In order to be able to calculate the forces on the keel and rudder of a sailing yacht more is to be known about their interaction. Both for determining the yaw balance of a sailing yacht as for the maneuvering it is of importance to have a good assessment on these forces because they determine the yaw moment to a large extent.
Therefore a research project was set up in the Delft Shiphydromechanics Department to investigate the influence of the keel on the rudder. Aim was to improve on the side force prediction of keel and rudder and to assess the wake of the keel and the downwash on the rudder in various conditions. Based on the measured results the the previous developped formulation within the DSYHS for the keel residuary resistance is validated and a new formulation for the downwash behind the keel is presented. In addition the expression within the DSYHS for the sideforce on the yacht is improved for higher aspect ratios.