Variable air cushion mode vehicle

A boat hull comprising at least one longitudinally extending hull having lateral extremities, an intermediate hull portion between the lateral extremities of said at least one hull, air entrainment means extending between the lateral extremities of the hull adjacent the rear end of the intermediate hull portion, means to raise and lower the intermediate hull portion relative to the remainder of the hull between a lowered position wherein the intermediate hull portion is in contact with the water in which the boat hull floats and a raised position wherein a chamber is defined, when air is introduced under pressure beneath said intermediate hull portion, between said intermediate hull portion, the water, said lateral extremities of the hull and said air entrainment means, and means to introduce air beneath the intermediate hull portion when it is in the raised position so that the hull may then be supported on a cushion of air.