NAMBA Propwash October 2017.pub

Simple steps can also reduce this wetted area. From the earlier parts of this series you can see that reducing the area in contact with the water is critical. Steps and strakes, sometimes in combination, are the most common ways this is done. However, at least two other methods have been used. The Dynaplane design by Eugene Clement cuts away the wetted bottom area with a specially contoured, vee shaped step as shown below. The hull is balanced on the step either by a hydrofoil or an aft planning surface. Ninety percent of the hull’s weight is carried by the step. Only one offshore race boat was built to this design; Smuggler. It had a brief run in the 1970 Cowes Torquay Cowes offshore race but had engine problems and did not finish. Another way to reduce the planing drag is with an interceptor. An interceptor is a small vertical plate that is pushed down under the planning surface. This creates a high lift pressure in front of the interceptor and a separation of the flow behind the interceptor. An air vent behind the interceptor helps assure this. Air vents have also been used behind steps. PROPWASH October 2017 15 Delta Force Strakes Calcraft Strakes Stepped Hull Wetted Area A Dynaplane Model Dynaplane Wetted Area Compared to a Conventional Interceptor Interc eptor Wetted Area – Midship Placement