Peter -- you are quite right about the sharp edge at the step & trailing edge. However (sorry), you are quite wrong about the surface texture. For a planing hull it should be glassy smooth if possible. A rough surface texture will require substantially more power to push, because of the macro-irregularities, and the greatly increased thickness of the boundary layer. In the case of separation, we are not speaking of flow separation in the sense of turbulent vs laminar flow in a single-phase environment, we are speaking of actual air-water interface separation, as planing hulls operate in a two-phase environment. The smooth surface minimizes the boundary layer thickness & parasitic form drag (from irregularities), while the sharp step ensures the transfer of air to the underside of the hull (a round edge delays, or prevents the water seperation)