Sailing employs the wind—acting on sails, wingsails or kites—to propel a craft on the surface of the water, on ice (iceboat) or on land over a chosen course, which is often part of a larger plan of navigation.
A sailboat or sailing boat is a boat propelled partly or entirely by sails and is smaller than a sailing ship. Distinctions in what constitutes a sailing boat and ship vary by region and maritime culture.
The keel is the bottom-most longitudinal structural element on a watercraft. On some sailboats, it may have a hydrodynamic and counterbalancing purpose, as well. The laying of the keel is often the initial step in the construction of a ship. In the British and American shipbuilding traditions, this event marks the beginning date of a ship's construction.
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.
A 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.
This glossary of nautical terms is an alphabetical listing of terms and expressions connected with ships, shipping, seamanship and navigation on water. Some remain current, while many date from the 17th to 19th centuries. The word nautical derives from the Latin nauticus, from Greek nautikos, from nautēs: "sailor", from naus: "ship".
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.
A leeboard is a form of pivoting keel used by a sailboat largely and very often in lieu of a fixed keel. Typically mounted in pairs on each side of a hull, leeboards function much like a centreboard, allowing shallow-draft craft to ply waters fixed keel boats cannot. Only the leeward side leeboard is used at any time, as it submerges when the boat heels under the force of the wind.
The winged keel is a sailboat keel layout first fitted on the 12-metre class yacht Australia II, 1983 America's Cup winner.
In sailing, hiking is the action of moving the crew's body weight as far to windward (upwind) as possible, in order to decrease the extent the boat heels. By moving the crew's weight to windward, the moment of that force around the boat's center of buoyancy is increased. This opposes the heeling movement of the wind pushing sideways against the boat's sails. It is usually done by leaning over the edge of the boat as it heels. Some boats are fitted with equipment such as hiking straps and trapezes to make hiking more effective.
A bulb keel is a keel, usually made with a high aspect ratio foil, that contains a ballast-filled bulb at the bottom, usually teardrop shaped. The purpose of the bulb keel is to place the ballast as low as possible, therefore gaining the maximum possible amount of leverage and thus the most righting moment. An example of a class of boats that use a bulb keel is the International 110 racing class, which uses a 300 lb (136 kg) cast iron bulb keel on a boat whose minimum racing weight is 910 lb (414 kg).
A canting keel is a form of sailing ballast, suspended from a rigid canting strut beneath the boat, which can be swung to windward of a boat under sail, in order to counteract the heeling force of the sail. The canting keel must be able to pivot to either port or starboard, depending on the current tack.
A ballast tank is a compartment within a boat, ship or other floating structure that holds water, which is used as ballast to provide hydrostatic stability for a vessel, to reduce or control buoyancy, as in a submarine, to correct trim or list, to provide a more even load distribution along the hull to reduce structural hogging or sagging stresses, or to increase draft, as in a semi-submersible vessel or platform, or a SWATH, to improve seakeeping. Using water in a tank provides easier weight adjustment than the stone or iron ballast used in older vessels, and makes it easy for the crew to reduce a vessel's draft when it enters shallower water, by temporarily pumping out ballast. Airships use ballast tanks mainly to control buoyancy and correct trim.
Ship motions are defined by the six degrees of freedom that a ship, boat, or other watercraft, or indeed any conveyance, can experience.
Twin keels or bilge keels are two keels that emerge at an angle from the hull of a sailboat, at or near the bilge. The angle allows the boat to have a shallower draft while still allowing for minimum leeway while sailing. The placement of the twin keels also allows the boat to stand upright when out of the water without additional support, as opposed to a single-keeled boat that would fall over if water levels dropped. Twin-keeled boats are typically used in coastal areas that experience extreme changes in tide. When the tide is low, the boat will sit on her keels and remain stable and upright. This configuration is especially useful for sailors in Britain and might in the future be applied in the parts of the Atlantic North America that are extremely tidal such as the Fundy waters that are shared by Maine, New Brunswick, and Nova Scotia.
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.
An LNG carrier is a tank ship designed for transporting liquefied natural gas (LNG).
Ballast is dense material used as a weight to provide stability to a vehicle or structure. Ballast, other than cargo, may be placed in a vehicle, often a ship or the gondola of a balloon or airship, to provide stability. A compartment within a boat, ship, submarine, or other floating structure that holds water is called a ballast tank. Water should move in and out from the ballast tank to balance the ship. In a vessel that travels on the water, the ballast will remain below the water level, to counteract the effects of weight above the water level. The ballast may be redistributed in the vessel or disposed of altogether to change its effects on the movement of the vessel.
A variable-buoyancy pressure vessel system is a type of rigid buoyancy control device for diving systems that retains a constant volume and varies its density by changing the weight (mass) of the contents, either by moving the ambient fluid into and out of a rigid pressure vessel, or by moving a stored liquid between internal and external variable-volume containers. A pressure vessel is used to withstand the hydrostatic pressure of the underwater environment. A variable-buoyancy pressure vessel can have an internal pressure greater or less than ambient pressure, and the pressure difference can vary from positive to negative within the operational depth range, or remain either positive or negative throughout the pressure range, depending on design choices.
