The colonisation of the islands of Polynesia was a remarkable episode in the history of human migration and seafaring, but one mystery that remains is how well the canoes could sail. Conservation of a large section of an early sailing canoe recently discovered on the New Zealand coast provides an opportunity to study maritime technology directly associated with early voyaging. A sea turtle carved on its hull makes symbolic connections with ancestral Polynesian culture. We employ methods of aerodynamic and hydrodynamic analysis of sailing routinely used in naval architecture and yacht design, but rarely applied to questions of prehistory. We compare the performance of different kinds of canoe hull representing simple and more developed forms. We conclude that ancient Polynesian canoes were able to make return voyages between islands on passages that encountered adverse winds as well as fair ones.