Pitch reduction in transit by using stabiliser fins

In the course of the design optimisation of a large motor yacht and in the ongoing quest for further increase in onboard comfort, the suggestion was made that lifting surfaces such as fins might not only be used for roll damping, but also to reduce the pitch response and related vertical accelerations in transit condition. Seakeeping tests were performed in December 2002 on a 60 metres motor yacht. The two pairs of fins, originally used as anti-roll devices and positioned around midships, were used to damp the pitch motion. The fin controls were then adapted to react on pitch motion and velocity. Pitch reduction was indeed measured together with a substantial reduction in vertical accelerations. The largest reduction in vertical accelerations occurred of course at the vessel’s extremities, resulting in an increased comfort level along the ship length. Of course such a system has its limitations as it only provides substantial gain in low waves and for a limited range of headings. When combined with roll reduction needs, the results were not so satisfactory. Another drawback would be the increase in added resistance and related fuel consumption.