Abstract: A muscle-powered watercraft includes flotation and propulsion structure having at least two blades which remain rigid under the stresses that are subjected to. The front edges of the blades are hinged about respective axes transverse to the watercraft's axis of propulsion, spaced from one another along the axis of propulsion on either side of the watercraft's center of gravity. Each of these blades extends symmetrically from the axis of propulsion. Abutment structure limits the angle of freedom of each blade about its hinging axis, and the volume of water displaceable by immersion of the flotation structure is selected to correspond to 1 to 2 times the total laden weight of the watercraft. The flotation structure has feet-supporting surfaces distributed about the craft's center of gravity, whereby a driver may impart to the watercraft a sinusoidal movement in and out of the water by pitching the craft and hence making the blades operate in opposition to one another between the abutments.