In sailing and boating, freeboard
means the distance from the waterline to the upper deck level, measured at the lowest point of sheer where water can enter the boat or ship. In commercial vessels, the latter criteria measured relative to the Ship's load line, regardless of deck arrangements is the mandated and regulated meaning.

1. Nautical.

:a. the distance between the level of the water and the upper surface of the freeboard deck amidships at the side of a hull: regulated by the agencies of various countries according to the construction of the hull, the type of cargo carried, the area of the world in which it sails, the type of water, and the season of the year. Compare load line.

:b. (on a cargo vessel) the distance between the uppermost deck considered fully watertight and the official Ship's load line.

:c. the portion of the side of a hull that is above the water.

2. Civil Engineering. the height of the watertight portion of a building or other construction above a given level of water in a river, lake, etc.

In yachts, a low freeboard is often found on racing boats, for weight reduction and therefore increased speed. A higher freeboard will give more room in the cabin, but will increase weight and may compromise speed. A higher freeboard also helps weather waves and reduce the likelihood of green seas on the weather deck. A low freeboard boat is susceptible to swamping in rough seas. Freighter ships and warships use high-freeboard designs to increase internal volume and also allowing them to satisfy IMO damage stability regulations due to increased reserved buoyancy.