PPT on basis Ship Design

7/29/2019 PPT on basis Ship Design

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BASIC SHIP DESIGN

1EME 4343 LT KDR MOHD AZZERI TLDM


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Hullform

Ship hull form refers to the shape of the hull, especially that

part of the hull that is under water in normal operating

conditions.

Many of the calculations that a naval architect must make in

order to design a ship are influenced by hull form

A great variety 'of hull forms have been successfully adapted

to ships, reason that their forms are so different from one

another is because the requirements of their separate

missions especially as regards their required speeds and

capacities, dictate that they should be different for each to

operate efficiently.



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Hull Form: Ship's Lines

The graphical display of the hull form of a ship is

called a lines drawing, or the lines.

A small scale sample of a lines drawing is shown inFigure 1-2.

The three views in a lines drawing have the same

relationship to one another as the front, side, andtop views in a typical orthographic engineering

drawing, but their names are special to ship's lines.



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Since its purpose is only to define hull form,

the lines drawing to show the hull only up to

the deck or decks to which the ship's side shell

plating extends. Deckhouses/superstructure

are not included.



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The view showing stations in true shape is

called the body plan. Only half of each station

is drawn, since the other half is symmetrical.

By convention, stations from the bow to the

midship section are drawn to the right of

centerline, and those from amidships to aft

are drawn on the left side.

Waterlines are also drawn on one side of the

centerline only, and they are all superimposed

in the half-breadthplan. 6EME 4343 LT KDR MOHD AZZERI TLDM


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The other side of centerline in the half

breadth plan is often reserved for drawing the

true shapes of intersections produced by

diagonal planes, which are auxiliary planes.

The lines that are drawn are shown the

waterplanes and buttock planes.



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On the third view of the lines drawing, called

theprofile plan or the sheer plan, the true

shapes of the buttocks are drawn.

The outline of the ship's centerline profile (as

seen from the side), showing bow and stern

profile shapes. The centerline plane is the

zero foot buttock plane, and one of thebuttock curves.



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Views and Reference Planes

As shown in Figure 2-2, a ship hull is imagined to be

resting on a horizontal plane called the baseline

plane, which is the reference plane from whichvertical measurements, or heights above baseline,

are made to any point on the hull.

The two symmetrical halves of the hull, starboard

and port, are separated by the centerline plane, a

vertical plane running longitudinally from bow to

stern.



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Transverse or athwartships dimensions called half-

breadths are measured from the centerline plane to

the hull.

The third reference plane, the midship section plane,is vertical and tranverse, thus it is orthogonal to both

centerline and baseline planes.

Amidships, refers to the location of the mid-ship

section plane. Define the location of the midship

section, which is at the midpoint between the

perpendiculars.



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Horizontal planes parallel to the baseline plane and at

intervals of a few feet or meters above it are called

waterplanes, and their intersections with the hull as shown in

the lines drawing are waterlines.

Planes parallel to the mid-ship section plane, shown usually at

either ten or twenty equal intervals along the ship's length are

called station planes and the true shapes of their intersections

with the hull are referred to as stations.

Stations are identified by numbers, starting with zero at thebow, increasing aft (the convention in the United States and

Great Britain), or with zero at the stern, increasing forward

(the convention in Europe and Asia).



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The set of planes parallel to the centerline

plane, at intervals defined by their distances

off centerline, are the buttock planes, which

intersect the hull in curves called buttocks.



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Molded Form, Dimensions

The shapes shown in a lines plan is called the molded

form of the vessel. The term derives from the fact

that before computer-controlled plate cutting andframe bending machines were developed, workers

called loftsmen made wooden full scale templates or

molds to confirm to a full scale lines craving laid out

on the floor. Each mold defined the shape of aparticular part of the hull structure.



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Theprincipal dimensions of a ship are those

important dimensions that define its basic size. Early

in the design process the waterline at which the

designer has estimated the ship will float when fullyloaded isdetermined.

That waterline is called the design waterline (DWL)

or the load waterline.

At the point of intersection of the DWL and the

forward extremity of the ship (called the stem), a

vertical line called theforward perpendicular (FP) is

drawn. 18EME 4343 LT KDR MOHD AZZERI TLDM


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The forward perpendicular thus defines the forward

end of the immersed portion of the ship's hull. This

definition of the location of the FP is universally

applied to all ships. An after perpendicular (AP)is also defined for each

ship, but its location is not specified by a unique

definition for all vessels. It is intended to be

representative of the after end of the ship'simmersed body. Common choices for the AP are the

centerline of the rudder stock, the after extremity of

the design waterline.20EME 4343 LT KDR MOHD AZZERI TLDM


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The length measured from the FP to the AP is

designated the length between perpendiculars (LBP) ,

a principal dimension that is used to determine the

ship's coefficients of form and for structuralcalculations.

For navigational and dockingpurposes, the extreme

length of the ship, or length overall (LOA) is

important.

In certain hydrodynamic analyses, such as ship

resistance calculations, the most characteristic length

is the length on waterline (LWL). 21EME 4343 LT KDR MOHD AZZERI TLDM


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A deck line is usually curved longitudinally, reaching

its highest point at the bow, its lowest point at or

somewhat aft of amidships, and again rising toward,

the stern. This curvature is known as sheer. The transverse, or athwartships, dimension of a ship

is called the beam (B)or breadth. Since ships are not

box-shaped, the beam varies with position along the

ship's length, but in a list of principal dimensions, themolded beam refers to the molded measurement at

the ship's widest point.



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In the half cross section shown in Figure (b),

assumed to be at amidships, the molded

depth (D), or depth at side, is shown.

It is the vertical distance at amidships from

baseline (upper surface of the keel plate) to

the top of the main deck beams at the side of

the ship.



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The deck may also have transverse curvature, called

camberor round of beam or round down, as shown

in the figure, such that it arches upward from the

deck at side to the centerline. The ship's bottom is not flat, but slopes upward

toward the sides, the bottom is said to have

deadrise, or rise of bottom, or rise of floor.

A flat plate keel, running along centerline, normally

has no deadrise, and the half-width of such a keel is

called the half-siding.



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Two of the dimensions shown in Figure,namely the draft and the freeboard, are

characteristics that depends on ship loading as

well as ship geometry. Draft (T)is the vertical measurement from the

waterline at any point on the hull to the

bottom of the ship. The design draft shownon a lines plan to the design waterline is a

molded draft, measured to the molded

baseline.26EME 4343 LT KDR MOHD AZZERI TLDM


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Freeboardis the vertical distance from the

waterline to the deck at side, or the difference

between the depth at side and the draft at

any point along the ship. Since freeboard is animportant measure of the safety of aship,

every ship is assigned a minimum acceptable

freeboard at amidships.



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As illustrated in of Figure (c), the sides of some ship

sections, curve inward from their maximum breadth

to the point at which they join the deck. This

characteristic is known as tumblehome, measured bythe horizontal distance from maximum breadth to

breadth at deck.

The opposite kind of curvature, outward as the deck

is approached, is calledflare, shown in the samefigure. Sections with flare are common at the bow of

most ships.



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Table of Offsets

In either case, the ship form information

documented in the lines plan must be expressed

numerically and at full ship scale. The numerical

equivalent of a lines plan is a table of offsets. To define the three-dimensional ship form

numerically, three coordinates of selected points on

the molded hull must be specified:

- Longitudinal distance front the FP, and AP

- Half breadth, from the centerline plane.

- Heightabove the baseline plane.30EME 4343 LT KDR MOHD AZZERI TLDM


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A typical table of offsets at stations is shown

in Figure 2-4.



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Fundamental Hull Form Characteristics

All of the hydrostatic properties to be calculated are

derived from the following fundamental

characteristics of the immersed hull form at eachgiven even keel waterline.



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Properties of the Waterplane

Four properties of each waterplane are required:

1.Area of the waterplane (AW.). The waterplane area

is required to determine the change in mean draft

when small weights are loaded or discharged. Units:

feet2 or meter2

A =Ai = yi x



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2. Center of flotation (CF). The CF is the centroid ofthe waterplane, also called the center of area or

center of gravity of the waterplane. It is required for

the calculation of changes in draft at bow and stern

as a result of loading, discharging, or shifting weightsaboard ship. The CF is located on centerline because

of the symmetry of the waterplane. Its longitudinal

position with respect to the midship section (or the

FP or AP if preferred as reference planes) must becalculated. The distance so determined is called the

longitudinal center of flotation (LCF).)Units of LCF:

feet or meters from reference plane.36EME 4343 LT KDR MOHD AZZERI TLDM


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3. Longitudinal moment of inertia (IL). This property

of the waterplane is its second moment of area

about a transverse axis passing through the center of

flotation. It is required for the longitudinal stabilityand trim (difference between forward and aft drafts).

Units: feet4 or meters4.

4.Transverse moment of inertia (IT).It is the second

moment of the waterplane about its centerline. It isrequired in the calculation initial transverse stability.

Units: feet4 or meters4



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Properties of the Immersed Volume of the Hull

Three quantities ass with the immersed volume must bedetermined:

1. Volume of displacement (V). This is the immersed volume

itself the volume of displacement because it is a measure ofthe volume of fluid displaced by the floating ship.

Fundamental property of hull form because the weight and

mass of the ship are equal respectively to the weight and

mass of the water displaced. The molded volume is calculated

directly from the offsets of the molded form. Volumes of the

shell and appendages like bilge, keel, rudder, etc., are then

added to determine the total displacement at each draft.

Units of V: feet3 or meters3.



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2. Longitudinal center of buoyancy (LCB). This is the

distance of B from a specified transverse reference

plane, usually the midship section. Or LCB may be

measured from FP or AP, so long as the reference axisis clearly stated. Units: feet or meters.

3. Vertical centerofbuoyancy (KB). KB is the height

of the center of buoyancy above the baseline or keel.

Units: feet or meters.



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Coefficient of form

The coefficients of form are also useful tools for

making first estimates of a ships resistance,powering and seagoing performance at early point in

the design of a new ship.

The most commonly used coefficients of form are

defined below:

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The coefficients most commonly used by naval architects are asfollows.

Block coefficient ( CB)

The ratio of the volume of displacement to the volume of

rectangular block having a length, beam and draft equal tothat maximum section area.

CB = /LBT

The block coefficients of typical ships may vary from as low as0.45 for a high speed combatant ship like a destroyer or fastfrigate to as full as 0.85 or more for a very large crude oiltanker.

EME 4343 41LT KDR MOHD AZZERI TLDM


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Block coefficient (CB)

Prismatic coefficientEME 4343 LT KDR MOHD AZZERI TLDM 42


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Prismatic coefficient ( CP)

It is defined as the ratio of the volume of displacement tothe volume of a prism whose cross section is shaped like theimmersed midship section, and whose length is the length of

the ship.

CP =/ L AM

The coefficient that describes the fineness of the ends (bow

and stern) of a hull without being influenced by its midshipfineness .

Typical values range from about 0.57 for a high-speed, fine-ended ship to 0.85 for a large bulk carrier or tanker.



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Midship section coefficient (CM)

The fullness of the midship portion of a hull is described bythe midship section coefficient (Cm), which is the ratio of the

immersed midship section area to the area of itscircumscribing rectangle

CM = AM

B T

Very fine hulls typical of destroyers might have a CM of 0.75 orless, but most large merchant ships have vertical flat sides and

a flat bottom at amidships, the section departing from a

rectangle only by virtue of rounded bilges, so their mid-ship

section coefficients are more like 0.95 to 0.995.EME 4343 LT KDR MOHD AZZERI TLDM 44


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Midship section coefficient (CM)

Waterplane coefficient (CWP)EME 4343 LT KDR MOHD AZZERI TLDM 45


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Water plane area coefficient (CWP)

Waterplane fullness or fineness may be quantified bydefining the waterplane coefficient(CWor Cwp). The ratio ofthe waterplane area at the designed or loaded waterline to

the area of the circumscribing rectangle.

CWP = AW / LWL B

Typical values of Cw at the design waterline vary from 0.67 to0.92.



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Where;

L = Length on the designed waterline

T = Draft to the designed waterline

B = Beam amidships at the designed waterline

= Volume of displacement at draft T

AM = Area of the midship section at draft T

AX = Area of maximum section to the designedwaterline

AW = Area of the waterplane at draft T

= Displacement tonnage at draft T



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The Measure of Ship Size

The ship size is usually characterized by

displacement or tonnage. Displacement of

ship is a statement of its weight and tonnage

is generally a measure of its volume or

capacity.



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General terms that are used to measure size of a ship:

Deadweight (dwt) the weight of cargo, fuel, water

stores, crew and effects (all variable loads).

Lightweight weight of hull and machinery andpermanent fixtures (all fixed weights)

Displacement the total weight, deadweight plus

lightweight. It is equal to the weight of water

displaced by ship (Archimedes Principle). It is usually

expressed in tons.



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Gross register tonnage (grt) a measure of the total

internal volume of the ship, including the hull, the

superstructure and all enclosed spaces. It is used as

the basis for such things as docking, pilotage andsurvey fees.

Net register tonnage essentially a function of the

total volume of cargo spaces and the number ofpassengers, a measure of earning capacity. It is used

as the basis for such things as port and harbour, light

and cargo dues.50EME 4343 LT KDR MOHD AZZERI TLDM


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Ship Drawing

Drawing is a communication language that uses graphics to present

an object, idea and design.

As in old saying A single picture saved thousand words has made

drawing as one of the most important entity and plays

important roles in engineering fields.

Ship is one of the engineering products that require a lot of

drawings to represent its unique shape, function, components,structures, construction process etc. Therefore it is essential for

those who involve in shipbuilding industry to understand the

various types of ship drawing and know how to draw them.



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Types of ship drawings

In general, drawing that associates with ship buildings can be

divided into following categories:

a. Lines Plan Drawing

b. General Arrangement Drawing (GA)

c. Shell Expansion Drawing (Scantling Drawing)d. Detail / Production Drawing

e. 3-D Product Drawing



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Lines planThe exterior form of ships hull is a curved surface

defined by the lines plan drawing or simply the lines. The

lines consist of orthographic projections of the intersections

of the hull form with three mutually perpendicular sets of

planes, drawn to a suitable scale.

General Arrangement Can be defined as the assignment of

spaces for all the required functions and equipment, properly

coordinated for location and access.



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Scantling drawing Is meant for the construction of the

structures and plating of ship during construction. The

structures dimensions and the plate thickness is determined

to withstand the load that is going to apply to vessel during

operation. Three locations of the structures are generallyshown in the scantling drawing are midship, location of 25%

from forward of perpendicular and location of 25% from

aftward of perpendicular.

Detail / Production drawing Production drawing shows the

details of the system onboard, the fabrication and assembly

process of the system.



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Types of Material Using On Ship Structure

Steel in ships

Steel is the most important shipbuilding material andincludes alloys containing Ferum with a contentcarbon (Fe-C) up to 15 per cent in terms of weight.

Depending on its particular use certain othersubstances are added to modify the physical,chemical and mechanical properties of the alloy.



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In general, the carbon content and the method of

annealing affect the microstructure that in turn

determines the strength and hardness of the metal.

Classifications societies such as the American Bureau

of Shipping, specify a range of grades of acceptable

structural steels with regulations pertaining to their

applications onboard ship.



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A single grade of steel cannot be used for all parts of

the ship because certain parts of ship structures are

more highly stressed than others, and because notch

sensitivity is strongly dependent on steel thickness.

They also specify higher-strength steels because ship

designers sometimes choose extra high strength

steels for critical, highly stressed parts of thestructure, so long as the added expense can be

justified by the weight savings.



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Ordinary-strength steels

Six grades of ordinary strength hull structural steels

are specified by the ABS. All must have a yield

strength of at least 34,000 psi (235 MPa), an ultimatetensile strength between 58,000 and 71,000 psi (400

to 490 MPa), and a minimum, of 24 percent

elongation of a 2-inch tensile specimen.

The various grade differ in their required level ofnotch toughness, the requirements increasing in

severity as the steel plate get thicker.



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Higher-strength steel

Two strength levels of higher-strength steels are

specified, with three thickness grades in each

strength category. The yield strength requirementsare 45,000 psi (314MPa) and 51,000 psi (353 MPa),

respectively. Ultimate strength range from 68,000 to

90,000 psi (471 to 618 MPa), and the minimum

elongation is 22 percent. These steels are used whenthe premium cost of 25 to 50 percent over ordinary-

strength steel and more difficult fabrications

procedures can be justified.59EME 4343 LT KDR MOHD AZZERI TLDM


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Special steel

Other steel with special properties are sometimes

needed for special applications in ship structures. Forlow service temperatures like those found in

refrigerated ships and liquefied gas carriers, low

temperatures steels have been developed that have

satisfactory notch toughness to service temperatures

as low as -67F (-55C).

For service in liquid cargo tanks that may be used to

carry a wide variety of liquids, special corrosion-resistant steelmay be used. Alternatively, ordinary

steel clad with corrosion resistant materials is also

available.



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Abrasion-resistantsteels that resists wear

caused by abrasive materials dropped into

holds, especially ores carried in bulk, are

sometimes used in ore carrier holds.



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Mechanical Properties of Steel

The properties of ship steels that relate to its

strength are called its mechanical properties. Many

of the mechanical properties of interests to ship

structural designers are determined from a standard

test known as the tensile test of the steel. In the standard tensile test, a test specimen is

subjected to pure tensile loading increasing from

zero to the load required to break the specimen. A

plot may be made of load against deformation, butthe more common procedure is to plot stress ( =

P/A) against strain ( = /L),



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As shown in Figure 7-6, the curve shown in the figure

is for typical mild steel or ordinary-strength hull

structural steel, the most common steel used in hull

construction.

It can be seen from the figure that, initially, the

relationship between stress and strain in a straight

line; that is, stress is directly proportional to strain.

This proportionality, known as Hookes Law, pertainup to point PL on the diagram, theproportional limit.



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At about the same stress as the proportional limit, or slightly

above it, a point (EL in the figure) called the elastic limitis

reached.

When loaded to any point below the elastic limit, steel has a

very remarkable propertythe deformation or strain causedby the stress is completely recoverable when the load (or

stress) is removed, and the piece of material return to its

original dimension. This property is known as elasticity, and it

is a most desirable quality of a structural material because astructure or machine part designed so that the elastic limit is

never exceeded will never deform permanently.



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At a stress slightly higher than the elastic limit, a mild

steel specimen begins to experience a rapid increase

in strain without any increase in stress. This

phenomenon is called yield, and the stress at which

it occurs is the yield stress or yield point, marked YP

on the figure.

Deformation beyond the elastic limit is calledplastic

deformation. Deformations or strains associated withyielding are not recoverable, and the material is said

to take apermanent set.



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Upon further loading, the steel the steel will

continue to deform plastically while the stress

increases to its maximum value, called the ultimate

stress, marked U on the diagram. The ultimate stress

of a material is a measure of its strength.

Reduction in stress that takes place after the

ultimate stress is reached, up to the point of rupture,

marked R.



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Aluminum in Ship Structures

Aluminum has not been used for the entire hull

structure of large ships, its high strength-to-weights

ratio makes it attractive for some special shopstructural applications.

Aluminum alloys are used as the principal hull

material in a variety small vessels, especially high-

speed craft such as planning boats, hydrofoil craft,

and surface effect craft.



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Aluminum is also very corrosion resistant, so long as

care is taken in fabrication of aluminum structures to

prevent them from being in direct contact with

dissimilar metals by the use of gaskets of special

coatings. The most prevalent use of aluminum in

large ships has been in the superstructures, where

the weight reduction results in improved stability.



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Composites

Composite laminates such as glass-reinforced plastics

have become common place as a hull structural

material for a great variety of small craft such asrecreational sailing and power yacht.

These materials have the advantages of a high

strength-to-weight ratio, low maintenance cost, and

the ability to be fabricated into a virtually endlessvariety of types of laminates and shapes of hull.



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Their disadvantages, however, mitigate against their

use as a hull material for large ships: the high initial

cost of the material compared to steel, a very

modulus of elasticity (in the order of only 10 percent

of that of steel), so that they deflect a great deal

under load, and the fact that they are combustible,

so that they cannot meet the fire-resistance

regulations applicable to ships.



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Ship Design Concept



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