free·board 
(frēbôrd′)
(frēbôrd′)n.
1. The distance from the water line to the gunwales of an open boat or to the main deck of a decked vessel.
2. The distance between normal water level and the top of a structure or mass that rises out of the water, such as a buoy, dam, or ice floe.
[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.]