Abstract: Conventional propeller blades, for use on water or aircraft, provided with a series of foldable fins on the rear surface of each propeller blade, a number of rows of fins being affixed along the length of each propeller blade and with each row of fins being tapered in height so as to be taller in height at the leading edge of each propeller blade and tapering to a small height at the trailing edge of each propeller blade, with the foldable fins projecting into a fully extended position when the propeller blades turn in a counter clockwise direction as when a vehicle is propelled forwardly and folding into a retracted position when the propeller blades turn in a clockwise direction as when a vessel is urged in a rearwardly direction. When a vessel is moved forwardly with the foldable fins in an extended position, the fins prevent the propellant medium, namely water or air from slipping along the length of the propeller blades and going off the ends.

Abstract: A rigid cylindrical collar with an inside diameter slightly larger than the outside diameter of a propeller which is mounted over a propeller and is used singly or in combination with a flexible extension thereto for maximizing the efficiency of propeller blades. The invention is adaptable to watercraft or to aircraft so as to prevent water or air from slipping off the ends of propeller blades so as to redirect energy lost as a result of slipping off the ends of propeller blades in the direction useful for advancing a water or air vehicle. The flexible extension is usable primarily on large watercraft, such as tug boats, ocean vessels and barges, and the like, and could be used with or without a rudder in order to steer a boat in the direction desired.