A wave-piercing boat hull has a very fine bow, with reduced buoyancy in the forward portions. When a wave is encountered, the lack of buoyancy means the hull pierces through the water rather than riding over the top, resulting in a smoother ride than traditional designs, and in diminished mechanical stress on the vessel and crew. It also reduces a boat's wave-making resistance.
A hull is the watertight body of a ship or boat. The hull may open at the top, or it may be fully or partially covered with a deck. Atop the deck may be a deckhouse and other superstructures, such as a funnel, derrick, or mast. The line where the hull meets the water surface is called the waterline.
The bow is the forward part of the hull of a ship or boat, the point that is usually most forward when the vessel is underway. Both of the adjectives fore and forward mean towards the bow. The other end of the boat is the stern.
Buoyancy or upthrust, is an upward force exerted by a fluid that opposes the weight of an 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 bottom of a column of fluid is greater than at the top of the column. Similarly, the pressure at the bottom of an object submerged in a fluid is greater than at the top of the object. The pressure difference results in a net upward force on the object. The magnitude of the force is proportional to the pressure difference, and is equivalent to the weight of the fluid that would otherwise occupy the volume of the object, i.e. the displaced fluid.
Design theory calls for very long thin hulls, so in practice most are multi-hulls such as catamarans and trimarans.
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.
A catamaran is a multi-hulled watercraft featuring two parallel hulls of equal size. It is a geometry-stabilized craft, deriving its stability from its wide beam, rather than from a ballasted keel as with a monohull sailboat. Catamaran is from a Tamil word, kattumaram, which means "logs tied together".
A trimaran is a multihull boat that comprises a main hull and two smaller outrigger hulls which are attached to the main hull with lateral beams. Most trimarans are sailing yachts designed for recreation or racing; others are ferries or warships.
The main current usage areas are passenger ferriesand naval ships.
A naval ship is a military ship used by a navy. Naval ships are differentiated from civilian ships by construction and purpose. Generally, naval ships are damage resilient and armed with weapon systems, though armament on troop transports is light or non-existent.
The Type 22 missile boat is a ship class in the Chinese People's Liberation Army Navy. The first boat was launched in April 2004 by the Hudong-Zhonghua Shipyard at Shanghai. The boats incorporate stealth features and are based on Australian-designed wave-piercing catamaran hulls that are more stable than other fast missile craft in high sea conditions. Approximately 83 of these missile boats are currently in service with three flotillas having been produced over a span of seven years.
The axe bow is a wave-piercing type of a ship's bow, characterised by a vertical stem and a relatively long and narrow entry. The forefoot is deep and the freeboard relatively high, with little flare, so that the bow profile resembles an axe. The bow cuts through the water, and is less affected by passing through waves than a bow with more flare, making this bow type much less susceptible to pitching. Because the deep forefoot does not generally rise above the water level, it is less susceptible to slamming. The axe bow moves the centre of lateral area forwards and the vessel may need considerably more rudder motion to hold its course, and this increases with the wave steepness.
In ship design, an inverted bow is a ship's or large boat's bow whose farthest forward point is not at the top. The result may somewhat resemble a submarine's bow. Inverted bows maximize the length of waterline and hence the hull speed, and have often better hydrodynamic drag than ordinary bows. On the other hand, they have very little reserve buoyancy and tend to dive under waves instead of piercing or going over them.
A multihull is a ship or boat with more than one hull, whereas a vessel with a single hull is a monohull.
A ship is a large watercraft that travels the world's oceans and other sufficiently deep waterways, carrying passengers or goods, or in support of specialized missions, such as defense, research and fishing. Historically, a "ship" was a sailing vessel with at least three square-rigged masts and a full bowsprit. Ships are generally distinguished from boats, based on size, shape, load capacity, and tradition.
A yacht is a watercraft used for pleasure or sports. The term originates from the Dutch word jacht, and was originally referencing light fast sailing vessels that the Dutch Republic navy used to pursue pirates and other transgressors around and into the shallow waters of the Low Countries. The yacht was popularized by Charles II of England as a pleasure or recreation vessel following his restoration in 1660.
A sailboat or sailing boat is a boat propelled partly or entirely by sails smaller than a sailing ship. Distinctions in what constitutes a sailing boat and ship vary by region and maritime culture.
The metacentric height (GM) is a measurement of the initial static stability of a floating body. It is calculated as the distance between the centre of gravity of a ship and its metacentre. A larger metacentric height implies greater initial stability against overturning. The metacentric height also influences the natural period of rolling of a hull, with very large metacentric heights being associated with shorter periods of roll which are uncomfortable for passengers. Hence, a sufficiently, but not excessively, high metacentric height is considered ideal for passenger ships.
Skjold-class corvettes are a class of six large, superfast, stealth missile corvettes in service with the Royal Norwegian Navy. The boats were formerly classed as MTBs but, from 2009, the Royal Norwegian Navy has described them as corvettes (korvett) because their seaworthiness is seen as comparable to corvettes, and because they do not carry torpedoes. They were built at the Umoe Mandal yard. With a maximum speed of 60 knots (110 km/h), the Skjold-class corvettes were the fastest combat ships afloat at the time of their introduction.
A proa, also seen as prau, perahu, and prahu, or prow, is a type of multihull sailboat. It is a vessel consisting of two (usually) unequal length parallel hulls. It is sailed so that one hull is kept to windward, and the other to leeward, so that it needs to "shunt" to reverse direction when tacking. The English term proa usually refers specifically to the South Pacific proa as described in the journals of the British ship HMS Centurion.
A Small Waterplane Area Twin Hull, better known by the acronym SWATH, is a twin-hull ship design that minimizes hull cross section area at the sea's surface. Minimizing the ship's volume near the surface area of the sea, where wave energy is located, maximizes a vessel's stability, even in high seas and at high speeds. The bulk of the displacement necessary to keep the ship afloat is located beneath the waves, where it is less affected by wave action. Wave excitation drops exponentially as depth increases. Placing the majority of a ship's displacement under the waves is similar in concept to creating a ship that rides atop twin submarines.
Capsizing or keeling over occurs when a boat or ship is turned on its side or it is upside down in the water. The act of reversing a capsized vessel is called righting.
Hull speed or displacement speed is the speed at which the wavelength of a vessel's bow wave is equal to the waterline length of the vessel. As boat speed increases from rest, the wavelength of the bow wave increases, and usually its crest-to-trough dimension (height) increases as well. When hull speed is exceeded, a vessel in displacement mode will appear to be climbing up the back of its bow wave.
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. Large ships with bulbous bows generally have twelve to fifteen percent better fuel efficiency than similar vessels without them. A bulbous bow also increases the buoyancy of the forward part and hence reduces the pitching of the ship to a small degree.
The Hobie Cat is a small sailing catamaran manufactured by the Hobie Cat Company. Hobie's line of products ranges from surfboards to catamaran sailboats to kayaks and stand-up paddle boards, though the Hobie Cat Company is most famous around the world for its catamarans. Hobie also designed a very successful monohull, the Hobie 33.
Ship stability is an area of naval architecture and ship design that deals with how a ship behaves at sea, both in still water and in waves, whether intact or damaged. Stability calculations focus on centers of gravity, centers of buoyancy, the metacenters of vessels, and on how these interact.
The pontoon effect refers to the tendency of a vessel whose flotation depends on lateral pontoons to capsize without warning when a lateral force is applied. The effect can be sudden and dramatic because pontoon boats usually cannot rely on the righting effect of a keel . The vessel is stable and self-righting up to the point that the centre of gravity shifts past the centre of buoyancy of the ship and the vessel rapidly capsizes.
Floats are airtight hollow structures, similar to pressure vessels, designed to provide buoyancy in water. Their principal applications are in watercraft hulls and aircraft floats, floating pier and pontoon bridge construction, and marine engineering applications such as salvage.
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