Abstract: The present invention consists of two asymmetrical hulls connected by a crossbeam or deck structure to make up a catamaran. Each hull has a rounded or shallow angled outer surface below the water line. The inboard side presents a vertical, or near vertical surface below the water line to act as an effective leeway preventer, to resist sideways movement under normal sailing conditions. The vertical surface may have a winglet at the keel and a flow directing vane to prevent vortexes and to maintain parallel flow of water along the whole length of the surface.