Chapter 2 CHOOSING THE HULL TYPEHull design terms and formulas. Semi-displacement or full-displacement hull types. Planing. Plan-ing strakes. Chine or round bilge. Power Catamarans. Displacement length ratios. Hull con-struction materials.

HULL DESIGN TERMS AND WHAT THEY MEANFor the purposes of explaining the various terms, assume that the hull includes any appendages thatmay be incorporated into the particular hull. In general terms, when one speaks of the hull, we mayalso be including the decks and superstructure. In this chapter we are concentrating on the hull only,the other areas will be covered in later chapters. Although not strictly accurate in nautical terminology,the terms stern and transom are often used to describe the aft end of the hull. Not all sterns havetransoms. Most cruising powerboats today have either a traditional transom or reverse transom stern. Onerelatively recent development is the advent of the ‘Sugar scoop’ stern which incorporates a verticaltransom within a reverse angle ending to the hull. This arrangement usually features steps for re-boarding from the water or when the boat is moored stern-to in European fashion. The reverse transomis also often fitted with boarding steps that are built into the transom itself. The above comments havebeen included as it would be easy to overlook one of the most important benefits of the reverse transom. Understanding the ‘lines’ is important and more so if you are building or buying a new boat. This setof drawings is commonly referred to as the lines plan. To fully understand the content takes consider-able experience, however there is much vital information that can be understood by all. A lines plangenerally consists of three views of the hull; body plan, profile and plan view. The hull is bisected by the stations, water lines and buttocks; see accompanying drawings. Whenstudying the lines and relating these to the hydrostatic information that normally accompanies thedrawings, you will be able to learn a considerable amount about how the boat will perform in a varietyof conditions and how it will accept various amounts of power. If you have engaged the services of anaval architect or qualified yacht designer then you should act on his advice; it would not be polite toseek advice from another designer. If you don’t trust the judgment of your chosen professional, changeto another.

LENGTHThis should be a simple indication of the size of a hull in at least one dimension, however even thissimple term can be confusing. The terms length over all, (LOA) and length over deck (LOD), areoften confused. Length overall in its true meaning is the actual length of the hull including any items

such as anchor platforms, swim platforms and thelike, that extend beyond the hull. Often the term LOAis used to express the length of the hull only; this isincorrect and our own design office has been guiltyof this mislabeling. One miss-measurement practicewe have never been guilty of is to measure the hullaround the sheerline and quote this as the ‘length’ ofthe boat. This latter measurement slight of hand wasused by some manufacturers of smaller powerboatsto increase the ‘apparent’ length of their offerings. Make sure you understand the true length of thehull; in its true expression it should read LOD orlength over deck. There is another associated term,LPD, length between perpendiculars, which is of-ten used to describe the length of the hull when boatsare ‘built to class’ such as Lloyd’s rules, the Ameri-

Extending the hull under the swim platformadds to the waterline length; will improvespeed. Do not undertake this modificationwithout your designers consent as there areother considerations such as hull trim etc.

can Bureau of Shipping or the more recently introduced European Boating Directive. This measure-ment indicated in a brochure or advertisement, is usually the same as LOD. One sure way to ascertainjust what you are getting for your money is to measure the boat yourself.

WATERLINE LENGTHThis measurement is usually expressed as LWL or DWL load or designed waterline length. Thewaterline runs from where the bow enters the water to where the stern or aft canoe body and the watermeet. The designer usually shows it from station 0 to station 10. This is the designer’s educated guessof where the waterline will come to on the hull. Many boats are advertised with a stated displacementand waterline length that may not be relevant to the actual boat cruising in trim. See Displacement.

BEAM and WATERLINE BEAMThese are BOA and WB respectively. Beam overall or beam (max) is used to express the widest part ofthe hull; usually at the sheer or deck line and near the longitudinal centre of the hull. In boats withtumblehome (that is where the widest part of the hull is below the sheer) the widest beam will be belowthe sheer or deck. WB or BW expresses the widest beam at the waterline, usually located a little aft ofthe location of the widest BOA.

DRAFTMore correctly spelt draught this measurement represents how much the hull draws, or in simplerterms the amount of hull and appendages that will be under the water / below the waterline. The draftmay vary depending of the loading of the hull; number of crew, state of the fuel and water tanks and theamount stores on board, can all affect the draft. It is very important for you to be able to quote thecorrect and accurate draft of your boat. You will need this measurement to successfully navigate yourboat through shoal waters. Marina owners and boat yards will need this figure when slipping or han-dling your boat. With certain reservations, when considering draft ‘Less is better’.

DISPLACEMENTTo those of you who have heard the joke about the three most often told lies, I add a fourth, displace-ment. The true displacement of the hull is the actual weight of the entire boat including the ballast keel,stores, water, fuel, equipment and crew. Usually the true displacement (when known) will be shown inlong tons (2240 lbs = 1 long ton) or tonnes, kilograms or even in cubic feet (35 cu ft of sea water = 1long ton). As fresh water weighs only 62.4 lbs per cu ft, your boat will draw more in fresh water. Thereason that the true displacement figure rarely appears in reviews and published information aboutmost boats is that light displacement has been held as a virtue in some quarters. I do not agree butconsider moderate displacement to be a desirable feature for a cruising powerboat. Within certainlimitations, the heavier the designed displacement, the more stores, water and fuel the boat can carrywithout adversely affecting the performance. The worst combination is an overloaded light displace-ment cruising powerboat.

CENTRE OF BUOYANCY and CENTRE OF GRAVITYUsually shown respectively as CB and CG, these terms refer to the centre of the displacement of thehull. If the hull is to float level as designed, then the CB must be directly over the centre of gravity(CG). The boat will change trim until the actual CB is over the CG. For example if you add in itemssuch as a new water tank, heavy anchor chain or davits, then you will change the centre of gravity ofthe boat and the trim will change until the CB is directly over the CG.

CENTRE OF FLOTATIONUsually expressed as CF, this is the centre of the area of the waterline. If you take a slice through thehull exactly on the waterline and then find the centre of the area of that section then that is the CF of thehull. On most hulls the location is a little aft of the CB and like the CB the CF is usually shown as a

distance aft of the bow or as a percentage of the waterline aft of station 0.

POUNDS PER INCH IMMERSION or KILOS PER CENTIMETRE IMMERSIONThese are shown respectively as PP/I or K/CM. These terms indicate the weight in either pounds orkilograms required to sink the hull evenly in the water either one inch or one centimeter. In hulls withflared sides, as the hull widens above the DWL so the number increases proportionally as the hull sinkspast its designed waterline.WETTED SURFACEShown as WS, this indicates the wetted surface area of the hull below the waterline. Some designersplace a great importance to this figure stating that the greater the surface area of hull that has to bepushed through the water the less performance can be expected from the particular hull. As there aremany other factors that contribute to the overall performance of a cruising powerboat, you should notput too much importance on this number.

PRISMATIC COEFFICIENTUsually indicated as PC or CP this is a figure that represents the underwater portion of the hull asfollows; if you take a block of wood that has the maximum length, width and depth of a the hull withthe shape of the midsection carved throughout its length and then carve the underwater shape of thehull from this block; the CP is the relationship of the volume of the finished block as opposed to theblock originally carved to the midsection shape throughout. The number represents the fullness of theends of the hull. The more you carve away the ends the smaller the PC number. PCs can range from justbelow 0.50 for a fine racing hull through to 0.70 or more for a motorboat. Tank testing has revealed that there is a matching PC for any given S/L. This means that when thehull is designed with the optimum PC to match the desired S/L then the amount of power required toreach the S/L will be reduced. The previously published table (see D. Phillips-Bart’s book NavalArchitecture of Small Craft) shown below illustrates the most desirable match between the desired S/L and the PC. The S/L ratios in excess of 2.0 enter the realm of the planing hull and when the S/L reaches 2.0 andabove then a boat is truly planing. There is some disagreement between designers and experiencedpowerboat operators just what S/L denotes a true planing hull but suffice to say that when the S/L of2.0 is reached you are bringing the forces of dynamic lift into play and this is what is needed to makea hull plane.

S/L P/C1.0 ......................................................................... 0.531.1 ......................................................................... 0.541.2 ......................................................................... 0.581.3 ......................................................................... 0.621.4 ......................................................................... 0.641.5 ......................................................................... 0.661.6 ......................................................................... 0.671.7 ......................................................................... 0.691.8 ......................................................................... 0.701.9 ......................................................................... 0.702.0 ......................................................................... 0.70

CENTRE OF LATERAL PLANE or CENTRE OF LATERAL RESISTANCEKnown as CLP or CLR these terms refer to the geometric centre of the underwater profile of the hull.If you were to attach a line to this exact point and tow the hull sideways then the hull should movethrough the water without turning one way or the other.

DISPLACEMENT LENGTH RATIOCommonly called the D/L ratio it is calculated by taking the displacement in tons and dividing by 0.01DWL cubed or Dt / (0.01 DWL) 3 or as follows: Displacement in long tons (2240 lbs =1 long ton) D/L ratio = (0.01 DWL) 3. The resulting figure can compare the fullness of hulls. Each designer has hisown pet theory as to the ideal D/L ratio for boats intended for different purposes. The ratio may varydepending on the waterline length so one has to consider this figure only in conjunction with otherfactors. When considering D/L ratios you may want to consider the following ratios:Displacement hulls generally have D/L ratios of 300 and above Semi-displacement hulls are usually inthe D/L range of 225 – 300. Planing hulls are best is the D/L ratio is between 225 and 230

SPEED LENGTH RATIOThe speed length ratio is the speed of the vessel measured in knots divided by the square root of thewaterline length in feet. This is the speed at which a wave as long the waterline will be created by yourvessel.

V knots___________________S/L = sq root (LWL)

For displacement hulls the generally accepted highest S/L is 1.34 and to drive any displacement hullbeyond this figure will require larger than desirable amounts of power and invoke many undesirablefactors such burying the stern and using unacceptable amounts of fuel. In a long range Passagemakera lower S/L is used so that the vessel will be able to operate at the most economical speeds; see chapteron Passagemakers for more detail on this subject. If you want to increase the S/L then you have toeither increase the waterline length or choose and semi-displacement or planing hull. Here is a list ofrelative speed length ratios, Full displacement hull – 0 to 1.34 … Semi-Displacement hull – 1.34 to2.5 … Planing hull – 2.5 to 3 and above. Remember that none of the above numbers represent an exactequation; there is considerable overlap between the various hull types.

HULL SPEEDThe term “Hull speed” is generally used to express the potential speed that any hull will achievewithout digging in at the stern or using an inordinate amount of fuel. This term usually enters theconversation when one is discussing a displacement hull or one that is trying to exceed the magic 1.34times the square root of waterline length.

ABOVE / BELOW WATERLINE RATIOThis is a ratio that seems to have been ignored by many designers of modern large powerboats. Whena boat is viewed in profile a percentage of the boat is above and below there waterline, the amountsexpressed in percentage represents the A/B ratio.

Area above waterline________________Area below waterline

A small A/B ratio is desirable for instance for a Passagemaker a ratio up to 2.5:1 is preferred for oceancrossings. For coastal and local cruising, a ratio up to 3.5:1 may be acceptable depending on theindividual design. You should be aware of this ratio and it is worth calculating it on any design thatinterests you. Remember the smaller the ratio the better.

RESISTANCEWhile you will be relying on your engine(s) to drive your boat in the desired direction, there are many

other related factors working against your intentions. One speed restriction is caused by wind resis-tance caused by the wind drag on areas such as hull topsides, superstructures and above deck append-ages. There are many other areas of your boat, which cause resistance including skegs and feathered orfreewheeling propellers.Now that we have a range of terms to refer to, let us consider the different types of hull that may besuitable to contain your ideal accommodation layout while providing a safe and comfortable vehicle totransport you and your family to your desired cruising locations. By this stage you should have de-cided on you’re cruising goals and have a preliminary budget so you can eliminate unsuitable hullsfrom your calculations.

HULL TYPESPowerboat hulls are divided into three main types namely, Displacement, Semi-displacement and Planinghulls. Each hull type can have many sub-types, which are closer to one or other end of the spectrum.Considering each hull configuration in detail will reveal its benefits and disadvantages, your choicewill be influenced by yourintended usage and the size of your wallet. The size of your intended power boat will also be a factor in your choice of hull type; for instance ifyou are considering a large power boat (large is a relative term) then you will be less likely to choosea full planing hull. Large fast planing hulls require large expensive engines and use huge amounts offuel so operating costs are relatively high. Below are the outlines of the qualities of the various types ofpowerboat hulls. Starting at the Displacement end of the range, these were the first to be developed and

to go back to the beginning of time; the original log canoe and eventhe ark (as far as we know) were all displacement hulls.

HEAVY DISPLACEMENTThese heavy displacement hulls include such craft as tugs and deep-sea trawlers. If you study these boats in profile you will notice thatthe stern rises above waterline. The mid-section of the hull is veryfull and deep in the water. The chine and buttock lines will revealthe full-bellied shape usually present in this type of hull. The heavydisplacement hull has to be able to carry great loads and in the caseof tugs, be able to get a great grip on the water in order to do its jobproperly. The “hull speed” of this type of vessel is generally lessthan that of other types.

MEDIUM DISPLACEMENTThese hulls include most regular workboats, general fishing boatsand the pleasure boats where speeds of 1.34 times the square root ofthe water line length (or less) are sufficient to fulfill their operatingrequirements. For instance let us consider a 40 ft / 12.19 M, LOA.

Motor cruiser with a waterline length of 36 ft / 10.97 M, the square root of the waterline is 6 somultiply this by 1.34 and you arrive at a potential speed of just over 8 knots / 14.8 kmh. This is aneconomical speed for this vessel taking into account power required and the amount of fuel used todrive the vessel at “hull speed”. Medium displacement vessels can only exceed the 1.34 rule by adding excessive amounts of power.If you already own an engine that has more horsepower than required to fall within the 1.34 calcula-tion, then consider building a longer hull or one that employs semi-displacement hull characteristics.In a medium displacement hull, the V at the transom is usually fairly flat with anything from 3 to 7degrees being the norm. Once the most economical speed is achieved, it takes a considerable amount of power to make adisplacement hull go faster. When this type of hull is over driven then the stern will drag in the water

Vessels like this RobertsTrawler 45 need heavy dis-placement hulls in order tofulfill their intended usage.

and usually create a large sternand bow wave. The boat mayreach such an extreme bow high,stern down angle, where watercould come in over the stern andswamp the vessel. Displacement hulls should notbe driven much in excess of their“hull speed”. For vessels rang-ing in size from 30 ft / 9.1 M to60 ft / 18.3 M waterline length,you should consider displace-ment hulls only if your speed re-quirement is around the 6 to 12knot mark respectively. Forhigher speeds consider semi-dis-placement or planing hulls. Oneimportant factor is that Displace-ment and Semi-displacement

hulls are generally considered better ‘Sea Boats’ and are more suitable for serious offshore cruisingthan the planing hull type. As with heavy displacement hulls, medium displacement hulls are not soaffected by weight as the semi-displacement and planing hull types.

SEMI-DISPLACEMENT or SEMI-PLANING HULLSAs the names suggest these hulls fit neatly in between the displacement and the planing hull types. Thestern of the Semi-displacement hull is lower and designed to be always below the water. The hull canbe round bilge form but is generally of the ‘Hard chine’ type. These hulls have less fullness than a fulldisplacement hull. The chine line runs aft with a small curve from where it enters the water and on backto the transom. The hull sections are moderately Veed. The semi-displacement hull will out perform the

displacement ‘Hull Speed’ rules andwill accept additional power and con-vert it to additional speed howeverthere are limits to this benefit. Gen-erally speaking for vessels with 30ft 9.1 M to 60 ft / 18.3 M waterlinelength, you should only considerSemi-displacement hulls if yourspeed requirements do not exceed 12to 18 knots. As you have seen with displace-ment hulls additional power iswasted, however with semi-displace-ment hulls often the extra power maybe utilised to advantage. If you al-ready have access to a certain size ofengine; or you already own theengine(s), then this factor may assistyou in making the decision as towhich type of hull best suits your situ-ation. As with Displacement hulls,Semi-Displacement hulls can be

This beautifully finished Trawler Yacht 43 built from a pre-cutkit in Australia is a true medium displacement vessel capableof offshore passages.

The Euro 1600 is a semi planing hull and capable of off-shore passagemaking. This boat is available as a steel kitor cutting files and is a very popular family cruising boat.

driven harder, but at the expense of greater fuel consumption and again the stern will tend to dig in athigher speeds. Existing semi-displacement hulls can be made to achieve extra speed with the samehorsepower by adding trim tabs or planing wedges at the stern. The trim tabs and the wedges will befixed after trials are completed to establish the best angle. In no case should you try to improve theperformance of your hull in this manner without the assistance of professional advice. If you are building a Semi-Displacement hull, you should try and keep the weight to reasonablelevels. The Semi-Displacement hull is a good weight carrier but it takes additional power and fuel toget the best out of an over-weight boat of this type. Finally this is the type I would personally choosewhen planning to undertake extended cruising, that is cruising that regularly involves cruising dis-tances of over 100 miles from home base.

PLANING HULLSThe planing hull is recognised by the straight run ofthe chine and buttock lines from amidships aft. Thechine and the bottom of the hull V will generally runparallel to the waterline. The V in section will gener-ally be constant from just aft of amidships to the stemThe angle between the baseline and the bottom ofthe V will be in the range of 12 to 20 degrees at thetransom. As with other types of hulls there is a greatrange of planing hull variations. Usually there is aplaning strake or flat at the chine and often severalplaning stakes on the bottom of the hull. You will often hear the terms ‘Deep V’ or ‘Moder-ate V’. These terms are meant to convey the amountof V at the transom and in addition to this they doexpress two different types of hull. A true ‘Deep V’

hull will have 20 to 24 degrees of V at the transom while a Moderate V hull is one with around 15degrees of V at the transom. The area in between 16 and 19 degrees can be described either way by theparticular designer or builder of the particular boat. Suffice to say that a hull with a V at the transom or20 degrees or over can be safely classified as a deep V and in my opinion should not be described as along distance or passagemaking cruising powerboat. When deep V hulls were introduced they were touted as the last word in planing hull design. Thesehulls do perform well at high speeds in rough water which is one reason that they are as successful asracing powerboats. Deep V planing hulls, depending on the particular design, can be driven at speedsin excess of 50 knots; however most are designed to cruise at speeds between 30 to 35 knots. Moderncomputers can accurately estimate the power requirements and speed expectations of all hull types andare especially helpful in the case deciding the power needed for individual planing hulls. Planing hulls are very popular, they make great pleasure boats if you are prepared to install sufficientpower and pay the larger fuel bills. Planing hulls do not like being operated at low speeds; theythrow a most unfriendly bow wave and they are not the best of sea boats especially in severe conditions.For local and coastal cruising it is worth noting that a planing hull may allow you to get home beforethe bad weather arrives. If your type of cruising lends itself to the advantages of a planing hull and ifthe disadvantages including high cost of operation do not bother you, then by all means consider thistype. In this situation a moderate V hull is recommended. On no account select a planing hull if youintend to operate your boat in the canal systems of USA or Europe; these hulls are not suitable if yourcruising area is restricted to low speed operations.

PLANING FLATS AND STRAKESAlmost all planing powerboat hulls are of single chine configuration and most have ‘chine flats’ or‘planing chines’ and occasionally ‘planing strakes’ that assist with getting onto, and maintaining the

The Waverunner 44 is a versatile design andcan be built in steel, fiberglass or wood ep-oxy as a semi-displacement or planing hull.This example was built in Russia by a cus-tomer who has built several of our designs.

planing attitude. It is my opinion that chine flatsare desirable on all planing craft. Intermedi-ate planing strakes may not be worthwhile onboats intended to perform at less than 30 knots.Planing chines or flats will start with a smallor no flat, at, or near the bow and the width ofthe flat will gradually increase, until it reachesits widest point somewhere just aft of amid-ships and maintains this width through to thestern. The efficiency of the ‘chine flat’ may beimproved by canting it downward by say 2 to4 degrees throughout its length.

ROUND BILGE or RADIUS CHINEHULL SHAPE

Hulls that are intended forPassagemaking are often ofthe round(ed) bilge hull form.It is possible to design a semi-displacement round bilge orround chine hull but Semi-displacement is more suitedto the chine hull configura-tion. Round bilge can be usedfor any displacement typehull especially those that areto be used for long distancevoyaging. One area we areexploring is the design ofsteel radius chine powerboathulls; our ideas are at the ad-

vanced developmental stageand I believe that this idea isworth further investigation.

TRAWLER CATS AND OTHER POWER CATAMARANSThese boats are becoming increasingly popular and come in a variety of hull configurations. It ispossible to design displacement, semi-displacement and planing hulls to be used with the catamaranconcept. Semi-displacement power catamarans offer promise as comfortable, roomy and economicalcruising powerboats. In the spirit of ‘there is no free lunch’ catamarans while offering more room andmore (faster) performance for a given length; do cost considerably more to design and are somewhatmore expensive to build.

Here we see the planing chines on twoWaverunner 44 planing hulls. The photo atleft shows a WR44 in Brazil and the lowerphoto shows a WR44 that was built in Omanas a fisheries patrol vessel.

The radius chine method will produce a beautiful rounded hulland is simple to build.

HULL CONSTRUCTION MATERIALSPlease note, my office designs boats in fiberglass, steel and aluminium; we receive the same price forplans no matter which material is to be used for building the vessel therefore I have no benefit inpromoting one material against another. My opinions will become apparent throughout this text; thesepreferences have been developed by my own personal observation as well as reports from over 30,000people who have built and operated my boats throughout the world. Here we open a large can ofworms! One book that was written a few years ago covering the subject of powerboats, wrote steel offin one paragraph. I am sure the Dutch would be interested to know just where they have gone wrongover the past 100 years. Now let us take serious look at the various materials that are available forbuilding your cruising powerboat.

FIBERGLASSIn days past one could be excused for thinking that there were as many hull types as there were boatsafloat. A visit to any marina will reveal that times have changed; the advent of series fiberglass produc-tion has produced rows of almost identical boats. Most of these boats are suitable for local and coastalcruising but very few should be considered for long distance voyaging. It

is a fact that most suc-cessful long distancecruising powerboats willnot be found at a boatshow; the most success-ful long distance cruis-ing boats are purpose de-signed and built. If you are building,having built a purposebuilt cruising powerboatthen you will be able tochoose the constructionmaterial you prefer. Ifyou are buying a produc-tion boat then thechances are that it willhave a fiberglass hulland you will live with

that choice. Often pro-moted as the wonder

Trawler Cats 35 - 40 -45 ft.Trawler Cats are becomingmore popular. The fiberglassTrawler Cat 35 is the small-est of these designs. The firstCat 35 & production moldsare being built in ThailandYou may order plans and fullsize frame patterns for theseTrawler Cats on our website www.bruceroberts.com

This fiberglass Waverunner 52 makes an ideal family cruiser. This andother versions can be seen on www.bruceroberts.com

boatbuilding material fiberglass, has its advantages and dis-advantages when used to build your cruis-ing powerboat. First let us consider the advantages of which there are many. Commercial production offiberglass boats started in the late 1950’s and after a tentative start fiberglass gradually ousted timberto become the most used material for boat construction. A well-built fiberglass hull can provide the basis for a fine cruising powerboat. In many cases ‘wellbuilt’ should read custom built. It is a fact that many boats spend much of their life securely tied to awell-protected dock and provided they can withstand the occasional coastal cruise then they are deemedto have fulfilled their role.

Unfortunately when considering a boat for serious coastal or offshore cruising one has to assume thatsooner or later the boat will have to withstand all that nature can offer. Not all ‘production’ fiberglasspowerboats can meet the criteria required to warrant the title of ‘serious cruising boat’. fiberglass hasthe potential to be formed into a hull that can withstand the type of punishment that you can expectyour boat to experience any time you venture offshore. I have cruised in many fine examples of suc-cessful fiberglass powerboats; most of these were custom and purpose built for serious cruising. If youare planning to purchase a production fiberglass boat then you may be able to have some input in thebuilding of the boat to the extent of selecting a modified laminate and additional strengthening if andwhere required. While I have designed and been involved in the building of many sandwich fiberglasshulls; my personal preference when considering fiberglass for a cruising powerboat would be for asingle skin hull. Why? Easier to repair problems if any would be more noticeable before they require any majorrepair. The sandwich material does provide excellent thermal and acoustic insulation and is ideal forcabin and superstructures. You can add suitable insulation inside a single skin hull in the areas whereit is required (usually above the waterline).One of the advantages of this material is ease of construction. Once a female mold exists it is a rela-tively straightforward matter to mold many boats from the same tooling requiring a minimum of prepa-ration between the laying up of the hulls. Good molds, with reasonable care, are capable of producing

Pacific Coast Fish-erman 40 (PCF 40)has proved to be agreat sailingtrawler. This boatcan be built in fiber-glass or from a pre-cut steel kit. One ex-ample motor-sailedfrom Australia toUK & Ireland.

hundreds of hulls and we have had production runs of up to 300 sets of hull moldings from several ofmy own designs and I am aware of much larger production runs that have been successfully made byothers. The down side of this is that original plug, mold and associated tooling costs many times theprice of one boat. The boatbuilder or manufacturer has to be very confident of selling a great numberof identical boats to amortize the costs of the tooling. Custom fiberglass boatbuilding has proven tooffer individual boats at affordable cost and over 8,000 of my own designs have been built using thesetechniques. Although more labour intensive than pulling a set of moldings from a female mold, thesemethods offer many advantages to the person who requires a well built cruising powerboat. In thisworld where almost every automobile looks the same and where almost all things in everyday life takeon a boring sameness, you may want your boat to be just that bit different and reflect not only yourcruising aspirations but your personality as well. A warning, do not be different just for the sake of being different; one day you will want to sell yourpride and joy so someone else has to like it too. Power boaters have a distinct advantage over theirsailboat counterparts when it comes to custom fiberglass boatbuilding. Most cruising powerboats fea-ture chine type hulls and it is a very simple matter to build an inexpensive one-off mold in which to layup a powerboat hull of any size. The method I refer to has been used to build fiberglass hulls from thesmallest to 150 ft / 45.72 m Mega yachts. As mentioned earlier fiberglass does have some disadvantages and these mostly show up in usedproduction powerboats that were badly built in the first place and built down to a price rather than upto a high standard. A badly built boat is a badly built boat no matter what material or whether it wascustom or series built you will need to make sure that the boat you plan to purchase is subjected to avalue and use survey. Stress cracks in fiberglass boats need to be thoroughly scrutinized as they maypoint towards more serious problems.Osmosis is one of the major potential problems to be found in used fiberglass boats. (See note at the end

of this paragraph). There are as many theories as to what causes osmosis as there are cases of thisdamaging problem but it usually comes down to poor work ethics in the manufacturing. Suffice to saythat the result is a varying number, and size, of blisters in the hull laminate, which eventually allowwater to penetrate the basic substrate and weaken the hull to varying degrees depending on how long ithas been allowed to continue. This can usually be remedied, at a cost. What about used custom fiber-glass boats? Well firstly custom boats of any type are often more carefully built than their productioncounterpart and secondly the very way in which custom fiberglass boats are built goes a long way topreventing the practices that encourage the onset of osmosis at a later stage.

The Atlantic 4050 & 55 have tobe consideredcruising boats asthey are oftenused far offshorewhen seeking thebest fishinggrounds. Alumi-num kits andalso fiberglassplans and fullsize patterns areavailable forthese designs.

Most custom fiberglass boats built in recent years have a light coating of filler covered with a layeror two of vinyl-ester resin which offers a far greater barrier to water than the gel coats used in produc-tion boats. Most custom fiberglass boats are painted with epoxy based materials. Painting a hull withthe correct marine paint when combined with other osmosis defeating practices used during the constructionstage can remove the worry of this insidious problem.ALUMINIUM / ALUMINUMNow widely accepted as a boatbuilding material, aluminium has the advantage of being about one-third the weight of steel, (this is partly offset by the fact that for boatbuilding a thicker material isnecessary). If you are considering a planing hull cruising powerboat, aluminum is easy to work andhand tools, including some woodworking ones, can be used with this material. Aluminium is ideal fordecks and superstructures where its light weight and easy forming characteristics can be used to advan-tage. In some areas of the world, aluminum has become extremely popular for building commercialcraft and fishing boats. The popularity with some commercial fishermen is due to the fact, that whenthe correct marine grades are used, the entire boat can be left unpainted. The disadvantages include greater cost and relatively greater susceptibility to corrosion. Aluminumrequires expert fabricators and experienced welders who are used to handling this material. It has lessimpact strength than other metals (on a dark and stormy night, think about those containers floatingaround in the ocean!). When and if repairs are required, then aluminum also needs welders who areused to handling the material; not a problem if you have ‘built your own’.STEELHaving owned several boats including three built from steel I have to say that when it comes to owninga cruising powerboat, steel is my favourite. As most steel boats are custom or at least semi-custombuilt I will discuss a few of the processes in the construction of a metal boat. With the advent of modernprotective coatings and proven boatbuilding practices, a steel boat can last or even outlast one built offiberglass or any other boatbuilding material. Steel is easy to protect from electrolysis and similarproblems. Another advantage of owning a steel cruising that I personally appreciate is the fact that inan electrical storm a steel boat acts as a Faraday cage and offers the ultimate protection in the event ofa lightening strike. I could go on about the advantages of steel but instead I leave further investigationto you. If you want to learn more about building, owning and maintaining a steel boat by reading mybook Metal Boats. Steel is the today’s bargain boatbuilding material. If you are building or having a boat built asopposed to buying either a new or used then, if possible, you should choose only pre-shot blasted andprimed materials. The terms sand blasting, grit blasting and shot blasting all have a similar meanings.When welding prime coated steel, you should wear a protective mask and avoid inhaling the fumesreleased as the prime coating is burnt off around the area of the weld. One of the main benefits of usingpre-shot blasted and primed materials, is that when you have completed the hull and deck you shouldnot need to shot or grit blast the interior. This part of the blasting process is the most time consumingand expensive. If you are working with raw steel, you should consider pre-shot blasting and primingyour metal before you start construction.BOATBUILDING STEEL SPECIFICATIONSMy choice for steel boatbuilding is low carbon plate. You will find there are many different grades ofsteel available, but we recommend LOW CARBON steel with a carbon content of less than 0.15percent or MILD steel that has a carbon content of between 0.15 and 0.23 percent. The highest carboncontent acceptable to most classification authorities is 0.23 percent, so it is recommended you staybelow that figure. Both low carbon and mild steel are available in various profile shapes for exampleL-angle, T-bar and flat bar as well as various size plates and offer good welding characteristics. Ascode numbers vary from country to country, you should seek advice from your steel supplier, to ensurethat you receive the correct materials as suggested above. Some builders increase the plate thicknesswithout consulting the designer. In a steel boat, this can have disastrous results. If you are unable toobtain plating as specified in your plans, always contact the designer for advice. Changing the platingthickness may require rescheduling the spacing and sizes of the framing.

COR-TEN STEELAvoid materials such as Cor-ten, high tensile steels, and other specialized products that were developedfor different uses. These steels have limited, or no boatbuilding applications. For instance, some boatdesigners have previously recommended Cor-ten, however this steel contains traces of copper andrather than inhibit corrosion, in salt water it is much more prone to electrolysis than mild steel. Cor-ten was developed for use in industrial applications such as water tanks on farm properties, and otheruses where it would receive little or no protection from the weather. Cor-ten is also more expensivethan mild steel and it works well when used for the purpose for which it was developed, but not forboatbuilding. Another disadvantage of this material is that it needs to be welded using copper cladcontinuous feed electrodes and Argon arc shielding. We do NOT recommend Cor-ten or other specialty steels for boatbuilding. Occasionally we areasked about the possibility of building a boat in stainless steel; simple answer is do not event thinkabout it! Elsewhere I will detail the uses of stainless steel but this does not include using it for hullconstruction or in other major parts of the vessel.TRADITIONAL TIMBER PLANKINGThe traditional heavily planked boats, and by heavily planked I mean a minimum of 1 1/2" / 35 mmthick planking backed up by massive frames and stringers, are usually many years old and most werebuilt as fishing workboats. The ones that survive, in good condition, are often converted to pleasureboats. Several of this type have made successful ocean crossings. Now before you get too excited aboutone of these magnificent beasts let me tell you that the upkeep and maintenance labour and costs willput a considerable strain on you resources. To sum up, these boats are worth considering if you have ayen for the ancient, have deep pockets and lots of free time in addition to the time you have allotted tocruising. Robert Beebe’s Passagemaker, although intentionally built a little lighter than the specifica-tions outlined above, does fall into the above category.LIGHT TIMBER PLANKINGThe second type of planked powerboat encompasses the more lightly planked hull, say 1in / 25 mm orless embodied by early Chris Craft, the older Grand Banks or the products of any one of hundreds ofbuilders of the 1950’s and 1960’s. These boats take an enormous amount of maintenance just to keepthem afloat and as for offshore cruising, no way. Don’t misunderstand me I love beautiful timber boatsboth old and new but they are not suitable for handling the rigors experianced in a cruising powerboat.Over the past 70 years many voyages of note have been accomplished by these boats. As we now havemore and better choices these beautiful creatures are best left to those who have the time, money andpatience to keep them as showpieces afloat and for the occasional weekend cruise.WOOD / EPOXY CONSTRUCTIONThis is the modern version of the planked boat but offers great improvement in strength and longevity.While I prefer other materials....really Bruce! I do admit that a well-built and finished wood/epoxyboat is a beautiful thing. Under the umbrella of the term wood/epoxy construction there are severalalternative methods that can be used singly or in combination with others. For instance strip plankingis often combined with diagonal or longitudinal veneers and then sheathed using a medium weightfiberglass cloth combined with epoxy resin. If woodworking is your thing and you plan to build yourown cruising powerboat then you can seriously consider a boat that was designed to be built using thewood/epoxy technique.TRAWLERS OR TRAWLER-YACHTSThe first thing we have to establish is that the hulls of most Trawler Yachts do not in any way resemblea fishing trawler as some manufacturers claim. It is possible to design a Trawler Yacht based on a truefishing boat hull and we have done this. These trawler based hulls are all of the displacement type so ifyou want a boat that performs at speeds over 8 knots / 15 kph then you should not expect your trawleryacht to have a genuine trawler hull. If you need to achieve speeds of more than 8 knots / 15 kph and you like the other features offered by

this type of cruising powerboat, then the modern Trawler Yacht is best matched with a semi-displace-ment configuration. A few manufactures have installed trawler style superstructures over planing hulls.In my opinion this is getting so far away from the concept of the trawler yacht as to border on theridiculous, as the owner may find out when it comes time to resell one of these boats. There are many fine semi-displacement Trawler Yachts available in all parts of the world and theGrand Banks series typifies some of the best features found in many of these boats. Trawler Yachts canand have been built in all boatbuilding materials. Most boats of this type on the used boat market willbe of fiberglass however there are now starting to appear a few more steel variations. If you are buyinga used boat of this or any other type, make sure you obtain a full survey before you part with yourmoney.DUTCH STYLE MOTOR CRUISERSThese boats are incredibly popular in Europe where they dominate the coastal and inland waterwaycruising scene. These steel-hulled cruisers usually feature semi-displacement hulls and can be used forcoastal, inland cruising. Subject to the sizes of the windows some of these boats can be used for seriousoffshore cruising. A few of these boats have been imported into the USA where they are popular withtheir owners. The Dutch and to a lesser extent other European manufacturer’s build three basic types of steel motorcruisers. Most popular is the aft cabin type where the aft sections of the hull are raised to form a roomypoop stern. Inside and outside steering stations provide great flexibility when operating in less reliablesummers of the northern latitudes. In the future I plan on designing one of these boats for myself andwill combine the features of the OC or aft cockpit boat with an aft cabin. This offers the benefits of thepoop stern type and offer a ‘walk out’ cockpit where one can have the saloon and cockpit on the samelevel. The other two types of Dutch style motor cruisers are known as OC and the familiar Trawler Yachtstyle. The OC stands for open cockpit; perhaps most readers would describe this type as aft cockpit. Aftcockpit powerboats are often the first choice of those moving from sail to power and as mentionedabove the advantage of walking on one level from the saloon to the aft cockpit has many practicaladvantages.OTHER TYPESOne has only to glance at any popular Powerboat magazine to see the huge variety of powerboats onoffer. Throughout the world there are many powerboats that have been developed from local workboatsand successfully redesigned as pleasure craft. Each country and area has its own favourite type as Ipersonally fondly remember the Australian ‘Morton Bay Cruiser’. This raised foredeck motor cruiserwhich usually featured small pilothouse is still popular in Southern Queensland waters. In the USAother types including express cruisers are the descendants of popular boats of another era.FISHERMEN TYPESTo me the small to medium sized pilothouse combined with generous sized cockpit typifies this type.The amount of accommodation will vary depending on the numbers that make up the permanent crew.Family fisherman definitely fit into this category. Sport fisherman! A few of these boats are used forcruising especially in some areas where the fishing grounds are a few or many miles down the coast.Some thoughtful owners will include all the family and ensure their enjoyment by combining somecruising with the offshore fishing trip.TRAILERABLE CRUISERSIf your budget does not run to a larger cruising powerboat or you prefer to keep your boat at home orperhaps gunkholing is your thing, then a trailerable cruiser may suit you fine. Many fine coastal voy-ages and trips through the inland waterways have been made in this type of powerboat. If you choosea trailerable boat that is so large that it can only be trailed with difficulty, you may end up with theworst of both worlds. There are many fine trailerable powerboats that are not cruising powerboats andas we are dealing with cruising boats I will not elaborate on these types.

This Coastworker 25/28 is trailerable; here we see a fiberglass version that was built in Thailand

Trawler Yacht 420 has awonderful history; she fea-tures a genuine workingtrawler hull which makesher an ultimate sea boat.there are over 200 examplesin service world-wide. Wehave now developed a steelkit & will also offer customfiberglass plans & patternsfor this genuine trawler.

This steel Coastworker 30 was built in the UK. This design makes a great family cruiser expeciallyif your interests include offshore fishing.