Active roll stabilisation system for ships

Abstract

 The invention relates to an active roll stabilisation system for ships, comprising at least one first rotatable stabilisation element extending below the ship's water line on a side of the ship, sensor means for sensing the ship's movements and delivering control signals on the basis thereof to driving means for rotatably driving the stabilisation element for the purpose of damping the ship's movements that are being sensed, as well as moving means for moving the stabilisation element with respect to the ship.
The object of the invention is to provide an active roll stabilisation system for ships as described in the introduction, which can only be used on moving ships. According to the invention, the active roll stabilisation system is to that end characterized in that said at least one rotatable stabilisation element can only rotate in one direction.

Description

[0001] The invention relates to an active roll stabilisation system for ships, comprising at least one first rotatable stabilisation element extending below the ship's water line on a side of the ship, sensor means for sensing the ship's movements and delivering control signals on the basis thereof to driving means for rotatably driving the stabilisation element for the purpose of damping the ship's movements that are being sensed, as well as moving means for moving the stabilisation element with respect to the ship.

[0002] Such an active roll stabilisation system for ships is known, for example from Dutch patent No. 1023921. In said patent it is proposed to rotate a stabilisation element that projects into the water from the ship's hull below the waterline about its longitudinal axis so as to compensate for the rolling motions that the ship undergoes while the ship is at anchor. 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 rotation of the rotatable stabilisation element as regards the direction of rotation and the speed of rotation as well as the moving of the damping stabilisation element with respect to the ship.

[0003] A correction force is generated under the influence of the rotary motion of the stabilisation element and the water flowing past as a result of the stabilisation element moving with respect to the stationary ship, which correction force is exerted in a direction perpendicular to the direction of rotation and the direction of movement. This physical phenomenon is also referred to as the Magnus effect, on the basis of which the correction force is used for opposing the ship's roll.

[0004] A drawback of the roll stabilisation system according to said US patent is that it can only be used while the ship is stationary. When such an active roll stabilisation system is used on moving ships, the system is opposed by the increased frictional resistance as well as the mass inertia of the system, because the direction of rotation of the stabilisation elements must be reversed each time.

[0005] The object of the invention is therefore to provide an active roll stabilisation system for ships as described in the introduction, which can only be used on moving ships. According to the invention, the active roll stabilisation system is to that end characterized in that said at least one rotatable stabilisation element can only rotate in one direction. Because the rotatable stabilisation element can only rotate in one direction, there is no need to impart a different direction of rotation to the stabilisation element each time, as is the case with the prior art system.

[0006] When a different direction of rotation needs to be imparted to the rotatable stabilisation element each time so as to dampen the ship's movements, the rotary motion of each stabilisation element must be reversed each time, involving successive deceleration and acceleration. The latter will make stabilisation more and more difficult, because the stabilisation element must rotate ever more quickly as the ship's speed increases, so that the usability of the construction is limited partially on account of the mass inertia of the stabilisation element.

[0007] When according to the invention the stabilisation element is rotated in one direction only and used so that only one stabilisation element at a time is active, it will no longer be necessary to drive the stabilisation element alternately in both directions.

[0008] In a functional embodiment of the invention, the roll stabilisation system comprises at least one assembly of a first and a further rotatable stabilisation element, which further stabilisation element can only rotate in one direction opposite the direction of rotation of the first stabilisation element. This, too, obviates the drawback of the prior art that the stabilisation element must be alternately rotated in both direction each time, so that the roll stabilisation system can also be used at higher speeds, in spite of the mass inertia.

[0009] According to another embodiment, the system is further characterised in that the moving means for each assembly alternately impart a pivoting movement with respect to the ship to the rotatable stabilisation elements while the ship is sailing. Thus the roll stabilisation system can be used actively also at higher speeds and in spite of the high mass inertia. Said alternating pivoting movement is imparted in the sailing direction.

[0010] According to another embodiment, the stabilisation element is connected to the ship by means of a universal joint, so that a pivoting or rotary movement of the stabilisation element with respect to the ship through the water is possible.

[0011] In a specific embodiment of this aspect of the invention, the stabilisation element can be accommodated in a recess formed in the ship's hull, so that the stabilisation element can be returned to its position in the ship's hull, if desired, while the ship is sailing, so that the friction between the ship and the water will decrease considerably while sailing.

[0012] Optionally, the stabilisation element can be accommodated in a guide formed in or on the ship's hull, which guide preferably extends at least partially in the longitudinal direction of the ship.

[0013] According to another functional embodiment, stabilisation elements may be provided on each long side of the ship or only on one side, whilst in another embodiment two or more stabilisation elements are provided at the front side of the ship.

[0014] The invention will now be explained in more detail with reference to a drawing, in which:

Figures 1-4 are views of prior art active roll stabilisation systems;

Figures 5 and 6 show various views of the movements of a ship fitted with a roll stabilisation system according to the invention.

[0015] In figures 1-4 embodiments of active roll stabilisation systems according to the prior art are shown. The stationary ship 1 floating on a water surface 3 is fitted with an active roll stabilisation system indicated by reference numerals 10-11-20-10'-20'. This known active roll stabilisation system for ships as described in Dutch patent No. 1023921 is comprised of rotatable stabilisation elements 4a and 4b, respectively, which project from a respective long side of the ship's hull 2 below the water line.

[0016] The prior art active roll stabilisation system also comprises sensor means (not shown) for sensing the ship's movements, more in particular the ship's roll. On the basis of the sensing results, control signals are delivered to driving means (not shown, either), which rotatably drive either one of the stabilisation elements 4a, 4b (depending on the required correction). Said sensor means may consist of angle sensors, speed sensors or acceleration sensors, which continuously sense the angle of the ship relative to the horizontal water surface 3, the speed or the acceleration caused by the ship's rolling motions 6.

[0017] Figure 1 shows an embodiment of a known active roll stabilisation system comprising a set or rotatable stabilisation elements. The active roll stabilisation system comprises moving means which move the rotatable stabilisation element 4 with respect to the stationary ship. More particularly, figure 1 shows an embodiment in which the moving means 10 impart a reciprocating translating movement between two extreme positions 4_a and 4_b to the rotatable stabilisation element 4, such that said movement comprises at least one component in the longitudinal direction of the ship. The longitudinal direction of the ship is indicated by the wide arrow X in figure 1.

[0018] In the translating embodiment of the active roll stabilisation system shown in figure 1 (see also figure 2), translating movement or movement of the rotatable stabilisation element 4 is made possible in that a guide 11 is mounted in the hull 2 of the ship 1, along which guide the stabilisation element 4 can move. The rotatable stabilisation element 4 is to that end accommodated in the guide 11 with its one end 4" via a universal joint 12, thus enabling translating movement in the guide 11 as well as rotary motion about the longitudinal axis 13.

[0019] Although this is schematically illustrated in the figure, the rotatable stabilisation element 4 is connected to the driving means 6 by means of a universal joint 12, which driving means rotatably drive the stabilisation element 4 for the purpose of damping the ship's movements being sensed. In this embodiment the assembly of the driving means 6 and the universal joint 12 (which enables the stabilisation element 4 to rotate with respect to the driving means 6 and the ship 1) can translate along the guide 11, for example by means of a rack-and-pinion transmission mechanism (not shown).

[0020] Also other translating transmission mechanisms may be used for this purpose, however.

[0021] The reciprocating translation of the rotatable stabilisation element 4 in the guide 11 between the extreme positions 4_a and 4_b in the longitudinal direction X of the stationary ship 1 combined with the rotation of the stabilisation element 4 results in a reactive force, also referred to as the Magnus force. Said force extends perpendicularly both to the direction of movement of the stabilisation element 4 in the X-direction and to the direction of rotation.

[0022] Depending on the direction of the ship's motion (the ship's roll) that is to be damped, the direction of rotation of the stabilisation element 4 must be selected such that the resulting Magnus force _FURTHERMORE opposes the rolling force F_R being exerted on the ship by the ship's rolling motion.

[0023] This is shown in figure 3, in which the translating, rotatable stabilisation elements 4a-4b are disposed below the waterline 3, near the centre of the ship (see Fig. 2B). The direction, the speed as well as the acceleration of the rolling motion can be sensed in a manner which is known per stabilisation element by means of suitable sensor means (angle sensor, speed sensor and acceleration sensor). On the basis of the sensing results, control signals are delivered to the respective driving means 6 and 10. On the basis of said signals, the driving means 6 will drive the stabilisation element 4 at a speed and in a direction that may or may not be varied, whilst also the operating means 10 will move the rotating stabilisation element 4 in the longitudinal direction X in the guide 10 at a certain speed.

[0024] Figure 4 shows another embodiment of a known active roll stabilisation system according to the invention, in which the operating means (indicated at 20 in this figure) impart a reciprocating pivoting movement between two extreme positions 4_a and 4_b with respect to the stationary ship 1 to the stabilisation element 4. In order to ensure that the active roll stabilisation system will function correctly with stationary ships, the pivoting movement that is imparted to the rotatable stabilisation element 4 by the operating means 20 preferably comprises at least one motion component in the longitudinal direction X of the ship also in the embodiment shown in figure 4.

[0025] Using the above arrangement and a suitable control and drive of the stabilisation element 4 in terms of speed and direction of rotation and speed and direction of pivoting, the Magnus effect will for example occur with a stationary ship that is at anchor, resulting in a Magnus force F_m comprising at least one force component directed towards or away from the water surface 3. Said upward or downward force component of the Magnus force F_m can be utilised very effectively for compensating the rolling motion of the stationary ship about its longitudinal axis X.

[0026] A significant drawback of the currently known active roll stabilisation systems functioning on the basis of the Magnus effect is the fact that they can only be used with stationary ships. At present no roll stabilisation systems based on the Magnus effect suitable for used with high-speed ships are available yet. Add to this the fact that a higher frictional resistance is experienced while sailing, which renders the known systems unsuitable.

[0027] Figure 5 shows various views of a ship fitted with a roll stabilisation system according to the invention during various stages of a ship's movement. The ship 10 is fitted with a set of stabilisation elements 40a-40b mounted in the ship's hull on either side of the ship. According to the invention, each stabilisation element of the stabilisation elements 40a-40b can be rotatably driven in one direction only, so that the roll stabilisation system is in particular suitable for damping movements of ships sailing at high speed.

[0028] As is clearly shown in figure 5, one stabilisation element, or both stabilisation elements, are moved in and out in dependence on the sensed ship's movement, so that the rotating stabilisation element, as a result of its movement through the water, will generate a resulting Magnus force F_m comprising at least one force component directed towards or away from the water surface 3. Said upward or downward force component can be utilised effectively for compensating the rolling motion of the ship about its longitudinal axis X.

[0029] To render the active roll stabilisation system suitable in particular for ships sailing at high speed, the two stabilisation elements 40a-40b can only be driven in one direction. Thus it is no longer necessary, in particular as a result of the high mass inertia, to have the rotatable stabilisation element rotate in both directions, thereby obviating the need for constant deceleration and acceleration of the stabilisation elements.

[0030] The latter results in a simple construction, because a simpler and cheaper driving mechanism, but also for example a simpler and cheaper bearing system for the rotatable stabilisation element, for example in the ship's hull, can be used.

[0031] Figure 6 shows another embodiment of the active roll stabilisation system according to the invention, in which a pivoting movement relative to the ship's hull is alternately imparted to each stabilisation element of each set of stabilisation elements for the purpose of effectively damping the ship's roll. The pivoting angle may vary from 0 to more than 90 degrees so as to thus realise an additional lifting force due to the Magnus effect. Said pivoting movement is preferably imparted in the sailing direction.

[0032] A more functional use of the stabilisation system according to the invention comprises the installation of a set of stabilisation elements near the front side of the ship. Using one or more rotatable stabilisation elements at the front side, the vessel can also be steered on the front side. Usually, this is already effected at low speeds by the use of so-called bow thrusters, but when the ship is sailing at high speed such bow thrusters can no longer be functionally employed, because the force of the water flowing past neutralizes the force generated by the bow thruster.

[0033] Rotatable stabilisation elements mounted near the front side of the ship do not exhibit this drawback. At higher speeds, the force component enables the rotatable stabilisation elements to impart an additional steering component to the ship. Although such front-mounted rotatable stabilisation elements encounter more resistance at higher sailing speeds, this phenomenon can be minimized by positioning the rotatable stabilisation element at an adjustable angle relative to the sailing direction.

Claims

1. An active roll stabilisation system for ships, comprising at least

- one first rotatable stabilisation element extending below the ship's water line on a side of the ship,

- sensor means for sensing the ship's movements and delivering control signals on the basis thereof to

- driving means for rotatably driving the stabilisation element for the purpose of damping the ship's movements that are being sensed, as well as

- moving means for moving the stabilisation element with respect to the ship, characterised in that said at least one rotatable stabilisation element can only rotate in one direction.

2. An active roll stabilisation system according to claim 1, characterised in that the system comprises at least one assembly of a first and a further rotatable stabilisation element, which further stabilisation element can only rotate in one direction opposite the direction of rotation of the first stabilisation element.

3. An active roll stabilisation system according to claim 1, characterised in that the moving means for each assembly alternately impart a pivoting movement with respect to the ship to the rotatable stabilisation elements while the ship is sailing.

4. An active roll stabilisation system according to claim 3, characterised in that the stabilisation element is connected to the ship by means of a universal joint.

5. An active roll stabilisation system according to one or more of the preceding claims, characterised in that the stabilisation element is accommodated in a guide formed in or on the ship's hull.

6. An active roll stabilisation system according to claim 5, characterised in that said guide extends at least partially in the longitudinal direction of the ship.

7. An active roll stabilisation system according to claim 5 or 6, characterised in that the stabilisation element is accommodated in a recess formed in the ship's hull.

8. An active roll stabilisation system according to one or more of the preceding claims, characterised in that a stabilisation element is provided on each long side of the ship.

9. An active roll stabilisation system according to one or more of the preceding claims, characterised in that said set of stabilisation elements is provided at the front side of the ship.

Drawing