CFD tools were used for turbulent flow analysis around a sailing yacht. Turbulent flows are solved around a sail system composed of main and jib sails with a mast to assess the sail performance and to determine the center of effort. Flows are also solved around a sailing yacht hull with keel and rudder with and without free surface effect. Both calculated results for the sails and hull of a yacht are compared with experiment. It is found out that CFD is a very effective tool for the evaluation of sails and hull with keel/rudder in various position of a sailing yacht, which can be costly if they are obtained from towing tank and wind tunnel tests.
Flow analysis around a sailing yacht is much more complicated than a commercial ship, because propulsive forces come from sails in the air and keel/rudder in the water and they should be balanced in yawed and heeled condition. Sails generate side forces as well as propulsive forces since they act like a system of zero-thickness foils with attack angle. The so-called lateral resistance of hull, keel, and rudder below the free surface should balance the side forces from the sails. Otherwise, the yacht would be drifted. The yacht should advance with the leeway angle (heading angle of the yacht centerline) to give attack angle so that the keel and rudder could generate compensating side forces. Both side forces from sails and keel/rudder also act like a coupling moment to heel the ship. The yacht would be heeled until the up-righting moment due to buoyancy will meet the heeling moment from sails and keel/rudder. The yacht design is usually based upon empirical formula and designer's experience. Towing tank and wind tunnel tests are occasionally utilized.
