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Transcript of PPT on basis Ship Design
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BASIC SHIP DESIGN
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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
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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.
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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
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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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