Ventilated Waterjets for High Speed Ships

A ventilated waterjet (VW) is similar to a conventional waterjet with a fully submerged inlet region. However, the exit of a VW is partially submerged and the impeller blade is designed for ventilating conditions. The partially submerged exit provides a natural supply of air for ventilating the blade surfaces under most operating conditions. A VW can be used for high-speed vessels where traditional propulsors fail to perform due to cavitation limitations. It also can address some of the shortcomings typical of super cavitating or partially submerged propellers. The 24" water tunnel at the David Taylor Model Basin was modified to accommodate the testing of a VW. A stock surface piercing propeller with trimmed blade tips was tested in the ventilating mode and the results compared with a modified version of a Propeller Unsteady Force computer program. The general operating characteristics of a VW were identified in the 24" water tunnel tests. The results indicate that a VW could have better-powering performance over a wider speed range as compared with either super cavitating or surface-piercing propellers.