Hull (watercraft)

A hull is the body or frame of a ship or boat. It is a central concept in water vessels. The hull is essentially what keeps the water from entering the boat and acts as the walls and floor of the vessel.

Related Topics:
Ship - Boat - Water - Vessel - Wall - Floor

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Nearly all watercraft, from small boats to the largest ships adhere to one general class of hull shapes that serve the needs of stability and efficient propulsion, featuring

Related Topics:
Boat - Ship

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• horizontal cross-sections that have narrow, usually pointed, fronts (at the bow),
• smooth widening from the bow until roughly the middle (the beam), and often narrowing smoothly but usually significantly to the extreme end (the stern), whose width may range from a large to an insignificant fraction of the beam width), and
• characteristic vertical cross-sections perpendicular to the beam.

Such a cross section will usually feature

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• an open top on a small boat (kayaks being the most familar exceptions), or a level deck (with various superstructures) on large boats or on ships,
• below that level, possibly widening and/or narrowing to some extent, smoothly, down the relatively sharp bend called the "knees",
• below the knees, either having a relatively flat bottom or narrowing smoothly to an angled seam at the center, and
• usually featuring either a keel or retractable centerboard at that centerline, or retractable sideboards roughly vertical and close to the most vertical portion of the hull.

Nevertheless, other general shapes are feasible; the coracle is a relatively extreme example, and many cargo barges, with all cross-sections close to rectangular, are a radical departure from both the coracle and the tapered hulls described above. Large ships have a bulbous bow to reduce effective drag and thus increase fuel efficiency.

Related Topics:
Coracle - Bulbous bow - Drag

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Especially important in hulls constructed from materials that are denser than water, such as steel, the hull traps a volume of air that lowers the overall density of the vessel, providing buoyancy so it floats. Hulls constructed of materials that are less dense than water, such as some types of wood, will float even when full of water, barring sufficient weight of heavier-than-water cargo and superstructure.

Related Topics:
Density - Buoyancy - Wood

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Hulls of the earliest design are thought to have each consisted of a hollowed out tree bole: in effect the first canoes. Hull construction then proceeded to keeled hulls, use of ballast, and on to modern double steel hulls with waterproof sections.

Related Topics:
Earliest design - Tree - Canoe - Ballast - Steel

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In the case of new sailing-ship designs as of 2004, hulls are often made of layers of foam and plastic, forming composite hulls, with a minimum of weight. Variations on the single hull can be found with outriggers, and multihull craft with at least one hull nested inside the outermost one.

Related Topics:
As of 2004 - Plastic - Composite - Outrigger - Multihull

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Hull construction is usually performed in a dry dock or on a slipway.

Related Topics:
Dry dock - Slipway

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Hull (watercraft): See also ►