Hull (watercraft)
A hull is the watertight body of a ship or boat. Above the hull is the superstructure and/or deckhouse, where present. The line where the hull meets the water surface is called the waterline.
The structure of the hull varies depending on the vessel type. In a typical modern steel ship, the structure consists of watertight and nontight decks, major transverse and longitudinal members called watertight (and also sometimes nontight) bulkheads, 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 contextthe 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. 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 fiberreinforced skins over a lightweight but reasonably rigid core of foam, balsa wood, impregnated paper honeycomb or other material.
Contents
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 needlesharp surface of revolution in the case of a racing multihull sailboat. The shape is chosen to strike a balance between cost, hydrostatic considerations (load carrying and stability) and hydrodynamics (speed, powering, and dynamic motion behavior). The frame or body of a ship, exclusive of masts, engines, or superstructure.
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 softchined. Examples are the round bilge, semiround bilge and sbottom hull.
 defined as smooth curves
 Chined and Hardchined. Examples are the flatbottom (chined), vbottom and multibottom 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. 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.
 Semidisplacement, or semiplaning
 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 flatbottomed, sometimes Vbottomed and sometimes roundbilged. 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), Hull speed).
Most used hull forms
At present, the most widely used form is the round bilge hull.^{[1]}
The inverted bell shape of the hull, with smaller payload the waterline crosssection 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.
Hull forms
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 semiround is that it is a nice middle between the Sbottom and chined hull. Typical examples of a semiround bilge hull can be found in the Centaur and Laser cruising dinghies.
Sbottom hulls are hulls shaped like an s. In the sbottom, 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 keel which still sticks a sword. Examples of cruising dinghies that use this sshape are the yngling and Randmeer.
Chined and hardchined 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 homemade constructed boats are chined hull boats. Benefits of this type of boating activity is the low production cost and the (usually) fairly flat bottom, making the boat faster at planing. Chined hulls can also make use of a sword or attached keel.
Chined hulls can be divised up into 3 shapes:
 Vbottom chined hulls
 flatbott chined hulls
 and multichined hulls.
Appendages
 A protrusion below the waterline forward is called a bulbous bow and is fitted on some hulls to reduce the wave making resistance drag and thus increase fuel efficiency. Bulbs fitted at the stern are less common but accomplish a similar task. (see also: Naval architecture)
 A keel may be fitted on a hull to increase the transverse stability, directional stability or to create lift.
Terms
Bow is the frontmost part of the hull
Stern is the rearmost 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 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 halfway from the forwardmost point on the waterline to the rearmost 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 sternmost point of the waterline.
 Length Between Perpendiculars (LBP or LPP) is the length of the summer load waterline from the stern post to the point where it crosses the stem. (see also p/p)
 Beam 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.^{[2]}
 Draft (d) or (T) is the vertical distance from the bottom of the hull to the waterline.
 Freeboard (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 (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^{[3]} 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}.
 <math>
 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}.
C_b = \frac {V}{L_{pp} \cdot B \cdot T} </math>
 2) Midship Coefficient (C_{m} or C_{x}) is the crosssectional 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 cutaway midsection and a high Cm indicates a boxy section shape. Sailboats have a cutaway midsection with low C_{x} whereas cargo vessels have a boxy section with high C_{x} to help increase the C_{b}.
 <math>
 2) Midship Coefficient (C_{m} or C_{x}) is the crosssectional 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 cutaway midsection and a high Cm indicates a boxy section shape. Sailboats have a cutaway midsection with low C_{x} whereas cargo vessels have a boxy section with high C_{x} to help increase the C_{b}.
C_m = \frac {A_m}{B \cdot T} </math>
 3) Prismatic Coefficient (C_{p}) is the volume (V) divided by L_{pp} x A_{x}. It displays the ratio of the underwater volume of the hull to a rectangular block of the same overall length as the underbody and with crosssectional area equal to the largest underwater section of the hull. This is used to evaluate the distribution of the volume of the underbody. A low Cp indicates a full midsection and fine ends, a high 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 will tend to have a low C_{p}.
 <math>
 3) Prismatic Coefficient (C_{p}) is the volume (V) divided by L_{pp} x A_{x}. It displays the ratio of the underwater volume of the hull to a rectangular block of the same overall length as the underbody and with crosssectional area equal to the largest underwater section of the hull. This is used to evaluate the distribution of the volume of the underbody. A low Cp indicates a full midsection and fine ends, a high 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 will tend to have a low C_{p}.
C_p = \frac {V}{L_{pp} \cdot A_m}
</math>
 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.
 <math>
C_w = \frac {A_w}{L_{pp} \cdot B} </math>
 Note:
 <math>
 Note:
C_b = {C_{p} \cdot C_{m} } </math>
History
Rafts have a hull of sorts, however, hulls of the earliest design are thought to have each consisted of a hollowed out tree bole: in effect the first canoes. Hull form then proceeded to the Coracle shape and on to more sophisticated forms as the science of Naval architecture advanced.
Notes
 ↑ [Zeilen:Van beginner tot gevorderde by Karel Heijnen]
 ↑ "International Convention on Tonnage Measurement of Ships, 1969". International Conventions. Admiralty and Maritime Law Guide. 1969623. http://www.admiraltylawguide.com/conven/tonnage1969.html. Retrieved 20071027., Annex 1, Regulations for determining gross and net tonnages of ships, Reg. 2(2)(a). In ships with rounded gunwales, 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).
 ↑ Rawson, E.C.; Tupper (1976). Basic Ship Theory Vol 1 (2nd ed.). Longman. pp. 12–14. ISBN 058244523X
References
 Hull (watercraft)
]] Hayler, William B.; Keever, John M. (2003). American Merchant Seaman's Manual. Cornell Maritime Pr. ISBN 0870335499.
 Turpin, Edward A.; McEwen, William A. (1980). Merchant Marine Officers' Handbook (4th ed.). Centreville, MD: Cornell Maritime Press. ISBN 087038056X.
See also


ms:Badan kapal
da:Skrog
de:Schiffsrumpf
et:Laevakere
el:Ύφαλα
es:Casco (náutica)
fr:Coque (bateau)
id:Lambung kapal
it:Scafo
lv:Korpuss (kuģa)
nl:Scheepsromp
ja:船体
no:Skrog (skip)
pl:Kadłub statku wodnego
pt:Casco (navio)
ro:Cocă (navigaţie)
ru:Корпус корабля
scn:Carina
sv:Skrov