Displacement

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For displacement hulls, see Displacement(hull)

Displacement

The displacement of a vessel is the weight of water a vessel displaces, as per Archimedes principle, to float at the designated waterline or draught. In the absence of a qualifying condition of load, this is taken as the design waterline (full load).

Contents

Units

In most countries, displacement is measured in tonnes. Commonwealth nations formally used long tons, and as such it was an international measure. The United States continues to use short tons for most of its vessels, with the exception of the US Navy (which uses long tons). Displacement is represented by the Δ symbol (Greek capital delta).

Underwater Volume

Underwater volume is a related measure, the volume of displaced fluids. Underwater volume is represented by the nabla symbol, ∇. Underwater volume, displacement, and a water density (ρ) are related by the formula;

Δ = ρ∇

Dynamic Effects

The displacement of a vessel can exceed it's total mass when it is subjected to hydrodynamic effects; for example, squat can cause the vessel to displace more water.

Moulded Displacement

Moulded displacement is a measure of the displacement which excludes shell plate thickness, as well as all appendages. Moulded displacement is used for coefficients of form.

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