SHIP STABILISER AUTOMATIC GAIN CONTROL SYSTEM

An improved fin stabilizer control system which has an automatic gain control (AGC) system which uses the difference between the control laws demand signals and the actual fin angles to calculate a gain factor to reduce the control laws demand until the non-linearities almost disappear. If more than one control law is used to generate a demand, the control laws can be prioritized and the available actuator power thus rationed. In particular, the automatic gain control (AGC) sub-system of the control law monitors the motions of the fins and detects when each fin is not following the control law demands. It adjusts the gain of the control law so as to reduce the slew rate limit and the fin angle limit effects. Although the automatic gain control (AGC) sub-system has the effect of reducing the control law loop gain, it reduces the ship motions below those achieved with a conventional control law because the phase lag between the demanded and actual fin angles is reduced and because generation of harmonics of the demanded fin angle is much reduced.