The Yaw Balance of Sailing Yachts Upright and Heeled

The present paper describes the results of a study carried out to improve the frequently used prediction methods for assessing the longitudinal position of the Center of Lateral Resistance (CLR) of a sailing yacht hull. To formulate these improvements use is being made from the extensive database of the Delft Systematic Yacht Hull Series (DSYHS) containing yaw moment measurements under various conditions with respect to speed, heeling angle and leeway. The data has been used to formulate alternative procedures and formulations for the existing methods for prediction of yaw moment as previously presented by J.Gerritsma (1971) and K.Nomoto (1979). The outcome of this modified procedure is compared with the experimental results obtained both within the DSYHS and the Delft Systematic Keel Series (DSKS). In the DSYHS one keel and rudder have been tested under a variety of hulls and in the DSKS a variety of keels have been tested under one particular hull. Finally the results are checked against the measured data obtained from two series of tests in the Delft Shiphydromechanics Laboratory with very large sailing yachts with low aspect keels. By matching these hydrodynamic data with the wind tunnel results on the position of the Center of Effort (CoE) of the sails and it change due to heeling angle a better analysis of the balance of the yacht can be made.