A hull is the watertight body of a ship

Ship

Since the end of the age of sail a ship has been any large buoyant marine vessel. Ships are generally distinguished from boats based on size and cargo or passenger capacity. Ships are used on lakes, seas, and rivers for a variety of activities, such as the transport of people or goods, fishing,...

 or boat

Boat

A boat is a watercraft of any size designed to float or plane, to provide passage across water. Usually this water will be inland or in protected coastal areas. However, boats such as the whaleboat were designed to be operated from a ship in an offshore environment. In naval terms, a boat is a...

. Above the hull is the superstructure

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...

 and/or deckhouse, where present. The line where the hull meets the water surface is called the waterline

Waterline

The term "waterline" generally refers to the line where the hull of a ship meets the water surface. It is also the name of a special marking, also known as the national Load Line or Plimsoll Line, to be positioned amidships, that indicates the draft of the ship and the legal limit to which a ship...

.

The structure of the hull varies depending on the vessel type. In a typical modern steel ship, the structure consists of watertight and non-tight decks, major transverse and longitudinal members called watertight (and also sometimes non-tight) bulkhead

Bulkhead

Bulkhead may refer to:* Bulkhead, a compartment of a building for preventing spread of fires, see Compartmentalization * Bulkhead , a retaining wall used as a form of coastal management, akin to a seawall, or as a structural device such as a bulkhead partition* Bulkhead , a wall within the hull of...

s, intermediate members such as girders, stringers and webs, and minor members called ordinary transverse frames, frames, or longitudinals, depending on the structural arrangement. The uppermost continuous deck may be called the "upper deck," "weather deck," "spar deck," "main deck" or simply "deck." The particular name given depends on the context—the type of ship or boat, the arrangement, or even the area where it sails. Not all hulls are decked (for instance a dinghy).

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

Keel

In boats and ships, keel can refer to either of two parts: a structural element, or a hydrodynamic element. These parts overlap. As the laying down of the keel is the initial step in construction of a ship, in British and American shipbuilding traditions the construction is dated from this event...

.
In fiberglass or composite hulls, the structure may resemble wooden or steel vessels to some extent, or be of a monocoque 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.

General features

The shape of the hull is entirely 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) and hydrodynamics (speed, power requirements, and motion and behavior in a seaway).

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:

• Moulded, round bilged or soft-chined
  Chine (boating)
  A chine in boating refers to a sharp angle in the hull, as compared to the rounded bottoms of most traditional boat hulls. The term hard chine indicates an angle with little rounding, where a soft chine would be more rounded, but still involve the meeting of distinct planes. Chine log...
  
  . Examples are the round bilge, semi-round bilge and s-bottom hull.

defined as smooth curves

• Chined and Hard-chined. Examples are the flat-bottom (chined), v-bottom and multi-bottom hull (hard chined).

have at least one pronounced knuckle throughout all or most of their length

Categorisation

After this they can be categorized as:

• Displacement

the hull is supported exclusively or predominantly by buoyancy

Buoyancy

In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...

. They travel through the water at a limited rate which is defined by the waterline length. They are often heavier than planing types, though not always.

• Semi-displacement, or semi-planing

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

• Planing

the planing hull form is configured to develop positive dynamic pressure so that its draft decreases with increasing speed. The dynamic lift reduces the wetted surface and therefore also the drag. They are sometimes flat-bottomed, sometimes V-bottomed and sometimes 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. (see: Planing (sailing)

Planing (sailing)

Planing is the mode of operation for a waterborne craft in which its weight is predominantly supported by hydrodynamic lift, rather than hydrostatic lift .-History:...

, Hull speed

Hull speed

Hull speed, sometimes referred to as displacement speed, is the speed of a boat at which the bow and stern waves interfere constructively, creating relatively large waves, and thus a relatively large value of wave drag...

).

Most used hull forms

At present, the most widely used form is the round bilge hull.

The inverted bell

Inverted bell

The inverted bell is a metaphorical name for geometric shape that resembles a bell upside down.In architecture, the term is applied, e.g., to describe the shape of the capitals of Corinthian columns....

 shape of the hull, with smaller payload the waterline

Waterline

The term "waterline" generally refers to the line where the hull of a ship meets the water surface. It is also the name of a special marking, also known as the national Load Line or Plimsoll Line, to be positioned amidships, that indicates the draft of the ship and the legal limit to which a ship...

 cross-section is less, hence the resistance is less and the speed is higher. With higher payload the outward bend provides smoother performance in waves. As such, the inverted bell shape is a popular form used with planing hulls.

Smooth curve hulls

Smooth curve hulls are hulls which use, just like the curved hulls, a sword 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

Centaur

In Greek mythology, a centaur or hippocentaur is a member of a composite race of creatures, part human and part horse...

 and Laser cruising dinghies.
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 in the fuselage. Boats with this hull have a fixed keel, or a kielmidzwaard. This is a short fixed keel, with a swing keel inside. Examples of cruising dinghies that use this s-shape are the yngling

Yngling (keelboat)

thumbA Yngling is a sailing boat which the International Yngling Association call an "agreeable cross between a planing dinghy and a keelboat." It can be regarded as a smaller version of the Soling although there are differences in sailing characteristics, proportion, and tuning requirements,...

 and Randmeer.

Chined and hard-chined hulls

A chined hull consists of straight plates, which are set at an angle to each other. The chined hull is the most simple hull shape because it works with only straight planks. These boards are often bent lengthwise. Most home-made constructed boats are chined hull boats. The Cajun "pirogue" is an example of a craft with hard chines. Benefits of this type of boating activity is the low production cost and the (usually) fairly flat bottom, making the boat faster at planing

Planing (sailing)

Planing is the mode of operation for a waterborne craft in which its weight is predominantly supported by hydrodynamic lift, rather than hydrostatic lift .-History:...

. Chined hulls can also make use of a daggerboard or attached keel.

Chined hulls can be divided up into 3 shapes:

• V-bottom chined hulls
• Flat-bottom chined hulls
• Multi-chined hulls.

Appendages

• A protrusion below the waterline forward is called a bulbous bow
  Bulbous bow
  A bulbous bow is a protruding bulb at the bow of a ship just below the waterline. The bulb modifies the way the water flows around the hull, reducing drag and thus increasing speed, range, fuel efficiency, and stability...
  
   and is fitted on some hulls to reduce the wave making resistance
  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 wake.-Physics:...
  
   drag
  Drag (physics)
  In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...
  
   and thus increase fuel efficiency. Bulbs fitted at the stern are less common but accomplish a similar task. (see also: Naval architecture
  Naval architecture
  Naval architecture is an engineering discipline dealing with the design, construction, maintenance and operation of marine vessels and structures. Naval architecture involves basic and applied research, design, development, design evaluation and calculations during all stages of the life of a...
  
  )

• A keel
  Keel
  In boats and ships, keel can refer to either of two parts: a structural element, or a hydrodynamic element. These parts overlap. As the laying down of the keel is the initial step in construction of a ship, in British and American shipbuilding traditions the construction is dated from this event...
  
   may be fitted on a hull to increase the transverse stability, directional stability or to create lift.

• Control devices such as a rudder
  Rudder
  A rudder is a device used to steer a ship, boat, submarine, hovercraft, aircraft or other conveyance that moves through a medium . On an aircraft the rudder is used primarily to counter adverse yaw and p-factor and is not the primary control used to turn the airplane...
  
  , trim tabs or stabilizing fins may be fitted.

Terms

Bow

Bow (ship)

The bow is a nautical term that refers to the forward part of the hull of a ship or boat, the point that is most forward when the vessel is underway. Both of the adjectives fore and forward mean towards the bow...

is the frontmost part of the hull

Stern

Stern

The stern is the rear or aft-most part of a ship or boat, technically defined as the area built up over the sternpost, extending upwards from the counter rail to the taffrail. The stern lies opposite of the bow, the foremost part of a ship. Originally, the term only referred to the aft port section...

is the rear-most part of the hull

Port is the left side of the boat when facing the Bow

Starboard is the right side of the boat when facing the Bow

Waterline

Waterline

The term "waterline" generally refers to the line where the hull of a ship meets the water surface. It is also the name of a special marking, also known as the national Load Line or Plimsoll Line, to be positioned amidships, that indicates the draft of the ship and the legal limit to which a ship...

is an imaginary line circumscribing the hull that matches the surface of the water when the hull is not moving.

Midships is the midpoint of the LWL (see below).
It is half-way from the forwardmost point on the waterline to the rear-most point on the waterline.

Baseline an imaginary reference line used to measure vertical distances from. It is usually located at the bottom of the hull.

Metrics

Hull forms are defined as follows:

• Block Measures that define the principal dimensions. They are:

• Length overall (LOA) is the extreme length from one end to the other.
• Length at the waterline (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 (LBP or LPP) is the length of the summer load waterline from the stern
  Stern
  The stern is the rear or aft-most part of a ship or boat, technically defined as the area built up over the sternpost, extending upwards from the counter rail to the taffrail. The stern lies opposite of the bow, the foremost part of a ship. Originally, the term only referred to the aft port section...
  
   post to the point where it crosses the stem. (see also p/p
  P/p
  Length between perpendiculars, often abbreviated as p/p, p.p., pp, LPP, LBP or Length BPP is a term describing the length of a ship. LBP refers to the length of a vessel along the waterline from the forward surface of the stem, or main bow perpendicular member, to the after surface of the...
  
  )
• Beam
  Beam (nautical)
  The beam of a ship is its width at the widest point. Generally speaking, the wider the beam of a ship , the more initial stability it has, at expense of reserve stability in the event of a capsize, where more energy is required to right the vessel from its inverted position...
  
   or breadth (B) is the width of the hull. (ex: BWL is the maximum beam at the waterline)
• Depth or moulded depth (D) is the vertical distance measured from the top of the keel to the underside of the upper deck at side.
• Draft
  Draft (hull)
  The draft of a ship's hull is the vertical distance between the waterline and the bottom of the hull , with the thickness of the hull included; in the case of not being included the draft outline would be obtained...
  
   (d) or (T) is the vertical distance from the bottom of the hull to the waterline
  Waterline
  The term "waterline" generally refers to the line where the hull of a ship meets the water surface. It is also the name of a special marking, also known as the national Load Line or Plimsoll Line, to be positioned amidships, that indicates the draft of the ship and the legal limit to which a ship...
  
  .
• Freeboard
  Freeboard (nautical)
  In sailing and boating, freeboardmeans the distance from the waterline to the upper deck level, measured at the lowest point of sheer where water can enter the boat or ship...
  
   (FB) is the difference between Depth and draft.
  • Form Derivatives that are calculated from the shape and the Block Measures. They are:
• Volume (V or ∇) is the volume of water displaced by the hull.
• Displacement
  Displacement (fluid)
  In fluid mechanics, displacement occurs when an object is immersed in a fluid, pushing it out of the way and taking its place. The volume of the fluid displaced can then be measured, as in the illustration, and from this the volume of the immersed object can be deduced .An object that sinks...
  
   (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.
• 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.
• Longitudinal Centre of Floatation (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.

• Coefficients help compare hull forms as well:

1) Block Coefficient (C_b) is the volume (V) divided by the LWL x BWL x T. 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 L_pp, beam (B) & draft (T) is filled by the hull. Full forms such as oil tankers will have a high C_b where fine shapes such as sailboats will have a low C_b.

2) Midship Coefficient (C_m or C_x) is the cross-sectional area (A_x) of the slice at Midships (or at the largest section for C_x) 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 C_x whereas cargo vessels have a boxy section with high C_x to help increase the C_b.

3) Prismatic Coefficient (C_p) is the volume (V) divided by L_pp x A_x. 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 C_p. Efficient displacement hulls travelling at a low Froude number

Froude number

The Froude number is a dimensionless number defined as the ratio of a characteristic velocity to a gravitational wave velocity. It may equivalently be defined as the ratio of a body's inertia to gravitational forces. In fluid mechanics, the Froude number is used to determine the resistance of an...

 will tend to have a low C_p.

4) Waterplane Coefficient (C_w) is the waterplane area divided by L_pp x B. 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 C_w figure indicates fine ends and a high C_w figure indicates fuller ends. High C_w improves stability as well as handling behavior in rough conditions.

Note:

History

Rafts have a hull of sorts, however, hulls of the earliest design

Stone Age

The Stone Age is a broad prehistoric period, lasting about 2.5 million years , during which humans and their predecessor species in the genus Homo, as well as the earlier partly contemporary genera Australopithecus and Paranthropus, widely used exclusively stone as their hard material in the...

 are thought to have each consisted of a hollowed out tree

Tree

A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3 m to...

 bole: in effect the first canoe

Canoe

A canoe or Canadian canoe is a small narrow boat, typically human-powered, though it may also be powered by sails or small electric or gas motors. Canoes are usually pointed at both bow and stern and are normally open on top, but can be decked over A canoe (North American English) or Canadian...

s. Hull form then proceeded to the Coracle

Coracle

The coracle is a small, lightweight boat of the sort traditionally used in Wales but also in parts of Western and South Western England, Ireland , and Scotland ; the word is also used of similar boats found in India, Vietnam, Iraq and Tibet...

 shape and on to more sophisticated forms as the science of Naval architecture

Naval architecture

Naval architecture is an engineering discipline dealing with the design, construction, maintenance and operation of marine vessels and structures. Naval architecture involves basic and applied research, design, development, design evaluation and calculations during all stages of the life of a...

 advanced.

See also

• Anti-fouling paint
• Boat
  Boat
  A boat is a watercraft of any size designed to float or plane, to provide passage across water. Usually this water will be inland or in protected coastal areas. However, boats such as the whaleboat were designed to be operated from a ship in an offshore environment. In naval terms, a boat is a...
  
  
• Cathedral hull
  Cathedral hull
  A cathedral hull is a hull shape used in modern boats, usually power-driven. It can be thought of as a kind of vestigial trimaran in which the center hull has two smaller side hulls which are so close to the main hull that there is no longer any open space. In fact a cathedral hull is a...
  
  
• Double hull
  Double hull
  A double hull is a ship hull design and construction method invented by Leonardo da Vinci where the bottom and sides of the ship have two complete layers of watertight hull surface: one outer layer forming the normal hull of the ship, and a second inner hull which is some distance inboard,...
  
  
• Draft
  Draft (hull)
  The draft of a ship's hull is the vertical distance between the waterline and the bottom of the hull , with the thickness of the hull included; in the case of not being included the draft outline would be obtained...
  
  
• Froude number
  Froude number
  The Froude number is a dimensionless number defined as the ratio of a characteristic velocity to a gravitational wave velocity. It may equivalently be defined as the ratio of a body's inertia to gravitational forces. In fluid mechanics, the Froude number is used to determine the resistance of an...
  
  

• Hull classification symbol
  Hull classification symbol
  The United States Navy, United States Coast Guard, and United States National Oceanic and Atmospheric Administration use hull classification symbols to identify their ship types and each individual ship within each type...
  
  
• Hull speed
  Hull speed
  Hull speed, sometimes referred to as displacement speed, is the speed of a boat at which the bow and stern waves interfere constructively, creating relatively large waves, and thus a relatively large value of wave drag...
  
  
• Monohull
  Monohull
  rightA monohull is a type of boat having only one hull, unlike multihulled boats which can have two or more individual hulls connected to one another.-Fundamental concept:...
  
  
• Multihull
  Multihull
  A multihull is a ship, vessel, craft or boat with more than one hull.-Description:Multihulls include: Proas, which have two differently shaped or sized hulls with lateral symmetry; catamarans, which have two hulls with longitudinal symmetry; and trimarans, which have a main hull in the center and...
  
  
• Naval architecture
  Naval architecture
  Naval architecture is an engineering discipline dealing with the design, construction, maintenance and operation of marine vessels and structures. Naval architecture involves basic and applied research, design, development, design evaluation and calculations during all stages of the life of a...
  
  

• Ship measurements
  Ship measurements
  Ship measurements consist of a multitude of terms and definitions specifically related to ships.-Definitions:Beam - The width of the ship...
  
  
• Shipbuilding
  Shipbuilding
  Shipbuilding is the construction of ships and floating vessels. It normally takes place in a specialized facility known as a shipyard. Shipbuilders, also called shipwrights, follow a specialized occupation that traces its roots to before recorded history.Shipbuilding and ship repairs, both...
  
  
• Submarine
  Submarine
  A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...
  
  
• Submarine hull
  Submarine hull
  The term light hull is used to describe the outer hull of a submarine, which houses the pressure hull, providing hydrodynamically efficient shape, but not holding pressure difference...
  
  
• Lift (force)
  Lift (force)
  A fluid flowing past the surface of a body exerts a surface force on it. Lift is the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is the component of the surface force parallel to the flow direction...
  
  

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