Abstract: A high speed, high efficiency, stable catamaran boat hull which comprises a boat hull structure having an under surface, a curved bow and a generally flat stern, a pair of spaced-apart sponsons on either side of the keel line of the hull and extending generally substantially from the bow of the hull, wherein the sponsons generally come to a point, to the stern of the hull. The sponsons generally have vertical, downwardly extending, inner side walls and a generally horizontal underwall connecting the inner walls to form an air tunnel, the inner side walls tapering inwardly from the bow to the stern of the hull structure to compact the air passing through the tunnel to lift the hull in operation.