Displacement in naval architecture is defined as what?

• A. The volume of water displaced by the hull.
• B. The weight of the water displaced by the hull, equal to the ship’s weight.
• C. The ship's total mass including cargo and fuel.
• D. The density of the seawater the hull displaces.

Answer: (B)

Displacement is the weight of water that the hull pushes aside when it is floating. By Archimedes’ principle, the buoyant force on a floating ship equals the weight of the water displaced, so at equilibrium the ship’s weight must equal that displaced water’s weight. That’s why displacement is expressed as a weight (or mass, with gravity accounted) and is why ships are described by their displacement in tons.

The volume of water displaced would depend on water density, and the ship’s own weight is the same concept as its displacement, so describing displacement as the weight of the water displaced is the precise definition. The density of seawater and submerged volume relate to the calculation, but they don’t define what displacement is.