Abstract: A ship's hull is constructed of a monohull forebody shaped to be lifted upwardly as the ship speeds through the water and a catamaran afterbody which extends to rear of the monohull forebody. A deck disposed over a tunnel defined between a pair of catamaran hulls which comprise the hull's catamaran afterbody is constructed and positioned to support most of the load of the ship thereon. Venting ducts extend from the deepest point at the boundary region between the monohull forebody and the catamaran afterbody to a location on the ship which remains at all times above water level. The venting ducts serve to maintain atmospheric pressure conditions within the tunnel. This prevents formation of undesirable subpressure conditions in the tunnel which if permitted to develop would interfere with the ability of the monohull to lift as the ship is accelereated.