An Investigation into the Efficiency of Gybing Daggerboards

This investigation was completed by the author as an undergraduate thesis to fulfill requirements for the Webb Institute of Naval Architecture. A one-quarter scale model of a Lark dinghy was equipped with a gybing daggerboard, a daggerboard allowed to rotate about its vertical axis. The model was tested in a conventional configuration at various leeway angles with the foil aligned to the center plane, in a gybing configuration at a series of angles relative to the hull, and in configurations combining hull yaw and gybing angles to simulate realistic performance. Side-force (lift) and resistance (drag) were measured and expanded to full-scale. The results were found to agree with the hydrodynamic theory of boats with gybing foils; namely that they have lower drag for a given lift force developed to place aerodynamic forces in balance. The exact change in performance is not known and requires a determination of velocity made good to windward in order to draw conclusions beyond the drag reduction found in this research.