This newly developed stern thruster helps sailboats during difficult manoeuvres such as, for example, passages through locks; but because of its high performance, it can also be used as a main drive unit. And to make sure that it does cause any flow resistance in sailing-only operation, it can be retracted. Accordingly, the energy supply system must also be flexible enough. Here an igus® E-Chain® of the Easy Chain® series was integrated into a guiding trough.