FLOW FIN

A human propelled watercraft having a pair of flexible fins supported by a mast extending into the water each adapted to oscillate through an arcuate path in a generally transverse direction with respect to the central longitudinal dimension of said watercraft. Pedals are provided for applying input force whereby as input force is applied, the flexible fins can twist to form an angle of attack for providing forward thrust with respect to the longitudinal dimension of the watercraft while moving in both directions along the arcuate path. Each of the fins preferably is composed of a layer of stiff and durable material that is wrapped around the mast. The two layers of material touch at the trailing edge and they are free to slide relative to each other. Preferably, each of the fins is provided with adjustable tensioning at the tip of the mast.