Abstract: A modified tunnel hull boat in which there are two downwardly extending sponsons defining a tunnel between their inner walls, the boat having a center rib projecting downwardly from the bottom of the boat into the tunnel and having a lower wall which acts as a planing surface. The distance between the inner walls of the sponsons and the outer walls of the center rib decreases from the bow to an area adjacent the midpoint of the boat fore and aft and then increases abruptly after this point so as to create a venturi throat. The reduced pressure adjacent the venturi throat tends to minimize the effect of head or tail winds upon the attitude of the boat. The amount of lift on the rearward portion of the boat is also increased so that the bow does not rise as much at high speeds.