Optimal Blade Design for Windmill Boats and Vehicles

Abstract

This paper discusses the theoretical problem of designing the optimal windmill blade for use on windmill boats and vehicles, sailing at any angle with respect to the wind. The analysis shows that the optimal design for this application is considerably different from that for a conventional stationary windmill. A theoretical comparison is given between the net forward thrusts produced by such a windmill thruster and an airfoil sail, for all sailing directions. The comparison shows that a windmill thruster should be superior to a sail for boat speeds of half windspeed or lower, and vice versa for boat speeds higher than half windspeed. Experimental results from a 4-m catamaran boat, using a 4-m-diameter wind turbine, and from a wheeled vehicle, using a 1.2-m-diameter wind turbine, have been obtained. The boat achieves an upwind speed of about 50 percent of the wind speed and the vehicle achieves about 100 percent, in agreement with theory.