add. ·vi of a boat, to plane (see plane, below).
2. hydroplane ·add. ·noun a projecting plane or fin on a gliding boat to lift the moving boat on top of the water; also, a gliding boat.
3. hydroplane ·add. ·noun 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 aeroplane.