Displacement (ship)

As the term indicates, it is measured indirectly, using Archimedes' principle, by first calculating the volume of water displaced by the ship, then converting that value into weight.[citation needed] Ship displacement varies by a vessel's degree of load, from its empty weight as designed (known as "lightweight tonnage"[2]) to its maximum load.Numerous specific terms are used to describe varying levels of load and trim, detailed below.The process of determining a vessel's displacement begins with measuring its draft.A merchant vessel has three matching sets: one mark each on the port and starboard sides forward, midships, and astern.
Draft marks , by showing how low a ship is sitting in the water, make it possible to determine displacement.
Shipboard stability computer programs can be used to calculate a vessel's displacement.
In this 1940 photo, USS Aaron Ward , left, and USS Abel P. Upshur are destroyers of comparable size, but because the latter is more heavily loaded, it sits lower, displacing more water.
Draft marksweightArchimedes' principledisplacedlong tonstonnestonnagenet tonnagegross tonnageport and starboardslide rulesUSS Aaron WardUSS Abel P. Upshurdunnageclassification societyload lineWashington Naval TreatyArchimedesdisplacementhydrostaticNaval architectureHull (watercraft)HydrodynamicsMilitary Sealift CommandUnited States Naval InstituteShip measurementsLength overallLength between perpendicularsLength at the waterlineFreeboardLoad line (Plimsoll Line)Under keel clearanceAir draftCompensated gross tonnagePanama Canal/Universal Measurement SystemThames measurement tonnageGross register tonnageNet register tonnageDeadweight tonnageTwenty-foot equivalent unitIntermodal containersBuilder's Old MeasurementMoorsom SystemInclining testAngle of lollMetacentric height (GM)AframaxBaltimaxCapesizeChinamaxHandymax/SupramaxHandysizeMalaccamaxPanamaxPénicheSeawaymaxSuezmaxYamalmax