Displacement

What it means

Displacement is the weight of the boat, so called because a floating hull displaces its own weight in water. It is usually quoted in kilograms or tonnes, and often as light displacement — the boat empty, without fuel, water, stores or people.

The figure has several versions

Light displacement, half-load and fully-laden displacement can differ by a large margin on a small boat, and a builder rarely says which one is on the specification sheet. On an electric boat the battery is a significant part of the total, so a light-displacement figure quoted without the pack is meaningless. Where the basis is unclear we record what the builder published and say so.

Why it matters

Weight is the tax on every mile. A lighter hull needs less power to hold a given speed, which means a smaller battery for the same range, which means less weight again. It is why the most convincing electric boats tend to be startlingly light for their length, and why adding equipment costs more range than it appears to.