Hydrodynamics of Three Slender Models Resembling Pacific Canoe Hulls

Abstract Ancient Pacific multi-hull vessels did not appear to have keels, and so the side-force had to be generated by the hulls. It is here hypothesised that the earliest vessels had rounded hulls and were used mainly for sailing downwind. However, evolution and technical innovation have caused a change in shape from circular to Vee, presumably because such shapes are better able to generate side force to enable the vessels to also sail across and against the wind. To investigate whether sharper Vee sections are better at generating side-force than a rounded hull, towing tank tests were carried out on three slender models at fixed sink and trim. At high yaw angles, such as those sailed by sailing vessels without appendages, the rounded hull showed lower drag than the narrower hulls. However, the narrowest hulls allowed higher lift and side force, resulting in the minimum resistance (aligned with the longitudinal axis of the vessel). These results support the hypothesis that narrower Vee-shaped hulls would generate more side-force and lower resistance when at leeway than a rounded hull, and this might have driven the design evolution of ancient Pacific vessels. Keywords ancient Pacific canoes; catamarans; upwind sailing; hull hydrodynamics; hull forms; side force