The invention relates to an active roll stabilisation system for ships, comprising at least one stabilisation element extending below the water line, which is mounted on a rotary shaft that extends through the ship's hull, sensor means for sensing the ship's movements and delivering control signals on the basis thereof to rotation means for rotating the rotary shaft for the purpose of damping the ship's movements that are being sensed by means of the stabilisation element.
Such an active roll stabilisation system for ships is known, for example from U.S. Pat. No. 3,818,959, the disclosure of which is incorporated herein by reference. In said US patent it is proposed to impart a reciprocating rotary motion to a fin-like stabilisation element that projects into the water from the ship's hull below the waterline so as to compensate for the rolling motions that the ship undergoes while sailing. To that end, the ship is fitted with sensor means, for example angle sensors, speed sensors and acceleration sensors, by means of which the angle, the rate of roll or the roll acceleration are sensed. Control signals are generated on the basis of the data being obtained, which signals control the direction of rotation and the speed of rotation of the stabilisation element via the rotation means. Another example of a sensing means is a rate gyroscope, as shown in U.S. Pat. No. 3,756,262, the disclosure of which is incorporated hereby by reference, and also a pendulum-type sensor as shown in U.S. Pat. No. 4,777,899, the disclosure of which is incorporated herein by reference.
A reaction force acting on the water can be generated by means of said fin-like stabilisation element while sailing, which reaction force imparts a counteracting lifting or torsional moment to the ship, which is to counter the ship's roll, if the stabilisation element is correctly controlled.
A drawback of the stabilisation system according to said US patent is the fact that it is fairly static as regards the control thereof and that it can only be used while the ship is sailing. The above-described lifting effect does not occur, or not to a sufficient extent, while the ship is stationary, because there is no functional water movement past the stabilisation elements, and consequently there can be no effective roll stabilisation.