A watercraft comprises a motor, an inertial mass, and a fin. The motor oscillates the inertial mass about an axis, producing a torque reaction on and oscillation of the motor. Oscillation of the motor is communicated to the fin, producing thrust. A fluke, fin, or wing comprises an angle of attack mechanism, wherein the angle of attack mechanism may use power from the fluke, fin, or wing to adjust an angle of attack of the fluke, fin, or wing relative to a surrounding thrust fluid.