hydroplanes

n. [ Pref. hydro-, 1 + plane. ] 1. A plane, or any of a number of planes, projecting from the hull of a submarine boat, which by being elevated or depressed cause the boat, when going ahead, to sink or rise, after the manner of an aëroplane. [ Webster 1913 Suppl. ]

2. A projecting plane or fin on a hydroplane{ 3 } to lift the moving boat on top of the water; also, a gliding boat. [ Webster 1913 Suppl. ]

3. a powered surface boat fitted with planes (hydroplanes{ 2 }) projecting below the hull, designed to lift the boat, when moving rapidly, so that the hull itself is lifted out of the water and the boat is supported by the hydrodynamic forces of the water on the hydroplanes{ 2 }, thus permitting higher speeds; formerly called a gliding boat. [ Webster 1913 Suppl. +PJC ]