Abstract: A boat includes a plurality of longitudinal keels below the deck. The space between the keels is closed, at both ends, to form an enclosed downwardly open cavity. Jet propulsion engines are provided at the forward end of each cavity, well above the waterline, to pressurize the cavities with exhaust gases. A cavity enclosing stern plate includes an open tube, fitted with a variable control valve, passing therethrough, well above the waterline. The stern plate, and a cavity enclosing bow plate are set at a forwardly leaning angle, and a flexible trailing seal is fixedly attached to the bottom faces of the plates.