Abstract: A self-feathering propeller for use on sail boats having an auxiliary power source. The propeller blades are rotated automatically to working pitch positions to provide an ahead or an astern thrust in accordance with the direction of rotation of the propeller shaft. When the shaft is stationary and water flow is substantially parallel to the shaft axis, as when the boat is under sail, the blades are automatically feathered thereby to minimize resistance to movement of the boat.