Displacement

The weight of the water a vessel displaces when it is floating, which is equal to the vessel’s own weight.

Displacement is a fundamental concept in naval architecture and marine operations, as it directly relates to a vessel’s buoyancy and stability. When a boat or ship is placed in water, it pushes aside or “displaces” a volume of water. According to Archimedes’ principle, the weight of the displaced water is equal to the weight of the vessel. This is why a vessel floats: the upward buoyant force exerted by the displaced water counteracts the downward force of the vessel’s weight. Displacement is typically measured in tonnes or long tons, and it is a key factor in determining a vessel’s draft (how deeply it sits in the water), stability, and overall performance at sea.

There are different types of displacement measurements. “Light displacement” refers to the weight of the vessel without cargo, fuel, passengers, or other consumables, while “loaded displacement” includes the weight of everything on board when the vessel is fully loaded. “Full displacement” vessels, such as cargo ships or large yachts, are designed to displace a large volume of water and generally have a slower, more stable ride. In contrast, “planing” vessels, such as speedboats, are designed to rise up and skim over the water, reducing displacement at higher speeds. Understanding displacement is crucial for ensuring a vessel’s safe operation and optimal performance.