Three bodies interact to drive a transmission having a pair of one-way clutches coupling a single length of drive chain or other elongate flexible member to an intermeshed pair of counter rotatable gears so as to drive a primary shaft in a single rotational direction. The three bodies are a fixed body, a floating body, and a suspended and usually submerged weighted body. The three bodies are interconnected by the single length of the elongate flexible member and are spaced apart there along. The weighted body is mounted at one end of the elongate flexible member. The primary shaft is mounted above the surface of a moving fluid mass to either the fixed or floating body. The end of the flexible member opposite to the weight is mounted to the other of the fixed or floating body.