Developed in the mid to late 20th century, the ‘wingsail’ is a rigid airfoil structure designed to replace fabric sails on sailing vessels. Though not as entirely adaptable as sail systems used on racing yachts, the wingsail offers very high efficiency and simplicity, eliminating the manual skills traditionally associated with managing fabric sail systems and allowing the sail vessel to be operated little different from a convention motor vessel. During the height of the 1970s Energy Crisis, many designers looked to the wingsail as a key technology for reducing the fuel costs of large vessel marine transport –though commercial shipbuilders remained reluctant to even experiment with the technology. Others were not so timid, however, and a variety of yacht class wingsail vessels have been bu