoceenne Sous-Marine, S.A.Power Blast ltdRockwool Co. (UK) ltdSigma Coatings LtdStone Manganese Marine LIdStone VickersStrommen Staal, A.S.Taylor Pallister and Co. ltdThe DeVilbiss Co_ LtdThe Ntn'aJ ArchitectVoith GmbHWilson Walton International ltd
Contents
The ship - its functions, featutes and types
2 Ship stresses and shipbuilding materials
3 Shipbuilding
4 Welding and cutting processes
5 Major structural itemsA Keel and bottom construction 72B Shell plating, framing systems and decks 77C Bulkheads and pillars 85D Fore end construction 92E Aft end construction 101F Superstructures and accommodation 116
6 Minor structural items
7 Outfit
8 Oil tankers, liquefied gas carriers and bulk carriers
9 Ventilation
10 Organisations and regulations
II Corrosion and its prevention
12 Surveys and maintenance
13 Principal ship dimensions and glossary of terms
Index
13
"72
125
134
165
185
197
213
223
229
235
1
The Ship- its Functions,Features and Types
Merchant ships exist 10 carry cargoes across the waterways of the world safely,speedily and economically. Since a large pan of the world's surface.approximately three·fifths. is covered by water. it is reasonable 10 consider thatthe merchant ship will continue to perform its funclion for many centuries 10come. The worldwide nalure of this function involves the ship, its cargo and itscrew in many aspects of inll~rnational life. Some It:atures of this internationaltransportation. such as weather and climatic changes, availability of cargohandling facilities and international regulations. will be considered in laterchapters.
The ship, in its various forms. has ~volved to accomplish its functiondqxnding upon three main factors - the type of cargo carried. the type ofconstruction and materials used. and the area of operation.
Three principal cargo-carrying Iypes of ship exisl loday: Ihe general cargoftSSel, !he lanker and the passen~r ve~1. The general cargo ship functionstoday as a general carrier and also, in several particular forms, for unit-based orunitised cargo carrying. Examples include container ships, pallet ships and 'roll·on, roll-ofr ships. The tanker has its spedalised forms for the carria~ of crudeoil, refined oil products, liquefied gases, etc. The passenger ship includes,senerally speaking, the cruise liner and some ferries.
The type of construction will affect the cargo carried and, in some generallyinternal aspects, !he characteristics of !he ship. The principal types ofconstruction refer to the framing arrangement for stiffening the outer shellplating, the three types being longitudinal, transverse and combined framing. Theuse of mild steel, special steels, aluminium and other materials also influencesthe characteristics of a ship. General cargo ships are usually of transverse orCOmbined framing construction using mild steel sections and plating. Mosttankers employ longitudinal or combined framing systems and the larger vesselsutilise high tensile steels in their construction. Passenger ships, with their largeareas of superstructure, employ lighter metals and alloys such as aluminium toreduce the weight of the upper regions of the ship.
The area of trade, the cruising ra.nge, the climatic extremes experienced, mustall be borne in mind in the design of a particular ship. Ocean-going vesselsreqUire several tanks for fresh water and oil fuel storage. Stability and trimIrrangemenu musl be satisfactory for the weather conditions prevailing in the
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The general cargo ship is the 'maid of all work', operating a worldwide 'goanywhere' service of cargo transportation. II consists of as large a clear opencarga<arrying space as possible. together with the facililies required for loadingand unloading the cargo (Figure I./). Access to the cargo storage areas or holdsis provided by openings in the deck caJled hatches. Hatches ar~ made as large asstrength considerations will allow to reduce horizontal mO\'emenl of cargowithin the ship. Hatch covers of wood or steel, as in most modern ships, are usedto close the hatch openings when the ship is at sea. The hatch covers are madewatertight and lie upon coamings around the hatch which are set some distancefrom the upper or weather deck to reduce the risk of flooding in heavy seas.
One or more separate de<:ks are fitted in the cargo holds and are known astween d~cks, Greater flexibility in loading and unloading, together with cargosegregation and improv~d stability. are possible using the tween deck spaces.Various combinations of derricks, winches and deck cranes are used for thehandling of cargo. Many modem ships are fitted with deck cranes which reduce
(I) General cargo ships.(2) Tankers.(3) Bulk carriers.(4) Container ships.(5) Passenger ships.
General cargo ships
2 Th~ Ship - 111 Functions, Features and Types
area of operation. The strength of the structure. its ability to resist the effects ofwaves, heavy sus. etc., must be much greater for an ocean-going \'essel than foran inland waterway vessel.
Considerations of safety in all aspects of ship design and operation must beparamoun!. so The ship must be seaworthy. This term relates to many aspects ofthe ship: it must be capable of remaining anoat in all conditions of wC3ther; itInust remain alloat following all but the most serious damage: and it muslremain stable and behave well in the various sea states encountered. Some of theconstructional and regulatory aspects of seaworthiness will be dealt with in laterchapters. Stability and other design aspects are explaincd in dt'uil III .VOl'o/Architecture {or Marine Enginccrs. by W, Muckle (Bulterworths, 1975).
The development of ship types will continue as long as there IS a sufficientdemand to be met in a particular area of trade. Recent ynrs ha\'c seen suchdevelopments as very large crude carriers (VlCCs) for the transport of oil. andthe liquefied natural gas and liquefied petroleum gas tankers for the bulkcarriage of liquid gases. Can tainer ships and \ roriou5 barge o.:arriers have developedfor general cargo transportation. Bulk carriers and combination bulk cargocarriers are also relatively modern developments.
Seveul basic ship types wiJI now be conSidered in further detail. Theparticular features of appearance. construction. layout. size. etc. will beexamined for the following ship types:
Many other types and minor \~.triations exist. but the above selection isconsidered to be representative of the major part (If the world's merchant neeL
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The tanker is used to carry bulk liquid cargoes, the most common type being Iheoil tanker. Many other liquids are carried in tankers and specially constructedvessels are used for chemicals, liquefied petroleum gas. liquefied natural gas. etc.
The oil tanker has fhe cargo<arrying section of the vessel splil up intoindividual tanks by longitudinal :lnd Iransverse bulkheads (Figure 1.2). The cargois discharged by cargo pumps fitted in one or more pumprooms either at theends of the lank section or SOmetimes in the middle. Each lank has its ownSuction arrangement which connects to the pumps. and a network of pipingdischarges the cargo to the deck from where il is pumped ashore. No doublehellam is filled in the cargo<anying section of an oil tanker. Fore and aft peaktanks are used for ballast. with often a pair of wing tanks Situated juSt forwardof midships. These wing tanks are ballasl-only tanks and are empty when theship is fuJly loaded. Small slop tanks are fined 3t the after end of the cargosection and are used for the normal carriage of oil on loaded voyages. On ballastruns the slop tanks are used for sloring the contaminated residue from tank.cleaning operations.
Large amounts of piping are 10 be seen on the deck running from the pump.rooms to the discharge manifolds positioned at midships, port and starboard.Hose.handling derricks are fiued porl and starboard near the manifolds. The
Tankers
Refrigerated general cargo ship
4 Th~ Ship - Irs Functions. F~QturesQndTypn
cargo·handling limes and manpower requiremenls. A special heavy.lift derrickmay also be fitted. covering one or two holds.
Since full cargoes cannot be guaranteed with this type of ship. ballast<arryingtanks must be fitted. In this way the ship always has a sufficient draught forslability and 10lal propeller immersion. Fore and afl peak tanks are fitted whichalso assisl in trimming the ship. A double bollom is filled which eXlends Ihelength of the ship and is divided into separate tanks, SOme of which carry fueloil and fresh water. The remaining lanks are used for ballast when the ship issailing empty or partly loaded. Deep lanks may be filled which can carry liquidcargoes or Water ballasl.
The accommodation and machinery spaces are USUally located with one holdbetween them and th'e aft peak bulkhead. This arrangement improves the vessel'strim when it is partially loaded and reduces the lost cargo space for shaftingtunnels compared with the cenltaJ machinery space arrangement. The Currentrange of sizes for general cargo ships is from 2000 to 15000 displacemenl lonneswith speeds of 12-18 knots.
The filling of refrigeration planls for the cooling of cargo holds enables thecarriage of perishable foodstuffs by sea. Refrigerated ships vary lillie fromgeneral cargo ships. They may have more than one tween deck, and all holdspaces will be insulaled to reduce heal transfer. Cargo may be carried frozen orchilled depending upon its nature. Refrigerated ships are usually faster thangeneral cargo ships, offen having speeds up to 22 knots, and they may alsocater for up 10 12 passengers.
Th~ Ship _ Itt FUllction!. Featu"S and Types 7
,c<:onltnodatiOn and machinery spaces 3re located aft in modem tankers. Therange of sizes fOf oil tankers at present is enorrnous. from small to 700000deadweight tonnes. S~eds range from 12 to 16 knolS. Oil lanke", 3rc dealt
W'ith in more detail in Chapter 8.
6
Bulk C8rrtel'$
(jquefied gas tankers are used to carry. usually at low tem~ratufe. liquefieduo
1eumgas (LPG) or liquefied natural gas (LNG). A ~parate inner tank is
~IY employed to contain the liquid and this lank is supported by the outer
.uall which has a double bottom (Figure 1.3).LNG tankers carry methane and other paramn products obtained as a by'
product of petroleum drilling operations. The gas is carried at atmosphericpressure and temperalUres 3S low as _164°C in tanks of special materials (seeT.b/~ 2.3). which can accept the low temperature. The tanks used may beprismatic. cylindrical or spherical in shape and self·supporting or of membrane~RStruction. The containing tank is separated from the hull by insulationwhich also acts as a secondary barriet in the event of leakage.
LPG tankers carry propane. butane. propylene, etc .• which are extracted(rom natural gas. The gases are carried either fully pressurised. part pressurisedpart refrigerated or fully refrigerated. The fully pressurised tank operates at 18bat and ambient temperature. the fully refrigerated tank at 0.25 bar and -saoc.Separate containment tanks within the hull are used and are surrounded byinsulation where low temperatures are employed. Tank shapes are eitherprismatic, spherical or cylindrical. Low temperature steels may be used on the
hull where it acts as a secondary barrier.Displacement siltS for gas carrie", range up to 60 000 tonnes, with speeds of
12-16 knots. liquefied gas carrie", are dealt with in mme detail in Chapter 8 .
Bulk carriers are single-deck vessels which transport single-commodity cargoessuch as grain. sugar and ores in bulk. The cargo-carrying section of the ship isdivided into holds or tanks which may have any number of arrangements,depending upon the range of cargoes to be carried. Combination carriers are bulkcarriers designed for flexibility of operation and able to transport anyone ofsew:ra1 bulk cargoes on anyone voyage. e.g. ore or crude oil or dry bulk cargo.
The general.purpose bulk carrier. in which usually the central hold sectiononJr is used for cargo. is shown in Figurcs 1.4 and 1.5(a). The partitioned tankswhich sunound it are used for ballast purposes either on ballast voyages or. inthe~ of the saddle tanks, to raise the ship's centre of gravity when a lowdenSIty cargo is carried. Some of the double·bottom tanks may be used for fueloil and fresh water. The saddle tanks also serve to shape the upper region of thec~go hold and trim the cargo. Large hatchways are a feature of bulk carriers,SUIte they reduce cargo-handling time during loading and unloading.. An ore carrier has two longitudinal bulkheads which divide the cargo sectiontnto wing tanks port and starboard, and the centre hold which is used for ore.The high double bottom is a feature of ore carriers. On baUast voyages the wing
Liquefied gas tankers
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The ore/bulkfoil carrier has a cross-section similar to the general bulk. carriershown in FIgUre 1.4. The structure is, however, significantly stf<;.nger, since thebulkheads must be oiltight and the double bottom must withstand the highdensity ore load. Only the central tank. or hold carries cargo, the other tank.areas being ballast-only spaces, except the double bottom which may cany oil
fuel or fresh water.Large hatches are a feature of aU bulk. carriers, to facilitate rapid simple cargo
handling. A large proportion of bulk carriers do not carry cargo-handlingequipment, because they trade between special terminals which have particularequipment for loading and unloading bulk commodities. The availability of<:argo-handling gear does increase the flexibility of a vessel and for this reason
The Ship _ Its Functioru, Frorures and Types 9
pnlc.s and double bottoms provide baUast capacity. On loaded voyages the ore is(;&fried in the central hold. and the high double bottom serves to raise the centreof pvity of this very dense cargo. The vessel's behaviour at sea is thus muchiJnproved. The cross·section is similar to that of the ore/oil carrier shown inFrpre J.5fbJ. Two longitudinal bulkheads are employed to divide the ship into~nue and wing lanks which are used for the carriage of oil cargoes. When orcis carried, only the centre tank section is used for cargo. A double bottom isfitted beneath the centre tank but is used only for water ballast. The bulkheads
and hatches must be oillig,ht.
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Container ships
The container ship is, as its name implies, designed for the carriage of containen.A container is a re·usable box of 2435 mm by 2435 mm section, with lengthsof 6055, 9125 and 12190 mm. Containcrs arc in use for most general cargoes,and liquid--earrying versions also exist. In addition. refrigcrated models are inuse.
The cargo--earrying section of the ship is divided into several holds which havehatch openings the full width and length of the hold (Figure 1.6). The COntaincrsarc racked in special frameworks and stacked one upon the other within the holdspace. Cargo handling therefore consists only of vertical movement of the cargoin the hold. Containers can also be stachd on the hatch covers where a lowderuily cargo is carried. Special lashing arrangements exist for this purpose andthis deck cargo to SOme extent compensates for the loss of underdeck capaCity.
The various cargo holds are separated by a deep web-framed structure toprovide the ship with transverse strength. The ship section Outboard of theContainers on each side is a box-like arrangement of wing tanks which provideslongitudinal strength to the structure. These wing tanks may be utilised forwater ballast and can be arranged to COunter the heeling of the ship whendischarging containers. A double bottom is also fitted which adds to thelongitUdinal strength and provides additional ballast space.
Accommodation and machinery spaces are usually lOCated aft to provide themaximum length of full·bodied ship for container stowage. Cargo-handling gearis rarely fitted, as these ships travel between speciaUy equipped terminals forrapid loading and discharge_ Container ship sizes vary considerably withcontainer-earrying capacities from 100 to 2000 or more. As specialist carriersthey are designed for rapid transits and are high powered, high speed vesselswith speeds up to 30 knots. Somc of the larger vessels have triple-screwpropulsion arrangements.
Passenger ships
The passenger liner, or its modern equivalent the cruise liner, exists to provide ameans of luxuriow transport between interesting destinations, in pleasantclimates, for its human cargo. The passenger travelling in such a ship pays for,and expects, a SUperior standard of accommodation and leisure facilities. Largeamounts of superstructure are therefore an essential fealure of passenger ships.Several tiers of declo are fitted with large open lounges, ballrooms, swimmingpools and promenade areas (Figuu J. 7).
AestheticaJly pleasing lines arc evident with Usually well.raked clipper-typebows and unusual funnel shapes. Stabilisers are fitted to reduce rolling and bowthrust devices arc employed for improved manoeuvrability. large passengerliners arc rare, the moderate-sized cruise liner of 12000 tonnes displacementnow being the more prevalent. Passenger-carrying capacity is around 600, withspeeds in the region of 22 knots.
10 Thf! Ship - Its Functions. F~Qtuns lUTd Types
it is sometimf!S fitted. Combination carriers handling oil cargoes have their owncargo pumps, piping systems. f!tc., for discharging oil. Bulk carriers are dealtwith in more detail in Chapter 8. Deadweight capacities range from small to150000 tonnes depending upon type of cargo, etc. Speeds arc in the range of12-J6 knots.
12
RoilingP'ICh,"'iI
Fif(Ure 1.1 Ship mOl'l!ml!nl - thl! silt dl!grl!~ offreedom
The forces may initially be classified as static and dynamic, Static forces are dueto the differences in weight and buoyancy which occur at various points alongthe length of the ship. Dynamic forces result from the ship's motion in the seaand the action of the wind and waves. A ship is free to move with six degrees offreedom - three linear and three rotational. These motions are described by theterms Ylown in Figure 2. J.
These static and dynamic forces create longitudinal, transverse and localstres.ses in the ship's structure. Longitudinal stresses are greatest in magnitudeand result in bending of the ship along its length.
13
The ship at sea or lying in still water is being constant!)' subjected \0 :I widevariety of sueues and strains. which result from the action of (orces fromoutside and within the ship. Forces within the ship result from structural weight.cargo. machinery weight and the ef(ects of operating machinery. Exterior forcesinclude the hydrostatic pressure of the water on the hull and the action of thewind and waves. The ship must at all times be able to resist and withstand thesemesses and strains throughout its struClUre. II mUSI therefore be conslrucledin a manner, and of such materials, that will provide the necessary strength. Theship must also be able to function efficiently as a cargo-carrying vessel.
The various forces acting on a ship are constantly varying as to their degreeand frequency. For simplicity. however. they will be considered individually andthe particular measures adopted to counter each type of force will be outlined.
2
Ship Stresses andShipbuilding Materials
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Ship Stresses and Shipbuilding MateriDls IS
Longitudinal stresses
Static loading
If the 1h.ip is considered floating in stm water, two different (orctS will be actingupon it along ils length. The weight of the ship and its contents will be actingvertically downwards. The buoyancy or vertical component of hydrostaticpressure will be acting upwards. In total. the two forces exactly equal andbalance one another such that the ship floats at some particular draught. Thecentre of the buoyancy force and the centre of the weight will be vertically inline. However. at particular points along the ship's length the net effect may bean excess of buoyancy or an excess of weight. This net effect produces a loadingof the structure, as with a beam. This loading results in shearing forces andbending moments being set up in the ship's struCture which tend to bend it.
The stalic forces acting on a ship's structure are shown in Figure 2.2(Q). Thisdistribution of weight and buoyancy will a.Iso result in a variation of load, shearforces and bending moments along the length of the ship. as shown in FlgU.res221bj-(d}. Depending upon the direction in which the bending moment acts,the ship will bend in a longitudinal vertical plane. This bending moment isknown as the still water bending moment (SWBM). Special terms are used todescribe the two extreme cases: where the buoyancy amidships exceeds theweight, the ship is said to 'hog', and this condition is shown in Figure 2.3;where the weight amidships exceeds the buoyancy. the ship is said to 'sag', andthis condition is shown in Figure 2.4.
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16 Ship Stressf?s and Shipbuilding Materials
Dynamic loading
If th\: ship is now considered to be moving among W<lves. the distribution ofweight will stll! be the sam\:. The distrihution of huoyancy. however, will varya.s a result of the waves. the movement of the Sllip will also intwduce dynamicf01C\:5.
The traditional approach to solving this problem is to convert this dynamicsituation into an equivalent statk une. To do this, the ship is assumed to bebalanced un a static wave of trochoidal form and length equal to the ship. Theprofile of a wave'll: sea is considered to be 1I trochoid. This gives waves where thecreslS are sharper than the troughs. The wave crest is considered initially atmidships and then at the ends of the ship. The maximumqagging and saggingmoments will thus occur in the structure far the particular loaded conditionconsidered, as shown in h'gure 2.5.
Ship Sm:,.~~·{·1' and Shipbuilding Materials 17
decks and compressive stresses in lh-e bottom shell. This stressing, whethercompressive aT tensile. reduc('s ill magniwuc lowuds a position kn'J'wn <lS theneutral axis. The neutral3xis in a ship is somewhere below half the depth and IS.
in eflect. a horizontal line drawn tluou.gh the centre uf gravity of the snip'ssection.
The fundamental bending cqmltiol1 for:1 beam is
r y
where M is tile bending moment, f is the second moment of area of the se-ctionabout its neutral axis, 0 is the stress at the outer flbre-s. and y is the distancefrom the neutral axis to the OUter fibres_
This equation has been proved in ful1·scalc tests to be applicable to thelongitudinal bending of a srup. From the eq uaLioll the expression
0=M
fly
Figure 2.5 Drnami.c loading oj" ,hips ,Irm:furc. ra) still waler cOf/dition: (bj ,aggin/fwndition, Ie) Jwgging condition
The total -shear force and bending moment are thus obtained and these willndude the still water bending moment t;onsidered preViously. If actual IoadJng~onditions for the ship aTe considered which will make the above conditionslIorse, e.g. heavy loads amidships when the- wave trough is amidships, then thenaximum bending moments in normal operating servic-c can be found.
The ship's stmcture will thus be subjected 10 constantly fluctuating streSSesesulling from these shear forces and bending moments as the waves move alonghe ship's lengtll.
;tressing of the structure
:he bending of a ship causes stresses to be set up within its structure. When ahip sags, tensile stresses are set up in the bottom shell plating and compressivetresses are set up in the deck. When the ship hogs, tensile stresses occur in the
is obtained for the stress in the material at some distance y from the neutralaxis. The values M. I and y can be determined for the ship, and the resultingstresses in the deck and bottom -shell can be fuund. The ratio f!y is known as tnesection modulus. Z, when y is measured to the extreme edge of the section. Thevalues are d-etermineJ for the midship scction, since the greatest moment willoccur at or near midships (see Figure 2.2). A mme detailed explanation of thisprocess is given in Muckle's work, Nrrval Architecture jar Marine Engineers,previously cited.
The stmctura.l materil:l1 induded in the calculation for the second moment Jwill be all the lungitudinal material which extends fm a considerable proportionof the ship's length. This material will include side and bottom shell platin;g,inner bottom plating (where fitted). centre girders and decks. The materialforms what is known as the hull girder, whose dimensions arc very largecompared to its thicknesS.
Transverse stresses
Static loading
A transverse section uf a ship is subjected to static pressure fmrn the surroundingwater in addition to -the loading resulting from the weight of the structure,cargo, etc. Although transverse stresses are oflesser magnLtude than longitudinalstresses, considerable distortion of the structure ~ould ocellI, in the absence ofadequate stiffening (Figure 2.6).
The parts of the structure which resist transverse stre-sses are transversebulkheads, Ooors'in the double bottom (where fitted), deck beams, side framesand the brackets between them and -adjacent structure such as tank top flooringor margin -p13tes.
Figure 2.6 SIiW"C woterpremm" Joadingo[a ship'! ~r/'lJCfur"
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Ship Stresses lmd Shipbuilding Muterials J9
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In heavy weather, when the ship is heaving and pitching, the forward end leavesand re-enters the water with a slamming effect (Figure 2.8). This slamming downof the forward region on to the water is known as pounding. Additional
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18 Ship Stresses and Shipbuilding Mat~rillh
When a ship is rolling it is accelerated and decelerated, resulting in forces in thestructure tendmg to distOIt it, This condition is known as racking and its- greatest
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stiffening must be fitted in the pounding region to reduce thl;' possibility ofdamage to the structure. This is discussed further in Section A of Ch..ptel 5.
---~ Panting
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effect is felt when the ship is in the- light or ballast condition (Figure 2. 7). Thebrackets and beam knees. joining horizontal and vertical items of structure areused to resist this distortion.
The movement of waves along a ship causes fluctuations in water pressme on the,plating. Th~ tends to create an in-and-out movement of the shell plating, knownas panting. The effect is particularly evident at the bows as the ship pushes itsway through the water.
The pitching motion of the ship produces additional ·..ariatiuns in waterpressure, particularly at the bow and stem, which also cause panting of theplating. Additional stiffening is provided in the form of panting beams andstringers. This is discussed further in Section 0 of Chapter 5
Localised stresses
The movement of a ship ill a: seaway results in forces being generated which aJelargely of a local nature. These forces are, however, liable to cause the structmeto vibrate and thus tranunit stresses to other pans of the structure.
Localised loading
Beary weights, such as equipment in the mac-hinery spa<:cs or particular items ofgeneral cargo, can give rise to localised distOItiOfl. of the transverse section(Figure 2.9). Arrangements fm sp-r-c-adil1g HLC load, addilional stiffening andthicker plating are methods used in de.aling with this problem.
20 Ship srresses {Jtld Shipbuilding MateriaA
Ddlec,;"" n', "Id·jng
-- --,--".
Cargo
foIgurc 2,9 Loca/ircd 'Mds rendinf{ to distort the ship's Hrur:W re
Superstructures and discontinuities
The ends of superslructures represent major discontinuities in the ship'sstructllTe where a considerabJ.e change in section modulus occurs. Loc.aJisedst,resses. will. occur wllich may result in cracking of adjacent structure. Sharp(flscontmuitle, are therefore to be avoided by gradual tapers being introJuced.Thicker strakes of deck and shell plating may also be fitted at these points.
Any aoles or -openings cut in decks create similar areas of hig.lllocal stre,s.Well-rounded comers musl be used where openings are necessary, and doublingplates may also be filled. In the case of hatchways the bulk of the longitudinalstrength matl;rial is concentrated outboard of the hatch openings on either sideto reduce the change in sccHan modulliS al tile openings, This is discussedfurther in Sections Band F of Chapter 5.
Vibr.ations
Vibrations- set up in a: ship due to reciprocating machinery, propellers, etc., canresult in the setting up of stresses in the structure. These are cyclic stresseswhich could result in fatigue failure of local items of structure leading to mmegeneral collapse, Balancing of machinery and adequate propeller tip clearancesc-an rcduoCC the effects of vibration to acceptable proportions. Aplirt fmmpossible damage to equipment and structure, the presence of vibration can bemost uncomfortable to any passengers and the crew.
The design of the slmcture is outside the scope of this book. The variousshipbuilding materials used to provide the structure will now hI; considered.
Steel
Ste~l is the basic shipbuilding material in use today. Steel may be regarded asan lron-carbon alloy, usually containing other elements, the carbon content flot
Ship Stresses and Shipbuilding Materials 21
usually exceeding ilbout 2%. Special steeh of high tensile strength are used oncertain highly stressed parts of Ihe shi~'s structure. Aluminium alloys haveparticular applications in the constructlOn of superstructures, espeCIally on
passenger ships.
Production
'Acid' OJ 'basic' are terms often use-d when referring to -steels. The re~erence is t.othe production process and the type of furnace lining, e.g. an alkaline or baSlclining i-s used to produce basic ~teel. The choke of furnace linmg IS dictated bythe raw mateJials used in the manufacture of the steet There are three partlcular
esses currently used for lne m-3TIufacture of carbon steeL namely the open~:th process, the oxygen or basic oxygen steel proces~ and the elec:tric furnace
racess. In all these processes the het molten metal is exposed to alT o.r oxygenp hich oxidises the impurities to refine the pig iron into high quality steeLW In the open hearth process a long shallow furnace is used which is fired fromboth ends. A high proportion of steel scrap may be used in this process .. Htghqua!jty steel is produced whose properties can be controlled by the addltlOn ofsuitable alloying elements. . ..
In the oxygen or basic oxygen steel proce-s~ the molten metal IS contamed ma basic lined furnace. A jet of oxygen is injected into the molten metal by anoverhead lance. Alloying elemcnts can be introduced into the rno1ten metal anda high quality steel is produced.
In the electric furnace process. an electric arc is struck between carbonelectrodes and the steel charge in the fum-ace. Accurate control of tne finalcomposition of the steel and a high standard of purity are possible with thisprocess,
Finishing treatment
Steels from the above·mentioned processes will all contain an excess of oxygen,usually in the form of iron oxide. Several finishing treatment~ are possible in thermal casting of the steel.
Rimmed ~teeJ is produced as ~ resuli of little ur no treatment to removeOxygen. In the molten state the oxygen combines with the carbon in the steel.roCleasing carbon monoxide gas. On solidifying, an almost pure iron ollter surfaceis formed. The central core of the ingot is, however, a mass of blow holes. Hotrolling of the ingot usually 'welds up' thes.e holes but tnick plates of this materialare prone to laminations.
Killed steel is produced by fixing tlw OXygCll hy the addition of aluminium or&ilicon before pouring. the steel into the mould. The uluminium or s.llicon.produoCes oxide~ reducing the iron oxides to iron. A homogeneous rnatenal otsuperior quality 10 rimmed s(cd is thus produced. , ,
Balanced or sl;mi·kilkd steels arc an intermediate form ot steel ThIS resullsfrom the beginning of the rimming process in the mould and its termination bytne use of deoxidi~ers.
VaoJ.U1ll degassecl steels are produced hy reducing the atmospheric pressureWhCli the steel is ill the llloltc-n state. The equilibrium between carb~)n and
'"I",
Ship Stresses and Shipbuilding MateriD/J 23
,.,
sundard steel sections
..nety of standard sections are produced ~ith vatting scantlings to suit their~tion. The stiffenin~ of plates and sections utihses one or more of these~. which are shown m Figure 2. J O.
Norma/u;ng. The steel is heated to a temperature of 850-950°C dependingupon its carbon content and then allowed to cool in air. A hard strong steel witha refined grain structure is produttd.
22 Ship Stresses and Shipbuilding MaleriDls
oxygen is thus obtained at a much lower level and the oxygen content becomesvery small. Final residual deoxidation can be achieved with the minimumadditions of aluminium or silicon. A very 'clean' steel is produttd with goodnotch toughness properties and freedom from lameUar tearing problems(lamellar tearing is explained in Chapter 4).
The composition of steel has a major influence on its properties and this willbe discussed in the next subsection. The properties of steel are further improvedby various forms of heat treatment which will now be outlined. In simplifiedterms the heat treatment of steels results in a change in the grain structure whichalters the mechanical properties of the material.
,.,.... 1.10 St.,.d4ud Jtt~l UCtiOllJ: (tI) fltlr plllr~: (b) Dffut bulb pllllt: (cJ tqutzl tln,le;(d) unequal tlfIIlt; (t) chtlMtI: tnla
Annazling. Again the steel is heated to around 850-950°C. but is cooledslowly either in the furnace or in an insulated space. A softer more ductile steelthan that in the normalised condition is produced.
Hardening. The Sleel is heated to 8S0-9S0°C and then rapidly cooled byquenching in oil or water. The hardest possible condition for the particular steelis thus produced and the tensile strength is increased.
Tempuing. This process follows the quenching of steel and involves reheatingto some temperature up to about 680°C. The higher the tempering temperaturethe lower the tensile properties of the steel. Ontt tempered, the metal is rapidlycooled by quench;-:g.
J[,,, ,., ,,,
Composition and properties
Various terms are used with reference to steel and other materials to describetheir properties. These terms will now be explained in more detail.
Tensile strOlgrh. This is the main single criterion with reference to metals. Itis a measure of the material's ability to withstand the loads upon it in service.Terms such as stress, strain, ultimate tensile strength, yield stress and proofstress are all different methods of quantifying the tensile strength of thematerial. The two main facton affecting tensile strength are the carbon contentof the steel and its heat treatment following manufacture.
Ductility. This is the ability of a material to undergo permanent changes inshape without rupture or loss of strength. It is particularly important wheremetals undergo forming processes during manufacture.
1fIlrdnen This is a measure of the workability of the material. It is used as anassessment of the machinability of the material and its resistance to abrasion.
Toughness. This is a condition midway between briulenm and softness. Itis often quantified by the value oblained in a notched bar test.
lIIlipbuiding .-Is
The steel used in ship construction is mild steel with a 0.15-0.23% carbonctJDtent. The properties required of a good shipbuilding steel are:
(I) Reasonable cost.(2) Easily welded with simple techniques and equipment.(3) Ductility and homogeneity.(4) Yield point to be a high proportion of ultimate tensile strength.(5) Chemical composition suitable for flame cutting without hardening.(6) Resistance to corrosion.
These features are provided by the five grades of mild steel (A-E) designatedby the C~fication societies (see Chapter 10). To be classed, the steel for shipco:;urucli?n must bt manufactured under approved conditions, and inspected,:' prescnbed tesu must be carried out on selected specimens. Finished material...;~ped Wi.~ the ~ety's brand. a symbol with L superimposed on R beingof r~OYd s ~gLSter. The chemical composition and mechanical properties
a Ie eClion of mild steel grades are given in Table 2./.
Tlble 2.1 PROPERTIES AND COMPOSITION OF SOME MILD STI::r:LS '"~UlIImult'
M/"Imllm /1'I1S1l1i MiltlmulIIC N, 51 S P A' yield SIfI'U SI'f!U f'/ollxallm, (1I/1"J)'(%) ,%) (%) (%) (%) (%) (N/mm') IN/mm') (%) (J)
LR 'A' 0.23 2.5)(. C 0.50 0.05 0.05 - 230 400-490 22mUd ncel mu. min. mlUl. mu. mux.
LR '0' 0.21 0.70- 0.10- 0.04 0.04 0.015 '" 400-490 22 413\mUd liCe! mix. 1.40 0," mu. m",. min. O·C
LR 'E' 0.18 0.70- 0.10- 0.04 0.04 0.015 '" 400 490 " 27 DImild stcel mIX. !.SO 0.50 mIX. mIX. min. -41f('
Tlble 2.2 I'ROPERTIES AND COMPOSITION OF SOME HIGHER TI~NSILE sn:I~LS
Uf,i",/I/tMillimum 1('II,IIt MI,,/"',m'
C N, 51 S P AI )'/t/d1/"'11 I/,rll "/WllfulltN' (7I/UP)'(%) (%) ("') (%) (%) (%) (N/mm') (N/mm'l f%' (J)
LR 11.1132 0.18 0.70- 0.50 0.04 0.04 0.015 "' 440-590 22 )1 a1m",. 1.60 mu. mu. max. min. UaC
LR AIU6 0.18 0.70- 0.50 0.04 0.04 0.015 '" 490-62U " .l4 almax. 1.60 max. max. mix. min. O"C
LR Eli 36 0.18 0.70- 0.10- U.04 0.04 0,0]5 '55 490-620 " )4 IIImu. 1.60 0.50 max. mu. min. -40·C
Table 2.3 PROPERTIES AND COMPOSITION OF TYPICAL LOW TEMPERATURE CONSTRUCTIONAL MAT1~RIALS
Mlllimum U1/fm/l/ey/tld or proof Itlullt Minimum
C N, Sf S P AI "' C, N. fl"" "rtnx,h e/onpl/on OI/1rpy("') (%) ("') (%) '''') (%) ,"') ''''' "'» (N/mm') (N/mm' ) (%) (l)
Low carbonstaWeu steel 0.03 1.2 0.75 0.02 0.02 - 10.7 18.5 - '" 560 SO 103 alAISI304 m.... -196"C
36% Nlalloy 0.09 0.3 0.' om 0.02 - 3.5.8 - - 11S 480 " 147 II((nvu) -196"C
51' Nillul 0.20 0.30- 0.15- 0.035 0.035 - 4.5- - - .., .590-740 20 881\m.... 0.60 0.35 mix. mIX. S.O -120'C
91' Ni steel 0.13 0.' 0.15- 0.040 0.035 - 8.5- - - 587 690-830 22 34 IIm.... m.... 0.)0 mIX. mu. •.s -196'C
C. N, 51 N, I:e AI Z, C, TI,"') ,"') ("') ,%) ("') ("') (%) (%) (%)
Aluminium 0.10 0.40- 0.40 4.0- 0.40 Rem. 0.2.5 0.05- 0.15 ". m 16Illoy S083 mu. 1.0 max. ••• m.... max. 0.25 max.
~~o.
N~0.
~~0.
2~0.
~~0.
N~0.
~~0.
-"<-
•24 longitudinal18 tnnsveue
"
24 Iongiludinal18 tnnsverle
2I5
'00
lIlrimtueunsile Yilld MinimumstTerJrtlt stms tlO#Igarion(Nfmm') (Nfmm' ) (%)
'00
'30
Si S P(':I) (':10) (")
C M.(':I) (':10)
Castings and forgings
The larger castings used in ship construction are usually manufactured fromcarbon or carbon manganese steels. Table 2.4 details the composition andproperties of these materials. Examples of large castings are the sternframe,bossings, A-brackets and parts of the rudder. The examples mentioned mayalso be manufactured as forgings. Table 2.4 also details the composition andproperties of materials used for forgings.
26 Ship Streue$ and Shipbuilding Materillls
Developments in steel production and alloying techniques have resulted in theavailability of higher strength steels for ship construction. These higher tensUestrength (HTS) steels, as they are caJled, have adequate notch toughness,ductility and weldability, in addition to their increased strength. The increasedstrength results from the addition of alloying elements such as vanadium,chromium, nickel and niobium. Niobium in particular improves the mechanicalproperties of tensile strength and notch ductility. Particular care must be takenin the choice of electrodes and welding processes for these steels. Low hydrogenelectrodes and welding processes must be used. Table 2.2 indicates the chemicalcomposition and mechanical properties of several high tensile steel grades. Aspecial grade mark, H, is uSt'd by the classification societies to denote highertensile steel.
Benefits arising from the use of these steels in ship construction inclUdereduced structural weight, since smaller sections may be used; larger unitfabrications are possible for the same weight and less welding time, although amore specialised process, is needed for the reduced material scantlings.
Cryogenic or low temperature materials are being increasingly used as aconsequenct of the carriage of liquefied gases in bulk tankers. Table 2.3 detailsthe properties and composition of several of these cryogenic materials. The mainaiterion of selection is an adequate amount of notch toughness at the operatingtemperature to be encountered_ Variow alloys are principally used for the verylow temperature situations. although special quality carbon/manganese steelshave been used satisfactorily down to -50°C.
Sleet castings 0.23 1.6 max. 0.60 0.04 0.04max. but nOI max. max. max.
less IhVl,X C
Slee) forgings 0.23 0.30- 0.45 0.045 0.045nwt. 1.70 mu. max. max.
Sleel forliDas 0.30 0.30- 0.45 0.045 0.045(not UlleDded 1.50 max. max.forwddind
28 Ship Srreues and Shipbuilding Marerials
AJuminium alloys
The increasin8 use of aluminium alloy has resulted from its several advantagesover steel. Aluminium is about one·third the weighcoLstee1 for~uivalent
volume of material. Ibe use or-aluminium alloys in a structure can result illreaucllons or~of the weight of an equivalent stul structure. This reductionin weight. particularly in the upper regions of the structure, can improve thestabi't 0 e vessel. This follows from the lowering of the vissel's centri:or.~ resu.!!ing...in.-arLiJ:lcr ase me en nc ~Sta6ility is discussed indetaIfliirluckle's Naval Archir«tu~ for MQrin~ Engineen. The corrosionresistance_of aluminium is very good but careful maintenance and insulationfrom the adjoining steel structure are necessary. The properties required of analuminium alloy to be used in ship construction are much the same as for steel.namely strength, resistance to corrosion, workability and weldabililY. Theserequirements are adequately met. the main disadvantage being the high cost ofaluminium.
The chemical composition and mechanical properties of the common shipbuilding alloys are shown in Table 2.5. Again these are classilication societygradings where the material must be manufactured and tested to the satisfactionof the society.
1 J 11FiKu" 211 Aluminium tll/oy J«riOllS
Aluminium alloys are available as plate and section. and a selection ofaluminium alloy sections is shown in FiguTf! 2.1 J. These sections are formed byextrusion. which is the forcing of a billet of the hot material through a suitablyshaped die. Intricate or unusual shapes to suit particular applications are therefore possible.
Where aluminium alloys join Ote stul structure, special insulatingarrangements must be employed to avoid galvanic corrosion where the metalsmeet (see Chapter II). Where rivets are used, they should be manufactured froma corrosion-resistant alloy (see Table 2.5).
Materials testing
Various qualities of the materials discussed so far have been mentioned. Thesequalities are determined by a variety of tests which are carried out on samplesof the metal.
The terms 'stress' and 'strain' are used most frequently. Stress or intensity ofstress, its correct name, is the force acting on a unit area of the material. Strainis the deforming ofa material due to stress. When the force applied to a materialtends to shorten or compress the material Ote stress is termed 'compressive
Ship Srreue! and Shipbuilding Marerial! 29
• When the force applied tends to lengthen the material the stress is termed..-:. tress'. When the force tends to cause the various paru of the material....; ~ver one another the stress is termed 'shear stress',..,. tensile test is used to determin.e the ~ehaviour of a material up to ,its
'fhe point. A specially shaped specimen piece (Figure 2. J2) of standard sue~ in the jaws of a testing machine. A load is gradually applied to draw• <Is of the bar apart such that it is subject to a tensile stress. The original......
1---- 5.65,S",----I
1_' 7.65"'S,,_o.._~-_.1,.,
";i 10 ......
I•
1---- t" • 511-----11_.--,.",·._.·.--_·1
101
~ 2.12 Ttrfsilt tnt sp«imt1U: (tI) [or pitltn. !rripl tI1Id ItcriOiU Itl • tJrickntlf o[mrHtrial): (b) [or hot-ToIftd btlr
IeIt length L1 of the specimen is known and for each applied load the newleasth L2 can be measured. The specimen will be found to have extended bySOIne small amount L2-L 1 • This deformation, expressed as
Extension
Original length
is known as the linear strain.Additional loading of Ote specimen will produce results which show a
~orm increase of extension until the yield point is reached. Up to the yield~t the removal of load would have resulted in the specimen returning to its~~. Stress and strain are therefore proportional up to the yield point, ore ~ limit as it is also known. The stress and strain values for various loadsCIn shown on a graph such as Figure 2. J3.
30 Ship Strene3 and Shipbuilding Materill/3Slr~,s
Ship Stresses and Shipbuilding Materloli 31
'['his coMtan t is known as the 'modulus of elasticity' (E) of the material and hasthe same units as stress. The yield stress. is the value of stress at the yield point.Where a clearly defmed yield point is not obtained a proof stress value is given.nus is obtained by a line parallel to the stress-strain line being drawn at somepercentage of the strain, such as 0.1%, The interse~tion of this line willi thes.treSS-strain line is considered the proof stress (see FIgure 2.14).
The bend test is used to determine the ductility of a material. A piece ofmaterial is bent over a radiused fanner. sometimes through 180 degrees. Nocracks or surface laminations should a.ppear in the material.
Impact tests can have a number of forms but the Charpy vee-notch test isusuallY spedfied. The test specimen is a 10 mm square cross-section, S5 rnm inLength. A vee-notch is cut in the centre of one face, as shown in Figure 2.15. The
St,iker
F,aClU'~
----==~----/
"Yi~ld PC"'''€laS;i~ limi,
Yiel-d <Ues;
Ultimateton,il.lIre \5
Figure 2.13 Srre~~-st/1lin gNIph for mild steel
Slress
Ultimate F-racluretemiie,lre.1P'u"f f,tr~ss
Speci",en
//
NotCh
/"
Figure 2.15 Chllrpy impilet test
St,ain
Figure 2.14 Stre!r-mairz graph /0' higher leftl'ile steel
-I '_O.'%I\ra'n
[1' thor testing worriO c()nlinued bey()nu Ilw ),jeld point the spcdml;."n wouLd'neck' or reduce in clUs:;-'edlon. Th-o loau value, divided by the originalspeClInen CIOSS-5Cc!lIJnal ale:> would give the ~harc shown in Figure 1.13. Thehighest value of stress is known a~ the ultimate tensile ,tress (llTS} of th~material.
Within the clastic limit, stre~:; i:; proportiumJ tll strain. and theretore
specimen is mounted horizontally with the notch axis vertical. The test involvesthe specimen being struck opposite the notch and fractured. A striker orhammer on the end of a swinging pendulum provides the blow which breaks thespecimen. The energy absorbed by the material in fracturing is measured by themachine. A particular value of average impact energy must be obtained for theDUlterial at the test temperature. This test is particulariy important for materialsto be used in low temperature regions. For low temperature testing the specimenia cooled by immersion in a bath of liquid nitrogen or dry ice and acetone forabout 15 minutes. The specimen is then handled and tested rapid.y to minUnlseany temperature changes. The impact test, in effect, measures a material'sresistance to fracture when shock loaded.
A dump test is used on a specimen length of ba.r from which rivets are to bemade. The bar is compressed to half its original length and no surface cracksmust .appear. Other rivet material tests include bending the shank until the twoends touch without any cracks or fractures appearing. The head must also acceptflattening until it reaches two and a half times the shank diameter.
== constantSIres:;
Shain
33
e•
e•
e e e e
• ~ • •L
t'-......... I':::L . ·v .
V
"" '/V V
l/ l/
o
•
, e e, • •-•-.
t-................. r--...~
b9-." ........
r; \~
'\
I)
1/ ~I)
/ 1/ ~~ ••"-7 V "
The main function of the shipyard's design and drawing offices is to produce theworking d~wings to satisfy the owner's requirements. the rules of thec1assifiation societies and the shipyard's usual building practices. A secondary,but nevertheless important, function is to provide information 10 the productionplanning and conlrol departments, the purchasing departments. etc .. to enablesteelwork outfitting and machinery items to be ordered and delivered to satisfythe building programme for the ship.
Closely follOWing the basic design drawings will be the production of thelines plan. This plan (Figu" 3.1) is a scale drawing of the moulded dimensionsof the ship in plan, profile and section. The ship's length between the forwardand after perpendiculars is divided into ten equally spaced divisions or stationsnumbered 1 to 10. Transverse sections of the ship at the various stations aredrawn to give a drawing known as the body plan. Since the vessel is symmelTical.half·sections are given. The stations 0 to 5 representing the after half of the shipare shown on the left side of the body plan with the forward sections shown onthe right. The profile or sheer plan shows the general outline of the ship, anysheer of the decks, the deck positions and all the waterlines. For clarity, thedeck positions have been omitted from Figure J.1 and only three waterlines areshown. The various stations are also drawn on this view. Additional stations maybe used at the fore and aft ends, where the section change is considerable. Thehalf-breadth plan shows Ihe shape of the waterlines and the decks formed byhorizontal planes at the various waterline heights from the keel. This plan isusually superimposed upon the profile or sheer plan. as shown in Figure 3.1.
The initial lines plan is drawn for the design and then checked for 'fairness'.To be 'fair' all the curved lines must run evenly and smoothly. There must alsobe exact correspondence between dimensions shown for a particular point inall the three different views. The fairing operation, once the exclusive province:of a skilled loftsman, is now largely accomplished by computer programs.
32
Building I ship is a complex prottSS involving the many departments of the shipbuilding organisation. the arrangement and use of shipyard facilities and themany skills of the various personnel involved. Those departments directlyinvolved in the construction, the shipyard layout, material movement and theequipment used will be examined in tum.
Drawing office
3
Shipbuilding
~•• ~.II "!.1~
'Q-• -l i ~~
i ~~• ~li
vi..;
~ •..;
~~
ii,,
tr> ~
f-
I/
/
f-
I--
,....-_c-
- f-f--
(
\\-\\-
\h
\UJ
With plan approval the ordering of equipment, machinery, steel section andplate, etc., will begin and the plans will be issued to the various productiondepartments in the shipyard. The classification society, the owners and theirrepresentatives in the shipyard also receive copies of the plans.
During the manufacturing processes, as a result of problems encountered,feedback from previous designs, modifications reque5ted by the owner, etc.,amendments may be made to plans. A system of plan recall, replacement ormodification in the production departments must be available. This ensuresthat any future ships in a series do not carl)' the same faults and that co"ectiveaction has been taken.
The fundamental design plans and basic constructional details must all receiveclassification society approval and, of course, the shipowner's approval. Unwuaiaspects of design and innovations in coostructional methods will receive specialattention, as will any depanures from standard practice. Progress is not hinderedby the classification societies, whose main concern is the production of a soundand safe structure.
The shipowner will normally have clearly indicated his requirements from thedesign inception and his approval of plans is usually straightforward. Most largeshipowning companie5 have a technical staff who utilise their practicalexperience in developing as near perfect and functional a design as possible.
Steel ordering
Plan approval
34 Shipbuilding
Once fairtd. the final lines plan is prtpartd and a tablt of offsets is compiledfor usc in producing the ship's plates and frames.
The traditional practice of drawing plans according to structural areas suchas the shell, the deck, the double-bottom framing, elC., is inconvenient in manycases since the ship is nowadays buill up of large prefabricated units. A unit mayconsist of shell plating, some framing and part of a deck. An expansion of aship's shell is given in Figure 3.2, sho.....ing the positions of the various units.Plans are therefore drawn in relation to units and contain all tht informationrequired 10 build a particular unit. A number of traditional plans arc stillproduced for classification society purposes, future maintenance and reference,but without the wealth of manufaclUring information which is only needed onthe unit plans.
The planning and production control departments require drawinginformation to compile charts for monitoring progreSS. compiling programmes,producing programmes for material delivery, parts production and assemblyand finally unit production and erection.
Plan issue
The ordering of steel to ensure availability in line with programmed requiremenU is essential. It must therefore begin at the earliest opportunity,
36 Shipbuilding37
•~
~.;:, ~
~ ~, •v~
;~,-~,,~,-g~
~<:•-;,:~~t
L
1
Il
" i i<<
"•• ,., - .".,
•"!• g
i "• •
H '1!ti.
t !r~\
~\~
On~Unth scale lofting
With one-tenth scale lofting the mould loft becomes more of a drawing officewith long tables. Fairing is achieved using the one-tenth scale drawings. Thescrieve board is made to one-tenth scale, perhaps on white-painted plywood.One-tenth scale drawings are then made of the ship's individual plates. Thesednwings may then be photographed and reduced in scale to one-hundredth offull size for optical projection and marlting of the plates. Alternatively, theone-tenth scale dnwings may be tnced directly by a cutting machine head.
occasionally before plan approval where delivery problems may occur. Thesteel ordering is a key function in the production process. requiring involnmenlwith the drawing office. planning departments. production departments and thest~1 supplier. The monitoring and control of stock is also important. since thesteel material for a ship is a substantial part of the ship's final cost. Stock heldby a ~ipyard represents a considerable capital investment.
Loh work
A numerical control system is one where a machine is operated and controlledby the insertion of numerical data. The numerical data is a sequence of numberswhich fully describe a part to be produced. In addition, the use of certain codenumbers enables instructions to be fed into the machine to enable it to operateautomatically. A reading device on the machine converts the numbers intoelectrical impulses which become control signals for the various parts of themachine which produce the finished part.
Numerical control
Loft work takes place in a mould loft. The mould loft is a large covered areawith a wooden floor upon which the ship's details are drawn to full size or somesmaller more convenient scale. Much of the traditional loft work is now doneby computer but some specialist areas still require wooden templates to bemade, mock-ups to be constructed, etc.
In the traditional mould loft operation the lines plan and working drawinginformation is converted into full-scale lines drawn on the 10ft noor. From theselines the (airing or smoothness of the ship's lines is checked and a scrieve boardproduced. A scrieve board is a wooden board with the body sections at everyframe spacing drawn in. Once the ship's lines arc checked and fair, a half-blockmodel is constructed by joiners usually to about 1!50th scale. This model hasthe exact lines of the ship and is used to mark out the actual plates on the shell,giving all the positions of the butts and seams.
The loftsman can now produce templates for marking. cutting and bendingthe actual plates using the full·size scrieve board markinp.s in conjunction withthe plate positions from the model. A table of offsets is produced finally for thevarious frames and plates, giving manufacturing information for the varioustndes involved in production.
38 Shipbuilding
. The i~pul data for the machine is initially produced from drawings and offsetInformal.lon. !he various parIS to be produced 3rc programmed and then coded~r deSCribed In numeri~~ terms. Punched card, punched tape or magnetic tapeIS then p~oduced contalrung I~e numerical data. The card or tape information isthen fe~ mlo a compuler neSlang program. The various pariS are then 'nested' orecono~lcally fi."ed into a standard plate size (Figurr 3.1). A final punched ormagnetIC tape IS. produ~ed Which. is. used for the operation of the numericallycontrolled machine. ThIS process IS illustrated by a simple now chart in Figu~4. rr
Shipbuilding 39
sler before, during and after the various pro~esses in shipbuildin~ utilisesuan handling appliances. such as overhead travelling cranes, vacuum 11ft cranes~l8JIetic cranes, roller conveyors, fork.li~t equipment, etc...o The various steel parts in plate and sectlon form are now Jomed to~ether by
lding to produce subassemblies, assemblies and units. A subassembly IS several~ of steel making up a tw<Htimensional part which, together with other:=emblies, will join to form a unit. Subassemblies may weigh up to 5 tonnes
are and examples would be transverses, minor bulkheads and web frames;;-;n 3.6). Assemblies consist of larger, usually three-dimensional, structures
Shipyard layout
The sh.i~yard layout is arranged to provide a logical ordered now of materialsan~ equlpme~l towuds the final unit build-up, erection and outfitting of theship_ The vanous production stages are arranged in work areas or 'shops' and asfar as .pracli~ble. in modem yards, take place under cover. The sequence' ofeve,U$ IS outlllled In Figu~3.5.
SVl'I\ITIeltd ---ItauUal
oPrdiminafy ship desip
Dra, oC delaikd plans • Slet! ordered
ApproVal oC plans and iuue Stet! dtlivUed
•LoClwork and production oC _______
taMe 0+ oirK'ls ~
lillie oC stet! and production begunt
Material prtpantion - lhot4:llutinl and priminl
•Manuearure oC plates and sections - marltins. euttinl. macb.in.in,: and shapina
Subassemblies and assemblies produced
Units CiriC&'ed and delivered to the berth
V· •
nits erected, Caired and wdded
Figuft 3.' Ship/NUdill1 ttqutnct Olt~nrlt
~t~el ~I~tes and sections are usually stored in separate stockyards and fed intotheu ,indIVIdUal sh~t-blasting and priming machines. The plates are cleaned byabrasl,ve .shot o.r gnt and then coated with a suitable prefabrication priming paintto a lumted thickness for ease of welding, The major areas of steel are thereforeprotected from corrosion dUring the various manufacturing processes whichfollow.
'J?te plates. and sect,ions follow their individual paths to the marking or direct.cutting ma~hiner;: w~ch produces the suitably dimensioned item, Flame cuttingor mechamcal. guillotmes ~ay be u~d. Edge preparation for welding may alsobe d~ne at this stage. Vanous shaping operations now take place using platebendmg rolls, presses, cold frame benders, etc., as necessary. The material
~Inpplng o<ad<~t
Notchtor~11
~m
Figt.lrt 3.6 SubotsrmbJ)' - "'rb fr(Jmr
of plating and sections weighing up to 20 tonnes. Flat panels and bulkheads areexamples and consist of various pieces of shell plating with stiffeners andperhaps deep webs crossing the stiffeners (Figure 3.7). The flat or perhapscurved panel may form part of the shell, deck or side plating of, for instance, atanker. Units are complex built·up sections of a ship, perhaps the comolete foreend forward of the collision bulkhead, and can weigh more than 100 tonnes(Figure 3.8), their size being limited by the transportation capacity of the yard'seqUipment.
The various subassemblies, assemblies or units are moved on to the buildingberth or storage area until required for eJl!ction at the ship. At this stage, orperhaps earlier, items of pipework and machinery may be fitted into the unitin what is known as pre-outfitting, Once erected at the berth the units are cut tosize, where necessary, by the removal of excess or 'green' material, The unitsare faired and tack welded one to another and fmally welded into place to formthe hull of the ship,
40 Shipbu.ildingShipbuilding 41
/,,-_-1
--r-"-
--.,. -._--
FiliUrc 1.8 lJmr
l(}ng',tud'ln~1
bulk"~6rl
Inn~r bottom plating
A typical m.achine will first water-wasb then heat·dry the plates hefore descalil1g.The plates are then simultaneously shot-blasted both siJ-e-s with metallic abrasive.The plate is fed in horizontally at speeds of llP to 5 mfmin, and around 300 trhof shot are projected on to it Blowers and suction deYi.ces remove the shotwhich is cleaned and recycled. The clean plates are immediately cove rca with acoat of primmg paint and dried in an automatic spraying machine (Fi/(Ure 3.10).A thickness of about 1 mm of compatib-le priming paint is applied to avoidproblems with fillet weLds on to the plating.
Plate straightening or levelling is achieved by using a plate rolls machine (Fi;;UTe3.]1). This consists basically of five large rollers, the b(lHom two being driven
Straightening
Shot.blasting and priming
Materials preparation
Plates and sections received from the stcel mill are shot·blasted to remove scale,primed with a temporary protectivc pai'llt and finally straightened by rolling to
remove any curvature.
SI,IFene,
Fij?Ufe], 7Assembly
Materials handling
The layout ,of .a shi~yard should aim tu reduce materials handling to.a minimumby appro~nate locatIOn of -",ark s~ations Dr areas. The building of large uni ts andthe <:apaclty to transport them will reduce the number of items handled but willre-quue greater care and more- sophisticated equipment. The building of a ship isas ~uch gov.erned by the shipyard layout as the materials handling equipmentand Its capacity.
An. actual shipyard ~yout is shown in Figure 3.9. The progression of~ate~a1S through the .vanous production stages can deaIly be seen. The various, arkinE pro~esses which the plates and sections undergo will naw be ex.aminedm more detail.
42 .. Shipbuilding 43
tain
,.,
Straightlmed plate
/Bottom sUPp<>rtingrolle.~
00000
Figure 3.11 Platestroighrcning
Bottom roller
Figure ).10 Automatic paint-spraying plant
T ra"e,..ngcarriage
Secti(Jn th,origh rQlle-r
v
Bent r;lale~
Pla~•
-
w.
],~."/iiltM
~0 Spray C()nUmina~Vf'late
"''' ", 11,...."ing._ - .r Plale -d~i~" -,
Filto<!',d
RQII"(, . -. • ai', - e,,-~.ustI
conveyor r -"---l
• •
and the top ones idling. The top roners can be adjus.ted for height independentlyat each end and the bottom rollers nave adjustable centres. A number of smallerSUpporting rollers are positioned around the five main rollers. The plate is fecithrough with the upper and lower rollers spaced at its thickness and issubsequently straightened. This machine is also capable of bending and flangingplate.
r;~ ,. ~~ ~i
1-:;='1"~':'~5,,~,;,~o~"~"~"~~=I-t- __ '~""'--__J_.~~~ ~ :i rluawlRaJl Jallaj,ll!; ::;: Ii;- --pJRl.lPOll Jaua,I!1-S /..eq AIQwi'lSRqnS
,•,!
l
-----------------------,Cuning .and shaping
Various machines and equipment are used for cutting.and shaping the steel partswhich ronn the subassemblies, assemblies and units.
44 ShipbuildillKShipbuilding 45
Contour or proftle-cutting machine
This machine is made up of a robust portal frame for longitudinal travel which istraversed by several burner carriages, .some of which are motorised (Figure 3.ll).A motorised carriage can pull one or more slave carriages for congruent ormiIIor-image operation. The bUffin carriages may be equipped with singlebumeTs or up to three heads which. l;an be angled and rotated for edgepreparation in addition to cutting, as shown in Figure 3.12. Fully automatic
\Plale
Trip~..·n"ulebead
C"m"~o IrTlovabl~ buttix~d when CU!!In9'
Rail
Swp-port ' I
Colwrn:"_l._.l._'L' -'-- --.J__.,,:-~ ~..L_...;._
,Cutt'ng l~bl.
Driven ganlr~
'\
MDlOrised Slav~
-cam"g~" carr;"'l~ '"
Sl",,~
ca"iage~
Mmmi,oocama""
Porlalframe
Flame pkmer
Mechanical planer
I
GanlrV'IJtior>ary
I"
Co"iage
Iirnmmg
/ f""IIranS\l~rS!!ly
•
I r l I
-.. I'j ,<I -......,..
Gantry rn"ving longitudinally
C~((i3ge ICarriage
5t~ti(",ary'tation~ry
I r l l I---.J
Carriage rn"~lng
G/¥ 'tation~,y
tran,versely
I Iw L- "-J
I
Rail
somewhat longer than for name planing, although the act~a.l mechanical cuttingoperation is much quicker. Modem machines use m.l1lmg heads. for edgepreparation to produce an accurate high standard of finish far s.uperl~r to gas.cuttillg techniques _ Figure 3.14(a). These machines. can also achieve high s~edshearing on the lighter gauges [}f plating. The mosl l;omplex edge prepa.rahonscan be obtained by the use of the rotatable head and assorted cutter shapes Figure 3.14(bJ,
Figure 3. /3 Flame plani"/{ mac/1in,., (aj flame plant"; (b) rhre.e-gl1.ntry operaricm offlame planer
TriplenOHle
\Cwtting labj~
Figure 3.12 Profile-rurting mllrhine
Track
Sid~
,up'port
Steel plate l;an also be planed or cut to size using roller shears, as in themechanical planer. The plates are held by hydraulic clamps. Setting-up time is
A typical flame planer can have up to three gantries whi.ch run on supportingcarriages. The gantries are traversed by one or two burner heads - Figure3_13(a). With triple-nozzle heads., cutting to size and edge preparation of one ormore edges of a plate can take place simultaneously. The operation of themachine is largely automatic, although initial setting up is by manual adjustment. With a three·gantry machine, the longitudinal plate edges can he rut tosize and also the transverse edges -- Figure 3.13(b). The transversely -cuttinggantries wilt operate once the longitudinal gantry is clear. The flame planer cansplit or cut plates to a desired length or width by straight-line cuts. The use of acompound or triple-nozzle head enables simultaneous cutting and edgepreparation of plates. All straight-line edge preparations, such as. V, X, Y or K,are possible with this machine.
operation is possible with punched paper tape input under numerical control.Semi-automatic operation can be acmelled by a photoelectric tradng table using}:1, 1:2.5, 1:5 or 1:10 scale drawings. Complex shapes such as floor plates indouble bottoms can be cut with these machines, and also plate edge preparationmay be carried out while cutting shell plates to the required shape.
46 Shipbuilding 47
,.,
'Ol
L
'"
70i•blockl
'0)
lo'
I
''''\
/R.m
I
FIf(Ure 3.15 Gap ptess operatiOn!: fa} edge curving: (bi plate f1auening:(ci platt flanging or bending; (d) plale straightening; (eJ p/Qle swaging
Gap or rillg press
The gap or ring press is a hydraulically-powered press which cold works steelplait. The operations of bending, straighteni~g. dishin~ and swedging of Sleelpl:lIcS can all be achieved by the use of Ihe dlffcrenl die blocks on the bed andthe Tam (Figure J. J5). The gap press provides better access all round and is moreversatile than the plaIt rolls.
(vi]H
'Ol
{;iil
til
0_3S0~
r;v;wflid
,.,
Hvdr • .,l,tclamp
M,llIng
"''''
Plale ro/ls
Figure 3.14 MechQniCilI ed,,: pUlfItr: M tUStmbly; (b) meclumiCi1Qy curedge preptUtlrio1l - (i) sinde M~tl withoot nOlt, SlIitJlb/e for btJrchn ofpl;ztn: Iii) rinpe bevel with shNf'td IIOU J.5 mm (5/8 in) l7l4l'imum ormilled lIOU; (iii) doubk ~tl tmd "0#; (Il'l J plTportftion tmd "auuring 'ciTculll,' cutter: (v) doubiN plTptITtltion; (vi) [acinp 0If flange,
o!,lnlcturrsl,tcn"OIlS
This machine has already been described with reference to plate straightening. Itis also used for roUing shell plates to the curvature required. By adjusting theheight of the top roUer and the centre distance of the bottom rollers. large orSmall radius bends can be made. Bulkhead flanging is also possible when the
ShiplJuiJdjnK 49
Ships' frames are shaped by cold bending on a hydraulicalJy,powCIcd inilchine.Three initially in-line cLamps hold part of the frame in position. The main ramsthen move the outer two clamps forward O[ ba\:kwards to ben\l the frame to thedesired shape (Figure ],17) The damps are then released <lnd the I'rame is
Frame br:nder
Guillotines
Hydr:lUJically-powercd shc-aril1g machines or guillotines are u~c:d for s.malljobbing work. The plates are fed. pusitioned and often held by hand. SmallitemS, such as brackets aJld machmery space nUOT plates, may bc produced inthis manner
RDIler C€nlrfs"dJlJSl~t,l~ torV;W;I"~ rad"
48 Shipbuilding
.~"i, - I
FigulV! 3./7 Frllme bender operol[on, (a) bow f/OJre bmd: (b) initial posirion; «:) bilge/urn bend
HyrlroUlcram
'0'
~··;i, __ 1:,
,.,
advanced through the machine by a motorised drive. The next portion is thensimilarly bent. Offset bulb and angle bar plate'S can be bent two at a time, placedback to back. In this way, port and starboa.rd frames are producedsimultaneously.
The machine can be controlled by hand :md the frame bent to match atemplate made of wood or stee1 strip. Modem machines arc now equipped for~e lIumericall;ontrol of frame bending which enables fUlly automatic operation"'.thout the use of templates.
fd,
Ffl[1UC j, 16 Roll pres~ opera/fans_ (OJ) slicer Hrake rc>liinJ,. (h) half·round rollin/! ./Or JJla5rl
durtclc posrs, etc, (rj 9rJ-ucjfr('cf/rm!{liIK. /d) DJAf/dread [langing
machine is fltted with a tllln,ging bar Llm] bottom block.. The~e variuus arrangement~ are shown in Figure 3.16. Control or lhe Illachine is by manu<ll setting,and operations carried out frOIll a comole located nearby. A shaped metal orwooden lathe is used to check the finishe-J. shape.
Punchrngand notching pre,ls
Air holes and drain holes requireu in many plates and ~ections can be cut un aprofile burner or by a punching press A fully automated press can be used topUllch round and elliptical holes, as well as rect:mgular and semicircular notches,at preset pitches a
'-'P,ne-I comple-It
50 Shipbuilding
traverses a gantry which is itself motorised to travel along rails mounted high onthe w~ls of the .hall or shop. Using this type of crane the sorting. loading andunload~~ o~rations can be combined and maximum use is made of the groundarea. !.:ifting 15 usually accomplished by magnet beams, vacuum devices or grabs.
Goliath cranes are. to be seen spanning the building docks of most new shipyards. Although of hIgh first cost, this type of crane is flexible in use and coversthe groun~ area .very efficiently. Some degree of care is necessary in the regionof the rails which run along the ground. Mobile cranes are used for internalmaterials movement, usually of a minor nature.
The equipment required for the manual welding of a ship's hull should enablethe operator to usc high amperages with large-gauge electrodes and yet still haveadequate control of current for the various welding positions adopted and lheplate thicknesses being welded. It should also be robust in construction and safein operation_
Multi-operator systems, in which a three-phase transformer supplies up to sixoperators, are favoured in shipyard. Each operator has his own regulator and asupply of up to ISO A. The regulator is fed from an earthed distribution box onthe transformer and provides a range of current selections. The regulawr shouldbe positioned fairly close to the welder both to reduce power losses and the timelaken when changing current sellings. Remote-controlled transformers, whosecurrent can be altered by the welder through his electrode holder cable, are nowfitted in some shipyards. The various welding processes are described inChapter 4.
Most modern shipyards use panel lines for the production of flat stiffenedpanels. A number of specialist work stations are arranged for the production ofthese panels.
The plates are first fed into the line, aligned, clamped and manually tackwelded together. The plate seams are then welded on one side and the plateturned over. The second side welding of the plate seams then takes place. Somepanel lines use a one-sided welding technique which removes the plate-turningoperation. The panel is now flame planed to size and marked out for the websand stiffeners which are to be fitted. The stiffeners are now injected from theside, positioned. clamped and welded on to the panel one after another. Thestiffened panel is then transferred to the fabrication area if further build up isrequired, or despatched directly to the ship for erection. The process is shownin Figure 3.18.
Panel lines
Shipyard welding equipment
Shipbuilding 5 I
Special motorised heavy-lift trailers or transporters are used to transfer unilsand large items of steelwork around the shipyard and to the berth or buildingdock. Fork-lift trucks. trailer.pulling trucks. roUer conveyor lines and variousother devices are also used for male rials movement of one kind or another.
Wtlding9In llV
...,m,
.., - ,Slifftnf'f cl,mping''''' welding 9Inlry
./V'
-
--
V .---"w
St. 3
P,nel CUI 10finished tIlt,nd mlrked off'Of tlifftfle-...
P,ne-IIlhingeflne
St. 1PI.tn POI\tioned ,nomlnu,lIV tICk Wllldc<l
'-'PIlle- st,ml weldedone IIde-. p,ntlturned OVtr Inds«ond lide welded
'-'Stlllt'llt... welded10 p,nel
Figu" 3.18 PilnellUle
Weldin}? a/ld Culling Processes 53
Figure 4.2 Elef'lric arc welding l:lrcuj[
"':'1IIe actu.al welding operation the welding rod and plate are fust touehee!and: quickly dr3wn ap3Jt some 4-5 mm to produce the arc across tne
:·,'.The temperature produced ls in the region of 4000°C and current !low. the metals. may be from 10 to 600 A. The current flow must be preset or
• depending upon the metal type and thickness and ttle 'Supply vo\1age.Yoltage across Ihe arc affects the amount of penetration and the profile or
,'j•.of the metal depos-ited. The c.urrent to a larg~ extent detCJ~ncs t~e~ of we1d metal dcpD'3i\eJ.. A \ugh quality weld \s proo'.lced With 'Se:enl- ... layers Or weld metal, but it is less costly to usc a single heavy depOSIt 01'_IIIClaI,
:j.lf excessive current is used weld s-p<ltter, i.e. tiny blobs of metal depositecJround the weld, may Occur.
For a satisfactory weld, atmospheric gases must be excluded and the controot~ arc must be- easily achieved. This is done by shielding the arc du.nng tht1t'e14ing process. A gas shield is produced by one of two basic meth.ods, etther b)the bllming of a flux or the provision of a gas shield directly,
k:: arc welding
" 'd . d between two metals in an electric circuit when tney, "3JClsprOIJ(;e -F 42Th
"_, e]ednc hort distance. The basic cin:ui! is shown 1Il 19Uie .. e-';\~'. separated b~;e~ (orms one electrode in the Cllcuit and the welding rod_or,,,,_tp.taJ to be W ther. The electric arc produ.eed creates a reglOn of 11l~h..::jtIe foflTlS the. h
Oelts and enables fusion of the metals to take place. ElectriC
.~ tute" whic ill h'hi,\;~P"" I' d "a vari3ble voltage J.e. transformers W Ie may supp y on:, is supp Ie VI ,
,':'" -', - e welding operations.-'.;;.. ;
~:;./i!f.I" l'/elrJ,ny,el
" "'---
\'II~ld <in"ct,on•
A gas flame pmduced by the bu.rning. of oxygen and 8;cetylene is llsed in thisprocess. A hand-held torch is used to direct the flame around the parent metal
Gas welding
In shiP?uilding, welding is now the. a-ccepted method of juining metal. Welding isthe fUSUlg of two metals by heatmg to produce a joint which is as ,trung orstronger than the parent metal. All metals may be welded, but the degree ofsimplicity and the me~hods used v.a:ry considerably. All shipyaId weldingprocesses are of the fUSIOn type. where the edges of the joint afC melted andfuse with the molten weld metal. The heat source for fusion welding may bepro....ided by gas torch, electric aTe or electric resistance
4
Welding and CuttingProcesses
1"I
I
,)'",
':i III11 '1
I!,,
Figurl' 4. I Gos wefdinK with an o-xy-acetylene torch
and filler rods proVide the metal f(lf the joint (Figure 4.1). Gas welding is littleused, having been superseded by the faster process of electric 3rc welding. OutfiTtr.ades, sud1 as plumbers, m.ay employ g.as welding 01 use the gas flame foobrazing or silver soldering.
52
"ocesses usi.ng flux
Manual welding
In the manual welding process a consumable electrode or welding rod is held iJ,. .. ~der and fed 011: to the parent metal by the operator. The welding rod is....
54 WeJdingandCUttingPtocesses
flux<oated mild steel electrode. The metal of the electrode Is normally rimmingsteel. 'Th:U is a ductile material which does not contain silicon or aluminium, bothof which tend to affect the electric arc. The rod coatinp are made up ofceUulose. mineral silicates. oxides, fluorides, basic carbonates and powderedmetal aUoys. The particular constituents used are held together with a bindingmaterial such as sodium silicate. The coating covers the length of the corewire, except where it fiu into the holder.
Electrodes are classified according to their flux coatings as given in theInternational Standard ISO 2560: 1973(E). The two basic types ue the rutilecoated electrode and the hydrogen<ontrolled electrode. Rutile is an almostpure mineral fonn of titanium oxide and is the principal ingredient of rutilecoated electrodes. It increases slag viscosity, decreases spatter and improvesslag detachability. Rutile electrodes are general-purpose, givina a JOOd finishand a sound weld. Hydrogen<Ofltrolled or basic electrodes deposit weld metalwhich is low in hydrogen content. They are used for the welding of highlystressed joints and the higher tensile stub. The coatings contain majorproportions of carbonates and fluorides which are baked on to reduce the watercontent of the coating to a very low level.
Welding and CUtting Proce$$C$ 55
•
~---\\
1.1 '" l<l
Direction., ....
Fi,un 4.J Wtldinl positions; M hori:onta! or dOM11/hand: (b) horilonta/lnrtiaJ!: (c))lutica!; (d) overlrad; (e) inclined
Manual welding may be accomplished in any direction, the three basic modesbeing downhand, vertical and overhead, and some combinations of these modesare shown in Figure 4.3. The correct type of electrode must be used, togetherwith considerable ~, in particular for the overhead and vertical weldingpositions. As far as possible, welding is arranged in the downhand mode.
The gravity welder is a device consisting of a tripod, one leg of which acts asa rail for a sliding electrode holder (Figure 4.4). Once positioned and the arcstruck, the weight of the electrode and holder cause it to slide down the rail anddeposit weld metal along a joint. The angle of the sliding rail will determine theamount of metal deposited. At the bottom of the rail a trip mechanism moves
Automatic welding
In the automatic machine welding process, travel along the metal takes place ata fixed speed with a flux<overed electrode fed 00 to the joint. The correct arclength and metal deposition is achieved by the machine, the speciaUy spiralledflux coating providing the shield during welding. Only downhand welding ofhorizontaljoinu is possible with this machine.
The arc may be additionally sealed with carbon dioxide gas to permit higher<:Urrents for high speed welding. A twin-fillet version is also available for stiffenerwelding to nat plates or panels (Figure 4.5).
Another automatic machine welding process, submerged arc welding, uses abue wire electrode and separately fed granulated flux. The flux melts toproduce a gas shleld for the arc and a molten covering. large metal deposiu athigh speeds, Without air entrainment, are therefore possible in this very efficientprocess. The process is shown diagrammatically in Figure 4.6(a). The unusedflux may be recovered for re·usc. This is a process for horizontal, i.e. downhand,operation only and may be operated nonnaUy welding both sides or as a one·aided welding process. In the nonnal process the downhand weld is made andthe plate turned over or an overhead weld is made from below. Some veeing out
the electrode to break the arc. One man is able to operate several of thesedevices simultaneously.
,.,'"
56 Wdd{n~aml Culting Processes Welding and Cu rring Processes 57
Figure 4.5 Automutic /lu.r-c[){]led dt'Ctnxlf' IVI'lding uSing a twin·hEadedmacJlinc
ILong,tudinal
WalWcooledliv,;ortra~elling
,h-oe
~,,~
-~
Bare ",ie. e'e<:trode
~b/~~";;t;~:
(;or""m~hl,,
/ ~U1d~
/
Di'~1iDn
of weld
Welding Luree-c,
f-Iu~
III
I,W"ld '
Di'eeti,m of weld ing
•r-- _ -, Starting
!:=======:::':':::!==:':::::!:'="::"""======::'0,,,/
I.'Figure 4.6 Submerged arc welding,' Ill) submerged arc IWlding; (b) l)(/cking
plate iJ"ange men! for one·sided welding
Wice f-eed Barer(>ll, ~C:) wire
/ elecHooe
GranulMed tfilMr,,",o~e-ry
! PWeldingCUfrent
7,J(J,'.nulated \flux Coppe,
'lfIp
Ngur.e 4. 7 EieClroslag wefdin;2,'
Run-on and fun·off plates are required at the beginning and end of the weld andno ~toppage must occur during the p-rocess. The arrangement is showndiagrammatically in Figure 4. 7.
Electrogas welding
1llis process is parHcularly suited 10 shipbuilding since vertkal plates of thickneues in the range 13-40 mm are efficiently joined. Cooled shoes are againused but a flux·coated electrode is now employed. Fusion is achieved by an arcbetween the electrode and the metal, and a carbon diQxide gas shield is suppliedthrough the upper region of the saoes. The arrangement is similar to Figure 4. 7,for e1ectroslag welding, with the carbon dioxide supplied through the top of theoboes.
of the joint may be necessary for the fmal run. In tae one-sided process variousforms of backing plate can be used, of which one example is shown in Figtm:
4.6(b). Any defects in the- weld will then have 10 be repaired by veeing out andwelding from the other side. This process is limited to indoor undercover use andis unsuitable for use on the berth.
Stud welding
.A macltine OJ gun as part of the electric circuit is used in stud welding. In oneIllethod the stud is fed into the clutch and a ceramic ferrule is placed over theend. The stud is placed against the metal surface and the operation of tae guntrigger withdraws the stud to create an arc (Fi!?UTe 4.8). After a period of lilrcing,
Figure 4.8 Stud weldin;:_ (a) ~rud and ferrule pkzud on plate; (v) arrdrawn; (c) weld completed
I
II
Electroslag welding
The vertical welding of plate thicknesses In excess of 13 mm is efficientlyachieved by this process. Initially an arc is struck but the process continues byelectrical resistance heating through the slag_ The weld pool is contajned bycooled shoes placed either s~de of the plate which may be moved up the platemechanic.a.lly or manually in separate sections. Alternatively, shoes the height ofthe weld may be fIxed in place either side. The bare wire electrode is usually fedfrom the top through a consumable guide and acts as the electrode of the circuit.
I" 1" 10>
G~.con"ols
Welding (lnd Cutting ProceSses 59
FIe-"bIE{"bing
,-~---------
€ lect<adll".....e-ccnlinuou.I','""
suPPly source is usually d.c::, and the proces; may be fully or semi-automatic:: inopention.
In steel welding using this ptoc:;ess. carbon dioxide may be the shielding gasand plating of any thickness may be welded. Controls within the wire feed unitenable a range of constant wire feeds related to the current to be selected. Withcarbon dioxide gas, the arc characteristic changes with the current from a shortcircuiting (dip transfer) arc at low currents to a spray arc at high currents. Dip
Processes usin g gas
The~... ,aIl'd WAelding processes employing a bare electrode or welding wire with
gas :>lue utom f ' . a.' a IC or sem.l-automatlC operation is usual. With automati~perat~on, once, set the. process is controlled by the machine. In semi-automati~peratl~n cert.am machine settings are made but the torch js h!lTld held and th
proces!3-IS to some extent controlled by the opefif.tor, e
58 Welding arid Cutting Pro-r:esses
the ~tud .i:s driven into the molten meta] I 'ferrule concentrates the are, reduces the ac~e~~ o~n: we11mg ~akes blace. Themetal area. Fhm is contained ill the end ofrhe stud. It an con mes t e rna ten
Another method uses a fUSible coUar over the d h .electricity to crea te the arc and then coil /n .of t e srud :-Vhich condUctsmetal pool and fanning the weld Weld dapse~, Dlelllg the stud m~o the molten
~~:~s~~a~~~~r~u~[~~::~~~~~~ings. ~th:~u()~p~~eo~~~:'o~se~~~~:min~~~;~~;
Tungsten inert gas (TlG)
This is a process for thin sheet metal such as steel or aluminium. A water-coolednon-consumable tungsten electrode and the plate material have an arc cre.ated •
Pial...Ga~ shield
-"~===~~b==""======7~~I<I
O"-e<:tlon of w~ld-
Tun~5ten
~Ieclfo<l~
Fille, ,,,d
"Plal~;.,:::::;:",:,~J~l2rL,~~~?~;~"O~'Zd='O"'Z'''210'2'Z'ZltZ'OI,?,?Z'Z'ZUZ''Z? 'N~ld
Figure 4.9 Tungsten inert gas prOCeJt
~etw~~ them by a high frequency discharge across the gap. The inert gas shieldJS USlJ Yargon gas. The process is shown in Figure 4,9.
Metal inert gas (MIG)
Figure 4.10 Metal inert "liS procesS
tnnsfer allows all positions of welding, but the -spray arc is downhand only. Diptnnsfer is ideaUy suited to thinner materials, since it produces less distortioneffects.. This process is being used increasingly in s.ltipbuilding.
Plasma metal inert gas
1bis is..a further development of the metal inert gas process which incorporates aplasma arc around the MIG arc. The plasma is an ionised stream of gas whichsurrounds the MIG arc and concentrates its effect on to the metal. The plasmaarc has its own set of controls fOJ its electric circuit. It is initially ignited by theMIG arc and with both arcs indiridually controlled the process can be finely'lUlled' to the material requirements. Automatic and semi·au tomatic versions arelV3.i1able. The semi-automatic version uses a dual-flow noule arrangement. asdi()Wn in Figure 4,11, with a single supply of gas, usually argon, as the shieldingand the plasma gases. The torch used i-s no heavier than a conventionaJ MrGtorch .and the process has the advantages of higher weld metal deposition ratesand tne use- of a narrower vee preparation which may be as small as 30 degrees.
~ ~:nsutnable metal wire electrode is used in this process and is fed through thet:rc~rt~r:rl~h from a feed unit (Figure 4.10). An inert gas is fed through the
e the arc and the tOrch and plate are part of an ele<:tric circuit. The
Thermit welding
lhis is a fusion process taking place as a result of the hea t released in a chemical~tion between powdered aluminium and iron oxide ignited by barium
60 Welding and Cutting Proces:sesWelding and Cutting Processes 61
C""sum•.,Ie- electrode- ",i~
E!oc~-qoug"
atter ,n'lial weld'"
'"
I
I
£Iil'C~ -gou9"al~e, iniual we~d
iel
,,'
+,,--f*\i r "
ArgOn (Ia'
Sh-i..ldi~g gal
Weldi~g ourre~1
v -----------.. f>lasma gas
f---- G•• 'SI1ield
./
/
1\
Pla.ma(~rrent
Wate<-coo~!ffi - ---101~ollie
Figure 4.12 Hu.tt wdd preparatiOI1,: fa) l./lIi'Qre Inm join 1, (b; si~lIk,-V burr joint. (l:)doubfe· V butt {oin!.- (d) dOI/Me- U hu rl joint
Figlue 4. II Plasma mef.al inert gao pmce.s
5ecri()nthff.)(lg/lMouJe
- Sr.ieldir>9 gas
Pla,ma 9'"
Fillet welds are used for righ.t·angled plate joints and lapped jOilltS. as showlJ.in Figure 4.13. Two paJticular terms are lIsed in relation to ftIlet welds - the leglength L ;Ind the throat thickness T - as shown in Figure 4. 13(a). The leg lengthis related to the thickness of the abutting plate and the throat thickness must beat least 7cYJ'<; of L. A full penetration type of fillet weld may be used wherespecial strength is required. A full penetration joint is shown ill Figure4.J3(c).The abutting plate is of V or J preparation to ensure full penetration wh.enwelding.
The fillet welds descrihed may be arranged in a number of ways, dependingon structural requirements. Fully continuous welds are used in important
peroxide. The parts to be welded are usually large sections, such. as a stemframe,and they are positioned together in .a sand or graphite mould. The molten steeland slag from th.e chemic..l reaction is first formed in .a cmcible and then runinto the mould_ Leg length -i-
, i
Wel~
Types of weld'-. (\,-,
(a) , Throa,Th,c~ne<;, r
A number of different welded joints are used, depending upon their situation,material thickness, re-quired strength, etc. The depth of weld may require morethan one- pass or run of weld 10 build up to the workpiece thickness, Reversingthe workpiece, gouging out and a final back-run will also be necessary unless aone·sided technique is employed.
The butt weld is the strongest joint when subjected to tension and isillustrated in Fif?Ure 4.12. The single--V type of preparation is used for the buttweld for plate thicknesses in excess of 6 mm up to a maximum of 20 mm. Below6 mm, a square- edge preparation may be employed and for very thick plates adouble-V preparation is used. A U·weld preparation is also used which requiresless weld metal and gives a better quality joint in return for a more expensiveedge preparation_
'"Figure 4.13 HUe! welds,' (a) flUei w.-ld, fb) lap weld; Ie) filler weld WIth ft<f1 penetrarioll
prepdration
!, ,
mstortion prevenflon
FilJUre 4.16 Edge prl!pl1TtItio/'l to redUce dirlOrriQl1: (8) ringle· Y preplJJdn'On,Mng cO/'lsiderob/e distort/em (1 fiNt welding ron, 2 Jecond we/ding nm.J third welding run, 4 final weldin!,: run), (b) double- V pre{Xlration givt,.,g
only slIght Ihril1~
Welding and Cutting Processes t1.:l
effect of thh, -afId the differell~e in deposited weld metal and parent metlklproperties, results in dbtortion of the wor.kpie-ce. The appea~ance of dJ.stortionmay be in onc or more of the followmg forms - longttudlnal shnnk.age,transverse shrinkage. and angular di.stortiDn. Figure 4.15 muatratts these vanouseffects. . _
The cause of di"torti-on may be attributable to s~veral pos.s.lble factors actUlgindividually or together. fhe con-centrated heating of the welded area ~d i~subseqtlent later con-traction will affect the weld metal and the workpIece III
~jffereJ1t ways. As a consequence, streSSes will be set up ill the weld, the twojoined workpieces and the overall structure. ." ,..
The degree of fe-stain t pe-rmiJ;ted to the welded Jomt Will affect its dIstOrtion.Where welded joints are unrestrained their subsequent weld shrinkage willJelie-ve any stresses se, up. Restrained jointS, by virtue of the rigidity of thestructure or some applied form of damping, induce high. stn:sses to the weldand cracking may occur if the COrrect welding sequences are not a.dopted.
The properties of the wmkpiece- and tne -pm.\ible stresses 'locked in' it due tomanufacturing processes may b-e altered or affected by welding and lead todis-tnrtioI\.
Restraint is the usual method of distortion prevention in shipbuilding. WhereUOIts are faired ready for welding they ue tack welded to hold them in placedUring welding. The parts will then remain dimensionally correct and the rig.id1tyof the structur-e will usually restrain any distortion. Strongba-cks or clampin~\tlmgements are also used on bu1t and fl11e1 weld" as shown in Figur.e 4.17.
All welds 'shrink', so the use of the correct procedure in welding can debJ,ueb to red~ dUi.tmti<m. The fewer runs involved in a welded joint, the le-~"ill be the distortion. SymmetricaJ welding either side of a joint with a double-\
Good design mould ensUTe as few welded joints as possible in a structure,particularly wilen it is. made up of thin section plate. Where they exist, welded]atn.u should be accessible, preferably for downhand welding.
The edge preparation of joints. can be arranged to reduce distortIon, as shownin FIgUre 4.16. A single-V preparation joint with four runs of welding willdistort as shown. A double-V pTepal<ltion }oirl.t welded with four runs in theorder shown will only exhibit slight shrinkage of the joined plates.
" //<'>
.-'///~ ///
,,", /
L"n9;I<Jdin~I/,i //",h"nl<age .-'
//
Ffgure 4. 1,5 DistOltfon effect:
Welding practice
Tile welding of the metal, because of the localised concentration of heat, givesrise to areas of plating which first -expand .and later contract on cooling. The
lo"g,ludin~1
! ,~ - .hrlnl<a9"
/,:i
'I
Welc\_ S,dfe"pr
(=~/1~"'"W~ld
strength connections and for oiltight and watertight connections_ Chain andintermittent welds are spaced sections of welding and are shown in Figure 4. ]4.&lme savings in weight and distortion are pOS5ible for lightly stressed materialwhich does not require watertight jQints.
Tack welds are short runs of weld on any joint to be welded. They are usedto initially align and hold the material prior to the finished joint. They areassembly welds and must be subject to a full welding procedure. They shouldnot be less than 75 mm in length to ensure a sufficient heat input and should notbe welded ovu.
Figure 4.14 Nan-COnnll1.lOUi fillet ....'flds· ffl) inrermit/ent WJ?/ding: (b-J ch4ill wdding
§§32§J~'" \ ..., ,W.ld St;ff~n.r
62 We-Iding and CutUng Processes
64
.....
Figuft 4.17 QampitlX 1Irr/11lltmttffS
_---:;-,• .-,_-;-_'+'_-:-_'.>I.'__~I••__.... -t< D,'ftlionOI~ 3 1 Ie 4 ,. 6 _Id
===::J:===C=::::::I==i==C:::!~:::I=~=:c=~=o..der01......._______Joonl pr;..eu>on,-------_,
Fi,utr 4. III B«k·$ttp _ldinK t~niqllt
___••.-, '.>I I.---;,---~ ;~__---t O;"llon4 2 6"· ", I· ,. o.....eld
===C=::::::I=~=C=I ====~=:J::=~J=::J:=~'~=Otdef 01..."-_______ Jo'nl Pfc:.,eu,OI',--------
I
Fiprt 4.19 Skip OT ...._dm"6 ....ddilt,'mniqllt
Welding Qnd Oltting Processes 65
preparalion will ploduce a dislortion·frce weld. Simultaneous welding by 1'010'0operalors is Iherefore ;I useful Icchniqut which should be practised wheneverpossible. Welding should always take place IOwards Ihe free or unrestrained endof a joint. For long welding runs several techniques are used to minimisediSl0l1ion. Th." b~ck-5te~ metJ.1od is iUustral.cd in Figllrt 4.18" Her,t the operatorlWeids the jOint In sections In IhC' numenC<lI order aJld direction shown. Avari3tion or this is 'skip' welding. which is shown in flgure 4.19. and likewiseproglesses in the numerical order and direction shown. Distortion may then becontrolled by balancing the welding as much as possible and allowing the weldshrinkage to occur rreely. Welding sequences taking Ihis into accounl should bewell thought out berore welding commences.
Distortion correction
Despite the most stringenl methodS to e1iminale il. distortion can still occur.Where the distortion in a joinl is considered unacceptable the joint must begouged. grooved or completely split. and then rewelded. Strongbacks may beplaced across the joint to restrain distortion during rewelding.
Straightrorward mechanical means may be used. such as hydraulic jacks orhammering on localised areas or distortion or buckling. Where such methodSinv~lve straining the welds, they should be examined ror cracks arter correction.Every errort should be made to avoid mechanically straightening structures ror
this reason.
c===tc:= =:J ::::::JI., 101
c===t t==:J (
1<1 '"Fiprt 4.20 SpOf hftlti",: (aj cu"'ed pltue: (b) h~ted: (e) exptJIuiofl: (dJ kvelled pfafe
The application of concentrated heat from a gas·burning torch may be usedfor correcting distortion in steels other than the higher tensile. quenched andtempered types. The process is shown in Figure 4.20. A small area is heated onthe side where the contraction would bring about an improvement. The steelis heated to a 'red heat' and the torch slowly moved along a previously drawntine, at such a speed that the 'red heat' does not pass right through the material.The area heated wants to expand. but is resisted by the surrounding material.The fecrystallisation absorbs the expansion and, on cooling, contraction occurs
66
1 I IIL JL ~_J ... __ ~
~.;. - - --'1- - - - - --- - -- -, 1- - --It U :'" ) HUlf'O , III , !eng"" 11
I: I I I:I. I.II II
II I ! "It III'
II II" n n I'II U U I'____ JL ...Jl _
----'r------------·r----II II
Welding and Curting Processes 67
which brings about a favourable distortion. thus correcting the original distortedSlfUclure (Figure 4.21).
Weld faults
The weld
Faults may occur in welding as in any other process. These faults may arise frombad workman.ship, incorrect procedures, wrong materials used, etc. A good weldis illustrated in Figtlrt! 4.22fa). In such a weld a degree of fusion should havetaken place at the sides of the weld. There should be no overlap or undercut atthe toe of the weld. A slight reinforcement or build·up of material should bepresent at the top surface and there should be root penetration along the bottomsurface.
A bad weld is shown in Figure 4.22(b). The absence of reinforcement androot penetration are the result of incorrect procedure or bad workmanship.Overlap is infused metal lying over the parent metal. Undercut is the wastage ofparent metal, probably caused by too high a welding current. Porosity is causedby gases trapped in the weld. Slag indusion is the result of inadequate cleaningbetween weld runs. Poor fusion or penetration between runs may be due to poorcleaning or incorrect voltage or current settings. The result of a bad weld is aweak or faulty joint. A bad weld can also be the starting point for a crack.
Figurt 4.2/ Distortion co".~tion
lamellar tearing
.........
Rool _trillIOn
Tutong
umellar tearing around welded joints has become a problem as plate thicknesseshave increased and structures have become more rigid. Lamellar tearing is abrittle cracking in steel plate as a result of tensile stresses at right·angles to theplate. It is caused by the contraction of weld metal when cooling. Lamellartearing is most likely to occur when thick plates, large weldments and highinternal connection restraint are all present. The characteristic 'tear' occurs inthe cross-plate of a T-configuration and may begin at the toe or rool of a weld orat some point below the weld (Figurt! 4.21).
One method of reducing the problem of lamellar tearing is the use of 'clean'steels such as those produced by the vacuum degassed process. Other measuresindude the use of joint configurations which avoid right angle tensile stressingof the plate, or preheating the plate before welding.
No inlf"""penetrl';on,}
;ncl",ion
No,ic!'efusion
St.,
Weld Ih,""ill loe Relnlo,c""""
Lillie Of noPorCl"!Y ..".IOtC~1
V""~"', \ / /""'''~
t
Oegoree \ t01 lU$"'" _ \_
O'_1I;01l0n \ I I" ,
j I
101
'" Lack 01 '001_trillion
lbl
Fftr,Ire 4.22 Ezilmpiet of_Ids: ra) 1I' tood wtld: (bJ 1I' bfld 'oIt>tld
Figl<rf 4.24 OXy.acdylcl1c cllttlng IOrcl!
P,ehea\ h(ll~,
/
~ CUlling o.y~en h"Io'~
Pi.,,, Vjew (l{ noul"
),-<)11 r>'e"UT~ ~"\\\'VJ O~"I'l"·nr=' ~~A",B- I~---- =L-_~
-I .1 Pr~I'ea\ln'Jo>\qenanr A,~lVI~'W Q~Y'J,",,~~i~~I ' In'lylp,,, m'~lur~ ~~I~e
,II! III
pI",,,
\
Wdding and Cutting Proce,~ses 69
and then oxidls-ed by a ~tream of lligh preSSUre ox.ygen whi.ch carries away theox.idised metal. A narrow g.ap with parallel sides remains along the line {:f the
t Small amounts of al10ying elcm('\lts in the steel plale call be removed In the~. h h' ~tclJ1tiag process, but large amount& o~ elements ~uc as c rn~llum may prevcutting. Tile introduction of an irorHICh pOWder mto the cutting area. OVeH;omesthis llwb\em, p-,nticu\arly with stainless steel. .. _ .
Acetylene or propane is usually used as the preheat.mg gas. m conjunctionwith oxygen. A typical cutting torch is. shown in Flgu~e 4.24. Automated;auangementS of cutting torches are used Ln ..anou" machl11es for edge pre?il':ration. flame planing, etc., a.Ji ~en~ioned In_ Chapter 3. An edge preparation.arraogewent of ton::hes is shown In FIglJ. ye 4.2,;,.
Several non·de~\luctive technique" a,e ul>ed 11, the eX:lminati"n 01 wehJedjoints. These include yjsuul examim;tion, dye pcnelr.aJlts, magnetic p<lrtides.radiography and ultrasonic method". Destructive- testing of special test plates andtheir welded .Joint" i~ r~'i\lirerl fOT certain da;,;.e-" of WOlk. but most :l-hipbuHo:lingweld testing is nun--destrUC:llve.
The trained experienced inspec;tur and surveyur can detect surface defe-e-tsand flaws ill welds by ...isual examination. He may abo WGue,,\ mmc detaileuexamination of known pwblem areas or regions of mgh stress His coMtantvigilance and attendance during the: we1diIlg up of a ship en"ures good work andsatislactOlY stalldard$ 1)[ welding.
Magnetic particle testing L" a surface examination technique. A mixture ofiron filings in thill white paint is &pread over <i welded joint. The joint is thenmagnetised by attaching "d laTg.e perman.eflt magnet to it. Discfmtinuitie-s thenshow up 3$ concentlations of iron filings, Iesultin,g from the distorted magneticfield.
Dye penetrams ale spread over the ?,uiface of a joint and then wiped orwashed off. The weld surface is then examined using an ultraviolet light. Anycrack will contain the luminous dye and will be readily visible.
Radiographic inspection i~ a means of 'photographing' welded joints.. Aph.Qtogr.aphic plate is exposed tu radiations from X-ray or gamma ray devices onthe far side of the joint. Any inclusions or gas holes will then show up on tItephotogr.aphic plate.
Ultrasonic insllection uses pulses of ultrasonic energy whkh ale reflected atany surface they meet. For the ultrasonic: waves to initially enter dIe metal acoupling medium is necessary. Cellulose paste has been found to be effectiveand peels. off easily after use. A cathode ray tube is used 10 'read' the reflectionpatterns and very minor flaws Illay be detected with this method of testing.It is particularly effective fOI detecting plate laminations and the degree of roO!penetration in welds_
Classification societY weld testing
The classification societies reqUire various tes.ts, Some of them destructive, inorder to approve weld materials and electrodc&. Joints. made between thematerials and the electro-des are then subjected to various strength. metallurgicaland other tests.
68 We!dingarld Cutting Processe~'
Weld testing
Cutting processes
The majo-rity of metal .eu tting in shipyards utilises gas cutting techniques. Plasmaarc and gouging cutting technique. are also being increasingly used.
Gas cutting
During gas. cutting the mC'tal is, in effect, "cut' by oxidising and blowing away anarrow band of material. The metal is heated by the preheat :section of the flame
\ ====3·.-·di,~-
I
,"Figure 4.25 Edge preparation: (tJ) triple-nozzle head; (b) pLIIl
new ofm)n(f3 showing order cf Ocperllrl/)"n
70 W~ldingand CUtting Proc~ne:s
Plasma arc cutting
The cutting torch consists of a lungsten electrode located in a waler-coolednozzle which acts as one eleclrode in the circuit (FIgU~ 4.26). The materia! 10
be cut is the other electrode and the circuit is completed by a stream of ionisedgas which will conduct electricity. This 'plasma gas' is supplied around thetungsten electrode and constricts the arc formed between it and the metal plale.
I./L------"~.cu.."nl
Flt:Urr 4.26 l'IIlunll IUC currin, t~h
A very high temperature region is created at the arc which melts the metal andcuts through it. The gas is initially ionised by a short electrical discharge betweenthe electrode and the nozzle. Inert gases such as argon have been used bUImodem developments have enabled air or oxygen to be used_ This is anautomated cutting process which is much faster than other methods.
Gouging
Gouging steel plate by 'arc-air' or by a special cutter fined to a gas torch is away of removing metal for the 'back-runs' of a butt weld. Gas or arc weldingprocesses may be modified for gouging purposes. Arc-air gouging consists of asolid copper-dad carbon graphite electrode in a special holder which has a
Welding and o,ttingPrtxesu1 71
compressed a;ir pipe at~a~hed. A stre~m ~ec;~~;~S::t~ra~ ~~;~~o~ ~~::;:to the workpiece 10 Oludtse and remo e cd 'de the high temperatureAnother arrangement useds tubthular. el~d",r ott~~ ~I~~~ode. The electrodes are
The air is blown own e my . h .arc.. The solid electrode anangement 15 s own Inconsumed In both these processes_FJ&Ure 4.27.
,
Plllie
i
C"nli"uou~
InnglhJd,nalBrac:k~t S.l;ffe~e' gifuer
"VIJ ~ ,long,tUrl,n~1
0 ", <1lif~ncc
Solid !floo, 0 1:''). i 4 11 ~~-- "I-Iat bar.. ,"i'iencr
Major Stmctu"a/ Items 73
Some double bottoms have a duct keel filled along ttIe cenLreline. Tnis is aninternal passage of watertight i,;onstTUction rUlJning some distance along thelength (l\ the sh.ip, (;fH~n (mm the forepeak tQ the f~Hwafd machinery spacebulkhead. Use is made of this pilssage to carry the pipework along the length ofthe ship to the various holds or tanks_ An entrance- is usually prQvided at theforward end of the machinery space via Ol watertight manhole. }iu dUd keel isnece-ssary ill the machinery spOlce or aft of it, SiflC'~ pipework will run Llbove theengine room douiJle bot/om and along the shaft tunnel, where one is fitt-ed.
5
Major Structural Items
SECTION A KEEL AND BOTTOM CONSTRUCTION
The ~otlom shell constI~c1ion consists of the central .keel of the ship. with thefloormg ~trUl;tllre and sure shell platIng on either side. Almost all """ssel, bUilt:oday , With the ex.ception oftankels, are fiued with a double botlom. This is an
thntcconal ~kin fitted about I rn above the outer shell pJalin 6 and supported by'
e oorffig structure.
,,
,I("~I plo1e Inmr,osto=
1,,~g·,nJ6,~,1
>t;tl~ner
Keel
Figure 5,} Hilt plale keel
Double-bottom s.tructure
Where a, double bottom ur inn(':r ~hcll is fitted it is watertight up to the bilgestnus proViding complete watertight integrity' s}\Ould the outer snell be pieree{in way of the double bottom The minimum depth is determined by rule requirements for the size of vessel but the- adual depth is sometimes increaseo in placeto suit double-bottom tank capacities. The douhle bottom may have a slopin:margin Leading to the bilge radiused plating or a l:ontimlOUS double bottonextending to tne side shell. The sloping margin CUtls-tructiol1 requires the use 0margin plates to connect up with the sirle hami"g and pTovirles",i collecting ba~
or well fur bilge water (Figure 5.3). The continuous tank top -or Oat margin mushave bUge water collecting points or drain 'hats' fitted into it (Figure 5.4:The flat margin is connected to the side framing by a flanged bracket. The l1amargin type of consttuction is much used in modern COllstruction.
The struclure is made up of vertical noms wnieh may be watertight, solid cof bracket constructicJn. The floor Structure is continuous from the centre girdeto the side shell and supports the inner bottom shell. Side girders are fitted i
The construction of the duet keel uses two longituuinal girders spaceJnot more than 2,0 m apart. This r-c,tril:!jull is to enSUfe that the lon~itlldinal
girders rest on the ducking blocb wJlen the ~Itip is in ilryduck. Stiffeners arefitted to shell and bottom platillg at alternate frame space-S and arc bracketed totlte longitudinal girders (Figure 5.2). The kce-l plale and the tank tCJ-P above theduct keel must have their sc:alltling~ inneaseJ 10 ..:ompensate for the reducedstrength ()f the transverse floors.
•
Longilu<:tinal~ljffen~r
:-- FI~tba'
Centre lone 'lrak~ ofct~<Jb~~-hot!Om Pla';"9
Keer plole
Centre Y;rder
501,.0floor
Th~ keel runs along the centreline of the bottom plating of the ship and for themaJoflty of merchant ships is of a fiat plate construction. At right-angles to theflat plate keel, r~nning alo~g the s~p's centreline from the fore peak to Ihe aftpeak bulkhead, IS a watertIght longItudinal division knowfl as the centre girderor vertical keel. WhcYC a double-bottom constructIOn is employed, th.e centreline
~t~.ake of, tank t.op plating results in the furmation of .an I·seclion keel (Figure. )'. ThIS prOVIdes conSlderable- strength to the structure- and resistance t
b~ndmg. The flat plate keel or 'middle hne strake of plating' is increased i.~~/kness fDr st:engt~ purposes and for a corrosiDn allowance, because of the
dl ~culty In mamtrunmg paint pIOteetion systems in way of the docking blocksunng the vessel's life,
72
When tramversely fr.a.med, rhe double-bottom structure L:onsists of solid plalcRoors and bracket floors with transver~e frames. The bracket flom is fiuedbetween the Widely spa-ccd solid noors. It consists of transverse bulb <Inglesutlons stiffening the shell and i~ner bottllm plating. Vertical suppon isprovided by brackets at the side shell and centre girder, any side girders andintermediate struts. The number of intercostal side girders fitted is determinedby classification ~ociety rules. Solid and bracket floors for a transversely' framedvessel are shown in Figure 5.4.
This is the system favoured as a resul.! of tests and it provides adequal:e resistanceto distortion on ships of 120 ll\ in length or greater. Off~et bulb plates are usedas longitudinal stiffeners on the shell and inner hottom plating, at intervals ofabout I m. Soiid floors provide support at transverse bulklleads and at intervalsnot exceeding 3.8 m along the length of the ship. Brackets are fitte-d at tnccentre girder and side shell at intermediate frame spaces between solid noors.The1;.e brackets arc flanged at the free edge and extend to the tlrst longitudinal.Channel bar or angle bar struts are provided to give support at intervals of notmore than 25 m wnerc solid floors arc widely spaced. Intercostal side girder~ areagain fitted, their number depending upon classification society rules. Solid andbr.a.cket fioors for a longitudinaUy framed vessel are shown in Figure 5.3.
Lonyitudinally framed double bottom
Transversely framed double bottom
,
. Major StrncturaI Items 75
. the longitudinal direction, their number depending on the width of th.e ~hip,
'.:' These side girde[~ are bwken either side of the floors and are therefore termed" wtercos-tal girders.
Watertight or oiltight floors are fitted beneath the main bulkhe.a.<ls and arealso used to subdivi-de the double-bottom spa!,;e into tanks. for various liqUids.Solid plate Ooors of non-watertight cunstruction_ usually lightened by manholes,arc positioned in other places as required to stiffcn the structure. Between solidplate floors. bracket floors are fitted. Bracket flours consist of plate bracketsattached to tlte centre girder find the ~ide shell with bulb plate stiffeners runningbetween, The stiffeners are supported by angle bar struts at intervals and anyside girders which are present in the S1fucture .
The arrangement of flooring will be determined by the type of framingsystem adopted, which may be either transverse or longitudinal.
8racket
lJ.t~ilof dr.-in 'h'-I'
Fla",!"
\
In tercoswl,ide girder
FlangeI
jI Bracket
,0,
Flat bar.tiffener
\"
Air hole
Longitudinal
./
I nter<:ostlll.io;le-girder
I.,
!LorogitudiMI
Angle IntereoSt.'bar ,ide\lru I girde.
/ /
Flat bar'tiffen..r",
Flat ba,niffenoer
Flange
Continuou,!centre-line~ird8r
Ship l
FIgure 5.3 wngltudtJrlIlly framed dOUble bottom: (a) bracket /1-00',- (b) solid floor
74
oilt
Suck'" ~;::t,:",_,~'-_J!._J~_!L~J~_t_l~_f~)Ship t. Conlinuou.
centreline.girder
Continu,Ju,cen"e 9irder Upper frame
I !
Brack..t Flange Bottom fr~me
Figure 5..4 TnllfSl'f!"eJy framed double b(Jtt~-."''' (a) IJrodei floor; (b) ~Qiid floor
ContinuDIJ$Centre !l"der I
Droin hole~
,1'11&'<:0'181,ide girde,
Machinery space double bottom
The construction of the double bottom in the machinery space regardless 01framing system has solid plate noors at every frame space under the m..irengine. Additional side girders are fitted outhoard of the maUl engine seating, a!required. The double-bottom height is usually increased 10 provi.de fuel oillubricating oil and fresh water tanks of suitable capacities. Shaft alignment als(requires an increase in the double·bottom height or a raised ~eating, the forme
Single-bottom construction
Pounding or slamming results from the ship heaving or pitching, Ihus causingthe forward region to 'slam' down on to the water. Additional structuralslrength must be provided from the forward perpendicular afl for 25-30% ofthe ship's length. The shell plaling either side of lhe keel i:. increased inthickness, depending upon the ship's minimum draught. The frame spacing isreduced, full· and half-height intercostal side girders are fined and solid floorsIre installed at every frame space. With longitudinal framing the longitudinalspacing is reduced. intercostal side girders are fitted and tran$Ye~ floors areinstalled at alternate frames.
In oil. tankers particularly, and some smaller vessels, a single-boltom constructionis employed. The oil tanker bottom structure is detailed in Chapter 8. Theconstruction of the single bottom in smaller ships is similar to double-bottomconstruction but without the inner skin of plating. The upper edge of all platefloors must therefore be stiffened to improve their rigidity.
Mflj<Jr 0>11.. " ...... , ......_
The side and bottom shell plating provides the watertight skin of the ship. Theshell plating also makes the greatest contribution to the longitudinal strenglh ofthe ship's structure. As a result of its huge area the shell plating is composed ofmany strakes or plales arranged in a fore and aft direction and welded together.The horizontal welds are termed 'seams' and the vertical welds are termed'butts'. Several strakes of plating are usually joined together as part of a unit. Ashell expansion by units was shown in Figure 3.2. The thickness of shell platingis largely dependent upon ship length and frame spacing. The fmal structuremust be capable of withstanding the many dynamic and static loads upon Ihehull, as discussed in C1l.apter 2. Some tapering off of .shell plate thicknesstowards the ends of lhe ship is usual, since the bending moments are reduced inthis region.
The strake of side plating nearesl to the deck is known as the 'sheerstrake'.The sheerstrake is increased in thickness or a high tensile steel is used. This isbecause this section of plating is furthest from the neutral axis and subject to Ihegreatest bending stress, as discussed in Chapter 2. The region where thesheerslrake meets the deck plating is known as lhe gunwale. Two particulararrangements in this region are used and are shown in Figure 5.7. With therounded gunwale arrangement no welding is permined on the sheerstrake
their capacity determined. All double-bottom tanks are tested on completionby the maximum service pressure head of waler or an eqUivalent air test.
SheU plating
SECTION B SHELL PLATING, fRAMING SYSTEMS ANDDECKS
Structure to resist pounding
,..""
CO,,,inuou5Cftlue!irw HNvy ~It ~It
gi«lItr Girder
Colf~
olubtic,ling oil d~;n 'lnt-I--+_o~oil tint
Figurt 5.S MQdlillU)' rpDU doubl~ bottom
o
76 Major Structunz/ Items
met~od usually ~ing adopted. Continuity of strength is ensured and maintainedby .~dualJy ~~pU1g the tank lop height and internal structure to the requiredpo~tion. Additional. sup~rl ~d stiffening is necessary for the main engines,bolkrs, etc., 10 proVIde a VlbratJon-resistanl solid platform capable of supporting~~ concentrated loads. ~n slow-speed diesel..engined ships lhe tank top pialingIS Increased to 40 mm lhlck or thereabouls in wlY of the engine bedplate. This
~ ach~eved by using a sp~cia.1 insert plate which is the length of the enginerncluding the ~rust block In SIZe (Figure 5.5). Additional heavy girders are alsofitte.d undet ~IS plate a~d i~ other positions under heavy machinery as required.Plating and guder maten.al In the machinery spaces is of increased scantlings inthe order of 10%.
Double-bottom tanks
M,td-51H'l PIdI Bouomllhtll
ed.r c1!r;z 4"~DockIng plug. btl'S or m"nleu 51eet T.....'ne Ino:l ted lti<! grommet
Access to the doUble-b~ttom tanks is usually by manholes cut in the tank top.These ma~holes are SUitably jointed and bolted to be completely watertightwhen not In use. Docking plugs are fitted in all double-bottom tanks and are ameans ~f c.ompletely draining these tanks for inspection in drydock (Fi,grJTt!5.~). Air pipeS are fitted to all double·bottom tanks to release the air whenfilling. Sounding pipes are also fitted to enable the tanks to be sounded and
16 MaiorStl'Uctura/ items
pounding or slamming results from the ship heaving or pitching, thus causingthe forward region to 'slam' duwn on to the water- Additional structuralstrength must be proVided from the forward perpendicular aft for 2S·-30'YL ofthe ship's length. The shell plating either side of the keel I:' increased inthickness, depending upon the ship-'s minimum draugllt. The fra'me spacing isreduced, full- and half·height intercostal side girders are fitted and solid floorsare installed at e'lery frame space. With longitudinal framing the longitudinalspacing is reduced, intercmtal side girders are filted and tranwerse floors areinstalled at alternate frames.
SECTION B SHELL PLATING, FRAMING SYSTEMS ANDDECKS
Maior Structural items 77
their capao;;ity determined. All double-bottom tanks are tested on completionby the maximum service pressure head of water or an equivalent air test.
Structure to resist pounding
In oil tankers particularly, and some smaller vessels, a single-battom constructionis employed. The oil tanker oottOlll structure is detailed in Chapter 8. Theconstruction of the single boltom in smaller ships is similar to double-bottomconstruction but without the Inner skin I)f pla.ting. The uppel edge of all platefloors must therefore be stiffened to improve their rigidity.
Single-bottom construction
Flat
""Girder
\
Heavy pl..t. seal
"Girder
\ Ii
Conti""")LJ'centrelinegircfer
/Drai"3go!..ran9<'mem
Heavyfl~l oorst,lf"noer
oo 0
r ~ I I.I--OI'''I'''ltank-+-_~LUbncalln~O'ld,amti'''k'I 1
0,,' I
I +---r-- 'ese- 01 tank --jCot1erdam Cottoerdam
Figure 5,5 Machinery space dvul1l" borlom
metho<l usually being adopted. Continuity of strength is ensured and maintaine<lby .g~adually ~~ping the tank top height and internal structllre to the requiredPO~tiOI1. AddItiOnal, supp~rt a~d stif~ening: is necessary for the main engines,bOilers, etc., to proVide a VlbratlOn-resmant solid platform capable of supporting~h~ concentr.ated loads. On slow-speed diesel-engined ships the tank top platingIS mcreased to 40 mm thICk or thereabouts in way of the engine bedplate. This
~s ach.!eved by using a special insert plate which is the length of the enginemcludmg the thrust block in size (Figure 5.5). Additional heavy girders are alsofiae.d under :his plate a~d i~ other posi:ions under heavy machinery as required.Platmg and glrder matenalm the machinery spaces is of increased scantlings inthe order of 100/0.
Shell plating
Figure 5.6 Dockin,; pfug and pad
Double-bottom tanks The side and bottom shell plating provides the watertight skin of the ship. Theshell plating also makes tne greatest contribution to the longitudinal strength ofthe ship's structure. As a result of its huge area the shell plating is composed ofmany strakes or plates arranged in a fore and aft direction and welded together.The horizontal welds are termed 'seams' and the vertical welds are termed'butts'. Several strakes of plating are usually joined together as part of a unit. Ashell expansion by unin was shown in Figure 3.2. The thickness of shell pLatingis largely dependent upon ship length and frame spacing. The final structuremust be capable of withstanding the many dynamic and static loads upun thehull, as discussed in Chapter 2. Some tapering off of shell plate thicknesstowards the ends of the ship is usual, since the bending moments are reduced inthis region.
The strake of side plating nearest to the deck is knl)wn as the 'sheerstrake'.The sheerstrake is increas.ed in thickne~s or a high tensile steel is used. This isbecause this section of plating is furthest from the neutral axis. and subject to thegreatest bending stress, as discussed in Chapter 2. The region where thesheerstrake meets the deck plating is known as the gunwale. Two partkuLararrangements in this region are used and are shown in Figure 5.7. With therounded gunwale arrangement no welding is permitted on the sheerstrake
Botoarn sh.11
Docking plug, bra"s Or 'lainl""lt".,
Access to the double-bottom tanks is usually by manholes cut in the t.ank top.These manholes are sUitably jointed and holted to be completely watertightwhen not -in use. Docking plugs are fitted in all double-bottom t:mks and are ameans of c:ompletely draining these tanks for inspection in drydock (Figure5.6). Air pipes are fitted to aU double-bottom tanks to release the air whenfilling. Sounding pipes are also fitted to enable the tanks. to be sounded and
MlliorSlructurul Items Deck beam 79
8eamkn~e
Tran.v"""fr~me
De;;kl gitudinals
Bonomlongitudinal,
fbi
//Deckc.nrr~
~ird.r
Centregird~r
C'l'nl'.giroe,
Side9irde,
----
I 1 i,
Ii
-, ...... ,, ,
, , ~-I,
centrel~.
g"d~r ,
. I, .,
V 0 0 °1 0 0°'1 000 I 0 0 0"
eroe "-1 ! 1 - """ "', L
, - -' -------T,anS\l''''" beams(hilt.... """ ~t"""'>\
T lI,
1I
:'-0 00 0 q.ldo'QTojot I - j 0
/ / ....
O~,
gi,-der
Deck~i'der
lleamknee -......
o~,
Side lonyitudi"al, Cal lon~itudinal
Si,le t7:r::':Jr'"';::]I'r<T'rnt;;:':']";';;:F';::::':!'i'=-~-T-j'girder - __
Tran.vers"
Bo-nomIOrlgitudinal5 _'S:.kbl,LLU-lClLLJCILLU-llLLI...llLUY
De-ck I,a,,;\,
Margin _bra"ket
Longitudinal't.... lkhead
101
Figure 5.9 FnIming tystel1lJJ; fa) traml'eT:l'€ framing; (b) /ollgtrudillsl framing; (c) c()mbine~framing
T'","w~··,e
ha~e
PIJllng<Trake
I P'.'ll"~, "rdk~
,i P .11;~~
! ,: ,alo.~
IPIJt;ng<mak~
~"rTle,
/",",
Tr,,'s~e rseI,,,mc
rrI
Figt./n' 5.7 Gunwale- arrangement,
Figure 5.8 Steala strake arrangement
S:~dl~r .
"r"H
Knee
'l:ause of the high stressing which could re~uJt in crack~ emanating from theoes' of fillet welds. Sucn welds reduce the resistance of components toacking. Where such structure is butt wclde-d the welding must blend into them:nt plate. Towards the ends of the ship, as the CJOss·section reduces, theniolls strakes of plating will taper in width. Where these plate widths becomenall, a stealer plate or strake is fitted (hgure 5.8).
All openings in shell plating must have rounded edges to avoid stress con·entr~t-;oll~ and usually some form of -compensation to avoid a discontinuiiy oflrength.
lie bottom shell and side plating are framed, i.e. stiffened along their length,gainst the compressing forces of the sea. Two different types of framing are in
:raming systems
Bilge keell-olf",\ \lulb platel
:JCllJ~1 ,,'q1,IoLe
,
MajorStrncturai Items 81
•
Transverse fr.aming of the shell plating consists of vertical stiffeners. either ofbulb plate or deep-flanged web frames, which are attached by brackets to thedeck beams and the flooring Structure. The sca:ntlings of the frames are- to someextent dependent upon their depth and also on the natu.re of their endconnections. Particular locations, such as at the ends of hatches, require framesof increased scantlings. Very deep web frames are often fitted in the machineryspace.
Framc spacing is generally not mOle than 1000 mm but is always reduced inthe pounding (cgion and at the fore and aft ends in the peak tank regions.
Longitudinal framing
Transverse framing
Longitudinal framing o-f the side shell employs horizontal offset bulb plates withincreased scantlings towards the lower side shell. Transverse webs are used tosupport the longitudinal frames, their spacing being dependent upon the type llfship and the section modulus of the longitudinal,. This constructiun is describedand illustrated in Chapter 8 with reference to oil tanker construction.
80 Majo, Stntctural hems
use, or a combination of the tW{) may he employed. These are known.respectively, as transverse, !-ongitudinal <lnd combine-d framing and are shown inFigure 5. 9. Cargo arrangements may influence the choice of framing systemsbut. generally, cons[deratiuns of longitudinal strength are the deciding factor.
Ibl
With a flat keel construction there is litde resistance to rolling of the ship. Abilge keel is fitted along the bilge radius either side of the ship to damp anytendency the ship Itas t() wll {Figure S.lO} Some improvement in longitudinalstrength at the bilge radius is a1so provided. The bilge keel must be arranged topenetrate the boundary layer of water along the hull but not too deep to havelarge forces acting on it.
The bilge keel is fitted at right·angles to the bilge radiused plating but doesnot extend beyond the extreme breadth line. It runs the extent of the midshipsection of the ship and is positioned, after model tests, to ensure the minimumresistance to forward motion of the ship. Construction is of steel plate with astiffened free edge or a section such as a bulb pla!e. A means of fastening to thehull is employed which will break off the bilge ked witllout damage to the hullin the event of fouling or collision. The ends are fastened to a doubling plate onthe shell, since the bilge plating is in a highly stressed region of the ship.
lee navigation strengthening
lee class no lations l·, I, 2 or 3 are assigned to ships which have additionalstrengthening as required by classification society rules. Various means of
Figure 510 Bilge keeL (a) pian view shO\l,1-ng ammgemellr at ends; rbj section rlJrought/ilge keel
-additional stiffening by increased frame scantlings, reduced frame spacing andincreased plate thickness. are required. The extent and nature of the stiffeningreduces from 1*, which is the highest classific-ation, to 3, which is the lowest.Some modifications to the stem -and stem region~ may also be required.
Decks
The deck of a ~hip is the horizontal platform which completes the enclosure ofthe hull. It must provide a solid working platfonn capable of supporting anyload~ resting upon it, and also a watertight top cover to the hull structure. Thedeck with its various forms of stiffening and its plating provides a considerablecontribution to the strength of the ship. Where tile deck is pierced by hatches,~pecial warnings or surrounds to the openings must be provided. These largeopenings require special compensation to offset their effect on the structuralstrength of the ship.
82 Major StTucrural /tems
Deck plating
The deck plating is made up of longitudinal strakes of plating across its width.The plates or strakes nearest to the deck edges are termed 'stringer plates'. Theyare of thicker material than the remaining deck plating since they form theiJriportant join between the side shell and deck plating. Towards the ends of theship the deck plating,like the shelJ plating, is reduced in thickness.
The large openings in the deck for hatchways, engine casings, pump roomentrances, etc., require compensation to maintain the section modulus of thematerial. The deck plating abreast of such openings is therefore increased inthickness. The plating between the hatches of a cargo ship is thinner than therest of the deck plating and contributes little to longitudinal strength.
The plating of the weather decks is cambered towards the ship's side to assistdrainage of any water falling on the deck. This camber is wually of the order ofone·fiftieth of the breadth of the ship at midships.
Major Strnctural Items 83
fitted on the ship which run alongside the hatchways and the beams arebracketed to these girders. In this way the unsupported span is reduced. Deckbeams arc usually offset bulb plates. For the length of the open hatch space thebeams are broken and bracketed to the longitudinal girder or hatch sidecoaming. The beams are likewise broken and br~cket~d to the. longitudinalgirders in way of the engine casing. A beam broken In th15 manner IS known as a'half·beam'.
Deck transverses support the longitudinally framed deck. These arc deep platewebs with a facing flat or a flanged edge. They are bracketed to the side framesby beam knees. Small tripping brackets are fitted between alternate longitudinalsand the transverse (Figurr 5.JJ).
Deck girders
Deck stiffening
The deck plating is supported from below in a manner determined by theframing system of the ship. With longitudinal framing, a series of closely spacedlongitudinals are used in addition to deep web lIansverses. With transversefnming, transverse deck beams art used at every frame space. Where hatches arefitted to a ship, continuow longitudinal girders are fitted over the length of theship running alongside the hatches.
Deck beams and transverses
Deck beams are fitted across the width of the ship and are joined to the sideframes by brackets known as 'beam knees'. Continuous longitudinal girders are
Deck girders exist in a number of forms, depending upon their location. Aflanged girder with tripping brackets will often be used ~ part of a hatchcoaming. Such a flanged girder is referred to as unsymmetncal and mwt havetripping brackets fitted at alternate frame spaces. The symmet~ca1 girder is oftenused, particularly as a centreline girder. Brackets join the girder to the. deckbums and are fitted at every fourth frame space. At hatch comers these gudersmust be additionally supported either by pillars or uansverse girders. Thesymmetrical and unsymmetrical types of girder are shown in n,gure 5.1!.
The combination of longitudinal girders with transverse beams IS much In
use in modem ships. The deck longitudinal girders extend as far as possible along
Local loading
On the deck where concentrated loads are situated or likely, additionalstiffening mus~ be provided. M2chinery such as winches, windlasses, etc., will
(.1 Ibl
Fifun 5.12 Girdef amlllrtmtnn: (a) lym~tricaJ; fb) unsymmttrical
... the fulJ length of the ship on the outside of the hatches. This continuouslongitudinal material permits a reduction in deck plate thickness, in terms ofclassification society requirements.
The deck between the hatches must be supported by longitudinal ortransverse beams. Where side girders join transverse beams, particularly beneathhatch openings, gusset plates are fitted (Figures 5.13 and 5.14).
OKk~.m
G.."" /
fxe flal
Fxingflat
Fifure 5.11 Deck bum
FXIII'lII~I
Hatch coamings
Majo, Stmcfllral Irems 85
also require seatings which arc discussed in detail in Chaplcr 6. Also. any bumsfitted in way of deep tanks. bunktr l:mks. etc.. must ha\"c increa~d scanllingsand perhaps reduced spans to be at leaSl equal in strength to Ihe boundary bulk·heads.
Discontinuities
A discontinuity. as discussed here, refers 10 any break or change in section.tttickness or amount of plating materi31. Greal cart must be 13k~n 10 compensalefor any discontinuities in shell or deck plaling resulting from doors, hatchways,etc. Where lhe loss of longitudinal material results. this compensation is ofparticular importance. Where changes in the alllount of plating material occur.such as at bulwarks, the change should be gradual and well radiused.
Well·radiused corners must be used and sometimes the filling of doublingplates or thicker insert plates, al Ihe corners of all openings. Any sharp cornercan produce a notch which. after stressing, could result in a crack. Figure 5./5shows an insert plate filled 3t the comer of a hatch opening.
The edges of all hatch openings are framed by halch coamings. On Ihe weatherdeck the coarnings must be at a minimum height of 600 mm according to theload line regulations. This is to reduce the risk of waler entry to the hoids.Internal coamings, e.g. those within the superstructure or holds. have no heightspecified and in tween-<ieck holds particularly are often made flush with thedeck for uninterrupted cargo stowage. The weather deck coaming must be aminimum of9 mm thick, and where Ihe height is in excess of 600 mm it must bestiffened by a horizontal stiffener and vertical brackets must be fitted not morethan 3 m apart. An edge stiffener must also be provided which may be apreformed section where wooden hatch covers are fitted (see Figure 7./. later)or a half·round steel bar as in Figllre 5./6.
The side cearning plates, as an extension of the longitudinal girder, are ofgreater thickness than the end coarning plales and are extended beyond thehatch opening in the form of brackets (Figure 5.16). These brackets also serve tosupport the platforms used for the hatch operating equipment. Smaller verticalbrackets are fitted around the remainder of the coaming structure to stiffen it(Figure 5./7).
/
0."P~I;ng
--"",1",,;"--
"'I,,----- :Gn(1t. I
F••meop«:1 f,_'I>oa!
GU\OO!I ;>1~lt
",,,,,=~~~~t~~~_"_=_"_=_"_~=~,~, "---- .... -,r-------r--
, ": 11, III II ..., "
=L
Figuf't j. / J H(uch cOnl,r KUsur plillt. ~it..V!d {rom ~lo ..'
Fi,un' J.14 GUSSf!t plott' uud in mKhinf!!ry SplIU COnlIn/trion
l ...... 01 1141
l4
FiJ$lrt.5. J.s I,Ut" p/4tf!! fittm at hatch r:omer
Welle1li'01 ,1td'UI
.Bult 10 be tI","" .feoaming bun
Ra<liU$Idfofined inrules}
SECTION C BULKHEADS AND PILLARS
Bulkheads
The vertical divisions arranged in the ship's structure are known as bulkheads.Three basic types are found, namely watertight, non·watertight and oiltight ortank bulkheads. Oihight or W1Ic. bulkheads are watertight in their constructionbut are subjected to more rigorous testing than a simply watertight bulkhead.
The transverse watertight bulkheads subdivide the ship inlo a number of watertight compartments and their number is -dictated by das~ification sadetyregulations. Oiltight bulkheads form the boundaries of tanks used for thecarriage of liquid cargoes or fuels. Non-watertight bulkheads are any otherbulkheads such as engine casings, accommodation partitions or storescompartments.
Watertight bu Ikheads
Major Structurtllltems 87
-In addition to subdividing the ship, transverse bulkheads also provideconsiderable structural strength as support for the decks and to resistdeformation caused by broadside waves (racking). The spacing of watertightbulkheads, whicn is known as the watertight subdivision of the ship, is governedby rules -dependent upon ship type, size, etc. All ships must have:
D~'stiffener
Trippingbrll(;ke'l
Coaminog
Gusset plate Hateh end".~,.,
Ramp for "ate" c"".. wtleels
Hateh. gi rde.
r\c"",er Coamir>g;eke! bracket Coaming
'"' \,tiffene'
~'" , II , ,I ,
~:, ,, , , \, , ,,J ~ t
, t. '~ I'. ~,
/ I '" ~
Side,~m
b'''''k
86
Offw1 0011> pla1e
'"Figure 5.16 Hareh cOflming: (a) elevation of hatch coammg (~teel hQtch Cov~TSJ: (b) pkm~ie\tl t:>fhatch cOflming Isteel hatch CQ~~)
Additional bulkheads are to be fitted according to the vessel's length, e.g. a shipbetween 145 and 165 m long must have 8- bulkheads with machinery midshipsand 7 bulkheads with machinery aft.
Fitting less than the standard number of bulkheads is permitted in approvedcircums.tances where additional structural compen~tion is provided. Water·tight bulkheads must extend to the freeboard deck but may rise to theuppermost continuous decle. The aft peak bulkhead may extend only to the nextdeck above the load waterline, where the construction aft of thi-s deck is fullywatertight to the sheIL
The purpose of watertight subdivision and tne spacing of the bulkheads is toprovide an arrangement such that if one compartment is flooded betweenbulkheads tne ship's w£terline will not rise above the margin line. The marginline is a line drawn parallel 10 and 76 mm below tlte upper surface of thebulkhead deck at the ship's side. The subdivision of passenger ships is regulatedby statutory requirements which are in excess of classification society rules forcargo ships, but the objects of confIning flooding and avoiding sinking are thesame.
Constrnction ojwatertight bulkheads
(1) A collision or fore peak bulkhead which is to be positioned not less than0.05 X length of the ship, nor more than 0.08 X length of the ship. fromthe forward end of the load waterline.
(2) An after peak bulkhead which encloses the sterntube(s) and rudder trunkin a watertight compartment.
(3) A bulkhead at each end of the machinery space; the after bulkhead may,fOI an aft engjne room, be the after peak. bulkhead.
w.atertight bulkheads, because of their Large area, are formed of several strake1of plating. They are welded to tne shell, deck and tank top. The plating strakesare horiz()ntal and the stiffening is vertical. Since water pressure in a tankincreases with depth and the watertigh.'t bulkhead must withstand such loading,the bulkhead must have increasingly greater strength towards the base. This is
JlIj
Figure- 5.17 COilming bnJt::ket
CoiImingcOt,~r
br~ket
Elliptical Half.rOUrl<:lCOfnBf Daf at
""
D~'plating
-If--- Bracket
flU
"..
OffllelItlgle
"..Hatch --t"~c""ming
: I
"""""--- - - - --r- -- +
r---r .... ---+I I ( ) I II
'" '-';~'5E:S=:::!5=':':'::i="=5":C, --_-I.: ',- --"-tT,--_-_-_ ....., _"Ir ----1----
---r·L.--.i~~,T~~~=-=b-----t 'I
Hat<:n
'"'""mlbelowl
HateMgirdMtH!low
•,c
Major Structural Items 89
achieved by increasing the thickness of the horizontal sirakes of plating towardsthe bottom. The collision bulkhead must have pia ling some 12% thicker thanother watertight bulkheads. Also, plating in the aft peak bulkhead around thestemtube must be: doubled or iJlcreased in thickness to reduce vibration. Thebulkhead is stiffened by vertical bulb plates or toe-welded angle bar stiffenersspaced about 760 mm apart. This spacing is reduced to 610 mm for coUision andoillight bulkheads. The ends of Ihe stiffeners are bracketed to the lanktop andIhe deck beams. In twecn decks. where the loading is less. Ihe stiffeners mayhave no end connections. A watertight bulkhead 3rrangtment is shown inFigure j. J8.
Welded se.m'"'
~ -cI Upper ,tool~lel...k
I .., I . I I !I,
l'-Jr..,, I I .IAa~ I ' " I' , I I 'I~'~'~I I 'I"·"' ' I .....te.. rght ,I .I• l)ulknuo:l •I ' I . I I I i I iI
. I I III '
I Lo- 'lool /i Double bOil""'
l Happe'l...k
t.,
Corrugated watertight bulkheads
The use of corrugations or swedges in a plate instead or welded stiffenersproduces as strong a structure with a reduction in weight. The troughs arevertical on transverse bulkheads but on longitudinal bulkheads they must behorizontal in order (0 add to the longitudinal strength of the ship.
•
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Jr
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td
FifUrt 5.19 Coffllpud _l~rtithtbulkhrlld_' (tl) WCriOll throut/lt:OfflIprion: (b) d~~llrion
o{bu/khtfld: (t) plDn ,ir.., oftorruprions
91
,
Stiffener
BrICkel
"""
Slif!ffief
Girder
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-----------
f----Pill¥
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,.,
,O!
Fip'" .5.21 lIIbulu piJiJI, llffllll'~mtnU: (a) pi11tzf hud COIlJl«POI"I:Ib) pillJu h«l COftntctiOlt
Non-watertight bulkheads
Testing o{watertight bulkheads
The main fore and aft peak bulkheads must be tested by filling with water tothe load waterline. Subdividing watertight bulkheads ate tested by hosing down.Oiltight and tank bulkheads must be tested by a head of water not less than2.45 m above the highest point of the tank.
Pillars provide a means of transferring loads between decks and fasteningtogether the structure in a vertical direction. The pillars which transfer loads, asin the cargo holds or beneath items of machinery. are largely in compression andrequire little or no bracketing to the surrounding structure. Pillars which tiestructure together and are subjected (0 tensile forces are adequately bracketed atthe head or top and the heel or bottom.
Hold pillars are usually large in section and few in number to reduce interference with cargo stowage to a minimum. Pillars are provided to reduce theneed for heavy webs to support the hatch girders or end beams. The use ofpiJlan also enables a reduction in size of the hatch girders and beams. since their
The corrugations or swedges are made in the plating strikes prior tofabrication of the complete bulkhead. As a consequence, the strues runvertically and the plating must be of unifonn thickness and adequate to supportthe greater loads at the bottom of the bulkhead. nus greater thickness of plateoffsets to some extent the saving in weight through not adding stiffeners to thebulkhead. The edges of the corrugated bulkhead which join to the shell platingmay have a stiffened fiat plate fitted to increase transverse strength and simplifyfitting the bulkhead to the shell. On high bulkheads with vertical corrugations,diaplrn.gm plates are fitted across the troughs. This prevents any possiblecollapse of the corrugations. A corrugated bulkhead arrangement is shown inFigure 5.19.
A watertight noor is fitted in the double bottom directly below every maintransverse bulkhead. Where a watertight bulkhead is penetrated, e.g. bypipework, a watertight closure around the penetration must be ensured by acollar fully welded to the pipe and the bulkhead.
Any bulkheads other than those used as main subdivisions and tank boundariesmay be non-watertight. Examples of these are engine room casing bulkheads,accommodation partitions, store room divisions, etc. Wash bulkheads fitted indeep tanks or in the fore end of a ship are also examples of non-watertightbulkheads. Where a non-watertight bulkhead perfonns the supporting functionsimilar to a pillar, its stiffeners must be adequate for the load carried. In allother situations the non-watertight bulkhead is stiffened by bulb plates orsimply fiat plates welded edge on. Corrugated and swedged bulkheads can alsobe used for non-watertight bulkheads.
Pillars
90 Major Structural Items
Maior Structuralltf!rns 93
P~IJng SI""9t'tperl..-lIed fl,1l
, "
...-~~-r-r-'l ' : : : ~OT;T;!J-:,..,k71r---pl.lI~<lem
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_-----------7 F..-ecastltdKk92 Major Stnl("t/lralllC'ms
unsupported span is reduced. Where pIllars are filled between a number ofvenical decks they should be in line below one another 10 efficiently transferthe loads.
Hold pillar sections arc usually a hollow fabricated shape manufaclured fromsteel plale. Typical sections are round. square and somelimes octagonal.Machinery space pillars are usually fabricatcd from sections and. while slllalicrin dimensions than hold pillars. a greatcr number are tined (FigllrC' 5.20).Additional slruclural matcrial must be pro\'ided at the head and heel of pillarsto evenly disuibuu: the load. AI the head a plate is used. orten with trippingbrackets to surrounding structure. At the heel an insert plate or doubling plateis used, wilh or wilhoul bracken depending upon Ihc type of loading (Figur('5.21).
Solid pillars may be fined in accommodation spaces or under poinls ofconcenuated loading. Solid round bar up to abolll 100 111111 diameter is filled.again with head and heel plates to spread the lead.
SECTION D FORE END CONSTRUCTIONFlKUtr 5.22 F(H'f! end ronStlllction
The forward end of a ship refers to the struClUre forward of the collision bulk·head. TIle forward end is designed to provide a smooth enlfY 10 Ihe water and asneamlined flow along the ship. As a result. resistance to motion is reducedto a minimum. The stem is the most forward pari of the ship and runs down tothe keel. It is constructed in two parIS - a bar stem from the keel to the loadwaterline and a plate stem up to the deck. TIle plate slcm usually rakes wellforward providing pleasing lines 10 the s.hip. an increased deck area and a readilycoUapsible region in the event of a collision. The side shell plating is narl~d OUI tofUrl her increase the de-ck are-a. This arrange-me", also serves to deflect sea walerand spray away from Ihe- ship in heavy weJ,the-r. The forward deck area orfore-castle houses the windlasses and winches required for anchor and mooringduties. The anchor chain is housed in a chain locke-r benealh the forecastle. Abulbous bow may be filled. which is a protrusion below the waterline designed10 reduce fhe ship's resistance to motion.
Fixutr 5.23 Sutton IhTOCiP plaIt'sum sho..inf brusthook
tDf ..~
Stem
The stem is the terminating point of the forward shell plating. It is made up of astem bar from the keel 10 the load waterline and a stiffened plate struclUre up tothe forecastle deck (Figure 5.22). The stem bar is a solid round bar which iswelded 10 the inside of the keel plate at the lower end. At its upper end the barjoins [he slem plate. The shell plating is welded to either side of the stem bar.
The stem plate conSlruction of curved plales is stiffened at intervals bybreasthooks which are small flange plates fined horizontally (Figure 5.23).A continuous bulb or flat bar stiffener may be fined where the sle-m plale radiusis considerable. Heavier than usual shell plating may be fitted at the stem plateregion.
Panting structure
Panting is an in·and-out movemenl of the she-II plating resulting from thevariations of water pressure as waves pass along the huU and when the vesselpitches. Special structural arrangements are necessary in the forward region ofthe ship to strengthen the ship's pia ling agai.nsl this action. The structure mu~t
be strengthene-d for 15-20% of the ship's length from forward to t~e ste~. Thl.sstiffening is made up of horizontal side mingers, known a~ 'pantlng stringers •fitted at about 2 m intervals below the lowest deck. Panting beams are fittedacross the ship at alternate frame- spaces and are bracketed .to the. pantingstringer. The intermediate frames are connected to the pantm.g strm~er b~brackets (Fjgu~J 5.24 and 5.25). A partial wash bulkhead or a senes of pillars 15fiue-d on the centreline to further support the structure-. Perforated flats may be
ITI
Bft<lllhook
'"~1
I I,\ I
Major Strocturalltems 95
fitted instead of beams but these must be not more than 25 m apart.Perforations of at lust 10% of the plate area are required in order to reducewater pressure on the flats.
Bulbous bowThe bulbous bow is fitted in an attempt to reduce lhe ship's resistance. Arrange.ments vary from a casting plated into the forward end to a fully radiused platedstructure, or in some cases a cylindrical shape plated into the forward end. Theerfectiven~s of the arrangement is the subject of much discussion but improvedbuoyancy forward is provided which will reduct the pitching of the ship.
The construction shown in Figurt $.16 consists of a vertical plate web whichstiffens the free edge of the breasthooks fitted right forward in the bulb. Deepframes with panting beams are fitted al every frame space with a wash bulkhead on the centreline. The panting stringers consist of perforated plates runningthe full width and length of the bulb. Another vertical plate web joins the bulbto the fore end structure. A small stem casting connects the top of the bulb tothe plate stem above the load waterline. The numerous manholes cut into thestructure permit access to all parts of the bulb. The anchor and cable arrangemenlS must ensure that the bulb is not fouled during any part of the operation.
~7====:j;====;:h. Sl';nget
_
.\H~"-Smnget
B•.,ktl
'~T==f======1======"iF=:;:::;;:1So_
SIde ,,,de<
94
1 \
Figun 5.26 Bulbous bow COI/Srnu:notl
Str,n9fr
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Collision -t1t~==iI===::jl===:~b\.Ilkh..d
96 Major S!fUcturalltems
Anchors and cables
The forecastle deck !louses the windlass or windlasses which raise and lowerthe anchor and cable. Variou~ items of mooring equipment such as bol1ardsfaide-ads, etc., ilrC also arranged around the deck edge. The a~chQrs are houseda,gains! the forward side shell, sometimes in speci'-llly recessed pockets. Theanchor cable passes throlJgh the shell via the hawse pipe on to the forecastledeck. It travels over tlte <::able stopper and on to the windlass cable lifter drum.From the cable lifter it drops vertically down into the chain locker below.
Hawse pipe
The hawse pipe is fitted to enable a smooth run of the anchor cable to the~indlass and to maintain the watertight integrity of the forecastle (Fixure:>.21). It. should be of ample size to pass the cable without snagging when raisingor lowenng the anchor. Construction is usually of thick plating which is attachedto a doubling pl.ate at the forecastle deck and a reinforced strake of plating:at
Bow.l<lp.,er
Major Stru,:luralltems 97
the side shelL A rubbing OJ chafing ring is also fitted at the outside shell. Asliding pbte cover is shaped to fit over the cable and close the opening whenthe ~hip is at sea.
Cable sto pper
Th~ ch:Jin, <:able OT bow stopper is fitted on the {(lrccastle deck in line with th~
run of the anchor cable. II is used to hold the anchor <:Jble in place while th(ship is riding at anchor OJ the a.nchor is fully housed. In this way th~ windlas~
is freed ami isolated from :lllY shocks or vibratiollS from the cable. The c]taiistopper i~ not designed to stop the moving cable, blJt onl}' hold it in place. Omtype is shown in Figure 5,28 :and wmists of a fabricated structure of he3vy plaHwith 3 roller which the cable passes over, A hinged har is designed to falbetween two vertical links and hold the cahle in place. The chain ~topper i~
welded Of bolted on [() a he.avy imeTt plate in the deck and i~ additionall)stiffened by h-rackets.
WindlassA~chorcable ,/
DotJbling plate
For~ca'tl"deo;k
----_ Sh,p',
Old"
./ --- --- Anchor
III,
Chafingring
Figure 5.2"7 Ha \tIl'e pipe
The windlass i~ the lifting devic-e for the anchm cables or chains and i~ also ll~~(
for moming and winching duties. Various drums or harre-Is can be 'clutched intliperform the diffnent duties_ For raising tl1~ anchor. the cable lifting drum iengaged.
This is a barrel with specially shaped 'snugs" which tlle cable links fit into an(pass round before dropping into the chain locker vi.a the spurling pipe. Tn.anchor cable is allowed to IGwer under its own weight wiLh Lhe lifting drundecliltched. while the brake band around it is used to ;;antrol the speed 0
descent,
Chain locker
The chain locker is llormally fitted forward uf the collision bulkhead, It is 0
dimensions adequate- to house all the allchor cable and stil1le.ave a considerabilempty space above. Two lockers or a centrally divided single locker will be fit telfor the port an-d starboard anchor cables. The chain locker should be as Iowapracticable to reduce Ihe height of the centre of gravity of the considerable masof the cables, A perforated false floor or ,grating is tilted at the hottom tlprovide a drainage well and keep the cable out of mud and wate-l.
Figure 5.29 shows an arrangcmcnt of a chain locker. It consists of a plat,stru-cture with vertical stiffeners armmd the outside. Plate webs which fornpart of the ship's internal structure are also utilised for stiffening. A raiselperforated false floor is fitted allli supported by so-lid floors. The well thuform-ed is connected to the bilge system and should be emptied every time thanchor is raised. The forecastle deck forms the top of the lucker wilh th~purling pipe at the centre. The spurling pipe is manufactured of heavy platwith a solid round bar .as a chaffln,g ring on the lower edge. Brackets radiate frorthe spurling pipe to lhe chain locker sides to strengthen the forecastle deck anithe spurling pipe. A U-section plate welded to the ,ide with footholes cut iJprovides access to the bottom of the chain locker from a watertight door at th
Ma;orStructural/tems 99
F OI'e.2'Itle deC:k
B'ack~1
P,n f.""" bv""n.ng ~wt>eelon IOfeoc;Kl~deock
Spu.ling pipe
1r>W1'1,,1.1",nc~,n
loc:~",
F,~l hn~
01 in<:horeihl~
Clench cable assembly
Solid.floor pliot..
The fmallink of the anchor cable is secured to the ship's structure by a clenchpin. On most modem ships this pin is positioned on the outside of the chainlocker and can be released easily and quickly. A situation may arise where thesafety of the ship does not allow time to raise the anchor. By releasing theclench pin all the cable can quickly pass out of the chain locker. leaving the shipfree to proceed out of danger. An arrangement is shown in Figure 5.30. where an
,.., '.. ~_'r :'.:....1.'
/~~:~Ci"ode"ng ',_', ,.. ) ~ '.
'..
Fixu~ $.29 Dllnn lockn-
upper deck. Provis.ion is also made for ~curing the frnallink oflhe anchor cable.The chain locker illustrated is one of a pair fitted port and starboard beneaththeir respective windlasses.
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98
- B•..,hl
I prapeller
The aft end of a ship terminates the structure and is designed to provide aSmooth water flow into and away from the propeller. The propeller and rudder
Tube: ......Idl!dd'reclly 10,,~
FiKU'" 5.32 Bow thrusrer tunlltl
Major Structural Items 101
shown in Figun 5.3/. A non-rotating servo motor located in the gear housing isused to change the pitch of the propeller blades. The force on the servomotorpiston is transmitted by a piston rod inside the propeller shaft to the crossheadand crank mechanism in the hub. Water now can thus be provided in eitherdireclion simply by changing the blade pitch angle. Any non-reversing primemover can therefore be used. e.g. a singie speed electric motol. The prime moverneed not be stopped during manoeuvring operations since the blades can beplaced at zero pitch when nO thrust is desired. The drive is obtained thsough aflexible drive shaft, couplings and bevel gears. Special seals prevent any sea waterleakage into the unit.
The complete assembly includes part of the athwartships tunnel throughwhich water is directed to provide the thrust. Grids must be fitted at either endof the tunnel and this can reduce the thrust to some eXlent. The actual tunnellocatiOn is usually decided by model tests to ensure !he minimum resistancewhen not in usc. A tunnel construction arrangement is shown in Figure 5.32.
Gill jet thrusters utilise a vertical axis propeller in a T-shaped tunnel. Water isdrawn in from both sides and leaves through the bottom of the hull. Rotatableg.ilI ftns djrect the water in One of a number of flXed positions around II circle.The hydrojet thruster has a similar arrangement but draws waler in from belowand discharges it at the sides with vanes directing the thrust. Steering vanes inthe diverging liquid path can also be used 10 maximise the thrust to one side orthe other. Ducted jet thrusters operate somewhat similarly to a tunnel thrusterexcept that the duct is usually curved. This duct may be located either on theship's side or the bottom shell and usually requires large openings.
An azimuth or rotating thruster usually consists of a dUCled propeller whichcan rotate through 36(f. The propeller may be flXed or controllable pitch. Thisunit is particularly sujted for dynamic positioning and some propulsion duties.When fitted to ships, an azimuth thruster is usually retractable.
SECTION E AFT END CONSTRUCTION
""""
. ,I
"9. Ollllk pin n·", 17. Servo mOtor piston
10. Crosshead bearing llOUS;/lg 18. Sen'O motor cylinder head1/. Toper roller t/'rust bearing 19. Feed bock IillkJlge/2. Crossheod 20. !Kn·o motor cylinder/1. Propeller shafr 21. Sul'O molar endCO~r/4. Prop~l1ershaft thrust 22 Spiral bel·el pinion
betJnnl 21. Drive shofr raper roller15. Spiral bC'1·el ...hed BearinX16. Pirtoll rod 2-1. Gear housl/lg
Fig/Ire 5.3/ Tunnel fllruster Im;f
100 Major SlrocturaJ Items
inser.t heavy pia Ie .pockel is filled into the chain locker side with a vertical pinh~ldmg Ih~ fmal Imk of anchor cable. A hand-wheel assembly on deck is used 10ralSe the pm and release the link.
A. thruster is .~su~y considered to be a device which assists in docking. manoeuvnng, or posllJon~g ~f a vessel which is moving at a low speed. Some fonn ofpropeller-type deVIce IS used 10 move water either freely or in a duct. The propeller may be fixed or. contr_o.llable pilch and the complete unit may be retractable or exposed, flXed In position or able to rotate (aZimuth).
ProbabJ~ the. most common unit Iitted on merchant vessels is the tunnelt~ruster .usmg either ~ fixed pitch or a controllable pitch propeller. The flXedpilch Unit wouJd require a reversible drive. A controllable pitch type thruster is
Thrusters
"
"--.
"
"~
" //""
1. Tunnel sulio/lZ. Motor nzOlilltillg stoolJ. Input dn·I'e shaft4. InpUl drive shaft cur";dgC'5. /'rolH""r shaft Jeal6. Propeller blade7. Blade palm sal8. Illlb bod)'
102 Major Stnu:tIlral Items MajorSttucruralltems 103
are also positioned :lnd supporled 3t the after end and require cenain structuralarran!lemcnts in order 10 operale S3lisfaclorily. The after end consrruetioninvoh'es an amount of overhanging structure to accept the sleering gear belowdeck and mooring equipment higher up on the wealher deck. This arrangemen!leads to large slamming forces in Ihis afler region. and an adequalely stiffenedslruclure is therefore ri."quiled.
Two main types of stern construclion have been u~d 10 dale - Ihe cluistrslern and the transom stern. The cruist'r stern is I3rely used in modemconstruclion but it IS slill to be $Cen in a large proportion of the ships 3t sea. The!ransom stern. "'ilh its slraig,ltt·linc form. Ii."nds itself well 10 currentmanufacturing techniques. It also provides a greater deck area aft and iscurrenlly much uSed for a variety of ship lypeS.
Cruiser SternThe COllslruclion of the cruiser stern (FigUff! 5.33) ensures adequate resisla.nce10 any pounding stresses which may occur. Solid pIalI' floors are fitted at.everyframe space and a heavy centreline girder is fitted below ~ach .of lh~ decks In thet rn A centreline web 35 a continuation of the centrelme guder IS fitted at the~f~er'end shell plating and runs down to the centreline girder in the n~ringregion. Special frames are radiused around the afler end and are ~nown as cantframes'. since they are set at an angle to the centreline of the ~up. These cantframes join cant beams which suppa" the deck at the radlUscd after e~d.Horizontal stringers may also be fitted to stiffen up the Slructure by connecungit to Ihe transverse frames further forward.
PooPdeek
Fi8W~ jJ4 TlVlUlOm Jft,.,.
Transom stern
Deep solid-plate floors are also a feature of the transom slem construction,together wilh a centreline girder (Figure 5.34) .. The ~at plate of the lIansomstem construction, however, allows use of verucal suffeners around the shell
St_;ngll~l
_ BulkheMl
S«fHl>f'l x-x
-- -
T'~nsve<~
dK'"'.mg"dro-
Sft;:ond deck
R_1tunk
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,,, :
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Upper deck
\IF====I;t[\\
105
\ .J\ [', ,~
'" '<' :-':-'--~-~
" \'C ;'. A, -- -
"<~.
,,
,,
Line of pl~li"~,,
\,,
FIMr
lW,gitudinalgirderFlO-Or
I\
Figure 5.35 Cast sputacle [rome
Tan.. tOP
\ ,
Floor
FI-(lo,
Plarr view
Palm
Elevirlion,looking afl
Rudder trunk
104 Major Structural/terns
plating. The vertical stiffeners are bracketed to the floor and to the deck heamswhich nm transversely across the stem. A deep hmizontal stringer can provideadditional stiffening to the >hen plating if required. A deep centre girder runsbeneath each of the deck:; at tlte stern and is bracketed EO the deep web at thecentreline of the after shell plating. This web is likewise bracketed to the variousfloors in the stern and finally 10 the solid-plate floor construction below.
Sternframe
The shell plating at the after end is temtinated by the stemframe (Figure 5.34).This is usually a casting, but fabrications and forgings are sometimes used. Insingle-screw shi ps the ste-rnframe has a boss on the cen treline for the tailshaft topass through and an adequate aperture is provided for the propeller to operatein. 1f sufficient clearance at the blade tips were not allowed then seriousvibrations would be set up in the after end of the ship. The lower part of thesternframe may provide a support for the rudder post or an overh.anging sectionmay provide gudgeons for the rudder pintles. Figures 5.34, 5.41 and 5.42 showdifferent arrangements. Various sections of the sternframe, particularly abovethe arch, provide- connecting points to the individual floors of the after endconstruction. The transom post and vibration post are two particularconnections (Figure 5.34). Sound connections at these points ensure thatpropeller-induced vibntions are kept to a minimum. Twin-screw ships have asternframe which is only required to support the rudder pintles and is thus muchreduced in size. Larger stemframes, particularly those of cast constmction, aremanufactured in two parts with provision made for bolting together and, aftercareful alignment, welding at the suitably prepared joint.
The rudder trunk is an open section which is left in the stern for the elltry of therudder stock into the steering flat (Figure 5.34). A horizontal platform is some_times fitted midw.ay up the trunk to fit a watertight gland. The (runking above i,then constructed to be watertight and access to this upper section and the glandis provided bya manhole.
A-brackets and bossings
Twin-screw vessels with their shafts set away from the centreline require supportfor the shaft overhang as it leaves the shell. Bossings are often used to increasethe vessel's width and allow the mafts to remain within the hull while stillretaining a streamlined flow ofwater to the propellers. The shafting is protectedand internal insp-ection is possible with this arrangement. These bossings aresymmetrical about the ship's centreline and give rise to the tenn 'spectacleframe' because of their appearance from aft of the vessel (Figure 5.35). Somemodern constructions make use of A-brackets set out from the huU to supportthe shafts (Figure 5.36). The f"mal A-bracket in addition to acting as a bearing,must support the weight of the propeller.
Both bossings and A·frames are led into the stern and solidly built into thestructure with additional local stiffening where required.
Figure 5.36 A_Bracket
106Major Srructurallt~ms 107
Stemtubes
,..
The propeller shaft enters the ship through the sterntube which acts as the rll1albearing and a watertight seal to the sea. Traditional practice saw the use oflignum vitae and certain synthetic materials as bearing surfaces within the sttrn·tube and these were lubricated by sea water. The increased loadings, as a resultof slow speed shafts and heavier propellers on more modem ships, has led to thewidespread use of oil.J.ubricated whitemet.al bearings. Wilh this arrangementwear down in service is much reduced but there is a need for more accuratealignment and for seals al each end of the stemtuhe. An oil-lubricated sterntubearrangement is shown in Figure 5.37. Additional details are given in Marin.eAuxiliary Machinery by D. W. Smith (6th edition, Buttcrworths Marine Engineering Series. 1983).
Propellers
B''''IeCtlonli
B~.
Proie<tedoutline
Developedoutline
COM
A propeller consists of a boss which has several helicoidal form blades. Whenrotated it 'screws' or thrusts its way through the water by giving momentum tothe column of water passing through it. The lhrust is transmiued along the shaft·ing to the thrust block and fmally to the ship's structure. The thrust block musttherefore have a rigid seating or framework which is integrated into the ship'sstructure to absorb the thrust. The propeller will usually be either of the fIXedpitch or controllable pitch type. In addition some special designs and arrange·ments are in use which offer particular aavantages.
A."
Although described as fixed pitch. a solid single.piece cast propeller has a pitchwhich varie~ with increasing radius from the boss. The pitch at any particularpoint on a blade is however fIXed and an average value for the complete pro·peller is used in all calculations. A fIXed pitch propeller is shown in Figure 5.38,where most of the terms used in describing the geometrical features are also
Fixed pitch propeller
F~ur(' 5.38 F"urd pitch propf'l/{'r
_+'_-+Tail.hatt
MajorStmcrural Item!> 109
1-I)/.cJ<a",licconne-ct;on
Load ingring
r~"'1 Se-aJ Di.tance
Connecting tu~,tem Seal
ghen. 11 should be note<l that the face is the surface farthest from the stem andis the 'working' surface. A cone is fitted to the boss to provide a smooth flow ofwl!ter away from the propeller. A propeller which rotates clockwise, whenviewed flom \\ft, h comiueIed to be tight·handed. Most sifl&\-e-screw ships haveright-handed propellers. A twin-screw ship wUl usually have a right-handed starbo.ard propeller and a left-handed port propeller.
Ca~t1\tior. ls the f",rmmg and bursting of vapc\l;r filled caviTIes or bubbles andoccurs as a result of .::ertain pressure variations on the back of li propeller blade.The re-sohs of this phenomenon are a loS'; ofihrust, erosion of the blade surface,vibra.tiom in the afterbody of the ship and lloise. It h umally limited to hjghspeed, heavily loaded propellers and is not a problem under nonnaI operatingconditions with a well-designed propeller.
The pIOpeUel, when turning in the ship's wake, is a. potential source ofvibration excitation. To some extent this can be minimised by having the leadingedges skewed back. Skew back is an advantage when the propeller is working in avarying wak.e <15 not al1 the blade is affected at the :same time_ Variations in thethrust and torque are therefore smoothed out. Since the vibrations are bladeexcited, then the number of blades is -significant and determines the vibrationf1e-quency. Where severe vibration problems exis.t it may ultimately be necessaryto change the propeller for one with a diffelent number ofbladcs.
108 Major Structural Items
Propeller mounting
The propeller is fitted onto a t.aper on the tailshaft and a key may be insertedbetween the two~ alternatively a keyless arrangement may be used. A large nut isfastened and J,ocked in place on the end of the tailshaft. A cane is then boltedover the end of the tailshaft to provide a smooth flow of water from the pIOpellel.
One method of ke--yless propeller fitting is the oil injection system. The propeller bore is machined with a series of axial and circumferential grooves. Highpressure oil is injected between the tapered section of the tailshaft and thepropeller_ This reduces the friction between the two parts and the propeller ispushed up the shaft taper by a hydraulic jacking ring. Once the pIOpeller ispositioned, the oil pressure is released and the oil runs back leaving the shaft andpropeller securely fastened together.
The Pilgrim Nut is a patented device which provides a predetermined frictional grip between the propeller and its shaft. With this arrangement the enginetorque may be tranSJTliUed without loading the key (where fitted). The PilgrimNut is, in effect, a threaded hYdraulic jack which is screwed onto the tailshaft,see Ffgure 5.39. A steel ring receives thru,t from a hydraulically pressurisednitrile rubber tyre. This thrust is applied to the propeller to force it Dnto thetapered tailshaft. Propeller removal is achieved by reversing the Pilgrim Nut andus.ing a withdr:awal plate which is fastened to the propeller boss by studs. Whenthe lyre is pressurised the pr(lpellel is drawn off the taper. Assembly and withdrawal are shown in Figure 5.38.
Controlla ble-pitch p rope Ilers
A controllable-pitch propeller is made up of a boss with separate blades mountedinto it. An internal mechanism enables the blades to be moved simultaneously
- Pro""il", QO'Ss~ooN,t,ile tv'"
4r I,
~~
Co C'- Lewi",!"n~
I - Withdr3wa,Dlat~....----- - Tail:shalt,,,,,
Figure 5.39" Pilgrim nUl operl1tion
through an arc to change the pitch angle and therefore the pitch. A typicalarrangement is shown in Figure 5.40.
When a pitch demand signal is received, a spool valve is oper:ated whichcontrols the supply of low pressure oil. to the aux.iliary servo-motor. This movesthe sliding thrust block assembly to position the valve Tad which extends. intothe pIOpt111er hub_ The valve rod admits high pJessure oil into one side or theothel of the main servO-motor cylinder. The cylinder movement is transferred bya crank-pin and ring to th~ pmpelleI blad~s.The pIopeller blade~ rotate togetheIuntil the feed-back signal balances the demand signal and the low pressure oil tothe auxilimy servo-motor is cut off. To enable emergency control of propellerpitch. in the event ofloss ufpowe-t, the $pool val..e~ can be opetated by hand.The oil pumps are shaft driven.
110 Majo, Stmcturalltems III
Rudders
The rudder is used to steer the ship. The turning action is largely dependent onthe area of the rudder, which is usually of the order of one-sixtieth to oneseventieth of the length X depth of the ship. The ratio of the depth to widthof a rudder is known as the aspect ratio and is usually in the region of 2.
Slrcamlined rudder of a double-plate construction are filled to all modernships and arc further described by the ammgement about their axis. A rudderwith all of its area aft of the wrning axis is known as 'unbalanced' (Figure5.4l). A rudder with a small part of its area forward of the turning axis is knownas 'semi-balanced' (Figure 5.42). When more than 2570 of the rudder area is
A number of specialised arrangements or types of propeller exisl and haveparticular advantages or applications. The Voith-Schneider propeller, the TipVortex Free propeller and the use of a duct or nozzle afC described here.
The Voith-Schneider prop€l~ a vertically-rotating device. The blades arcvertically positioned around a disC\.!!l-d can be rotated by cams in order tochange the blade angle at a particular point in each revolution. Thjs results in alhrust whose magnitude and direction is determined by the cams. It is, therefore,in some respects(similar to a controllable-pitch propeller in that the disc is drivenand the blades can be positioned independently of the main drive. This unit caneffectively thrust in any direction and will respond rapidly to the pitch controlmechanism. The complete assembly is unfortunately complex, noisy in operation and considerable maintenance is necessary. II is often used for main propulsion in ferries and vessels requiring considerable manoeuvrability. It may alsobe used as a thruster or proplusion device for drill ships or fioating cranes whichrequire accurate positioning.
. The use of a duct or nozzle around the propeller can result in an improvement of the propeller performance. Furthennore the aerofoil shape of the ductcan produce a forward thrust which will offset any drag it creates. The duct alsoprotects the propeller from damage and reduces noise. It is usually fitted onships with heavily loaded propellers, e.g. tugs, and has been used on largervessels. One particular patented design of duct is known as the Kort Nozzle.
The Tip Vortex Free (TVF) propeller is a recent special design which resultsin much improved propeller efficiency. The blade tips are fitted with pieces atright angles to lhe plane of rotation. The initial impression is that the bladeedges have been bent over towards the face, i.e. away from the ship. The attachments at the blade tips serve to generate thrust across the whole propeller bladeand thus improve the propeller efficiency. A nozzle surrounds the propeller anda tunnel structure under the stern on either side is used to direct the incomingflow of water.
The control mechanism, which is usually hydraulic, passes through the tail·shaft and operation is from the bridge. Varying the pitch will vary the thrustprovided and since a zero pitch position exists the engine shaft may tum con·tinuously. The blades may rotate to provide astern thrust and therefore theengine does not require to be reserved.
Special types
,
ir--'
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,
.--~-
1
'ludder;lOll
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pl.l~
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A
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L'n~ 01shell
~I~ti"q
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'I
~he rudder, depending on Ils type and 3fIangement, will turn on either pi.ntles,r bearings_
The balanced rudder in Figure 5.34 has a rudder axle fitted at its turningxis. Upper and lower bearings are D.tted in the rudder, as shown in Figure.43. The bearing consists of a stainless steel bush in the rudder and a ~tainless
teel liner on the axle_ The stainless steel bush i> spirally grooved to permitlibrication. Other materials arc in use, such as gunmetal for the liner and lignumilae or lufnol for the bush. The uppeT and lower pair of tapered bearing ringsre fitted between the rudder and the stem frame. These are fitted with a small:learance but may support the weight of the rudder should the carrier fail.
The semi-balanced rudder shown in Figure 5.42 turns on pintlcs. Arrangeaents vary but the pintle (ol\sists of a bearing, length of constant ,harneter 31111 aapered l.ength which is drawn into a similarly tapered hole on the rudder orternframe gudgeon. The pintle i5 drawn in by a laIge nut pulling on thehreaded portiOll of the pintle. The pintle nut b securely locked in place afterightening. A locking pintle has <l shoulder ofim;reased diameter <\t its lower endvhich prevents excessive lift of the rudder. A bearing or heel pintle has .alearing surface at its lower edge wrJ1ch rests OIt J hard steel disc. This bearing)jJltlc: is only requiIc:d to support the weight of the rudder in the event of theud-der caHier failing. Both types of pintle are shown in Figure 5.41. Liners ofHass UI sometimes sta.in1css steel are filted to the pinJle hearing surfa.ce. Tilelearing material i~ held in a cage in the gudeon and j;; u~ually tufnol or somelard-weariJlg synthetic material Lubrication is provided by sca water which IS'rce to circulate around the bearing sur[.a-l:CS of botb pin tIes.
[2 Major Stnlctural Iterm
~udder pintles and bearings
lrward of the tU01ing axis there is no torque on the rudder stock at certainrlgles and such an arrangement is therefore knoVlll as a 'balanced rudder'"~igure 5.34).
Tile constructi.on of modem rudders is of steel plate sides welded to all
ltemal webbed framework. Integral with the internal framework may be heavyJrgings which form the gudgeons or bearing housings of the rudder. The upperIce of the rudder is fonned Illto a usually horizontal nat palm which acts as theoupling. point for the ruddcI stock. A lifting hole is provided in the rudder tona.ble a vertical in-line lift of the rudder when it is berng titted or removed. Apedal lifting bar with eye plates is used to lift the rudder. On the unbalancedod semi·balanced rudders showrl. in Figures 5.41 and 5.42 can be seen a famiorl.r eddy plate at the forward edge. This is welded in place after me rudder isitted to provide a streamlined water flow into the rudder. After manufadUIe,very rudder is ai.I tested to a pre,sure equivalent to a head of 2,45m above the:lop of the rudder to ensure its watertight integrity. The internal surfa~es aresually coated with bitumen or some similar coaring to pmtect the metal shou~db.e pl:lting leak. A drain hole 1S provided at the bottom of the rudder to checkor water entry wilen the ship is examined in dry Jock.
==Iudder stock and carrier
fhe ,tack. passes through a gland and a rudder carrier before entering the:teering .compartment. The gland and carrier may be cQrnbined ur separate .items)[ el.juipmen t.
___ --l ~
,
v~nic,', sriff.ener
Figure 5,42 Semi-baumced rudder
II:
SIDC~
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FipTfl 5.45 ....'lIurri/:hr Ihllld for rudder stock
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SU;d
114 Ma;orStructll.rQllrems
SI.,"leo<<IMI-,
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'- Slock
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c~
,
Figu.re 5.44 R,.dd".r carTi".r
The rudder carrier consists of (wo halves which provide an upper and a lowerbeating surface (Figure 5.44). The upper pari of Ihe rudder carrier is keyed tothe stock so Ihal they turn logelher. The major pan of the rudder's weight js
Fiture 5.46 Combined rudder amitr and gland
J J6 Major Structural hems
transferred 10 the rudder carrier by either a shoulder. as part of the stockforging, or a collar filled between the tiller and the carrier. The rudder weight isthus transferred to the lower bearing surface of lhe carrier which is greaselubricated. A flat or conical bearing surface may be used depending on theparticular design. The lower half of the carrier is bolted into a heavy insert platein the deck of the steering flat and is chocked against fore and aft and athwart.ships movement.
A separate walertight gland is often filled where the stock enters the rudderlrunk. This arrangement provides access to a grealer length of the rudder slack.removes the need for a watertight construction of the carrier bearing and reducesthe unsupported length of the stock (Figure 5.45). A combined type of watertight gland and rudder carrier is shown in Figure 5.46. It is essential for ease ofopera lion of the rudder lhat the pin ties and rudder stock turning axes are in theSame vertical line. Great care must be taken during installation to ensure thiscorrect alignment.
SECTION F SUPERSTRUCTURES AND ACCOMMODATION
The superstructure is that part of the ship's structure built above the uppermostcomplete deck and is the full width of the ship. Deckhouses are smallerstructures not extending the full width and one or more storeys high. They maybe built on to the superstructure or at the base of maslS, etc. The constructionof Superstructures and deckhouses uses frames. plating, girders and brackets in asimilar manner to the hull. but of smaller scantlings. However. superstructuresextending 15% of the ship's length are considered to contribute to thelongitudinal strength of the ship. As such, they must have equivalent scantlingsand strength 10 the main hulL
The most forward section of the superstructure is known as the 'forecastle'.Any section of the SUperstruclure around the midships region of the ship isreferred to as a 'bridge structure'. The deck area aft is known as the 'poop' andany SUperstructure located aft is likewise known. A raised quarter deck is aweather deck extcnding for some portion of Ihe ship's length from aft and ispOsitioncd above the upper deck.
Most modern ships have most of the superslructure and accommodationsituated aft abO\'e the machinery space. The wperstructure and de<:khousesusually tOtal four or five storeys. The major part in this space. excepl for thaIlosl to Ihe machinery casing, is used for crew accommodation.
Forecastle
All ships must be filled whh a forecaslle or an arrangement to provide aminimum bow height. as defined in c1assificalion socielY rules. It is, usual to fitforecastles, and where this is done they must extend from the Slem a distance0.07 L afl (where Lis lhe freeboard length). The side plaling orlhe forecastle.beint; a continualion of the shell pIa tint;, is thicker thal1the end pia ling. Adequ:lIearrallt;ements for stiffening of the forecastle pia tjng must be provided.
Major StTUC(lIralltcms I J7
Bridge structure
Where a bridge structure exceeds 15% of Ihe ship's length. lhe side plating thi~k-
must be increased by 15<;t abo\'e that of other superstructures. A I~ea\'ily
n~::ed bridge front is required with the aftcr end plating somewhat hglner.~ 'ffener scantlings will likewise be increased al the forward end and reduced att~~ after end. Web frames or partial bulkheads must be fitted to supportstruc\Ure abo\'e. particularly al the corners of deckhouses abO\·e. Ho~se lOpS ordecks in way of davit.unust be strengllll:,n"d and supported from belo'tl..
Poop structure
The poop front must be adequately plated and stiffened as for lite bridge f~onl.
The internal stiffening will include webs and partial bulkheads as reqUired,articular1~' where deckhouses are located above. The. after end of the poop.
~eing exposed. requires a more substantial constructIOn than thaI of the aftends of olher structures.
Raised quarter deck
The raised quarter deck results in a greater depth of ship over its length.Increased scamlings must therefore be provided for the. frames. shell. deckplating and beams. Structures may be built on to the raised quarter deck asalready described.
Discontinuities
The ends of superstructures represent major discontinuities in ~he stru:ture ofthe ship. Longer structures such as bridges and forecastles r~qUlre conSlden.blestrengthening at the ends. Classification society rules reqUire the upper decksheerstrake thickness to be increased by 20%, except where Ih~ struc~ure doesnot extend to lhe side shell. Deck plating at superstructure en~s IS also l~creased
in thickness. Side plating forming part of the superstructure IS well radluscd atthe ends towards the side shell (Figure 5.47).
Watertight opening and doors
Where doors are filled into structures abo\'e the fr~e~ard d:ck they must be ofadequate strenglh and able to maintain the watertight mtegnty of the structure.The openings have radiused corners to reduce the str~~ effe~lS o.f thediscontinuity. A substantial framing is also fitted or addltlo~al stlffenmg toretain the strength of the structure. Doors fined to the o~enmgs are of steelSUitably stiffened, with a rubber gasket filled to effect watertightness. The doors
Major Structural/tems J )9
Sq,,;tr~
H.ndle Selllock,"9 nul_',an
Sp<,ngSf,1I lockIng nul
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have securing dips or 'dogs' which can be operated from either side. The dogsfasten on wedges wh.ich puU Ihe frame edge into the gasket. sealing the doorshut. Details of the door construction and closing arrangements are shown inFigures 5.48-5.50.
FO<~lI~OfCk
,.,
------- ---'----;- ------1
118
Fq;un 5.48 DoorclllmPJ: flJ) psrizhr dotN dDmp; (b) _rhutiQltdoord#mp
Rubbe. Itrip
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'boxhl
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'"Fiplre SA7 Discontinuirin; (tI) fo~ctUtle deck pllltin6 bred: (b) poop dtck pl4tirtg bfeDk
120 Major Structurul Items121
811d.00f'\
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Toi1l1
Toilet
SiMi""
2nd engOrlftf',..,,-(...c~=t-t===+-Enginee",,'ehanging.
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Engineeasing
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o 0 1 000110: 1 :l l_~ l. _-------------
Swimming-..../" Deck
Opmingallin10~,ing
Clamll /POSi,ion
Fipn 5.j() Steel doon
Accommodation
The superstructure will comprise several storeys of cabins. public rooms, offices,navigation areas and machinery rooms. A typical arrangement of cabins androoms is shown in Figure 5.51. Stiffened steel bulkheads are used to support thestructure above and provide subdivision for fire containment (see Chapter 10).Intermediate partitions are used to create individual cabins. Plastic laminateseither side of a fire-resisting material core are used for the partitions. They areset into U-section light-plate channels at the deck and the ceilings, as shown inFigure 5.52(a) and (b). Ceiling panels are fitted on to wood grounds orbattens between the partitions_ Typical Ooor coverings comprise a bituminouscoating with vinyl tiles fitted to provide an easily cleaned hardwearing surface,
F~ 5,51 Accommodtltion tI17l1ngtmclr
B.~
Ce.llng ...&o 'J,1l1'Ogeq"....1oe<l110bulkhud
32 mm deep Il 1611tift! ch.nr>elwelded 10 hinge'
Bulkh8d
Figure 5.S2(b} PuriNO" collstruction - dtckhtad bCIJm.t
12
2'5"""" 3 mmneel~ll600mm
..... centres
8ulkhUd
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Deck she"h'ng.nd",.I.ee COlI.., ~O¥ed bYOtP¥lrnenl 01 TrMle lno:!InctuWV
FiKJU~ S.S2{t1) Panirion conltnlC'tiO/1 - htQd imd foot detaill
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0."
76 mm " 38 mm " 48 min ...~«>l1eel lugs; weId«IiO deck"JIlO mm ","un.. Min. of 2lugo pe< panel
J2 ...... deeP. '4 II lift!d\M1nel weIdelS 10..........
122
124 Major SlructrJ,ral Ilt:nu
F~ 5.51 O'ew cabin
COamin~ strips .are fi~ted at the edges to complete the arrangement. The cabinsare proYJded WIth vanous arrangements of built-in furniture and fittings for crewcomfort~ as shown in Figr,ur 5.53.
o,
Bun~ bftI,.. --- ..,..-----, ", ", "
"
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6
Minor Structural Items
Minor structural items are now considered which, while not contributing greatlyto the strength of the vessel. can nevertheless be considerable in size and haverequirements for strength in themselves.
FunnelIn reality the funnel is a surround and support for the variow uptakes whichensure the dispersion of exhawt gases into the atmosphere and away from theship. The shape of the funnel is sometimes detennined by the shipowner'srequirements but largely by smoke-clearing arrangements and the need forstreamlining to reduce resistance. The owner's house mark or trademark is oftencarried on the outside of the funnel structure.
The funnel is constructed of steel plaling stiffened internally by angle bars orflat plates fitted end on (Figurr 6.1). Brackets are fitted at the stiffenerconnections to the deck and the plating of the funnel is fuDy welded to thedeck. A base plate may be fitted between the funnel plating and the deck.Internal flats are fitted 10 the funnel and are made watertight with scupperdrains to coUecl ;my rainwatn. The number of flats fitted is dependent upon theheight of Ihe funnel. The various main engine ;md auxiliary uptakes afl~ fittedwithin the funnel casing, usually on sliding feet to permit expansion. Someuptakes are arranged to stand proud of the funnel casing.
In the funnel shown in Figure 6./ ventilalion louvres are fined on the afterend below Ihe upper lainOat. These louvres disperse the exhausts from thevarious ventilators led up the funnel. Fire flaps are fitted in the airtight flatbeneath these ventilators and are used to shut off the air outlet from the engineroom in the event of a fire. A hinged watertight door is filled in the funnelleading out on 10 the deck upon which the funnel stands. Holes or grilles are cutinto the forward face of the funnel towards the top, and the whistle is fittedon a smaJJ seat just aft of the opening.
Ladders and platfonns are also provided inside the funnel for access purposes.Lugs are fitted around the outside top shell plating to permit painting of thefunnel.
Engine casing
The accommodation or upper deck spaces are separated from the engine room ormachinery spaces by the engine casing. Access doors are provided at suitable
125
26 Minor Structural Irems
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, Min.or Structural Items 127
PI",'or'·'
Sfluion rl1roug!l</; ffcne,
Pia" vie ....M
engine(iI.mg
/XlFe""Brack~t
,.~ .._~~"':"Ce'_~ t
I
Bulkh..,<:l-lmoler
Shaft tunnelWhere a ship's machinny space is not right all an enclmed area or i.ulmd i'prOVided to lead the shafting to the after peak bulkhead, The tllnnel must be ()
The casing top is of ~tiffene-d plate construction. with Jeep girders andbnn;kets alOtlnd \lie openings fDr the uptakes. Hea\l;l bracket, connect th-etransverse beams to the vertical stiffeners. Thi, HnmgemcI11 ensures aJeq\~atc
support for the funnel which sits on tlle casing top.
,',,' ,qhtI!a:
L-,,,·..~r"''''9'''
Altern,'t'"Ui>l"h"
Main
_ ""9' neUD'3k~
<
BoilerUfl.o k" -
Sec',on ",'''''00" t'al
poil1ts between the engine casing and the accommodation. The volume enclosedby lhe 1:3:>ing is made as ~mal\ as possible but d ~uffkient dimemiol1:S to ..\lowmaintenam:e and machinery removal from the- engine- room, The casing leads lipto the up-per decks, finishing below the funneL fresh air is drawn in throughjalousies OJ louvres in small fan rooms off the casing and passes down tJUnkinginto the engine room, The- hot air rises up the engine room into the casing. andout of the funnel at the top.
The cons.truction of a typical engine c.asing is shown in Figure 6.2. The casingi.s a ligiltly plated structUIe with dosely spaced vertical stiffeners. These bulbplate or angle bar stiffeners are fitted on the machinery room side of the casingto ensure wntinuity. Swedged or corrugated bu\khcarls could aho be 1.11;.cd fOlthe casing sides. Stringers and brackets are filted at wrious heights, where noflats ex.i~t, to furt her strengthen the structLJre.
The casing sides are also used to support $eats for certain auxiliaries and assecuring points for pipe clips or hangars. TIle casing is supported on a deepgirder runnittg around tnc engine toDffi. This deep girder is in turn supported bythe pillars, transverses and bulkheads of the engine room structure (see Figure6.2).
".
,...."""PIlll'''9
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,>I
{ ·n ti g' bul....·arkFiKUre !SA Bul ....·arkJ: (a) ~'I bul....·uk or roili,rg: (bl arrangement 0 J'(Xt n
Deep tanks
Deep tanks are fined in some ships for the carriage of bunker oil, b~as~w~~ror li uid cargoes such as tallow. The entrance 10 the deep tank from t e ec IS
ofte~ via a large oiltight hatch; this enables the loading of bulk or general cargoes
Slanch,on
Wherr the solid bulwark meets the deck. freeing ports must ~e fittedf:o allohwthe ~ id drainage of any water shipped. which could senou~y ~ eCI t estabil/y of the ship. Sometimes a 'floating' type of constfUCtlOn
r'h' "rsed .to
• C'.. 6 4(b) The depth 0 t e reemgprovide a continuous freemg port area. rlguTe. .
pori must be restricted to 230 mm. hi h .o n bulwarks consist of rails and stanchions sUPporled by stays w .c ag~
are : back from the deck edge. The lower rail spa~ing must ~ a m;;~um 0
230 rom whereas the rails above may have a maxunum spacmg 0 k I ~m.Bulwa'rks of both types are usuaUy 1 m in ~cigh~. Bulwar p a~m~,
particularly in the forecastle region, is increased m thickness where It IS
penetraled by mooring fittings.
Minor Structuralltcnu 129
·d d "d o""n - the solid type being constructed principally ofare consl ere so or yv
pla~h;h;u~:~kt~ak~~i~~r;~~~~b~~~~~'~~~ludinalstrength and as such_ in
;;; solid form. is of relatively thin plate supported by S~ys ~~~:" ~; ~~~~h~r~s are RI back from the deck edge and must not .w. . .
'Uy. This avoids the high stresses, particularly al the. nudsJups secllon. bemg~~e. ~ ngI~nsmitled to the bulwarks and possible crac g cecum .
Ollwl Du'b pl.ne
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0 Wlll~wllY ",tlener
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The structure must be capable of withstanding the water pressure should thetunnel become open to the sea. The scantlings must therefore be equivalent toth~ of a watertight bulkhead. The width of the tunnel is decided by access andmaintenance considerations and will be reduced to the minimum necessary. Araised Ooor is usually fitted and pipework is run along beneath it. The shaftbearings which arc positioned at intervals along the tunnel are carried on stoolsor seats. These slools are welded 10 the lank top and the tunnel structure toform a rigid platform. The lunnel is opened out into a larger area at Ihe after endto provide an adequate working space for withdrawal of the tailshaft. The sparetailshaft is usually mounted on the sheU in Ihis open area or recess.
Shaft tunnels must be hose tested on completion to ensure their watertight.ness.
watertight construction to provide integrity should the shart ~al cease tooperate correctly. The forward end of the tunnel is filled with a sliding water.tight door to ~al of( the tunnel if necessary. The tunnel is made of sufficientproportions to enable access for maintenance to the shafting, and an escaperoute is provided from the after end.
Two types of construction arc used. either a curved top or roof, or a nat roof.The curved roof is monger and can therefore be made of lighter plate than theOat-roof type. The nat.topped construction does. however. lend it~lf to morestraightforward construction and provides a Oat platform in the hold above.The plating is stiffened by bulb plates usually fitted in line with the frames. Acominuous ring of stiffener bar is fitted with the curved·roof type of tunnel. TheOat-roof type has brackets connecting the roof stiffeners to the verticalstiffeners. Examples of each are shown in Figure 6.3.
128 Minor Structumlltem!
Bulwarks
Bulwarks are barriers fitted to the deck edge to protect passengers and crew andavoid the loss of items overboard should the ship roU excessively. Bulwarks
131
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The construction of a deep tank used for bunker oil is shown in Figure 6.5.The tank is one of two and extends for half the width of the ship. The strakesof plating which fonn the oiltight bulkheads of the tank increase in thicknesstowards the bottom of the tank where the loading is greatest. The after oiltight bulkhead is stiffened by closely spaced vertical bulb plates. The forwardoiltight bulkhead is stiffened externally by II series of diaphragm plates. Thediaphragm plates form a cofferdam between the bunker tank and the oiltightbulkhead orthe cargo hold forward.
Three horizontal stringers are fitted across the tank, a transverse washbulkhead and a longitudinal wash bulkhead. The stringers are bracketed to thestiffeners at the tank sides and to the wash bulkheads which they join. Thewhole structure is therefore stiffened by a series of deep 'ring· girders in both ahorizontal and vertical direction. A very strong structure is thus formed withconsiderable restrictions to liquid movement within the tank.
Corrugated or swedged bulkheads may be fitted to deep tanks, parlicularlythose intended for liquid cargoes which require the tank to be cleaned.Conventional stiffening could be positioned on the outside of small deep tanksto similarly facilitate cleaning. Heating coiis may be fitted in tanks intended forcargoes such as tallow. Deep tanks must be tested on completion by a head ofwater equivalent to their maximum servict: condition or not less than 2.44 In
above the crown of the tank.
FiKurr 6.5 Dup '""k: (II) pl4n l·;tW: (b) tln'Drion lookinz ourbotl,d
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130 Minor Srructuralltf!mJ
if required. A deep lank is smaller than a cargo hold and of a much strongerconstruction. Hold bulkheads may distort under the head of water if flooded,say in a collision. However. deep tank bulkheads which may be subjected to aconstant head of oil or water must nol denect at all. The deep tankconstruction therefore employs strong webs. nringer plates and girders. fitted asclosely spaced horizontal and vertical frames. Wash bulkheads may be: fitted inlarger deep tanks to reduct: surging of the liquid carried. Deep tanks used forbunker tanks must have wash bulkheads if they extend the width of the ship. toreduce free surface effects of the liquid.
132 Minor Stnlctural/tems
Machinery seats
Main engines, auxiliary machinery and associated items of equipm~nt ar~
fast~n~d down on a rigid fram~work known as a seating or seat. These seats ar~
of plat~_ angle and bulb construction and act as a rigid platform for th~
equipment. They are welded directly to the deck or structure beneath, usuaUy in1in~ with the stiff~ning_ The $eat is design~d to spread the concentrated load overthe supporting structure of the ship. It may be extended to the adjac~nt
structure or additional stiff~ning may b~ supplied in way of the seat. Steelchocks are often fitted between the seat and th~ machinery item 10 enabl~ ac~rtain amount of fitting to tak~ place and ensure a solid 'bed'. The it~m canthen be bolted down to the seat without pen~trating th~ doubl~ bottom or deckb~low.
Seats in the machinery space also serve as platforms to raise the pumps,cool~rs, etc.. to th~ floorplate lev~l for easi~r access and maint~nanc~. A typicalpump seating as used in an engine room is shown in Figure 6.6. It is constructedof steel plale in a box-type arrangem~nl for rigidity. A shell-mounted s~aling isshown in Figure 6. 7.
Sea tubes and inlet boxes
Mosl valves having a direct inlet or oUllel to the sea ar~ mounted on a sea tub~
which is fitled inlo the shell. A sea tube is a thick-walled steel tube with a flange
Minor StnlcturaJ lrom 133
., h' ed flat to form a watertight joint with theon the inboard side which IS mac In 'd bollom shell and fully welded insidevalve. The tube is let into the lower SI e or
and out, Figure 6.8(0). be fitted into inlet box~s which ar~ usually fit~edA number of sea tubes may. bel w th~ waterline. A box-like
in the forward corner.; of the englne T~~h~ s~a through one or mOTe holesstructure is fitted to Ihe shell and opensb 0 let into this box. or valves can bewith grids fitted. Several sea t~bes can t~e inlu box Figure 6.8Ib).mounted on to flang~s welded dU~~~IY to t strength~n the shell plating around
The sea tubes or mlet boxes a~ serv~ 0the discontinuity resulting from the hole in the shell.
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Outfit 135~'.........."~l,-h
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Hatch covers Cwr"'''''
Hatch covers are used to make the cargo halch watertight, 10 protect the cargoand to stiffen up the structure of the hatch opening. Two basic types are ingeneral use - the wooden hatch coveT fitted across halch beams and the patentsleel covers of various designs. The halch covers fit on top of the halchcoarnings, which have been described in Chapter S. The weather deck coarningsare al a height set by the load line rules (see Chapter 10). The tween deckcoarnings are set flush or almost flush with the deck 10 reduce interference withcargo stowage in this area.
Wooden hatch covers
A combination of transverse beams and longitudinal hatch boards make up thewooden hatch cover arrangemenl (Figure 7.1). I-seclion girden, the widlh of Ihehatch. are fitled at intervals along the length of the hatch and are known ashatchway beams, shifting beams or webs. The ends of the beams fil either inloslols or carrien in the coaming side or lock into pos.ition on a trackway if theyare of the sliding type. The beam ends are additionally stiffened by a doublingplate. The beams which lake the ends of the hatchboards have a vertical natfined to hold the boards in place.
The hatchboards 3re filled longitudinally over the hatch beams and areprotected at their ends by a metal band. The boards are at least 60 mm thickand more for a span greater than 1_5 m. The roller beam arrangement of hatch·boards is the same. the roller beam simply speeding up the opening and closingof the halch. At least two tarpaulins must be fitted over the hatchboards andsuitably fastened down around the hatch coaming. Bauens, cleats and wedgesare used 10 'dog' down the tarpaulins. Steel locking ban or some suitableaddilionallocking device are required to secure each of the hatch cover sectionsafter battening down the tarpaulins_
Steel hatch covers
Patented steel halch covers of a variety of designs are available from severalmanufacturers, Most designs employ a number of .self·supporting steel covers
134
•8'.1<:1."1 ~("I Il,tr'qI'lQ<m,ng 1'>~lch "de.'-
which completely enclose (he hatch opening. O~ning ~nd :Iosing arr~~e::~~
'".1", a ·singl. pull' via a winch wire or hydraubc or e ectnc power. .
" " h "oop Th. "pante sectionsn wheels on a trackway along the hatc coamlOg .~~; ~ther hinged together or joined by ch~ins to olle another. The covers finally
slOW at some poinl clear of the halch opening. .. 72 The halchA MacGregor sleel halch cover arrangement is shown In F~re .. d' gI
d ned b hydraulic power or a wUlch-operale sIn e:;=~u~~nAb~r~~~:ay°i: ~:nned f~r Ihe hatch rollers by a pl~lform~oP on ~he'''-'n."A venical plale is positioned each side of the coarrung ahl h "htowmg-,. " Th oUers on I e atc coverend of the halCh on the coarning trackway. e upper r
Figurt 7,2 MacGrtlor su~1hafch co~~r
136 Outfit
ride up on lhi> platl' .and the C()Vef the ... h _ _ _ /are thus COlll"act]'w' ~LlJw~d 'I f II" hIps 1n, tD I c vntlc,1! posItIon, The covers
.- ~ - ~ L car () H~ atcl opel1in..:r TI )- heccentric rollers which act as wheels' 11, "<..I <>: _ Ie lak covers rull uncoamin,g in the low d _ _ _ In le !aJSl.~ POSition and are dear of the
ere POSltlOli to <'flab-Ie tl:e covers to be fastened d 'III Thtc C()Y~rs ~~ of fabricatea' sted plate witll stiffeners or webs to ~treng~;:~'
c s ru~tur('. e eads of the covers overlap in the c1()~~d l' _ ,fitted with compresSible pa'k' . P~SltlOI1. Gromesth C lIlg surround the outside edges of the -c-ovcrs Vt'he
e cO,vers .HC fastened dOwn by deat~ on to a raised ed can Ih' .:oa··' nwatertIght seal is formed and no tarpaulin is re'luired. Th~ athwa:tshi fmn,g. ah~twcen the,. covers have a similar sealing arrangemell t The cleating arra~S ;J~~~~s {)W~ m hgure, 7-2 b automatic, The cover wheels -drop into slots g. th~f~J:ll11gb plate pnOl to cleating and are raised hydr3l1lically after UJld:~tjf\gea[~ mg, ars are fitted along the side and end coamings under the top rail Hook~
positIOned at thc cleating. pomls and L:all pivot thlougl I . h .'1 D bl 'h ' . 1 a s ot m t e COamlltg
Ell. ou e·ac1lng ydraultc cylllldcrs move the bars to raise or lower the h k00 s.
Cle" lug
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Fi',;ure 7.3 A,.itoml!tic peripheraf denting
In t,he raised position the hooks engage deal lugs which pull the I' t 11sections down on to th I" 'F la c cover
, c sea mg stnp. or transverse deating a torsiun bararrangement IS used. Lever arms on the end of the torsion bar are pushed 'the hatch closes and rolat th - up ase c torsIOn bar. This presses cleating lugs on topressure pad~ on the end of the :J.djacent hatch section. A peripheral 'Ie iarrangement IS shown in Figure 7.3, c a
Minor hatch covers
A number of small access openings. tank entmnces, elc., are fitted with .halch covers of steel construction. mmor
A t~pica1 small hatch COWr is shawn in Figure 7.4. The coamin ed e isforced mto a r~bber gasket by a number of fastening clips or 'dogs' ar~un: thecover, a watertight seal being thus formed. The handles are .arranged for internalor e.xtental oper.atlon on accesses. A c(lunterbalance weight is sometimes fittedto ease the opemng of the cover.
Mooring equipment and arrangements
The ",:,inches and windlasses positioned on the forecastle and poop decks andsometimes the upper deck perform the mooring and warping duties reqUired by
figure 7.4 Small wala-rigl'lt harch wver.- (a) section rhmugh hatch. (b) p-Ian ,'leW ojnt1tch cwoer
the ship when arriving and departing its various ports of call. Various fittings areprovided on the deck and around the deck edge to assist in the mooringoperation and provide a deaT run or lead for the mooring and warping wires.Examples of these fittings are bollards and the various types of fairlead whichare found on board ship.
The windlass, as mentioned in Section D of Chapter 5, has warping endswhich are used when mooring the ship. One or more warping winches are fittedon the poop deck aft for similar dutie'S. Solid seatings, as mentioned in O1apter6, transmit the loads to the deck and also stiffen the deck. Larger vessels havemooring winches fitted on the upper deck also. Bollards or ffiQoring bitts areused to moor the ship once it is alongside and are welded OJ bolted to the deckor to a box,like structure which is welded to the deck, Figure 7.5(a). Adequatestructural support must always be pflJvided in way of bollards and all mo-oringfittings, usually by additional stiffening to the deck beneath.
Fairleads arc used to guide the bawsers or mooring wires to the boUards Qfmooring winches. Fairleads are attached to the deck, a raised seat or the deckand the bulwarks. Several different types are to be seen, such as the multi,angledfai.rlead, the pedestal faidead, the roller fairlead and the panama £aidead. Amulti.angled fairlead consists of two horizontal and two vertical rollers with thewire passIng through the hole between the rollers, Figure 7.5(0). A pedestalfairlead consists of a single horizontal or vertical roUer mounted on a raisedpedestal 01 seat, Figure 7.5(c). A roller faidead is one or more vertical rollers ona steel base which may fasten directly to the deck or to the deck and bUlwarks,Figure 7.5(dj. The panama fairlead is an almost elliptical opening formed in acasting which is fitted into a suitably stiffened aperture in the bulwark, Figure7.S( 'I"
The multi-angled fairlead is fLtted at the deck edge and reduces the number ofguide rollers or other faideads required to give a clear lead of wire to the winch.The pedestal faidead guides the wire across the deck to the winch clear of anyobstructions. The roller fairlead is used at the deck edge to lead in the mooring
Fil!Jl~ 7.6 AnonKtmtrtf O[Jrt:Jdf
Outfit 139
and warping wires. A panama fairlead is lilted in the foremost position in theforecastle bulwark on the centreline of all ships which pass through the PanamaCanal. Panama fairleads are also used in other positions around the deck edge asrequired.
For the various mooring and warping arrangements possible on a ship an'arrangement of leads' drawing is provided. This shows the runs of the variouswires through and over the various fairleads and winch warping drums on thedecks of the ship. Such an arrangement for the fore end of a ship is shown inFigure 7.6.
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Outfit 141
Union purchase
Figun 7.8 Union fXl,duut ,ig
To winch
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over l\aleh
Haleh
To winch
SlllV
Toppirogwire
Derrick rigs
The derricks used for catgo....andling work can be arranged or rigged in severaldifferent ways to provide for different manpower requirements, cargo-liftingcapacities or lifting cycle times.
The union purchase rig is a much used arrangement for cargo loading anddischarging. Two derricks are used, one arranged to plumb the hatch and the
Some m3Sts on general cargo ships als11 double 3S support pOStS for the derricksused for cargo handling. 53rnson posts are also used more specifically forsupporting derricks. Tied arrangements of Samson posts, or bipod masts as theyare sometimes called. are :lIso used. The scantlings and construction of masts andposts used in cargo....andling work are given in the c1assifiC3tion society rules andare dependent upon the safe working load (SWL) of the derrick boom. Mostmasts are self-supporting by virtue of their construction and attachment to thedttk. Only special heavy·lift derricks require wire stays or prcventers betweenthe post top and the deck.
Samson post construction is of tubular steel section, stiffened internally bywebs. Thicker plating or doubling plates 3re provided where atlachments aremade to the post. Derrick booms are of seamless tubing usually with a greaterdiameter at the middle region where the bending moments are greatest. Thevarious goosenecks and end fittings are welded inserts in the tube ends.
The post attachrmnt to the deck varies but must always provide adequatestiffening and support. Mast houses are fitted at the base of some masts orsamson posts and mayor may not assist in stiffening the structure. Some postsate let into the tween decks or are attached to the comers of superstructure toobtain support. The greater the derrick load the more stiffening is required.often by fitting additional webs below decks and heavier than usual bulkheadstiffeners and brackets below the mast or post.
Samson posts
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140 Outfit
Masts, derricks and deck cranes
Masts
Figlue 7.7 Oil rtmlce, !o,emDJf
The. ship's mast acts. as a lookout platform and a mounting point for navigationequIpment s~ch as hghts: radat. aerials, etc. Access to the upper platform is bya ladder which. depending upon the mast size, may be fitted externally orinternally.
A foremast. as filled to an oil tanker, is shown in Figure 7.7. Construction isof light plate stiffened by internal webs. A O.type cross·section is often used for
irs streamlined, reduced-resistance form. The upper platform is additionallysupported by brackets to the outer plating of the mast. The mast is fully weldedto the deckhouse on the forecastle deck and to the upper deck. A solid roundbar is used to stiffen each of the ftee edges of plating and before erection themast is coated internally with a bitumen solution.
1
Outfit 143
".1
o1/ S..-j~c:1 eye for flemish hook.12 FlemisJl·hook.I] Ladder.14 Gooseneck pin fockn.15 FQHclling d/'I'iu fa' la ..-ef CQfga
block.16 l1e/'1 fitting./7 Derrick pin.18 Gooseneck Qrld goof/'n~k pin sackel.19 lI'incil('S.
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/ Derrick ileQd filling.2 Pendulum block {it/ing wilh guide ,oilers.] Uppe' CQ'go bloch4 Conn~ti"g f/Qu.5 Lo....t:r spQn block.6 Span s....il'el.7 C,oss·t,ee.8 1t,/('/ fo, rhe hauling PQrt.9 £O ••.-C, CQrgo blocks.
/0 Connecting rrQI·t,se.
F'iguf/' 7./ / Sliilk/'n heQI'y·liff derrick
Heavy-lift derrick
For loads heavier than Ihe safe working load of a single derrick, two derric~s
coupled together by a 'yo-yo' gear arrangemenl may be us,ed, as sh?wn I~Figure 7.10. The derrick heads must be kept c1o~ together dunng operation an
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To IOI'l""Ywinch
142 Outfit
olher to plumb the qU:ly 01 over th~ ship's side. The falls or wires frol11 bothderricks are shackled 10 the same cargo hook. Thus. by using the two winchcontrollers separately and together Ihe hook is raised or lowered O\'er Ihe hold.travels over the deck and ClIll be raised and lowered over the ship's side.
This arrangement is safe. in that only the load moves. and requires tworeliable operators for the winches. It is. however. only Suitable for light loads upto about 1.5 tunnes. A union purchase rig is shown in Figu11' 7.8.
Swinging derrick
The fastest and most reliable method of cargo h:lI1dling is achieved by Iheswinging derrick rig. A long derrick boom with a deJr arc of swing is necessaryfor this arrangement. An adjustable Span is usu:llly arranged 10 facilitate theplumbing of the hatch and the quay over the ship's side. This is achieved by atopping wire and winch which is independent of the cargo winch. A swingingderrick rig is shown in Figurl' 7.9.
Sin'son _,~,
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Crane platfurm
Derricks have been replaced on many modern l:argo ships by del:k cranesmounted on platforms between the holds (Figure 7.12). The deck crane providesan immediately operational cargo·handling de-vice with minimal rigging reqUire.ments and simple, straightforward one·man operation. The safe working load ofthe crane is determined by its c3rgll·handling duties, and designs are avail.ablcfrom 3~5 tannes and up to 10-15 tonnes as requilcd. Double gearing is afeature of~some of the larger cranes to enable speedier handling of ligh tel loads.Three basic types of cranes are available - gener.al cargo cranes, grah-bing cranesand twin-crane arrangements.
The general cargQ crane is for use {In cargo ships and hulk carriers. Thegrabbing crane is for use with a rnechanically-operated grab when handling hulkmaterials. It requires a multiple-wire arrangement for the operatIon oJ the grab.Twin cranes utilise standard cranes whidl can be twinned u[iJperate-d in unisonto lift heavier loads such as containers, if requireu A single operamr [, usualwith this system by utilising a master and s1ave control ~ystem in the two cranes.The use of a C(JmmOIl revolvin.g platform makes this arrangement possible-
Figure 7.] 3 Crane pede~tal and seat
P~de,tdl I'",pl~l~
Outfit 145
Deck cranes
The deck crane i, located on a platform pusitioned SOIlle distance from the deckto provide the crane operator with a clear uninterrupted view of the hold andthe quayside (Figurf: 713). The dane also revolves around this platform. The
i ..
Figure 7./2 (jeneral CIlTgO Nan"
~
f'.~,
••tII-- Operat-or'l cab
the central travelling blo~k which equalise~ the load must have a s.afe workingload greater than the cargo being lifted. A special heavy·lift derrick is titted tomany general cargo ships, with suitable rig and purchase gC"ur for its designed safeworking load.
.,various patent heavy·lift derricks .are a:vailable, one example being theStulken derrick shown in Figure 7./1. The StUlken derrick has a safe workingload up to 300 tonnes and is positioned lJ.etween two outwardly raked taperingtubular c:,lumus., Several winches are provided for the various hoisting, ~lewingand tOPPing duties. The controls are all arranged as levers in one console. which~n be operated by one man, This heavy·lift derrick can be arranged to serveeither of the hat-ches forward and aft of it. Smaller derricks are also rigged fromthe tubular columns for normal cargo work.
144 Outfit
HoistingmdluffingTlotors
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B,lge p,pe _
Bilge system
Figure 7./ oS (al Bilge S/1'l1m bo~; (b) bilge mud box
Outfit 147
Strum boxes are filled on all bUI machinery and tunnel space suction pipes.Perforations of 10 mm maximum diameter are made in the plate to provide asuction area at least twice that of the suction pipe. In the machinery and tunnelspace bilge !ines, mud boxes are fitted. The mud box fits between lengths ofpiping and has a perforated centreplate. The use of strum and mud boxesprevents the entry of large objects to the pipeline and safeguards the internalparts of the pump (Figure 7.15).
Suction valves for the individual compartments must be of the screw-downnon-return (SNDR) type to prevent reverse now. All other valves must be of the
For the many services required on board ship. various piping and pumpingsystems are provided. Some systems. such as bilge drainage and fire mains. arcslatutory requirements in the event of damage or fire on board ship. Each of thevarious systems will be examined in turn.
The bilge piping system of any ship must be designed and arranged such that anycompartment can be discharged of water when the ship is on an even keel orlisted no more Ihan 5 degrees 10 either side. In the machinery space at least twosuctions must be available. one on each side. One suction is connected to thebilge main and the other to an independent power-driven pump or ejector. Anemergency bilge suction must also be provided and is usually connected to thelargest capacity pump available. A diagrammatic arrangement of a bilge pumpingsystem for a 26000 deadweight tonnes bulk carrier is shown in Figure 7.14.
pUmping and piping arrangements
seat on which the crane rests is usually circular and of steel plate constructionwith closely spaced vertical ribs or brackets. This seat is usually welded to or isan integral part of the raised post or plalform which is welded to the deck of theship. Adequate structural support and stiffening should be provided both aroundand under the seat.~
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{equiremenls for the hallast system of a dry cargo ship are largely similar tohose fm the bilge- system. There must be adequate protection provided againstJallast water I;'otering dry cargo or adjoining spaces. Connections between bilgemd ballast lines must be by non·return valves. Locking v-alves or b-lanking.mangements musi prevent accidental ernptying of deep tanks or flooding.'ftLere tanks are employed for oil fuel ar baltast, effeo:::tive isolating sy&tcrns mUllt,e used.
A ballast pumping arrangement for a 26000 deadweight tonnes bulk carriers shown in FiKUre 7.16.
W paSsenger sllips of 4000 gross tonnes and above mllst have at least threeJower-driven fire pumps. All cargo ships in excess of 1000 gross tonnes mustlave at least two independently driven fire pUmps. Where these two pumps are.ceated in one area -an eme[gen.cy fiI~ pump must be pmvided and locatedremote from the machinery space. The emergency fire pump must beindependently driven by a compression ignitiun engine or other approved means.Water mains of sufflcient diameter to provide an adequate Water supply for the,imu.ltaneous operation {)f two fire hoses must be Connected to the fire pumps.An isolating valve :is fitted tQ the machinery space fire main to enable the~me[gency fire pump to supply the deck lines, if the machinery spaCe main is'rokea or the pump is out of action.
A di.agIamm<l.tk a.rrangement of a fire and washrlcck system is shOwn in
3aljast System
On·return (NR) type. The port Jnd stathOard hoLd bilge valves are usually~ouped ill distribution chests a.t the forward end of the machinery spa.:e. Bilgeiping is made up of the fore arld aft mains and suction branches to theldividu.al compartments. Piping is arranged, where possible, in pipe tunnels. o(uct keels to ,avoid penetrating watertight double-bottom tanks. Bilge ripes areIde-pendent of piping for any other duties such as hallasl or fre-sll water.a"se-nge-t "hip bilge main:. romt mn at lea:.t 20'% of the ,hip's beam i.nsioe of thede shell; in addition, any brandIeS further outboard must have a non-return
alve fitted.
Bil,gc pipe suction lines are sized according to ail empirical formula. Minimumranch and main siz:e-s -are 50 mm and 65 mm, respectively, and the maximumile is 100 rnm for both. Bilge piping may be constructed Qf cast iron, steel,opper or other suitable approved ma.terials. It is usual to employ galvanisedteel piping in bilge s}'~tems.
At \cast foU( inclepelldent puwel-dri'fe,n pump'" must be conn.ected to thelilge main. Mmt ships employ two bilge pumps and have bilge main c-onnec.1ionsIII the ballast and main circulating pumps. \Vhere POSSible these pumps should)e loc,Hed in separa~e- watertight compartments. One bilge system pump must)e capable of operation under reason<lble damage conditions. A submersiblemmp, remotely contrOlled, would provide this facility. Pumps fitted to the bilgeystem must be self-priming or connected to a priming system or device.
48 OUtfit
Fire ma~n
S~II
Outfit 151
General services
SCUllPl!< pipe
Direct drainage of the open decks above (he freeboard deck is adlleved by meansof scuppers. A typical arrangement is shown in Figure 7.18. In enclosed spaces.such as bathrooms or galleys. the scuppers are led 10 the bilges. A scupper potis fitted in a deck and acts as the collecting point for water. A pipe is connectedto the underside to drain the water directly to the bilge (Figure 7.19).
Scuppers
Figure 7.17. The system is designed 10 supply valves with hose connections onall the superstructure and upper decks. Relief valves are fitted at either end ofthe main to ensure thai working pressure is not exceeded. The water may besupplied by the machinery space lire pump. Ihe lire and tank-eleaning pump orIhe emergency fire pump located ill the forec3stlc. Additional lines arc led (0
,....---the hawse pipe for anchor washing and the garbage tank for nushing.The emergency lire pump in (his arrangement is supplied by a boosler pump
lit I'd nc~ar the bOllom of Ihe ship. The booster pump is driven hydraulicallyfrom one end of the emergency fire pump. the other end having another seawater pump 10 furlher pressurise Ihe w:ller. A diesel engine drives the pumpsfilled at either end.
Many other pumping and plpmg services are filled In ships for the variousdomestic. cargo and machinery requirements. For further details uf thesesystems reference can bt' made 10 the previously mentioned work. Marini:Auxilwry Machint:ry. by Souchotte and Smith.
>o
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//
ISO
Cargo pumps and piping systems aTe installed on tankers 10 diSl.:harge and loadIhe liquid cargo. Separate ball:lSI-pumping systems are also provided for ballaslonly lanks which are filled during ballast voyages.
System choice :md its flu;jbilily depend upon lhe range of calgces. thevessel"s uading pattern and what the owner is prepared 10 pay fOl. The standaldsyslem employs several ring mains along the tank length with branches off tothe individual tanks. Other systems are in usc. for inslance. employing largesluice valves to empty the tanks one to another. The pump suclions arc thentaken from the aftermost lank with the \'esseluirnmed by the stern.
An example of a ring main system for a very large crude carrier is showndiagr:l.I11matical1) in Figure 7.2/. Three mains are employed 10 serve the varioustanks. This arrangemenl also enables different grades of oil to be carried in thelanks served by each main. Branches ale led off into each of the centre and wingtanks and are fitted with isolaling valves. Cross-connections are arrangedbetween Ihe mains. and direct-loading pipes from the deck manifolds join Ihemains. Two stripping mains are also fitted and led forward with branches off 10the various tanks. The stripping lines arc uscd 10 discharge the last few hundredtonnes of cargo which the main suctions cannot handle.
The main cargo pumps are stt'am-driven horizontal or verlinl single·stagecentrifug:lt pumps. For the system shown in Figure 7.2/ one pump is providedfor ('itch main. The driving motor or lurbine is located in the machinery spaceand the drive p:lsses through a gastight seal in the pumproom bulkhead.
The SHipping mains are connected in the pumproom to lwo stripping pumpswhich are usu:ll1y of the posilive-displacemcnt type.
Outfit I S3
A particular feature of tankers is the large quantity of piping seen on deck. Atypical arrangement is shown diagrammalically in Figu.re 7.22. The cargo pumpsdischarge inro mains which p:lSS up through the pumproOIll and along the upperdeck to midships. The mains branch into crossovers to port and starboard and
Ikek pipl'"I\vrk
Cargo systems
Sounding pipes
Sounding pipes :m: fitted 10 all tanks 10 enable soundings to be taken and Ihedeplh of liquid pre~rl1 (0 be measured. Reference (0 the tank calibralion lableswill then permit the quantity of liquid present in the lank to be found.
Sounding pipes are made as straight as praclicable and are led above the bulkhead deck. except fOr certain machinery space tanks (Figure 7.20). A minimumbore of 32 mm is required for sounding pipes. This may be greater where arefrigerated space is passed through 10 allow for icing up. Where Lite soundingpipe does not emerge abo~ the bulkhead deck. sornt fonn of self<losing deviceshould be fitted. e.g. a weighted cock. This would prevent nooding, in the eventof an overn~w. contamination due to the entry of other liquids or the escape of;tazardous gases from the tank. A striking plate is filled al the bottom of an openpipe where the sounding rod falls; alternatively. a closed pipe arrangement maybe used (Figure 7.20). A number of patent sounding devices are available andmay, with approval, be fitted instead of sounding pipes.
,I OPen-PIpe
: I "'II'I~nt:I S,rok"'9 plile
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152
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Thermal insulation
Many tankers operate in the ballast condition on ev:ery other voyage. Asufficient quantity of ballast sea water must therdore be loaded on board toprovide the ship with satisfactory seakeeping propelties. Certain tanks 3redesignated ballast only and are filled by the ballast pump and piping system.Certain cargo tanks may be loaded with sea water ballast using the cargo pumps
with a sea suction.
A ship's steel hull and structure will conduct heat very well. In way of heatedtanks. refrigerated spaces and exposed accommodation spaces some form ofinsulation is necessary to reduce the heat flow to an acceptable le~el.
Various materials such as glass fibre, cork and some foam plastics are in u~ asinsulation. Glass fibre matting or sheet is used in modern ships since it is easilyfitted. is fire resistant. does not rot :lnd does not support animal life. Theamount of insulation filled in a compartment is decided by the temperaturewhich is to be maintained or accepted in the compartment (Figure 7.23).
Fastening is now largely by tandom pinning. using a stud gun to rut the pinsto the steelwork. The pins penenate the insulation. and caps fitted on the endsof the pins hold the insulation in place. Some slab insulation may be glued to thesteelwork. Joins between ~ctions of insulation are ~aled, usually with anadhesive tape. In accommodation spaces. insulation will be behind decorativepanels. In places where it is exposed 10 possible damage. a protecti~e cladding orlining, such as galvanised mild steel sheeting. may be fitted. Insulation on tank·tops must likewise be protected from possible damage or be of a substantialnature in itself. ()ver oil tanks a space must be left to avoid possiblecontamination of the insulation. This space is not required when a bituminouS
covering is placed o~er the steel surface.Plugs over manholes in cargo tanks and also hatch co~ers must be insulated
to a~oid any areas through which heat might be conducted. Special scupperarrangements are necessary 10 avoid heat transfer in refrigerated holds. This isachieved by a brine seal in an S-bend trap. The bilges may thus be pumped outbut the sealing liquid. although diluted. will not be removed (Figure 7.24).
Insulation
Ballasting Q"Qtlgements
More complex piping arrangements with independent lines are necessary onproducts tankers to avoid contamination between the different cargo ·parcels·.More than onc pumproom may be fitted on such ships. or individual pumps inall tanks with no pumprooms. Anangements for flushing lines using water or apOrtion of Ihe cargo may increa~ the flexibility of a particular sy5lcm.
ProdUClJ la"kers
Outfit 155
are filled with V-pieces at the manifolds which arc grouped near to the ship's
side.
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Fif:Uff 7.14 Rtfri~ntltt'd hold K1Jp/Nr (fVP
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Outfit 157
Watertight bulkheads are. of coune, specificaUy designed and constructed toensure their watertightness. Where openings are necessary in these bulkheads
Watertight doors
Sound results from the movement of air particles and travds in the form ofwaves away from the source. There arc many sources of sound on board ship.such as propulsion engines. auxiliary engines. large fans and ventilation plants.These would have a cumulative disturbing affect on p(rsonnel if allowed 10continue unchecked.
Various countries now have either codes of practice for noise levels in ships.or regulations relating to noise levels in ship spaces. Maximum noise levels aregiven for particular spaces using a weighted sound pressure level or db{A) value.Most ships at sea, however, would not meet these criteria. New ship designswill require consideration of noise levels in the very early stages if an acceptablenoise environment is to be obtained.
Two approaches are made to the solution of the problem. First, rooms andareas which are occupied for any length of time are fitted out in such a manneras to be as sound absorbing as possible. The second method is to isolate orsilence the sound from occupied spaces.
Increasing the sound·absorption capacity of a room is achieved by using avariety of sound absorbers. These include membrane absorbers such as lhinpanels, resonant absorbers such as perforated ceiling boards and porousabsorbers such as mineral wool. Sounds can be isolated by the use of nexibleconnections in ducting. nexible mountings on machinery, and sound insulatingthe surroundings of a noisy space. Air-<:onditioning plant noise can be eliminatedby the use of duct and bafne silencers and sound attenuating supply and exhaustfittings. Figures 7.25(0) and 7.25(b) illustrate the problems to be found in aship's accommodation and the various solutions that can be adopted.
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,)'rt("nt.5 Airborne Irolltm;I/("U sQlltld.6 Sound from Ilin.7 /lull ~;bra/iuns.
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f'ifUrt 7.25(bj SOltnd infUUuion _ accO/nmodll/ion ""lIlt X(}(W round comluff
D Hand pump (focal).E Srop v<lrre (~e,.,idng).
F Combined u1<mn closing limit turdindicaTor liidlr switch,
G OpeMing limit ~wi/ch.
H Switl;~ srrik:ers,J Door stop sited behind doo' cylfndl?'r 'AK Warning plate.r. Alarm.M Bridge colltro[[er!indicu!or,N Key-op-e/'flud iwl<Jring ~witcli (I eal;h
~jde of the bulk:he<ld),P NOM-return rlJll'e,
A Dcwr·op..rllting r:ylimler.B Door·COlltrol valrc. solenQld!manU4J
operated.C rowa unit comprising:
Pumpond motorufllrMotor starter!kJ.uf_['()ntro! vof"" (fl]amUJi)Relief v/llve /lnd pre~S(lre gaugeRed and r.reffi IfJ:h / Indica/iunHand pump (emergi!/lcy rem ore)Supply tunkLevel gauge (dirmick)Oil filter and srr<liner.
Outfit 161
special w:ltertight doors must be fitted. On cargo ships with a shaft tunnel, thetunnel entIilflce will have a watertight door fitted. On passenger ships, Ylith their].nge area5 ()f 3c-commodation and access requirements, a greater number ofwatertight doors will be I1tted.
"'here ,-,penlngs are cut into bulkhead~ ,hey must be reinforced tu maintainthe strerrgth of the bulkhead. This is particularly so in the lower regions ofwatertight bu.Jkhc:ads, where the greatest loading occurs. Where stiffeners afB cutor incr(.'3s_ed in spacing in way of a watertight door, adequate reinforcing isrequired. The watertight door has a heavy framework which further stiffensthe bulkhead in w~y of (he opening. The size_of the opening is kept as small as
possible.All doors fitted below the waterline are of the sliding type, either horiwntal
or vertical ill operation. It is usual to use horizontal sliding doors, except wherespace limitations require the vertical type.
The sliding door must be able to close against a list of 15 degrees to port orstarboard. It must be operable hom the vicinity of the door, in addition to apoint above the bulkhead deck. The remote operating point must have anindicator showing the duoT position.
A hori7.0ntal sliding, watertight door of Stone Manganese Marine Ltdmanufacture is shown in Figure 7.26. A stout door frame is fitted directly intothe bulkhead and provides the trackway along whkh the deor slides. The door ismoved by a hydrauli..:: cylinder Wl1ich may be power operated or nand pumped.A special solenoid ,-pool valve which may be remotelY or manually operatedproVides the basis of the cuntrol system. Bridge operation, local manual ove-rride operation and local emergency control of the dam are possible. Operatingthe hand pump together with manual movement of the solenoid valve provideslocal or remote- emergency operation. Powered operation is possible from thebridge or by manual movement of the solenoid valves at eitner the local orremote pumping stationS.
Bridge operation is only llsual on passenger ships where there may be a largenumber ofwat-ertight GOaTS,
WatertigM duurs are pressure tested under a head of water cOrIesponding totheir bulknead position in the event of the ship flooding. This usually takesplace at the manufacturers' works.
Ab()ve tne waterline, in certain approved positions, hinged watertight doorsare permitted. TIlese will be similar in construction to the weathertighl doorsdescrihed in Section f of Chapter 5.
-{S.
Figure 7.26 lfori:::onral sliJinK warerti~ht door
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160
162 Outfit
Stabilisers
163
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Upperlrunnionbr,..;kel
hilllep
The motions of a ship in a seaway can result in \'arious undesirable effects.examples of which ate cargo damage and human discomfort, Only the rolling ofa ship can be elTectiYely reduced by stabilisation, Two basically different stabilis.ing systems are used on ships - the fUl and the tank. Both systems attempt toreduce rolling by producing an opposite fOtCe to that atlempting to roll the ship.
f.nbol< stifl--. itn.igned with ship'l',-"i",
o
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Fin stabiliser
One or more pairs of fUlS are fitted on a ship, one on each side. see Figure 7.27.The size or afea of lhe fins is governed by ship factors such as breadth. draught,displacement. and 50 on, but is Yery small compared with the size of lhe ship.The fins may be retractable, i.e. pivoting or sliding within lhe ships fonn. orflXed. They act to apply II righting moment to the ship as it is inclined by a waveor force on one side. The angle of tilt of the fm and the resulting momenl on theship is determined by a sensing control system. The forwlIrd speed of the shipenables lhe fins to generate the thrust which results in the righting moment.
FiKure 7.27 Fill stabilist!f
164 Outfit
. The opera ling system can be compared 10 that of the sleering gear. in Ihal asignal from the control unil CilUseS a mO\'cment of the fin which. when it reachesthe desir~d value, is ~r~ughl 10 r~sl. The fin movement takes place as a result of3 hydraulic p~wer unit mcorporallng a type of variable displacemenl pump.
The effectiveness of the fms as stabilisers depends upon their sp«d of mO\·e.ment. which must be rapid from one extreme point to the other. The fms arerectangular in shape and streamlined in section. The use of 3 movable nap or afIXed and movable portlon is to provide a greater restoring moment to the shipfor a i1ighdy more complicated mechanism.
The control system is based upon an acceleration sensor. This unit provides asignal which after electronic integration provides a measurement of roll velocityand angle. These various parameters arc all used to bring :lbout a suitable llnmovement which will oppose the roll.
Fin stabilisers provide accurate and effective roll stabilisation in return for acomplex installation which, in merchant vessels, is usually limited to passenge,ships. It ~ to be noted that at low ship speeds the stabilising power falls off, andwhen stalionary no stabilisation is possible.
Tank stabiliser
A tank slabiliser provides a righting or anti.rolling force as a resull of the delayedflow of fluid in a SUitably positioned transverse tank. The system operation isindependent of ship speed and will work when the ship is at rest.
. Consider a mass of waler in an athwartships lank. As the ship rolls the waterwil! b~ m~ved, but a moment or two afler the ship rolls. Thus, when the ship isfinlshmg ItS roll and about 10 return, the still moving waler will oppose thereturn roll. The water mass thus acts against the roll at each ship movement. Thisathwartships tank is sometimes referred to as 'flume'. The system is consideredpassive, since the water flow is activated by gravity.
A wing tank system arranged for controlled passive operation is shown inFigurc 7.28. The greater height of tank 3t the sides permits a larger water build.up and thus a greater moment to resist the roll. The rising nuid level must nothowever ftll the wing tank. The air duci between the two Wing tanks conlainsvalves which a~e operated by a roll sensing device, The differential air pressure'between tanks IS regulated to allow the fluid flow to be controlled and 'phased'for maximum roll stabilisation.
A lank system must be specifically designed for a particular ship by usingdata from model tesls. The water level in the system is critical and must beadjusted according to the ship's loaded condition. Also there is a free surfaceeffect .resulting from the moving water which effectively reduces the stability ofthe shtp. The tank system does however stab~ise at zero speed and is a much lesscomplex installation than a fin stabiliscr.
8
Oil Tankers, Liquefied GasCarriers and Bulk Carriers
Oil tankers, because of theit sheer size and numbers at sea. are worthy of specialconsideration. The liqUid nature of their cargo requires special forms ofconstruction and outfitting of these vessels. Cas carriers for the bulk transport ofliquefied gases are also an increasing.ly important specialist type of ship. Thebulk carrier in its many forms is increasing in its unit size and numbers such thatit too is worthy of individual attention.
Oil tankers
Longitudinal and transverse bulkheads divide the cargo-carrying section of t~e
vessel into a number of tanks. In addition to separation of different types of oiLthe individual tanks also reduce the effects of the liquid's free surface on thestability of the ship. Since oil contracts and expands with changes oftemperature, tanks are rarely completely full and movement of the liquid takesplace. The bulkheads, decks. etc., must therefore be oiltight even when stressedor loaded by the movement of the oil in addition to the normal static loads.Longitudinal stresses are considerable in tankers and great strength is thereforerequired to resist bending and stiffen the hull structure.
Fire and explosion are an ever-present hazard on tankers and special systemsof ventilation are necessary. Void spaces or cofferdams are also fitled in placesto separate the cargo tank section from other parts of the ship, such as pump·rooms and fore peak tanks. Cargo-handling equipment is provided in the form ofpumps located in a pumproom, usually positioned between the machinery spaceand Ihe cargo tanks. More than one pumproom may be fitted depending uponthe cargo carried or the piping arrangements. Suction pipelines run through Ihecargo tanks, and discharge lines leave the pumproom and travel along the deck tothe crossover lines and manifolds situated al midships.
Two main types of oil tanker are 10 be found at sea today. The very largecrude carrier (VLCC) and the products carrier. The main difference is in sizeand the products carrier has a larger number of tanks with a more complexpiping system. This enables the carriage of many different cargo 'parcels' o~ anyone voyage. The various aspects of tanker construction will now be exammed.
165
F'-'ged buckel
O"t'vht Ifinswersebulkhud
Oocking brakell
Oeck eMue',ne g"~f
0,119'1 " __lebulk....,
FiguTt 8.2l::lt~,uion 0/ c:entrdint 0/ Illnk (iongitudinill/filming)
deep transverse webs. A number of longitudinal stringers are filled. dependingon the depth of the tank. Brackets and knees are used 10 tie the side frames tothe underside of the deck. the bottom plating and the stringers (Figures 8.3 and8.4).
Bottom structure
Str,ngeo
AU tank~rs 3ft conslructed using dther the longitudinal or the combinedtype of framing system. Ships greater than 198 m in length must be framedlongitudinally. A fully longitudinal system of C005111.\I;lioo will have longitudinalstiffeners along the ship's sides throughout the tank length. Thn.e longitudinalsare usually offset bulb plales of incft'3sing dimensions towards the ballam mellof the ship. Buill-Up stiffeMrs. consisting of webs with symmetrical nat platenange.i. have also Men used. Side IIans~rses 3ft filted in line with the ballamtransvenes to suppon the longitudinals against compressive loadings (Figures 8./and 8.1). The combined framing system uses side frames with intermediate
Oil Tanker:s, Liquefied Gas Carriers and Bulk Carriers 167
Framing
The bottom structure is longitudinally framed over the cargo tank length. Bulbplates and built-up T-sections are usually employed. The bottom transversesprovide support and are spaced at intervals of around 3.8 m on smallet ships andup to S m on longer vessels. The longitudinals are continuous and pass throughnotches cut in the transverses (Figure 8..5). Aat bar make-up plates are fitted tothe transverses where the longitudinals pass through. At watertight bulkheads afully welded collar is fitted (Figure 8.6). The longitudinals are also bracketed tothe transverses. The transverses are usually a plate web with a heavier flat barflange. Horizontal stiffeners are fitted where a considerable transverse depth isemployed (Figure 8.1).
A centre girder is fitled. except where there is a centreline bulkhead. Variousarrangements of continuous or intercostal longitudinal side girders are alsosometimes fitted. The arrangements used will determine the scantlings of thememben employed in the construction. The centreline girder is stiffened andsupported by vertical docking brackets fitted between each transverse (Figure
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These are of much the same construction as described in Chapter 5. The loalline rules require pJ(JtecUve housings around openings in the freeboard and othel
Superstructu res
A wash bulkhead is similar il1 constructioll 10 a tran,ve-rse bulkhe~d but is !lotoil tight. Large holes or perforations exist in the plaling These holc~. whileallowing the oil to mo-ve through. do restrict the: speed and force- of itsmovement and provide additional transverse strength to the ship.
Framing at ends
Oil Tlmkers, Liquefied Gas earners ond Bulk Canters 171
Beyond the cargo tank length the -vessel may be tnmsversely or of (ombinedframing consHucti{)n and must ha-ve certain additional strengthening fitted. Adeep tank or tanks is often fIlted forward of the (argo tank space Wheretransverse franling is employed. solid floors are fitted at every frame space, Intercostal side girders of depth equal to the floors are also fitted in line with everyother bottom shclliongitudinal in the deep lank space_ The deep tallk is fittedwith web frames nOT mme than five frame spaces aparI. A centreline bulkheadmust also be fitted, unless llle mai11 10ngitwJinal bulkheads extend through thedeep tank. With longitUdinal framing, transverses are fitted in the deep tank notmore than 3 m apart. Intercostal side girders are also fitted either side of thecentreline, On larger vessels th,; cargo tank structure may extend into the deeptank itself. Panting and pounding arrangements are also necessary and will besimilar to th{)se described ill· Chapter 5.
All modern tankers now have the machinery space and accommodationlocated aft. Web frames arc fitted not mClre than five frame sp.aces apart in themachinery space, with fixed or portable beams acrosS the casing opening.Tranverse framing of the bottom i" u"ua\ i.ll the machinery space andconstruction is similar to that mentioned in Chapter 5. Transve-r~e orlongitudinal framing of the sides a.nd deck may be used from the machineryspace to the after end of the ship. Deck longitudinals must extend into themachinery space a distance equivalent to one-third of the ship's breadth. Pantingarrangements are also fitted in the after peak. as described in Chapter 5.
Wash burkheads
Trlln:werse hulkheads
Transverse bulkheads are similar 11\ cOllStruction to longitudinal hulkheads andmay be nat with stiffeners or cmrugatcd. Vertical wc-bs must be fitted totransverse hulkheads in line with the centre girder and may be Htted in line withside girders Conugated~bulkheads may luse vertical or hori-lontal corrugationswith stiffening webs l1tted ...t right·angles to the i.:UTfugations. lJJngituJinalstiffeners ·arc arranged contil1Uously through transverse bulkheads and areattach.ed by brackets
Transverse bulkheads must lwt be spaced greater than one·fifth of the ship'slengtll apart. Where the tank length is greater than one-tertth Df the ship's leng.th.or 15 m. a perforated or wash bulkl1e~-d must be fit led.
~ Plate make up pleo:e
- Bonorn h;tr)yitudi,,~1
i
-,,,,
Centreline glrr1er
/ ,Bracket ;t Brockel
V ,Flange
/ / ~ \
/~"" -A<tiffene. ,
3ulkheads
),7) .. A hl.'uvi,er platl.' fl,ange is fitted .at the uppcr edge of the tentreline girder.\ddltlUnal stlffemng ot the centreline girder is provided either by hmizuntal or'crlical flat bars.
Iip"!, 8. 7 D()d,illl brllckel
three lypes of bulkhead arc to be found on tankers - longitudinal, transverseLnd wash
70 Oil Tankers, Liquefied Gas Carriers tmd Bulk Carriers
Jnderdeck structure
.ongitudinal bufkhe.ads
rhis is largely the same as that for the buttom structure, with transvcnes fittedn hac with those below. A continuuus centreline girder and perhap3 intercustalJr continuuus side ~rders are fitted l:J.eneath the: deck.
:13t stiffened or corrugated oiltight bulkheads may be employed. The stiffening; largely the same as .that, of the ~ide shell, I.e. horizontal stiffeners along the,~lkhead where- lOll gJt uJrnal shell stiffening IS used. Brackets fasten the~Iffeners to the transverse bulkheads at the ends. Where side transverses areItled to the snell, correspondingly positioned vcrtical webs are fitted at the,u!khead, Horizontal stringers at the ship's si-de are matched by horizontallrtngers on the bulkheads. A continu{lus rin,g·type structure of considerablelrength is thus builT up within the tank space.. This ring·type structure i~ further brace-d by the use of beams known as cro-ss.les fitted between the transverses or side stringers and the longitudinal bulkead!>.
Where corrugated bulkheads are employed the corrugations must nmorizofltally. Vertical webs are fined at e...'ery bottom transverse, in order to.lpport the bulkhead.
T"PrJed 'l"rtln~ hule Clear Ofilled 110'1>5
00 0 0 0
0 C
0 0
~,0 a
0 00 0 "0 0 0 0
(al
No<, --'';=:;:'''''''-: Waslle.Coverplate
==l..,-_Joint Ot ga~k.et
Tappin~ ,trog
[==~=~=====:::l- Deck
Access to the cargo t.ank spaces is by oil tight hatches. Circular or oval shapes areusually employed with cQamings at least 225 mm high. Steel covers with suitableoiltight fastening arrangements are usual, Figures 8.8(a) and 8.8(b). Patentedcoven -of other approved materials are also available. Other tanles and cofferdamspaces may have similar hatches or manholes for access (Figure 8.9).
Hatches
Oil Tankers, Liquefied Gar Carrier!: an.d Durle Carriers 173
decks and a furecastle extending 7% of tbe ship's length from forward. Bc-cal.l~e
of a (linker's hig.h ,",ending slroes5es extra care must be taken with di~c()ntinuities
at the superstructure ends.
General
Cofferdams.- are filted between oil tanks and other compartments and must be atleast 760 mm wide. Pumprooms l)f water ballast tanks may, subject t{) certaincOllditiom, be accepted instead of cofferdams. Special arrangements arenecessary in tanker~ becallSe of the redu.ccd freeboard to clear tlle decks ofwater. Open rails are fitted for at least half the length of the weather deck. Solidbulwarks are usually fitted only at the forecastle and around the superstructure.
CJ "':k I :_t.n'!
_.--L
h"1il/7'f" 8.8((;I} Carl'O lank hale!!
H",~" andm"n,e,b"I~"c<
~C======i:;:.-/="c"c,co,=.=m=·c"c,,,~;:I=~c~Oc"=':=·"==J· ~,I.a:~~:~.n1-= / = I ,ee F,y 8!Jtbi
I ---
,_ H'l~h
I co",m",~
,
Hat~h
,ov~,
171
'b'F'l'tu/'e 8,8{h) Derail ofhatch dampiflg ammgemenr Figure 8.9 MQlthole cover: j{l) plate, (b) detail of:ecu";ngQmmgement
74 Oil Tankers, Liquefied Gas Carriers and Bulk Carriers
lentilation
'enliJation arrangem-ellis an' fully described ill Chapter 9.
nert gas plants
IIcrt gas plants are being fitted to an ever·increasing rmnthcr of tankers tonprove their operational safety. The plallt provides an inert gas blanket overrlC ~llrface of the cargo to stop the build·up of flammable vapuurs which might~ad to explosions.
A typical system is ~howl1 in Figurr:13.1 O. The plant uses exhaust gas which isfawn flOm the boilu flue uptakes, where available, or frurn a separateombustion chamber. The gas enters:a scrubbing tower via a water seal which isirculated b)' sea water. The gas is cooled, solids and unwanted gases are~rubbed out and it then passes through a demister which removes water vapour.'he inert gas which contains less than 5% uxygen is then pumped into the cargomks, Using fan units to drive the gas along the supply main. A deck-mountedrat-er seal is fitted in the main to prevent the back·flow of flammable gases fromle cargo tanks.
During unloading the inert gas proVides a positive pressure on the cargoJrface which assists discharging in addition w ensuring a safe operation. Inert3S is fed into tanks prior to loading and when fu11. the fans are stopped. DuringJading the ltigh velocity venting valves are opened to vent the inert gas totmosphere. When loading is complete the valves are closed and inert gas isJpplied to produce a slight pressure- in the- tanks. During loaded passage thelert gas pressure is monitored and maintained.
)ther outfit items
pedal circular openings with removable gas-tight covers are provided for tank.leaning operations. A number of fixed or portable tank-eleaning machines areJwered into the cargo space through these openings.
Tank sounding gauges, wltich give local and often remote readouts of liquideptlls, arc fitted to each cargo tank usually on to a 'pot' or cylindrical seat.
Heating coils are Htted in many tankers to improve the discharging of theil. Steam is passed through coils fitted on the tank bollom to heJit the cargonot to discharge. Gares will be releared dmmg heating and the ...enting system111st therefore be open.
-iquefied gas carriers
he past 25 years hJlve seen the emergence of the bulk transport Gf n.atur31il.ses both for use as fuel and as a refrigerant. Specialist ships are now used tomy the various types of gas in a variety of tank sys.tems, combined witnrrangements for pressurising or refrigerating the gas.
Natural gas is found and released as a re~ult of oil·drilling operations. It ismixture of such gases as methane, ethane, propane, butane and pentane. The
.___ 0
r" • '3.."-·-0.- '"~.g'
Crn
•,o
175
'"lIQuidllghlc~ntrd,ne
;I"headCa<go ,."k
heavier gases. propane and butane, are separated by liquefaction ,md are termed'peuoleum gases'. The remainder consisting largely of methane are known as'natural gas'. The properties and therefore the behaviour of these IWO basicgroups vary considerably, thus requiring different means of containment andStorage during uansportation,
Natural gas is, by proportion. 75-95% methane and hasla boiling point of-162°C at atmospheric pressure. Methane has a critical temperature of -82°C.The critical temperature is the temperature abo\'e wllich it cannot be liquefiedby the application of pressure. A pressure of 47 bar is necessary to liquefymethane at -82°C. Thus, natural gas cannot be liquefied by pressure at normaltemperatures. Liquid natural gas tanken are therefore designed to carry the gasin in liquid form at atmospheric pressure and a low service temperature in theregion of -164°e. The problems encountered. therefore, deal with protectingthe steel structure from the low temperatures, reducing the loss of gas andavoiding the leakage of gas into the occupied regions of the ship.
Petroleum gas consists of propane, propylene and butane or mixtures of thesegases, all of which have critical temperatures above normal ambienttemperatures. Thus they can be transported either as a liquid at low temperatureand pressure or at nonnal temperature and under pressure. The design problemsfor this type of ship 3re similarly protecting the steel hull where lowtemperatures are employed. reducing gas loss and avoiding gas leakage, with theadded consideration of pressurising the tanks.
176 Oil Tanken, Liquefied Gas CAmen and Bulk CAmen
Liquefied natural gas tankers
The tank types of LNG carriers are ~If-supporting and either prismatic,cylindrical or spherical in shape or :I membrane construction which is supportedby insulation, Materials used include aluminium,9~ nickel steel or membranescomposed of stainless steel or nickel iron.
Tank designs are split into Ihree categories, namely self·supporting or freestanding, membrane and semi-membrane. The self-supporting tank is strongenough by virtue of ils construction to accepl any loads imposed by the cargo itcarries. A membrane tank requires th~ insulation between the tank and lhe hullto be load bearing, such an arrangement being termed an integrated tank design.Single or double metallic membranes can be used, with insulation separating thetwo membrane skins. The semi-membrane or semi·integrated design is similarto the membrane, except that the tank has no support at its comers.
A double·hull type of construction is used with each of the above designs, thespace between being used for water b:J1l3sl. Thl:' basic configurations are shownin Figure 8.11.
,.,Dome T"" h.,,~
1. /o.,,~ ...,,_r;:.;~\~O;;t~~In huU_ Memb<_ I....k
l laIOO.. _
'lfUClure ~~======~
'"
Comparison 0/ tunk types
Membrane and prismatic tanks use the underdeck cubic capacity mosteffectively, Cylindrical and spherical tanks involve constructional probkms bypenetrating the upper deck but pro\'ide greater safety in the event of collision orgrounding. Membrane tanks are cheaper to build but the insulation which mustbe load be:lring is more expensive, The insulation of spherical tanks need not be
,W'ter tylLast
FlZUfe 8.11 Tank arTIIII~mtl lOT liqutMd lU,"lIfll p: (tl) pnmuttie ttlnk: (6) spherial.'tank: (e) c:ylindrictJ1 tank; (d) membrr'M ftlnk: (t) doublt-mtmbt"tlnt tank: m sem1
mtmbnmt ttulle
179
Hull and
"'lO"dar~
/ barrie'
S-e~anM~(~
t>.'"er
SeumtJ'" V- b.rriel
Hull~.
)
II
__J,-_.
Wat.. ,
t>a·""'l
Fuel ail
P..n~tr~tin9dom~
Spl"hqu~,d
FiglHe H 1J Alt dome tallk amMKl;mm[
Fi",rc 8.12 Cylhldrical rronk fanli. anan/[ement
---n
r--" T~1
~ I --=---'~.•.. [- 1__
1
[
.c. ~=.= Imul~liCln 1 , I
1[ •••.··1 I .~.
r uel WaterQi' b,llla.t
Figure 11.14 Tank <1n'an,;.ell1enr with hull as scmmlary barri""
-iquefied petroleum gas tankers
'oi!-ojf
78 Oil Tankers, Liquefied G(Jj Carriers and Bulk Carrien
)ad bearing ~ince it is only :1 partial se\;ondary 1)arrieL if needed at all ill this~spect The hull alld machinery cost~ arc ahout clIl.lal fDr each tyre All Ihelfferen t types are- in se n'icc. wi th the firmly cslabli\hcd desigm heing prismatic,phcrical and membrane- types
'hrec basi( lype~ of liquefied petroleum gas tankers MOO '::lJrrcnt]y used lJleJl1y pre~surised tank, the semi'pressuriscd partially rdri&c-Titlc.u lanK. and thelily refrigerated atmmpheric preSSlJre tank.
The fully pressurised tallk areHies ~t Jhllilt 175 18.0 bar and requireseavy expensive tanks of carb-(JTT steel W11ir;h <lrc lISually cylindrical in shape. Thisigh pressure is equivalent l() the vapour pressare of the cargu <It the higheslossible ambient temperaLare. uS\Jally taken as4S°c. The tank domes. penetratele upper deck and have (IUtU all the nccessary ClllTTlections for loading,ischarging, sampling, ele.
Semi-prcssurised lanks llpenltc <It about ~ har and a temperature of aholll-7°C must be rnaintail1ed in lite tanks. Insulation is therefore required afllund11; tank and, since some cargo will boil off.. -a re-liquefaction plant is needed.[milo-fital rylindrical tank conflgara!i(lIh are again used. Low lemperaltlfe:eels for temperatures dOWTl tu around - 45"C must be used for the Lanks.
Fully refrigerated atmo$pheric preSSllfe tank systems nave serlClce?mperalurcs about -SO°C and maximum working pressures of 0.28 bar Thcmks are insuLated, self-supporting and prismatic in shape. The tank materiallUst be ductile at low lemperatures and is usually a fme-g,rai[l hCal-tleated steelJcll as Arctic D or a low alloy niockel steel A secundary bartier capable of~tainjng the cargo in the cvent of main {ank fracture is required by classificationxiety rule-s. Three lank types are used with fully refrigerated LPG sh.ips:
(I) A c-entral trunk runs along the top for the length of the cargo tank. Wingballast tanks are Ii.Hed, their innet >Ulf-:aCC acting 3S the secondary barrier(Figure 8.12).
(2) A large dume is situated aft at the top of the tank and wing b-allast tanksare fitted (Figure 8.lJ}. The inner surface of the wing tanks acts as thesecond-ary barrier.
(3) A large dome is situated aft at the top of the tank but no Wl[lg ballasttanks are fitted (Figure 8.14). Hopper tanks are used for ballast whennecessary. The hull itself acts as the secondary barrier and must be oflow temperature carbun steel in way of the cargo tanks,
iquc-fic-d natural gas is continually boiling in tanks when lr;msporto.:d by S('8.be-re is therefore a lll::e-d to (eleasl:: this gas tu ;II/uid a pr~'s,ure nuild-up ill theInk. It may be n'"nte-d dire-c!iy to atillosphere or bum( in boilers or in sT,cc'";:lllydarted dual fL1ele[lgines. Barningthe hoil-(Iffg-ilsin a flare mounted on a hO(lill.:mote from the ship is another possible solution. Rc-liqud,tCiio!l is 110t~onomical because of the- large- p'Jwer and IllJ~e cost <If the machineryecel..SJ,ry.
180 Oil T/lnken, Liquefied Gas Q:miers and Bulk CIlm-ers
Comporiwn of tank types
The reduction in weight of tank mat~ri<ll in a semi-prcs:.urised tank design isoffset by the need fer refrigerating. plant allll insulation around the tank. The u.seof low pre~sure tanks does, however, permit better utillsation of the underdeckcubic capacity of the Yessel. The fuJly pressurised lank has no need of insulationnor a secondary barrier.
Oil Tmkers, Liquefied G/lS Carrien and Bulk Carriers 181
1 d' the machinery spa\:e, the side shell in way of the \:argo tanks, the;:~I~Yt:n~: or upper hopper tanks, the main deck in-side of the ~lfie of ha~che~.the forecastle deck ami the fore and aft peak tanks. LongitudInal ~rammg IS
employed at the bottom shell. the tank lap and the upper det:k olltslde of the
line of hatches. . h . FOA section through a typical floor in a l()wer hopper tank IS sown III 19ure
816 The longitudinal framing structure can be clearly seen. Above the ~opper
t~nk can be Seel] the transversely framed hold with the bracket connectmg the
Le-",,~' he-pr>er tank
FIDor ~Iale
Transv~r5~
frameV
r1. II Brd~ket
'~ ~- I\..¥'
\\1 Hoo~er tank ,icle pla,e
S,de,hellplating
Fi!\lm: 8,15 Bl,lk carrier rranSl'erse ~ation
Sirl~
'rame
The various regulatory bodies have rules for the construction and cl:Jssiflc<llionof ships carrying liquid gases in bulk. These rules follow dosely the 1\-10 codefor this type of vessel.
A complete or partial secondary barrier is required in ull but pressLl-re vesselsoperaling at ambient temperatures down to --10"C. This secondary barrier is aliquid-resisting outer skin which will temporarily contain any leakage of thcliquid cargo from Ihe primary barrier or tank. The secondary barrier should alsoprevent the structure temperature [wm dropping and should llot fail under th~same circumstances as the primary harrier.
Bulkheads or cofferdam arrangements are necessary between cargo tanks,depending upon the temperature of the cargo carried.
Cargo-pumping pipework systems must have no interconnection with othersystems. INhere a cargo tank has no secondary barrier:l suit:lble drainage systemmust be provided which does not enter the machinery space. \\'here secondarybarriers are used drainage musi be provided to de.al with any leakage, again frol11outside the machinery space.
Special ship survival arrangements are required which limit the width of tanksin relation to the ship's breadth. Double-b\Jttom t:mk heights are also stipulated.
Arrangements of tank design or internal bulkheads where possible must beu~d to restrict c.argo movement and the subsequent dynamic loading ufstructure. Membrane tanks, for instanc-e, cannot have internal bulkheads and aretapered off in section tow.nds the top.
Materials of construction and those ured in piping system.s are dealt with inconside-rablc detail in the rules.
Construction as-pects of LNG and LPG carriers
Fi1[1.1l'e 8.16 SQlid·fluor- arrangemmt in (J lower hopper tank
LOfl~'tudina.
,t,llener
Tank loOP
Bulb 1,lat"<liflene.
o
I
Oi~/,-~
I. <
Longitudinal ._stdfener
Bulk carriers
The bulk carriage o-f single-commodity cargoes has been il continually advancingtrend with the development of specialist types of ship to sUit. nil' desire forflexibllity of operation has also led to variuus desigm to enable different bulkcargoes to be carried on different voyages. Such vessels have become known ascombination bulk carriers, -oil/bulk/ore (aBO) and oil/ore (00) are examples.
Some particular aspects of bulk carrier construction will nowbe examined indetail. A transverse section through a general-purpose bulk carrier is shown inFigure 8.15. TIte cargo hold is Seen 10 be shaped by the upper hupper or s.addlctanks, the lower hopper tanks and the double bottom. A wmposite framingsystem is. iJsed in common with most bulk carders. Transverse framing is
<2 Oil Tankers, Liquefied Gas Carriers and Bulk: Carriers 183
i__ H.t,h
__ -, co.>rn,n9
rT ,,"k ,;(/eplate
,,//" j
)
"_/
.~
, '
D~ck "Ia"n"
"
Sill.""l.'1Jpl.ling
Hop,,",lan~
Flat.- ~ liar~
, ' ,titf~n.r
Faceflal
I-I"pi>'" iidetaper b'ack~t
Strin~ef
bracket
'\;,~-;t--~,ilt__~."."·~ Bracket
Strinqer,
\Frame.nHener
Hopper"de laper l>racket
./
/c/
h--_/,," ,4__ 8r"ck','
\../,,
-1ot----- Trar,v~"" home
IJ
1>,
ure 8.17 Tapering-off 01 hopper tan.k at a{ter end" ra) plan vie-wan hopper tank end(t;) sectiOil 01'1 hopper lank end .
fr:am.... to the hopper hmk. At the end~ of the hupper tank region a considerablechange in section lKcurs. The construction used to reduce the effect of tl1isdiscontinuity is snown in Fignn> 8.17. A large tapered bracket is used wnich isconnected to tile surrounding transversely framed structure as shown,
A section through an upper hopper t.:mJ,; or saddle tank is shown in Figure8.18, The longitudinal framing under the deck can be seen as well as the bracketconnecting the aprer edge of the transverse frame to the tanL The side shellpmtion of the tank is transversely framed by offset bulb plates with plate webs,as shown in Figure 8./8. fitted at every fourth frame. A deep-flanged bracketjoins the inuer tank side to the hatch side girder.
Details of a bulkhead stool are shown in Figure 8.19. With a corrugatedtrausverse hulkhc:ad as :shown, the stool arrangement is used to shape theforward and after lower regions of the <:3rgo hold. This !lush tapering shapepermits easy discharge of bulk cargoes and simplifies cargo lIold cleanin.g.Shedder plates are fitted inside the troughs of the corrugated bulkhead for thesame reason.
184
9
Accommodation
The single duct system
In the single Juct system the central unit mixes outside air with some returnedor recycled ait. This air is then filtered, heated and perhaps humidified orcooled. This conditioned air is thell distribllted along a single -duct to theindivi.Jual supply units in the different spaces. The amount of supply air can becontrolled within the particular cabin lJr space. Figure 9,] shows- thearrangement of the sing.le duct system.
An ucc3n-goillg ~hip i~ required 10 operate in a ~'afi['ty {le ....ery different climates.Air temperature~ m.ay range from -15°C to 50°(' and sea water temperuturesfrom aOc to 3-8°C The moisture wnlen! of the air will vary considerahly andsolar radhnion may ;lllect one or Illore of the ship's exposed surfaces. All thevarious forms of good lmd bad weatllcr will Jlsu be experienced. The air fromthe air-conditioning and ventilation plauts is therefore rcq,Jired to provide allaccepl<lble climate for the crew to live and work in, su{fiden1 air fm machineryusc an-d to m<untain temperature and humidity al acceptablt: levels to the cargo.All this must be achieved reg.ardkss of tlu:: conditions prevailing externaltn theship_ The design of suitahle systems will therefore require infonnatioll about theship's trade [l)ute~, type, or cargo and machinery imtalbtintl
Most ships' air-conditioning systems employ centrally situated units. These unitsare s-elf-contained and supply the cabins and sraces within a particular area viatmnking. The contrDI possihle in imiividual c..bins or spaces depends upon thenature and wmp]exity of the central unit. Three ha,il: systems are in use - thesingle duct. the twin du~t and the twin dun with reheat. In each case the centralunit will deall. supply warm or cool. humidify or lkhumidify tile air supplied tothe cabins.
Ventilation
I
!--~
I
II:
1"--~
,
..~\-
...---JIi
---LI,
The twin duct system
Jl,.gain, outside and returned air are mixed in the cen tral unit then filtered,preheated and perhaps humidified. Some of the air leaves the unit before it
18S
,6 Ventilation Ventilation 187
r
]'~ ====~:'i
s""plv "~.""g I""3,r co,1
""'''" 19t"J,:S~~ll()l1~ T ,
R~wrn L 1- ,." r- _ L
/r,lIe, /
C"OI,nq'.nil D,.I""ulOo"
,eel"",
{\" ,u""ly~"n"(J1 "" 1
,~" ,,,pplycon",,1 unit
A" 'L1Ppl~
£ontrol u,,,t"'" <upplyco"trol un;,
Figure 9,} The ll/Tgle dun svstenl FiKIJN' 9_1 The.ingle dll£'1 ""il~ r~heat srsrem
.aches the cooler, to be reheated; the amount is increased as the outsidemperature tails. The remainder of the air passes over the c(loling coil. The !W(lI supplies at different conditions are passed through separate ducts tomtrolled mixing units in the individual spaces, The air temperature- andmdition can then be selected for the particular space. Figu.re 9,2 shows therangement of the twin duct ~y~tem.
RetLl,n
", ;--=-~~4-
Ventilation of non-ins.ulated cargo holds
The purpose of ventilation ill non-insulated holds is t(l remove surplus heat an,dhumidity, to prevent the cundensing of rn01sture 011 cargo or hun and to remmegases pf()[lllCed in the ripening process of some fruit and vegetahle cargoes.Natural and mechanical yen tibtion systems are lIsed for thIS purpose.
dischargin.g, the storage and ventilation must be suitable and satisfa<:t~TY .Inadequate, poor quality air supplies can seriously damage most cargoes. FalT~Ysimple systems of cargo ventilation and attendant proce,dures can prevent sUi,;hdamage. Different cargoes react to the climate 00 board III as complex: a manneras the human body, with often irreparable damage as ihe result , ,
Certain general cargoes, some fruit and vegetable cargoes and hygroSCOpIc(water-absorbing or emitting) cargoes are carried in non-msulated holds: As aresult they are exposed to all climatic changes which may cause c~ndens.atlOn onthe hull or cargo. Ventilati.on of the holds in which they .are. carned IS thereforenecessary. Refrig.erated and £Iozen cargoes are canied ill Insulated holds tutbecause of the living, gas-producing nature of the cargo they also reqUlreventilatiun.
Ai, '''llply~()nlrol L1nit
ReCiealing C"olinq
P,elleJli"g un;t ~<l11 P'"",ure
/ \, L DI\llilJ"ti"n"'ct,on
Fifi!:Ure 9_2 1'1". twin dun sysrem
Aic SUPPlycOnl,,",1 unll
he single duct with reheat system
he central unit mixes outs.ide and return air, mters, preheats and humidifies orlOis the air to the lowest required temper.atllre for .any part of the system. Ther then passes along one duct to individual units in the spaces. Within tneserUts is a controlled healer over which the air passes. Heating may be achievedy circulating hot water or an electric heater. The air supply and its temperaturelay therefore be regulated. Figure 9.3 shows the arran gement of the s.ingle ductith reheat system.
argo spaces
:c~" I,I
, 1
-T 1
Louvre
',,'et~opening..~
"I'm i ~, 1->1 n<j~d-[~",w~r
!
J'
he primary function of ships is to transport goods from place to place. TheU"go must be delivered in good condition and, in addition to careful10ading and Fir;Lm' 9.4 Niltural vennlarion of {ween·,kcK space or workshop
188 Veil tiTalian Ventilation 189
Q[l 0 0"
.-.-
//f!)
_'4"
~ I
~- /1+ 11;,j I
Venti lation of refrigerated cargo holds
R f' rated c;lfgo holds ret:.Juirc 3. carefully controneLl Jir-rcplacing system f~r
ea:J:l~~dividual space. Cooled a.ir is sllpplicQ !() the- refrigerated no~d wlle~e ~:ains he-at from ripening cargoes and entrains the ga-ses produced. ThIS 31.r I~
g. • lod ,od a c:'teful balance must be maintained between lJllet andt en ex aus'v" U .•• '
exhaust gas quantities, regardles~or the outside chm~tlc comhtlOns.", olefOne s '-stem achieve~ this by drawing outmJe aIr down to a blink of" l.
t ubes vi/ a central unit. The delmmidifled air thell passes lllto th.: cargo ,bold,',h Id 1 gh d t· back to tne- "entraTIle exhaust gases are drawu from the 0 t \fOU .lIC.~, outlet
"t od ,.'", returned to the outside atmosphere. The lmkmg of mlet and Iuma ... " . 1 h\dF" 97~now:;t1evalves ensures a constant ;lir supply at all times to t If 0 . l!!,Ur" . .
arrangement of such a system.
P t "", IypD~ of shin have their associated GlIgO ventilation problemS,e,g,"ar It.:U ar ..~ t' f d" 1 ct"n, '"• li li· ff shi.r~ and the vehicle exhau~t umes urlllg 03 I "
rO -on, 10 0, 1 "I t The partlcul:Hdischarging. Bulk. carriers umally only require natura venti a l(JIi, . , toproblems for each ship type must be considered early on at the deSign stageensure a suitable system is provid~u.
, I " d t ~irJ[ellljrdampa,Figure 'J,() Cio~ed pentiJatirm rySlem I j reClr('~ MIll); all [!i'r, _
3 e:duwM air damper,
•
,~
II~ "I:1
•- ---!
<'
n
" II ".-- r:- _. r ._~--'_l-"~f"~'- J1
,,~=L~e-- f----
L_ t I t ,7- rF-I· -r - -
r~'~~~~;' it • '_ .'
(1;-, ,"
'F f - - - .,.1
Natural ventilation is accompUshed by inlet and outlet pipe'S and trunking toeach cargo sp.a-cc. Thesc inlets and outlets consist of cowls or vcntilators ofvarious designs. Air is forced in by the action of tnc winu ordr.awll in as a resultof all ejector type of c:xhaust drawing air out which is then replaced. Where theforce of tlle wind is utilised the cowls must be manu:ally positioned, and are large.cumbersome fittings which must be well stayed to the deck. Figure 9.4 shows cl.
natur.al ventil.ation .arrangement for a tween deck or workshop. Most modernships utilise mech.anical ventilation for reliability, improved performan::e and thereduced size ofl;owls necessmy. .
Mechanical ventilation operates in two distinct systems - the open and thedosed,
Ine open system uses axial flow fans fitted in the inlet and exhaust trunks.The tnmks may have separate cowls or be incorporated into sampson posts ormasts. The air is supplied along trunkjng and dUds to the bottom of the hold.
11.1
FiguJ'c 9.5 Open vI'ntiwtion s)'sJem. (a) normal d,.culotior/;(b) rel'er;ed crrcuwrirm - to pre-venT underdeck drculotl'o/1 at
low Outside tempaalure
The air is drawn from the top of the hold ju~t below the decks. The exhaust fanscan be reversed if condensation is likely near the deckheads, for example with alow outside air temperature. Figure 9.5 shows the arrangement of the openmechanical ventilation system.
The closed system recirculates air and a contfulled amount of fresh ail l:an beadmitted. The ventilating air is distributed around the hold and cargo, fonningan insulating wall or curtain between the two. Ex.haust air is drawn from theboltom of the hold. This system affords every possible mode of cantm] and iswidely used in somewhat varied forms. Figure 9.6 shows the c\-osed ventilation~ystem.
190 Ventilation Ventilation 191
Control rooms
The prOVISion of control rooms in most modern machinery spaces e~~ures c~os:careful control of the climate in such spaces, often with lhe pTOV1Slon 0 alT
rovides air through ducls to outlets at the various platforms.. Figure 9.10Pses medium pressure axial now fans to provide a through trunklllg system 10~he various outlels at the various platforms. This method has proved 10 be th~best. A diagrammatic arrangement o~ m~.dium pressure a:<i:ll now fans anlrunking in a Inat:hinel)' space is shown In "'gllrl' 9,11.
,I
-"•,
I
"l----l
"",.--'~,
Hp".. 9.8 (Ie[rl ModI/'ll".'" sf>au w:mi/<I'IlI'm llfill}ol medium prl"S5I1<" <I.Ylal flo ..'
[all
ffYl'''' 9.10 IIx.>rtom ri~ltll Ma(hinr,yspa(l" "tnti/ariun Ilsin~ mt'diutll pressu,r<I.rial flQ'" [at/J and a Ih'OI,~h lru/lkjn~
sysrrm
HYllTl> 9.9 (bottom Itlt) Machillt?,spurr "l"JltilaliOfI uiin~ 10...•p,rJSll«. ~fltllpo...· Ian and hi~h prtffUrr rtnrn/upl
pm
--
~ ""•,
I
~
I'I
"
I,J
. til,'j~--'l '~',' --'---I
Conl<ol "'''1
Inlel ao,
Machinery spaces
The machinery space fequires an air supply for the operation of boilers.combustion engines. compressers, etc.. and to lIlainlain a satisfactory climatc forthe operating staff to work in.
Certain machinery consumes or requires air for its operation and sufficient airat as Iowa temperature as practically possible should be provided. Underpressureoccurring in Ihe machinery space will affect the efficiency and performance ofinternal combustion engines. Overpressure may lead to leakage of hOI air illlothe accommodation. Ventilalion is also necessary to remove the heiH generatedwithin the machinery space and thus provide a reasonable climate for staff !owork in, This very difficult task is achieved by the provision of ducled suppliesof fillered but uncooled air to as lIlany regions:ls possible. P:lrlkular areas suchas workshops and control rooms. being sl11all. may be :lir conditioned and morefeadily provided with an acceptable working c1imale.
Various systems of air supply to the machinery spaces and casing are in useand are shown in Figures 9.8 9./0.
Figure 9.8 utilises a medium pressure axial now fan supplying air down alrunking. which is proportionally released at the various platfonn levels andexhausts through Ihe top of the casing. Figurr 9.9 uses a low pressure axialnow fan to supply air into the casing area. Also. a high pressure cenlrifugal fan
<ntsI'Ill'illeopening
Bonotn .nell
cowling
= Inltl
~A".Jfl~'O'fi~d_
r-; 0 -0
BINI (lKlc I' ~..C-
o 0
, ~,
Pump,oom ,~lrilflCt
Uppe<ded,L-
e......$1
trunk""
Wilt<I,ghl
bulk",
Machinef" Pump- ,-Wlrtlto;ll~ _"p(ltO' deck
F.nmOIO<~c.nlrit"lPl
f- ..-,~Eltnrioll 01 rrunlcirlg
Trunkin91ed ~outboMdSttul-allflap ~
~ Shvl·oll Ol)eflled from ~~i..flap upper deck Oller
LongitudInal ~I--::;stiffeners
I I I I
conditioning in addition 10 ventilation. This climate control provides thtpersonnd wilh 3. Cum(ollable working area isolated (rom Ihe main m3chinerysp;la. Also. dchc:Jle equipment in need of careful climatic conuol is able 10receive it. The satisfactory opcral.ion :lOd continuous per(onuanct of moderncontrol equipment requires a carefully controlled environment which. by using3. control room. call be achieved.
A ~parate dueted supply is led inlO the control room and usually through afiltering ~iT<onditiul1ing plant or unit which is SCi to function aUlomaticallywilh controls located in the' control room_ A match~d exhaust will r~move stalewarm air from the connol room_ FiX'IN' 9. J2 shows such an arrangemenl.
Ventilation 193
E,,"••lSIoo.nltl
-----'--------------------.J--Sllfl1
fiX'Jn' 9. / J MachjlltrJ' rp«l' I'('miltllion _ di4J(rQmmQlir rurant:rmtr/t
\
192
An ...""lyIan _duel'....
Figurt' 9. J2 Control room Vt"rilan"ofl Fi1:Ure 9./3 PlJmproom venn-/ariM
FjKl.tre 9.14 Ai, pipt' ht'ad
During loading and discharging of lhe cargo t~e \'entil~t~on req~irements areconsiderable. Air must be drawn in or removed m quantities eqUivalent. to thecargo oil discharged or loaded. In addition, during th~ loading operaUon thehydrocarbon vapours issuing from the tank ~ust be dlS~ned well above th.edeck. This is achieved by the use of high velOCIty gas ventmg valves. One t~pe: ~s
shown in Figure 9.15, The arrangement consists of a fixed cone around whIch I.Sa movable orifice plate. A counlerweight holds the orifice plale closed untilsufficient gas pressure builds up to lift the plate. TIle gas is throuled throughthe orifice and issues at high velocity, dispersing into the atmosphere well abovethe deck. During discharge the cover is opened and a linkage from the coverholds the orifice plate in the fully open position.
FiflUre 9. J.s lIixh "e/veir)' ~as ,'e"ri"g I'al,·t
Slandifd A S A, ISO lIangll!
Ventilation 195
P,,,onq led 10 1.,"~
A.." ll.i$h";'~ l'llt'<!",t_,,,,,,,"nl
=
Ventilalion of doubk-bollom tanks is provided by means of an air pipe situatedrcmote from Ihe filling pipe and usually at the high~St point in the tank to avoid
Double.bottom tanks
194 Vemilation
Pumprooms
Tank~1 pumprooms lequirt \'~nlil:uion to cany away poisonous cargo fumesr~suhing from leaking glands 01 pipe join IS. T11~ working climate in this spac~
well below d~ck level must also be comfortable for any pc-rsonnel present.Mechanical exhausting of air is achk\'~d by the uSC' of axial flow fans andtmnking. The trunkin& dr:Jws from th~ pumproom floor and ~metg~ncy intakesat a height of2.15 m from the working platform. These emergency intakes mustbe filled with dampers which can be opened or closed from the wealher deck orthe working pl;lIform. The fan motors are located in the machinery space anddrive the f;lns lhrough gastight seals in lhe bulkhead. Supply is through cowls orlounes at the top of the pumprOOIll. An arrangement is shown in Figure 9.1 J.
unvenlilated pockets. The air pipe is led up to the weather deck to a gooseneckor patenl type of head. Air pipes from fuel tanks arc positioned in low risk areasand have flame $Crun g3uzes fitted (Fig"re' 9.14).
Cargo tanks
Types of ventilator head
Various different Iypes and arrangements of ventilator head are in usc. Figure9.16 shows a selection of the more common designs.
Ventilation of cargo lanks avoids overpressure or partial pressure conditionswhkh could occur during loading and unloading of cargo, Temperaturefluctuations during a voyage could have a similar effect. Vapour pipelines fromthe cargo halch arc led to pressure/vacuum relief valves which are usuallymounted on a standpipe some distance above the deck. Individual vent lines arefitted for each tank on large lankers and a common venting line is led up a maslor sampson post on smaller vessels.
196
1./
10
Organisations andRegula,tions
Classification societies
Uoyd's Register of Shipping (UK).Ameritan Bureau of Shipping (USA).Bureau Veritas (France).Det Norske Veritas (Norway).Germanischer Uoyd (Germany).Registro lIaliano (Italy).Register of Shipping (USSR).Nippon Kaiji Kyokai (Japan).
The construction of merchant ships is considerably influenced and regulated bya number of organisations and their various requirements.
Classification societies. with their rules :Ind regulations relating \0classification, provide a set of st:lndards for sound merchant ship constructionwhich have developed over many years. lllCse rules aTe based on experience.practical knowledge and considerable research and investigation.
The International Maritime Organisation (IMO fomlerly IMCO) is an inlernational organisation which is attempting 10 develop high standards in everyaspect of ship construction and operation. II is intended ultimately to applythese stanoards internationally to every ship at sea.
A vast :J.moont of legislation is applied to ships and is usu:J.lly administeredby Ihe appropri:J.te government department. The load line rules and tonnagemeasurement are twO p3rticular legislative requirements that are outlined in this
chapter.
A classification society exists to classify Of "3rrange in order of merit' such ships3S are built according to its rules or are offered for classification. A classed shipis therefore considered to have a particular standard of seaworthiness. There areclassification societies within most of the major maritime nations of the worldand some are listed below:
I1,1
IC'M$·ltttfH>fJl/l ........
Sul»O<l ban
pipe
"'_. ~~~~'M~":'~I'oom'co..",",ut-to< ,n Nfl A
open llOSu,onIo$ed Dv ""Pw'ng
own cove< pille] r~~~r---'-l;;;;dGaule filled ~
Ve-n!;IJI;Ofl Ifunlo;in9
I'"
Gum~
fIlled IOCcwn
{{'-::"",,:>'\JlI\ P"le
V~ntilalorhmds" (a) "ODS k. " tflee Iype; (bl musJ"oom type; leJ jUf"d mushQ~f" ~m
, -' /V
/' "I~
,TI'I'eilded Rwindle ,
I-SllIM,
II Declo; 101..'
Figuf? 9./6
198 Organwuion and Reguldtion
Consultation blClween the societies takiCs place on mattcn of common illterestfhrough the [nlerTl~tioJlalASSodation of Clas~iflCatiml Societies (lACS).
The classif[(.atiol1 societics oper~te by publishing rules and regulations relatingto the structural eflkiency ~nd the rdiabilily of the propelling machinery andequipmenL These rules an~ the result of years of expcrience, research andinvestigatio[J into ship design Olnd (Qllslrudion_ They are ill fact a set ofstandards There is no compulsion all a shipowno ro have his ship da~sincd.Howe,'er, the insurance premiums de-pend h'ry rlluch upon the class ofa shipthe higher the standard the lower the p!.emiuTll. Also, hy being c1as~ifled a s!J.ipis shown to be of sound COllstwl:tion and a safe mean~ of transport for cargo orpaS~eIlgers There is no connedioll betweeTi the insurance companies anu tllec1.assification wcielies.
The opc-ration Jnd organisatiun of LJoyd\ Register 'Of Shipping, the oldestclassification society, ",ill JiUW be considered. ThmughOLlt this book allreferences 10 claSSification sudety rules are to thuse of LlOYd's Register ofShipping, This Socidy is run Ily J general corTlmitree composed of members ofthe world community and the industry which jt Snves. National committees areformed in many (llUntfies for liaison pllrpO>-C>-. A technical COmmittee advisesthe gener<Jl cummitlee ,)n tedmical problems connecled with the society'sbusiness and any proposed alterations in tile rules. The society publishes it>;Rules and Rcguhltions for the Classification of Ships' in book form, which isupdated as neCC-Ssary, and also 'Extr-ac1s' fmlll the~e niles and 'Guidance Notes'rdating to morc specifk stluctures and equipment. The society employssurveyors who ensure compliancc wit h the TIlJe~ hy attendancc duringconstruction, repairs and maintellJnc(" IhrougItout the life of dassed ships.
To be classed with Lloyd's. apPlIJval is n~cessary for the constIll(;tionaJ plans,the materials used and tile C011structiOilai methods and standards, as observedby the surveyor. The rules govfrnillg the :scallllings of the ship'.; structure havebeen deve!r.lped from theoretiC,ll Ind ('mpiric-al considerations. Llllyd's wlJectinform,Hion on the WIlUfe and <:aus-e of all ship casu~Ities. Analysis of thisinformation uften result, in modifications to the rules to produce a structurewh.kh is wlE~id-ered tIJ be -a-dequate, Much research alld ill\'estigaliort is aIs-ocarried DUt by tllC society. bIding likewise to modificatiolls <Jnd amendments tothe rules.
The assigning of a da£s then follows acceplancc by the general wmmittee ofthe surveyor's report on the ~hip The highesl clas, awarded by Lloyd's is + lOOAI. This is made up as fOJ!llW,
100 A refers to the hull when bUilt to Ow highest standards laid down ill therules.
refers to the E'quipment, such as the anchors and cahles, being in goodand effide-nt condition.
+ indk:.Jtes thal the ,essel has b(en built under the supervision of thesocict~/, SurveyUIs.
It is also usual to name the type of ship foll owmg the classification, ego+- I 00 AJ Oil Tanker. Machinery i, al,o sUf'leyed and the notation lMC (Uoyd'sMachiaery Certificate) is U$ed where the machinery has been built a.ccording. tothe society's rule, and satisfactorily proved nn sea trials This informationregarding the classitkation of a ship is eJltered ift the Register of Ships. The
Organiliation and Regulation 199
. .' inin the names, classes and general infonnationRegister of Ships ~s a ~ook c~nt~IO ~'s Register of Shipping., and also particuLarsCOllcernmg. the ships classed y y hi - the world of 100 tons g,ro~ (aof aJI known ocean-gOlJlg merdlant s ps III
ulpacity measure) and upwanls, _ _ cd by the society in requiring, all vesselsThe maintaining of ,talJd~rd). IS ensm ecial surveys are also required every
t.o lI,we ;mn~al sur'''Yd~ 0, t ex,"thmel1~~~~~~;~y for classification. More detail withtour veaTS hom tIe lJ C 0
regard to tbese surveys is given in Cdlttap~e~t la~·an <lssigning authoritv. This meansI h "ety is also empowere o ....t; , , f h
e soC! h cnt ~n admi.ni,tering certam {) t ethat it acts 3S the agent for t e goYemm 1. I. f h' . 'e, the load me ru es,m-alldatory reqUlrements or s Ippmg, - .
IMO
trade has led finally to the organisation ofThe international llaturc of selborn~ tal c;--operation on matters, . I body '0 provide mtcrgovernmena.n interna IOna ' It U ~ the aUi;,nic-e>, of tne United Natious. 1- shippin, amI t e seOl I\'Uer '" ,1concemlllg S1IPS, " ,_ ' .. I (1~'10} fOfll11Orly 1\-leO was forme",the Illterllatiolw] \1.antlll1( Orgdnlsall~1 th nrst assembly mel in London inFollowing its formal approval by 21 stale" e I
1959., . in out many studies, producing detailed recom-[MO IS responSIble for carry d' d o'Nding fonowing conventions, man-
d , . d eloving standu ~ an pr.. , Ih.men a Ions, ev , clion outfitting and operation. e reqUlIedatol}' requirements f7 ~l.~~~~~::::eIflationa1Convention for the Safety of Li~emen ts ~uch as those 0 t ~ hen ado ted by the government of the vessel sat Sea only become mandator)' W P f involvement by IMO can be seenIegi~tered country. Some of the many areas 0
in the following list:
(I) Navigationale-quipment.(2) Ufe·saving equipment,(3) Personnel tf-aining. .(4) Tanker construction and equipment.(5) Fire s-afety in ships.(6) Radio comll1unkatiorls.(7) Search and rescue techniques.(8) Suhdivision and stability,(9) Carriage of dangerous goods.(IQ} Marine pollution.
Items (4) and (5) will now be examined in some detail, since they embodymany aspects affecting the construction of merchant ships.
Tanker construction and equipment
, 'of oil tankers will continue to be a source ofThe constructlon i!,nd eqUipment ,",., of oil ha" h,en and are still being,, " . elargequanlts ,much mvestlgatlon SlnC f d d hips Efforts are being made with thedischarged fJllm damage~ o.r. oun ~:ti S of' the sea (and shore} by oil Twoohie(t of preventmg or limIting po on
200 OrganiHltion and Regulation
panicular avenues of <lpproach are currently being adopled The tlrst deals wltllpreventing the escape of the cargo oj] ill the- event IIf ~I collision tlr grounding_The se-cond appmach is 10 altempt to limit sLet, of cenlre tanks and Wing tanks.
The first arrangement utilises segrega1ed or dean bJllast tanks (SBT lH C8T).Proposals for the fitting of double·bottom tanks over the c.ng\) rank length andWing ballast tilnks have been put forward.1hese tanks arc t{J be segregated, thati.s, for the carriage of clean water ballast only. The second method aims atrestricting cargo tank sizcs 10 50000 m' [Or centre tanks and 30 000 m~ forWing tanks. This would limit the extent of pollution in the event of damage ton particular tank..
Other proposals following the 1973 Marine Pollution. Convention which arenow in force includc:
(1) For new crude carriers over ::!OOOO deatlwooight tonnes, segregated banasttanks (SBT}, crude ui] washing (COW) and an iller! gas system (JCS;' wi])be required.
(2) For -existing crude c:Jrrier~ O\'cr 40000 deadweigllt lonnes, CBT, SBT01 cow will be required.
(3-) For existing .:rude carriers over 70000 deadw-eight ttlnnes, lCS will bemandatory,
(4) For products carriers over :20000 deadweight tonnes, IGS will berequired.
(5} For products carriers over 30000 deadweight tOl1Oes. SBT will herequired
Crude oil waJ:hillg
With this system, cargo lanks are equipped with fixed washing machines throughwhkh crudc oil (cargo) is pumped, Thc uil spray impinges all the lankextremities and frees the sludge \.vhich has separated DUt during shipment. Crudeoil washing can therefon' mean m-orc cfficient discharge of cargo, while alsobeing a useful aid to the load·un-top cleaning system.
Fire Safety in ships
I'ire [\l sea i<; an evcr-presem and much feared hazard. For pa%enger ships the·ccommendations, rules am] r~guliltiom following the 1()74 fmemanonl11 Crm'e/'enee on the SafeD-' of Life at Sea ale extcns.ive. They cover the many aspect~)f detection, restrictiOII awl extinguhhing of fires. Cargo ships, panicul.n]y ilJ,he accommodation arc as, must likewise huve arrange men t:; [0 deal with I1res,
The arrangcments fm fire protection, by virtue of det.ails oJ arrangemc-nt of:omtruction, a, detailed in the 1974 lmernar.ional Confernrce on Safety of Lifert Sea und Uoyd's Rules, <If(: applicahle tu passenger ~Jlips carrying more than\6 passengcrs ilnd eargo ships of more than 4000 tonnes gross. The followingJrincip-les are the basis of the regulations
. The use of tllcrmal and structural boundaries to divide the <;Ilip into mainvertical zones,
Organisation a.n.d Regulation. 20!
d ' tc: tiLe aCCOIUJlWlbliUflTlle-nnal clild slrlJ..:tur<l1 boul1llarics al-e usc- ,0 sep:lr~
s)~I('e~ rrom the re:;t oftbc :;hip. ,3 1\~ 11~C 01 CUl1lhustibk materials i:; to he n:strlded . I d I .., ....,,_
\ t' I Id b det'cUd contained 'I lid extlllgul~ lC w lere 10 o<.<.ur,,_4. i IlV Ire s lilU e ~ '. - d f5 Ac~ess must be pl()vided lo enable I-ile fig.hllll!\ and a pro~cl·le me~ms I)
() ~\~~l:~l;~·intlamm"bk CHg.O -VarlllH exi:;ts the pos~il1ility of ils igllition IllUst be
III inimis_cd.
Variuus definitions ilTt: gi"VCtl for the special telms used. Non-co)11husti'o]Cmatcrial m8aJlS LI material \-\ hid.l neither b urn~ nor gi'{~<;_0 E1 tJ~ tlam maol", vajJo;,,:sin a sufficient quantity trJ sdf·lgl1lte wilen heated to .1:,:>0 C III iHl approved t ..Anl-' ,,,her maleltlll is combustihle. A standard ftlc test i, "vhen sp~c:tm~n'i of t]-:e
I , t l Ikl . d' ,n docks ·He expo\.\'d in a ksl furnace 10 a particular tcmpera-reevan )I.J Ha 'v,.... ,ture lill;] cerl:Jin peril\d of r.illle_
rhc 'A' Cl.ass division'i me those dil'isiollS fOmlc-d hy bulk.heads and dc-ckswhicb comply with the following.:
1. The-v shaUne construded of steel or otller equivalent material..., Thc;" shall be suilably stiffened. . . .. .3. TileI' sh.all he cOll'itructcd to prevent the passlige of smoke aIld name for a
onc:!1(Jur standard nrc test. . .4 Th.e]' Illust be insulated such tl1at the unexposed side_wlllllOt nse Illorenl~n
139°C or any point more than 180°C above the ongm.al tcmperature ",~nhl~times as foUmvs: Class /\ -60, 60 mmutes: A-JO. ],0 mtnl.JleS, A -1), l)
minutes: A-O, 0 millute~.
The 'W Class division~ are those divisions l"ormc:d by bulkheads which are, COll~., .(od co prevent tlle r>as,ag" of fi-ame for a hall-hour st:mdard fIre test. rheysruc" ~ . I IJ90C-r
l 1 t,d ~" 'h"t tJle Ul1cxp(}~ed side win not nse Illore t Lall ., umust IC UlSU a ~u L '-' - .. , . . __ rl'.. ' ( ~")~o(~ .,I-.ov~ the original tcmper8ttlre witfUll tlmcs as [ollnw~. lISS.any pOlll " ,," v .
H--15, 15 minutes and BO, 0 mlnutf5. _ . 0The 'C' Class divisions ate made of non-<.;omh-tlstible matenals but meeL II
other rcquirements.The main veltical zones an: those section, into which Lhe hull, -\Uperst~t1et~re
and deckbOl.Jses me divided by ':'\' Class divisions, lhc mean \engt1-l of whiCh
:;llOUld not ex.c:ccd 40 m. - 1The hull, supcrstruclure, bulkheuUs. decb und deckhouscs m~st be of stee OJ
other material which has structural a.J1d firc integrity properties equlvalenl tnsted_ Pipe materials aiTe-eleli by heat must not be used for nutl~ts near thewaterline. The use of combustiole matcnals should be kepi to lHl absQlutemillimum. Pjints, varnishes, elC., with a nitIOcel1ulos.e base musi. not be used ...
The hun, superstructure and (lcckhouscs must be SU?dlVlde~ , .1I1to matnvertical fire miles of 40 m length or less_ "A' Class fire·reSlStmg dlVl~lOns are tobe u-sed from deck to deck and shell or other houndaric~. 'A' Clas~ h.ound~rybulkheads above thc hulkhead del:k should, where pDssible, be U1 hne WIthwalcrtight bulkheads below. _ _ _.
. . 'A' ('loco "'uJkhead~ must be made good Jar tne-reSlStmgAny ()pemng~ Ill, ,,-.,~ u _ . .,.._Ilumoses. Dampers must ile fitted IT! vent trunks and ducb <Ina shuuld be ope,
202 Organisation an.d Regulation
able from c-ith;or side of lh.c l:Julkhead; irHlk:u.tors should also fl{: fi',0ct n ,,''A' '-'I ~ ,,'- . U()(H, III'- ass :,ulkhc~ds must be as fire resistant .as tlie hulkhe.ad ant.! .,hol.ilJ IJ.C"
c~~able .oj heing llpcncd from <:ithcr side by one person. Fire d()or~ must 11csdl-closlng, even ill <In indiJll'd posi1ioll 01 3.5".
Ot~er bulkh('ad~ in main H'rli-cal fire lO]1t~ rnU,1 he (If 'B"Clas;; firc-retardillom<tlenal. BoundaT)' bulkheads (lnJ dcc'k.'i .'.epar'lting the JC~'l)lllmndijli()n froll~holds or cargo Sp,ICCS or m:ilo.:hinocIY 'Ilace:; must be A 611 ('I' 1-' -,, . . - , _. .' - . <iSS ue-rC,jstlTl~
?lv:slons. I)<'ck covcnng~ wlthm the aCl,;oJllmodJ.tiulj spaces should be of lI11n'.Ignitahle marc-flal.
, ,St.airw.1Y., and Uft, ~rc 10 he sled-framed ;md "",'itllin enc!osul'e, funned by,ft (lass c11Vlswm. Sdj·clo~lIlg dums witll positive means uf closure should betltted.at all OP:lllllgS, and be as effective asthe bulkhead in ",..]lk:h fitted. lor fireCO!ltammcnt. C.~ll;[I)1 slatH)I.lS, slH:h as the radio foarn. bridge, etc. must b.csurruunded by. A -class dIVI,IOns. Skylights in mJchi!J()'ty SPilCc, sholllil havemeans of cklsmg (rom outside the spa<.:e and alsu sleel Sliii·lt Iattached. - , ers permunent y
. Ventilation systems .other than carg{) and illdchincry spaces must haye t\\.'oJlldcpcnde~1t control pomt: where all machinery can he stopped ill the e\{ent (Jf afire ..Ma-elullCry ,space velllllallOll must he capable oi being stopped from ouhide~h~ ,;pac~. All IOkts and ou,!-cts lllllst be able [0 Ile dosed from oubide the~pace, I~lr Spaces 1Il thc accommodatio1l behind ceilings, Linings. etc. must behtt~d "', Jth draught stops nol morc than 14 m IIp<trt,
The .abovc arrangements ar-e made hJ ensure that in the: event of, r-boa d I' 't ill b 'il <l lre onr S lip I IN e contamc witltin the Lune in which it uccur- Ark n I 'thcn be madeif' h I f' ~, IpS CJIl, . 0 ex mgUl, t te Ire or, at ",'orst, escape. Stairways 3!ld lift trunksact as dnmneys \.l-'hlCh encDurage the fire and ',\' Cla~s bulkheads arc used he!'cto ensure that tl115 does not occur.
Orgnnisatiol1 and Regulation 203
loadcd, willi adequate stability and strcngth. A nUTr.ber of terms aud dimensionsare used in the -computation of frcrhoard.
Freehomd deck, This is the upperm{lSl continuous deck exposed to thewe-ather and thc sea v.-hich has permanent means for the watertight closure ofall exposed openings on th-e dcck and in the side shell below.
Dl'ck fine, This is a horlzonul tine 300 mIll Long and 2S mm wide which ispositioned umidship~ port and starboard, The upper edge of the line is locatedlevel with the uppn surface of the freeblJa.rd deck plating on the outcr shell.
Length. The freeboard length is the greater of the following two measurements: (I) on a W4JerliIle at 8570.- of the least muulded depth. 96% of the lengthalong the waterline; or (2) on the same W.ale-lLille, the distance from the fore sideof the stem to the axis of the rudder stock.
Breadth Measured:l\ amidships, [his is the ma:>;lrnum hreadth to the mouldedline.
IJepth moulded. This is the vertical distance between the upper edge of thekeel and the upper edgc of the freeboard deck beam measured at the ship'sside.
Displacement. TlJis lli the moulcteod displacement of the ship, elle-!udingbossingg-, measured at 85* Cfthe least muulded depth.
Block coefficient. This is determined using the values of ;lisplacement, length.breadth and a V'lhle of dr'lught which is 85% of the leust moulded depth, i.e.
The load line rules - freeboard Block coefficient, Cb =Displacement
Length X Breadth X Draught
~~~ebOJld is lbe distance ll1eaSl~I.cJ hom th~' watcrline to the upper ed'i(c of theck platll1g at lhe slde of the lr('ehouru ucck 3Ifl1dslll l" TI" I d I' I_ _ _' , ,,(la me ni e-s set
out ,lhc.req unemcllt',I(H a mtnlInUtTl frcehuard wlikh tllust be indkMed 011 t.heslup s sld.c b...., a spc:clal 10<JJ ll1le mark Tilis minimUIll freeboaru is a stalll!{)[vrequlTement U11d-er tll<': Merdl,mt Shipping (Loadli1ll') Rules of 19"'1'; TI 'I'.areh d II 19 I - - ~'- leS<'IIlC:S
, asc Oil 1e 66 nternatliJnal Loadline COllveJitiun calkd 11V [)1(0 andraulled by each of lll~ colll11ries taking part. '
A minimum fr-ecboanl is reqUired pl'incipaliv to ensur'" t""· -I" 01' "wo If· I. _ . . - . ... "Ll' ~ IIp I~ sea·r ly WIn! load-ed The mllllmum fweboard providc:s the ship ''''h '
of h' I ' h " ·d a rc:serv-euoyancy w lie enables It [0 flse as it passe~ Thrau"I, "';~"·o d " 'larel-d'- - , " .,,- E"'''''',,~oan lUsremalll
g) r:'!- on Its decks Tim rescrl-'~ hllOVanC\' al<c. implo',' th j''bT d- -, _'~V' '" evessessta Illy an In the n"entof damage will enahle- it to remain aOoat i1H!l:finitelvor at least fOl a tnne to dlee! l}le ('scupe of the: crew. ~'
The- assigning of freeboalD full(IWS a calculalion which cOllsiJers the h' ,length: breadth, depth and sheer, the density oj the Water und thc'arnollsn:Po~'waterllght superstructures and other feaLurcs of the ship Additi'l j't',oj as ' I' . ona C01l( I 10m
, signmenl Jrt .a so made relatlllg to certain openinos and fitt! a TI 'h 'assIgned b' . .- r "n"s, ie S ip IS
.- a lbS1C ffilntmum reeboard on the assumption that it' is correctly
Superstrucmre. This is a structure of adequate strength on the fteeboard deckwhich extends transversely to at least within 0.04 times the breadth from theship's ~idc The snperstrut:lure length, S, is taken as the mcan length of thatpart of Hie superstrudurc within tlte freeboard length of the ship,
Freeboard categories
In order to assign freeboards. ships are divided into Types A and B, Type A shipsare those -designed specifical1y for the carriage of liquid cargoes in bulk. Thecargo tanks have only small openings for access which arc closed by watertightcovers of adequate strength. Type B ships are al1 those wnkh are not of TypeA. The greater freeboard requiled for tbe Type B ship may be reduced in certaincircumstances. In ships whele steel hatch covers are fitted, special subdivisionarrangements exist, improved water freeing arrangements are provided and betterprotection for the crew is given, a reduced freeboard is permitted. This reductioncan re~ult in an almost equivalent value to that of a Type A ship. Whele thisvalue is almost equivalent the notation Type B·IOa is used, indicating a 100'%
204 Organlsatir>n and Regulation
reduction I~f the freeboard differencc between Type~ A and B, Tho;;: notationTYf1c B·60 is used where a 60';1c, reduction of freeboard difference is obtained.Bulk carriers particularly benellt from this reductiOll in freebOJnJ.
The freeboard is detnmined from a i.::l]cu)aliol1 wl1ere iJ rabulal freeboardfigure hased nn the ship's length and type is adjusted hy se'Vcr:al corrections.These corrcclions lire t{) .aecouIlt tor the v.aTiations between the actual ship andthe standard ship on which the tabular freeboard is based
I
""-
A Type B ship of less th:an 100 In lell~th llaving superstructures with an effe-divelength, E, of up to 35% of the freeboard length, L, may have its freeboardincreased by
(, ,)7.5 (100' r\,0.35 -"i millimetres
where E LI the effective length of the superstructure, in metres. With the SUper.strllcture length, S, known the cffective length, F, may be found from the loadline rutes.
Block coefficient co"cction
'rVhere t]l1:: actual block coefficient, C", of the ship cueeds 0.6&, the freeboard,mended by the flush deck corrcction, if relevant. is multiplied by the ratio
Cb + 0,68
136Cb is obtained as defined earlier.
Depth cOlrection
The formula for the freeboard depth, D, is given in the rules. Where D is greaterthan the freeboard len,gth, L, divided by 15. the freeboard is increased by
where R "" L{O.48 for ships less than 120 m in length, or 250 for ships greaterthan 120 m in length, If D is less than 015 no deduction is made, except wherethere is art enclosed superstIUcture extending 0,6L at midships. ntis deduction....auld be determined as for the flush deck correction.
Orgrmisatian and Regulatiol1 20S
an 85 m ship length and 1070 mm for all ship lengths greater than 122 :n0Intermediate length deductions are- obtained by interpo!allon; .wlIh eHe-etlvelengths less than 1.0f. the dedudinn is a percentage of the values glven,
Sheer con-cetion
The -differences be-tweeTl the actual sheer profile and a standard sh~er prof1Ie aredetermined. Tlle correction is Ihen the- deficie-ncy or excess mulhplled by
(075. ~L)
wht:re S is the mean length of the superstruct~rc. ,.for a defickncv of sheer, the correction IS added t{) the freeboard. ~lth an
excess, a dcdwctjo~ is permitted where the superstructure covers O.lL af~ an,d0.11. forward of midships f'm le$SeT lengths of superstructure, thc dedllctlOlllSobtained by interpolation. A maximllm deduction of 125 mlTl per 100 TIl of shiplength is permitted.
With the tabular value amended bv the cOffections, the freeboard value willbe that for the maxi-mum summer ·i1raught in sea W'..lief- This .·a/tlc may befurther amended if, for instance, the bow height is insuftlcient as defincd In therules. cargo pmts or openings are fitted in the sides below the freeboard deck orthe shipowner requests a freeboard corresponding to a draught less than themaximum permissible.
load line markings
The maximum summer draught, as determined above, is indicated by a load linemark. This consists of a ring of 300 mm outside: diameter and 25 mm wide,intersected by a noriwntat line 450 rnm long and 25 mm wide. The upper edgeof this line passes through the centre of the ring. The ring IS pos~tioned. atmidships and at a distance below the upper edge of the deck lme whichcorresp-onds to the assigned minimum summer freeboard. This value may not bekss than 50 mm,
A series -of bad lines are situated forward of the load line mark and thesedenote the minimum freeboards within certain geographical zones or in freshwateL The summer load line is level with the centre of the ring and marked S.The tropical T and winter W load lines are found by -deducting and adding,respecti'Ve1y, 1/48 of the summer moulded draught. For a shiP. of tOO ~ l:ng~
Of I.ess a Winter North Atlantic (WNA) zone load line is permttted. This lIne 1S
positioned at the winter freeboard plus 50 mm. The fresh water freeboaIds Fand IF are found by deducting from the summer Or tropical freeboard the'Value
wh-ere TPC is the toones per centimetre immersion in salt water at the summerload waterline.
Superstructure co"ecrion
For an effecti'Ve length of superstructure, F, of 1.0 times the freeboard length, L,:he freeboard may be reduced by 350 mm for :a 24 m ship length, 860 mm for
Displacement in salt water
4X TPCmillimetres
-450mrn--_
206 (Hgtmisation and Regulation
C=====~I Deck lin~
, ,,---300 mm----',,,,
,c=~
,====s~r-230 ~=11 ' T
iL
b:" ,WNA
~ 540 mmforw<lrd_,' 1-230mm..j
Figll.re 1 (), 1 Load li"e- "'Ilrkin~ (all/rm:s 25 mm /hic-kr".s~'J
Tne~e markings arc shown in Figure IO_l. In .all cases, measurements are tothe IJpper edge of tae line.
Organisation tmd Regulation 207
Superstructuore end bulkheads
Such buLkheads for Emclosed superstructures must be adequately conslructed.Any openings. must have" minimum sill height of 380 mm above the deck,
Hatchways
Portable cOJ-'ers secured by tarpaulins
Substantial coamings. of mild steel lH equivalent material must be fitted to allhatchw<lYs. Minlmum neights are 600 illm in Position 1 aml450 mm in Position2. Requirements must be met in respect of thickness of covers, strength, loadingof covers and beams, carriers or s-ocket design, cleats, battens, wedges, numberof tarpaulins and securing arnmgcmen ts.
Watertight steel corers
There are similar requirements forcoamings. but these may be reduced ill heightor dispensed with where the safety of the snip is not affected. Again requirements must be met in respect of cover strength. construction and watertightsecuring arrangements.
Machinery space openings
Conditions of assignment
Position t, E.xpose~ rreeboard, SUpers.1IUcture and raised quarter decks withinone·quarter of the ShLp s length from the forward perpelldicular.
~:;s.tion was made earlier of t ne conditions of assignment relating. to freeboard.e a~e certaln reqUIrements which must be met to ensLJrc tbe wate t-ght
of ope lungs and the ~bility of the ship to rapidly free itself of water 00 Ct' d Ok'"Refe ill b d' I S ec s.
renee w e rna e to two partIcular positions which are now defined.
Position 2, Exposed superstILIcture deckslength from the forward perpendicular.
outside one-quarter af the ship's
Machinery space openings in Posit ian 1 or 2 must be effidently framed andplated for strength. Openings are to have watertight doors with sill heights of600 mm in Position I and 380 mm in Position 2, All other openings are to haveattached steel covers which can be secured weathertight if required.
Other openings in freeboard and superstructure decks
Manholes an-d scuttles (portholes.) must have covers fitted to efficiently securethem. All doorways are to have a minimum sill height of 600 mm in Position Iand 380 mm in Position 2. All openings other than hatchways, machinery spaceopenings, manholes and seuttles, where in an exposed position, must be enclosedby a stIu.;ture of equivalellt strength and watertightness to an enclosed superstructure.
Ventilators
Structural strength and stability
Th~ ship i& required to have the necessary structural strength for the f b dassIgned. Certain criteria with regard to stability must be mot d reel·o~re. b.' '" an an me mmgxpenment :must e ca.rned out III order to ell&Ure compliance.
Coamings 011. ventilators must be 900 mm above deck in Position 1 and 760 nunin Position 2. Where exposed to severe weather or in excess of 900 mm high,ooamings are to be suitably bracketed to the surrounding structure or deck.Some m-eans of permanent closure, either attached Of close by, is required for allventilators except those of height in ex.;ess of 4.5 m in Position 1 or 2.3 m inPosition 2.
208 (}rganisation and Regulation
Ai, pipes
Cargo ports and similar opening.,
Organisation and Regulation 209
IJlber means "f access 1("luiIed itl tl,e (lOllrse ,)1' tile-iT work mllst be provi(leol1fOl till' en· ...,
SpE!c~al conditions of assignment for Tvre A ships
,Had/illlY1' caS/ilKS
Ally cargo port~ mUl! be fltled with lhJOrss!ruct~ral i:l-!ld watertight iflll:grity of the shippart 01 ItS opemng bela'>'.' the load line deLks
and tr"lInc~ ",'hid, 1\1<lil11:ain th:No door is to be fiHed With an'y
An enclosed poop. bridge or >tilTldarl1 height or J dcckhouse of eqlliv.alcnt'-lrengih \\lid "eight llt\lS\ protect t\l<: l\\';l(:n(l\Cry ~asiI\.g. An cxrro~ed casing isallo\\.,'cd withoul doors or with a dDuble-door arrangemenl. provided it is ofweathertight c-onstrllt:lion
<;cupp"rs, int"rs {lnd discharges
All di~l;harges from above or below Ill,", freebOJrd de 'k I 0 'I 'to have ff1 " I . l rum ~JiL 11\(.",-, s]lilces are
an e lelen lH!-n-return arrangemenl filled ,,-.. ,:ontrol are sp-ecificd <lccordillo to J " ,. , rraJlgclJ1enlS and theirI,aterline Manned 'I _ " tIe ~lscJlargc -r.hstanc<;; from lhe- SlllTHner IliadlCcessible' controls a~nal.: lInerl' spocc Inlets alll: olltkts ilr~ to Ila"", readily)C l-ed .uirectly overbo~[~~lve poS1tlon IllUIGlturs, Scuppers from open spaces may
lide scu (ties (porrholes)
:very side s-:uttle below lhe lreeboard uec\..: is to b~ fiiteu ·'in h-llate or -deadlight which may !'le securelv closed and Illa ..... \ a, mgeo,c-over-.;:uttles 111.1\.· be fitted bolow 2 5".', Ill'" , b de wille-rtlght. !\'() sIde
J '-. /G I 1e S up s readth -00 'he greHter, above the load waterline or -~ min. whlchever is
;reel'lg ports
Vhe~e bulwarks on any exposed decks form wells h- ,fficlCnt means for Iapidly freeing the decks ofwat l ey m.llsl.be prmHled With01 the determination of the freeing , I _ er, SpeClal formulae are gh'ens height and the sheer of the deck area In re atlOn to the l~ngth of the b-ulwark,
s close to the deCK as possible. T~~~i~~:~~~~~e-fof the Jre~Jl~-PQH should beear the lowest pOint of til" sh . 'h reemg area,s ould be IOl::ate-d
_ .... eer curve \>, ere sheer eXlsts th d klpemngs are restricted in height to "30 m,n bv b. b· I 011 e ec./h h - lars emg p .ae.ed acro h_o~ja~~~e:.s or flaps are fitted to these openings they ~hould be P::Y:l1~~d
'rOlection of the crew
11.' exposed freeb.oard and superstructure decks must have bulw k . diUS fitted at thelr perimeter with a minimum height of I ..~ s or .gu,nitted the d k d I . , m.... nere ralls are
ec an ower rad spacmg must not exceed 230 rom d th il80 mm. Eff-ective protection and safety in the form of gangway~pa~s.ag:s~n:
HlIu:l!wavs
All exposed hatchways are to h<Jve efficient I'.,'atertight covers of ~te-el orequivalent strength material
Frecin.f!, arrangements
Opcn ,ails mU~L be fitted for at least half of the exposed length or the deck. Theupper edge of the ~h-ecr strake should be kept as low as possible. Where a trunkconnects parts of the Sllperstruetur~, open rails should be fitted at the perimeterof the deck in way of the trunk.
Protectiun. oj the crew
Where separate superstructures exist they should be connected hy a raised gangway at the level of the superstructure deck. An acceptable alternative would bea passageway below deck. With a sillgle superstrut:;ture, ade4uate safearrangements should ex.ist for access to all work areas on the ship.
Tonnage
Tonnage, as disc-ussed in this section, is a measure of cubic capacity where 1 t-onrepresents 100 ft3 or 2.83 m3 • Trmnage is a measure of the ship's internalcapacity, with two values being used. The gross tonnage is the total internalcapacity of the ship and the net tonnage is the revenue-earning capacity.Tonnage values are also used t-o determine port and canal dues, safety equipmentand manning requirements and are -n statistic31 basiS for measuring the siLe of acountry's merchant fleet. All ships prior to registry must be- measured accordingto their country's tonnage regulatiorts. The differences in the various measuringsystenlS have 1ed to ships having several tonnage values and to unusual designswhich exploited aspects of tonnage measurement. The 1969 ]~10 InternationalConference on Tonnage Measurement of Siljps led to .an international review ofthe subject and a r;ystem which will ultimately be universany adopted.
boilc! space if tlH'se arc' oUlside the
Dcduaed S(){l(:(:.1
meJ~d al1d nun then b·v J<:ddctedgive lITe nd tOllJlage I:::xamples uf.,
210 Organisation il1Jd Regulation
Rffe-rence will now be made to the British liJllnage rlIeaSllremcnt SyStem andalso the 1969 (0I1ventitln mea~UreTTlent syslL:m.
British tonnage
The current regulations governing tonnage measurcmenr ,lIe the Mereh,wt~hipj1lng_ (T-oJlnae-'t') Regul.... tions 1967(1 I). 11H~ me::t,uremenl uf tonnagetalluws Irolll VarJOll.' sp<::dalist term, ~md values which will now be defined intunl.
Tonnaxc deck This is the senmd deck, except In single· LIed: ships
Tunnage kngth. An. imaginary liM i" dmwn across Ihe :l-Ilip at the stern andst-ern un the Inside of tlte hold frames iJT spJrring. The tunnage length is thedIstance between these Imes measured along the ship's centreline on the tonnagedeck.
Tonnage depth This is measured frum the upper surface ofrhe tanktop to theunderSIde of the tonnage dCl;k Ci1 the centreline. with a deduuion of one-thirdof the camber. The height of flooring, d{)uble or single, is limited
TUNnage brmdtll. The breadtJI of the sbi.p to the imide of the hold frame:> orsparring,
UnJerdeck tonllage. This is the tonnage of the space bElow the tonnage deck.It is found by dividing the tOllnage iength into a specified 'number of parIs. Ateilcn crosS-~ctiDll fmmed '0)' this diVision, the tonnage depth is similarly dividedup. The tonnage breadtlJ, at tl,esc points are then measureu. The measureddist.1nces are then put through Simps-on's rule to provide the urlJerdeck volumcwhJch is converted into a tonnage value.
":J'wss tonnage
fltis is tIle total of the underdeck tonnage and the ~onnage of the following'paces:
(I) Any tween·deck spaces hetweel\ the second anrl upper rlecks.(2) Any 'odo"" 'poe" ,bo," Ih, opp" "eck.(3) Any excess of hatchways over 0.5% of the groflS tonnage,(4) At the shipowner's option and with the- surveyor's approval. any engine
light and air s-paces- on ur above the upper deck.
[he term gross register tonn3ge (CRT) is also llsed.
Organisation and Regulation 211
f.xem/rr<'d ~pat'CS
Th~;;~ l~e spaces wlli(h Jrc n01 rne~I~\lTed f'Jr the grllSS tonllage ~·~k\llali('n
Stich wa.;~'\ Illn be- ~b"H' <>r helow 1111' t<HHH)1,C dcck <lnd itldwk
(]) \\-11edhousc. cllartr<1Ilm. l"adirTl'lll,n, <lnc! nal'ig:llion aids (UOItI.C) Spaces fined wiIh and fllr the lise of ll1a,~bil1cr~ 01 cUI1Jcm<'I~.
0) Safety equipment ill1d hilrtl'l) Sp.K<::;,
(4) 51abilit} Lmks and Jllilchinery,(5) (;alky ami ha!-;e 1')' SP;KI:~.
(6) Skylights. dDmes and trunks,(7) Washing and s:mitary accmllllwuatiull furllliflg par! III tile dl:l-\ J«<1Ill
trllJdJtiol1
The [{)flnage lJf th~sc ,pa~es must fil~t hefrom the g:ross tOllnage lJr" tht: sll ip tndeducted spilces arc'
(1) \faster's a-ecomffiodation.(2) (reR,' accommodatioll and an ~llowal).:e for pW\'ision s!ore~,
(3) Chain locke-r, steering gear 'pal,;e. anc1H)1 ge,lI and cap<;t:J1l spaL'e(4) Space -COr safet)· equipmell1 and batteries helo\\' the Lipper \~eck,
(S) Workshops and stOTerooms for rLlnlplTl~n. r!t:;:tricians, carpenter. andboat-swain
(6) Donkey engille "tid c1{lllke.,machinery space.
(7) Pumprooms, where these are outside tne ma.;;hinery SpJL'e(8) 'Vater haUast tanks, w~lere tbey aro{) for the ex.clu,ive carriage of wat<,r
b.a1l3st, 3 ma.\iJlturn limit of 19S" of the 2,105> tOlltuge is impos<:J.(9} Propelling power allcTIvance - this is the largest d-::dllcti{1TI and is
determined aU'0rding tu cenail) nileJi:; ,15 follows:
If the machinery space tonnage is bel\veel1 l:en and 20S. of the guJSS lonn:;g:e.the pfLlpelling power allowance tS 32S"t- of the gro,s IOlImgc If tbe IlI8chiner~
space tonnage is less than J 3'7 of 1he gms., tDnnage then the propdlillg. powerallowance is the aJl10llnt expressed as a proportion of 32'1 of the f!ro>s !unnag:cv,'here the mal'hiTlery space- tonnage- is more than 20~" of the gross tonnag,,- the~ropel1in!!.. power ,,"l1ow,,"nce is 1-':; time, Lhe machinery space tonnage. There j,
a maximum limit of 550 of the ,HDSS ((}llIlage lell t!le ;)f(1;Jdhng pcnNer
allow,lTIce If any pJrt of the light alld air space is inclu(!cd m the grms t()nlla~e
rhen it may also be included itl the machinery space 1ll11lu.ge.
Set forlilaxe
This i~ tile :amragc value obwined hy deducting fron; the glO" t\I[ll1Clgc lite totalv::tlue of the deducted spaces. The net \(11l[lage is considered to reprcserlt lh~
earning capacity of the ship. The tt:lTll net r<:gi!':tCr t011nage (~Rn is also used.
TOlllwg(' lIIarkldu'I!I<'
The- tlJTln<lge mark scheme \vas devised h) cxempl from tonnage measure-mcrltthe tween deL'k ,pace between tlle uppermost complete deck aad the second
212 Organisation and Regulation
deck. provided a special tOllnage dr"ught Illark was not submerged. The positionof this nlark on the ship's -'ide \.\ias tu ~enerally (;orrespIJnd to the draughtwhich \\-'uuld be obtained if the freehoard had been cakuLated Cor the seconddeck being Ihe freeboard deck. A special l11iUk is u~ed and is shown in Fi?:/lJ'e
fU!. The position of Ihe mark on the ship·s $ide is g,i"'en in the amcndmcnt tothe load line mles dealin[l: with the tonnage mark lchclllC.
___ 3-00 ,,,,n ___
_ n(J".,C"-
Figure) D,] 7of!{I(Jg" mark
(ailliriCS 25 mm lliitll/WSS)
When the tonnagc mark is at or above the waterline the ship i~ considered10 !l.ave a modified tonllage When the tonnage mark is below the waterline theship is cOJlSidercd to be at its full tll1l11age.
1969 Tonnage Convention
Two IDnnage values, the gross and the net, arc u~ed. The ....arious positiom andcxtcnt of l11eaSl1rem~nts of Icngth. breadth and depth ,lie defined and differslightly from the British tonnage system. Excluded spat:es. a -c-argo space andother terms are clearly defilled. The gros~ ttlIlnagc b computed frum an empirical formula, the terms uf which relale to the defilled tOlln:lge distances or La
conwln ts which are dete rmined from the form ulae given. Nel tonnage is ~imilarly
founll hy linlllhcr empiricat formula consisting of measurements and constants.The COllvention advocates the- me of thc term, 'U~S (~ross' and 'L:MS Net' asdimensionless values instead ofgro~s and net tonnages in tom. The acceptance ofthis c(Il1VentiOll will remove \he tonnage mark. scheme whidl has been thesubiect of much con tmve rsy .
ConsequenCl:s of the 1969 Convention
Gross tonnage measurements or VMS Gross are, in general, fairly close to thoseval\le~ determined f{Om c'J.trcnt Iegt.\latiom•. ShijJs with la(ge ex.empted spaceswill have somewhat Larger gross. tonnages under the new mles. Net tonnages doshow sigllificant v-ariations between the measured values for individual ships. Oreand bulk -carriers with their high density cargoes will have a reduced net tonnageunder (he new rules. Again, ships with large exempted spaces will ha ....e largernet tonnages under the new rules.
Apart from the purely quantitative aspects, the uni-....ersal adoption of !he newrules wUl provide for safer ships. This is because construdional methods andunusual design features will no longer be inOuenced hy tonnage measurement.The task of measurement will he simpler. since the necess<try information can bctaken directly from plans. Thc levies drawn from tonnagc measurement willrequire some adjustment bu.t will ultimately provide all conGemed with a clear,precise hasis for their ;;harges.
11
Corrosion and its Prevention
The prevention of corrosioll on board ship is an immense onf'{)ing processdemanding the attention and skills of t:omidcrable numbers of pcrsonnel Theship because of its size. its phy,ical CIlvironmcn! alld tile TTlalcri;!ls 1I.led in itsconstruction is subjcct. to attack from the ....ariOll'; funllS or corrosion
Corrosion
Co[ro~ion i~ the wasting of metals by chemical {If cleTtr-lJchemical reactions withtheir surroundings Erosioll is.a term often a,sodated with corrMion. and refersto the de~tru~tion of a meral by abrasion_ Emsion is therefore a mechanicalwastage pw.ccss that exposes hare metal which can tlten c'-'rrode.
Iron ana steel corrode in an attempt to regain their oxide forlll which i5 in abalanced state with the earth's atmosphere:, This oxidising, or rusting as it iscommonly termed, will take place whenever steel is expmcd to oxygen andmoi~ture, The prevention of corrosion therefore de-als with the isolation of stedfrom its environment in order to stop this oxidation taking pla.ce,
In addition, the presence of a ship almost l,;onst-antly in sca water enables anelectrochemical reaction to take place on unprotected steel surfaces. A cOlTosioncell is then si:lid to have been formed. This is often referred to as a 'galvaniccdl'. since its wnent flow is a result of a potential difference between Iwometals (not necessarily different) in a solution such JS sea water. This currentHow ,CSLlltS in metal being removed from the anode metal or positi .... e de-drude,while the cathodic metal or negati ....e electrode is protected from corrosiun. Mostcommon metals can be arranged in what is known as a gal.... anic series. accordingto their electrical potential in sea water, as shown in Tablt' 11.1.
A simple example of a corrosion cell would be a plate of copper and one ofiron placed in a sea water solution and joined by a wire. Reference to Table 11,1will show that .copper will becollle the cathode ()[ protected end JIld the steelwill become anodic and corrode. This is shown in Figure 11J The chemicalreactions taking, place and the electmIl flow occurring will result in the ar."Iodicmetal combinmg with di"wlvcd (Jx.y~en to form its o;,table oxide form (mst).
Corrosion .can also o.ccur as a result of stress, either set up in the mate-riatduring manufacture or as a result of its 'working' in the sea. The e{feds of stressand fatigue are to provide area~ where cracking may occur. but even thesesometimes minute cracks cre<ltc conditions under which gal ....anic corrosion willpro.ceed. The -combine-d action of the two has a considerable effect on thematerial.
'"
214 Corrosion and its Preven'ionCorrorion and its Prevention 215
T.ble ILl GALVANIC SERIES OF METALS AND ALLOYS IN SEA WATER
Ietuhodit or noble m('wlg(pror«Ud marerial)
Anodic (N ipob/~ m~rllJs
(<<1'7Odi"K _rerilll)
j
Pl;ltinun;'"Go~
GraphiteSilverPusive sUlinless sU'dsPusive h~h nickl'l alloysPusivl' nickdSilver soldersCopprr-nickl'1 alloysBronusGunml'lalCoppaBran (10/30)Anivl' h;,h nickel aUoysAnivl' nickdMiU scakNaval brass and brass (60/40)TinlndLad-lin SOkll'TSActivl' 51ainkss Srff!s:CaSI ironIron and 51fflAluminium alloysCadmiumAluminiumlineM:lJ:nesium alloysMagnesium
types of corrosion prevention are usually complementary to one another in thatboth are nonnally fitted on modem ships. Finally, it should be noted that aknowledge of the processes of corrosion can ensure the reduction or preventionof conosion on board ship. particularly on the internal structure, by the use ofgood design and arrangement of structural members.
Paint
Protective coatinp refer 10 the application of a suitable paint system. Paint isa mixture of \.bree ingredients - the pigment, the binding agent or vehicle andthe solvent. The pigment is responsible for the colour and covering capacity andmay also refer to certain additives, depending upon the properties required ofthe final product. The binding agent or vehicle, depending on ils proportion inthe paint. will decide the consistency and ease of application.of the paint. Thesolvent or thinner is added to make the paint flow easily.
Most paints consist of solid pigments. usually in a fmely divided form,suspended in a liquid binder or vehicle which when spread thinly over a surfacewill eventually dry out. A thin dry film is then left adhering to the surface. The'drying' process associated with ships' paints is usually the evaporation of thesolvent from the vehicle. Good ventilation is therefore essential and moisture·laden atmospheres are to be avoided during the drying process. The coatingapplied must also be thin to ensure that it dries out correctly. The appropriatesolvent is essential to ensure the correct drying time; tOO quick and blisteringcan occur, too slow and the paint may end up immc~ed before it is dry.
The common vehle es m use are.
Corrosion prevention
The prevention ~f corrosion deals in the first place with the provision of anadequate protective coating for the ship's structural steel and its continuedmain.tenance.. Se~ondly. a means of preventing electrochemical wastage isrequired. which IS known as cathodic protection. The two distinctly different
(I) Bitumen or pitch - bitumen or pitch in a white spirit solvent, or blendsof pitch with other materials.
(2) Oil based - vegetable drying oils. e.g. linseed oil. dehydrated caSlor oil.(3) Oleo-resinous - natural or artificial resins mixed into drying oils.(4) Alkyd-resin - a special type of(3).(5) Chemical resistant - chlorinated rubber. epoxide resins and coal larl
epoxide are examples.
jCurr8'l now j
All the above vehicle types are suitable for above·water use. Only types (1) and(5) and certain types of (3) are suitable for underwater use, because of theneed to resist alkaline deposits formed at the anodes of corrosion cells.
Figurt JJ.1 Corrosion ull
Anr;·folllillg painl
Fouling is the covering of a ship's underwater surface with marine organismssuch as green slime, weeds and barnacles. Fouling occu~ usually only when theship is at rest and is dependent on water temperature. salinity. the se:ason. theplace. etc.
The slower speeds of the larger tankers and bulk carriers has resulted inincreased fouling problems. since some marine organisms can survive and grow:atspeeds of 10-15 knots. The result of fouling is increased hull resistam::e andsubsequent loss of the ship's speed or increased fuel consumption.
216 Corrosion and its Prevention Corrorion rmd irs Prevention 217
()mlr:n<,,'ater areas
Prr/lilrariorr tlild prill/ing
- Top,icle,
Figure ii. 2 !'nlicipa! pl1f"Ung oreaS
s upc" 'cue' u,,'
•
Bnfll "'1'1-" ,,~:;,,:,:,,:,,~, -"':===-::':-=-;-;:l.:-::':::':=~=~~~=-~-~=~8mlOf'l pl"l.ny
Thc sUlface preparation of the steel platt' must iirst he good 111 {)flier to ensurethe- sue'eelsful operation of tile- ~rplied (laillting sy~tell1 The steel plates used inship conslfl1ctiorL Jre fint shot-blasted to relTl(fVe all traces of rusting and mIllscale which may be present. The plating is thell immediately primed with aquick-drying prefabrication primer This all takes place as part of a continuousundercover process under contJolled conditions This coating is usually adequateto pIOtect the plate- during the various fabrication rf{)ee"e~ leading to itsine-orporation into the hull of the ship. Final painting will progress with theconstruction 01 the ship.
The underwater and hoot copping pl<lting r~gion will have paint types appliedaf1cr consideration of the presence and type {ll cilthodk protection applied tothe hull and the degree' of anti-corrosive and anti-fouling paint whkh is requiled.Highl\' alkaline conditions are to be found mar the anodes of cathodicprotection sv,tems. and paing of an epoxide type ale therefore required to
resist thc:se 'chemical condLtiollS. Anti-foulirtg properties are also required forpaints used in this region to emit POiS011S tllat will kill the marine- org.anismswhich ten-d to collect on ships' hulls. While fouling ill the main increases shipresistance there are certain bacteria which reduce sulphates in sea water andrelease oxygen wllich can In.cn take part in the corrosion process. The antifouling ploperties of a paint for the underwater regions are therefore important,TIle actual choice of paint type and its particular composition is usually made bythe shipownel bearing the above factors in mind.
Modern practice makes little or no distinction between the paint used on thebottom sl1ell and that used around the boot lopping region. The boot toppingregion is. however, more likely to suffer damage due to mechanical abrasion(erosion) and the action of waves. Some suitable vehicle types of paint for thisregion would be bitumen or pitch, oleo-resinous cpoxide, coal tar/epox:id€- Tesinand chlorinated rubber. A compatible primer would be applied first, then theparticular paint type and a final coat of anti-fouling paint if it is to be used.
forms of trcatment are the underwater pl.ating and boot topping region, the topsides, the superstrue-ture and the weather deeks (Figure 11.2).
Anti-fouling paints functi{)[l hy slowly rdea~ing a poisoll into the laminar seawater layer swrrounding the ship. Ti!is S~a water soilible poison is toxic to marineolganisms which rJlllst pass thmugJ.t::'is Laminar layer in order to attach them·selves to the ship. The poi'i{)1l is released al a controlled raLe, determined by thetype of lOX in and also the lkgree ,,"Ild ratc (If solubility nfthe binder,
Two basically dilfcrcll( tyres uf anti-fouling puint curr~ntly exist - nonpo!ishillg 1111(.1 self-polislling.
Non-polishing anti-fouling may have either a solub-le or insoluble matrix, Thesoluble matrix: consists mainly of rosill (colophon)-') which IS slightly sea·watersoluble. 111e Ilio-activc marc:ri~ls (poisons) are released in sea waler together VI'iththe binder. Ihe insoluble matrix: type uses a large proportion of po1ymeril;binders which are insoluble in sea water, The biu·a(;tive materials are releasedtogether with otlier components ",.. !licl. act as leaching aids. This leaves behind areleased layer of insoluble binueJ. The release rate of 1I1e bio-active materials ineach type will decrease with time in -:;ervice of the vessclThc bio-active materialswill induJe cuprous oxide and organulin compounds.
The amount or 'loading' of these materials is vilric:d according to tile vessel'srcquiremenb. Sm<tll amounts would be us.cd [or vessels trading In cold andtemperate climates witll short Idle periods alld long sailing times. Large amountswould be used for u vessel trading wor1d·'wide in warm climates with short·tumcdium idle time and varled sailing periods. Different strengths uf binder resultill the me of one· or two-cout svstems to achieve a particular dry film thickness.The dry film thickness de-tcrmi;es the quantity of bio·active materials availahleand the system life tIm;:. Por any particular dry docking illterval a suitable life:time must be selected. Tt should be noted that the hio·actiw materials ill thesystem are consumed faster during high speed sailing.
Self-polIshing anti·fouling is designed to wear down slowly while maintaininga bio-active in((:rfaec: between the coating and the watcr One type of this paintuses a trio lily Itin copolymel hinder aJld reinforcing bio-active compounds whkhproduce a synergistic (assisting one another) dfect with trihutyltin 1IIlti-foulallts.The tributyltin copolymer produces lributyltin oxide (TBTO) in a hydratedform by hydrol)'slS (iOilic dissociation) with sea watel. The reinforcing bio-adivecompOLlI1ds are comprised of cuprous oxides and organotill coillpounds. Theyleach <IS th;: triblityltin copolymcr rdeases its tributyltill content. The copoly.mer then becomes waler soluhle and is washed off. This renews lind activatesthe n;:x t layer of tribu ty hin molecules.
The self-polishing rate is determined during paint manufacture by the natureof the copolymer binder. One manufactur-cr provides thlee self-polishing ratcswhicll, together with tW{) possible degrees or fouling protection, results in sixpossible types of coating. The fouling pJlJtectioll may be either 11 ormal or severe.The three self-polishing rates relate to low-to-rnediUlIl speed, medium-to·highspeed and vClY high speed hulls. The degree ofhull roughness acceptable il1crea~es
in the ~ame order and dry film thicknesses are 100 jJ.m, HO pm and 60 j.lll1 percoat minimum respectively, The self·polishin~ r'dte wdl incle~se with ~peed andloIverage hull roughness.
Painting the ship
The paint used must be appropriate for the degree of protection required at tlleparticular area or section of the ship. The principal areas requiring. different
218 C01TO~ion and its fuventiO/t Corroldon and its Prel'€ntion 219
Topsides and superstrnctures
T(Jpsides and superstructures are usually adequately coated with primer, anundercoat and a finish.ing paint. Paint based un alkyd resins, modified alkydresins and enamels arc used in this region_ Since appearance is of someimportance, good colour- and gloss-retaining properties O'f the paints used onthese parts i~ essential.
Two means of cathodic pmtectiun arc in general use on ships - tne sacriflda1anode type .and the impresso::d current type, The sacrifldal antJde type {)fcathodic protection uses metals such as illuminium and zinc which form theanode of a C()rros~on ceB in preference to steel (see Table 11./). As aconseq,'ence. these sacrificilll a1lodes lire gradually eaten. away and requi.rerepiacemcnt after a period of time. The impress-ed wrreIlt -system provides theelectric:>.l potential difference from the ship's power supply Hnoug.h an anode ofa 1ol'.g-life hig?ly corrosion-reSistant materi.al such as platinised titanium.
Weather dec ks
The- paint fln the weather deck area requires excepti.onally good resistance towe-ar and abrasion and Sume non-slip quality. The deck coating should also beresistant to any oils or chemica.ls carried as cargo or fuel. Initial protectivewatings topped by grit-reinforced oleo-resinous p-aints have been used successfully, as have primers and chlorina ted rubber deck paints. Certain metalli.c finaicoats have been tried With considerable success, more partiCUlarly on navalvessels. The constant abrasio!J on weather decks from traffic, cargo handling andseneral ship operation makes long-term protection by paint alone almostlmpossible. Self·sealing coatin,gs utili8ing epoxide resins have been used with>orne success- on top of epoxide resin paint for a hard-wearing deck covering_
Sa(;n"!icia[ amtde system
Sacrificillt anodes <tre, in practice. arranged as blocks and are securely bolted orwelded to tne ship's null by their steel. core 1:0 give a g.ood electTicai connedio1l.Their metal composition is aluminium or zint. usaaily in alloyed form. They aredesigned to CllSure uniform wcar~ng away and to provide a constant current tothe protected Sleel. 'The amOllllt of sacrificial anode material fitted to a ship'shull is based -on the wetted surface area of hull and a meas\lre of the hull's-elcctrk:al pot~ntial. Tile aJllflllnt of anode material should proVide a protectivecurrent of 12· 20 mAlm2
_ Modem sacrificial anodes nave a life of 3-4 yearsbefore n:quiring replacement.
Tanks[mfJrened current Sl'stem
The impressed current system consists of a SallICe of direl.:t current, anodes,apparatus for Illeasuring and controlling, tllc current afld a hi~ yuality inertprotccti,'e coating around the areas orlile hull nearesr to the anodes. Continuouscon tJol of the impressed cunel1 t reguire-ll rn r adequate prntection va ries with tbeimmersed area. the ship speed. the salinity of tne water and 1h-e c0l1di1ion uf thehull p<lintwork.. Modern equipmcllt is capable of aWlolllatic ClifTent controlunder an of these conditions, This control is usually obtailled hy the llse ofreference anodes positiuned some distance from the operating an()J~. If 100great a currcnt '.H~Je fo now it wu)d actually blister or destroy paint coatings onlhe ship's hull. Around the lIrlodes a pwtective shield of epoxy resin is applieddirectly to lhe hllli for a radius of 1 III or more, sim;c 11ighly alkabne conditi-ons
Fi;f!,llre 113 /"'wenetl run-em carlrodi<: pmu<:tioJI syflem
Be/"r"ncranocle
C"ntrn·ler
I"'",ode i\nD<1~
,Shalt qrou"dinq Refer""",3;s~m'olv onoo,
Ruooer stock~rQ.,Jnd~(1
Ballast, cargo/ballast and fresh water tanks requiTe spedal coati.ngs, dependingupon the nature of their contents. Treatments used include two coats of e-poxideresin or a three-coat phenolic resin·based paint, with care taken to enSUlecompatibility with the tank contents. Fresh water tanks can be satisfacto~ily
protected by bitumen or tar paint~. Drinking water tanks must have a non-taintcoating such as artifu:::ial bitumen to BS 3416 Type 2.
When a metal is in contact with an electrolyte, e.g. the steel of a ship's hull In
lea water, small corrosion cells may be set up due to slight "'ar~ations in theelectrical pOtential of the met.a1's surfac~. Electric currents flow between theiigh and low potential points, with the result that meta.! is corroded from thep-oint where the current leaves the metal (the anode). At the point wllere the:urrent re·enters the metal (the cathode) the metal is protected. Cathodicprotection operates by providing a reverse current flow to that of the corrosivelystem. With current then entering the metal at every point, Le. the whole metalmrface becomes a cathode, it is tnerefore .cathodically protected.
When the potential Qver the immersed hull surface is 0.SO-0 ..85 V morerlegative than .a reference silver/silver cWoride electrode in the water nearby,then the hull IS adequately protected, Current density of the order of 20-100mAim
2h usually suffident on a pamwd hull to reverse any L"orrosiO!J current
md cease further metal corrosion. Currcnt density necessarily increases for apOO~I~ painted hull and therefore cathodic protection sllOuld be regarded as anlddlhonal protection to painting and by no means a substitute.
Cathodic protection
--
//
\,
Corrosion and its Prevention 221
,
,-./
.'
n,~;"'A', ---..:. "?
~,
220 COffosion and its Prev~tion
arise near the anodes. An irnpres)e9_~1l~ren( system for a ship is shown in Figur(!11.3. Details of an anode and a reference anode together with the ~offerdam
cable arrangements are given in Figures llA md 115 A propeller shaft bondingarrangement must be fitted with impressed current systems to ensure propellerprotection (Figure 11.6).
Cathodi,· protection of tanks
The cathodic protection of ballast md cargo/ballast tanks is only ever of-..!;,hesacrificial anode type using aluminium, magnesium or zinc anodes_ The use ofaluminium and magnesium anodes is restricted by height ilInd energy limitationsto reduce the possibility of sparks from falling anodes. Magnesium andaluminium anodes are nDt permitted at all in cargD oil tanks or tanks adjacentto- cargD oil tanks. The anodes are arranged acrDSS the bottom of a tank and upthe sides, and only those immersed in water will be active in providing protectivecurrent flow. Current density in tanks v~ries from 5 mA/m2 for fully-watedsurfaces to about 100 mAim' fOl ballast-only tanks. Deckheads cannot be
~ ~-Fpo"ycoat;"~
,,,
"2,.3
"c
~, ,"cv ,. ' 0
,, c , "" ~"
,0 'ii ,0
iJ0 0
~' lAc'
l~c
'.,~
!,I,,,
I,,,,,,
,,,.,,,,,,,,,,,,,,,..
!\,,-- -+ ---,..,
Cov~r 'Ianw
<l"<lngement: (11) I1n(Jde; (b) secrirJnlh~oul:h anoue
F;IfU~" 11.4 Anode
,.,
A"()rI~
__ Ca,,:e
222 CorrosiQrl and its Prevention•
cathodically protected, since t,mks are rarely full: they are therefore givenadequate additional protectiv~ coatings of a suitable paint fm the upper 1.5 mDf the tank
Corrosion prevention by good design 12
The third method of corrosion prevention is by good design based on aknowledge of tht corrosion processes. Good design. therefore. should avoid thetrapping of corrosive agents or the setting up of corrosion cells in places wllkhcannot be reached. are pourly ventilated. ur rarely protected ur maintained.
Small pockets, crevices, etc.. where sail spray; water. etc .. can collect willresult ultimately in severe ru.sting. Since this involves an inuease in volume ofthe material it will he followed hy distortion QT frao:;ture of tne stlllctllralmembers. Scaling of slJcll -crevices by welding or concrete, or their avoidance inthe design stage. should he ensured. Dripping water as a r-c'Sult of poorly designeddischarge, {)[ scuppers should be avoided. Condemed mQisture on the undersideof encluscd ,(mctures will cause cOfIo~ioll and good design should ensureadequate ventilation ul these areas. Steel decks covered by wood will corrodeunless the steel is suitably protected and the wood is 'sealed' by a bitumencoating. All joints should be sealed by a suitabk filler and any baits through thewood should have washers under the nuts to prevent the entry of water. Paint.to be an effective protection requires an adequate thickness over the metalsUlface. The surface should be made as accessIble as possible to enable goodcoveral:1e al1d a uniform ttry paint thickness. Welding can be used to fill smallcrevices. however, any welded surface must be suitably prepared prior topainting to enS-lile protection against currosion. Smooth rounded surfaces arealways easier to paint and less liahlc to damage and subsequent corrosion.
Tile atmosphere Qf machinery spaces and boiler rOOI11S, with the presence ofheat. moisture o vibralion and fou1 air, presents ideal conditions for the corrosiveprocess to take place. Surfaces should therefore be kept water-free and.a~ cool aspossible by good drainage, insulation of steam pipes, ek" and good ventilation,Inaccessible places such as machlnery seats should 1J-e well protected by paintln,gbefore any machinery is fitted. Double-bottom tanks under boilers are some·times left empty and specially coated with heat-resistant paint. All double·botlum tanks shoul<! be re£Ularly inspected and maintained but only afteradequate ventilation ha'; been ensured. Maintenance should take tne form ofpainting with bitumastic paint mixtures or in some cases cement wash. Anydouble-bottom tanks regularly used for oil will have little or nQ need forcorrosion protection.
Two different metah in contact in tile prescm:e of an electrolyte such asrain, spray or condensatIon. can result in a corrosion cell. This can createproblc:ms in areas where light alloy members such as aluminium are in contactwith steeL as in the superstructure of passenger ships. ~Qdc:rn practice with ~uch
joints is to use insulating fenules, such as neoprcne or SQme inert filler, betweenlhe- metal surfaces_ Problems do 51j]] arise where such Joints are made by boltingor riveting, and regular maintenance and attenti.on Is required_
INhere stainless steel is used in a marine environment the passive mode shouldbe selected. since it is <llmost immune to electrochemical action.
.,
"
Surveys and Maintenance
In C0J11rnC'>J1 with all machinery a ship requires regular overhaul and maintenafL(e.The particularly severe operilting conditions for an almost all·steel stll.lcturenecessitate constant attention to the: ~teelwork. The operations of berthing,cargo loading ;.md discharge. [(lostant immersion ill sea water and the variety ofclimatic extremes encoUl1tered all take their toll on the structure and itsprotective coatings. Th.e dassifi;;ation societies have requirements forexamination or survey of the ship at set periods lhwughout its life. The natureand extent of the survey increases as the ship- be-wrnes older.
Periodical surveys
All ships must have an annual sul"\.'e'.... , which is carried out by a surveyoremployed by the dassific3Uon society. This survey should preferably take placein a dryduck but the period between in-dock surveys may be extended up to2'1% years. Slich an extension is permitted where the ship is coated with a highresistance paint and an approved automatlc impressed current cathodicprotection system is fitted Tn-water surveys are permitted f-or ships which areless than 10 years old and greater than 38 m in breadtll and have the paint and(:athodic protllctjOl1 systems already referred te.. Special surveys of a morerigorous nature are required every 4 years, Continuous surveys are permittedwhere all the various hull compllrtments are examined in rotation over a perioduf 5 years betweeo consecutive examinations.
During an ant~\.\~i~urvey the various closing appliances on all hatchw3ys andotller hull openings through which water might enter must be checked to be inan effident condition. Water·clearing arrangements, such as seu ppers and bulwarkfreeing porls. must also operate satisfactorily. Guard rails, lifelines and gangwaysare also examined.
\\!hen surveyed in drydock the hull plating is carefully examined fer anysigns of damage or corrosion. The sternframe and rudder are also examined forcracks. etc. The wear in the rudder and propeller shaft bearings is also measured.
The fire prote<:tion, derection and extinguishing arrangements for passMgerships are examined every year and for cargo ship'S every two years.
For a special survey, the requirements of the annu31 survey must be mettogether with additional examinations. A detailed examin-ation of structure byremoving covers afld linings may be made. Metal thicknesses at any areas
223
225
ROlal<nq
""""....
''''',ROlaling~~
"..224 Surveys and Maintenance
showing wast<lgc may have It) be chcdc:ed. The double-bottom and peak I:1l1ksmust be tested by fillh}g 10 the maximum service head ..... ith water. "c decks.casings and superstructures. logclher with any <lleas of discontinuity. must beexamined for cracks of'signs of failure. All escape rOliles from occupied orworking spaces must be checked, Emergency cOll1lnunio;atiOllS 10 the machineryspace and the auxiliary steering position from the bridge must also be proved.
For tankers. additional special survey requirements include the inspection ofall cargo tanks and cofferdam spaces. Cargo tank bulkheads must be tested byfilling 10 the lOp of the hatchway of all or :l!lernate 1:lflks. The greater the ageof a mlp lhe grealer will be the detail of examination and testing of sus~ctor corrosion.prone spaces.
Uqudied gas tankers have requirements for annual surveys. as mentionedearlier, and several additional items. All tanks, cofferdams. pipes, etc., must begas freed before survey. Who:re the ma.'(imum vapour pressure in the tanks is0.7 bar or less the inner tank surfaces are 10 be examined. In addition, the tanksmust be water tested by a head of 1.45 m above the top of the tank. All tanklevel devices. gas detectors. inerting arrangements. elc .. must be proved 10 beoperating satisfactorily. The special survey requirements are as previously stated.together with the examination internally and externally where possible of alllank areas. Tank mountings. supports. pipe connections and deck sealingarrangements must also be checked. Sa:mples of insulation, where filled, must beremoved and the pia ling beneath examined. Pressure-relief and \'3cuum valvesmust be proved to be efficient. Refrigeration machinery. where fined, must beexamined.
Figurr 12.1 'Scan' utldtr_/tr sun'l'y I·thir/f' (from 'I4If"Nlocking of IDTKt ships'. in In·k'D/trMDinttnDnCf! Confurnrl'. 1975. b)' D.F. JonN)
U,nll,llCal ubi.
.Jock~_
PW1O<.Jltd'.I~...,ng pl~l.
l,ght
\
35 n"n 'lOti umwa
~A"bollie W!>llly 10 1J<l0vancv tank ""'====""'''- ~
---
Hull surveys of very large crude carriers
The very size of these ships necessitales considerable planning and preparationprior 10 any sun·ey. large amounts of staging is necessary to provide access tothe structure. Good lighting. safe access and some means of t:ommunication arealso required. Surveys are often undertaken at sea. with the gas freeing of thetanks being one of the main problems. In·water surveys of the ouler hull are alsodone. Some thought at the design slage of Ihe ship should enable Ihe stern bush.pintle and rudder bush clearances to be measured in the water. Provision shouldalso exist for unshipping the propeller in the water. Anodes should. be bolted tothe shell and therefore easily replaced. Blanks for sealing off inlets should becarried by the ship. 10 enable the overhaul of shipside valves. The framemarkings should be painted on Ihe outside of the ship at the weather deck edgeto assist in identifying frames and bulkheads. An in·water survey plan shouldbe prepared by the shipbuilder. The hull plaling surface must be clean prior 10
survey. This can be achieved by the use of rotary hand·held brushes which maybe hydraulically or pneumatically powered. In·water cleaning of the hull ispossible, with divel~ using Ihese brushes or specially designed boats with longrOlaling brushes altached.
One particular system uses a 'Brush Karl'. This is a hydraulically·poweredvehicle with three brushing heads. It is driven by a diver over the surface of thehull 10 clear the pJa!ing of all forms of marine fouling. The Brush Kart is shownin Figure 12.1. The sheU plating may then be surveyed by using an underwatersurvey vehicle such as the 'Scan' unit shown in figure J2. 2. The various camera
!6 Surveys and Maintenance
lit5 enable dose scrutiny of all the areas of the shell plating by tne surveyor'semng tile monitoring units. The Scan unit is fully manoeuvI<lbL over the~lwili~. &
xamination in drydock
he drydocking of a ship pTOvides a Tare opportunity for examination of thenderwater areas of a ship. Every opportunity ;hou~d th~iefQre~ taken~ thelip's staff, the shipowner and tile classification society to examine the shiploroughly. Some -of the more important areas are now listed.
ht'll plaring
'he snell plating must be-thoroughly examined fm any corrosion of welds,amage, distortion and cracks at openings or discontinuities. Any hull attachlents such as lugs, bllge keels, etc., must be checked for corrosion, security o-fttacllment and any damage. All openings for grids and sea boxes must also be'xamined.
"Athodic protection equipment
Sacrificial anodes should be checked for security of attaehment to the hull andthe degree of wastage that has taken pLace. WLth impressed current systems themodes and reference anodes must be checked, again for security of attachment.The inert mields and paintwork near the anodes ShOllld be examined for anyiamage or deterioration.
Rudder
The plating and vwble strUcture of the rudder should be examined for cracks:and any distortion. The dialn plugs should be removed to check fot the entry ofany water. Pintle or bearing weardown and clearances should be measured andthe security of the rudder stock coupling bolts and any pintle nuts should beensured.
Sternframe
The surface should be carefully checked for cracks, particularly in the areaswh-ere a change of section occurs or large bending moments are experienced.
Propeller
The cone should be checked for s.ecurity of attachment and also the rope guard.The blades should be examined for corrosion and cavitation damage, and any
,\
SloIn>eys andM4jnte~~ fl;;;'''.~"""T'
cracks or damage to the b1ade tips-. It is us-ual to O'xamine any tailshaft seals andalso measure the tailshaJt weardown.
Paintwork
The shell plating shOUld be examined for areas of paintwork whieh must berepaired. The whole surface of the shell will tnen be cleaned and prepared forrecoatirtg with paint. In some instances- tile hull may be cleaned down to thebare metal and completely recoated; most situations, however, will only lequirepreparation of the surface fDr reeoating.
Prepararion
Several methods are used for cleaning. the ~hip's hull prior to rt'coatin~ Some ofthe more common ones will no.. be discussed
Martual wire brushing and scraping wl.th steel scrapers usually takes place onthe wet surface as the water le..el drops in the dock. The finish is poor, theoperation slow and the effecti..eness ..aries accQrding to the ~k.m "nd effcHt ofthe operatives involved. _
power discing or wire brushi.ng uses either all electrically or. pneumatt~al1ydriven machine which is hand held. The method is slow but pr'lVIdes a re1atiVelygood finish.. .
High pressure water jelling 1; being. lncreasingly used (or hull cleamng. Waterat pressures of 150-500 b3r is directed on to the hull b'y.a tubular steel. lance.The lower pressure is sufficient to remove weed fouhng growths, while ~ehigher pressure will clean the hull down 'to the bare metal Th,e result~ from thlSmethod are excellent and very fast, although lime is lost while waiting for thehull to dry. It is, however, a skilled operation reqUiring competent tlamedpersonnel for efficient safe performance. _ '
Shot-blasting or abrasive-only cleaning utilises a Jet of abraslve at 5-7 barpressure fired from a nozzle on to the ship's hulL This .method rapidly producesa clean dry surface ready for painting. The dusty, dITty nature of the work,however, stops any other activities in the area. _
Ab-rasive and water-blasting combines in effect the foregomg two methodsand claims the advantages of each. The method is fast, dean and effect~ve, th~abrasive speeding the cleaning and the water suppressing. the dust. Wtth thiSmethod and water jetting, corrosion inhibitors are added te the water te allowtime between cleaning, drying and painting.
Painting
The successful application of paint requires the correct technique duringpainting and roii:able conditioIl-S during which the allplication. takes place_
PElinting should take place in warm dry weather but not ill dtrect sunlight.The presence of moisture in the air or on the metal surface may d~~age th~paintwork or slow down its curing process. Where poor COndttlOn~. atunavoidable, spedally formulated paints for curing under these- conditionS
228 SuTlleys and Mainterumce
should be used The- use of shelters or awning~ perhaps supplied with warm airwill greatly improve curing and adllCsinn of the paint. Any scuppel" dischargesor ovcrnows which may direct wa{er on to the surfllce to be painted should beblocked or diverted herore wurk is begun.
The principal methods of paint application are the aide-ss spray, th~ air·assisted spray, the roller and the brush. Brush <lnd roller applicaHon is employedwhere rough surfaces exist and small ofte-n inaccessible areas are to be covered.The method is slow, labour intensive and difficult with certain types of paints,Air-assi~ted spraying has been largely replaced by the aidcs5 spray technique forwhich most modern paints are formulated. Airle5s spray is the faste~t andcleanest application method. High huild materials life suitable for this method ofapplication with dry film thicknesses up to 300 pm possible in one application.
Throughout the preparation and painting of a ship the need for good, safe,suitable means of access is paramount. Freedom of movement to maintain theappropriate distances for water jetting and paint spraying, for example, isessential. hee·standing scaffolding is used to some extent and also hydraulicallyoperated mobile platforms.
A final mention on the subject of safety is required. Paints in their various[DIms can be- poisonous, skin irritants and of a highly inflammable nature.Adequate protection and vefltilation is therefore flecessaT)'. In addition, care isrequired in the location and operation {)f equipment to avoid the possibility offires and explusions. Most manufacturers apply their own symbols to paintcontainers to indicate the various hazards, in addition to any mandatury requirements on labelling.
13
Principal Ship Dimensionsand Glossary of Terms
Principal ship dimensions•A ship is defined and described in size, shape and furm by a number of particularterms, which are listed below and some of which are shown in Figure 13,1.Forward perpendicular. An imaginary line drawn perpendicular to the waterline
at the point where the forward edge of the stem intersects the summer loadline.
After perpendicular, An imaginary line drawn perpendicular to the- waterline,either {I) where the after edge of the rudder post meets the s.ummer loadline, or (2) in cases where no rudder post is fitted, the centreline of therudder pintles is taken.
Length between perpendiculars (LBP). The distance between the forward andafter perpendiculars, measured along the summer load line.
Length overall (LOA). The distance be-tween the extreme point~ of the shipforward and aft.
Amidships. The point midway between the forward and after perpendiculars. Aspecial s.ymbol is used to represent this pointJFigure 13.1).
Extreme breadth. TIle maximum breadth over the extreme points port andstarb-oard of the ship.
Extreme draugllt. The distance from the waterline to the underside of the keel.Extreme depth. The depth of the ship from the upper deck to the underside
of the keel.
Moulded dimensions are measured to the inside edges of the plating, i.e. they arethe frame dimensions.Base line. A hori7.0otalline drawn along the top edge of tne keel from midship&.Moulded breadth. The greatest breadth of the ship, measured to the inside edges
of the shell plating.Moulded draught. The distance from the &ummer load line to the base line,
measured at the rnid~hip sectiOll.Moulded depth. The depth of the ship from the upper deck to the base line,
measured at the midship section.Half-breadth. At any particular section half-breadth distances may be given sinoe
a ship is"'symmetricalabout the longitudinal centreline.
Principal Ship DirnemiOJIS arid Glos:sary 7'enns 231Freeboard. The vertical distance from tlte summer load waterline t-o the top f
the freeboard deck plating, measUIed at the ship's side amidships. The upp:'.mas!: complete de4. exposed to the weather and the sea is normally thefreeboard deck, The freeboard deck must have pennanent means of dosl.lre ofall openings in it and below it.
Sheer. The curvature of the deck in a longitudinal direction. It i~ measuredbetween the deck height at midships and the particular point on the deck.
Camber. The curvature of the deck in a transverse direction. Camber is measuredb.-tween the deck height at the anlre and the deck height al the side,
Rise of 11001. The height of the bottom shell plating above the base line. Riseof floor is measured at the moulded beam line"
Bilge radius. The radius of the plating. jOining tne side shell to the bottom shell .It is measured at midships.
Plat ot keel. The WIdth of the horizontal portion of the bottom shell, measuredtransversely.
Tumblehome. An inward curvature of the: midship side shell in the region of theupper deck .
Flare. An outward curvature of the side shell at the forward end above thewaterline.
Rake. A line inclined from the "Vertical or horizontal.Parallel middle body. The sfl!p's length for which the midship section is constant
in area and shape.Entrance. The imntersed body of the ship forward of the parallel middle body.Run. The immersed body of the ship aft of the paralLel middle body.Displa~ement. The weight of the ship alld its contents, measured in tonnes. The
value w.iJI vary accordin,g to the ship's draUght.Ughtweight. The weight of the ship, in tonnes, complete and ready fOJ sea but
withoul crew, passengers, SIDres, fuel OJ cargo Dn bDard.Deadweight. The difference between the displacement and the lightweight at
any given draUght, again meaSured in tonnes. Deadweight is the weight ofcargo, fuel, stores, etc., that a ship can carry.
Tonnage. A measure of the internal capacity of a ship where 100 ftJ or 2.8:3 m3
represents I ton. Two values are currently in use - the gross tonnage and thenet tonnage. ~
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Glossary of terms
Aft. In the direction of, at, OJ near the stern.Aft peak. A watertight compartment between the aftermost watertight bulkhead
and Ine stern.Athwartship. ]n a direction across. the ship, at right·ang.les to the f-ore and aft
centreline.Ballast. A weight of Liquid positioned in a ship- to change the trim, increase the
draught or improve the seaworthinesS-.Bilge. RoundeC: region between the side and shell plating; (he space where watCJ
wllects after draining down [rom cargo holds, et-::.Bitter end. The enu of the anchor cable which is secured in the chain locker by
the dench pin.
232 Prlndpll1 Ship Dimensions and GloUQ1')' Temu
Bollard. A pair of short metal columns on a rigid baseplate which are used tosecure the mooring ropes or wires.
Bow. The forward end of a ship.Bracket. A plate which is used to rigidly connect a number of structural parts: it
is often triangular in shape.Break. The paint at which a side shell plating section drops to the deck below,
such as the poop or forecastle.Bulkhead, aft peak. The first major transverse watertight bulkhead forward of
the sternframe.Bulkhead, collision or forepeak. The foremost major watertight bulkhead.Cofferdam. A void or empty space between two bulkheads or floors which
prevents leakige from one to the other.Cowl. The shaped top of a natural ventilation trunk which may be rotated to
draw air into or out of the ventilated space.IJreep tanks. Tanks which extend from the shell or double bottom up to or
beyond the lowest deck. They are usually arranged for the carriage of fuel oilor water ballast but may be filled with hatches and used for cargo.
DeviJ's claw. A stretching screw with two heavy hooks or claws. It is used tosecure the anchor in the hav.rse pipe.
Dog. A small metal fastener or clip used to secure doors. hatch covers. etc.Erection. The positioning and temporary fastening together of units or
fabricated paru of a ship prior to welding.Fabrication. The various processes which lead to the manufacture of structural
paru for a ship.Fair. To smoothly align lhe adjoining parts of a ship's struclUre or its design
lines.F.airlead. An item of mooring equipment used to maintain or change the
direction of a rope or wire in order to provide a straight lead to a winchdrum.
Flange. The portion of a plate or bracket bent at right-angles to the remainder:to bend over at right angles.
Flat. A minor section of internal deck often without sheer or camber. alsoknown as a platform.
Forepeak. A watertight compartment between the foremost watertight bulkheadand the stem.
Forward. In the direction of. at, or near the stem.Frame. A transverse structural member which acts as a stiffener to the shell and
bottom plating.Gasket. A joint. usually of flexible material. which is positioned between metal
surfaces to prevent leakage.Gooseneck. A fitting on the end of a boom or derrick which connects it to the
mast or post and permits a swivel motion.Grommet. A ring of soft material positioned beneath a nut or bollhead
to prOVide a watertight join!.Gudgeon. A solid lug on the sternframe or rudder which is drilled to take the
pintle.Gusset plate. A bracket plate usually positioned in a horizontal or almost
horizontal plane.Holds. The lowest cargo stowage compartments in a ship.Inboard. In a direction towards the centreline of the ship.
IJbrIensJons and GloUQ1')' o{l'erms ljj
Intercostal ,ts. non<ontinuolls.Offsets. n;",COtllPoSCd of separa~e,p2forfl1 ' .au b cO-Qrdinates ~a shiP s centreline of the ship.
t oard In d' f lllthe .Pantin . .a treclion aw y rO faship'S platlllg. .Pi II g. The In and out movement 0 pes of rudder swmg.p n e. The hinge pin on which cert2in tfacing forward.Son. The [eft·hand side ura ship ....he~. place of a mast to support derricks.Samso~ POSt. A rigid vertical post use I~ural items ofa ship. e.g. frames. girJers.
cantllngs. The dimensions of the strucpi "
Seu Jtlng. ell.'. water. rain water Of condensation.Se Ppcrs. Deck drains to remove se~tem of machinery or c:qUlpmeni.
at. The structUTa! support for an.1 ship which has adequate strength. free·Sea\\,onhy. A term used to descnbe a and deliver its cargo in good condition.
board and stability in order. to ca~h projectS oUlboard from the ship andSpectacle frame. A large casllng W shaft in a twin sclew ship. The caSlin~ is
supports the end of the propeUer
plated into the surrounding sheD.. h facing forward.Starboard Th "gh -h d 'deofash1pw en. en t an 51 the head of a mast. sampson post orStays. Wires or ropes from the deck to
b 'd t r prevent movement.S
__~m to proVi ~ supJK>.rd 0 ._, which replaces tWO narrow plates in adjal;enttlCiUer strake. A sll1g1e WI e p.. e
strakes. -Stem. The after end of a ship. . 'rr I"Stiffener. A nat bar. section or built-up section used to Sll en p aung.Tarpaulin. A tough waterproof canvas-type cloth cover used to cover non-
watertight hatch covers.TiUer. A casting or forging which is keyed to the rudder stock :lOd used to tum
the rudder. . . r b d 10T " " A " .......d to raise lower or fIX the posttlon 0 a oom anoppmg Wlte. Wlt...-. ,
support it. . r h h" "Transverse. A direction at right-angles to the centrehne 0 t e s Ip or an Item
of structure in lhis position.Tripping bracket. A nat bar or plate fitted to a deck girder, stiffener, beam. etc.,
to reinforce the free edge. . rTrunk. A passage extending through one or more decks to proVlde access 0
ventilation to a space. . .Tunnel. A watertight access passage surrounding ~~e propeller shaf~ w~lch IS
filled on a ship where the machinery space is pOSItioned towards midships.Tween decks. The upper cargo stowage compartments or the space between any
twO adjacent decks. .Uptake. A metal casing or large bore piping which carnes eud1aust gases up
through the funnel to the atmosphere. . ' .Web frame. A deep-section built·up frame which proVldes additional strength to
the structure.WeU. A space into which bilge water drains.. . . .Winch. A machine which utiUses the wmdmg or u~wmdmg of rope or
wire around a barrel for various cargo and mooring duties.Windlass. A machine used for hoisting and lowering the anchor.
232 PrinctpaJ Ship Dimen.dolU and Glossary Terms
Bollard. A pair of short melal columns on a rigid baseplate which are used tosecure the mooring ropes or wires.
Bow. The forward end of a ship.Bracket. A plate which is used 10 rigidly connect a number of struClural parts; it
is orten triangular in shape.Break. The point at which a side shell plating section drops 10 Ihe deck below,
such as the poop or forecastle.Bulkhead, aft peak. The first major transverse watertighl bulkhead forward of
the stemfnme.Bulkhead, collision or forepeak. The foremost major watertight bulkhead.Cofferdam. A void or empty space between two bulkheads or floors which
prevents leakage from one to the other.Cowl. The shaped top of a natural ventilation trunk which may be rotated to
draw air into or out of the ventilated·spacc.Deep tanks. Tanks which extend from the shell or double bottom up to or
beyond the lowest deck. They are usually arranged for the carriage of fuel oilor water ballast but may be fitted with hatches and used for cargo.
Devil's claw. A stretching screw with IWO heavy hooks or claws. It is used tosecure the anchor in the hawse pipe.
Dog. A small metal fastener or clip used to secure doors, hatch covers, etc.Erection. The positioning and temporary fastening together of units or
fabricated parts of a ship prior to welding.Fabrication. The various processes which lead to the manufacture of structural
parts for a ship.Fair. To smoothly align the adjoining parts of a ship's structure or its design
lines.F.air~d. An item of mooring equipment used to maintain or change the
direction of a rope or wire in order to provide a straight lead to a winchdrum.
Flange. The portion of a plate or bracket bent at right-angles to the remainder:to bend over at right angles.
flat. A minor section of inlernal deck often without sheer or camber. alsoknown as a platform.
Forepeak. A watertight compartment between the foremost watertight bulkheadand the stem.
Forward. In the direction of. at, or near the stem.Frame. A transverse structural member which acts as a stiffener to the shell and
bottom plating.Gasket. A joint. usually of flexible material. which is positioned between metal
surfaces to prevent leakage.Gooseneck. A fitting on the end of a boom or derrick which connects it to the
mast or post and permits a swivel motion.Grommet. A ring of soft material positioned beneath a nut or bolthead
to provide a watertight joint.Gud~n. A solid lug on the stemframe or rudder which is drilled to take the
pintle.Gusset plate. A bracket plate usually positioned in a horizontal or almost
horizontal plane.Holds. The lowest cargo stowage compartments in a ship.Inboard. In a direction towards the centreline of the ship.
Principal Ship Dimensions and Glossary a/Terms 233
Intercostal. Composed ofseparale parts. non<ontinuous.Offsets. The co-ordinales of a ship's form.Outboard. In;j direclion 3\9.;))' from the centreline of the ship.Panting. The in and OUI movement of a ship's plating.Pinde. The hinge pin on which certain types of rudder swing.Port. The left·hmd side of a ship when facing forward.Samson post. A rigid vertical post used in place of a mast to support derricks.Scantlings. The dimensions of the struclural items of a ship. e.g. frames. girJers.
plating. elc.Scuppers. Deck drains to remO\'e sea .....aler. rain waler or condensation.Seat. The structural support for an ilem of machinery or eqUlpmenl.Seaworthy. A lerm used to describe a ship which has adequate strength. free·
board and stabililY in order to carry and deliver its cargo in good condition.Spectacle frame. A large casting which projects outboard from the ship and
supports the end of the propeller shaft in a twin screw ship. The casting isplated into the surrounding shell.
Starboard. The right.hand side ofa ship when facing forward.Slays. Wires or ropes from the deck 10 the head of a mast. sampson post or
boom to provide support or prevent movement.Sfealer slrake. A single wide ilate which replaces two narrow plates in adjal;ent
strakcs.Stem. The after end of a ship.Stiffener. A flat bar. section or built·up section used to stiffen plating.Tarpaulin. A tough waterproof canvas·type cloth cover used to cover non·
watertight hatch covers.TaBer. A casting or forging which is keyed to the rudder stock 3nd used to tum
the rudder.Topping wire. A wire used to raise, lower or ftx the position of a boom and to
support it.Transverse. A direction at right·angles to the centreline of the ship or an item
of structure in this position.Trippinl bracket. A flat bar or plate fitted to a deck girder, stiffener, beam, etc ..
to reinforce the free edge.Trunk. A passage extending through one or more decks to provide aCcess or
ventilation to a space.Tunnel. A watertight access passage surrounding the propeller shaft which is
fitted on a ship where the machinery space is positioned towards midships.Twoe:en decks. The upper cargo stowage compartments or the space between any
two adjacent decks.Uptake:. A metal casing or large bore piping which carries e\haust gases up
through the funnel to the atmosphere.Web frame. A deep-section built·up frame which provides additional strength to
the structure.WeD. A Space into which bilge water drains.Winch, A machine which utilises the winding or unwinding of rope or
wire around a barrel for various cargo and mooring duties.WmdJass. A machine used for hoisting and lowering the anchor.
Index•
A-brackets. 104, IDS'A' class bulkhcids, 201. 202Accommodation. 120, 121Aft peak bulkhead, 87. 232Afl end construction, 101-116Au pipe. 76.194, 208Aluminium,
alloys, 27, 28rMU, 27, 28seedORS, 28
Aluminium/steel conn«tions. 28. 222Anchon and ables, 96-99Anodes, 219-221ArC wdding, 53-60Assembly, 39, 40
'S' tins divisions., 201. 202Ballast, 231
Pipinllsystcm, 148, 149tanks,148, ISS
"'m.eant, 102, 103dedi:. 82-83half, 83
Beam kn«. 18,79Ikndin&.
eqWltion, 17mommt, 14-16
Bil&c, 231kC'tI.80mud OOlt,I47piping system, 146-148strum box, 147
Biner end, 231Block coefftcient, 203BoU-ofT, 178Bollard, 137, 138.232Bottom ruuetufll. 73
in Iankers,167Bo...... 232
bulbous,9Sstopper. 97,98thrust unit, 100, 101
Bridge SlfUcture. 117Bulk carrier, 7-I 0, 180-184BulkhC3d. 85, 87-90
',4,' cla5s. 201, 202collision, 89, 232conup.ted. 89-90, 126. 130, 170. 171fonpak. 89, 232IongitvdirW, 170non'W:llertight,9Ooiltlahl, 85, 87.89. 1]0, J 70lesting.90Ir.insvcrse,171wash, 93-95, 130, 171waterti.!hl,87-89
Bulwarks, 128, 129. 173, 209Butts, 77
Cabin, 124Cable clench assembly, 99, 100Cable Slopper, 97,98Cargo pumping system, 153-155, 180Cathodic protection, 218-222. 226
Impressed curren I. 219, 220, 223of tanks, 220sacrincial anode, 219
cavitation, 108Chain locker. 97, 99CbssiflClltion societies, 197-199
hull malerial teslS, 23, 26....dd tests, 68
Oench pin, 99,100Coamings, 85. 86 ....CotTerdam, 165, 173, 180, 232Container ship, 10, 11Corrosion, 213
cell, 213, 214, 222pnvcntion, 214, 222
C,anes,dec::k, 144, 145shipyard,49-50
Crude oil washing (COW), 200Cruiser slem, 102, 103Cutting prOCC$$eS, 68-71
235
236 IndexCUlling processes (rollt.)
ps.68-69pluma arc. 70
Dead....cipll. 7.10.231Deck CDnt'. 144. 14S
platform. 145.141DeckhouSt'. 116. 117[kelts.81-85
b<'ams.82prdcQ.83platin,.82stiffening. 82
Derrick rip. 141_144heavy lift. 143. 144s.....in~n~. 142union purchase. 141. 142yo-yo. 142. 143
Devil's cia ...... 232Discontinuities, 20.85.117Displacement. 4. 7. 231Distonion.
correction. 65-61pn:..cnlion, 63-65
Doc:kin5bDckel,161,168.110Doc:kin& p1u!- 16~.119.232
000••W3ten~hl. 157,160. 161wealhcnight.117.119
Double bollom.longitudinally fr.lmcd, 15machincry spacc. 75-76tanks. 76uansvcrsdy frdmcd. 75
Drain hat. 73. 74Dra..... in)!. office. 32Duct keel, 73
Edge prepar.ltion, 44--46. 60. 63Ek<:trodcs.54-56Enpneo:asin;..I25-127ErCl;tion. 39. 5 I. 232Erosion. 213Eumin;Uion in dry dock. 226-228
Fairin~. 32. 34. 36. 232Fairlead. 137-139.232
multi~n~. 137. 138panama. 137-139pedestal. 137, 138roller. 137-139
Fire main. 148. ISOFire safety in ships. 200-202Flame pl;aner. 44, 45Flal marltin. 73, 74!'Iat pbte keel. 72Floor.
bnoekel.13_15
Floor (oorr/.)lo .....er hopper tank. 172solid. 73-75"'atertil:ht, 73-75
Flux. 54Fore end construetion. 92-95I'orec;mle. 117. 118Fname.232
anI. 102. 103$pt'Ctaek. 104.105.233..-eb. 80. 171. 232
I'r.lmc bender. 49FraminJ,78-80
at t:nds (oill;mkers). 171combined. 79.80, 167.168.180lonl;itudinal. 79. 80,166,167.183transverse. 79. 80, 166. 167. 183
Frccbollld. 202. 205. 2JIcalegorks. 203. 204condilions of assignment. 206-209corrections. 204. 205
Freeing POliS. 129.208Funnel. 125, 126
G;alvank krks. 213. 214Gap press." 7Gn ,,·e1dinl!. 51Gener31 ~o ship. 1-4Girder.
cenlle, 72. 74. 167deck,83longitudinal. 73side. 73. 74.167
Gouginj(. 70- 71Gravity welder. 54-55Gross tonnagl·. 210.21 IGudgeon. 112.232Guillotine. 49Gun .....a1e.77_78
HaJr41readth plan, 31. 33Halch.
arlO I:Ink.171,173coamin5. 85, 86rowers. 134-136minor. 136. 137opt-nings. 84. 85steel. 134-136. 207wooden. 134. 135. 207
Hawse pipe. 96-97Ho~inl:. 15. 16
Ice strenj(thening. 80-81Inelll!asplant.I74.175In~1I plate. 84. 85Insulation.
aeouuic,I57_159thermal. 155.156
1n!t:rcoJtal. 73-75. 77, 133f
Interlowernmental t.britime Consult;ativeOrganisation (IMeO). 20. 188.190-193
International t.britimc: orpri'h:ation(IMOI.197.199-202
K«I.71-73biJ&e.80.81duet. 73rht pbte, 72
Keel plate. nKorl noz.zJe. III
L:tmellar tearing. 22. 67Lines plan. 31,33Liquefied gas tanken. 1. 174, 176. 180
natural ~a5. 7. 176-178petroleum ~. 7. 178-180
Uoyd's Register of Shipping, 23. 197. 198Lo;ad lines.
markinp. 205. 206ruks.202-209
Loading.dynamic. 16local. IS. 19.83Slatie.15.17
Machinery seals. 13 I. 132Main vertical (fire) zones. 201Manhole. 113Marilin plate. 73. 74Masts.140 .Materials,
handling. 40handllns equipmcnl. 49preparation. 4 1
Meehania;1 pbner. 44--46Mooring equipment. 1]6-139Mould loft. 36
Natural pJ. 7. 174. 176Nt'$tc:d pbtes. ]5. 38NOlches.167.169Notching press. 48Numerical conuol. 36-38
OfrSt'ts. ]4. ]6. 37. 233Oilfbulkforc carrier, 180Oil lanker. 4. 5. 7.165-174.199-200Ore carrier. 7.9Ore/oil carrier. 9. 180O"y-Qcct)'kne cuning. 69O"yoQCl:t)'lenc wddinll. 52
hints. 215-218anti4ouun~. 215.216
Index 237
Paints (corll.)application. 227. 228primil'lg. 41. 217wehides.215
I';aint .....ork.cnmin;tion.221rtcoaling. 227surface prep:&r.ltion. 41. 211l:;anks. 218toPJide and superstructures. 217undel"'"'llter areas. 217..-uthcr docks. 217.218
Panclline. SO. 5 1Panting. 19.9].233
structure 10 resist. 93-95Passenger ship. 10. 12Petroleum I\lls, 7. 176Pillars. 90-92Pin ties. I 12-114. 23]Pipes.
air. 76.194. 208$Cunding. 76_77.152.153
Pitching. 13. 19Plans. 32-]4Pbte.
b<'ndin,. 38cutting. ]8.43.44eddy,lllfa,Ulion, 1I2prepal1ltion. ]8.4\roUs machine. 41. 43. 41-48S1l"3ightening.41~trinj(er. 82
Platinj(.deck. 82shell. 77
Poop S1fuctUl"C. 117. 118Pounding. 19. 77Products tanker. ISS. 165Prol11e-culling machine. 44 ,Propeller. 107-111
controllable pitch. 108-111<",amina-lion. 226, 221fi"ed, pitch. 101. 108mountinjl. 108. 109ske..... back. 108Tip Vorte:'O. Free. IIIVoilh·Sneider. III
Pumpin~and pipinJ arran~ments. 147-ISSPumproom .....nIUation.193. 194Punehinl: press. 48
Racklnjl. 18Raisl'd. quarter deck. 117Refri~crated t:cner.i1 cargo ship. 4Ring press. 47Ruddcl.III-113.226
axles. 112babnced. 103. 112tarrier. 112-1 16uamin;ation.226
2:38 Index
Rudder (conI.)pintle,,112,11]~emi-h"l:mced, 111, i 12slock 113,114trunL,102-1I14unha1a[l~ed,111-113
Sacrificial anndes, "219. noSagging, 15, 16Samson posts, 141,233Scantlinp, 73, 3D, 2:03Scri"ve board, 36Scupper" 151, 2111:1, 233
tup, 155, 1.57Sea inkt box, 132, 133Sea tube~, 132, 133Seams, 77Seats, 233S:cawo.thy,2,-233S:e~ond:lIY barrier, 178-181S.cction mndu11.1" 17Self-polislling antifouling paint, 216Shaft tunnel, 127,128Shear force, 14 16Shedder plates, 11:!3, 184Sh",er plan, 32Sheerstrake, 77Shell pbJing, 77-81Shipyard.
layout, 38-39,42wddill.g equipment. 51
~h()tblaning, 41, 227ling1e-hottom structure, 77, 169, 170Slammiuj';, 19Sounding pipes, 76-77,152,153Spectade frames. 10-4, 105.233Spurling pip~, 9'7, 99Stabilh~rs, 162-164
fin, 162, 164tank, Hi3, 164
5taHcllS,31,33~lealcI ~trake, 78, 233Steel, 20-26
casting>, 16nyugcnic, 25, 2&fini~hing tre~tm~nt, 21furgings,26l1it:her tensile, 24, 2:6producti{ln, 2: IpropertiC.l, 22:, 24shi-p-lJ.uilding.23~\aTHlald ~eoCti()m, }1
"tern, 92, 93Stern,
cruiser, 102, 103tramom, 103,104
iternframe, Hill 104examinati()'l,226
,terntube, 1G6, J07,tiffener, 75, 30, 233
Stiffening,bulld,,,ad,87de~k, I'lllocal luading:, 83
Still water bending mument (S-\\'BM), i5Strain, 29, 3()Strake, 72, 77--78, 8.2:Stress,28 30
compres,iw,28proof, 3\shea,. 28tenslk,28-
Stress-strain gr<lph, 30Stresses,
cnmpreRsive, 17dynamic, 1:8lociliscJ, Hl-W1Qrrgitudirral, 1.5-11, 165ship, 16te-n~ile, 16transverse, 17
Stringer plate, 82Stringers, 167, liDStrue-lure,
duuble bottom, 73tel re,ist pantillg, '93-95[0 re,ist pounding, 77
SuIJa,semblj',39SupcIslructures, 20, 116,171,173,203Sur~ei'S, 199, 223-226
armuai,223hull "rVlCC. 214in w-al~r, 223Wed:>l, 223, 224
Table of offset~, 36Tank top, 7(,lank lyp~s,
LNG, 176-178, 180lPG, 178-180
Tanh.s,4 7Tanh,
balla~t, 148.155(leep, 129, 130, 232doub1~-bottom, 7{,-77Clopper, 180-182segr("gatecl b:>llast (S BT), 200
Tarpaulins, 134, 135, }07, H3Tes!.
bencl,31dLlmp,31impact (Charpy), 3 \temlle,19
Te,tin!, materials, 2!lThruster. ]()O, 101
azimllth,IOldllcted jet, 10 1gill jet, 101h;'(llCJ jet, 101tunnel, 100, 10J
TilleI:. 116,117,233Tonn~g~, 2()')-211
British,210-212cOn\rcnti(ln i 969, 212decLl10gross. 210,211marL, 211, 212noel, 211
Tr<lrlROm,pust, 103~tem, ]\)3, Hl4
Transversc, 133d.:ck,81-83
Trip-ping bacht, l:l3, 233Tunnd,sh<lft,127,128Typ~s o[shi-p,,'-12
UMS grMs, 212UMS net, 212Unit, 39,41
Ventilation, 185-196,202accClmmodation, 185-, 186cargo space, 186-190cargo tanks, 194, 195corH.r\J1 [(loms, 191 193double-bMtom tanks, 194mac1lineryspaccs, 190-193,202mcchani<:a.l,
dosed, ISS, 189open, 188
[l<lluml.188non-insulated ~argo holds, 187, IS8pumproom,193,1'Hrefri.l'elitt~.(\ cargo ho1d~, 189singie du;;t, 185, Hl6
Index 239
VentiLation (c'.Jrlt.'~inglcJuct wilh reheat, 18-6, lIntwin duct, 185, 186
Venlilatm, 207hcad,195,196
Vibration pust, 1()4Vibration, ship, 10, 1lI4, 108
Water!i~ht dorm, 157, lbll_ 161Weathe;tight dorm, 117, 119'Web frame, 80, 171,232Weld,
bad, 66, 67guod.66,67t~stiflg, 68types, 60-62
Welding, 52-58"utom;lli~,55--56back-step, 64. 6:5chain, 62ele<:tric arc,S 3c1eetrocle,,54-56"lectIog;t" 5 7electrosl"g, 56-57g~s, 52in termittent, 62manual, 53n:eM inert gas (YHGj, 58 59plasma metal inert gas, 59, 60po~itions, 54practice, 62--65-,kip, tiA, 65stud, 57-58the-rmit,:59-60tungsten inert gas (TIG), 58wandering, 64, 65
Windlass, 97, 1 37, 233
•
