Abstract: A method for propulsion of water-going vessels (1) comprising a plate (9), which is located in the water (2) and extends across a desired direction of motion for the vessel (1), where the plate (9) is moved from a first position (P1) to a second position (P2) and back. Under the influence of a motive force the extent of which varies sinusoidally, the plate (9) is brought into translatory and rectilinear oscillation about a neutral position (N2) between the first and the second position (P1 and P2 respectively), the neutral position (N2) being determined by a static equilibrium between spring forces influencing the plate (9). The plate (9) is controlled in such a manner that its plate plane extends perpendicularly to the vessel's (1) direction of motion, and a greater resistance is exerted by the plate (9) against the water when it is moved opposite to the vessel's desired direction of motion than when it is moved in this direction. A device for performing the method.