A boat for traveling at speed across a body of water includes a center hull having a vee-shaped bottom with a center planing surface, and an opposing pair of sponsons or ski-like structures attached outboard of the center and extending substantially alongside the central hull. Importantly, the sponsons or skis each have a substantial opening such that large volumes of water are able to pass through in an outboard direction away from the boat, advantageously minimizing forces on the hull when there is substantial vertical downward movement of the boat. The boat is designed so that planing surfaces of the keel and sponsons operate beneath the surface of the water to lift the hull free and isolate it from the rough water surface.