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A hull is the watertight body of a ship, boat, or flying 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.
A multihull is a boat or ship with more than one hull, whereas a vessel with a single hull is a monohull. The most common multihulls are catamarans, and trimarans. There are other types, with four or more hulls, but such examples are very rare and tend to be specialised for particular functions.
A canoe is a lightweight narrow water vessel, typically pointed at both ends and open on top, propelled by one or more seated or kneeling paddlers facing the direction of travel and using paddles. In British English, the term canoe can also refer to a kayak, while canoes are then called Canadian or open canoes to distinguish them from kayaks. However, for official competition purposes, the American distinction between a kayak and a canoe is almost always adopted.
A jetboat is a boat propelled by a jet of water ejected from the back of the craft. Unlike a powerboat or motorboat that uses an external propeller in the water below or behind the boat, a jetboat draws the water from under the boat through an intake and into a pump-jet inside the boat, before expelling it through a nozzle at the stern.
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.
Carvel built or carvel planking is a method of boat building in which hull planks are laid edge to edge and fastened to a robust frame, thereby forming a smooth surface. Traditionally the planks are neither attached to, nor slotted into, each other, having only a caulking sealant between the planks to keep water out. Modern carvel builders may attach the planks to each other with glues and fixings. It is a "frame first" method of hull construction, where the shape is determined by the framework onto which the planks are fixed. This is in contrast to "plank first" or "shell first" methods, where the outer skin of the hull is made and then reinforced by the insertion of timbers that are fitted to that shape. The most common modern "plank first" method is clinker construction; in the classical period "plank first" involved joining the edges of planks with mortise and tenon joints within the thickness of the timbers, superficially giving the smooth-hull appearance of carvel construction, but achieved by entirely different means.
Capsizing or keeling over occurs when a boat or ship is rolled on its side or further by wave action, instability or wind force beyond the angle of positive static stability or it is upside down in the water. The act of recovering a vessel from a capsize is called righting. Capsize may result from broaching, knockdown, loss of stability due to cargo shifting or flooding, or in high speed boats, from turning too fast.
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 waterline is the line where the 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, that indicates the draft of the ship and the legal limit to which a ship may be loaded for specific water types and temperatures in order to safely maintain buoyancy, particularly with regard to the hazard of waves that may arise. Varying water temperatures will affect a ship's draft, because warm water is less dense than cold water, providing less buoyancy. In the same way, fresh water is less dense than salinated or seawater with a similar lessening effect upon buoyancy.
Ballast is used in ships to provide moment to resist the lateral forces on the hull. Insufficiently ballasted boats tend to tip or heel excessively in high winds. Too much heel may result in the vessel capsizing. If a sailing vessel needs to voyage without cargo, then ballast of little or no value will be loaded to keep the vessel upright. Some or all of this ballast will then be discarded when cargo is loaded.
A stealth ship is a ship that employs stealth technology construction techniques in an effort to make it harder to detect by one or more of radar, visual, sonar, and infrared methods.
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. The aft end of the boat is the stern.
A vessel's length at the waterline is the length of a ship or boat at the level where it sits in the water. The LWL will be shorter than the length of the boat overall as most boats have bows and stern protrusions that make the LOA greater than the LWL. As a ship becomes more loaded, it will sit lower in the water and its ambient waterline length may change; but the registered L.W.L it is measured from a default load condition.
Tumblehome is a term describing a hull which grows narrower above the waterline than its beam. The opposite of tumblehome is flare.
The draft or draught of a ship's hull is the vertical distance between the waterline and the bottom of the hull (keel). The draught of the vessel is the maximum depth of any part of the vessel, including appendages such as rudders, propellers and drop keels if deployed. Draft determines the minimum depth of water a ship or boat can safely navigate. The related term air draft is the maximum height of any part of the vessel above the water.
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 topsides on a boat, ship, watercraft, or floating production storage and offloading (FPSO) vessel, is that part of the hull between the waterline and the deck. It includes the visible parts of the bow, stern, sheer, and, if present, tumblehome.
The Hatsuharu-class destroyers were a class of Imperial Japanese Navy destroyers in the service before and during World War II. The final two vessels in the class, completed after modifications to the design, are sometimes considered a separate "Ariake class".
Ship measurements consist of a multitude of terms and definitions specifically related to ships and measuring or defining their characteristics.
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