05 Naval Architectural and Maritime Basics

Learn the basics of navalarchitecture. After thismodule you understandhow to calculate thestability of a barge orvessel and how much abarge will list when youadd or shift a cargo on abarge or vessel.

Learn the basics of navalarchitecture. After thismodule you understandhow to calculate thestability of a barge orvessel and how much abarge will list when youadd or shift a cargo on abarge or vessel.

05 Naval Architectural and Maritime Basics

19 May, 2021 www.seacamel.com 1

ARCHIMEDESDOMENICO FETTI

– Engineering is Not BLACK or WHITE– The difference between stability and balance.– Unstable– Indifferent stability– Stability of Heavy Lift Ships - Introduction– Stability of (Heavy Lift) Ships – Definitions (1)– Stability of (Heavy Lift) Ships – Definitions (2)– Anatomy of a barge– Stability of Heavy Lift Ships – K, B, G and M– Why do ships stay upright?– Stability curve– Calculation of Metacenter of a ship– Moment of inertia of the water plane area and

BM.– Calculation of GM Value– Ballast water and free Surface Areas– Stability Requirements of IMO for ships– How can the Stability of a Ship be influenced?

– CoG of load when freely suspended in crane– Stability example– Advanced stability, orthogonal tipping: 1– Advanced stability, orthogonal tipping: 2– Advanced stability, orthogonal tipping: 3– Calculation GM Value and list due to ballasting.– Calculation using GM Value Cont’d– Sea fastening of Cargo on Heavy Lift Ships– Motion Analysis of vessel– “20 deg 10 Barge” DNVGL-ST-N001 Marine

operations and marine warranty.– “20 deg 10 Rule”, simple rule and in general

conservative.– Combine Motion Program with Finite Element

Analysis


Module Summary

Engineering is Not BLACK or WHITE

Stern quartering seas

We can not calculate everything.Volvo crashes about 400 cars each year.


Stability can be seen as a ball in a bowl.The bowl can have:• gentle / steep slopes• A high or a low edge


The difference between stability and balance.

Stable(Tender ship)

Very stable(Stiff ship)

1. The vectors move away from each other whenthe system is destabilized.

2. The more energy is required to destabilize thesystem, the bigger the stability is.Beam seas

Unstable

519 May, 2021 www.seacamel.com

Unstable Very unstable

The vectors move towards each other whenthe system is destabilized.

Indifferent stability is the boundarybetween stable and unstable.When vessels have an indifferentstability, it is not possible to correct thelist by ballasting.This can be a very dangerous situation ifnot understood.


Indifferent stability

Indifferent

The vectors move neither away not towards otherwhen the system is destabilized.

High and low stability


The Stability of a vessel is defined by:1. The weight distribution of the ship (which depends

on the stowage of the cargo)2.The shape of the underwater body of the ship (this is

fixed for a certain type of vessel)

A ship can have a large or small stability, this expressedin the GM Value:1.Small Stabilityè Low GM Value = Long rolling period

small acceleration/deceleration forces ⇒ comfortablefor crew and cargo (less sea fastening needed)

2.Large Stabilityè High GM Value = short rollingperiod resulting in higher acceleration/decelerationforcesè uncomfortable for crew and cargo (moresea fastening needed)

AHT shape ofvessel is fixed

SAL Vessels are fast (up to 20 knts) and shaped sharply(Offer Less Stability)

Jumbo Vessels are slower (up to 17 knts) andmore box shaped (Offer More stability)

No Stability: vessel capsizesNOTE:Stability of shipsis a veryintensive subjectand cannot becovered entirelyin the context ofthis lesson.We discuss thebasics.

Definitions (1)


Water displacement (in m3) is the volume ofthe underwater part of the vessel, incl. hull,propellor, and other protrusions

Symbol = s

Displacement (in tons) is the weight of thedisplaced water by the vessel. This is equal tothe total weight of the complete vessel (Law ofArchimedes)Symbol = ∆

Depth

Lpp = Length between Perpendiculars

LOA = Length over all

Creep lineheight

Free boardWaterline

Keel

Definitions (2)


G = Center of Gravity (Centre of Gravity of ship and cargo)B = Centre of Buoyancy (Center of Gravity of the displaced water)M = Metacenter (A virtual point around which the ship rotates)K = Keel of the shipT = Draught of the vessel (is the depth minus the freeboard)D = Depth (height of the hull measured at the side)

• G

• K

• M

• B

D T

Anatomy of a barge


Longitudinals

Longitudinal bulkhead

Transverse bulkhead

Web-frame or web

Longitudinal girder

Deck plating

Bottom plating

Side shell

Double bottom

11

G = GravityB = BuoyancyM = MetacentreK = Keel1. All the weights of the ship and cargo can be

concentrated in one point G ( This virtual point isthe overall Center of Gravity of ship and cargo). Thisis a fixed point, provided the cargo is not replaced.This point is defined by VCG, LCG and TCG (in threedirections)

2. All upward forces created by the underwater shipcan be considered acting in one point B (Centre ofBuoyancy ) The position of B is completely definedby the underwater shape of the vessel. This pointchanges, when the ships starts to heel.

3. The Initial Stability is depending on the shapestability of the ship and the division of weights. TheInitial Stability is defined by the GM-Value.

4. Roll angle phi f or j


Stability of Heavy Lift Ships – K, B, G and M

G·

· B

M ·

K·

f

· Z

· B

12

Why do ships stay upright?


The Metacenter or the Metacenter Height is very important in theStability of the ship.

When a ship is heeled, the centre of buoyancy of the ship movestransversely. The point at which a vertical line through the heeledcentre of buoyancy crosses the line through the original, verticalcentre of buoyancy is the metacenter. The metacenter remainsdirectly above the centre of buoyancy regardless of the tilt of afloating body, such as a ship.

1. The metacentric height (GM) is a measurement of the initial staticstability of a floating body. It is calculated as the distance betweenthe centre of gravity of a ship and its metacentre.

2. A larger metacentric implies greater initial stability. Themetacentric height also effects rolling period of the hull. A verylarge metacentric heights being associated with shorter periodsof roll which are uncomfortable for passengers and increasesseafastening loads

3. Hence, a just sufficiently high metacentric height is consideredideal for passenger ships.

· M

Stability curve


Stability Range:This is the range of heel angles for which the GZ valueis bigger then zero. Within this range the ship has apositive Stability and when the heeling moment isremoved, it will return to its initial equilibriumposition.

M·

G


The Stability greatly depends on:

1. Width

2. Draught (avoids the bilge coming out of the water)

3. Depth (avoids the deck being submerged)

Shape Stability of thevessel

The metacenter can be calculated using the

formulae:

Where:

KB = centre of buoyancy (height above the keel)

KG = the distance from the keel to CoG

I = the moment of inertia of the water plane in metres4

(also referred to as second moment of area)

G ·

· B

· M

·

Calculation of Metacenter of a ship

= + −

K xxIB M =Ñ

The waterplane area is the horizontal planewhich passes through a floating ship on alevel with the waterline.See the hatched blue surface in the picture

For a rectangular water plane area, such asthat displaced by a pontoon barge, the ‘rollinertia’ is

and (for a box shaped barge) the ‘displacedvolume’ is

(where L is the length, B is the beam, T is thedraught).

BM can now be calculated as:


Moment of inertia of the waterplane area and BM.

x

x

B

L

y

x

L B TÑ = ´ ´

3 2

12 12xxI L B BBM

L B T T×

= = =Ñ × × × ×

3

12xxL BI ×

=


For a flat top deck barge (rectangular shapedpontoon) the GM value (for small angles <6o)can be calculated as below:

Were:

KG is calculated using the moment equation.

Calculation of GM Value

= + −

= 2

= 12

Question #6Give the best answer. The simplifiedmethod for calculating GM can onbe used for barges/vessel with:

A More or less vertical side shellsB That have more or less a box

shapeC A small heel angleD More or less vertical side shells

and small heel angles

The period of roll can also beestimated from the followingequation:

2 ..

xxkTg GMp

=

2

12 2B TGM KG

T= + -

Ballast water is used to:• adjust the heel and trim of the ship• increase the stern draft to ensure sufficient propeller

draft.• Increase bow draft to reduce the risk of damage due

to bottom slamming.• To lower or raise the overall CoG of the ship• Reduce the longitudinal bending moment of the

vessel• Change draft to improve manoeuvrability• …

1. If a tank is completely filled, water has the sameeffect to the Stability as a solid mass

2. If a tank is partially filled with water, the so-called Free Surface Area (FSA) influences theStability

2. When the ship rolls, the free water in the tanksflows with it, resulting in a shift of the CoG of theship.

3. Due to the shifting of the CoG, the ship will evenroll more.

4. Therefore the ballast tanks are usually dividedacross the ship with bulkheads.See below:


Ballast water and free Surface Areas

Tank completely filled withwater: No Free Surface Area

One Tank half filled with water:Large effect on Stability due toFree Surface Area

Tanks split in 2 smaller tanks half filledwith water: Less effect on Stability dueto Free Surface Area

IMO is the United Nations specialized agency with responsibility for the safety andsecurity of shipping and the prevention of marine and atmospheric pollution byships.

The Maritime Safety Committee (MSC) deals with all matters related to maritime safety and maritime securitywhich fall within the scope of IMO, covering both passenger ships and all kinds of cargo ships. This includesupdating the SOLAS Convention and related codes, such as– dangerous goods,– life-saving appliances and– fire safety systems.The MSC also deals with human element issues, including amendments to the STCW Convention on trainingand certification of seafarers. The MSC has a wide range of issues on its agenda, including goal-basedstandards, autonomous vessels, piracy and armed robbery against ships, cyber security, e-navigation and themodernization of the Global Maritime Distress and Safety System (GMDSS)Resolution MSC.267(85) the resolution on intact stability addresses design criteria for1. Fishing vessels2. Pontoons3. Containerships greater than 100 m4. Offshore supply vessels5. Special purpose ships and6. Mobile offshore drilling units (MODUs)


IMO – the International Maritime Organization

Pontoon is considered to be normally: .1. I non self-propelled;2. Unmanned3. carrying only deck cargo4. having a block coefficient of 0.9 or greater5. having a breadth/depth ratio of greater than 3

and6. having no hatchways in the deck except small

manholes closed with gasketed covers.

Intact stability criteria.1. The area under the righting lever curve up to the

angle of maximum righting >= 0.08 metre-radians

2. The static angle due to wind speed of 30 m/sshould not exceed an angle at half the freeboard

3. The minimum range of stability should be– for L <= 100 m 20°– For L >= 150 m 15°– intermediate lengths by interpolation.

(If we check this curve, we estimate the area as atriangle and quickly see that we comply. )


PONTOONS; MSC.267(85); (recommended)

Maximum rightinglever at 10Maximum rightinglever at 10°

range of stability~ 23.5range of stability~ 23.5°

Transport of theValemon jacketon barge H627

3600.08 0.08 deg2

4.58 deg

meter rad meter

metrep°

× = × ×

= ×

1.80 10 9 deg2

Area metre× °» = ×

Ships have to comply with MSC.267(85) severe wind androlling criterion or weather criterion:1. STANDARD CRITERION and the severe wind and2. WEATHER CRITERION or rolling criterionThese criteria take more work to check compared withthe barge stability criteria.The STANDARD CRITERIA consider “static” aspects ofstability and are:1. The area under the righting lever curve (GZ curve)

I. >= 0.055 metre-radians up to j 30°II. >= 0.09 metre-radians up to j 40°

2. GZ shall be at least 0.2 m at an angle >= 30°3. The maximum righting lever at >= 25°4. GMo >= 0.15 m.

In the WEATHER CRITERION the ability of thevessel to recover from rolling is checked(dynamics). When rolling towards windward,energy is built up which is released when rolling toleeward. Hereby, the areas A and B are comparedwhereby area b >= a

The calculations of the various angles j is doneusing tables, factors and formulas based on thevessel particulars.Check Resolution MSC.267(85) were it is explainedclearly. (http://www.imo.org/)Also here, these checks can be done using stabilitysoftware.


Special purpose ships; MSC.267(85)

Transport ofa submarineon a SemiSubmersibleHeavy LiftVessel

WindleverWindlever

1. A Ship with a small GM has a long rolling period (“Tender” Ship)

2. A Ship with a large GM has a short rolling period ( “Stiff” ship)In general we prefer a high GM for loading and discharging and a low GMfor sailing.How can we influence the Stability of the Ship?1. Fill up the bottom tanks of the vessel (CoG is loweredè GM

increasesè Stability increase)2. Empty the double bottom tanks and fill up the upper anti heeling

tanks (CoG is higherè lower GM valueè Stability decrease)3. Stow the cargo on the Tween-deck or on deck instead of the lower

hold.(CoG is higherè decrease of Stability)

Advantages of a “Tender” vessel:Small GM results to long roll period and therefore low accelerations® comfortable for Crew or passengers (Cruise vessels)® low seafastening forces.® sea fastening of cargo® low internal force in cargo


How can the Stability of a Ship be influenced?

Barge loaded with Gas turbine, Trafo’sand Generator and ballasted down toapprox. 10 cm Freeboard, in order topass underneath the bridge at LowTide. Is this allowed?

Important:With a freely suspended load in the crane, thevessel acts as if the load is placed in the crane tip,independent of the height of the load above deck.

By lifting the load off the quay, the Cargo rises, KGincreases abruptly. This can even cause animmediate negative GM.


CoG of load when freely suspended in crane

=

tcg

vcg

®

Cargo on quay Freely suspended cargo

Data:A piece of Cargo (100t) on deck is ready to be lifted (Slingsconnected)

Displacement of barge + cargo = 8000 tGM = 2 mKG = 5 mCoG of Cargo on deck = 11 m above KeelHook is 15 m above KeelTop of jib is 40 m above KeelPivot point jib at Crane 8 m above keel

Answer:The Correct Answer is (B). As the load is already on deck thedisplacement does not change. Also the underwater body ofthe ship does not change, so the moment of Inertia remainsthe same.Only KG is changing.The load CoG shifts to the top of the jib, when we start lifting,which now becomes 40 m above the keel (instead of 11 m).Shift in CoG can be calculated with the moment equation as:

As all the other parameters remain the same, the GM-valuewill change with 0.36 m and will decrease to 1.64 m.

#7 Question:The piece of cargo will be lifted 10 m up from deck.During this operation the jib remains in the sameposition.What will be the new GM-value?

(A) GM remains the same(B) GM becomes 1.64 m(C) GM becomes 1.825 m(D) Not enough info to complete the calculation(E) GM becomes 1.975 m


Stability example

′ =100 × (40 − 11 )

8000 = 0.36

= + −

IMPORTANTThe previous explained method is only valid for:• Small angles and• barges or vessels with

“a vertical side shells”.


Advanced stability, orthogonal tipping: 1

New CL of the waterplane area

Top view at waterplane are

Cross section at stern

Side view

Output fromhydrostatic

software

For non-ship/barge shape objects like drilling rigs, vessels withextreme heel or list and object with an asymmetric water plane area,the transverse stability is not necessarily the smallest stability! Thestability is to be approached in a different wayEnergy is needed to increase the vertical distance between the vcgand cog.We can use this to create an “Energy to heel surface” (Use 1st Law ofNewton)For a matrix of heel and trim combination, the distance between vcgand vcb can be calculated and presented in a contour plot.



ABS TECHNICAL PAPERSOrthogonal Tipping in Conventional Offshore Stability Evaluations

Paths ofminimumenergyLow stability

1 1( )pE B Z BGd = D -

Energy to heel surface for a barge.The path of minimum energy is in transverse direction



ABS TECHNICAL PAPERSOrthogonal Tipping in Conventional Offshore Stability Evaluations

Path of minimum energyLow stability

Path of minimum energyLow stability

ASSUME A DAMEN STAN PONTOON TYPE B27‘NORTH SEA STANDARD BARGE’.

Length 91.50 mBeam o.a. 27.40 mdraught 4.90 mDepth at sides 6.10 mDeadweight 9.800 tonAllowable deck load 15.0 ton/m 2Deck thickness 20 mm

The barge is floating without list. It has 1longitudinal bulkheads creating 2 adjacent tankswith equal volumes.

Question #9: What will be the GM?Question #10: What will be the list if we move 1000

ton ballast water from PS to SB?Use:

•

• Weight transfer formulae• Assumptions

Answer:It is safe to assume that KG = at half Dè KG = 3.05 m


Calculation GM Value and list due to ballasting.

∇= × × = 12284.79

Tcg shift = 1000 × 27.40

212284.79

= 1.11 m

= 12 + 2 −

=27.40

12 × 4.90 +4.90

2 − 3.05 = 12.17 m

= 12 + 2 −

Calculation using GM Value Cont’d


Almost there…

= atan1.11

12.17

= 5.2°

M ·

G·

Why do we need to secure the cargo?• As the vessel moves due to the Sea Condition in 6 degrees of freedom, cargo must remain in the same

position and be secured against the worst sea conditions• Vessel motion is caused by:

– Motion by waves– Motion by wind– Increased rolling due to these effects

With a floating vessel we have 6 degrees of freedom in motions:• 1 Roll, 2 Pitch, 3 Heave and• 4 Yaw, 5 Sway, 6 Surge


Sea fastening of Cargo on Heavy Lift Ships

Motion Analysis of vessel


Disadvantage:

Only valid for:

• given loading conditions,

• Season

• stowage

• Cargo location

Advantage:

• More realisticValues for aparticular voyage

• Save seafasteningtime and cost.

Main Factors affecting Securing Forces:• Acceleration/deceleration of cargo due to ships motions

• List of ship

• Forces due to Wind pressure

Methods to define the accelerations:• Ship owners Own Rules• Rules defined by the Classification Societies• Better is: Custom made computer analysis

o Strip-theory program (frequency domain)o Panel Methods (3-D Potential Theory, time domain)

Extra engineering is paid for by a reduction onseafastening costs and time.


“20 deg 10 Barge” DNVGL-ST-N001 Marine operations and marine warranty.


“20 deg 10 Rule”, simple rule and in general conservative.

SUBJECTTRANSPORT ACCELERATIONS ACCORDING GUIDELINES FOR MARINE TRANSP.0030/ND 7.9.1

PROJ No.

PHASE/CTR

ACTIVITY

PROJECT

REVISION DATE BY CALC. No.

A1 7-Feb-16 Rob Hoekstra SHEET 1

InputName Topside

Weight cargo 2000 [mt]

Length of barge 100.00 [m]

Width of barge 20.00 [m]

Depth of barge 5.00 [m]

Block coeff 0.90 [m]

lcb (=0.5L) 50.00 [m]

T 3.00 [m]

Cargo lcg 0.00 [m]

Cargo tcg 0.00 [m]

Cargo vcg 16.00 [m]

Roll angle 25 [degr]

Roll frequency 10 [s]

Pitch angle 15 [degr]

Pitch frequency 10 [s]

Heave 0.2 [g]

Results Transverse LongitudinalR 13.00 51.66 [m]

angular acc. 0.17 0.103 [rad/sec2]

Acc horizontal* 6.39 7.71 [m/sec2]

Acc vertical 1.96 7.13 [m/sec2]

F_horizontal due to motions 1301.78 400 [mt]

F_vertical due to motions 400.00 1454 [mt]

*Including gravity * sin(roll°/pitch°)

For very complex analysis FE analysis give the best result. It is the less conservative way of analysis. Vessel orbarge is modeled in detail to revealing all area’s that are highly loaded but also the area’s not utilized


Combine Motion Program with Finite Element Analysis

www.argonautics.com

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05 Naval Architectural and Maritime Basics