Abstract: A device for the roll-stabilization of a watercraft in motion, at anchor, or at zero speed, and/or for influencing the course of the watercraft, includes a fin-carrying shaft on which a guide fin is disposed. For changing an actual angle of attack of the guide fin in the water, the fin-carrying shaft is drivable by an electromechanical drive unit, and the drive unit is disposed on the hull using a base. An electromechanical drive unit is configured with a synchronous motor that drives the fin-carrying shaft using a reducing eccentric transmission. The device thereby has a significantly reduced installation space requirement, causes only slight operating noises, and is also optimally electronically regulable.