Freeboard

The vertical distance between a vessel’s waterline and a defined deck or upper reference point.

In formal ship measurement, freeboard is measured to the assigned freeboard deck or deck line under the applicable load-line rules. In everyday small-craft use, the word often describes the height from the water to the deck edge or another stated point.

Freeboard changes with loading, trim and water density and contributes to reserve buoyancy and protection from water on deck. It should not be confused with clearance to the lowest opening, which may be a separate downflooding measurement.