Displacement

The mass or weight of water displaced by a floating vessel, equal to the vessel’s total mass or weight in equilibrium.

Displacement is commonly quoted as a mass in tonnes even though the traditional word “weight” is often used. Light displacement describes the vessel in a defined light condition, while loaded displacement includes cargo, people, fuel, water, stores and other variable loads aboard.

For the same displacement mass, the submerged volume and draught change with water density, trim and loading distribution. Planing craft still displace water and remain buoyant at rest; dynamic lift changes their supported condition at speed rather than abolishing displacement.