Some English technical terms about ship

Three linear motions

Three rotational motions

• Length Between Perpendiculars (LBP or L): The distance between forward and aft perpendiculars.
• Beam (B): The breadth of the ship at the widest point. Molded beam is measured amidships or at the widest section from the inside surface of the shell plating.
• Draft (T): The depth from waterline to the deepest part of the ship.
• Depth (D). Total depth from bottom to the top watertight deck. Depth = freeboard + draft.
• Length Overall (LOA): The extreme length of the ship.
• Length on Waterline (LWL): This is the length at the waterline in the ship's design loaded condition.
• Freeboard (F): Distance between the waterline and the uppermost watertight deck.
• Sheer: The rise of a deck - usually toward bow and stern. Sheer increases freeboard, and helps keep the vessel from shipping water in rough seas - particularly at the bow.
• Camber: The convex upwards curve of a deck. Also called round up, round down, or round of beam, usually around one-fiftieth of the beam. Not all ships have cambered decks; ships with cambered weather decks and flat internal decks are not uncommon.
• Tumblehome: Inward slope of hull sides above the waterline - the opposite of flare. Tumblehome was a usual feature in sailing ships and many ships built before 1940. Only seen on tugs and icebreaking vessels, sometimes used to reduce topside weight, and for reducing radar cross sections.
• Flare: The outward curvature of the hull surface above the waterline, i.e., the opposite of tumblehome. Increases buoyancy when immersed. Flaring bows are often fitted to help keep the forward decks dry and to prevent "nose-diving" in head seas.
• Deadrise: Rise of the bottom from baseline to molded breadth measureed amidships. Also called "rise of floor" or "rise of bottom". Full-bodied ships, such as cargo ships and tankers, have little or no deadrise, while fine-lined ships have much greater deadrise along with a large bilge radius.
• Rake: Slope of profile lines - esp rake of stem (angle between the stem and vertical)
• Cut-up: When a keel departs from a straight line at a sharp bend, or knuckle, the sloping portion is called a cut-up. High-speed combatants usually have a long cut-up aft (extending 13 to 17 percent of LWL) to enhance propeller performance and maneuverability.

• Displacement Volume (V): The volume of the underwater hull at any given waterline.
• Displacement (W): The weight of water of the displaced volume of the ship, which equals the weight of the ship and cargo.
• Buoyancy: The upward push of water pressure, equal to the weight of the volume of water the ship displaces (W).
• Reserve Buoyancy: The watertight volume between the waterline and the uppermost continuous watertight deck.
• Moment of Inertia (I): Also called the Second Moment of Area unless specified otherwise. It is proportional to bending strength.
• Tonnage: Cargo capacity of a merchant ship, measured by volume.
• Trim: Longitudinal tilt. Stern draft - bow draft
• List, Heel, and Roll: Angular transverse inclinations. List describes a static inclination such as list due to side damage. Heel describes a temporary inclination generally involving motion, such as wind or turning, while roll indicates periodic inclination from side to side such as wave action.
• Center of Gravity (G). The center of all mass of the ship, acting vertically downward.
• Center of Buoyancy (B). The geometric center of the submerged hull, acting vertically upward.
• Metacenter (M). When the ship is inclined at small angles, the metacenter is the intersection of the buoyant force with the ship centreline. If the metacenter is above the center of gravity then the ship is stable.
• Center of Flotation (F). The geometric center of the waterline plane, about which the ship trims fore-and-aft.