It is not uncommon to see references to primitive and vernacular architecture when discussing sustainability. The point is that most of the earth’s land surface has been colonised by man sheltered by such dwellings without the use of fossil energy. Modern building design is on the other hand almost synonymous with high energy use, one of the main threats to sustainability. It is interesting to draw a parallel with ships. A glance at a world map as at the end of the last century will show all the main seas and coasts charted. This was all achieved by the sailing ship. Furthermore, as late as the 1930s the grain ships, descendants of the great clippers, were crossing oceans, and even up to the 1950s Thames sailing barges were carrying goods around our coasts. Since then however, development in sailing vessels has taken a dramatically different course from that of the modern building. The emphasis has been on pleasure and sport rather than utility and in many cases has allowed the purest zero-energy principle to be maintained. Under the incentive of competition, scientific and engineering sophistication has resulted in the modern sailing yacht becoming the ultimate passive machine. It has to function in an extremely complex environment between the sea and air. The surface may be rough or smooth, the hull upright or heeled. It will pitch, yaw and roll in response to waves. It has to move with speed and safety, and most would agree that is has to be a thing of beauty at the same time. These complex criteria mean that yacht design method is a rich mix of intuition, experience and analysis; a close parallel with architectural design. This paper describes and illustrates this process and suggests that there might be useful lessons for sustainable architecture.