Ship measurements

Ship measurements consist of a multitude of terms and definitions specifically related to ships.

Beam - A measure of the width of the ship. There are two types:

Carlin - similar to a beam, except running in a fore and aft direction.

Complement - The full number of people required to operate a ship. Includes officers and crewmembers; does not include passengers. For warships, the number of people assigned to a ship in peacetime may be considerably less than her full complement.

Cube - The cargo carrying capacity of a ship, measured in cubic feet. There are two common types:

Displacement - A measurement of the weight of the vessel, usually used for warships. (Merchant ships are usually measured based on the volume of cargo space; see tonnage). Displacement is expressed either in long tons of 2,240 pounds or metric tonnes of 1,000 kg. Since the two units are very close in size (2,240 pounds = 1,016 kg and 1,000 kg = 2,205 pounds), it is common not to distinguish between them. To preserve secrecy, nations sometimes misstate a warship's displacement.

Draft (d) or (T) - The vertical distance from the bottom of the keel to the waterline. Used mainly to determine the minimum water depth for safe passage of a vessel.

Draft, Air - Air Draft is the distance from the water line to the highest point on a ship (including antennas) while it is loaded. Technically, standard draft is the distance a ship can pass over, air draft is the distance a ship can pass under.

Length - The distance between the forwardmost and aftermost parts of the ship.

Shaft Horsepower (SHP) - The amount of mechanical power delivered by the engine to a propeller shaft. One horsepower is equivalent to 746 watts in the SI system of units.

Summer Water Line - The waterline when ship has standard load. Sometimes called Design Waterline.

Ton - The unit of measure often used in specifying the size of a ship. There are three completely unrelated definitions for the word. One of them refers to weight, while the others refer to volume.

Tonnage - A measurement of the cargo-carrying capacity of merchant vessels. It depends not on weight, but on the volume available for carrying cargo. The basic units of measure are the Register Ton, equivalent to 100 cubic feet, and the Measurement Ton, equivalent to 40 cubic feet. The calculation of tonnage is complicated by many technical factors.

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