n.

1. Nautical. The distance between the water line and the freeboard deck of a ship.
2. The distance between normal water level and the top of a structure, such as a dam, that impounds or restrains water.
3. The distance between the ground and the undercarriage of an automobile.

[Probably ultimately partial translation of Anglo-Norman franc bord, land claimed outside the fence of a park or forest : franc, free + bord, bort, border; see border.]

n. the height of a ship's side between the waterline and the deck.

See the Introduction, Abbreviations and Pronunciation for further details.

In a water tank, the vertical distance between the maximum water level and the top of the tank.

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Putting the best face on a controversial design feature
Until the 1960s and 1970s, free-board—the height of a boat’s deck edge above the waterline—was comparatively low on sailing yachts but often substantially higher on powerboats. Low free-board didn’t help a sailboat’s accommodation space, which was already constricted by narrow beam, but it certainly added to a boat’s looks. Sailboats from that

The higher the freeboard, the greater the topside surface area exposed to the force of a breaking wave. High freeboard is an advantage on the down-wave side of a boat, however, making the deck edge less likely to submerge and contribute to a danger of capsize.

era are still greatly admired for their pretty sheerlines and graceful overhangs.Today’s boats have far more beam and freeboard. Among sailboats, racers started the fashion for beam because it helps them carry more sail. Production cruising sailboats added freeboard to help reduce the height of ugly deckhouses needed to satisfy the new demand for standing headroom in small boats. Because most production sailboats today are fin-keeled and flat-bilged, their cabin soles are not as deep as in a traditional sailboat. In the search for headroom, the only place to go is up.The average height of free-board in a classic cruising sailboat was 2½ inches per foot of beam (about 190 mm/m) and, considering how narrow those boats were, it didn’t result in much freeboard.Freeboard creates windage, so the more freeboard you have, the poorer your performance to wind-ward. In a storm, high freeboard also gives a breaking wave a bigger target. Today’s boats have plenty of freeboard and—because high freeboard is said to provide a greater range of stability—suddenly it’s not being rued as detrimental, but rather touted as one of the most important features contributing to safety.It is difficult to know the truth. Freeboard is far from the only factor contributing to a large range of stability; it may not even be the major factor. And there were no protests in the old days about lower freeboard making boats less safe. So it seems quite possible that modern designers are putting the best face on a feature that exists primarily for creature comfort and has little to do with seaworthiness.In a powerboat, too, high freeboard is a mixed blessing where seaworthiness is concerned. A hull with higher free-board forward ships less solid water on deck and gives a drier ride. This is why sportfishing boats combine high freeboard forward with low freeboard aft (for handling fish). High freeboard aft might make it possible to run down-sea in steep waves without being pooped—a point at which sportfishing boats, for one, are vulnerable. A high-freeboard boat will also remain stable through greater roll angles and is less likely to trip over a submerged deck edge while sliding sideways down a wave face. On the other hand, high topsides expose a larger surface to the energy of a breaking wave and also move a boat’s center of gravity higher, especially when combined with a high superstructure (e.g., flying bridge, tuna tower). In heavy weather, a high center of gravity is the last thing you want. Consider, too, the windage of high topsides and superstructures, which will make a boat harder to handle in high wind.

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