The paper presents results of free running test of a windmill boat with an air propeller coupled to a water propeller. The windmil is 4-blades, 2.0m diameter. The length of boat is 3.0m, and the breadth is 1.0m. The basic mechanical layout consists of windmill which can be rotated on a vertical axis to face any direction, mounted on the top of the mast. It drives via a bevel gear, a vertical shaft inside the mast, which in turn drives the water propeller shaft via another set of gears at the base of the mast. The two set of the gear in the drive result in a 1:2.5 ratio so that the water propeller rotats two and half as fast as the windmill. The performance of windmill is calculated out by linear lifting line model. The resistance of hull and performance of water propeller are carried out tank test. The simulation study is carried out to make the comparison between calculation model and experiment. In addition, the simulation results are in good agreement with experiment results.
