Abstract: A boat hull includes a pair of demi-hulls. Each demi-hull has a running surface configured to contact water when the hull is planing. The running surface extends longitudinally along a keel between an outer chine and an inner chine and aft to a running surface trailing edge. The running surface has most of its surface area outboard the keel. A first step extends laterally across the running surface and between the outer chine and inner chine. A first planing surface is aft the first step along the running surface. The first planing surface has an outboard convex curved surface on an outboard side of the keel extending from the keel to the outer chine and an inboard convex curved surface on an inboard side of the keel extending from the keel to the inner chine.