Aero-hydrodynamics of a racing sailing yacht, focusing on sails, keel and rudder design

Abstract

Understanding the aerodynamics and hydrodynamics as well as the interaction between these is essential for the design of sails, keels and rudders, particularly for performance racing yachts. The project takes a previously designed Delft Schematic Yacht Hull Series (DSYHS) hull and designs the sails, keel and rudder. The design process starts by calculating the canoe hull displacement, which is the hull displacement, without ballast or rig, followed by adding the internal structures which are essential for the yacht to function. The design process begins with market research, where several yachts of the same function and similar length are analysed. Data is gathered regarding the dimensions of sails and ballast. The design process uses of design ratios which are dimensionless parameters used to compare features between yachts. Firstly, the ballast ratio (BR) is used, which shows how much of the total yacht displacement is ballast and by using the previously determined canoe hull displacement it is possible to determine the required ballast mass to satisfy a particular ballast ratio. The displacement of the yacht influences the displacement to waterline length ratio (DLR). Depending on the DLR obtained, the yacht may be classified into different racing yacht categories. The sail area to displacement ratio (SAD) is used to size the reference sail area of the yacht. The use of the BR, DLR and SAD allows for the generation of different configurations of ballast and sail area are compared to the market research for validation and to help decide between the combinations of displacement and sail area. The resulting design constitutes a high aspect ratio keel, designed on the One Design Class rules and statistical data, containing a T-Bulb lead ballast of 1.7 tonne. The reference sail area of 74 m2 is then optimised to a square top mainsail and a larger jib for which the rig is designed. The yacht makes use of a high aspect ratio rudder which guarantees maneuverability and a well-balanced yacht due to the careful consideration of the relative position of the centre of effort of the sail plan. The final design is tested using the Maxsurf software by Bentley for the total resistance as well as for velocity prediction. The results obtained were highly satisfactory and the objective set were reached throughout the project, resulting in a performance racing yacht which passes all the necessary stability criteria while being competitive in its class.