TECHNICAL FIELD

The invention relates to a system for controlling the movement of a marine vessel relative to a marine vessel location area. Moreover, the present invention relates to a steering and propulsion arrangement for steering and propelling a marine vessel as well as to a marine vessel. Further, the present invention relates to a method for controlling the movement of a marine vessel relative to a marine vessel location area.

The invention can be applied in marine vessels. Although the invention will be described with respect to a marine vessel comprising an outboard propulsion unit set, the invention is not restricted to marine vessels with such a steering and propulsion arrangement. Instead, the present invention may be used in marine vessels with any type of steering and propulsion arrangement, such as marine vessels with an inboard propulsion system. BACKGROUND

Present-day marine vessels may be equipped with a steering and propulsion arrangement. Moreover, contemporary marine vessels may also comprise a system for controlling the movement of a marine vessel by issuing control input to the steering and propulsion arrangement.

For instance, the system may be adapted to receive information indicative of the position of the marine vessel, for instance information indicative of the position of the marine vessel relative to another reference point or reference area, and thereafter automatically issue control input to the steering an propulsion arrangement such that the marine vessel can move in a predetermined manner relative to the reference point or reference area.

For instance, US2017/0205829 A1 , discloses a system with a plurality of transducers operable to sense a relative distance between a marine vessel and an object, such as a slip walkway, and thereafter control the movement of the marine vessel accordingly.

However, the system disclosed in US2017/0205829 A1 generally requires a clear field of view from the transducers to the object in order to control movements of a marine vessel in a desired manner. SUMMARY

An object of the invention is to provide a robust system for controlling the movement of a marine vessel.

The object is achieved by a system according to claim 1 .

As such, a first aspect of the present invention relates to a system for controlling the movement of a marine vessel relative to a marine vessel location area. The system comprises a receiver adapted to be located on the marine vessel. The receiver is adapted to receive signals actively transmitted from each one of at least three, preferably at least four, stationary transmitters at least partially delimiting the marine vessel location area to thereby determine relative positions between the receiver and each one of the stationary transmitters.

According to the first aspect of the present invention, the system is adapted to automatically issue a control input to a steering and propulsion arrangement of the marine vessel in response to the relative positions. The above recited system, being adapted to receive signals from the above-mentioned transmitters, implies that the position of the marine vessel location area may be determined with a relatively high level of accuracy, even in conditions when there is not a clear line of sight between the receiver and the transmitters. Moreover, by virtue of the fact that the transmitters at least partially delimit the marine vessel location, an operator may adequately define the marine vessel location area by placing the transmitters accordingly.

As used herein, the term "transmitter" is intended to encompass any component that is adapted to at least transmit a signal but the term "transmitter" is not limited to components the sole purpose of which is to transmit a signal or signals. For instance, at least one but possibly each one of the transmitters presented in this application may also be adapted to receive signals. In a similar vein, the term "receiver" is intended to encompass any component that is adapted to at least receive a signal but the term "receiver" is not limited to components the sole purpose of which is to receive a signal or signals. For instance, at least one but possibly each one of the receivers may also be adapted to transmit signals. Purely by way of example, each one of the transmitters may be adapted to receive signals transmitted from each one of the receivers.

As such, in embodiments of the invention, the transmitters and the receivers may communicate with each other. Purely by way of example, each one of the transmitters and the receivers may be of the same type. In such an example, each one of such components may be referred to as a transceiver.

Purely by way of example, a receiver may be adapted to transmit a signal to the transmitters in order to initiate an operation of determining the relative positions.

Optionally, the system is adapted to determine a target position of the marine vessel within the marine vessel location area.

For instance, the marine vessel location area may be associated with a berth and the target position may be a docking position within the berth. Owing to the fact that there are generally relatively short distances between the at least one receiver and the transmitters, the target position may be accurately determined. Moreover, the target position may be determined as a set of distances between the at least one receiver and each one of the transmitters. Thus, an appropriate target position may be determined without necessarily requiring detailed information as regards the marine vessel's position in a global coordinate system.

Optionally, the system is adapted to determine the target position in response to input received from an operator of the system. Thus, once an operator has determined that a specific position within the marine vessel location area is preferred, for instance having regard to mooring equipment and/or platforms, the operator may for instance use an interface for issuing a signal to the system and upon receipt of such a signal, the system may store the target position. Optionally, the system is adapted to determine a start position of the marine vessel outside the marine vessel location area. The system is adapted to automatically issue the control input to the steering and propulsion arrangement of the marine vessel to move the marine vessel from the start position to the target position and vice versa.

A port or a harbour, for instance a port or a harbour for leisure boats, is generally associated with limited space for manoeuvring vessels within the port or harbour. Thus, by virtue of the above automatic movement between the target position and the start position, the movement between the two positions may be carried out with a limited manoeuvring area requirement for the vessel, in particular since motions of the marine vessel may be controlled on the basis of the relative distances between the at least one receiver and the transmitters.

Optionally, at least two of the stationary transmitters are entrance stationary transmitters defining at least one entrance for the marine vessel into the marine vessel location area. The system is adapted to automatically issue the control input to the steering and propulsion arrangement of the marine vessel such that the marine vessel moves from the start position to an intermediate position at least partially outside the marine vessel location area from which intermediate position the marine vessel can move into the marine vessel location area, via the entrance, by means of a substantially longitudinal motion.

Thus, between the start position and the intermediate position, the marine vessel may be controlled by prioritizing yaw and sway motions of the marine vessel such that the vessel is properly oriented before the marine vessel is moved towards its target position. Since the marine vessel location area may be relatively confined and since yaw and sway motions may have a relatively large impact on the position of the outmost portions of the marine vessel, it may be beneficial to prioritize yaw and sway motions before entering the marine vessel location area.

Optionally, upon detection that the marine vessel is within a predetermined distance from the start position, the system is adapted to automatically issue the control input to the steering and propulsion arrangement of the marine vessel such that the marine vessel moves to the start position. Thus, when for instance entering a port or harbour but before being close to the transmitters, the system may automatically guide the marine vessel to a predetermined start position for the marine vessel. Such an automatic guide implies that the marine vessel may thereafter be moved in a straightforward manner from the start position to the target position.

Optionally, upon detection that the marine vessel has reached the start position, the system may be adapted to automatically issue the control input to the steering and propulsion arrangement of the marine vessel such that the marine vessel moves in a desired manner.

For instance, if the marine vessel has reached the start position from a position outside the marine vessel location area, the system may issue the control input to the steering and propulsion arrangement of the marine vessel to move the marine vessel from the start position to the target position. Optionally, when the marine vessel has reached the start position from the target position, the system may be adapted to automatically move the marine vessel from the start position, for instance following a predetermined route that has been input by an operator of the system. Optionally, the system comprises a positioning system, preferably a global positioning system, in addition to the receiver, the system being adapted to determine a position of the marine vessel relative to the start position by means of the positioning system.

Thus, the start position need not necessarily be determined by virtue of the at least one receiver. This in turn implies that the system may be able to determine the start position even when the marine vessel is at relatively large distance from the start position.

Optionally, the system is adapted to determine an exclusion zone between the target position and the locations of the stationary transmitters. The system is adapted to automatically issue the control input to the steering and propulsion arrangement of the marine vessel such that the marine vessel is prevented from being moved into the exclusion zone.

The exclusion zone may for instance be used to obtain a safety margin to objects that are located in or adjacent to the marine vessel location area. Example of such objects may be bollards or a slip walkway. Purely by way of example, such a safety margin may be useful in order to have a margin for wind, wave or current induced motions of the marine vessel when the vessel moves from the start position to the target position or vice versa. Optionally, the system is adapted to use a target speed for the marine vessel wherein the target speed is dependent on a determined relative distance between a current position and the target position of the marine vessel. Purely by way of example, the target speed may be reduced as the marine vessel approaches its target position. Such a speed reduction will enhance the possibilities to stop the marine vessel at the target position and the speed reduction also implies a thorough control of the marine vessel's motions as the marine vessel is approaching the target position.

Optionally, the receiver is adapted to receive signals actively transmitted from each one of at least four stationary transmitters at least partially delimiting the marine vessel location area to thereby determine relative positions between the receiver and each one of the at least four stationary transmitters.

The use of at least four stationary transmitters may further increase the accuracy when determining the relative position between the marine vessel and the marine vessel location area.

Optionally, the system further comprises an additional receiver adapted to be located on the marine vessel. The additional receiver is adapted to receive signals actively transmitted from each one of the stationary transmitters at least partially delimiting the marine vessel location area to thereby detect relative positions between the additional receiver and each one of the stationary transmitters. The system is adapted to automatically issue a control input to the steering and propulsion arrangement of the marine vessel in response to the relative positions associated with each one of the receiver and the additional receiver.

The use of the receiver and the at least one additional receiver implies that the position of the marine vessel may be determined with an increased level of accuracy. For instance, the use of the receiver and the at least one additional receiver implies that the yaw of the marine vessel relative to the marine vessel location area may be determined with a sufficiently high level of accuracy and this in turn implies that the moving of the marine vessel relative to the marine vessel location area may be carried out with an appropriate level of accuracy.

Optionally, the system further comprises the stationary transmitters. Thus, the system including the transmitters may for instance be delivered as a system package.

Optionally, the system comprises means for identifying a location with the stationary transmitters even in situations when the first and second receivers cannot receive signals actively transmitted from each one of the stationary transmitters. Preferably the means comprises at least one of a look-up table and communication means for communicating with a source of information comprising at least one location with the stationary transmitters.

The above capability implies that a marine vessel, for instance travelling at sea, may identify a port or harbour having the at least three transmitters. An operator of the marine vessel may then decide to go to such a port in order to ensure that e.g. an automatic docking operation may be performed.

A second aspect of the present invention relates to an assembly for steering and propelling a marine vessel, said assembly comprising a steering and propulsion arrangement, which in turn comprises at least one propulsion unit, and a system according to the first aspect of the present invention.

A third aspect of the present invention relates to a marine vessel comprising the assembly according to the second aspect of the present invention and/or a system according to the first aspect of the present invention.

A fourth aspect of the present invention relates to a method for controlling the movement of a marine vessel relative to a marine vessel location area. The marine vessel comprises a receiver and a steering and propulsion arrangement. The method comprises:

- receiving signals actively transmitted from each one of at least three, preferably at least four, stationary transmitters at least partially delimiting the marine vessel location area to thereby determine relative positions between the receiver and each one of the stationary transmitters, and - automatically controlling the steering and propulsion arrangement of the marine vessel in response to the relative positions.

Optionally, the method comprises determining a target position of the marine vessel within the marine vessel location area.

Optionally, the method further comprises determining a start position of the marine vessel outside the marine vessel location area. The method comprises automatically controlling the steering and propulsion arrangement of the marine vessel to move the marine vessel from the start position to the target position and vice versa.

Optionally, at least two of the stationary transmitters are entrance stationary transmitters defining at least one entrance for the marine vessel into the marine vessel location area. The method comprises automatically controlling the steering and propulsion arrangement of the marine vessel such that the marine vessel moves from the start position to an intermediate position at least partially outside the marine vessel location area and from the intermediate position automatically controlling the steering and propulsion arrangement such that the marine vessel moves into the marine vessel location area, via the entrance, by means of a substantially longitudinal motion.

Optionally, the method further comprises, upon detection that the marine vessel is within a predetermined distance from the start position, automatically controlling the steering and propulsion arrangement such that the marine vessel moves to the start position. Optionally, the method comprises determining an exclusion zone between the target position and the locations of the stationary transmitters. The method comprises automatically controlling the steering and propulsion arrangement such that the marine vessel is prevented from being moved into the exclusion zone. Optionally, the method comprises imparting a target speed to the marine vessel wherein the target speed is dependent on a determined relative distance between a current position and the target position of the marine vessel.

Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples.

In the drawings:

Fig. 1 illustrates a vessel with an embodiment of a system for controlling the movement of the marine vessel;

Figs. 2 to 6 illustrates various embodiments of the system for a vessel located close to a port, and Fig. 7 is a flow chart for a method for controlling the movement of a marine vessel.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

Fig. 1 illustrates an embodiment of a marine vessel 10. The Fig. 1 marine vessel 10 is exemplified as a boat, such as a leisure boat. As a non-limiting example, embodiments of the marine vessel may have a length (length between perpendiculars) within the range of 3 to 20 meters.

As may be gleaned from Fig. 1 , the embodiment of the marine vessel 10 illustrated therein comprises an assembly 12 for steering and propelling the marine vessel 10. The assembly 12 comprises a steering and propulsion arrangement 14, which in turn comprises at least one propulsion unit 16, and a system 18 for controlling the movement of the marine vessel 10 relative to a marine vessel location area (not shown in Fig. 1 ). Purely by way of example, the system 18 may be adapted to receive signals and to issue control input on the basis of the received signals. As a non-limiting example, the system 18 may comprise an electronic control unit (not shown).

Moreover, as indicated in the Fig. 1 embodiment, the system 18 comprises a receiver 20 adapted to be located on the marine vessel 10. The receiver 20 is adapted to receive signals actively transmitted from each one of at least three stationary transmitters (not shown in Fig. 1 ) at least partially delimiting the marine vessel location area to thereby determine relative positions between the receiver and each one of the at least three stationary transmitters. The Fig. 1 embodiment of the system 18 further comprises an additional receiver 22 adapted to receive signals actively transmitted from each one of the above-mentioned at least three stationary transmitters (not shown in Fig. 1 ). As indicated in Fig.1 , in the event that the system 18 comprises a receiver 20 and an additional receiver 22, the receivers 20, 22 may preferably be adapted to be located at a distance from each other on the marine vessel 10. Purely by way of example, and as illustrated in Fig. 1 , the receiver 20 may be adapted to be located at the stern and the additional receiver 22 may be adapted to be located at the bow of the marine vessel 10, or vice versa.

Furthermore, the system 18 is adapted to automatically issue a control input to the steering and propulsion arrangement 14 of the marine vessel in response to the relative positions thus determined.

Embodiments of the marine vessel 10 may comprise a steering and propulsion arrangement 14 comprising two or more propulsion units (not shown). Purely by way of example, it is envisaged that the embodiments of the marine vessel 10 may comprise at least a bow thruster (not shown in Fig. 1 ).

Moreover, the system 18 may be adapted to receive instructions from an operator via an interface 24. Purely by way of example, the interface may comprise at least one of a lever, a knob, a button or a touch screen (not shown). Moreover, the marine vessel 10 may comprise a positioning system 26, such as a global positioning system, which may be adapted to communicate with the system 18. Unlike the receivers 20, 22, the positioning system 26 can determine the position of the vessel 10 without requiring the signals from the transmitters.

Fig. 1 also illustrates a coordinate system for the marine vessel 10 and as well as presenting a nomenclature for rotations of the marine vessel 10. To this end, the coordinate system has a longitudinally extending X-axis, a transversally extending Y-axis and a vertically extending Z-axis. The X-, Y- and Z-axes are perpendicular to each other. Moreover, Fig. 1 illustrates that rotation around the X-axis is referred to as roll, rotation around the Y-axis is referred to as pitch and rotation around the Z-axis is referred to as yaw. Furthermore, a movement along the X-axis is referred to as surge and a movement along the Y-axis is referred to as sway.

Possible capabilities of the system 18 will be described hereinbelow. To this end, reference is made to Fig. 2 illustrating a port or a harbour 26 comprising a set of berths 28, 30, 32. In the example illustrated in Fig. 2, each berth 28, 30, 32 is at least partially delimited by boat parking dividers 34, 36, 38, 40 but is it also envisaged that the berths 28, 30, 32 may be delimited in other ways, for instance by means of buoys (not shown) or bollards (not shown). Moreover, Fig. 2 also illustrates an embodiment of a marine vessel 10 with a system 18 as has been discussed hereinabove.

Moreover, as indicated in Fig. 2, at least one berth 32 is associated with at least three stationary transmitters 42, 44, 46. Each one of the three stationary transmitters 42, 44, 46 at least partially delimits a marine vessel location area 48 which is indicated by a dashed and dotted line in Fig. 2. In the Fig. 2 example, each one of the transmitters 42, 44, 46 is located on the edges of the marine vessel location area 48. It should also be noted that in other implementations, the transmitters 42, 44, 46 need not necessarily be associated with a berth 32. Instead, the marine vessel location area 48, delimited by the transmitters, may be located at sea, for instance defining a suitable leisure, swimming or fishing area for the marine vessel 10. As a further example, the marine vessel location area 48 may be associated with a boat launching ramp (not shown). Purely by way of example, each one of the transmitters 42, 44, 46 may be connected to a power source (not shown), for instance an electric power source such as a battery or a cable. Moreover, though again purely by way of example, each one of the transmitters 42, 44, 46 may be adapted to actively issue signals, for instance electromagnetic signals such as radio waves or microwaves. As a non-limiting example, such signals may comprise information indicative of the identity of the transmitter and possibly also indicative of the position of the sensor.

The at least one receiver 20 of the system 18 is adapted to receive signals actively transmitted from each one of at least three stationary transmitters 42, 44, 46 at least partially delimiting the marine vessel location area 48 to thereby determine relative positions between the at least one receiver 20 and each one of the at least three stationary transmitters 42, 44, 46. As such, the at least one receiver 20 and the at least three stationary transmitters 42, 44, 46 may be such that at least a communication from the transmitters to the at least one receiver 20 is obtained. For instance, the transmitters 42, 44, 46 and the at least one receiver 20 may communicate via electromagnetic waves of a predetermined frequency or within a predetermined frequency range.

Furthermore, the system 18 may for instance be adapted to determine the distance from the at least one receiver 20 to each one of the transmitters by evaluating the elapsed time from the issuance of the signal from each one of the transmitters 42, 44, 46 to the receipt of the signals by the at least one receiver 20. As another non-limiting example, the system 18 may be adapted to determine the distances using the Doppler effect.

Further, the Fig. 2 vessel comprises the previously discussed additional receiver 22. In a similar vein as for the receiver 20, the additional receiver 22 of the system 18 may be adapted to receive signals actively transmitted from each one of at least three stationary transmitters 42, 44, 46 at least partially delimiting the marine vessel location area 48 to thereby determine relative positions between the additional receiver 22 and each one of the at least three stationary transmitters 42, 44, 46.

Moreover, the system is adapted to automatically issue a control input to the steering and propulsion arrangement 16 of the marine vessel 10 in response to the relative positions thus determined. Purely by way of example, and as illustrated in Fig. 2, the system 18 may be adapted to determine a target position 50 of the marine vessel 10 within the marine vessel location area 48. Such a target position 50 is indicated by a dashed line in Fig. 2. As a non-limiting example, the system 18 may be adapted to determine the target position in response to input received from an operator of the system 18.

As such, when an operator of the marine vessel 10 has determined that a specific position within the marine vessel location area 48 is preferred, for instance having regard to mooring equipment and/or a distance to a jetty, the operator may issue a signal to the system 18, for instance using the interface 24 discussed hereinabove in relation to Fig. 1 , and upon receipt of such a signal, the system 18 may store the target position. Purely by way of example, the target position may be defined in terms of relative distances between each one of the transmitters 42, 44, 46 and the receiver 20 and possibly also the additional receiver 22 if the system 18 comprises such an additional receiver 22. With reference to Fig. 3, the system 18 may be adapted to determine a start position 52 of the marine vessel 10 outside the marine vessel location area 48. The system is adapted to automatically issue the control input to the steering and propulsion arrangement of the marine vessel 10 to move the marine vessel from the start position to the target position and vice versa.

Thus, the system 18 may be adapted to automatically dock the marine vessel 10. As such, when the marine vessel 10 is in the start position 52, the system 18 may be adapted to automatically dock the marine vessel 10 such that the vessel 10 arrives at the target position 50 without the need for manual steering of the marine vessel 10.

Moreover, the system 18 may be adapted to automatically launch the marine vessel 10. As such, when the marine vessel 10 is in the target position 50, the system 18 may be adapted to automatically move the marine vessel 10 such that the vessel 10 arrives at the start position 52 without the need for manual steering of the marine vessel 10. Once the marine vessel 10 is in the start position 52, an operator of the vessel 10 may thereafter control the movements of the vessel 10 or the marine vessel may be actuated so as to follow a predetermined route.

Further, Fig. 3 illustrates that at least two 42, 44 of the at least three stationary transmitters 42, 44, 46 may constitute entrance stationary transmitters defining at least one entrance 54 for the marine vessel 10 into the marine vessel location area 48. Put differently, the marine vessel 10 may move into and out from the marine vessel location area 48 via the entrance 54. As indicated in Fig. 3, the entrance 54 may be a line connecting the entrance stationary transmitters 42, 44.

Additionally, the system 18 may be adapted to automatically issue the control input to the steering and propulsion arrangement of the marine vessel 10 such that the marine vessel moves from the start position 52 to an intermediate position 56 at least partially outside the marine vessel location area 48 from which intermediate position 56 the marine vessel 10 can move into the marine vessel location area 48, via the entrance 54, by means of a substantially longitudinal motion, i.e. a substantial surge motion.

Thus, as indicated by the arrows in Fig. 3, when moving from the start position 52 to the intermediate position 56, the system 18 may control the motions of the marine vessel such that yaw and sway motions are prioritized. Moreover, when moving from the start position 52 to the intermediate position 56, information indicative of the relative distances between the receiver 20 or receivers 20, 22 and the entrance stationary transmitters 42, 44 may be prioritized in order to ensure that the marine vessel 10 is adequately placed in an intermediate position 56 wherein the width of the marine vessel 10 is located within the entrance stationary transmitters 42, 44.

Purely by way of example, when moving from the start position 52 to the intermediate position 56, the system 18 may control the motions of the marine vessel such that an extension of the longitudinal centre line of the marine vessel 10 intersects, or at least substantially intersects, a horizontal centre point of the entrance 54. As a non-limiting example, should the entrance stationary transmitters 42, 44 be located symmetrically around the entrance and should the receiver 20 or receivers 20, 22 be located along the longitudinal centre line of the marine vessel 10, the system 18 may control the motions of the marine vessel 10 such that the relative distances from each one of the entrance stationary transmitters 42, 44 and the at least one receiver are substantially equal.

Furthermore, though again purely by way of example, when moving from the start position 52 to the intermediate position 56, the system 18 may control the motions of the marine vessel such that longitudinal motions, e.g. surge motions, of the marine vessel 10 are prevented until the marine vessel has reached the intermediate position 56. Such a prevention of the longitudinal motion of the marine vessel 10 may reduce the risk that the marine vessel 10 inadvertently enters the marine vessel location area 48 before the marine vessel 10 is adequately oriented and positioned relative to the entrance 54. To this end, though purely by way of example, the system 18 may prevent longitudinal motions of the marine vessel 10 until distance errors, being the difference between desired distances and measured distances between the transmitters 42, 44, 46 and the receiver(s) 20, 22, are below a predetermined threshold value. Moreover, when the marine vessel 10 is in the intermediate position 56, the marine vessel 10 may move from there to the target position 50 by means of a substantially longitudinal motion, or a substantial surge motion, as indicated by arrow 58 in Fig. 3. When moving from the intermediate position 56 to the target position 50, information indicative of the relative distances between the receiver 20 or receivers 20, 22 and rear stationary transmitter 46 may be prioritized in order to enable that the marine vessel 10 can move to the target position 50. In a similar vein, when moving from the target position 50 to the intermediate position 56, the system 18 may be adapted to control the marine vessel 10 such that the vessel 10 moves substantially longitudinally. Thereafter, the vessel 10 may be rotated, and possibly also be imparted a sway motion, such that the marine vessel 10 arrives at the start position 52.

In order to ensure that the marine vessel 10 does not undergo undesired sway or yaw motions as the marine vessel 10 is moved in the marine vessel location area 48, the distance between the 42, 44, 46 and the receiver(s) 20, 22 may be monitored as the marine vessel 10 moves in the marine vessel location area 48. Here, the presence of the additional receiver 22 may be advantageous since the such an additional receiver 22 may be used for determining if the marine vessel 10 undergoes undesired sway or yaw motions when the marine vessel 10 moves in the marine vessel location area 48, for instance to or from the target position 50. Furthermore, the system 18 may be adapted to move the marine vessel 10 automatically to the start position 52. To this end, reference is made to Fig. 4 illustrating the system 18 may be such that, upon detection that the marine vessel 10 is within a predetermined distance from the start position 52, the system 18 is adapted to automatically issue the control input to the steering and propulsion arrangement of the marine vessel such that the marine vessel 10 moves to the start position 52. Purely by way of example, the system may use a positioning system, preferably a global positioning system, such as discussed hereinabove with reference to Fig. 1 for determining the position of the marine vessel 10 relative to the start position 52. To this end, Fig. 4 illustrates the marine vessel 10 in a cruising position 60. For instance, the marine vessel 10 may have been on a voyage and is returning back to the port or harbour 26. When the distance between the cruising position 60 and the start position 52 is less than a predetermined distance, which distance is exemplified by the circular 5 envelope 62 in Fig. 4, the system 18 may automatically issue the control input to the steering and propulsion arrangement of the marine vessel 10 such that the marine vessel 10 moves to the start position 52.

From the start position 52, the system may thereafter issue control input such that the 10 marine vessel 10 moves to the target position 50, for instance using the procedure discussed hereinabove with reference to Fig. 3.

Moreover, with reference to Fig. 5, the system 18 may be adapted to determine an exclusion zone 64 between the target position 50 and the locations of the at least three 15 stationary transmitters 42, 44, 46. Moreover, the system 18 is adapted to automatically issue the control input to the steering and propulsion arrangement of the marine vessel 10 such that the marine vessel is prevented from being moved into the exclusion zone 64.

As indicated in Fig. 5, the exclusion zone 64 may for instance comprise portions of the 20 boat parking dividers 38, 40 in order to avoid that the marine vessel 10 impacts the boat parking dividers 38, 40 as the vessel 10 moves relative to the marine vessel location area 48.

Moreover, as also exemplified in Fig. 5, the exclusion zone 64 may also comprise a safety 25 margin outside the boat parking dividers 38, 40. Purely by way of example, such a safety margin may be useful in order to have a margin for wind, wave or current induced motions of the marine vessel when the vessel moves from the start position to the target position.

Furthermore, with reference to any one of the embodiments of the system 18, the system 30 18 may be adapted to use a target speed for the marine vessel 10 wherein the target speed is dependent on a determined relative distance between a current position and the target position 50 of the marine vessel 10. Purely by way of example, the target speed may be reduced as the marine vessel approaches its target position 50. Although the embodiments of the system 18 discussed hereinabove with reference to each one of Fig. 2 to Fig. 5 illustrates that the receiver 20, and possibly also the additional receiver 22, is adapted to receive signals actively transmitted from each one of at least three stationary transmitters 42, 44, 46, it is also envisaged that in embodiments of the 5 system 18, the receiver 20, and possibly also the additional receiver 22, may be adapted to receive signals actively transmitted from each one of at least four stationary transmitters 42, 44, 46, 66.

To this end, reference is made to Fig. 6 illustrating a scenario in which a marine vessel 10 location area 48 is delimited by four stationary transmitters 42, 44, 46, 66. Purely by way of example, and as indicated in Fig. 6, the four stationary transmitters 42, 44, 46, 66 may be located in the corners of the marine vessel location area 48.

Moreover, irrespective of the number of stationary transmitters, the system 18 may 15 comprise means for identifying a location with the at least three, possibly at least four, stationary transmitters even in situations when the first and second receivers cannot receive signals actively transmitted from each one of at least three stationary transmitters. Preferably the means comprises at least one of a look-up table (not shown) and communication means (not shown) for communicating with a source of information 20 comprising at least one location with the at least three stationary transmitters.

As a non-limiting example, the look-up table may be stored in the system 18. Moreover, by way of example only, the communication means may for instance be adapted to be connected to the internet, for instance using a wireless connection, and be able to 25 communicate with a database containing information indicative of ports or harbours equipped with three or more transmitters that are adapted to communicate with the receiver(s) 20, 22 of the system 18.

Fig. 7 illustrates a flow chart of a method for controlling the movement of a marine vessel 30 10 relative to a marine vessel location area 48. The marine vessel 10 comprises a receiver and a steering and propulsion arrangement 14. The method comprises:

S10 receiving signals actively transmitted from each one of at least three, preferably at least four, stationary transmitters at least partially delimiting the marine vessel location area to thereby determine relative positions between the receiver and each one of the at least three stationary transmitters, and

S12 automatically controlling the steering and propulsion arrangement of the marine vessel in response to the relative positions.

It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.