TECHNICAL FIELD

The present invention relates to an arrangement for automatic control of turns of a marine vessel comprising a hull with an angular bottom portion, which marine vessel is empowered by at least two propulsion pod units being mounted onto the hull with their respective vertical axis in an angle against the horizontal plane, said arrangement comprising at least a steering angle acquiring unit, a speed acquiring unit and a control unit arranged to automatically compensate to improve comfort and/or improved fuel economy.

BACKGROUND ART

Automatic systems for controlling the movements and course of marine vessels are previously known and used for various types of watercrafts. The possibility of providing stabilization to the vessel during driving leads to the advantages of maintaining comfort as well as safety while underway and to that the driving situation for the captain is significantly improved. An automatic stabilizing unit for watercrafts is disclosed in WO2008/110519 where an electrical controller is provided which stabilizes the water position via actuating members in the form of trim tabs. Trim tabs attached on the trailing edge of the hull are widely used on planing- or semi-planing type boats such as cruisers or sport fishing boats, and serve the purpose of adjusting the pitch attitude during traveling and to adjust unwanted list generally caused by wind or uneven loading of the vessel. Normally an increase of speed would cause an ascent of the bow leading to imperfect orientation of the hull, while use of trim tabs will develop lift forces in the aft thus keeping the boat at an efficient pitch attitude. Another system is described in US2007/0276563 which shows a marine vessel comprising lift force difference generating units in the stern for providing stability and controlling the heel angle during steering. Flaps are respectively attached to a port-side and a starboard-side in a pivotal manner and serve as lift force generators which are maneuvered by a control module to nullify the heel angle. A general drawback with the use of flaps shown in US2007/0276563, as well as other trim tabs, is that in order to efficiently counteract the movements of the hull or reduce the heel angle upon turning, enormous forces are required to actuate the trim tabs fast, pushing a large amount of water and consequently also heavy and space-demanding equipment for controlling the flaps. Hydraulic driving means have been used in order to operate the trim tabs, however hydraulics is quite undesirable since it results in a slow system and a large time delay if weight and space are to be kept at acceptable levels. Such a time delay may lead to an unbalanced system where unsynchronized compensation measures may cause rolling movements of the vessel, which is of course a major drawback. In some cases electric driving means have been used, but here the problem is that the motors need to be big for providing the necessary transmission which is undesired since it occupies a lot of space.

Within the field of vessel hydrodynamics there has lately been an increasing interest in propulsion pods (POD), meaning propulsion units (e.g. propellers) positioned below the stern of a vessel, each unit being mounted in such a way rotatable around a central axis. Hereby propulsion pods are able to combine propulsive and steering functions which lead to an excellent propulsion efficiency and turning capacity. These pods are often used in combination with vessels having a deadrise other than zero degrees, that is, having a hull with an angular bottom section for instance in the shape of a "V" or a "U". Use of propulsion pods has also great advantages regarding maneuvering

characteristics, fuel consumption and flexibility in machinery arrangement. Commonly at least a pair or propulsion units are used in combination for attaining best steering possibilities, for instance by connecting them to a Joystick system.

However, a disadvantage is that when the propulsion units are installed perpendicular or nearly perpendicular to a hull surface inclined to an angle, as is common in the case of a V- or U-shaped hull, the hull may heel (tilt) more than desired when turning the boat. For best comfort, a ship should heel a certain amount depending on radius of turn and speed of the ship. Rotation of the propulsion units for turning also leads to that a lifting force is developed which is increased as a result of the V- or U shape of the hull.

Consequently a roll moment is developed which may result in a large heel angle upon turning. The arisen boat heel angle is often too large for the passengers to feel comfortable and also, any loose items will fall or move during turning which of course is undesirable and may even represent a safety issue.

A related kind of problem is caused when cross winds are present. In order to keep a straight course when running the vessel in cross winds the driver will need to steer somewhat to compensate for the drift caused by the wind. Also in this running condition, the boat will heel more as a result of that the propulsion units are mounted perpendicular or nearly perpendicular to an inclined hull surface as in the case of a V- or U shaped hull.

In view of the foregoing it is obvious that during turning, there is a need for an improved heel control system for propulsion pod marine vessels, and in particular for propulsion pod marine vessels having a V- or U-shaped hull.

DISCLOSURE OF THE INVENTION

The object of the present invention is to eliminate or at least to minimize the problems described above. This is achieved by an arrangement for automatic control of turns of a marine vessel comprising a hull with an angular bottom portion, which marine vessel is empowered by at least two propulsion pod units being mounted onto the hull with their respective vertical axis essentially perpendicular to the hull, said arrangement comprising at least a steering angle acquiring unit, a speed acquiring unit and a control unit arranged to automatically compensate to improve comfort and/or improved fuel economy. The control unit is arranged to automatically and instantaneously generate a command signal to control a moment generating device arranged to provide an intercepting roll moment based on input from said steering angle acquiring unit and said speed acquiring unit respectively. Said moment generating device comprises at least two individually, adjustably displaceable blades of interceptor members arranged on the hull. Preferably the at least two interceptor members are located at the aft portion of the hull at different sides of the keel of the hull respectively.

In case a vessel lacks interceptor units, during a turn the propulsion pod units create a torque MPOD that rotates the ship to a heel angle that is sometimes other than optimal leading to that the efficiency of the operation of the ship is lowered and to passengers present on the ship a feeling of unease can be caused. This problem in particular for vessels having a deadrise other than zero degrees. A person skilled in the art will perceive that the "heel angle" refers to how far from upright the vessel is, meaning the inclination of the hull towards port/starboard side.

Thanks to the inventive arrangement for automatic control a so called coordinated turn can be achieved, coordinating the movement of the rotatable pod units with the moving interceptor members. As a result of this coordination a turn can be performed while reducing unease to the passengers that may otherwise be caused by the heeling and turning movement. Another benefit is that the fuel efficiency of the vessel will be significantly improved. In cross winds, the boat will heel less into the wind when the driver keeps the course by steering up against the wind. Also, the performance of sharper turns with a higher degree of control over the turning movement is enabled by the arrangement according to the invention. According to the invention, activation of an interceptor member leads to the generation of forces acting on the hull of the ship in front of the corresponding interceptor blade. These generated forces will in their turn result in said intercepting roll moment, comprising a lifting force and also, due to the angular hull bottom portion, a steering force. This is particularly advantageous in combination with propulsion pods since the steering force originating from the activated interceptors will contribute to a turning movement of the ship, thereby reducing the need to steer with the pod unit and consequently also reducing the risk of developing uncontrolled roll moment and undesirably large heel angle during turning. The acquired steering angle of the vessel (meaning the direction of movement of the vessel) is used for controlling and activating the interceptor members. As is previously known, interceptor members are exceptionally quick and can be displaced into the water virtually without any delay. During a turn, displacement of the interceptor blades may be performed very quickly, for instance the moving of an interceptor blade from a fully retracted position up and away from the water to a position of maximum projection into the water can be performed in a very short time, typically around 3 s, depending on the motor used for the operation. The speed of the interceptors will contribute to that the counteracting force required to control the heel angle of the ship can be achieved essentially simultaneously with the pod rotation to balance the unwanted part of the heel and act on the ship already at the beginning of the turn, before the undesirable conditions of the turn arise. Thanks to the present invention the time (At) between upcome of roll moment MPOD and generation of the desired intercepting roll moment Mi can be essentially eliminated, meaning the movements of the propulsion pods and the interceptor blades are essentially completely synchronised. Preferably At is between 0 s and +/- 1 s, more preferably between 0 s and +/- 0.5 s, even more preferably between 0 s and +/- 0. 1 s. This will lead to the advantage that time delays are eliminated and no risk that the automatic control system causes uncontrolled rolling of the vessel. Instead the synchronised cooperation between the pod units and the interceptors will lead to highly controlled movements of the vessel, and to the operation of the ship and to the passengers, the effect will be that the turn is performed in a controlled and efficient manner, without undue fuel consumption or feelings of unease on board. Interceptors mounted onto a hull with angular bottom portion and used within a control arrangement according to the present invention will lead to a surprisingly efficient and highly reactive control system for increased comfort, safety as well as improved fuel economy and optimized operation of a vessel, where arisen heel during a turn may be compensated extremely quickly so that the unwanted heel substantially may never even occur.

According to one aspect of the invention the steering angle of the vessel is acquired in immediate connection to the steering device (e.g. the steering wheel) of the ship, meaning the steering command (the steering angle and the rate of turn) of the steering wheel is registered and directly used for further control of the interceptor members. According to this aspect the steering command of the steering wheel is interpreted within a preprogrammed system, for instance a MAP system, so that a certain turning rate/steering angle leads to a predetermined activation of the interceptors. This leads to that the steering wheel will maneuver both the pod units and the moment generating device (i.e. the interceptors) simultaneously, and steering movements with the pod units is therefore compensated by adjustments of the interceptors in a completely

synchronised manner. Thus the control system becomes extremely reactive and compensates for any undesired roll moment (M _POD ) in such a fast way that

uncomfortable heel is essentially instantly cancelled out.

According to another aspect of the invention the steering angle of the vessel is acquired by a sensor able to register real-time turns and the real-time turning angle. For instance a Gyro sensor may be used, but obviously any other suitable sensor is equally conceivable. The data in the form of registered real-time turning angle is transferred to the control system (control unit) along with the speed of the ship and is used for controlling and/or adjusting the moment generating device in the form of said interceptors. DESCRIPTION OF THE DRAWINGS

The invention will now be described more in detail with reference to the appended drawings, wherein:

Fig. 1 shows a planar side view of a ship with a preferred embodiment of the invention,

Fig. 2 shows a planar view of the ship of Fig. 1, seen from behind, and

Fig. 3 shows a schematic view of the control system according to the invention. DETAILED DESCRIPTION OF THE INVENTION

The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying figures. Further, the description, and the examples contained therein, are provided for the purpose of describing and illustrating certain embodiments of the invention only and are not intended to limit the scope of the invention in any way. Fig. 1 shows a side view of a ship with an angular hull 1, beneath which at least one pod unit 2 is mounted for propulsion of the ship. Said pod unit 2 is a propulsion unit comprising a rotatable thruster that is arranged to be rotated around a first axis 21 that extends essentially perpendicularly from a bottom surface 41 of the hull 1 of the ship. The thruster is mounted in a casing 22.

When the ship is in operation, the at least one pod unit 2 can be rotated in such a way that a driving force exerted by the pod unit 2 on the surrounding water can be directed in a suitable direction. This rotation of said pod unit 2 can be effected by being coupled to a steering device (not shown), in such a way that manoeuvring said steering device, such as a steering wheel or other, also means a rotation of the pod unit 2.

A pod unit 2 generally comprises a suitable propulsor, such as for instance one or several propellers 20 or a jet device (not shown). The ship further comprises a stem 3 and a stern 4. At the stern 4 is mounted at least two interceptors 11 each comprising an adjustably displaceable blade 10, as is known prior art. For instance, the interceptors may be arrangements according to application No. W099/55577, which is hereby incorporated into the present application by way of reference. The blades 10, 10' of the corresponding interceptors 11, 11 ' are individually displaceable. Preferably the interceptor 11 is attached to the substantially vertical surface of the stern 4 of the vessel. In the shown example the interceptors are aligned with the angular hull so that the respective blade 10, 10' are mounted in an angle a against the horizontal plane (see Fig. 2), however it is to be understood that other alignments of said blades are also possible. Said interceptor 11 comprises a fastening section that is mounted onto the ship, for instance by bolts (screws), and a drive unit such as an electric motor or an hydraulic driving means that is connected to the blade 10 and can move the blade upwards or downwards in a direction that is essentially perpendicular to the hull bottom, depending on command signals. The generation of such command signals is further described below. It is to be understood that the design of said interceptors 11, 11 ' leads to that the blades 10, 10' are very easily and quickly displaceable into different positions, i.e. downwards/upwards, meaning that comparably small driving units (electrical or hydraulic) may be used for maneuvering the blades.

When the vessel is running across a surface of a water volume activation of said interceptor blade 10 will result in a lifting force Fn acting on the region of the hull 1 whereto the interceptor 11 is attached. It is to be understood that activation of the interceptor 11 means movement of said interceptor blade 10 downwards/upwards along a direction substantially perpendicular against the bottom of the hull 1. In operational mode the blade 10 is brought to project at least partially below the lowest part of the hull 1 interfering with the water volume across which the vessel is running. Increase of vessel speed will lead to an increase of F _L i.

Thanks to the use of interceptor blades 10, 10' the forces required to counteract the imperfect heel of the ship can be achieved through only a relatively small force provided by an electrical motor or the like for operating the blade 10, 10'. The forces generated by the water coming into contact with the interceptor blade 10, 10' will for the most part be transferred to the bottom surface 41 of the ship, where they are most needed for lifting the ship in the counteracting movement.

In Fig. 2, the ship of Fig. 1 is shown from the stern 4, i.e. in a view taken from the left of Fig. 1. As seen in the figure the hull 1 has an angular bottom with a V-shape, the bottom surface 41 extending downwards to a keel 42 in such a way that an angle a is created between the bottom surface 41 and a horizontal line. Obviously the hull may equally have a U-shaped bottom.

On each side of the keel 42, a pod unit 2, 2' is mounted along the bottom surface 41 with the respective vertical axis 21, 21 ' in an angle β against the horizontal plane.

Each pod unit 2, 2' is mounted at a distance A from the chine 8 and at a distance B from the keel 42, said chine 8 being at an outer limit of the bottom area 41, where said bottom 41 is in contact with an adjacent side 6 of the hull 1. Preferably an interceptor member 11 , 11 ' is mounted so that it is positioned at least partly at the area of the hull 1 along said distance A. According to a preferred embodiment of the invention the interceptor 11, 11 ' is mounted completely within the area A preferably also covering an essential portion of the area A, however it is equally possible positioning an interceptor 1 1 , 1 1 ' at the area behind a pod unit 2, 2' and/or partly also covering area B. An interceptor will become more effective the closer it is to the chine 8, since such a positioning will generate a more efficient intercepting roll moment Mi.

The pod unit 2, 2' and the interceptor members 1 1, 1 1 ' may be mounted to the hull 1 individually, but it is also possible to provide modular units leading to that a propulsion pod 2, 2' may be mounted onto the hull 1 together with a an interceptor 1 1 , 1 1 ' as one entity.

One or more interceptor members may be mounted onto each side of the keel 42.

Moreover each of the port and starboard side of said stern portion 4 of the hull 1 may comprise large interceptor members 1 1 , 1 1 ' or a plurality of smaller ones, although in the example of Fig. 2 only one interceptor 11 , 1 1 ' per side is shown.

In the example of Fig. 2 the port side interceptor 1 1 ' is activated and has been displaced to a position where the respective interceptor blade 10' is protruding downwards from the lowermost portion of the stern part 4 of the hull 41. According to the invention the port side interceptor 1 1 ' is activated as seen in Fig. 2 for compensating a heel angle caused by a port turn.

Referring now to mainly to Figs. 2 and 3, the present invention relates to an

arrangement for automatic control of turns of a marine vessel empowered by at least two propulsion pod units 2, 2' being mounted onto the hull 1. Said arrangement comprises at least a steering angle acquiring unit 5, a speed acquiring unit and a control unit 12 arranged to automatically compensate to improve comfort and/or improved fuel economy. The control unit 12 is arranged to control a moment generating device (i.e. the interceptors 1 1, 1 1 ') automatically and instantaneously generating a control action/signal to provide an intercepting moment Mi based on input from said steering angle acquiring unit 5 and the speed acquiring unit respectively. Said moment generating device comprises at least two individually, adjustably displaceable interceptor members 1 1 , 1 1 ' arranged on the hull 1.

The operation of the ship with the interceptor assembly will now be described in more detail. When in operation, the direction of movement of the vessel can be controlled by a driver operating a steering device (for instance in the form of a steering wheel). Turning is performed by turning the steering device thus directing the pod units 2, 2' which is done by rotating each unit 2, 2' around the respective central axis 21 , 21 ' . Known propulsion pods are for instance rotatable around approximately +/- 25° from a straight forward position. During operation, the interceptors 1 1 , 1 1 ' are used for keeping the ship in a desired position with regards to the surface of the surrounding water. At times when the speed is high enough for the boat to heel when turning, a lowering of the interceptor on one side of the centre line will keep the ship steady and with a more suitable heel angle. This is beneficial for keeping a high degree of control over the operation of the ship, and also for reducing the amount of fuel needed.

For instance Fig. 2 schematically shows a hull 1 during a port turn, said pod units 2, 2' being positioned accordingly, giving rise to forces F _L pi, F _S pi, F _L p ₂ and F _S p ₂ respectively which in their turn result in roll moment MPOD causing the hull to heel. Moreover, the port side interceptor 1 1 ' is activated and the blade 10' lowered so that it projects below the hull 1 of the vessel. The lowered blade 10' will give rise to force F _L i and due to the hull bottom angle a also to force Fsi. Forces Fn and Fsi will act on the hull portion in front of the interceptor 1 1 ' resulting in an intercepting roll moment Mi.

Thanks to the angular hull an activated interceptor unit 1 1 , 1 1 ' will give rise to a lifting force FLI as well as to a steering force Fsi acting on the hull bottom, leading to that not only the pod units 2, 2' but also the interceptors 1 1 , 1 1 ' will contribute to a turning movement of a vessel. Hereby the need to steer the ship with the pod units is reduced and thereby also the risk of too large heeling caused by rotation of propulsion units when turning the ship. Interceptor blades 10, 10' mounted onto an angular hull will thus contribute to achieving an optimal heel angle during a turn (also called a coordinated turn) in two ways: firstly for cancelling undesired part of said roll moment M _PO D, and secondly for generating a steering force Fsi contributing to a turning movement so that the need for using pod units is reduced.

During a so called coordinated turn the theoretical ideal heel angle corresponds to the inclination when all the side forces acting on an object on board during turning are cancelled. This is achieved by tilting the vessel during turning so that a certain optimal heel angle arises which, according to the invention, is performed by controlling the intercepting roll moment Mi by adjusting the interceptor blades 10, 10' . In accordance, the undesired part of said roll moment MPOD is cancelled by intercepting roll moment Mi SO that a perfect heel is achieved and comfort, safety and operation of the ship are optimised. Preferably the interceptor blades 10, 10' are controlled in a continuous manner so that movements of the vessel during turns are compensated for

instantaneously and synchronised with the pod units 2, 2' .

It is to be understood that in a majority of situations the ideal position of the vessel is when the heel is such that the side forces acting on an object on board are cancelled; however there are situations when a certain offset to the correction of the heel angle is beneficial for maintained comfort on board. By correcting a few degrees more than "optimal", passengers can sometimes perceive an even better comfort.

Fig. 3 is a schematic illustration of a control system 7 and a principle example of arrangement propulsion pod and interceptor coordinated turn system according to the invention. Although in the example of Fig. 3 the POD control unit 14 and the control unit 12 are shown as separate units it is possible that both may be integrated into one common control unit, as will also be described later.

The control system 7 is provided in the ship and serves to continuously monitor the steering angle of the ship along with its speed by using a steering angle acquiring unit 5 and a speed acquiring unit 9 respectively. For instance the vessel may be provided with a rate-of-turn sensor 5 and/or a GPS antenna 9 for registering input data for the system in form of steering/turning angle and speed of the ship. Evidently it is possible to achieve corresponding input data in other ways, for instance any kind of sensing device, such as a Gyro or a GPS sensor, may be used for acquiring the turning degree of the vessel. Also, the number of revolutions of the engine or a driveshaft can be used as input instead of the speed of the ship.

According to one preferred example of the control system 7 the steering angle is registered by acquiring the steering command of the steering device 5, which steering device 5 may for instance, but not necessarily, be in the form of a steering wheel. The steering command may comprise information both in form of the angle of the steering device 5 (e.g. to what extent the steering wheel is turned) and the rate of turn (e.g. how fast the steering wheel is turned). The registered command of the steering device 5 may be automatically interpreted for instance by a conventional MAP system provided in the ship prior to transfer to the control unit 12 along with the speed of the vessel for further control of the moment generating device 1 1 , 1 1 ' . The control unit 12 is preferably arranged to automatically and instantaneously generate a command signal to control the moment generating device 1 1 , 1 1 ' arranged to provide an intercepting roll moment Mi based on input in the form of turning angle and speed of the vessel. The moment generating device comprises said interceptor members 1 1, 1 1 ' which, via control by the control unit 12, are displaced accordingly in order to generate an intercepting roll moment Mi thus compensating for any undesired roll moment MPOD during turning. By using said input data in the form of the steering angle and the speed of the vessel, the control system 7 can determine when a turn is made and how sharp the turn is, so that a blade 10, 10' of the right interceptor 1 1 , 1 1 ' can be lowered into the water in order to generate an intercepting roll moment Mi for controlling the turn of the ship.

When a turn is made, the control system 7 is activated to analyze the movement and determine what response should be given by the interceptors 1 1 , 11 ' in order to counteract any unwanted roll moment MPOD a counteracting force Mi is required, which can be achieved thanks to the use of interceptors 1 1 , 1 1 '. After determining the desired magnitude of this counteracting force/roll moment Mi the control system 7 determines what action needs to be taken by the interceptor 1 1 , 1 1 ' in order to create this force. By lowering one or more interceptor blade/s 10, 10' into the water to such an extent giving rise to said required force Mi, the heel angle is reduced, and thus a coordinated turn may be performed where the turning movement is efficient but also where feelings of unease are avoided that may otherwise be generated by an imperfect heel angle. As an example, a registered speed of 20 knots and turning rate of 100% may correspond to an ideal difference between the port side and starboard side interceptors of 70%. If, for instance, both interceptor blades 10, 10' are fully retracted at this point one of them is simply moved out 70% of maximum projection. If, on the other hand, both blades 10, 10' projects 60%> of maximum projection, both blades could be moved but in opposite directions, one is withdrawn and the other is projected, until the difference between the two equals 70%>.

Obviously at another speed and/or another turning rate the ideal difference between the interceptor blades 10, 10' may be another percentage. The adjustments of the interceptors are decided and monitored by the control system 7, which according to one example of the invention may be preprogrammed, for instance comprising a MAP system. Displacement of the interceptor blades 10, 10' may be performed virtually without any delay. For instance, the time from that to that an interceptor blade 10, 10' has moved from a fully retracted position to maximum projection is between 0.1 - 5 s, preferably 0.1 - 3 s, even more preferably 0.1 - 2 s.

Further, since only a small interference by the interceptor members 1 1 , 1 1 ' is enough for generating the desired intercepting roll moment Mi the system can become very fast. In fact a few millimeters of blade projection below the hull 1 of the vessel may often be enough to generate the required counteracting roll moment. The time from that a command signal is generated to the moment when an intercepting roll moment Mi is started to get generated may be between 0.1 - 1 s, preferably 0.1 - 0.5 s.

According to one embodiment of the invention, simultaneously to communicating with the control unit 12, the steering device 5 may maneuver the pod units 2, 2' via an engine/pod control unit 14. This means the steering wheel 5 maneuvers both the pod units 2, 2' and the moment generating device (i.e. the interceptors 1 1 , 1 1 ')

simultaneously and in a coordinated manner, and steering movements (MPOD) of the pod units 2, 2' are thus immediately compensated by adjustments of the interceptor blades 10, 10' in a synchronised manner.

According to another embodiment of the control system (not shown), the control unit 12 and the engine/pod control unit 14 are integrated into one single control unit which receives input data from the steering device 5 and the speed acquiring unit 9

respectively, and transmits command signals both to the interceptors 1 1 , 1 1 ' and to the pod units 2, 2'. Such a system is advantageous in case the interceptors 1 1 , 1 1 ' and the propulsion units 2, 2' respectively are powered by the same kind of driving unit, for instance an electrical motor. Thus one type of command signal may control both parts of the system (e.g. interceptors and propulsion units), meaning the interceptors 1 1 , 1 1 ' and the pod units 2, 2' will receive command signals simultaneously and will therefore become extremely well synchronised during operation of the vessel.

Common for all possible embodiments of the control system 7 is that the time (At) between upcome of roll moment MPOD and generation of the desired intercepting roll moment Mi is essentially zero. Preferably At is between 0 s and +/- 1 s, more preferably between 0 s and +/- 0.5 s, even more preferably between 0 s and +/- 0.1 s. Thus it is to be understood that generation of intercepting roll moment Mi may precede upcome of roll moment MPOD as well as the other way around depending on the inherent delay in the propulsion system and the interceptor system respectively. The overall aim of the arrangement according to the invention, however, is that At shall equal zero which is achievable thanks to the inherent speed of the interceptor blades 10, 10'. Preferably, the movement of the interceptor blade 10, 10' can be monitored during turn to correspond at any given time to the movement and the speed of the ship, and the whole of the turning movement can thereby be adapted to achieve a coordinated turn where the best possible conditions for the operation of the ship and the well being of the passengers can be achieved.

The invention is not to be seen as limited by the preferred embodiments described above, but can be varied within the scope of the appended claims, as will become readily apparent to the person skilled in the art. For instance there may be more than one interceptor on each side of the keel 42.