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A hull is the
watertight Waterproofing is the process of making an object or structure waterproof or water-resistant so that it remains relatively unaffected by water or resisting the ingress of water under specified conditions. Such items may be used in wet environmen ...
body of a
ship A ship is a large watercraft Watercraft, also known as water vessels or waterborne vessels, are vehicles A vehicle (from la, vehiculum) is a machine A machine is any physical system with ordered structural and functional propertie ...

ship
,
boat A boat is a watercraft Watercraft, also known as water vessels or waterborne vessels, are vehicles A vehicle (from la, vehiculum) is a machine A machine is any physical system with ordered structural and functional properties. It m ...

boat
, or
flying boat A flying boat is a fixed-winged seaplane A seaplane is a powered fixed-wing aircraft capable of taking off and landing of Ryanair makes a smoky landing at Bristol Airport (2016) lands on a moving trailer as part of an airshow. ...

flying boat
. The hull may open at the top (such as a
dinghy A dinghy is a type of small boat, often carried or Towing, towed by a Watercraft, larger vessel for use as a Ship's tender, tender. Utility dinghies are usually rowboats or have an outboard motor. Some are rigged for sailing but they differ ...

dinghy
), or it may be fully or partially covered with a deck. Atop the deck may be a
deckhouse A cabin or berthing is an enclosed space generally on a ship A ship is a large watercraft that travels the world's oceans and other sufficiently deep Sea lane, waterways, carrying goods or passengers, or in support of specialized missions, ...
and other
superstructure A superstructure is an upward extension of an existing structure above a baseline. This term is applied to various kinds of physical structures such as buildings, bridges, or ships having the Degrees of freedom (mechanics), degree of freedom ze ...
s, such as a funnel, derrick, or
mast Mast, MAST or MASt may refer to: Engineering * Mast (sailing) , a vertical spar on a sailing ship * Flagmast, a pole for flying a flag * Guyed mast , a structure supported by guy-wires * Mooring mast , a structure for docking an airship * Radio m ...
. The line where the hull meets the water surface is called the
waterline The waterline is the line where the Hull (watercraft), hull of a ship meets the surface of the water. Specifically, it is also the name of a special marking, also known as an international load line, Plimsoll line and water line (positioned Amid ...
.


General features

There is a wide variety of hull types that are chosen for suitability for different usages, the hull shape being dependent upon the needs of the design. Shapes range from a nearly perfect box in the case of scow barges to a needle-sharp surface of revolution in the case of a racing multihull sailboat. The shape is chosen to strike a balance between cost, hydrostatic considerations (accommodation, load carrying, and stability), hydrodynamics (speed, power requirements, and motion and behavior in a seaway) and special considerations for the ship's role, such as the rounded bow of an
icebreaker An icebreaker is a special-purpose ship A ship is a large watercraft that travels the world's oceans and other sufficiently deep Sea lane, waterways, carrying goods or passengers, or in support of specialized missions, such as defense, rese ...
or the flat bottom of a
landing craft Landing craft are small and medium seagoing watercraft, such as boats and barges, used to convey a landing force (infantry and vehicles) from the sea to the shore during an Amphibious warfare, amphibious assault. The term excludes landing ships, wh ...

landing craft
. In a typical modern steel ship, the hull will have watertight decks, and major transverse members called bulkheads. There may also be intermediate members such as
girders A girder () is a support Beam (structure), beam used in construction. It is the main horizontal support of a structure which supports smaller beams. Girders often have an I-beam cross section (geometry), cross section composed of two load-bearin ...
, stringers and webs, and minor members called ordinary transverse frames, frames, or longitudinals, depending on the
structural arrangement A structure is an arrangement and organization of interrelated elements in a material object or system A system is a group of Interaction, interacting or interrelated elements that act according to a set of rules to form a unified whole. A sy ...
. The uppermost continuous deck may be called the "upper deck", "weather deck", "spar deck", "
main deck The main deck of a ship A ship is a large watercraft that travels the world's oceans and other sufficiently deep Sea lane, waterways, carrying goods or passengers, or in support of specialized missions, such as defense, research, and fishing. S ...
", or simply "deck". The particular name given depends on the context—the type of ship or boat, the arrangement, or even where it sails. In a typical wooden sailboat, the hull is constructed of wooden planking, supported by transverse frames (often referred to as ribs) and bulkheads, which are further tied together by longitudinal stringers or ceiling. Often but not always there is a centerline longitudinal member called a
keel The keel is the bottom-most longitudinal structural element on a vessel. On some sailboats, it may have a hydrodynamic In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ...

keel
. In
fiberglass Fiberglass (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. Currently, American Englis ...
or composite hulls, the structure may resemble wooden or steel vessels to some extent, or be of a
monocoque Monocoque (), also called structural skin, is a structural system in which loads are supported by an object's external skin, in a manner similar to an egg shell. The word ''monocoque'' is a French language, French term for "single shell". First u ...
arrangement. In many cases, composite hulls are built by sandwiching thin fiber-reinforced skins over a lightweight but reasonably rigid core of foam, balsa wood, impregnated paper honeycomb, or other material. Perhaps the earliest proper hulls were built by the
Ancient Egypt Ancient Egypt was a civilization  A civilization (or civilisation) is a that is characterized by , , a form of government, and systems of communication (such as ). Civilizations are intimately associated with additional char ...

Ancient Egypt
ians, who by
3000 BC The 30th century BC was a century A century is a period of 100 years. Centuries are numbered ordinally in English and many other languages. The word ''century'' comes from the Latin ''centum'', meaning ''one hundred''. ''Century'' is sometimes ...
knew how to assemble wooden planks into a hull.Ward, Cheryl. "World's Oldest Planked Boats," in ''
Archaeology Archaeology or archeology is the study of human activity through the recovery and analysis Analysis is the process of breaking a complexity, complex topic or Substance theory, substance into smaller parts in order to gain a better underst ...
'' (Volume 54, Number 3, May/June 2001).
Archaeological Institute of America The Archaeological Institute of America (AIA) is a North American nonprofit organization devoted to the promotion of public interest in archaeology, and the preservation of archaeological sites. It has offices on Beacon Hill, Boston, Beacon Hill i ...

Archaeology.org
/ref>


Hull shapes

Hulls come in many varieties and can have composite shape, (e.g., a fine entry forward and inverted bell shape aft), but are grouped primarily as follows: * Chined and hard-chined. Examples are the flat-bottom (chined), v-bottom, and multi-chine hull (several gentler hard chines, still not smooth). These types have at least one pronounced knuckle throughout all or most of their length. * Moulded, round bilged or soft- chined. These hull shapes all have smooth curves. Examples are the round bilge, semi-round bilge, and s-bottom hull.


Planing and displacement hulls

* Displacement hull: here the hull is supported exclusively or predominantly by
buoyancy Buoyancy (), or upthrust, is an upward exerted by a that opposes the of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the pressure at the bo ...

buoyancy
. Vessels that have this type of hull travel through the water at a limited rate that is defined by the waterline length. They are often, though not always, heavier than planing types. * Planing hull: here, the planing hull form is configured to develop positive
dynamic pressure In incompressible fluid dynamics In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids—liquids and gases. It has several subdisciplines, including ''aerodynamics'' (the study of ...
so that its draft decreases with increasing speed. The dynamic lift reduces the wetted surface and therefore also the
drag Drag or The Drag may refer to: Places * Drag, Norway, a village in Tysfjord municipality, Nordland, Norway * ''Drág'', the Hungarian name for Dragu Commune in Sălaj County, Romania * Drag (Austin, Texas), the portion of Guadalupe Street adja ...
. They are sometimes flat-bottomed, sometimes V-bottomed and more rarely, round-bilged. The most common form is to have at least one chine, which makes for more efficient planing and can throw spray down. Planing hulls are more efficient at higher speeds, although they still require more energy to achieve these speeds. An effective planing hull must be as light as possible with flat surfaces that are consistent with good sea keeping. Sailboats that plane must also sail efficiently in displacement mode in light winds. * Semi-displacement, or semi-planing: here the hull form is capable of developing a moderate amount of dynamic lift; however, most of the vessel's weight is still supported through buoyancy.


Hull forms

At present, the most widely used form is the round bilge hull. It gives hulls the rough al shape of an
inverted bell The inverted bell is a metaphor A metaphor is a figure of speech that, for rhetorical effect, directly refers to one thing by mentioning another. It may provide (or obscure) clarity or identify hidden similarities between two different ideas. Me ...
. With a small payload, such a craft has less of its hull below the
waterline The waterline is the line where the Hull (watercraft), hull of a ship meets the surface of the water. Specifically, it is also the name of a special marking, also known as an international load line, Plimsoll line and water line (positioned Amid ...
, giving less resistance and more speed. With a greater payload, resistance is greater and speed lower, but the hull's outward bend provides smoother performance in waves. As such, the inverted bell shape is a popular form used with planing hulls.


Chined and hard-chined hulls

A chined hull does not have a smooth rounded lower cross-section. Instead, its contours are interrupted by hard angles where components of the hull meet underwater. The sharper the intersection ( the more acute the angle ), the “harder“ the chine. The Cajun "pirogue" is an example of a craft with hard chines. Benefits of this type of hull include potentially lower production cost and a (usually) fairly flat bottom, making the boat faster at planing. A chined hull resists rolling ( in smooth water ) more than does a smooth bilge hull ( the chine creates turbulence/drag, as it moves through the water, the smooth-bilge just slips down or up ). In rough seas, this can make the boat roll more, as the waves' water drags 1st down, then up, on a chine: round-bilge boats are more seakindly in waves, as a result. Chined hulls may have one of three shapes: * Flat-bottom chined hulls * Multi-chined hulls * V-bottom chined hulls. Sometimes called hard chine. Each of these chine hulls has its own unique characteristics and use. The flat-bottom hull has high initial stability but high drag. To counter the high drag, hull forms are narrow and sometimes severely tapered at bow and stern. This leads to poor stability when heeled in a sailboat. This is often countered by using heavy interior ballast on sailing versions. They are best suited to sheltered inshore waters. Early racing power boats were fine forward and flat aft. This produced maximum lift and a smooth, fast ride in flat water, but this hull form is easily unsettled in waves. The multi-chine hull approximates a curved hull form. It has less drag than a flat-bottom boat. Multi chines are more complex to build but produce a more seaworthy hull form. They are usually displacement hulls. V or arc-bottom chine boats have a Vshape between 6and 23degrees. This is called the deadrise angle. The flatter shape of a 6-degree hull will plane with less wind or a lower-horsepower engine but will pound more in waves. The deep Vform (between 18and 23degrees) is only suited to high-powered planing boats. They require more powerful engines to lift the boat onto the plane but give a faster, smoother ride in waves. Displacement chined hulls have more wetted surface area, hence more drag, than an equivalent round-hull form, for any given displacement.


Smooth curve hulls

Smooth curve hulls are hulls that use, just like the curved hulls, a centreboard, or an attached keel. Semi round bilge hulls are somewhat less round. The advantage of the semi-round is that it is a nice middle between the S-bottom and chined hull. Typical examples of a semi-round bilge hull can be found in the
Centaur A centaur ( ; grc, κένταυρος, kéntauros; ), or occasionally hippocentaur, is a creature from Greek mythology Greek mythology is the body of myth Myth is a folklore genre Folklore is the expressive body of culture share ...
and
Laser A laser is a device that emits light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that is visual perception, perceived by the human eye. Visible light is usually defined as h ...
cruising
dinghies A dinghy is a type of small boat A boat is a watercraft Watercraft, also known as water vessels or waterborne vessels, are vehicles used in water, including boats, ship A ship is a large watercraft that travels the world's ocea ...
. S-bottom hulls are hulls shaped like an ''s''. In the s-bottom, the hull runs smooth to the keel, as there are no sharp corners on the exterior. Boats with this hull have a fixed keel, or a ''kielmidzwaard'' (literally "keel with sword"). This is a short fixed keel, with a swing keel inside. Examples of cruising dinghies that use this s-shape are the
Yngling The Ynglings were a semi-historical dynasty of kings, first in Sweden and later in Norway, primarily attested through the poem ''Ynglingatal''. The dynasty also appears as Scylfings (Old Norse ''Skilfingar'') in ''Beowulf''. When ''Beowulf'' and ...

Yngling
and Randmeer.


Appendages

* Control devices such as a
rudder A rudder is a primary control surface used to steer a ship A ship is a large watercraft Watercraft, also known as water vessels or waterborne vessels, are vehicles A vehicle (from la, vehiculum) is a machine A machine is any ...

rudder
,
trim tabs Trim tabs are small surfaces connected to the trailing edge of a larger Flight control surfaces, control surface on a boat or aircraft, used to control the trim of the controls, i.e. to counteract hydro- or aerodynamic forces and stabilise the ...
or stabilizing fins may be fitted. * A
keel The keel is the bottom-most longitudinal structural element on a vessel. On some sailboats, it may have a hydrodynamic In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ...

keel
may be fitted on a hull to increase the transverse stability, directional stability or to create lift. * A forward protrusion below the waterline is called a
bulbous bow A bulbous bow is a protruding bulb at the bow (ship), bow (or front) of a ship just below the waterline. The bulb modifies the way the water flows around the Hull (watercraft), hull, reducing Drag (physics), drag and thus increasing speed, range, ...

bulbous bow
. These are fitted on some hulls to reduce the
wave making resistance Wave-making resistance is a form of drag that affects surface watercraft, such as boats and ships, and reflects the energy required to push the water out of the way of the hull. This energy goes into creating the wave. Physics of 1.34 For small ...
drag Drag or The Drag may refer to: Places * Drag, Norway, a village in Tysfjord municipality, Nordland, Norway * ''Drág'', the Hungarian name for Dragu Commune in Sălaj County, Romania * Drag (Austin, Texas), the portion of Guadalupe Street adja ...
and thereby increase
fuel efficiency Fuel efficiency is a form of thermal efficiency In thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and the physical properties o ...
. Bulbs fitted at the stern are less common but accomplish a similar task.


Terms

* Baseline is a level reference line from which vertical distances are measured. *
Bow Bow often refers to: * Bow and arrow The bow and arrow is a ranged weapon A ranged weapon is any weapon A weapon, arm or armament is any implement or device that can be used with the intent to inflict physical damage or harm. Weapons ar ...
is the front part of the hull. *
Amidships This is a glossary of nautical terms; some remain current, while many date from the 17th to 19th centuries. See also Wiktionary's nautical terms, :Nautical terms, and Nautical metaphors in English. See the Further reading section for additional ...

Amidships
is the middle portion of the vessel in the fore and aft direction. *
Port A port is a maritime Maritime may refer to: Geography * Maritime Alps, a mountain range in the southwestern part of the Alps * Maritime Region, a region in Togo * Maritime Southeast Asia * The Maritimes, the Canadian provinces of ...
is the left side of the vessel when facing the bow from on board. *
Starboard Port and starboard are nautical Seamanship is the art Art is a diverse range of (products of) human activities Humans (''Homo sapiens'') are the most populous and widespread species of primates, characterized by bipedality, oppos ...
is the right side of the vessel when facing the bow from on board. *
Stern The stern is the back or aft Aft :''For the acronym, see AFT (disambiguation).'' Aft, in naval A navy, naval force, or maritime force is the branch of a Nation's armed forces A military, also known collectively as armed forces, ...

Stern
is the rear part of the hull. *
Waterline The waterline is the line where the hull of a ship meets the surface of the water Water (chemical formula H2O) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substa ...
is an imaginary line circumscribing the hull that matches the surface of the water when the hull is not moving.


Metrics

Hull forms are defined as follows: Block measures that define the principal dimensions. They are: *
Beam Beam may refer to: Streams of particles or energy *Light beam, or beam of light, a directional projection of light energy **Laser beam *Particle beam, a stream of charged or neutral particles **Charged particle beam, a spatially localized group ...
or breadth (B) is the width of the hull. (ex: BWL is the maximum beam at the waterline) *
Draft Draft, The Draft, or Draught may refer to: Watercraft dimensions * Draft (hull), the distance from waterline to keel of a vessel * Draft (sail), degree of curvature in a sail * Air draft, distance from waterline to the highest point on a vessel ...
(d) or (T) is the vertical distance from the bottom of the keel to the
waterline The waterline is the line where the Hull (watercraft), hull of a ship meets the surface of the water. Specifically, it is also the name of a special marking, also known as an international load line, Plimsoll line and water line (positioned Amid ...
. * Freeboard (FB) is depth plus the height of the keel structure minus draft. *
Length at the waterline Length is a measure of distance. In the International System of Quantities, length is a quantity with Dimension (physical quantity), dimension distance. In most Measurement system, systems of measurement a Base unit (measurement), base unit fo ...
(LWL) is the length from the forwardmost point of the waterline measured in profile to the stern-most point of the waterline. *
Length between perpendiculars Length between perpendiculars (often abbreviated as p/p, p.p., pp, LPP, LBP or Length BPP) is the length of a ship A ship is a large watercraft Watercraft, also known as water vessels or waterborne vessels, are vehicles A vehicle (fro ...
(LBP or LPP) is the length of the summer load waterline from the
stern The stern is the back or aft Aft :''For the acronym, see AFT (disambiguation).'' Aft, in naval A navy, naval force, or maritime force is the branch of a Nation's armed forces A military, also known collectively as armed forces, ...

stern
post to the point where it crosses the
stem Stem or STEM may refer to: Biology * Plant stem, the aboveground structures that have vascular tissue and that support leaves and flowers ** Stipe (botany), a stalk that supports some other structure ** Stipe (mycology), the stem supporting the c ...
. (see also p/p) *
Length overall __NOTOC__ Length overall (LOA, o/a, o.a. or oa) is the maximum length of a vessel's hull Hull may refer to: Structures * Chassis, of an armored fighting vehicle * Fuselage, of an aircraft * Hull (botany), the outer covering of seeds * Hull ( ...
(LOA) is the extreme length from one end to the other. * Moulded depth (D) is the vertical distance measured from the top of the keel to the underside of the upper deck at side., Annex 1, ''Regulations for determining gross and net tonnages of ships'', Reg. 2(2)(a). In ships with rounded
gunwale The gunwale () is the top edge of the Hull (watercraft), hull of a ship or boat. Originally the structure was the "gun wale" on a sailing warship, a horizontal reinforcing band added at and above the level of a gun deck to offset the stresses c ...
s, the upper measurement point is take to the point at which the planes of the deck and side plating intersect. ''Id.'', Reg. 2(2)(b). Ships with stepped decks are measured to a line parallel with the upper part. ''Id.'', Reg. 2(2)(c).
Form derivatives that are calculated from the shape and the block measures. They are: *
Displacement Displacement may refer to: Physical sciences Mathematics and Physics *Displacement (geometry), is the difference between the final and initial position of a point trajectory (for instance, the center of mass of a moving object). The actual path c ...
(Δ) is the weight of water equivalent to the immersed volume of the hull. * Longitudinal centre of buoyancy (LCB) is the longitudinal distance from a point of reference (often midships) to the centre of the displaced volume of water when the hull is not moving. Note that the longitudinal centre of gravity or centre of the weight of the vessel must align with the LCB when the hull is in equilibrium. * Longitudinal centre of flotation (LCF) is the longitudinal distance from a point of reference (often midships) to the centre of the area of waterplane when the hull is not moving. This can be visualized as being the area defined by the water's surface and the hull. * Vertical centre of buoyancy (VCB) is the vertical distance from a point of reference (often the baseline) to the centre of the displaced volume of water when the hull is not moving. * Volume (V or ∇) is the volume of water displaced by the hull. Coefficients help compare hull forms as well: *1) Block coefficient (Cb) is the volume (V) divided by the LWLx BWL x TWL. If you draw a box around the submerged part of the ship, it is the ratio of the box volume occupied by the ship. It gives a sense of how much of the block defined by the LWL, beam (B) & draft (T) is filled by the hull. Full forms such as oil tankers will have a high Cb where fine shapes such as sailboats will have a low Cb. C_b = \frac *2) Midship coefficient (Cm or Cx) is the cross-sectional area (Ax) of the slice at midships (or at the largest section for Cx) divided by beam x draft. It displays the ratio of the largest underwater section of the hull to a rectangle of the same overall width and depth as the underwater section of the hull. This defines the fullness of the underbody. A low Cm indicates a cut-away mid-section and a high Cm indicates a boxy section shape. Sailboats have a cut-away mid-section with low Cx whereas cargo vessels have a boxy section with high Cx to help increase the Cb. C_m = \frac *3) Prismatic coefficient (Cp) is the volume (V) divided by LWLx Ax. It displays the ratio of the immersed volume of the hull to a volume of a prism with equal length to the ship and cross-sectional area equal to the largest underwater section of the hull (midship section). This is used to evaluate the distribution of the volume of the underbody. A low or fine Cp indicates a full mid-section and fine ends, a high or full Cp indicates a boat with fuller ends. Planing hulls and other highspeed hulls tend towards a higher Cp. Efficient displacement hulls travelling at a low
Froude number In continuum mechanics Continuum mechanics is a branch of mechanics that deals with the mechanical behavior of materials modeled as a continuous mass rather than as point particle, discrete particles. The French mathematician Augustin-Louis Cau ...
will tend to have a low Cp. C_p = \frac *4) Waterplane coefficient (Cw) is the waterplane area divided by LWL x BWL. The waterplane coefficient expresses the fullness of the waterplane, or the ratio of the waterplane area to a rectangle of the same length and width. A low Cw figure indicates fine ends and a high Cw figure indicates fuller ends. High Cw improves stability as well as handling behavior in rough conditions. C_w = \frac * Note: C_b =


Computer-aided design

Use of
computer-aided design Computer-aided design (CAD) is the use of computers (or ) to aid in the creation, modification, analysis, or optimization of a design. This software is used to increase the productivity of the designer, improve the quality of design, improve com ...
has superseded paper-based methods of ship design that relied on manual calculations and lines drawing. Since the early 1990s, a variety of commercial and freeware software packages specialized for naval architecture have been developed that provide 3D drafting capabilities combined with calculation modules for hydrostatics and hydrodynamics. These may be referred to as geometric modeling systems for naval architecture.


See also

* * * * * * * * * *
Hull classification symbol The United States Navy ), (unofficial)."''Non sibi sed patriae''" ( en, "Not for self but for country") (unofficial). , colors = Blue and gold  , colors_label = Colors , march ...
* * * * * * * * * *


Notes


References

* * {{Authority control
Shipbuilding Marine engineering Production and manufacturing by product Ships Vehicle technology Heavy industry {{CatAutoTOC ...
Watercraft components Naval architecture Structural system Structural engineering Ship measurements Egyptian inventions