Based on a fuzzy model of a fast ferry, a fuzzy control system has been implemented to stabilise the vertical motion of the ship, which is the main cause of seasickness. The fuzzy system controls the working angles of some appendages (flaps and T-foils) that have been added to the craft. The goal of the controller is to reduce the pitch acceleration by moving the control surfaces. Experiments have been carried out in a scaled-down replica of the ship, and results have proved highly satisfactory.