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Ship Tonnage

Merchant ship tonnage is the volume measurement of the areas used to carry cargo. A ton is 100 cubic feet. The cargo capacity of a ship is called Gross Registered Rate Tonnage (GRT). This is not the weight of cargo a ship can carry. Cargo capacity of some ships is expressed in barrels, a barrel is 100 cubic feet of cargo capacity and so is equal to the GRT.
German language web sites and books may list tonnage as Bruttoregistertonnen (BRT) which in English means gross registered tonnage and is the same as GRT.
War ship tonnage is calculated as the weight of the water displaced by the ship when fully loaded. This is called displacement tonnage or dead weight tonnage (DWT). The water displaced by a ship is the weight of the ship. So a ship that displaces 850 tons of water weighs 850 tons. These are long tons, 2,240 pounds each. Displacement tonnage is sometimes given in kilograms. A ton weighs 1,016 kilograms. So a ship displacing 850 tons of water weighs about 850,000 kilograms.

Last Revision: March 4, 2007.
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