Abstract: The present invention relates to a wing type air foil assembly that is adapted to be utilized by boats or vessels, or even vehicles, that is designed to function in the same general manner as a wind sail for providing driving thrust to the vessel or vehicle. In the case of a vessel, the wing type air foil is rotatively mounted about a generally vertical axis and includes a central spar journaled about a holding shaft extending upwardly from a pylon supported by the vessel. Provided about the upper end of the spar is a tip member while a root member is provided about the lower portion of the spar. Extending around and between the root and tip members is a flexible line that includes a forward run that forms a part of the leading edge of the wing type air foil assembly and a rear run that also extends between the tip and root members that forms a part of the trailing edge of the entire air foil assembly.