FIELD OF THE INVENTION

This invention relates in general to the field of marine mooring equipment and, in particular, to fairleads used for guiding a mooring line.

BACKGROUND OF THE INVENTION

Fairleads are an important tool in marine environments to guide a line, e.g. a rope, cable or chain, around an object, or to prevent lateral movement of the line. Some fairleads, known as moveable fairleads or rotating fairleads, are capable to rotating around a vertical axis to allow for changes in the direction of the line, without having an angle in the line.

Figure 1 is a schematic diagram showing a moveable fairlead 1 according to a prior art implementation. The moveable fairlead 1 is generally attached to the hull of a floating vessel such as, for example, a ship or floating platform. The moveable fairlead comprises a pair of brackets 10, a rotating support shaft 20 and a guide member 30.

The brackets 10 are for attachment to the floating vessel. For example, the brackets 10 may be welded to the hull of the floating vessel. The rotating support shaft 20 is coupled to the one or more brackets and configured to rotate with respect to the brackets 10. In some implementations, a single rotating support shaft 20 may extend vertically between the two brackets 10, or a pair of rotating support shafts may support the guide member 30 between them.

The guide member 30 typically includes a guide wheel 31 or a fixed guide channel for the cable or chain to pass through. The guide member 30 can include connecting plates 32 e.g. to connect the guide wheel with the rotating support shaft 20. The guide member is attached to the rotating support shaft(s) and is configured to rotate with the rotating support shaft(s). In this way, the fairlead 1 can rotate around a vertical axis and can guide the line without having an angle in the line.

A problem with these moveable fairleads arises where an offshore unit or floating vessel is not anchored and is moving or being moved, and one or more fairleads attached to an exterior of the hull are rotating freely. Freely rotating fairleads can often slam against the floating vessel, causing damage to the vessel and/or the fairlead itself due to the waves and movement of the vessel.

The present invention aims to address these problems in the state of the art.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provided a locking unit for a moveable fairlead on a floating vessel according to claim 1 .

According to a second aspect of the present invention, there is provided a moveable fairlead according to claim 11 .

According to a third aspect of the present invention, there is provided a method of retrofitting a locking unit to a moveable fairlead on a floating vessel according to claim 12.

Optional features are as set out in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention and to show more clearly how it may be carried into effect, reference will now be made by way of example only, to the accompanying drawings, in which: Figure 1 is a schematic diagram showing a moveable fairlead according to a prior art implementation;

Figure 2 is a schematic diagram showing a locking unit according to an embodiment;

Figure 3 is a schematic diagram showing a stopper plate according to an embodiment;

Figure 4 is a schematic diagram showing a locking pin according to an embodiment;

Figure 5 is a side-elevation view showing a locking unit according to an embodiment;

Figure 6 is a cross-section view showing a locking unit according to an embodiment; and

Figure 7 is a flowchart showing a method of retrofitting a braking unit according to an embodiment.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a locking unit for attachment to a moveable fairlead, and a method of retrofitting the locking unit to a moveable fairlead. In particular, the locking unit prevents movement of the fairlead by passing a locking pin through a locking hole in a stopper plate.

Figure 2 of the accompanying drawings shows a locking unit 100 for a moveable fairlead 1 on a floating vessel according to an embodiment. The locking unit 100 comprises a stopper plate 110, a locking pin 120 and a locking actuator 130. The stopper plate 110 is configured for coupling to a rotating support shaft of the moveable fairlead 1. The stopper plate 110 is configured to be coupled in a position where an axis of the rotating support shaft is normal to the stopper plate 110. The stopper plate is of part-disc shape. The stopper plate 110 includes one or more locking holes 111 extending through the stopper plate 110. The locking pin 120 is configured to pass through one of the locking holes 111 in the stopper plate 110. The locking actuator 130 is configured to move the locking pin 120 into a locked position where the locking pin 120 extends through one of the locking holes 111 in the stopper plate 110.

In this way, the locking unit 100 can prevent swinging of a moveable fairlead 1 which has the potential to cause damage to the floating vessel or the fairlead 1 itself. The locking unit 100 can be provided in a modular unit which can be retrofitted to an existing fairlead 1 in situ on a floating vessel.

The locking unit 100 can be attached or retrofitted to any form of floating vessel, e.g. a ship or floating platform. The locking unit 100 can be made compatible with any of the large variety of moveable fairleads used on such floating vessels. For example, the locking unit 100 can be attached to a fairlead 1 with a guide wheel or guide channel, with or without connecting side plates, and with a single support shaft or a pair of support shafts supporting a guide member in between. The locking unit 100 can be made compatible with any other variation in form or size of moveable fairlead 1 .

In some examples, the stopper plate 110 may be configured to directly attach to the rotating support shaft. In some examples, the stopper plate 110 may be configured to attach to a guide member which is attached to the rotating support shaft and configured to rotate with the rotating support shaft. For example, the stopper plate 110 may be configured to attach to a connecting side plate which is coupled to the rotating support shaft, or supported between two rotating support shafts, and supports a guide wheel.

In some embodiments, the stopper plate 110 may have a semi-circular form with a straight edge and a semi-circular edge. The stopper plate 110 may be configured to be coupled to the rotating support shaft at a mid-point of the straight edge.

In this way, the stopper plate 110 can be directly attached at a central point of rotation to a rotating element of the moveable fairlead 1. As the stopper plate 110 is rotated by movement of the moveable fairlead 1 , the stopper plate 110 can pass the locking pin 120 in a semi-circular arc.

Fig 4 shows a schematic diagram of a stopper plate 110 according to an embodiment.

In some examples, the stopper plate 110 may be shaped for attachment to the moveable fairlead 1. For example, the stopper plate 110 may include a notch configured to fit around the rotating support shaft or any other rotating element of the moveable fairlead 1. The stopper plate 110 may be formed from steel, or any material suitable for marine construction.

In some embodiments, the stopper plate 110 may include a plurality of locking holes 111. The locking holes 111 may be spaced along a circular arc of the stopper plate 110 arranged to be centred on the axis of the rotating support shaft. In this way, as the stopper plate 110 is rotated by movement of the moveable fairlead 1 , locking pin 120 will pass over each of the locking holes 111 in the circular arc.

In some examples, each point on the circular arc may be formed to slope towards an adjacent locking hole. In this way, when the locking actuator 130 moves the locking pin 120 towards the locking position, the locking pin 120 will either pass directly through a locking hole 111 , or will contact a sloped portion of the circular arc.

In some examples, pressure applied between the locking pin 120 and the sloped portion may force the stopper plate 110 to rotate until the adjacent locking hole 111 aligns with the locking pin 120. In some examples, the locking pin 120 and/or locking actuator 130 may be configured to flex or move laterally. Pressure applied between the locking pin 120 and the sloped portion may cause the locking pin 120 to flex and/or move laterally until the locking pin 120 aligns with the adjacent locking hole. In some examples, when the locking pin 120 is in the locking position, a restoring force (e.g. a spring or internal flexion) acting on the locking pin 120 and/or locking actuator 130 may cause the stopper plate 110 to rotate until the locking pin 120 returns to its original lateral position.

In some examples, each point may be formed to slope towards the nearest adjacent locking hole. Alternatively, in some examples, a sloping profile along the circular arc may be biased (e.g. a 'sawtooth' profile) to bias the stopper wheel in one direction over the other. In some implementations, the sloping profile may be formed by machining or casting the stopper plate 110.

In some examples, the stopper plate 110 may be formed from any sector of a circle e.g. subtending an angle of more or less than 180, and configured to be attached at the centre point. In some examples, the stopper plate 110 may include a curved edge passing substantially through the central point. In some examples, the semicircular edge may be smooth or may be formed or shaped as required.

In some embodiments, the locking pin 120 may include a roller 121 arranged to contact the stopper plate 110. Figure 4 shows a schematic diagram of the locking pin 120, according to an embodiment. In some examples, the roller 121a may be implemented with a wheel and axle arrangement. In some examples, the roller 121 b may be implemented with a ball in socket mechanism. By providing a roller 121 on the locking pin 120, friction between the locking pin 120 and the stopper plate 110 can be reduced. In this way, excess wear or damage can be prevented to the locking pin 120 and/or locking plate, caused by contacting the locking pin 120 to the locking plate at a point not directly aligned with a locking hole. Where the stopper plate 110 is implemented with a sloped profile as described above, the roller 121 can improve a passage of the locking pin 120 from the sloped portion to the locking hole.

In some embodiments, the stopper plate 110 may be configured to extend through a socket 140 formed in a hull of the floating vessel. The locking pin 120 and locking actuator 130 may be arranged in an interior of the hull.

Figure 5 is a side-elevation view showing a locking unit 100 according to an embodiment. The locking unit 100 is shown from an interior of the hull. As shown, a socket 140 may be formed in the hull and the stopper plate 110 can extend through the socket 140 to the interior of the hull. A portion of the stopper plate 110 furthest from an attachment point of the stopper plate 110 may extend through the socket 140, i.e. a portion of the semicircular edge may be inside the hull of the floating vessel. The locking pin 120 and locking actuator 130 may be arranged below the stopper plate 110, as shown. Alternatively, the locking pin 120 and locking actuator 130 may be arranged above the stopper plate 110.

In some examples the socket 140 may be rectangular, as shown. The size of the socket 140 may be approximately the same as the portion of the stopper plate 110 extending through. In some examples, the socket 140 may be sized such that the full stopper plate 110 will not pass through. Alternatively, the socket 140 may be any shape or size which allows at least a portion of the plate to pass through. In some examples, the socket 140 may be already present on the hull, e.g. a maintenance hatch for the fairlead 1 , or the socket 140 may be cut into the fairlead 1 in order to retrofit the locking unit 100.

In some examples, the socket 140 may include a seal, e.g. a rubber seal arranged to fit tightly against the stopper plate 110 and allow rotational movement while preventing water from entering the hull. Alternatively, or in addition, the locking unit 100 may be separately sealed to prevent the ingress of water from inside the socket 140.

By extending the stopper plate 110 through the hull, and arranging the locking unit 100 in the interior of the hull, the locking unit 100 can be protected from seawater. For example, where the socket 140 and/or locking unit 100 is sealed or substantially sealed, the locking unit 100 can be isolated from seawater. In this way moving/mechanical parts of the locking unit 100 can be protected from corrosion. In addition, the locking unit 100 can be accessed more easily from the interior of the floating vessel, to maintain or repair components of the locking unit 100.

Alternatively, the locking unit 100 may be positioned on an exterior of the floating vessel e.g. where it is not possible to provide a socket 140 in the hull of the floating vessel. Individual components of the locking unit 100, e.g. the locking actuator 130 may be individually sealed to isolate them from seawater.

In some embodiments, the locking unit 100 may further include a rectangular enclosure 150 attached to the socket 140. The enclosure 150 may be arranged to receive the stopper plate 110 within. The locking pin 120 may be configured to pass through an opening in an upper and/or lower wall of the enclosure 150.

Figure 6 is a cross-section view showing a locking unit 100 according to an embodiment. As shown, the enclosure 150 may be a rectangular box shape which is open at one side. The open side of the enclosure 150 may be configured to attach to an interior side of the hull of the floating vessel, with the socket 140 within the open side. In this way, the interior of the enclosure 150 may be open to the exterior of the floating vessel.

The enclosure 150 may include one or more openings in an upper and/or lower wall of the enclosure 150. Each opening may be configured to allow the locking pin 120 to pass through the opening. In some examples, the enclosure 150 may include a pair of openings positioned in opposition on the upper and lower walls, such that the locking pin can pass fully through the enclosure 150. Alternately, in some examples, only one opening is provided such that the locking pin 120 can pass into the interior of the enclosure 150 to engage with the stopper plate 110.

In some embodiments, at least one of the openings includes a shaft seal. The shaft seal is configured to allow movement of the locking pin 120 through the opening and prevent water passing through the opening. In some examples, the seal may be a ring seal arranged within the opening and configured to fill a space around the locking pin 120. In some examples, the seal may include a closing mechanism configured to seal the opening when the locking pin 120 is removed from the opening.

In this way, the mechanical components of the locking unit 100 such as, for example, the locking actuator 130, can be isolated from seawater which may enter the hull through the socket 140. The locking pin 120 can be mounted such that locking pin 120 is exposed to the interior of the enclosure 150 but the locking actuator 130 is isolated from the interior of the enclosure 150. The enclosure 150 can fix a lateral position of the locking pin 120. In this way, the locking pin 120 can resist or prevent lateral or rotational movement of the stopper plate 110 when the locking pin 120 is engaged with the stopper plate 110. In some embodiments, the locking actuator 130 may include one or more hydraulic cylinders. The hydraulic cylinder allows for electronic control through a direct or remote operation. By using bi-directional hydraulics the locking actuator 130 can be activated or deactivated to control a locking function. Alternatively, a one directional hydraulic cylinder may be used and the locking actuator 130 may be biased to a deactivated position e.g. by one or more springs. In this way, a fail-off mechanism can be provided. If required, a fail-on mechanism can be provided by reversing the bias/actuation direction. In some examples, the hydraulic cylinders can be controlled to position the locking pin 120 at a specified point along an axis of travel.

Alternatively, the locking actuator 130 may be implemented by other means e.g. an electric motor or pneumatic system, or a manual actuator may be used e.g. a pump or lever based actuator. A manual actuator may be provided in addition to any other actuator as a failsafe in the event of a mechanical failure or power outage.

In some embodiments, the locking unit 100 may include a locking controller to control the locking actuator 130. The locking controller may be implemented by any suitable processor or processing unit.

The term "processor" may refer to a computational element that is operable to respond to and process instructions to perform operations. In an example, the processor may be a microprocessor, a microcontroller, a complex instruction set computing (CISC) microprocessor, a reduced instruction set (RISC) microprocessor, a very long instruction word (VLIW) microprocessor, or any other type of processing circuit, for example as aforementioned. The processor may be operated individually or as a part of a computation system.

The locking controller may be configured to activate the locking actuator 130, and/or deactivate the locking actuator 130. The locking controller may also be configured to control the locking actuator 130 to move the locking pin 120 into a certain position. The locking controller may be configured to control the locking actuator 130 to move the locking pin 120 upwards or downwards.

In this way, the locking controller provides improved control of a locking function, in a way which can be operated directly or remotely. Fine grained control over the timing and locking pin 120 positioning can be provided by the locking controller. Where a plurality of locking actuators 130 are provided, the locking controller can ensure synchronised control, improving locking efficiency and reducing component wear.

In some embodiments, the locking controller may be remotely operable through a wired and/or wireless connection. For example, the locking controller may be operated from a central control point of the floating vessel, e.g. a bridge or cockpit. Alternatively, or in addition, the locking may be operated from a control point removed from the floating vessel. The locking controller may be remotely operable through a connection including any selection or combination of suitable wired connections (e.g. serial, parallel, USB, ethernet etc.) and wireless connections (e.g. Bluetooth, Wi-Fi, cellular network, satellite network etc.).

By remotely operating, the locking unit 100 removes the need to reach the location of the fairlead 1 on an interior or exterior of the hull. In some cases, this can remove the need to raise the floating vessel out of the water, or reach the fairlead 1 underwater to control the locking unit 100. Where locking units 100 are installed on multiple fairleads, the remote operation allows the synchronised operation of some or all of the fairleads. In this way, the locking unit 100 can be more responsive, e.g. to changing weather conditions, or the operation can be more effectively synchronised to a mooring/relocating operation of the floating vessel. Alternatively, the locking controller may be operated directly, e.g. via a terminal or control panel co-located with the locking unit 100.

In some embodiments, the locking unit 100 may include one or more braking pads 160 and a braking actuator 170. The braking pads 160 may be configured to resist a rotational movement of the stopper plate 110. The braking actuator 170 may be configured to move the braking pads 160 into a braking position where the braking pads 160 are in contact with the stopper plate 110.

In this way, the locking unit 100 can reduce swinging of a moveable fairlead 1 which has the potential to cause damage to the floating vessel or the fairlead 1 itself. By providing brake pads 160 and a braking actuator 170, the locking unit 100 can reduce axial forces which act on the locking pin 120 during the locking, which have the potential to damage the locking pin 120.

Fig. 5 shows an example of a locking unit 100 with braking pads 160 and braking actuators 170 in position. In some examples, as shown, the braking pads 160 may be arranged in pairs above and below the stopper plate 110. The braking pads 160 may be formed from steel, or any material suitable for marine construction. In some examples, the material of the stopper plate 110 and the braking pads 160 may be selected to avoid galvanic pairs, to prevent excess corrosion.

Alternatively, in some embodiments a braking unit of other types may be provided. For example, a braking element such as, for example, brake pads 160 or a braking belt, may be configured to engage with an edge of the stopper plate or engage the rotating support shaft directly.

In some examples, the pads 160 may include one or more hydraulic cylinders for each of the one or more braking pads 160, or a hydraulic cylinder may be connected to multiple braking pads 160. The pads 160 may include a shoe or shell configured to hold the braking pads 160. The shoe or shell may be connected to the hydraulic cylinder or any other form of actuator. By implementing hydraulic cylinders, the braking unit is capable of exerting a sufficiently large braking force on the stopper plate.

By implementing hydraulic pads 160, the locking unit 100 can allow for electronic control of the braking mechanism through a direct or remote operation, substantially as described above with respect to the locking actuator 130. By using bi-directional hydraulics the pads 160 can be activated or deactivated to control a braking function by moving the braking pads 160 towards or away from the stopper plate 110. Alternatively, a one directional hydraulic cylinder may be used and the pads 160 may be biased to a deactivated position e.g. by one or more springs. In this way, a fail-off mechanism can be provided. If required, a fail-on mechanism can be provided by reversing the bias/actuation direction.

Alternatively, the pads 160 may be implemented by other means e.g. an electric motor or pneumatic system, or a manual actuator may be used e.g. a pump or lever based actuator. A manual actuator may be provided in addition to any other actuator as a failsafe in the event of a mechanical failure or power outage.

Also provided is a moveable fairlead 1 , according to an embodiment. The moveable fairlead 1 comprises one or more brackets, a rotating support shaft, a guide member and a locking unit 100 substantially as described above.

The brackets are configured for attachment to a floating vessel. For example, the brackets may be welded to the hull of the floating vessel. The moveable fairlead 1 may be attached to any form of floating vessel, e.g. a ship or floating platform.

The rotating support shaft is coupled to the one or more brackets and configured to rotate with respect to the brackets. In some implementations, a single rotating support shaft may extend vertically between the two brackets, or a pair of rotating support shafts may support the guide member between them. The guide member is attached to the rotating support shaft and is configured to rotate with the rotating support shaft. The guide member may include a guide wheel or a fixed guide channel for a cable or chain to pass through. In some examples, the guide member may include one or more connecting plates e.g. to connect the guide wheel with the rotating support shaft.

As described above, the stopper plate 110 of the locking unit 100 is coupled to the rotating support shaft in a position where an axis of the rotating support shaft is normal to the stopper plate 110.

In this way, the locking unit 100 can prevent swinging of a moveable fairlead 1 which has the potential to cause damage to the floating vessel or the fairlead 1 itself. The locking unit 100 can be provided in a modular unit which can be retrofitted to an existing fairlead 1 in situ on a floating vessel.

Figure 7 of the accompanying drawings shows a flowchart representing a method of retrofitting a locking unit according to an embodiment. The method starts at step S11.

At step S12, the method may include cutting a socket into the hull of a floating vessel.

In some examples the socket may be rectangular. The size of the socket may be approximately the same as a portion of the stopper plate of the locking unit which is to be passed through the socket. In some examples, the socket may be sized such that the full stopper plate will not pass through. Alternatively, the socket may be any shape or size which allows at least a portion of the plate to pass through. In some examples, the socket may include a seal, e.g. a rubber seal arranged to fit tightly against the stopper plate and allow rotational movement while preventing water from entering the hull. Alternatively, or in addition, the locking unit may be separately sealed to prevent the ingress of water from inside the socket.

Alternatively, in some examples, a socket may be already present on the hull, e.g. a maintenance hatch for the fairlead. Alternatively, in some examples, the locking unit may be positioned on an exterior of the floating vessel e.g. where it is not possible to provide a socket in the hull of the floating vessel. Individual components of the locking unit, e.g. the locking actuator may be individually sealed to isolate them from seawater.

At step S13, the method may include passing a portion of the stopper plate through a socket in a hull of the floating vessel, and positioning the locking pin and locking actuator adjacent to the portion of the stopper plate within the hull.

By extending the stopper plate through the hull, and arranging the locking unit in the interior of the hull, the locking unit can be protected from seawater. For example, where the socket and/or locking unit is sealed or substantially sealed, the locking unit can be isolated from seawater. In this way moving/mechanical parts of the locking unit can be protected from corrosion. In addition, the locking unit can be accessed more easily from the interior of the floating vessel, to maintain or repair components of the locking unit.

At step S14, the method includes coupling the stopper plate of the locking unit to a rotating support shaft of the moveable fairlead in a position where an axis of the rotating support shaft is normal to the stopper plate.

In some examples, the stopper plate may be configured to directly attach to the rotating support shaft. In some examples, the stopper plate may be configured to attach to a guide member which is attached to the rotating support shaft and configured to rotate with the rotating support shaft. For example, the stopper plate may be configured to attach to a connecting side plate which is coupled to the rotating support shaft, or supported between two rotating support shafts, and supports a guide wheel.

In some embodiments, the stopper plate may have a semi-circular form with a straight edge and a semi-circular edge. The stopper plate may be configured to be coupled to the rotating support shaft at a mid-point of the straight edge.

In this way, the stopper plate can be directly attached at a central point of rotation to a rotating element of the moveable fairlead. As the stopper plate is rotated by movement of the moveable fairlead, the stopper plate can pass the locking pin in a semi-circular arc.

In some examples, the stopper plate may be shaped for attachment to the moveable fairlead. For example, the stopper plate may include a notch configured to fit around the rotating support shaft or any other rotating element of the moveable fairlead. The stopper plate may be formed from steel, or any material suitable for marine construction.

In some embodiments, the stopper plate may include a plurality of locking holes. The locking holes may be spaced along a circular arc of the stopper plate arranged to be centred on the axis of the rotating support shaft. In this way, as the stopper plate is rotated by movement of the moveable fairlead, locking pin will pass over each of the locking holes in the circular arc.

In some examples, each point on the circular arc may be formed to slope towards an adjacent locking hole. In this way, when the locking actuator moves the locking pin towards the locking position, the locking pin will either pass directly through a locking hole or will contact a sloped portion of the circular arc.

In some examples, pressure applied between the locking pin and the sloped portion may force the stopper plate to rotate until the adjacent locking hole aligns with the locking pin. In some examples, the locking pin and/or locking actuator may be configured to flex or move laterally. Pressure applied between the locking pin and the sloped portion may cause the locking pin to flex and/or move laterally until the locking pin aligns with the adjacent locking hole. In some examples, when the locking pin is in the locking position, a restoring force (e.g. a spring or internal flexion) acting on the locking pin and/or locking actuator may cause the stopper plate to rotate until the locking pin returns to its original lateral position.

In some examples, each point may be formed to slope towards the nearest adjacent locking hole. Alternatively, in some examples, a sloping profile along the circular arc may be biased (e.g. a 'sawtooth' profile) to bias the stopper wheel in one direction over the other. In some implementations, the sloping profile may be formed by machining or casting the stopper plate.

In some examples, the stopper plate may be formed from any sector of a circle e.g. subtending an angle of more or less than 180, and configured to be attached at the centre point. In some examples, the stopper plate may include a curved edge passing substantially though the central point. In some examples, the semi-circular edge may be smooth or may be formed or shaped as required.

In some embodiments, the locking pin may include a roller arranged to contact the stopper plate. In some examples, the roller may be implemented with a wheel and axle arrangement. In some examples, the roller may be implemented with a ball in socket mechanism. By providing a roller on the locking pin, friction between the locking pin and the stopper plate can be reduced. In this way, excess wear or damage can be prevented to the locking pin and/or locking plate, caused by contacting the locking pin to the locking plate at a point not directly aligned with a locking hole. Where the stopper plate is implemented with a sloped profile as described above, the roller can improve a passage of the locking pin from the sloped portion to the locking hole.

At step S13, the method may include attaching a rectangular enclosure to the socket. The enclosure may be arranged to receive the stopper plate within. The enclosure may be a rectangular box shape which is open at one side. The open side of the enclosure may be configured to attach to an interior side of the hull of the floating vessel, with the socket within the open side. In this way, the interior of the enclosure may be open to the exterior of the floating vessel.

The enclosure may include one or more openings in an upper and/or lower wall of the enclosure. The locking pin may be configured to pass through one or more of the openings. The openings may include seals configured to surround the locking pin, to isolate the locking actuator from the interior of the enclosure.

In this way, the mechanical components of the locking unit such as, for example, the locking actuator, can be isolated from seawater which may enter the hull through the socket. The locking pin can be mounted such that locking pin is exposed to the interior of the enclosure but the locking actuator is isolated from the interior of the enclosure. The enclosure can fix a lateral position of the locking pin. In this way, the locking pin can resist or prevent lateral or rotational movement of the stopper plate when the locking pin is engaged with the stopper plate.

The method finishes at step S16.

Although aspects of the invention herein have been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the scope of the invention as defined by the appended claims.