System and method for laying a flexible subsea power cable

Abstract

Disclosed is a system for laying a flexible subsea power cable (20) in a sea, the cable comprising at least one fitting (16) to at least one end of the cable. The system comprises a tower (10) mountable on a deck (12) of a vessel (14), the tower comprising a firing line (34) for laying the cable; an arcuate guide (22) for the cable, the arcuate guide being rotatable around an axis (24) on the tower; a first handling arm (26), the first handling arm being rotatable around the axis, configured to hold the cable, and configured to move the fitting along a path outside of the arcuate guide; and a tensioner (30) for the cable, the tensioner being movable in and out of the firing line. The system comprises a second handling arm (40), the second handling arm being configured to position the cable to allow the tensioner to move into the firing line around the cable by guiding the cable end further away from the arcuate guide than the first handling arm.

Description

[0001] SYSTEM AND METHOD FOR LAYING A FLEXIBLE SUBSEA POWER CABLE

[0002] Technical Field

[0003] The present disclosure relates generally to laying of power cables in the field of offshore structures and more generally to the renewable energy industry. More specifically, the present disclosure relates to a system and method for laying a flexible subsea power cable in the sea, for example, onto the seabed.

[0004] Background

[0005] An offshore structure producing energy has normally at least a power cable connected to the offshore structure. This allows electric energy to be transferred from the offshore structure.

[0006] Power cables are sometimes stored subsea, and this is also known as a wet- parked power cable. Where a cable has a damageable fitting on it, it is a problem how to deploy the power cable from the vessel without damaging the fitting, including where the cable or fitting cannot go through a tensioner. The tensioner can not hold a fitting, because the fitting is too thick and will be damaged. The tensioner can only hold onto the power cable as such and feed the power cable.

[0007] It is desirable that any solution can use an existing vessel without too much of a change or need to rebuild the deck and / or the vessel. It is a problem to comply with the relevant regulations technically and in a cost-effective manner. Any solution also needs to be flexible and fit different types of power cables.

[0008] A further technical problem is that any part of handling a power cable on a vessel must be safe and function without a possibility to fail, fulfil technical and legal requirements, and be easy to use. It is desirable that any solution is simple, not expensive to produce, and is reliable. It is a further technical problem to avoid cumbersome arrangements that are expensive to realise.

[0009] The present disclosure is directed to overcoming one or more of the problems as set forth above.

[0010] SUMMARY

[0011] It is an objective of the present invention to provide a method and system for laying a flexible subsea power cable. This objective can be achieved by the features as defined in the independent claims. Further characteristics are defined by the dependent claims. According to one aspect, there is provided a system for laying a flexible subsea power cable in the sea, the cable comprising at least one fitting to at least one end of the cable, the system comprising: a tower mountable on a deck of a vessel, the tower comprising a firing line for laying the cable; an arcuate guide for the cable, the arcuate guide being rotatable around an axis on the tower; a first handling arm, the first handling arm being rotatable around the axis, configured to hold the cable, and configured to move the fitting along a path outside of the arcuate guide; and a tensioner for the cable, the tensioner being movable in and out of the firing line; wherein the system comprises a second handling arm, the second handling arm being configured to position the cable to allow the tensioner to move into the firing line around the cable by guiding the cable end further away from the arcuate guide than the first handling arm. The second handling arm may be movably mounted on the tower and arranged such that an end of the second handling arm interacting with the cable is being movable along a travel path of the firing line.

[0012] According to another aspect, there is provided a method for laying a flexible subsea power cable in a sea using the system as described herein, the method comprising at least the steps in any order of: moving the fitting with the first handling arm to a position where the second handling arm can receive the cable; holding the cable with the second handling arm; and moving the fitting along the firing line to allow the tensioner to move into the firing line; and holding the cable with the tensioner.

[0013] A tower having both first and second handling arms allows the fitting to be pulled down so that the tensioner can engage the cable without the first handling arm being in the way and without damaging any fitting, for example a bend stiffener. This also provides for a more compact lay tower, because the first handling arm and the tensioner can be arranged close to each other.

[0014] At least one of the aspects and embodiments defined in the present application provides one or more solutions to the problems and disadvantages with the background art. Other technical advantages of the present disclosure will be readily apparent to one skilled in the art from the following description and claims. Various embodiments of the present application obtain only a subset of the advantages set forth. No one advantage is critical to the embodiments. Any claimed embodiment may be technically combined with any other claimed embodiment or embodiments.

[0015] Brief Description of the Drawings

[0016] The disclosure will be further described with reference to examples depicted as schematic illustrations in the accompanying figures in which:

[0017] FIG.s 1 and 4 are schematic illustrations of systems according to embodiments of the invention; and

[0018] FIG. 5 shows steps of a method according to an embodiment of the invention.

[0019] Detailed Description

[0020] Power cables are sometimes stored subsea, and this is also known as a wet- parked power cable. Where the cable has a damageable fitting on it, it is a problem how to deploy the power cable from the vessel to a wet-parked position or location without damaging the fitting, including where the cable or fitting cannot go through a tensioner. There are further problems to keep in mind, such as providing a compact lay tower while ensuring that the tensioner can engage the cable instead of a fitting, such as a bend stiffener, on the cable.

[0021] According to one aspect, there is provided a system for laying a flexible subsea power cable in the sea, the cable comprising at least one fitting to at least one end of the cable, the system comprising: a tower mountable on a deck of a vessel, the tower comprising a firing line for laying the cable; an arcuate guide for the cable, the arcuate guide being rotatable around an axis on the tower; a first handling arm, the first handling arm being rotatable around the axis, configured to hold the cable, and configured to move the fitting along a path outside of the arcuate guide; and a tensioner for the cable, the tensioner being movable in and out of the firing line; wherein the system comprises a second handling arm, the second handling arm being configured to position the cable to allow the tensioner to move into the firing line around the cable by guiding the cable end further away from the arcuate guide than the first handling arm.

[0022] In this way, the tower can be more compact, because at least the first handling arm does not need to be big or long enough to position the cable by itself to allow the tensioner to move into the firing line around the cable. The second handling arm may pull the fitting further down so that the tensioner can move into the firing line and engage the cable above the fitting and not the fitting. Additionally, this allows the handling of the cable and its fitting to be made in a controlled manner and with a minimum of involvement of an operator. With the fitting being brought over the lay tower by the first handling arm, the second handling arm may connect to the fitting, prior to disconnecting the first handling arm. This provides support to the fitting, cable, throughout and movement of the fitting is restricted, which improves safety and provides controlled handling. Besides mitigating damage to the fitting, for example a bend stiffener, the system opens up vessels that may potentially be used, because a vessel crane in no longer needed. The vessel with the system may be a vessel with a lower specification and the system may be placed on a vessel outside of the working radius of a crane.

[0023] The power cable may be an inter array power cable to be used for a floating offshore structure, for example, with a wind turbine. The power cable may be an electrical power cable, an assembly of one or more electrical conductors, for example held together with an overall sheath. The power cable may be used for transmission of electrical power. The power cable may be used to export energy harvested on the offshore installation. An “inter array” power cable or a power cable in general, can extend from the floating structure into the body of water. One power cable is a dynamic inter array cable, or ‘DIAC’.

[0024] The firing line is the travel path of the cable from the lay tower into the sea. The firing line may be substantially perpendicular to the sea surface, but may have an angle to the sea surface in other embodiments.

[0025] The flexible subsea power cable can have one or two defined end sections, and an end section may start from the very end of the power cable and extend along the cable. Each end section may be the same or different. Each end section may extend for a pre-determined length along the cable. One or both end sections may include a fitting.

[0026] The fitting may be any single component or combination of components that is damageable. The fitting may be damageable by excessive force thereon, including being directly on the arcuate guide of a tower in a weight bearing position. Optionally, the fitting is a bend stiffener, and may have a pig tail. The fitting may be one or more of the elements described below, for example a connector, a cable termination, a cable armoured termination, a buoyancy module, bend stiffener, bend stiffener connector, a weight, a tether clamp, and / or a pig tail.

[0027] The arcuate guide may be a suitable curved or grooved wheel, typically shaped to complement the shape and usual dimensions of a power cable in the field of offshore structures, for example the diameter of a typically circular cable itself, and generally being the majority of the cable length before any end fittings. Such a arcuate guide-shape cannot be complementary to the different shape of fittings added to the cable for its use and installation, such as a bend stiffener, so that the interaction between the fitting(s) and the arcuate guide during the laying of the cable would damage the fitting(s).

[0028] The tower may have two or more main support structures extending from a base position, such as the deck of the vessel, and one or more cross supports. Optionally, the arcuate guide is on an orthogonal axis between the support structures at or near the top of the tower. The tower may be a lay system structure.

[0029] A larger the lay tower requires not only a larger vessel to accommodate and support such a tower, but also greater power and supporting ancillaries. Longer time is also required to use larger towers. Where an installer may wish to lay a number of cables, for example for an offshore installation array such as an offshore wind farm, the longer and more expensive is the use of a larger tower and vessel. Thus, a more compact tower reduces the capital and operating costs for laying such cables, both in terms of size of vessel required, and ease and speed of operation.

[0030] Optionally, the cable includes one or more elements as well as the fitting. Such elements may include a further same fitting, a connector, a cable termination, a cable armoured termination, a buoyancy module, bend stiffener connector, a weight, a tether clamp, and / or a pig tail. The addition of one or more elements to be added to the one or more parts of the cable may be for preparation of the cable for subsequent installation of the cable with an offshore installation. For example, an inter-array cable in a wind farm array may be given a certain buoyancy, and the addition of an element(s) to the cable can be to achieve such buoyancy in use. The number and / or nature and / or relative positioning of element(s) may be varied, and the present invention is not limited by the number and / or nature and / or relative positioning of the fitting and any elements on the cable. Optionally, the cable being laid is being wet-parked to provide a wholly or substantially wholly static cable on a sea bed that is conveniently parked or stored away from other activities, such that the cable can be parked for longer periods than hitherto expected in the art, i.e. extending months and even years. Such a cable may include additional protection.

[0031] In the present invention, the first handling arm is configured to hold the cable. The first handling arm may be configured to directly hold the cable, or configured to indirectly hold the cable. The term “hold the cable” as used herein includes, but is not limited to, the first handling arm holding the fitting, or holding a suitable element at one end of the fitting, or holding an element on the cable, such as the elements described herein. The first handling arm may have only one sheave for holding the cable. The first handling arm may have means for latching on to the fitting and / or cable. The first handling arm may be hinged, and / or may comprise a hinged function to be moved out of the way, for example to allow space for the tensioner.

[0032] Optionally, the first handling arm is configured to hold the cable via a clamp on the cable. Where the cable includes an armoured termination on the cable, optionally the first handling arm is configured to hold the cable via a clamp on the armoured termination. In addition, or as an alternative, the first handling arm may comprise a clamp.

[0033] In the present invention, the first handling arm is rotatable around an axis on the tower. Optionally, the first handling arm has a distal end at the other end of the first handling arm from the axis. Optionally, the distal end is configured to hold the cable.

[0034] In the present invention, the first handling arm is rotatable around the same axis as the arcuate guide. Optionally, the first handling arm has a length, or is extendable, to a position under the tensioner. Optionally, the first handling arm may be configured to rotate between in-board side of the tower and an out-board side of the tower without the need to rotate 360 degrees, for example by rotating over the top of the tower. The first handling arm may not be able to rotate 360 degrees, and this allows a simpler and more reliable rotation of the first handling arm.

[0035] The first handling arm may extend over and / or around the arcuate guide. The first handling arm may be telescopic, for example movable in its extension so that the first handling arm can be made longer or shorter. A telescopic arm provides a more controlled manner to move the one or more elements along a path outside the arcuate guide, because the first handling arm may be made shorter. A telescopic arm also allows for lowering a first end of the cable to the worktable or deck of the vessel. A telescopic arm also allows longer fitting, for example a longer bend stiffener.

[0036] Optionally, the first handling arm is a single sided first handling arm, i.e. supported only on one side of the arcuate guide. Such a first handling arm further frees the space around the handling arm and arcuate guide, allowing bigger fittings to be laid by the present invention, rotation of the first handling arm for further use in the present invention, or both.

[0037] Where the cable includes one or more elements as described herein, the present invention includes further use of the first handling arm and / or the second handling arm, to move the one or more elements along a path outside the arcuate guide.

[0038] Optionally, the movements of the first handling arm may be restricted by the position of the tensioner. For example, if the tensioner is on one side of the lay tower, then the first handling arm may not be able to swing to the same side because the tensioner is in the way. Optionally, the first handling arm is also moveable to a position on either side of the tower without limitation of the position of the tensioner. Where the tensioner is not in a firing line position, for example in a first or inoperative position, the first handling arm may be moveable to a first or in-board side of the tower and a second or out-board side of the tower, and vice versa, by rotation of or about a rotational axis. Where the tensioner is in a firing line position, for example in a second or operative position, the first handling arm may be moveable to a first or in-board side of the tower and a second or out-board side of the tower, and vice versa, by rotation of or about a rotational axis, and / or by having a shape able to manoeuver around the tensioner, for example being a one-sided handling arm.

[0039] Further movement of the first handling arm may be required to assist the movement of other fittings or elements on the cable along a path outside of the arcuate guide. Such fittings include a fitting at the second or other end of the cable to the cable end having the fitting discussed herein. For example, each end of the flexible subsea power cable may include a fitting, such as a bend stiffener, a pig tail, armoured tensioner, or both. After laying a first end with a fitting and the majority of the cable thereafter, the second end of the cable, with a fitting on the in-board side of the tower, can still be deployed or laid by the present invention. The second end may be laid with the first handling arm and the winch wire. The winch wire may hold the cable while the first handling arm swings the fitting over the arcuate guide. The tensioner may be retracted or swung away, and the first handling arm and the winch wire may lower the cable along the firing line into the sea. A more compact design of the tower for the system for the present invention still allows laying of such a cable where the first handling arm can rotate and rotate back to an in-board position, where it can engage and position the fitting and second end of the cable in the same manner as described herein.

[0040] The first handling arm is configured to move the fitting along a path outside of the arcuate guide. In this way, there is no weight-bearing of the fitting on the arcuate guide.

[0041] The tensioner is movable in and out of the firing line. This allows the fitting to be positioned by the present invention further down the firing line than the working or operative position of the tensioner, and prior to engagement of the tensioner with the cable for the subsequent laying of the cable into the sea. The tensioner may be movable away from the firing line to give space for the first handling arm or any other equipment. The tensioner may hinge open to allow the fitting to pass through. The tensioner may be hinged to completely, or partly, be swung away from the firing line to give space for the first handling arm or any other equipment.

[0042] Optionally, the tensioner is a single tensioner. The system may lay the flexible subsea power cable in a sea with only one tensioner. A second tensioner may not be needed.

[0043] Optionally, the tensioner is part of the tower, or at least partly supported by the tower. Optionally, the tower includes one or more guide rails to allow translational movement of the tensioner relative to the tower between a first inoperative position and a second operative position in line with the firing line of the tower. The direction of this movement of the tensioner may be parallel to a path of the arcuate guide and the first handling arm.

[0044] Optionally the second handling arm is movable in and out of the firing line. That is, at least a part of the second arm, optionally a distal end, is movable in and out of the firing line. Optionally, at least a distal end of the second handling arm is in line with the firing line when configured to position the cable to allow the tensioner to move into the firing line.

[0045] Optionally, the second handling arm is movably mounted on the tower and arranged such that an end of the second handling arm interacting with the cable is being movable along a travel path being the firing line. The travel path may be along the firing line or may be parallel to the firing line. The travel path may be substantially perpendicular to the sea surface or vessel deck. The travel path may extend from the vessel deck, or a human operator working level, up to the bottom of the tensioner, or the end of the first handling arm when positioned to hand over the cable to the second handling arm. The travel path may extend further up than the bottom of the tensioner, for example all the way up to the arcuate guide.

[0046] Optionally, the second handling arm is movably mounted on or along a support structure, for example a leg, of the tower. This movement may be parallel to the firing line. The second handling arm may be an integral part of the support structure.

[0047] Optionally the second handling arm holds the cable in the same manner as the first handling arm holding the cable. The second handling arm may be configured to directly hold the cable, or be configured to indirectly hold the cable. The term “hold the cable” as used herein includes but is not limited to the second handling arm holding the fitting, or holding a suitable element at one end of the fitting, or to an element on the cable, such as the elements described herein. Optionally, the second handling arm is configured to hold the cable via a clamp on the cable, optionally on or near an armoured termination on the cable. Optionally, the second handling arm holds the cable via the same manner as the first handling arm holing the cable. This may be by means of a latching mechanism.

[0048] In the present invention, the second handling arm has a distal end. Optionally, the distal end is configured to hold the cable. The second handling arm comprises an exchangeable end. The exchangeable end may comprise a gripper, a latching mechanism, a clamp, a sheave, a sheave for the winch wire, or a holder. This allows the second handling arm to be used for other activities in addition to pulling the first cable end down. For example, a clamp may be used for pulling the cable down as is already described and another type of gripper or sheave may allow the second handling arm to transport buoyancy modules from the inboard ship side to the firing line for installation on the cable. The second handling arm may be configured to move the exchangeable end in one or more linear directions and around one or more rotational axes. Such movements and positioning of the exchangeable end may allow the second handling arm to pick up an item and rotate around the tower and into the firing line. The second handling arm may be a robotic arm. The second handling arm is not the crane that many vessels for laying cables have. Optionally, the system further comprises a winch wire for handling the cable. Optionally, the winch wire is routed through an inside of at least the first handling arm. This provides the winch wire to be connected to the second end of the cable when laying the last part of the cable. The winch wire may be any suitable wire able to work with the expected weight of the cable in the operation of the present invention.

[0049] Optionally, the winch wire is able to help lay the cable onto the seabed from the vessel.

[0050] Optionally, the winch wire is also routed through an inside of at least a part of the tower. The winch wire may be routed inside a support structure of the lay tower.

[0051] Optionally, the winch wire is routed at least partly through or along the axis of the arcuate guide. Optionally, the winch wire may be routed over the arcuate guide.

[0052] Optionally, the winch wire may be routed from the vessel deck, or the worktable, over the arcuate guide and be connectable to the end of the cable, the fitting, to lift the cable, the fitting, vertically toward the arcuate guide. With the fitting below the arcuate guide the first handling arm may latch on to the fitting. At this stage the winch wire may no longer be required but may still be used and disconnected later. The fitting may then be brought over to the other side as described herein using the first handling arm.

[0053] Optionally, the winch wire is wholly or substantially operable automatically once attached to the cable. Where the winch wire is attached to one end of the cable prior to movement of the cable and fitting around the tower in line with the present invention, the position of the winch wire relative to the tower is intended to be accommodated wholly or substantially in or along the tower, to minimise any operator interaction or closeness, and so help reduce the risk of accidents or hazardous interaction between the winch wire and a human operator.

[0054] Optionally, the present invention includes a winch to operate and reel the winch wire. The winch may be positioned in the vicinity of the tower, and act as a dedicated winch for the tower.

[0055] Optionally, the tower has a height that is substantially equal to the sum of the travel path of the second handling arm, the height of the tensioner, and the diameter of the arcuate guide. The tower may have a height that is substantially equal to the sum of a working height of a human operator, the travel path of the second handling arm, the height of the tensioner, and the diameter of the arcuate guide. The tower may have a height that is substantially equal to the travel path of the second handling arm, the length of the first handling arm, and the radius of the arcuate guide. This provides a compact configuration of the tower. The tower may in this way be compact and still be able to handle any length of fitting. The tower can be formed to be shorter, lower, more compact, or a combination of same, than a conventional laying tower.

[0056] In this way, the tower can be relatively compact compared to conventional lay towers or cranes that accommodate the positioning of a cable and fitting on a vessel to a laying position from the vessel by extending much higher from the deck of the vessel. The larger or higher the apparatus needed to position a cable and fitting on a vessel to a laying position from the vessel, the greater the size and stability of the vessel must be. A larger vessel requires larger capital and operating costs.

[0057] The tower of the present invention is mountable on a deck of a vessel. Optionally, the lay tower is also dis-mountable from or re-locatable on the deck of the vessel, such that the vessel is not limited to being a single-purpose vessel.

[0058] Optionally, the system is configured such that a distal end of the first handling arm reaches a distal end of the second handling arm. The system may be configured such that the distal end of the first handling arm may transfer the cable, or fitting, to the distal end of the second handling arm. The distal end of the first handling arm may be in a low or lowest position, while the distal end of the second handling arm may be in its upper position along the travel path. In a similar manner, this provides a compact tower.

[0059] Optionally, the arcuate guide and the first handling arm are movable along a path that is perpendicular to the firing line. The axis of the arcuate guide and the first handling arm may move in a straight line perpendicular to the firing line. This may provide a compact tower compared with moving along an arcuate line.

[0060] Optionally, the system includes one or more work platforms able to provide a workstation(s) to the present invention. Optionally, one or more of the work platforms is moveable in and out of the firing line of the tower. Optionally, the tower includes one or more work platforms, optionally formed of one or more moveable gantries, able to provide a user with working access to a part of the cable.

[0061] Optionally, the tower includes a moveable one-part or two-part workstation, able provide a user with working access to either the first handling arm, the second handling arm, or both. For example, being able to provide a user with working access to either the end of the first handling arm, or the end of the second handling arm, or both, for attachment and / or detachment of the cable and / or any winch wire thereto and therefrom.

[0062] According to another aspect of the present invention, there is provided a method for laying a flexible subsea power cable in the sea using the system according to any one of the preceding claims, the method comprising at least the steps in any order of: moving the fitting with the first handling arm to a position where the second handling arm can receive the cable; holding the cable with the second handling arm; and moving the fitting along the firing line to allow the tensioner to move into the firing line; and holding the cable with the tensioner.

[0063] Optionally, the method further comprises the further steps, in any order of: the second handling arm releasing the cable and moving away from the firing line; and the tensioner feeding the cable out along the firing line into the sea.

[0064] Optionally, the method further comprises the further step of connecting a winch wire to the cable. The winch wire may be as described herein, and may be located in or along or otherwise relative to the tower as described herein.

[0065] Optionally, the first handling arm releases the winch wire from the cable when the second handling arm holds the fitting.

[0066] Optionally, the first handling arm is moved out of the proximity of the firing line when the second handling arm holds the fitting.

[0067] Optionally, the method is for laying the cable onto a seabed. Optionally, the method is for wet-parking the cable on a seabed, ore optionally wet-parking the entire cable flat on a sea-bed.

[0068] Optionally, the second handling arm may move the fitting along the firing line in separate steps. For example, the second handling arm may move the fitting down; then the tensioner (on the in-board side) or a winch wire may hold the cable; the second handling arm may release the fitting, move up, and clamp onto the fitting again; and subsequently move the fitting further down to allow the tensioner to move into the firing line.

[0069] At least one of the above embodiments provides one or more solutions to the problems and disadvantages with the background art. The second handling arm allows the fitting to be pulled down and away such that the tensioner can engage the cable without damaging the fitting. The second handling arm also allows for a very compact tower. Other technical advantages of the present disclosure will be readily apparent to one skilled in the art from the following description and claims. Various embodiments of the present application obtain only a subset of the advantages set forth. No one advantage is critical to the embodiments. Any claimed embodiment may be technically combined with any other claimed embodiment or embodiments.

[0070] Turning to the drawings, figures 1 to 4 show an embodiment of a system for laying a flexible subsea power cable 20 in the sea, the cable comprising at least one fitting 16 to at least one end of the cable 20, the system comprising a tower 10 mountable on a deck 12 of a vessel 14, the tower 10 comprising a firing line 34 for laying the cable 20; an arcuate guide 22 for the cable 20, the arcuate guide 22 being rotatable around an axis 24 on the tower 10; a first handling arm 26, the first handling arm 26 being rotatable around the axis 24, configured to hold the cable 20, and configured to move the fitting 16 along a path outside of the arcuate guide 24; and a tensioner 30 for the cable 20, the tensioner 30 being movable in and out of the firing line 34.

[0071] The first handling arm 26 may be telescopic, for example movable in its extension so that the first handling arm 26 can be made longer or shorter. This is illustrated with a longer first handling arm 26 in figure 1 compared with the length of the first handling arm 26 in figure 2.

[0072] The system shown in figures 1 to 4 also comprises a second handling arm 40, the second handling arm 40 being configured to position the cable 20 to allow the tensioner 30 to move into the firing line around the cable 20 by guiding the cable end further away from the arcuate guide 24 than the first handling arm 26.

[0073] In the example of the system shown in figures 1 to 4, the fitting 16 is a bend stiffener. Bend stiffeners can be damaged through impact or weight-bearing contact with an arcuate guide, especially where the arcuate guide 22 has a grooved wheel, typically shaped to complement the shape and dimensions of the (thinner, circular and symmetrical) power cable 20. The shape of the fitting 16 may be such that the interaction against edge or circumference of an arcuate guide during the laying of the cable 20 would damage the fitting 16.

[0074] Figures 1 to 4 show the cable 20 comprising the fitting 16 and a termination 18. The fitting may be a bend stiffener 16 and the termination may be a pig tail 18.

[0075] In figures 1 to 4, the tower 10 has two main support structures 11 extending from a base, a platform, on the deck 12. In this example, the platform is on the side of a deck 12 of the vessel 14 having a firing line 34 over the side of the vessel 14. The tower 10 has one or more cross supports, with the arcuate guide 22 being on an orthogonal axis 24 between the support structures 11 at or near the top of the tower 10.

[0076] The first handling arm 26 has a distal end 27 configured to hold the cable 20, for example via a clamp on the cable 20 on or near an end of the termination 18 on the cable between the end of the cable 20 being first deployed into the sea, and the fitting 16. The distal end 27 of the first handling arm 26 can hold the cable 20 at other positions at or near the end of the cable 20, but preferably the first handling arm 26 is configured to move the fitting 16 along a path outside of the arcuate guide 22.

[0077] As shown in figures 1 to 4 and discussed hereinafter in more detail, the first handling arm 26 is rotatable around the same axis 24 as the arcuate guide 22. The first handling arm 26 is also a ‘single sided’ first handling arm 26. That is, the first handling arm 26 extends outwardly from the axis 24 only on one side of the arcuate guide 22. Such a first handling arm 26 frees space around the first handling arm 26 and arcuate guide 22, allowing for bigger fittings to be laid by the present invention, for rotation of the first handling arm 26 for further use in the present invention, or for both. The first handling arm 26 may be configured, for example C-shaped, to move at the side of the tensioner 30, such that the first handling arm 26 may swing as shown in figure 1 but outside the tensioner 30 if the tensioner 30 was in the firing line 34.

[0078] The first handling arm 26 is configured to move the fitting 16 along a path outside of the arcuate guide 24 from an in-board side of the tower 10 to an out-board side of the tower 10 shown best in figure 1 beyond the side of the vessel 14. In this way, there is no weight-bearing of the fitting 16 on the arcuate guide 22.

[0079] Figure 1 shows the cable 20 and the fitting 16 and the termination 18 being in the firing line 34 of the tower 20, i.e. ready to deploy into the sea (below the vessel 14, and not shown in the drawings). Figure 1 also shows that the tensioner 30 is not yet able to move towards and around the cable 20, due to the position of the bend stiffener 16 and / or the position of the first handling arm 26.

[0080] As illustrated in Figure 1, the tower 10 has a second handling arm 40, which is movable in and out of the firing line 34. That is, at least the distal end 42 of the second handling arm 40 is movable in and out of the firing line 34. The distal end 42 may be exchangeable such that the distal end 42 may comprise a gripper, latch, sheave, end effector, or a handling mechanism for ancillaries as described herein. Figure 1 shows the distal end 42 of the second handling arm 40 being in line with the firing line 34 when configured to position the cable 20 according to the present invention, and to subsequently move the fitting 16 to the position shown in figure 3, to allow the tensioner 30 to move into the firing line.

[0081] As illustrated in figure 1, the first handling arm 26 may hold the fitting 16 when the first handling arm 26 is in a lower position. The second handling arm 40 may move up and hold, latch on to, the fitting 16. As illustrated in figure 2, the first handling arm 26 may then release the fitting 16 and the second handling arm 40 may start to move down, moving the fitting 16 further down along the firing line 34. In figure 3 the first handling arm 26 ha moved away, for example to the top, and the second handling arm 40 has moved the fittign16 down so that the tensioner 30 can move into the firing line 34 and hold onto the cable 20 without engaging the fitting 16. In figure 4 the second handling arm 40 has released the fitting 16 and the tensioner 30 can now feed, lay, the cable 20 with the fitting 16 out along the firing line 34. This hand over from the first handling arm 26 to the second handling arm 40 may be made automatically, without the need for an operator to attach or release the fitting 16 from or to the arms 26, 40. The hand over may be fully automatic, performed only by the two arms 26, 40.

[0082] The second handling arm 40 is movably mounted on a support structure 11 of the tower 10, and arranged such that the distal end 42 interacting with the cable 20 is being movable along the travel path of the firing line 34 to the position shown in figure 2. The second handling arm 40 may move up and down with reference to figure 1 along its travel path parallel to the firing line 34. Hereby the cable 20, with the fitting 16, may be moved down below the tensioner 30. Interaction of the cable with the first and second handling arms 26, 40 is further described hereinafter.

[0083] Figure 3 shows the lower position of the fitting 16 relative to the tower 10. This position allows the tensioner 30 to move into the firing line 34. The tensioner 30 may move from a first position, optionally within the general dimensions of the tower 10, such as partly or substantially between the support structures 11 of the tower 10, to a second position, being in line with the firing line 34 of the tower 10.

[0084] Movement of the tensioner 30 may be taken from figures 1 to 4 and is shown as translational relative to the tower 10. The tower 10 may include support able to move the tensioner 30 between the first position and the second position in line with the firing line 34 of the tower 10. With the movement of the tensioner 30 to the second position, moveable tracks 32 of the tensioner can be positioned around the firing line 34, and thereby the cable 20, of the tower 10 so that all the tracks 32 symmetrically surround the cable 20, to operate in a coordinated manner, able to support the weight of the cable 20 and achieve motion of the cable 20 for laying. By operating the tensioner 30 the cable 20 may be moved, for example into the sea along the firing line 34.

[0085] Figures 1 to 4 also show the example embodiment of the system having one or two work platforms. A first work platform may be a hang-off balcony 50, for example a moonpool table, extending from the side of the vessel 14, and having moveable trap doors 52 to allow the passage of the cable 20 and the fitting 16 therethrough when required.

[0086] A second work platform may comprise a hinged gantry 54, moveable between a first position out of the path of the firing line 34 and a second position wherein, for example, an operator can work on the cable 20. Optionally, the gantry 54 provides a user with working access to the distal end 27 of the first handling arm 26 and the distal end 42 of the second handling arm 40, to allow for attachment and detachment of the cable 20 or the fitting 16 or the pig tail 18 from the first and second handling arms 26, 40.

[0087] Figure 4 shows the engagement of the tensioner 30 with the cable 20. The tensioner 30 may feed the cable into the sea along the firing line 34.

[0088] A winch wire 60, best taken from figure 4, may be attached to the end of the cable 20 prior to going over the tower 10, to help guide such end if required. As the winch wire 60 can be routed from a winch 62 on or near the tower 10, and through at least a part of the tower 10, the axis 24, and the first handling arm 26, the winch wire 60 can be conveniently routed to avoid hazardous positioning relative to any worker at or around the tower 10. Optionally, the winch wire 60 is wholly or substantially operable automatically once attached to the cable 20. The winch wire 60 can then be detached from the cable 20 to allow engagement of the distal end 42 of the second handling arm 40 with the cable 20.

[0089] As best illustrated in figures 1 and 2 the system may be configured such that the distal end 27 of the first handling arm 26 reaches the distal end 42 of the second handling arm 40. This provides for a compact tower 10. It also provides for the compact tower 10 to handle very long fittings 16, 18, even if longer than the height of the tower. A method for laying the flexible subsea power cable 10 in the sea using the system as described herein may be taken from all figures. Figure 5 illustrates schematically that the method comprises moving 410 the fitting 16 with the first handling arm 26 to a position where the second handling arm 40 can receive the cable 20, for example via a clamp around the armoured termination 18; holding 420 the cable 20 with the second handling arm 40; moving 430 the fitting 16 along the firing line 34 to allow the tensioner 30 to move into the firing line 34; and holding 440 the cable 20 with the tensioner 30.

[0090] Following the above steps, the second handling arm 40 can release 450 the cable 20, the fitting 16, and move away from the firing line 34. The tensioner 30 may now feed 460 the cable 20 out along the firing line into the sea.

[0091] Figure 5 is a schematic illustration of an example of the system and method steps of the present invention as described herein. Figure 5 illustrates these steps as defined herein and optionally their further characterisation disclosed herein. Such steps can include the further step of connecting and / or disconnecting the winch wire 36 to the cable 10. For example, releasing the winch wire from the cable once the first handling arm 26 has provided the cable 20 and fitting 16 into the firing line of the tower 10 as described above, and before or during the second handling arm 40 holding the cable 20. The method show in the figures may be for laying the entire cable 20 onto a seabed. The method may include handing over from the first handling arm 26 to the second handling arm 40 automatically as described herein.

[0092] It will be apparent to those skilled in the art that various modifications and variations can be made to the method and system for laying a flexible subsea power cable in a sea. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed system and method. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.

Claims

CLAIMS1 A system for laying a flexible subsea power cable (20) in a sea, the cable comprising at least one fitting (16) to at least one end of the cable, the system comprising: a tower (10) mountable on a deck (12) of a vessel (14), the tower comprising a firing line (34) for laying the cable; an arcuate guide (22) for the cable, the arcuate guide being rotatable around an axis (24) on the tower; a first handling arm (26), the first handling arm being rotatable around the axis, configured to hold the cable, and configured to move the fitting along a path outside of the arcuate guide; and a tensioner (30) for the cable, the tensioner being movable in and out of the firing line; wherein the system comprises a second handling arm (40), the second handling arm being configured to position the cable to allow the tensioner to move into the firing line around the cable by guiding the cable end further away from the arcuate guide than the first handling arm.2 The system according to claim 1 , wherein the second handling arm (40) is movable in and out of the firing line.3 The system according to claim 2, wherein the second handling arm (40) is movably mounted on the tower (10) and arranged such that an end of the second handling arm interacting with the cable (20) is being movable along a travel path of the firing line.4 The system according to any one of the preceding claims, wherein the first handling arm (26) is a single sided first handling arm supported only on one side of the arcuate guide (24).5 The system according to any one of the preceding claims, wherein the second handling arm (40) comprises an exchangeable end.6 The system according to any one of the preceding claims, further comprising a winch wire (36) for handling the cable (10), the winch wire being routed through an inside of the first handling arm (26) and / or routed through an inside of at least a part of the tower (10).7 The system according to any one of the preceding claims when dependent on claim 3, wherein the tower (10) has a height that is substantially equal to the sum of the travel path of the second handling arm (40), a height of the tensioner, and a diameter of the arcuate guide (22).8 The system according to any one of the preceding claims, wherein the system is configured such that a distal end (28) of the first handling arm (26) reaches a distal end (42) of the second handling arm (40).9 The system according to any one of the preceding claims, wherein the arcuate guide (24) and the first handling arm (26) are movable along a path that is perpendicular to the firing line.10 A method for laying a flexible subsea power cable (20) in a sea using the system according to any one of the preceding claims, the method comprising at least the steps in any order of: moving (410) the fitting (16) with the first handling arm (26) to a position where the second handling arm (40) can receive the cable; holding (420) the cable with the second handling arm (40); and moving (430) the fitting along the firing line (34) to allow the tensioner (30) to move into the firing line; and holding (440) the cable with the tensioner.11 The method according to claim 10, further comprising the steps in any order of: the second handling arm (40) releasing (450) the fitting (16) and moving away from the firing line; and the tensioner (30) feeding (460) the cable (20) out along the firing line into the sea.12 The method according to any one of claims 10 or 11 , when dependent on at least claim 5, further comprising the step of connecting the winch wire (36) to the cable (20). 13 The method according to claim 12, wherein the first handling arm (26) holds the fitting (16) and transfers the fitting to the second handling arm (40), the second handling arm (40) then holds the fitting (16) and the first handling arm (26) releases the fitting (16). 14 The method according to any one of claims 10 to 13, wherein the first handling arm (26) is moved out of the proximity of the firing line when the second handling arm (40) holds the fitting (16).15 The method according to any one of claims 10 or 14, to wet-park the cable (20) on a seabed.

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