Handling a transfer line comprising a cable connector of a power cable for electrical power transfer

Abstract

Disclosed is method of handling a transfer line, comprising a cable connector of a power cable for electrical power transfer between an offshore power source and an offshore unit, such as a vessel. The method comprises obtaining a trigger indication indicating that at least one predetermined condition is met; and on the basis of the trigger indication, causing a feed line of the offshore power source, which feed line is detachably connected to the transfer line, to be paid out from the offshore power source in order to move the transfer line towards the offshore unit.

Description

HANDLING A TRANSFER LINE COMPRISING A CABLE CONNECTOR OF A POWER CABLE FOR ELECTRICAL POWER TRANSFERTECHNICAL FIELD

[0001] The present invention relates to a method of handling a transfer line that comprises a cable connector of a power cable for electrical power transfer between an offshore power source and an offshore unit, to a method of withdrawing a transfer line comprising a cable connector of a power cable for electrical power transfer between an offshore power source and an offshore unit, to a control system configured to perform one of the methods, to a vessel comprising such a control system, to an offshore power source comprising such a control system, to a remotecontrol centre comprising the control system and remote from the offshore unit and the offshore power source, and to a power transfer system comprising an offshore power source and the control system remote from the offshore power source.BACKGROUND

[0002] There is a growing interest in the development of electrically powered vessels, or providing power to vessels to allow turning off any onboard engines, particularly for use in the maritime industry. These vessels require systems that can efficiently and safely transfer electrical power to them from an offshore power source, ideally from renewable or sustainable energy sources. Such electrical power may be transferred to such a vessel for charging one or more batteries of the vessel or for powering one or more systems of the vessel, such as for providing idle load power while the vessel idles. The vessel may idle, for example, when waiting for a berth at a port or terminal, or when the vessel is not required for other purposes.

[0003] One approach to supplying electrical power to such a vessel involves the use of a heavy electrical cable that is connected to the vessel's electrical system, while the vessel is moored or on dynamic positioning at an offshore power source. However, the handling and connection of such heavy electrical cables present several challenges and risks. The weight and rigidity of such cables makes them difficult and dangerous for crew to manually handle on the vessel's deck. This can lead to potential injuries and accidents, as well as damage to the vessel and its components due to excessive tension on the cable, or wear and damage of the cable from contacting the vessel's surfaces, should an unplanned event or incident occur. Moreover, connecting and disconnecting the electrical cable to the vessel's electrical system can beinefficient and time-consuming processes, further increasing the risk of accidents and injuries during manual handling. Additionally, improper connection or disconnection of a connector of such a cable to a power connector of the vessel can result in damage to the connector or the power connector.

[0004] Therefore, there is a need for an improved electrical-power transfer system that can safely and efficiently handle a power cable, such as during a process of connecting the power cable to a vessel or during a process of disconnecting the power cable from a vessel, while reducing the risks associated with manual handling, cable tension and connector orientation.

[0005] W02024 / 105403A1 discloses assisted dynamic position control of a vessel during offshore charging from a power station. When the vessel approaches the power station, it moves to a position suitable for a connector receptacle of the vessel to engage with a cable connector on a charging cable of the power station. During the approach, the vessel positions itself in a favorable orientation, based on wind and tidal forces, and shares its position with a controller at the power station, e.g., via a wireless or a wired communication link. The charging cable is fed from a reeling drum of the power station. A Motion Reference Unit (MRU) on the vessel is used to measure vessel movement and data is provided to the power station to initiate compensation movement of the charging cable fed from the reeling drum.SUMMARY

[0006] According to a first aspect of the present invention, there is provided a method of handling a transfer line, comprising a cable connector of a power cable for electrical power transfer between an offshore power source and an offshore unit, the method comprising: obtaining a trigger indication indicating that at least one predetermined condition is met; on the basis of the trigger indication, causing a feed line of the offshore power source, which feed line is detachably connected to the transfer line, to be paid out from the offshore power source in order to move the transfer line towards the offshore unit; and causing the feed line to be retracted back into the offshore power source, after detachment of the transfer line from the feed line.

[0007] Such a method may help to facilitate offering or passing of the transfer line, and thus the cable connector, to the offshore unit, particularly when the transfer line, the power connector or the power cable is relatively heavy and cumbersome. In turn, this may make the process quicker, simpler and safer.

[0008] As used herein, the term “offshore unit” refers to a self-propelled or non-self-propelled or unpropelled body which is at least partially floating at the surface of, or submerged in, water or fixed on the surface of water with respect to an area of reference. The offshore unit is an intended recipient of electrical power from the offshore power source. The offshore unit may be a floating or buoyant offshore unit, or a non-floating or non-buoyant offshore unit. Examples of such offshore units include vessels, such as self-propelled vessels, non-self-propelled vessels, unpropelled vessels buoys and offshore platforms.

[0009] Optionally, the obtaining the trigger indication comprises receiving the trigger indication, such as from a system at the offshore unit.

[0010] Optionally, the transfer line comprises a messenger line connected to the power cable. Optionally, the messenger line is connected directly to the cable connector of the power cable. Optionally, the messenger line is detachably connected to the power cable, such as detachably connected to the cable connector of the power cable.

[0011] Optionally, the feed line is detachably connected directly to the messenger line.

[0012] Optionally, the feed line is detachably connected to the power cable only via the messenger line. This may avoid a need for the power cable to have an interface for physical connection to the feed line, thus simplifying the power cable.

[0013] Optionally, the causing the feed line to be paid out comprises causing rotation of a crane winch of a crane of the offshore power source, around a spool of which crane winch a portion of the feed line is wound. This may provide a mechanism that is compact for storing the feed line when not in use and yet simple and convenient for paying out the feed line when needed.

[0014] Optionally, the feed line has a weight attached thereto. Optionally, the weight is buoyant in a body of water in which the offshore power source is located. Optionally, the weight is nonbuoyant in a body of water in which the offshore power source is located. Such a weight may help to control movement of the feed line and / or help identify a location of the feed line, particularly in bad weather or when the feed line is partially submerged.

[0015] Optionally, the method comprises, on the basis of the trigger indication, causing movement of at least one part of the crane from a first position to a second position relative to a main structure of the offshore power source, before or during the causing the feed line to be paidout. This may facilitate offering or passing the transfer line to the offshore unit, such as by enabling the feed line to be paid out more closely to the offshore unit so that the transfer line is closer to the offshore unit.

[0016] Optionally, the at least one part of the crane comprises a first section of a boom of the crane.

[0017] Optionally, the movement comprises a linear movement of the first section of the boom relative to a second section of the boom to extend the boom. This may help to improve a reach of the crane, thus facilitating offering or passing of the transfer line to the offshore unit.

[0018] Optionally, the movement comprises a rotational movement of the first section of the boom to rotate the boom relative to the main structure of the offshore power source. This may help to reduce a distance between the offshore unit and the feed line and transfer line, thus facilitating offering or passing of the transfer line to the offshore unit.

[0019] Optionally, the at least one predetermined condition comprises that the offshore unit is less than a threshold distance from the offshore power source. This may increase a chance of the feed line or the transfer line reaching the offshore unit when the feed line is paid out to move the transfer line towards the offshore unit.

[0020] Optionally, the threshold distance is less than 50 metres from the offshore power source, such as less than 30 metres from the offshore power source, such as 20 metres from the offshore power source.

[0021] Optionally, the at least one predetermined condition comprises that the offshore unit is travelling at less than or equal to a threshold speed relative to the offshore power source. This may increase a chance of the feed line or the transfer line being captured at the offshore unit when the feed line is paid out to move the transfer line towards the offshore unit.

[0022] Optionally, the threshold speed is less than two metres per second, such as less than one metre per second, such as less than 0.5 metres per second, such as 0.25 metres per second.

[0023] Optionally, the method comprises causing the pay out of the feed line from the offshore power source to cease. This may help avoid an excess of the feed line being paid out, which in turn could reduce a chance of the feed line becoming tangled or snagged on something in the surrounding environment. Optionally, this comprises causing rotation of a crane winch of a craneof the offshore power source, around a spool of which crane winch a portion of the feed line is wound, to cease.

[0024] The causing the feed line to be retracted back into the offshore power source, after detachment of the transfer line from the feed line, may help to avoid the feed line becoming damaged or tangled, such as with the transfer line, particularly if there are local high winds.

[0025] Optionally, the feed line has a weight attached thereto, and the weight remains attached to the feed line while the feed line is retracted. Not needing to detach the weight from the feed line may help to simplify and quicken the method and may help preserve the weight. Optionally, the weight is buoyant in a body of water in which the offshore power source is located. Optionally, the weight is non-buoyant in a body of water in which the offshore power source is located.

[0026] Optionally, the causing the feed line to be retracted comprises causing rotation of a crane winch of a crane of the offshore power source, around a spool of which crane winch a portion of the feed line is wound.

[0027] Optionally, the method comprises causing the retraction of the feed line back into the offshore power source to cease, such as after the feed line is fully retracted into the offshore power source. Optionally, this comprises causing rotation of a crane winch of a crane of the offshore power source, around a spool of which crane winch a portion of the feed line is wound, to cease.

[0028] Optionally, the method comprises causing feed out of the transfer line from the offshore power source to be initiated.

[0029] Optionally, the causing feed out of the transfer line from the offshore power source to be initiated occurs after detachment of the transfer line from the feed line. This may help avoid damage to the feed line that may otherwise be caused by the feed out of the transfer line.

[0030] Optionally, the causing feed out of the transfer line from the offshore power source to be initiated occurs after the causing the feed line to be paid out.

[0031] Optionally, the causing feed out of the transfer line from the offshore power source to be initiated occurs after causing the pay out of the feed line from the offshore power source to cease.

[0032] Optionally, the causing feed out of the transfer line from the offshore power source to be initiated occurs after causing retraction of the feed line back into the offshore power source. This may help avoid the transfer line becoming tangled with the feed line, which at this point has a loose end. Optionally, the causing feed out of the transfer line from the offshore power source to be initiated occurs after causing the retraction of the feed line back into the offshore power source to cease, such as after the feed line is fully retracted into the offshore power source. This may further help avoid the transfer line becoming tangled with the feed line.

[0033] Optionally, the method comprises obtaining a tension indication indicating a tension in the transfer line, wherein the causing feed out of the transfer line from the offshore power source to be initiated is performed on the basis of the tension indication. This may better ensure that the transfer line is fed to the offshore unit successfully and as intended.

[0034] Optionally, the tension indication indicates a magnitude of the tension in the transfer line. Optionally, the causing feed out of the transfer line from the offshore power source to be initiated is performed only when the magnitude of the tension indicated by the tension indication is above a tension threshold. This may better ensure that the transfer line is fed to the offshore unit along an intended path. Optionally, the method comprises comparing the magnitude of the tension to the tension threshold.

[0035] Optionally, the obtaining the tension indication comprises receiving the tension indication, such as from a tension sensor at the offshore unit or from a tension sensor at the offshore power source.

[0036] Optionally, the tension in the transfer line is measured at an umbilical winch at the offshore power source, around a spool of which umbilical winch a portion of the transfer line is wound. This may provide a convenient and compact mechanism for enabling the tension to be measured. Optionally, the obtaining the tension indication comprises receiving the tension indication directly or indirectly from the umbilical winch at the offshore power source.

[0037] Optionally, the tension in the transfer line is measured at a pull-in winch at the offshore unit, to which pull-in winch the transfer line is connected. This may provide a convenient and compact mechanism for enabling the tension to be measured.

[0038] Optionally, the obtaining the tension indication comprises receiving the tension indication directly or indirectly from the pull-in winch, such as from a tension sensor of the pull-in winch.

[0039] Optionally, the pull-in winch has a spool, a pull-in line is attached to the pull-in winch with at least a portion of a pull-in line wound around the spool of the pull-in winch, and the pull-in line is attached to the transfer line so that the transfer line is connected to the pull-in winch via the pull-in line. This may facilitate pulling-in the transfer line at the offshore unit. Additionally, or alternatively, it may enable the transfer line to be (indirectly) connected to the pull-in winch at a location remote from the pull-in winch that might be more accessible or convenient than a location of the pull-in winch itself.

[0040] Optionally, the causing feed out of the transfer line from the offshore power source to be initiated comprises causing rotation of an umbilical winch at the offshore power source, around a spool of which umbilical winch a portion of the transfer line is wound.

[0041] Optionally, the causing feed out of the transfer line from the offshore power source to be initiated comprises causing rotation of a pull-in winch at the offshore unit, to which pull-in winch the transfer line is connected. Further optionally, the pull-in winch has a spool, a pull-in line is attached to the pull-in winch with at least a portion of a pull-in line wound around the spool of the pull-in winch, and the pull-in line is attached to the transfer line so that the transfer line is connected to the pull-in winch via the pull-in line.

[0042] Optionally, the causing feed out of the transfer line from the offshore power source to be initiated comprises causing rotation of both the pull-in winch and the umbilical winch. This may help to reduce a strain experienced by the transfer line.

[0043] Optionally, the method comprises causing the feed out of the transfer line from the offshore power source to cease. This may help avoid an excess of the transfer line being fed out, which in turn could reduce a chance of the transfer line becoming tangled or snagged on something in the surrounding environment.

[0044] Optionally, the causing the feed out of the transfer line from the offshore power source to cease comprises causing rotation of an umbilical winch at the offshore power source, around a spool of which umbilical winch a portion of the transfer line is wound, to cease.

[0045] Optionally, the causing the feed out of the transfer line from the offshore power source to cease comprises causing rotation of a pull-in winch at the offshore unit, to which pull-in winch the transfer line is connected, to cease. Further optionally, the pull-in winch has a spool, a pull-in line is attached to the pull-in winch with at least a portion of a pull-in line wound around the spool ofthe pull-in winch, and the pull-in line is attached to the transfer line so that the transfer line is connected to the pull-in winch via the pull-in line.

[0046] Optionally, the causing the feed out of the transfer line from the offshore power source to cease comprises causing rotation of both the pull-in winch and the umbilical winch to cease. This may help to better control how much of the transfer line is fed out from the offshore power source.

[0047] Optionally, the method comprises obtaining a latch indication indicating that part of the power cable is engaged by a latch mechanism of the offshore unit, wherein the causing the feed out of the transfer line from the offshore power source to cease is on the basis of the latch indication. This may further help avoid an excess of the transfer line being fed out, which in turn could reduce a chance of the transfer line becoming tangled or snagged on something in the surrounding environment.

[0048] Optionally, the part of the power cable is the cable connector. Avoiding engagement of the latch mechanism with another part of the power cable instead may help avoid damage to that other part, particularly when that other part is more susceptible to damage than the cable connector.

[0049] Optionally, the obtaining the latch indication comprises receiving the latch indication, such as from the latch mechanism.

[0050] Optionally, the method comprises causing further feed out of the transfer line from the offshore power source, while a distance between the offshore power source and the offshore unit increases. This may help to avoid the transfer line experiencing excessive tension as the distance increases, and also enables an end of the transfer line at the offshore unit to remain relatively stationary relative to the offshore unit.

[0051] Optionally, the causing the further feed out of the transfer line from the offshore power source comprises causing rotation of an umbilical winch at the offshore power source, around a spool of which umbilical winch a portion of the transfer line is wound.

[0052] Optionally, the method comprises causing the further feed out of the transfer line from the offshore power source to cease, when the distance between the offshore power source and the offshore unit increases reaches a predetermined distance.

[0053] Optionally, the predetermined distance is more than eighty metres, such as more than one hundred metres, such as two hundred metres. Optionally, the predetermined distance is less than five hundred metres, such as less than three hundred metres. Such distances may be sufficiently close to the offshore power source that an excessively long transfer line is not needed, which otherwise could result in greater inefficiency of power transfer and more space being required at the offshore power source for storage of the transfer line. Such distances may additionally, or alternatively, be sufficiently far from the offshore power source to sufficiently reduce the risk of a collision between the offshore unit and the offshore power source during power transfer.

[0054] Optionally, the causing the further feed out of the transfer line from the offshore power source to cease comprises causing rotation of an umbilical winch at the offshore power source, around a spool of which umbilical winch a portion of the transfer line is wound, to cease.

[0055] Optionally, the method comprises causing flow of an electrical current through the power cable to be initiated, once the cable connector is electrically connected to a power connector of the offshore unit. This may be safer than attempting to cause the flow of energy before the cable connector is properly electrically connected to the power connector.

[0056] Optionally, the method comprises obtaining a connection indication indicating that the cable connector is electrically connected to the power connector of the offshore unit, wherein the causing flow of the electrical current is on the basis of the connection indication.

[0057] Optionally, the obtaining the connection indication comprises receiving the connection indication, such as from a system at the offshore unit or from a system at the offshore power source.

[0058] Optionally, the method comprises obtaining a stability indication indicating that the offshore unit is stable at a predetermined distance from the offshore power source, wherein the causing flow of the electrical current is on the basis of the stability indication. This may help avoid the transfer line experiencing excessive tension due to movement of the offshore unit relative to the offshore power source, which could otherwise lead to breakage or disconnection of the transfer line, with associated risks of injury and accidents to human operatives and damage to surrounding structures such as the offshore unit or the offshore power source.

[0059] Optionally, the predetermined distance is more than eighty metres, such as more than one hundred metres, such as two hundred metres. Optionally, the predetermined distance is less than five hundred metres, such as less than three hundred metres.

[0060] Optionally, the obtaining the stability indication comprises receiving the stability indication, such as from a system at the offshore unit.

[0061] Optionally, the stability indication indicates that the offshore unit is undergoing less than a predetermined degree of roll, heave and / or pitch. Optionally, the stability indication indicates that a rate of change of a position of the offshore unit relative to the offshore power source is less than a predetermined rate of change.

[0062] Optionally, the method comprises obtaining an emergency release indication during the flow of electrical current through the power cable and causing disengagement of a latch mechanism of the offshore unit from part of the power cable on the basis of the emergency release indication. This may help to lessen or avoid the chance of damage to the transfer line or to the offshore unit in an emergency situation and / or may facilitate independent movement of the offshore unit relative to the offshore power source to avoid a collision between the offshore unit and another entity, such as the offshore power source or an obstacle in the water.

[0063] Optionally, the emergency release indication indicates that a magnitude of a tension in the transfer line is above an allowable magnitude.

[0064] Optionally, the emergency release indication indicates that the offshore unit is insufficiently stable.

[0065] Optionally, the emergency release indication indicates that the offshore unit is less than a predetermined distance from the offshore power source.

[0066] Optionally, the part of the power cable is the cable connector.

[0067] Optionally, the method comprises causing the flow of the electrical current through the power cable to cease on the basis of the emergency release indication. Optionally, the method comprises causing the flow of the electrical current through the power cable to cease before causing the disengagement of the latch mechanism of the offshore unit from the part of the power cable, on the basis of the emergency release indication. This may help to increase safety of the method.

[0068] Optionally, the method comprises causing the transfer line to be at least partially paid out from the offshore unit on the basis of the emergency release indication. This may help to lessen or avoid the chance of damage to the transfer line or to the offshore unit in an emergency situation and / or may facilitate independent movement of the offshore unit relative to the offshore power source to avoid a collision between the offshore unit and another entity, such as the offshore power source or an obstacle in the water.

[0069] Optionally, the causing at least partial pay out of the transfer line from the offshore unit comprises causing rotation of a pull-in winch at the offshore unit, to which pull-in winch the transfer line is connected. Optionally, the pull-in winch has a spool and a portion of the transfer line is wound around the spool of the pull-in winch. Further optionally, a pull-in line is attached to the pull-in winch with at least a portion of a pull-in line wound around the spool of the pull-in winch, and the pull-in line is attached to the transfer line so that the transfer line is connected to the pull- in winch via the pull-in line.

[0070] Optionally, the obtaining the emergency release indication comprises receiving the emergency release indication, such as from a system at the offshore unit or from a system at the offshore power source.

[0071] Optionally, the method comprises obtaining a transfer completed indication indicating that transfer of electrical power to the offshore unit is complete and causing the flow of the electrical current through the power cable to cease on the basis of the transfer completed indication. This may help to avoid an attempt to transfer excess electrical power to the offshore unit, with associated risks of damage to the offshore unit.

[0072] Optionally, the obtaining the transfer completed indication comprises receiving the transfer completed indication, such as from a system at the offshore unit.

[0073] Optionally, the method comprises causing retraction of the transfer line back into the offshore power source, while a distance between the offshore power source and the offshore unit reduces. This may help avoid the transfer line becoming tangled with the offshore unit, such as with a propulsion system (when provided) of the offshore unit.

[0074] Optionally, the causing the retraction of the transfer line back into the offshore power source comprises causing rotation of an umbilical winch at the offshore power source, around a spool of which umbilical winch a portion of the transfer line is wound.

[0075] Optionally, the method comprises causing the retraction of the transfer line back into the offshore power source to cease. Optionally, this comprises causing rotation of an umbilical winch of the offshore power source, around a spool of which umbilical winch a portion of the transfer line is wound, to cease.

[0076] Optionally, the method comprises causing disengagement of a latch mechanism of the offshore unit from part of the power cable. Optionally, the part of the power cable is the cable connector.

[0077] Optionally, the method comprises obtaining a second trigger indication indicating that at least one second predetermined status is met; and on the basis of the second trigger indication, causing the feed line of the offshore power source to be paid out again from the offshore power source, in order to facilitate detachable reconnection of the feed line to the transfer line. This may facilitate collection of the transfer line by the offshore power source.

[0078] Optionally, the at least one second predetermined status comprises that the offshore unit is within a threshold distance from the offshore power source. Optionally, the threshold distance is less than 50 metres from the offshore power source, such as less than 30 metres from the offshore power source, such as 20 metres from the offshore power source.

[0079] Optionally, the at least one second predetermined status comprises that the offshore unit is travelling at less than a threshold speed relative to the offshore power source. Optionally, the threshold speed is less than two metres per second, such as less than one metre per second, such as less than 0.5 metres per second, such as 0.25 metres per second. Optionally, the at least one second predetermined status comprises that the recipient is stationary relative to the offshore power source.

[0080] Optionally, the obtaining the second trigger indication comprises receiving the second trigger indication, such as from a system at the offshore unit.

[0081] Optionally, the causing the feed line to be paid out again comprises causing rotation of a crane winch of a crane of the offshore power source, around a spool of which crane winch a portion of the feed line is wound.

[0082] Optionally, the method comprises causing the pay out of the feed line again from the offshore power source to cease. This may help avoid an excess of the feed line being paid out, which in turn could reduce a chance of the feed line becoming tangled or snagged on something in the surrounding environment. Optionally, this comprises causing rotation of a crane winch of a crane of the offshore power source, around a spool of which crane winch a portion of the feed line is wound, to cease.

[0083] Optionally, the method comprises causing the feed line to be retracted back into the offshore power source, after detachable reconnection of the feed line to the transfer line. This may help to preserve the feed line and / or the transfer line after their use.

[0084] Optionally, the feed line has a weight attached thereto, and the weight remains attached to the feed line while the feed line is retracted. Not needing to detach the weight from the feed line may help to simplify and quicken the method and may help preserve the weight. Optionally, the weight is buoyant in a body of water in which the offshore power source is located. Optionally, the weight is non-buoyant in a body of water in which the offshore power source is located.

[0085] Optionally, the causing the feed line to be retracted comprises causing rotation of a crane winch of a crane of the offshore power source, around a spool of which crane winch a portion of the feed line is wound.

[0086] Optionally, the method comprises causing the retraction of the feed line back into the offshore power source to cease, such as after the feed line is fully retracted into the offshore power source. Optionally, this comprises causing rotation of a crane winch of a crane of the offshore power source, around a spool of which crane winch a portion of the feed line is wound, to cease.

[0087] Optionally, the method comprises obtaining a trigger indicator indicating that at least one predetermined state is met; and causing the feed line of the offshore power source to be retracted on the basis of the trigger indicator. This may help to ensure that the feed line is retracted at an appropriate time.

[0088] Optionally, the at least one predetermined state comprises that the feed line is detachably connected to the transfer line. Accordingly, this may help better ensure that the transfer line is carried, such as away from the offshore unit, by the feed line.

[0089] Optionally, the at least one predetermined state comprises that the cable connector is electrically disconnected from a power connector of the offshore unit, such as in accordance with an emergency procedure. This may help to improve safety of the method.

[0090] Optionally, the at least one predetermined state comprises that part of the power cable, such as the cable connector, has been disengaged from a latch mechanism of the offshore unit, such as in accordance with an emergency procedure. This may help to reduce a chance of straining or damaging the feed line, the power cable and / or the latch mechanism.

[0091] Optionally, the at least one predetermined state comprises that the transfer line is mechanically disconnected from the offshore unit. This may further help to reduce a chance of straining or damaging the feed line, the power cable and / or the latch mechanism.

[0092] Optionally, the at least one predetermined state comprises that the offshore unit is within a threshold distance from the offshore power source. Optionally, the threshold distance is less than 50 metres from the offshore power source, such as less than 30 metres from the offshore power source, such as 20 metres from the offshore power source.

[0093] Optionally, the at least one predetermined state comprises that the offshore unit is travelling at less than a threshold speed relative to the offshore power source. Optionally, the threshold speed is less than two metres per second, such as less than one metre per second, such as less than 0.5 metres per second, such as 0.25 metres per second.

[0094] Optionally, the feed line has a weight attached thereto, and the weight remains attached to the feed line while the feed line is retracted. Not needing to detach the weight from the feed line may help to simplify and quicken the method and may help preserve the weight. Optionally, the weight is buoyant in a body of water in which the offshore power source is located. Optionally, the weight is non-buoyant in a body of water in which the offshore power source is located.

[0095] Optionally, the causing the feed line to be retracted comprises causing rotation of a crane winch of a crane of the offshore power source, around a spool of which crane winch a portion of the feed line is wound.

[0096] Optionally, the method comprises causing the retraction of the feed line into the offshore power source to cease, such as after the feed line is fully retracted into the offshore power source. Optionally, this comprises causing rotation of a crane winch of a crane of the offshore power source, around a spool of which crane winch a portion of the feed line is wound, to cease.

[0097] Optionally, the obtaining the trigger indicator comprises receiving the trigger indicator, such as from a system at the offshore unit.

[0098] Optionally, the offshore unit is a vessel.

[0099] Optionally, the offshore power source comprises an offshore substation. Optionally, the offshore power source is a floating offshore power source. Optionally, the offshore power source is fixed to a bed of a body of water.

[0100] Optionally, the method is performed by a control system at the offshore unit.

[0101] Optionally, the method is performed by a control system at the offshore power source.

[0102] Optionally, the method is performed by a control system at a remote-control centre remote from the offshore power source and remote from the offshore unit.

[0103] Optionally, the method is a computer-implemented method.

[0104] According to a second aspect of the present invention, there is provided a method of withdrawing a transfer line, comprising a cable connector of a power cable for electrical power transfer between an offshore power source and an offshore unit, from the offshore unit to the offshore power source, the method comprising: obtaining a trigger indicator indicating that at least one predetermined state is met; and on the basis of the trigger indicator, causing a feed line of the offshore power source, which feed line is detachably connected to the transfer line, to be retracted in order to move the transfer line away from the offshore unit.

[0105] Such a method may help to preserve the feed line and / or the transfer line after their use closer to, or at, the offshore unit. It may additionally, or alternatively, help make handling of the transfer line quicker, simpler and safer, particularly when the transfer line, the power connector or the power cable is relatively heavy and cumbersome.

[0106] Optionally, the at least one predetermined state comprises that the feed line is detachably connected to the transfer line. Accordingly, this may help better ensure that the transfer line is carried, such as away from the offshore unit, by the feed line.

[0107] Optionally, the at least one predetermined state comprises that the cable connector is electrically disconnected from a power connector of the offshore unit, such as in accordance with an emergency procedure. This may help to improve safety of the method.

[0108] Optionally, the at least one predetermined state comprises that part of the power cable, such as the cable connector, has been disengaged from a latch mechanism of the offshore unit, such as in accordance with an emergency procedure. This may help to reduce a chance of straining or damaging the feed line, the power cable and / or the latch mechanism.

[0109] Optionally, the at least one predetermined state comprises that the transfer line is mechanically disconnected from the offshore unit. This may further help to reduce a chance of straining or damaging the feed line, the power cable and / or the latch mechanism.

[0110] Optionally, the at least one predetermined state comprises that the offshore unit is within a threshold distance from the offshore power source. Optionally, the threshold distance is less than 50 metres from the offshore power source, such as less than 30 metres from the offshore power source, such as 20 metres from the offshore power source.

[0111] Optionally, the at least one predetermined state comprises that the offshore unit is travelling at less than a threshold speed relative to the offshore power source. Optionally, the threshold speed is less than two metres per second, such as less than one metre per second, such as less than 0.5 metres per second, such as 0.25 metres per second.

[0112] Optionally, the feed line has a weight attached thereto, and the weight remains attached to the feed line while the feed line is retracted. Not needing to detach the weight from the feed line may help to simplify and quicken the method and may help preserve the weight. Optionally, the weight is buoyant in a body of water in which the offshore power source is located. Optionally, the weight is non-buoyant in a body of water in which the offshore power source is located.

[0113] Optionally, the causing the feed line to be retracted comprises causing rotation of a crane winch of a crane of the offshore power source, around a spool of which crane winch a portion of the feed line is wound.

[0114] Optionally, the method comprises causing the retraction of the feed line into the offshore power source to cease, such as after the feed line is fully retracted into the offshore power source. Optionally, this comprises causing rotation of a crane winch of a crane of the offshore power source, around a spool of which crane winch a portion of the feed line is wound, to cease.

[0115] Optionally, the obtaining the trigger indicator comprises receiving the trigger indicator, such as from a system at the offshore unit.

[0116] Optionally, the offshore unit is a vessel.

[0117] Optionally, the offshore power source comprises an offshore substation. Optionally, the offshore power source is a floating offshore power source. Optionally, the offshore power source is fixed to a bed of a body of water.

[0118] Optionally, the method is performed by a control system at the offshore unit.

[0119] Optionally, the method is performed by a control system at the offshore power source.

[0120] Optionally, the method is performed by a control system at a remote-control centre remote from the offshore power source and remote from the offshore unit.

[0121] Optionally, the method is a computer-implemented method.

[0122] According to a third aspect of the present invention, there is provided a control system configured to perform the method of the first aspect of the present invention or the method of the second aspect of the present invention.

[0123] The control system may comprise a computing system comprising one or more processors and a non-transitory storage medium accessible by the one or more processors and storing machine-readable instructions that, when executed by the processor or processors, cause the processor or processors to perform one of the methods. The memory may be local to, or remote from, the processor(s), or a combination of local and remote.

[0124] According to a fourth aspect of the present invention, there is provided a non-transitory storage medium storing machine-readable instructions that, when executed by a processor or processors of a computing system of a control system, cause the processor or processors to perform the method of the first aspect of the present invention or the method of the second aspect of the present invention.

[0125] According to a fifth aspect of the present invention, there is provided a vessel comprising the control system of the third aspect of the present invention or the non-transitory storage medium of the fourth aspect of the present invention.

[0126] Optionally, the vessel is the offshore unit. Optionally, the vessel is distinct from the offshore unit.

[0127] According to a sixth aspect of the present invention, there is provided an offshore power source comprising the control system of the third aspect of the present invention or the non- transitory storage medium of the fourth aspect of the present invention.

[0128] Optionally, the offshore power source comprises an offshore substation. Optionally, the offshore power source is a floating offshore power source. Optionally, the offshore power source is fixed to a bed of a body of water.

[0129] According to a seventh aspect of the present invention, there is provided a remote-control centre comprising the control system of the third aspect of the present invention or the non- transitory storage medium of the fourth aspect of the present invention, wherein the remotecontrol centre is remote from the offshore unit and remote from the offshore power source.

[0130] Optionally, the remote-control centre is land-based. Optionally, the remote-control centre is a floating remote-control centre, distinct from the offshore unit.

[0131] According to an eighth aspect of the present invention, there is provided a power transfer system comprising an offshore power source and the control system of the third aspect of the present invention or the non-transitory storage medium of the fourth aspect of the present invention, wherein the control system or the non-transitory storage medium, respectively, is remote from the offshore power source.

[0132] Optionally, the offshore power source comprises an offshore substation. Optionally, the offshore power source is a floating offshore power source. Optionally, the offshore power source is fixed to a bed of a body of water.

[0133] It will be appreciated that optional features of aspects of the present invention may be equally applied to other aspects of the present invention, where appropriate.BRIEF DESCRIPTION OF DRAWINGS

[0134] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0135] Figure 1 shows a schematic side view of a power transfer system comprising an offshore power source, a vessel, a floating remote-control centre and a land-based remote-control centre,

[0136] Figure 2 shows a schematic perspective view of an umbilical winch of the offshore power source, to which umbilical winch a transfer line is attached with a power cable of the transfer line partially wound around a spool of the umbilical winch,

[0137] Figure 3 shows a schematic end view of a cable connector of the power cable of the transfer line of the offshore power source,

[0138] Figure 4 shows a schematic side view of the cable connector,

[0139] Figure 5 shows a schematic perspective view of the cable connector,

[0140] Figure 6 shows a schematic perspective view of a power connector module of the vessel,

[0141] Figure 7 shows a schematic side view of the power connector module, in which a wall of the power connector module is removed so that an interior of the power connector module is visible,

[0142] Figure 8 shows a schematic perspective view of a latch mechanism of the power connector module,

[0143] Figure 9 shows a schematic cross-sectional side view of the latch mechanism,

[0144] Figure 10 shows a schematic cross-sectional side view of the latch mechanism with the cable connector partially inserted into a zone thereof,

[0145] Figure 1 1 shows a schematic cross-sectional side view of the latch mechanism with the cable connector retained in the zone by the latch mechanism,

[0146] Figure 12 shows a schematic end view of a power connector of the power connector module,

[0147] Figure 13 shows a schematic perspective view of the power connector of Figure 12 and a power connector positioning mechanism of the power connector module,

[0148] Figure 14 shows another schematic side view of the power transfer system of Figure 1 , in which the floating remote-control centre and the land-based remote-control centre are omitted for clarity, and a boom of a crane of the offshore power source has been rotated towards the vessel as compared to its position in Figure 1 ,

[0149] Figure 15 shows another schematic side view of the power transfer system of Figure 14, in which a feed line of the crane has been paid out to move a messenger line of the transfer line, which messenger line connects the feed line to the cable connector of the power cable, towards the vessel,

[0150] Figure 16 shows another schematic side view of the power transfer system of Figure 15, in which the messenger line has been caught by a human operative on the vessel and attached to a pull-in line of the power connector module of the vessel,

[0151] Figure 17 shows another schematic side view of the power transfer system of Figure 16, in which the messenger line has been detached from the feed line and the feed line is being retracted by the crane,

[0152] Figure 18 shows another schematic side view of the power transfer system of Figure 17, in which the feed line has been fully retracted by the crane,

[0153] Figure 19 shows another schematic side view of the power transfer system of Figure 18, in which a pull-in winch of the power connector module is retracting the pull-in line, and the umbilical winch is paying out the transfer line, so that the transfer line is pulled into the power connector module, thereby moving the cable connector of the power cable of the transfer line towards the power connector of the power connector module,

[0154] Figure 20 shows another schematic side view of the power transfer system of Figure 19, in which the cable connector of the transfer line is engaged by the latch mechanism of the power connector module and engaged with the power connector of the power connector module,

[0155] Figure 21 shows another schematic side view of the power transfer system of Figure 20, in which the vessel has sailed away from the offshore power source while the umbilical winch waspaying out the transfer line, and the vessel is now stationary relative to the offshore power source and an electrical current is flowing through the power cable to the power connector,

[0156] Figures 22A and 22B show respective first and second portions of a method of handling the transfer line, and

[0157] Figure 23 is a flow chart showing a method of engaging the power connector with the cable connector.DETAILED DESCRIPTION

[0158] Figure 1 shows an example of a power transfer system 1 comprising an offshore power source 10, an offshore unit in the form of a vessel 20, a floating remote-control centre 30, and a land-based remote-control centre 40. Each of these elements is described in turn below. The vessel 20 is an intended recipient of electrical power from the offshore power source 10. The offshore power source 10 may supply electrical power to the vessel 20 for charging one or more batteries of the vessel 20 or for powering one or more systems of the vessel 20, such as for providing idle load power while the vessel 20 idles. The vessel 20 may idle, for example, when waiting for a berth at a port or terminal, or when the vessel 20 is not required for other purposes.

[0159] The offshore power source 10 is a structure located offshore that is used to provide electrical power to offshore units, such as vessels. The offshore power source 10 has a main structure 102 that is fixed to a bed of a body of water. A water line WL of the body of water is shown in Figure 1. The offshore power source 10 is connected to a power supply, which in this example comprises an offshore wind farm (not shown), has a power supply circuit 108 including a bank of batteries electrically connected to the power supply, and has a power cable 130 electrically connected to the power supply circuit 108. In some other examples, the power supply comprises a different supply of renewable or sustainable energy, such as an offshore solar farm, a wave farm, a tidal farm, or any combination of these farms. A cable connector 160 at an end of the power cable 130 is electrically connectable to a power connector of the vessel 20 to supply electrical power from the bank of batteries of the power supply circuit 108 to the vessel 20 via the power cable 130.

[0160] The offshore power source 10 has a platform 104 extending from the main structure 102, upon which platform 104 a control system 106, an umbilical winch 110 and a crane 120 aremounted. The control system 106 and the umbilical winch 1 10 are shown in more detail in Figure2.

[0161] The umbilical winch 110 comprises a spool 1 12 that is rotatable about a horizontal winch axis WA, a tension sensor 1 14, a slip ring 1 16 (not visible), and an open-topped slide 118.

[0162] The tension sensor 1 14 comprises a strain sensor, which is mechanically connected to the power cable 130 of a transfer line 150 that is partially wound around the spool 112, so as to sense a magnitude of tension in the transfer line 150. The tension sensor 1 14 includes a processor (not shown) and a communications interface (not shown), and the processor is programmed to output a tension indication, indicative of the magnitude of the tension in the transfer line 150, via the communications interface to the control system 106.

[0163] The slip ring 1 16 is located between the spool 112 and wiring (not shown) that is connected to the power supply circuit 108. The slip ring 116 enables rotation of the spool 112 relative to the platform 104 while maintaining electrical connections between the wiring and the power cable 130.

[0164] The slide 118 is fixed relative to the platform 104, is inclined at an angle of about seventy degrees to the water line WL and is approximately aligned with a tangent to a base of a channel 112a at an outer edge of the spool 1 12, in which channel the power cable 130 is located. Therefore, the power cable 130 is able to slide along the slide 1 18 as the power cable 130 is fed out from the spool 1 12 or retracted back onto the spool 1 12, during rotation of the spool 112 relative to the platform 104. The slide 118 has a first end 118a distal from the spool 112 and a second end 118b proximal to the spool 1 12. The first end 118a is wider than the second end 118b and a width of the slide 1 18 decreases with distance from the first end 118a towards the second end 1 18b. Accordingly, the slide 118 acts to funnel the power cable 130 into alignment with the channel 1 12a at the outer edge of the spool 1 12, as the power cable 130 is drawn onto the spool 1 12. The width of the slide 1 18 is sufficient to accommodate the cable connector 160 of the power cable 130, for example when the power cable 130 is fully retracted. The cable connector 160 is shown in more detail in Figures 3 to 5.

[0165] The cable connector 160 has a tubular housing 161 , a circular end face 162 at a first end of the housing 161 , and a tubular bend stiffener 167 at an opposite second end of the housing 161. The cable connector 160 is a three-phase electrical connector having three electrically conductive terminals 163a-c at the circular end face 162. The electrically conductive terminals163a-c are circumferentially arranged equidistantly relative to each other about a centre of the end face 162, so that centres of adjacent ones of the electrically conductive terminals 163a-c are offset from each other by one hundred and twenty degrees. As shown in Figure 5, the cable connector 160 includes removeable protective caps 168a-c on the respective electrically conductive terminals 163a-c, to protect the electrically conductive terminals 163a-c from damage during manipulation of the cable connector 160. The cable connector 160 also has a pilot wire 165 that is exposed at the end face 162 offset from the centre of the end face 162 and between two of the electrically conductive terminals 163a-c. It will be appreciated that there may be multiple pilot wires in practice, but only one is referred to herein for sake of clarity. Electrically conductive wires (not shown) of the power cable 130 extend through respective interiors of the housing 161 and the bend stiffener 167 and along the rest of the power cable 130 from the electrically conductive terminals 163a-c to the power supply circuit 108, and the pilot wire 165 extends through the interiors of the housing 161 and the bend stiffener 167 and along the rest of the power cable 130 from the end face 162 to the control system 106. The bend stiffener 167 acts to limit a bend radius of these electrically conductive wires and the pilot wire 165, and thus the power cable 130, as the cable connector 160 is manipulated during use, thus protecting against damage due to excessive bending of the power cable 130.

[0166] As discussed in more detail below, the electrically conductive terminals 163a-c are for contacting respective electrically conductive terminals 263a-c of a power connector 260 of a power connector module 200 of the vessel 20, and the pilot wire 165 is for contacting a pilot line 265 of the power connector 260 for transmission of communication signals between the cable connector 160 and the power connector 260, when the cable connector 160 is engaged with the power connector 260. An outer surface of the housing 161 defines an annular groove 166, which extends fully around the outer surface and with which projections 246a-b of a latch mechanism 240 of the power connector module 200 engage to retain the cable connector 160 relative to the power connector module 200 when the cable connector 160 is engaged with the power connector 260.

[0167] The cable connector 160 also has an engagement member in the form of a loop 164 at the centre of the end face 162, so that the electrically conductive terminals 163a-c are circumferentially arranged relative to each other about the loop 164. The loop 164 comprises a protrusion with an aperture 164a therethrough, as shown in Figure 4. In addition to the power cable 130, the transfer line 150 comprises a messenger line 140 that has a first end attached to the loop 164, as shown in Figure 2. More specifically, the end of the messenger line 140comprises a shackle 142 and a pin 144, as shown in Figure 10, and the pin 144 is located in the shackle 142 and the aperture 164a of the loop 164 to attach the first end of the messenger line 140 directly to the loop 164. While the messenger line 140 is detachably attached to the cable connector 160 of the power cable 130, the messenger line 140 is never detached from the cable connector 160 in this example.

[0168] As best shown in Figure 14, the crane 120 comprises a tower 125 fixed to the platform 104, a boom 126 extending from an upper end portion of the tower 125, a crane winch 128 rotatably mounted on the boom 126, a feed line 122, and a weight 124 attached to the feed line 122. The boom 126 is rotatable relative to the tower 125 and thus relative to the platform 104 and the main structure 102 of the offshore power source 10. The boom 126 is a telescopic boom that can extend and retract. More specifically, the boom comprises first and second boom sections 126a, 126b that are relatively moveable to adjust a reach of the boom 126 from the tower 125. The first boom section 126a is connected to the tower 125 via the second boom section 126b, and the crane winch 128 is mounted on the second boom section 126b. An end of the feed line is attached to the crane winch 128 and a portion of the feed line 122 is wound around a spool (not shown) of the crane winch 128. The feed line 122 runs from the spool of the crane winch 128 along the first and second boom sections 126a, 126b to an opposite end of the feed line 122, to which the weight 124 is attached. The weight 124 is buoyant in the body of water in which the offshore power source 10 is located and is provided in order to encourage the feed line 122 to hang vertically downwards. In some other examples, the weight 124 is instead non-buoyant in the body of water. The feed line 122 is detachably connected to an opposite second end of the messenger line 140 using transfer rigging at the second end of the messenger line 140, so that the messenger line 140 connects the feed line 122 to the cable connector 160 of the power cable 130. In other words, the feed line 122 is detachably indirectly connected to the power cable 130 via the messenger line 140.

[0169] The control system 106 of the offshore power source 10 is operatively connected to the umbilical winch 110 and the crane 120, so as to be able to control all operations of these elements of the offshore power source 10. The control system 106 is also communicatively connected to the communications interface (not shown) of the tension sensor 114 so as to be capable of receiving the tension indication via the communications interface. The control system 106 also includes a wireless communications interface for sending and receiving information, such as instructions or indications, to and from the control system 206 of the power connector module 200.

[0170] The vessel 20 will now be described in more detail, with particular reference to Figures 6 to 13. The vessel 20 includes a hull, a deck and an electrical system 2, which electrical system 2 comprises an electrical circuit 290 and the power connector module 200, which is located on the deck and is electrically connected to the electrical circuit 290 by electrically conductive wires.

[0171] The electrical circuit 290 comprises one or more batteries (not shown) for receiving and storing electrical charge for use in powering one or more systems of the vessel 20, such as a propulsion system for propelling the vessel 20, a hotel load supply system for supplying power for a hotel load of the vessel 20, and a communication system for communication between the vessel 20 and other locations.

[0172] The power connector module 200 comprises a steel base 202, a control system 206, an enclosure 210, an open-topped chute 220, a cable guide 230, the latch mechanism 240 mentioned above, a pull-in winch 250, the power connector 260 mentioned above, a pull-in line 270, and a power connector positioning mechanism 280.

[0173] The base 202 is compliant with ISO 668:2020. The base 202 has corner castings (only three 202a-c of which are visible in Figure 6) at its respective four corners, each of which complies with ISO 1 161 :2016. More specifically, the base 202 is a base taken from a Twenty-Foot Equivalent Unit (TEU) shipping container. As a result, the power connector module 200 engages with an ISO 668:2020-compliant interface of the deck of the vessel 20, so as to be stably retained on deck during sailing of the vessel 20. In some other examples, the power connector module 200 may be engaged with any other ISO 668:2020-compliant interface at any location or be stacked on top of a shipping container that also complies ISO 668:2020.

[0174] As best shown in Figure 7, the enclosure 210 encloses the control system 206, an interior portion 234 of the cable guide 230, the latch mechanism 240, the pull-in winch 250, the power connector 260 and the power connector positioning mechanism 280. The enclosure 210 sits on the base 202, has a floor 212 adjacent to the base 202, and has a series of four walls and a roof made of corrugated steel. An interior height H of the enclosure 210, measured between the floor 212 and the roof, is a little over 1 .8 metres, so as to comfortably accommodate a human operative HO or crew member. Two doors 218a-b are provided in respective opposite side walls of the enclosure 210, which doors 218a-b are openable to enable the human operative HO to access the interior of the enclosure 210, and closable to prevent entry during flow of an electrical current through the power cable 130 and into the power connector 260.

[0175] As shown in Figure 6, one 214 of the walls of the enclosure 210 defines an opening 216 through which the cable connector 160 is passable to engage the power connector 260, and the chute 220 is fixed to the base 202 at a position outside the enclosure 210 and is dimensioned and positioned to guide the cable connector 160 away from the base 202 and towards the opening 216 as the cable connector 160 is drawn towards the power connector 260 during use. More specifically, the chute 220 has a pair of side walls 222a-b that are upstanding from a smooth, convex surface 224 of the chute 220. The cable connector 160 is able to slide along the surface 224 of the chute 220 as the cable connector 160 is pulled into the enclosure 210 or fed out from the enclosure 210. The chute 220 has a first end 220a distal from the enclosure 210 and a second end 220b proximal to the enclosure 210. A width of the chute 220 is more than sufficient to accommodate the cable connector 160. The side walls 222a-b are angled relative to the surface 224 so that the first end 220a is wider than the second end 220b of the chute 220, and specifically the surface 224 thereof, narrows with distance from the first end 220a towards the second end 220b and thus towards the opening 216. Accordingly, the chute 220 acts to funnel the cable connector 160 into alignment with the opening 216 in the wall 214 of the enclosure 210, as the power cable 130 is drawn by the pull-in winch 250 as described below.

[0176] The cable guide 230, best shown in Figures 6 and 7, is for guiding movement of the cable connector 160 from the chute 220 to the latch mechanism 240. The cable guide 230 has an exterior portion 232 located outside the enclosure 210, between and connecting the second end 220b of the chute 220 to the opening 216. The cable guide 230 also has the interior portion 234 located inside the enclosure 210 and extending from the opening 216. The cable guide 230 is open-topped and of substantially constant cross-sectional area and shape along its length from the chute 220. The interior portion 234 of the cable guide 230 includes eighteen rollers 236. Six of these rollers 236 form a bed of the interior portion 234 of the cable guide 230, a further six of the rollers 236 form a first side of the interior portion 234 of the cable guide 230, and the remaining six of the rollers 236 form a second side of the interior portion 234 of the cable guide 230. The rollers 236 are rotatable about respective axes that extend perpendicularly to a direction of the length of the cable guide 230. That is, the respective axes of the rollers 236 that form a bed of the interior portion 234 are parallel to the floor 212 of the enclosure 210, and the respective axes of all the others of the rollers 236 are perpendicular to the floor 212 of the enclosure 210. The rollers 236 are all freely rotatable about their respective axes, to act as friction reducing elements that facilitate movement of the cable connector 160 along the cable guide 230 in use. In someother examples, one, some or al of the rollers 236 may be driven to rotate to further aid movement of the cable connector 160 along the cable guide 230.

[0177] The latch mechanism 240 will now be described with particular reference to Figures 7 to 9. The latch mechanism 240 is for retaining the cable connector 160 relative to the power connector module 200 ready for connection of the cable connector 160 to the power connector 260, and also is for retaining the cable connector 160 relative to the power connector module 200 during flow of an electrical current through the power cable 130 and into the power connector 260. The latch mechanism 240 has a tube-shaped structure 242 formed by an annular first part 244 and an annular mouth part 248. The first part 244 and the mouth part 248 are bolted together but may be securely joined in any other way in some other examples. The structure 242 surrounds an open space, or zone Z, having a central latch mechanism axis LA running from the first part 244 to the mouth part 248. It is into this zone Z that the cable connector 160 is received in use, in the direction of the latch mechanism axis LA. The mouth part 248 defines a funnel 248a at an end of the mouth part 248 opposite to the first part 244, to facilitate insertion and alignment of the cable connector 160 into the zone Z.

[0178] The latch mechanism 240 also has the first and second projections 246a-b mentioned above and a projection driving mechanism (not shown) that is operatively connected to the control system 206 so that the control system 206 is able to control the projection driving mechanism. The projections 246a-b are circumferentially arranged equidistantly relative to each other about the zone Z, so that the projections 246a-b are offset from each other by one hundred and eighty degrees. In other words, the projections 246a-b are on diametrically opposite sides of the zone Z. The projection driving mechanism is arranged to drive the projections 246a-b to project into the zone Z from respective recesses in the first part 244 of the structure 242, in order to engage the groove 166 in the surface of the cable connector 160 to retain the cable connector 160 relative to the power connector module 200. The projections 246a-b are moveable by the projection driving mechanism, relative to the structure 242, out of the zone Z and back into the recesses in order to disengage the groove 166 to permit removal of the cable connector 160 from the zone Z. In some other examples, the projections 246a-b are instead biased by respective springs to project into the zone Z, and the projection driving mechanism is used to move the projections 246a-b, relative to the structure 242, out of the zone Z against the bias of the springs. The latch mechanism 240 includes a processor (not shown) and a communications interface (not shown), and the processor is programmed to output a latch indication, indicative of the projections 246a-b being in the zone Z and thus engaged with the groove 166, via the communications interface to the control system 206 of the power connector module 200.

[0179] The pull-in winch 250, shown in Figure 7, is for pulling the cable connector 160 towards the power connector 260 when the transfer line 150 is connected to the pull-in winch 250. The pull-in winch has a spool 252 and a tension sensor 254. The pull-in line 270 mentioned above is partially wound around the spool 252 of the pull-in winch 250. The tension sensor 254 comprises a strain sensor, which is mechanically connected to the pull-in line 270, so as to sense a magnitude of tension in the pull-in line 270, and thus in the transfer line 150 when the pull-in line 270 is attached to the messenger line 140 of the transfer line 150. The tension sensor 254 includes a processor (not shown) and a communications interface (not shown), and the processor is programmed to output a tension indication, indicative of the magnitude of the tension in the transfer line 150, via the communications interface to the control system 206 of the power connector module 200.

[0180] The power connector 260 and the power connector positioning mechanism 280 of the power connector module 200 will now be described with reference to Figures 12 and 13. As mentioned elsewhere herein, the power connector 260 is for engaging the cable connector 160 of the power cable 130, in order to receive the flow of electrical current from the power cable 130 and, ultimately, from the power supply circuit 108 of the offshore power source 10.

[0181] The power connector 260 is a three-phase electrical connector having three electrically conductive terminals 263a-c at a circular end face 262 of a body 261 . The electrically conductive terminals 263a-c are circumferentially arranged equidistantly relative to each other about a centre of the end face 262, so that centres of adjacent ones of the electrically conductive terminals 263a- c are offset from each other by one hundred and twenty degrees. The power connector 260 also has the pilot line 265 mentioned above, which is exposed at the end face 262 offset from the centre of the end face 262 and between two of the electrically conductive terminals 263a-c. Electrically conductive power wires 266a-c extend through the body 261 from the electrically conductive terminals 263a-c to the electrical circuit 290, and the pilot line 265 extends through the body 261 from the circular end face 262 to the control system 206 of the power connector module 200. The electrically conductive terminals 263a-c are for contacting the respective electrically conductive terminals 163a-c of the cable connector 160 discussed above, and the pilot line 265 is for contacting the pilot wire 165 of the cable connector 160 for transmission ofcommunication signals between the cable connector 160 and the power connector 260, when the power connector 260 is engaged with the cable connector 160.

[0182] The body 261 defines a hole 264 therethrough. The body 261 acts as a guide for guiding the transfer line 150 through the hole 264 and relative to the power connector 260, as the spool 252 of the pull-in winch 250 rotates about a horizontal axis to pull the cable connector 160 towards the power connector 260 via the pull-in line 270 and the transfer line 150. The hole 264 opens at the centre of the end face 262, so that the guide has an open end at the end face 262 and so that the electrically conductive terminals 263a-c are circumferentially arranged relative to each other about the hole 264 and, therefore, about the open end of the guide. The hole 264 extends into the body 261 from the end face 262 in a direction orthogonal to the end face 262, whereby a guide direction in which the guide is to guide the transfer line 150 is orthogonal to the end face 262.

[0183] The power connector positioning mechanism 280 is for positioning the power connector 260 relative to the enclosure 210 ready for connection of the power connector 260 to the cable connector 160. More specifically, the power connector positioning mechanism 280 is adjusting rotational and translational positions of the power connector 260 relative to the cable connector 160 and the enclosure 210, when the cable connector 160 is retained relative to the power connector module 200 by the latch mechanism 240 as described above. Furthermore, the power connector positioning mechanism 280 is for retaining the power connector 260 relative to the power connector module 200 during flow of the electrical current through the power cable 130 and into the power connector 260.

[0184] The power connector positioning mechanism 280 comprises a stand 282 that supports a pair of linear rails 284a-b that define a track. The power connector positioning mechanism 280 also has a cradle 286 that is engaged with the rails 284a-b of the track. The body 261 of the power connector 260 is rotatably mounted to the cradle 286 about a central rotational axis RA that passes through, and parallel to, the hole 264, coaxially with the guide direction, so as to adjust the rotational position of the power connector 260 relative to the enclosure 210. A rotation lock (not shown) is provided for the human operative HO to selectively lock the body 261 at a given rotational position relative to the cradle 286. Each of the rails 284a-b extends in a direction perpendicular to the end face 262 of the power connector 260 and aligned with the guide direction in which the guide is configured to guide the transfer line 150. Therefore, the cradle 286 is moveable translationally along the rails 284a-b, to move the end face 262 of the power connector260 along the track towards and away from the latch mechanism 240, so as to adjust the translational position of the power connector 260 relative to the enclosure 210. A translation lock (not shown) is provided for the human operative HO to selectively lock the cradle 286 at a given translational position relative to the rails 284a-b.

[0185] Four handles 267a-d extend from the body 261 of the power connector 260 and are graspable by the human operative HO to help them adjust the rotational and / or translational position of the body 261 , and thus the electrically conductive terminals 263a-c and the pilot line 265, relative to the cradle 286 and the enclosure 210. In some other examples, the power connector positioning mechanism 280 comprises a drive system for driving the power connector 260 relative to the enclosure 210. Such a drive system could be controlled by one of the control systems 32, 42, 106, 206 mentioned herein, either automatically or in response to commands received by the control system 32, 42, 106, 206 from a remote human operative. The drive system may be operable to drive the power connector 260 rotationally relative to the cradle 286 and / or to drive the cradle 286 translationally along the rails 284a-b so as to move the power connector 260 along the track. In some such other examples, the handles 267a-d may be omitted.

[0186] The control system 206 of the of the power connector module 200 is operatively connected to the latch mechanism 240, the pull-in winch 250 and the power connector positioning mechanism 280, so as to be able to control all operations of these elements of the power connector module 200. The control system 206 is also communicatively connected to the communications interface (not shown) of the tension sensor 254 so as to be capable of receiving the tension indication via that communications interface, and communicatively connected to the communications interface (not shown) of the latch mechanism 240 so as to be capable of receiving the latch indication via that communications interface. The control system 206 also includes a wireless communications interface for sending and receiving information, such as instructions or indications, to and from the control system 106 of the offshore power source 10.

[0187] The control system 106 of the offshore power source 10 is communicatively connected to the control system 206 of the power connector module 200. Both the floating remote-control centre 30 and the land-based remote-control centre 40 are remote from the offshore power source 10 and remote from the vessel 20. The floating remote-control centre 30 comprises a control system 32 that is communicatively connected to the control system 106 of the offshore power source 10, to the control system 206 of the power connector module 200, and to a control system 42 of the land-based remote-control centre 40. Similarly, the control system 42 of the land-based remote-control centre 40 is communicatively connected to the control system 106 of the offshorepower source 10, to the control system 206 of the power connector module 200, and to the control system 32 of the floating remote-control centre 30. The control systems 32, 42, 106, 206 comprise respective computing systems (not shown), each computing system comprising one or more processors and a non-transitory storage medium accessible by the one or more processors and storing machine-readable instructions that, when executed by the processor or processors, cause the processor or processors to perform any of the methods described herein. As such, each of the methods may be considered a computer-implemented method.

[0188] A number of methods will now be described, each of which is performed by the control system 206 of the power connector module 200 of the vessel 20. However, in other examples, any of the other control systems 32, 42, 106 may perform any one or more of the methods.

[0189] The first method is a method 500 of handling the transfer line 150 (hereinafter referred to as the transfer line handling method, for brevity). The transfer line handling method 500 is described with reference to the schematic views in Figures 1 and 14 to 21 and the flow chart that bridges Figures 22A and 22B.

[0190] The method 500 comprises receiving 502 a trigger indication at the control system 206 from another system onboard the vessel 20, namely a navigation system of the vessel 20, and the trigger indication is generated by that other system in a manner that would be immediately discernible by the skilled person. The trigger indication indicates that a distance D between the vessel 20 and the offshore power source 10, and more specifically between the chute 220 of the power connector module 200 and the slide 1 18 of the umbilical winch 1 10, is less than a threshold distance DTof twenty metres. The trigger indication also indicates that the vessel 20 is travelling at less than or equal to a threshold speed relative to the offshore power source 10, that threshold speed being 0.25 metres per second. The vessel 20 is operating under dynamic positioning (DP) and is considered to be at a final DP position at this point.

[0191] The method 500 comprises, on the basis of the trigger indication, causing 504 rotation of the boom 126 of the crane 120 relative to the tower 125 of the crane 120 so that the boom 126 no longer is positioned solely over the platform 104, and causing 506 telescopic extension of the boom 126 by way of linear movement of the first boom section 126a relative to the second boom section 126b to increase the reach of the boom 126 from the tower 125. These operations are performed by way of the control system 206 sending instructions to the control system 106 of the offshore power source 10, which in turn operates to control the crane 120. Moreover, theseoperations cause the crane 120 to transition from the position shown in Figure 1 to the position shown in Figure 14, so that an end of the boom 126 distal from the tower 125 holds an end of the feed line 122 so that it is close to overhanging the chute 220 of the power connector module 200.

[0192] The method 500 then comprises causing 508 the crane winch 128 to rotate to cause the feed line 122, a portion of which is wound around the spool of the crane winch 128, to be paid out from the offshore power source 10 and towards the water line WL. This operation is again performed by way of the control system 206 sending instructions to the control system 106 of the offshore power source 10, which in turn operates to control the crane 120. As the weight 124 is attached to the feed line 122, the feed line 122 tends to be fed out approximately vertically from the boom 126 of the crane 120, as denoted by the arrow F in Figure 15. Moreover, as the feed line 122 is detachably connected to the second end of the messenger line 140 of the transfer line 150, this paying out of the feed line 122 results in movement of the transfer line 150 towards the vessel 20, and more specifically towards the power connector module 200.

[0193] The method 500 then comprises causing 510 the crane winch 128 to cease rotating, to cause the pay out of the feed line 122 to cease when the feed line 122 or the messenger line 140 is on or proximate to the vessel 20. This operation is again performed by way of the control system 206 sending instructions to the control system 106 of the offshore power source 10, which in turn operates to control the crane 120. The instructions may be sent on the basis of one or more manual inputs to the control system 206, such as by the human operative HO on the vessel 20 who is watching the transfer line 150 approach the power connector module 200.

[0194] The method 500 then pauses while the human operative HO on the vessel 20 undertakes some operations.

[0195] Specifically, the human operative HO ensures that an end portion of the pull-in line 270, distal from the pull-in winch 250, passes through the hole 264 in the power connector 260, then through the zone Z of the latch mechanism 240, then through the opening 216 in the wall 214 of the enclosure 210, and then along the chute 220, so that a distal end of the pull-in line 270 is outside the enclosure 210. The human operative HO then catches the messenger line 140 or the feed line 122, such as by using a crook, and attaches the second end of the messenger line 140 to the distal end of the pull-in line 270 using the transfer rigging at the second end of the messenger line 140, so as to connect the transfer line 150 to the pull-in winch 250 of the power connector module 200 of the vessel 20. The power transfer system 1 is then in the state shown in Figure 16.

[0196] The human operative HO then detaches the feed line 122 from the transfer rigging so as to detach the feed line 122 from the messenger line 140, ensures that the pull-in line 270 is trailing down the smooth, convex surface 224 of the chute 220 to the messenger line 140, and that the messenger line 140 has an unhindered route to the chute 220. The weight 124 remains attached to the feed line 122, so as to cause the feed line 122 to tend to hang approximately vertically from the boom 126 of the crane 120. The human operative HO then stands back from the chute 220 and the feed line 122.

[0197] The method 500 then resumes with causing 512 the crane winch 128 to rotate in an opposite direction to that of block 508 to cause the feed line 122 to be wound onto the spool of the crane winch 128 and retracted back into the offshore power source 10 in the direction of the arrow R in Figure 17, and then causing 514 the crane winch 128 to cease rotating once the feed line 122 is fully retracted into the offshore power source 10, as shown in Figure 18, to cause the retraction of the feed line 122 to cease. These operations are again performed by way of the control system 206 sending instructions to the control system 106 of the offshore power source 10, which in turn operates to control the crane 120.

[0198] The method 500 then comprises receiving 516, from the communications interface of the tension sensor 254 of the pull-in winch 250 or from the communications interface of the tension sensor 1 14 of the umbilical winch 1 10 via the control system 106 of the offshore power source, a tension indication indicating a magnitude of a tension in the transfer line 150. In some examples, the method 500 comprises causing the pull-in winch 250 to rotate to pull the pull-in line 270, and thus create the detectable tension in the transfer line 150. The method comprises comparing 518 the magnitude of the tension to a threshold tension and, if the magnitude of the tension is greater than the threshold tension, causing 520 both the pull-in winch 250 and the umbilical winch 1 10 to rotate to cause feed out of the transfer line 150 from the offshore power source 10 to be initiated. This results in the pull-in line 270, to which the transfer line 150 is connected, being pulled up the chute 220, along the cable guide 230, through the zone Z of the latch mechanism 240, through the hole 264 in the power connector 260 and wound around the spool 252 of the pull-in winch. In turn, this causes the cable connector 160 of the power cable 130 of the transfer line 150 to move down and off the slide 1 18 of the umbilical winch 1 10 towards the vessel 20, and more specifically towards the power connector 260 of the power connector module 200, as shown in Figure 19. The causing the pull-in winch 250 to rotate is performed by way of the control system 206 sending instructions to the pull-in winch 250, and the causing the umbilical winch 1 10 to rotate is performed by way of the control system 206 sending instructions to the control system 106 of the offshorepower source 10, which in turn operates to control the umbilical winch 110. While the umbilical winch 1 10 may be operated to maintain a constant torque to maintain tension in the transfer line 150, the pull-in winch 250 may pull with a force that is sufficient to overcome this torque to control the tension in the transfer line 150.

[0199] At this point, a method 600 of engaging the power connector 260 with the cable connector 160 (hereinafter referred to as the connector engagement method, for brevity) is performed. For convenience, the connector engagement method 600 is described below, after completion of the present discussion of the transfer line handling method 500. As a result of the connector engagement method, the cable connector 160 of the transfer line 150 is latched by the latch mechanism 240 and engaged with the power connector 260, and the power transfer system 1 is in the state shown in Figure 20.

[0200] After completion of the connector engagement method 600, the transfer line handling method 500 continues with the control system 206 then receiving 522 a connection indication indicating that the cable connector 160 is electrically connected to the power connector 260. This connection indication is received at the control system 206 as a result of the control system 206 causing a communication signal to be sent along the pilot line 265 and the pilot wire 165 to the control system 106 of the offshore power source 10. An acknowledgement, received at the control system 206 of the power connector module 200 from the control system 106 of the offshore power source 10 via the pilot wire 165 and the pilot line 265, which acknowledgement acknowledges receipt of the communication signal, acts as the connection indication. In some other examples, the control system 206 obtains or receives the connection indication in a different way, such as by detecting that a low-voltage electrical current successfully flows to or from the offshore power source 10 through one or more of the electrically conductive terminals 263a-c of the power connector 260, or by receiving a signal manually input to the control system 206, or to another system of the vessel 20 that is communicatively connected to the control system 206, by the human operative HO.

[0201] The vessel 20 is then commanded to sail slowly away from the offshore power source 10 in DP mode, while the control system 206 causes 524 the umbilical winch 1 10 to begin rotating again to cause further feed out of the transfer line 150 from the offshore power source 10, while the distance D between the offshore power source 10 and the vessel 20 increases. During this time, the pull-in winch 250 is not rotating since the cable connector 160 is retained by the latch mechanism 240. When the distance D between the vessel 20 and the offshore power source 10reaches a predetermined distance of about two hundred metres, the vessel 20 is commanded to stop sailing and to set its heading in an attempt to optimise the heading in relation to wind and currents in the water, and the method 500 comprises causing 526 the rotation of the umbilical winch 1 10 to cease, so as to cause the further feed out of the transfer line 150 from the offshore power source 10 to cease. Furthermore, the boom 126 of the crane 120 is caused to rotate relative to the tower 125 of the crane 120 so that the boom 126 is positioned solely over the platform 104.

[0202] The control system 206 then receives 528 a stability indication. The stability indication indicates that the vessel 20 is undergoing less than a predetermined degree of roll, heave and pitch and that a rate of change of a position of the vessel 20 relative to the offshore power source 10 is less than or equal to a predetermined rate of change of 0.25 metres per second. The stability indication thus indicates that the vessel 20 is in a stable DP position at the predetermined distance from the offshore power source 10, and that the vessel 20 is ready for power transfer from the offshore power source 10 via the power cable 130. The stability indication is received at the control system 206 from another system onboard the vessel 20, namely the navigation system of the vessel 20, and is generated by that other system in a manner that would be immediately discernible by the skilled person.

[0203] As shown in Figure 22A, the method 500 then comprises causing 530 a flow of an electrical current through the power cable 130 to be initiated, on the basis of the connection indication and the stability indication, by the control system 206 sending a suitable instruction to the control system 106 of the offshore power source 10 to cause the control system 106 of the offshore power source 10 to close an output breaker. The power transfer system 1 is then in the state shown in Figure 21. The flow of electrical current is from the offshore power source 10 to the vessel 20, and more specifically from the power supply circuit 108 to the batteries of the electrical circuit 290 of the electrical system 2 of the vessel 20. In this example, the supply of electrical power to the vessel 20 is for charging the batteries of the electrical circuit 290, but in some other examples the supply of electrical power to the vessel 20 from the offshore power source 10 may be for a different purpose, such as providing idle load power while the vessel 20 idles.

[0204] The method 500 then comprises receiving 534 a transfer completed indication indicating that transfer of electrical power from the offshore power source 10 to the vessel 20 is complete, and then causing 536 the flow of the electrical current through the power cable 130 to cease as a consequence, by the control system 206 again sending a suitable instruction to the controlsystem 106 of the offshore power source 10 to cause the control system 106 of the offshore power source 10 to open the output breaker. The transfer of electrical power may be deemed complete on the basis that, for example, a certain predetermined amount of electricity has been supplied to the vessel 20 from the offshore power source 10, the transfer of electrical power has occurred for a certain predetermined length of time, or the batteries of the electrical circuit 290 have reached a certain predetermined level of charge. The transfer completed indication may be received at the control system 206 from another system onboard the vessel 20, such as the electrical system 2 of the vessel 20, from the control system 106 at the offshore power source 10 either wirelessly or via the pilot wire 165 and the pilot line 265, or by receiving a signal manually input to the control system 206, or to another system of the vessel 20 that is communicatively connected to the control system 206, by the human operative HO.

[0205] The vessel 20 is then commanded to sail slowly back towards the offshore power source 10, while the control system 206 causes 538 the umbilical winch 110 to rotate in an opposite direction to that of block 524 to cause retraction of the transfer line 150 back into the offshore power source 10, while the distance D between the offshore power source 10 and the vessel 20 reduces. During this time, the pull-in winch 250 is not rotating. When the distance D between the vessel 20 and the offshore power source 10 is less than the threshold distance DTof twenty metres, the vessel 20 is commanded to stop sailing and the method 500 comprises causing 540 the rotation of the umbilical winch 110 to cease, so as to cause the retraction of the transfer line 150 to cease. These operations involving the umbilical winch 110 are performed by way of the control system 206 sending instructions to the control system 106 of the offshore power source 10, which in turn operates to control the umbilical winch 110.

[0206] The method 500 then comprises causing 542 disengagement of the latch mechanism 240 from the cable connector 160. This is performed by way of the control system 206 controlling the projection driving mechanism to move the projections 246a-b of the latch mechanism 240 out of the zone Z and the groove 166 of the power connector 160 and into the respective recesses in the first part 244 of the structure 242 of the latch mechanism 240.

[0207] The method 500 also comprises causing 544 the crane 120 to be repositioned so that it reverts to the position shown in Figure 14. This involves the boom 126 of the crane 120 rotating relative to the tower 125 of the crane 120 so that the boom 126 no longer is positioned solely over the platform 104, and the boom 126 telescopically extending again to increase the reach of the boom 126 from the tower 125 and to cause the end of the boom 126 distal from the tower 125 tohold the end of the feed line 122 so that it is close to overhanging the chute 220 of the power connector module 200.

[0208] The method 500 then comprises receiving 546 a second trigger indication and, on the basis of the second trigger indication, causing 548 the crane winch 128 to rotate to cause the feed line 122, with the weight 124 attached, to be paid out again from the offshore power source 10 in order to facilitate detachable reconnection of the feed line 122 to the transfer line 150. This operation is again performed by way of the control system 206 sending instructions to the control system 106 of the offshore power source 10, which in turn operates to control the crane 120.

[0209] The second trigger indication is received at the control system 206 from another system onboard the vessel 20, namely a navigation system of the vessel 20, and is generated by that other system in a manner that would be immediately discernible by the skilled person. The second trigger indication indicates that the distance D between the vessel 20 and the offshore power source 10 is less than the threshold distance DTof twenty metres, and that the vessel 20 is travelling at less than or equal to the threshold speed of 0.25 metres per second relative to the offshore power source 10.

[0210] The method 500 then comprises causing 550 the crane winch 128 to cease rotating, to cause the pay out of the feed line 122 to cease when the feed line 122 is on or proximate to the vessel 20. This operation is again performed by way of the control system 206 sending instructions to the control system 106 of the offshore power source 10, which in turn operates to control the crane 120. The instructions may be sent on the basis of one or more manual inputs to the control system 206, such as by the human operative HO on the vessel 20 who is watching the feed line 122 approach the power connector module 200.

[0211] The method 500 then pauses again while the human operative HO undertakes some operations.

[0212] Specifically, the human operative HO causes the pull-in winch 250 to operate to allow the pull-in line 270 and the transfer line 150 to pay out from the enclosure 210 through the opening 216 in the wall 214 of the enclosure 210, so that the distal end of the pull-in line 270, which is attached to the messenger line 140 of the transfer line 150 by way of the transfer rigging at the end of the messenger line 140, is outside the enclosure 210. The human operative HO then catches the feed line 122, such as by using the crook, and detachably reconnects the feed line 122 to the transfer line 150 using the transfer rigging at the end of the messenger line 140. Thehuman operative HO then detaches the pull-in line 270 from the transfer rigging so as to detach the pull-in line 270 from the messenger line 140, pushes the messenger line 140 off the end of the vessel 20, and causes the pull-in winch 250 to operate to draw the end portion of the pull-in line 270 back into the enclosure 210. The human operative HO then stands back from the feed line 122.

[0213] The method 500 then resumes with the control system 206 receiving 552 a trigger indicator manually input to the control system 206, or to another system of the vessel 20 that is communicatively connected to the control system 206, by the human operative HO. This trigger indicator indicates that the feed line 122 is detachably connected to the transfer line 150, the cable connector 160 is electrically disconnected from the power connector 260 and mechanically disconnected from the vessel 20 (and thus disengaged from the latch mechanism 240), and that the vessel is less than the threshold distance DT of twenty metres from the offshore power source 10 and travelling at less than or equal to the threshold speed of 0.25 metres per second relative to the offshore power source 10.

[0214] On receipt of this trigger indicator, the control system 206 causes 554 the crane winch 128 to rotate in an opposite direction to that of block 548 to cause the feed line 122 to be wound onto the spool of the crane winch 128 and retracted back into the offshore power source 10, and then causes 556 the crane winch 128 to cease rotating once the feed line 122 is fully retracted into the offshore power source 10, to cause the retraction of the feed line 122 to cease. These operations are again performed by way of the control system 206 sending instructions to the control system 106 of the offshore power source 10, which in turn operates to control the crane 120.

[0215] The transfer line handling method 500 of this example is thus complete.

[0216] During flow of the electrical current through the power cable 130 that results from performance of block 530, the control system 206 may receive 532 an emergency release indication. The emergency release indication indicates that any one or more of the following conditions are true: the magnitude of the tension in the transfer line 150 is above an allowable magnitude, the vessel 20 is insufficiently stable, and the vessel 20 is less than the predetermined distance of two hundred metres from the offshore power source 10 or has otherwise moved out of position limits. The emergency release indication may be received at the control system 206 from another system onboard the vessel 20, such as a navigation system of the vessel 20, thecommunications interface of the tension sensor 254 of the pull-in winch 250, or the communications interface of the tension sensor 114 of the umbilical winch 1 10, or may be manually input to the control system 206, or to another system of the vessel 20 that is communicatively connected to the control system 206, by the human operative HO.

[0217] On the basis of the emergency release indication, the control system 206 causes 532a the flow of the electrical current through the power cable 130 to cease, such as by sending a suitable instruction to the control system 106 at the offshore power source 10 to cause the control system 106 of the offshore power source 10 to open the output breaker, and then causes 532b disengagement of the latch mechanism 240 from the cable connector 160 in the same way as described above for block 542. In some examples, the control system 206 also causes the pull- in winch 250 to rotate to enable the transfer line 150 to be at least partially paid out and the cable connector 160 to be ejected from the vessel 20, on the basis of the emergency release indication. As the messenger line 140 remains connected to the cable connector 160 and to the pull-in line 270 throughout the method 500, pay out of the messenger line 140 and the cable connector 160 from the vessel 20 is controllable.

[0218] It is to be noted that blocks 552 and 554, and optionally block 556, may be performed in isolation as a method of withdrawing a transfer line, such as the transfer line 150 discussed above, the transfer line comprising a cable connector of a power cable, from an offshore unit (such as a vessel) to an offshore power source, such as the offshore power source 10 discussed above, regardless as to how the transfer line was previously handled or offered or provided to the offshore unit.

[0219] The connector engagement method 600 mentioned above will now be described with reference primarily to Figures 2 to 13 and the flow chart in Figure 23.

[0220] As mentioned above, the causing 520 the pull-in winch 250 and the umbilical winch 110 to rotate results in the pull-in line 270 being pulled through the hole 264 in the power connector 260 and wound around the spool 252 of the pull-in winch 250. As the pull-in line 270 is connected to the messenger line 140 of the transfer line 150, once the pull-in line 270 has fully passed through the hole 264, the messenger line 140 follows. Accordingly, the method 600 comprises the control system 206 causing 602 movement of the transfer line 150, while causing the messenger line 140 of the transfer line 150 to be drawn through the hole 264 so as to be guided by the guide of the power connector 260.

[0221] As the messenger line 140 is attached to, and leads, the cable connector 160 during this movement, this movement causes the cable connector 160 to enter the chute 220 of the power connector module 200, slide up its convex surface 224, be guided by the exterior portion 232 of the cable guide 230 to pass through the opening 216 in the wall 214 of the enclosure 210, and then roll along the rollers 236 of the interior portion 234 of the cable guide 230. As shown in Figure 10, the cable connector 160 is then directed by the funnel 248a of the mouth part 248 of the latch mechanism 240 to enter the zone Z surrounded by the structure 242 of the latch mechanism 240 in the direction of arrow I in Figure 10. Passage of the cable connector 160 through the zone Z causes the end face 162 and the tubular housing 161 of the cable connector 160 to deflect the projections 246a-b out of the zone Z and into the respective recesses in the first part 244 of the structure 242, despite the projection driving mechanism attempting to urge the projections 246a-b into the zone Z under control of the control system 206. Thereafter, when the groove 166 in the surface of the tubular housing 161 of the cable connector 160 is aligned with the projections 246a-b, the projection driving mechanism is able to drive the projections 246a- b into the groove 166, as shown in Figure 1 1 , to retain the cable connector 160 relative to the latch mechanism 240 and the enclosure 210. That is, the method 600 comprises the control system 206 causing 604 the projections 246a-b to engage the groove 166.

[0222] The method 600 then comprises the control system 206 receiving 606, from the communications interface of the latch mechanism 240, a latch indication indicating that the cable connector 160 is engaged by the latch mechanism 240, and more specifically that the projections 246a-b are in the zone Z and engaged with the groove 166. As a result of receiving this latch indication, the control system 206 causes 608 the rotation of the pull-in winch 250 and the umbilical winch 110 to cease, so as to cause the feed out of the transfer line 150 from the offshore power source 10 to cease, and thus the movement of the messenger line 140 through the hole 264 to cease. The causing the pull-in winch 250 to stop rotating is performed by way of the control system 206 sending instructions to the pull-in winch 250, and the causing the umbilical winch 1 10 to stop rotating is performed by way of the control system 206 sending instructions to the control system 106 of the offshore power source 10, which in turn operates to control the umbilical winch 110.

[0223] It should be noted that the messenger line 140 remains connected to the cable connector 160 at this point, and indeed throughout the entire method 500, including during subsequent flow of the electrical current through the power cable 130. However, in some other examples, themessenger line 140 is uncoupled from the loop 164 of the cable connector 160 once the cable connector 160 is latched by the latch mechanism 240.

[0224] In some examples, the method 600 next comprises the control system 206 causing 610 the power connector 260 to be positioned relative to the cable connector 160 while the projections 246a-b of the latch mechanism 240 engage the groove 166 to retain the cable connector 166 relative to the power connector module 200, by way of the control system 206 causing the drive system mentioned above to drive the power connector 260 rotationally relative to the cradle 286 and / or to drive the cradle 286 translationally along the rails 284a-b so as to move the power connector 260 along the track. Such driving of the cradle 286 translationally along the rails 284a- b causes the electrically conductive terminals 263a-c of the power connector 260 to be brought into contact with the respective electrically conductive terminals 163a-c of the cable connector 160, and the pilot line 265 of the power connector 260 to be brought into contact with a pilot wire 165 of the cable connector 160. In other examples, such as the present example, instead of the control system 206 performing blocks 610-614, the method 600 ceases and the human operative HO enters the interior of the enclosure 210 through one of the doors 218a-b and instead undertakes these operations by grasping one or more of the handles 267a-d of the power connector 260 and imparting suitable forces on the power connector 260 to move the power connector 260 relative to the cable connector 160. The human operator HO then exits the interior of the enclosure 210 through one of the doors 218a-b and ensures that both of the doors 218a-b are then closed, and optionally locked. In either case, the transfer line handling method 500 is then resumed.

[0225] Example embodiments of the present invention have been discussed, with particular reference to the examples illustrated. However, it will be appreciated that variations and modifications may be made without departing from the scope of the invention as defined by the appended claims.

[0226] For example, while in the illustrated embodiment the offshore power source 10 is fixed to a bed of a body of water, in other embodiments the offshore power source 10 may be, for example, a floating offshore power source. Moreover, while in the illustrated embodiment the offshore unit is a vessel, in other embodiments the offshore unit may be, for example, a different type of floating offshore unit such as a buoy, or may be a non-floating offshore unit, such as an offshore platform that is fixed to a bed of a body of water. Furthermore, while in the illustrated embodiment the transfer line 150 includes the messenger line 140, in some other embodiments the messengerline is omitted and the feed line 122 is detachably connected directly to the power cable 130, such as to the cable connector 160. In some examples, the offshore power source itself is connected to a cable ending at the shore, with the cable connected to a main electrical grid.

Claims

CLAIMS:1 . A method of handling a transfer line, comprising a cable connector of a power cable for electrical power transfer between an offshore power source and an offshore unit, the method comprising: obtaining a trigger indication indicating that at least one predetermined condition is met; and on the basis of the trigger indication, causing a feed line of the offshore power source, which feed line is detachably connected to the transfer line, to be paid out from the offshore power source in order to move the transfer line towards the offshore unit.

2. The method of claim 1 , wherein the causing the feed line to be paid out comprises causing rotation of a crane winch of a crane of the offshore power source, around a spool of which crane winch a portion of the feed line is wound.

3. The method of claim 2, comprising, on the basis of the trigger indication, causing movement of at least one part of the crane from a first position to a second position relative to a main structure of the offshore power source, before or during the causing the feed line to be paid out.

4. The method of any one of claims 1 to 3, wherein the at least one predetermined condition comprises that the offshore unit is less than a threshold distance from the offshore power source.

5. The method of any one of claims 1 to 4, wherein the at least one predetermined condition comprises that the offshore unit is travelling at less than or equal to a threshold speed relative to the offshore power source.

6. The method of any one of claims 1 to 5, comprising causing the feed line to be retracted back into the offshore power source, after detachment of the transfer line from the feed line.

7. The method of any one of claims 1 to 6, comprising causing feed out of the transfer line from the offshore power source to be initiated.

8. The method of claim 7, comprising obtaining a tension indication indicating a tension in the transfer line, wherein the causing feed out of the transfer line from the offshore power source to be initiated is performed on the basis of the tension indication.

9. The method of claim 8, wherein the tension in the transfer line is measured at a pull-in winch at the offshore unit, to which pull-in winch the transfer line is connected.

10. The method of any one of claims 7 to 9, comprising causing the feed out of the transfer line from the offshore power source to cease.11 . The method of claim 10, comprising obtaining a latch indication indicating that part of the power cable is engaged by a latch mechanism of the offshore unit, wherein the causing the feed out of the transfer line from the offshore power source to cease is on the basis of the latch indication.

12. The method of claim 11 , comprising causing further feed out of the transfer line from the offshore power source, while a distance between the offshore power source and the offshore unit increases.

13. The method of any one of claims 1 to 12, comprising causing flow of an electrical current through the power cable to be initiated, once the cable connector is electrically connected to a power connector of the offshore unit.

14. The method of claim 13, comprising obtaining a stability indication indicating that the offshore unit is stable at a predetermined distance from the offshore power source, wherein the causing flow of the electrical current is on the basis of the stability indication.

15. The method of claim 13 or claim 14, comprising obtaining an emergency release indication during the flow of electrical current through the power cable, and causing disengagement of a latch mechanism of the offshore unit from part of the power cable on the basis of the emergency release indication.

16. The method of any one of claims 13 to 15, comprising obtaining a transfer completed indication indicating that transfer of electrical power to the offshore unit is complete, and causingthe flow of the electrical current through the power cable to cease on the basis of the transfer completed indication.

17. The method of any one of claims 1 to 16, comprising causing the feed line to be retracted back into the offshore power source, after detachable reconnection of the feed line to the transfer line.

18. The method of claim 17, comprising: obtaining a trigger indicator indicating that at least one predetermined state is met; and causing the feed line of the offshore power source to be retracted on the basis of the trigger indicator.

19. A method of withdrawing a transfer line, comprising a cable connector of a power cable for electrical power transfer between an offshore power source and an offshore unit, from the offshore unit to the offshore power source, the method comprising: obtaining a trigger indicator indicating that at least one predetermined state is met; and on the basis of the trigger indicator, causing a feed line of the offshore power source, which feed line is detachably connected to the transfer line, to be retracted in order to move the transfer line away from the offshore unit.

20. A control system configured to perform the method of any one of claims 1 to 19.

21. A non-transitory storage medium storing machine-readable instructions that, when executed by a processor of a control system, cause the processor to perform the method of any one of claims 1 to 19.

22. A vessel comprising the control system of claim 20 or the non-transitory storage medium of claim 21 .

23. An offshore power source comprising the control system of claim 20 or the non-transitory storage medium of claim 21 .

24. A remote-control centre comprising the control system of claim 20 or the non-transitory storage medium of claim 21 , wherein the remote-control centre is remote from the offshore unit and remote from the offshore power source.

25. A power transfer system comprising an offshore power source and the control system of claim 20 or the non-transitory storage medium of claim 21 , wherein the control system or the non- transitory storage medium, respectively, is remote from the offshore power source.

Images