70 KNOTS WITH A HIGH-SPEED MOTOR YACHT, NOT A CONCEPT BUT REALITY

摘要

High-speed vessels are equipped with propulsion configurations, which can operate in different modes. A typical example is the Millennium 140 motor yacht with two wingjets and a boosterjet. For top speed all waterjets are used, but at cruise speed only the wingjets are required. This results in a large variation of the operating point of such waterjet installation. However, large variations in ship speed result in relative small variations of the pump working point. Consequently, the pump can operate at a high efficiency level over a large range of ship speeds. The flow phenomena in the waterjet inlet are related to the Inlet Velocity Ratio (IVR). This IVR changes significantly, if the ship speed increases from cruise speed to top speed. Analysis of the streamtube of the ingested water shows a clear dependency between IVR and the cross-sectional area. A gradually increasing diffuser angle is found. The concept of an artificial diffuser is used to examine the pressure distribution along the streamtube. This pressure distribution is responsible for a lift force in the inlet. A numerical method is used to determine the actual lift force in a high-speed inlet geometry. At very high IVR a significant positive lift is found, which can be about 10 to 20% of the thrust.