Methodology for improving stern gear design of high speed craft using cfd simulation

Stern gear design for luxury high speed yachts currently relies on an estimation of the inflow velocity at the propeller plane and the propeller race. These components are often located within tunnel features on the hull and the flow regime will be influenced by the vessel trim and planning speed. Typically, the flow into the propeller is taken as an average over the entire propeller area and does not take into account the variation of the flow into the propeller due to appendages and hull shape. Computational fluid dynamics (CFD) simulations allow this variation to be calculated. These data are coupled with a potential based lifting surface program and are used to improve propeller design.In order to optimise the design of the rudder, the propeller race must be known. A method of introducing the propeller forces back into the CFD flow is investigated. This improved method has the advantage of providing a more accurate flow field into the rudder, which allows the rudder design to be improved. It is expected that this procedure will reduce the rudder drag and cavitation. The development and validation of this CFD methodology applied to high speed planning craft propulsion using open source software is illustrated with regard to two case studies for P bracket and propeller design optimisation, and to estimate the toe-in angle for the rudder in order to align it with the propeller race