Method and system tethering dynamic subsea cable
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2026-02-03
- Publication Date
- 2026-08-13
Smart Images
Figure EP2026052684_13082026_PF_FP_ABST
Abstract
Description
[0001] P398009.W0.01
[0002] 1
[0003] METHOD AND SYSTEM TETHERING DYNAMIC SUBSEA CABLE
[0004] Technical Field
[0005] The present disclosure relates generally to tethering of a dynamic subsea cable. More specifically to a method of changing a configuration of a dynamic subsea cable, and a system tethering the dynamic subsea cable to the seabed where the system is configured to change the configuration of the dynamic subsea cable. The dynamic subsea cable may be connected to a floating offshore structure.
[0006] Background
[0007] Energy produced by a floating offshore structure may be transported in a dynamic subsea cable. The dynamic subsea cable extends from the floating offshore structure to the seabed. The same cable, or a different cable, continues to shore where the energy is used. The dynamic subsea cable is suspended between the floating offshore structure and a touch down point, TDP, on the seabed. It is desirable that the dynamic subsea cable doesn’t overbend near the TDP. An initial installation of a dynamic subsea cable gives the cable an initial configuration, i.e. a curvature from the TDP to the floating offshore structure. The initial configuration may be referred to as start-of-life configuration. With time there is less uplift in the buoyancy section of the configuration pulling the cable up to the floating offshore structure, for example due to marine growth on the cable. With time the configuration of the cable changes to an end-of-life configuration and the cable can overbend near the TDP. This may damage and shorten the life of the cable.
[0008] It is challenging how to change the configuration of the dynamic subsea cable after the initial installation has been done. CN116221500B discloses a buoyancy releasing module where three mooring chains are connected to a connecting clamp. Each of the hanging rings, on the connecting clamp, for the mooring chains differs in that they erode at different times. When the first mooring chain drops of the connecting clamp due to the erosion, the weight of the connecting clamp changes because only two chains remain connected. Thereby the connection clamp raises and changes the configuration of theP398009.W0.01
[0009] 2
[0010] dynamic subsea cable. CN116221500B may be useful for understanding the background.
[0011] It is a problem how to extend the life of a dynamic subsea cable. It is further a problem how to improve when and how to change configuration of the dynamic subsea cable. External factors may change and call for a sooner or later change of configuration that does not match a predetermined time, such as erosion time. It is desirable to be able to control how much the dynamic subsea cable bends near the TDP at a given time. A further problem is that any solution should be practical in real life, inexpensive, and installable preferably with existing equipment. The present disclosure is directed to overcoming one or more of the problems as set forth above.
[0012] SUMMARY
[0013] It is an objective of the present invention to provide a method of changing a configuration of a dynamic subsea cable, and a system tethering a dynamic subsea cable to the seabed where the system is configured to change a configuration of the dynamic subsea cable. This objective can be achieved by the features as defined in the independent claims. Further characteristics are defined by the dependent claims.
[0014] According to one embodiment, a method of changing a configuration of a dynamic subsea cable 10 is provided. The method comprises: providing a first connection line 110 between a tether clamp 20 and an intermediate connection point 200, the tether clamp 20 being connected to the dynamic subsea cable 10; providing a second connection line 120 between a tether base 30 and the intermediate connection point 200, the tether base 30 being located at the seabed 2, and the first and second connection lines being initially load bearing; providing a third connection line 130 between the intermediate connection point 200 and the tether clamp 20 or the tether base 30, the third connection line 130 having a longer length than the first or second connection line 110, 120 parallel to the third connection line (130); and disconnecting one of the first or second connection lines 110, 120 such that the third connection line 130 becomes load bearing together with the remaining connected first or second connection line 110, 120, respectively.
[0015] According to one embodiment, the method may further comprise checking the curvature of a hog bend 18, or the sag bend 19, or both, of the dynamic subseaP398009.W0.01
[0016] 3
[0017] cable 10 to decide when to disconnect. The checking may comprise determining if the hog bend 18, or the sag bend 19, or both, of the dynamic subsea cable 10 has sunk deeper than a predetermined amount to decide when to disconnect. In addition, or as an alternative, one may check if marine growth thickness on the dynamic subsea cable 10, or on attached ancillaries, is more than a predetermined amount to decide when to disconnect.
[0018] According to one embodiment, the disconnecting may comprise finding a visible marking 122, 132 on the first or second connection lines 110, 120, the visible marking indicating one, or both, of: which connection line to disconnect and where to disconnect. A visible marking may also be added where not to disconnect.
[0019] According to one embodiment, the disconnecting may be done by cutting the first or second connection lines 110, 120 with a tool operated by a remotely operated vehicle, ROV. According to one embodiment, the third connection line 130 may comprises different properties than at least the connection line 110 or 120 to be disconnected. According to one embodiment, the intermediate connection point 200 may be the branch point in a Y-shaped tether or a delta plate. According to one embodiment, the method may further comprise providing one or more additional connection lines parallel to one, or both, of the first connection line 110 and the second connection line 120.
[0020] According to one embodiment, a system tethering a dynamic subsea cable 10 to the seabed 2 is disclosed. The system is configured to change a configuration of the dynamic subsea cable 10. The system comprises: a first connection line 110 between a tether clamp 20 and an intermediate connection point 200, the tether clamp 20 being connected to the dynamic subsea cable 10; a second connection line 120 between a tether base 30 and the intermediate connection point 200, the tether base 30 being located at the seabed 2; wherein the first connection line 110 and the second connection line 120 are initially load bearing; a third connection line 130 between the intermediate connection point 200 and the tether clamp 20 or the tether base 30, wherein the third connection line 130 has a longer length than the first or second connection line 110, 120 parallel to the third connection line (130); and the first connection line 110 or the second connection line 120 being configured to be disconnected such that the third connection line 130 becomes load bearing together with the remaining connected first or second connection line 110, 120, respectively.
[0021] According to one embodiment, the configuration of the first connection line 110 or the second connection line 120 to be disconnected may comprise a visibleP398009.W0.01
[0022] 4
[0023] marking 112, 122 on the first or second connection lines 110, 120 indicating one, or both, of: which connection line to disconnect and where to disconnect.
[0024] According to one embodiment, the third connection line 130 may comprise different properties than at least the connection line 110 or 120 to be disconnected. For example, the different properties may be one or more of fibres, internal structure, flexibility, material, and mixture of materials.
[0025] According to one embodiment, the intermediate connection point 200 may be the branch point in a Y-shaped tether. According to one embodiment, the intermediate connection point 200 may comprise a plate 210, and the plate 210 may comprise attachment means for each connection line 110, 120, 130.
[0026] According to one embodiment, a connection point 32 for one or more of the connection lines 120, 130 on the tether base 30 may be configured to swivel with two or three rotational degrees of freedom.
[0027] According to one embodiment, the system may further comprise one or more additional connection lines parallel to one, or both, of the first connection line 110 and the second connection line 120. The additional connection line may be a fourth connection line between the between the intermediate connection point 200 and the tether clamp 20 or the tether base 30. The fourth connection line may be longer than the third connection line. Correspondingly, the system and method may comprise a fifth connection line.
[0028] According to one embodiment, the system may further comprise a touch down point 50, TDP, for the dynamic subsea cable 10 on the seabed 2; the tether clamp 20; the tether base 30; a floating offshore structure 40; the dynamic subsea cable 10 extending from the TDP 50 to the floating offshore structure 40; and the floating offshore structure 40 comprising a renewable energy device. The renewable energy device may be one or more of a windmill, solar power, or wave energy producer.
[0029] According to one embodiment, the connection lines 110, 120, 130 may comprise one or more of the following: rope, wire, fibres, and chain. There may be a fourth or fifth connection line. Some embodiment may not use a chain, because it may be more cumbersome to disconnect a chain.
[0030] At least one embodiment allows for positive intervention, or not, depending on the through life configuration of the cable. Prior art allows for automatically changing the configuration, due to corrosion or materialP398009.W0.01
[0031] 5
[0032] degradation, even in the event it is not required. This could be detrimental to the cable in the event, for example, where minimal or no marine growth exist and the first chain connection releases resulting in a very different configuration shortening the cable life. One of the challenges in designing dynamic subsea cables is the sheer size and scale of a windfarm project and area, where there is a very different soil, metocean, and conditions across the site. In addition to this, industry codes and regulations must be followed for marine growth. This makes it very challenging to find cable configurations to work for the full design life. At least one embodiment disclosed herein allows to comply with industry codes and regulations and at the same time design for very onerous marine growth, and in addition design for even worse or less marine growth. The cable configuration can then be adjusted as necessary over time.
[0033] 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.
[0034] Brief Description of the Drawings
[0035] The disclosure will be further described with reference to examples depicted as schematic illustrations in the accompanying figures in which:
[0036] FIG 1 is a schematic illustration of a dynamic subsea cable suspended from a TDP to a floating offshore structure;
[0037] FIG 2 is a schematic illustration of a dynamic subsea cable tethered at the TDP according to an embodiment of the invention;
[0038] FIG 3 is a schematic illustration of a dynamic subsea cable tethered at the TDP according to an embodiment of the invention;
[0039] FIG 4 is a schematic illustration of an embodiment of the invention;
[0040] FIG 5 is a schematic illustration of an embodiment of the invention;
[0041] FIG 6 is a schematic illustration of an embodiment of the invention;P398009.W0.01
[0042] 6
[0043] FIG 7 is a schematic illustration of an embodiment of the invention;
[0044] FIG 8 is a schematic illustration of an embodiment of the invention; and FIG 9 is a flow chart of a method according to embodiments of the present invention.
[0045] Detailed Description
[0046] Turning first to figure 1, a dynamic subsea cable 10 is suspended from a floating offshore structure 40 to a touch down point, TDP, 50. The TDP 50 is where the dynamic subsea cable 10 touches the seabed 2. The floating offshore structure 40 in figure 1 is a partly submerged floating offshore platform 40, where one part may be below the sea surface 4 and one part may be above the sea surface 4. The curvature of the dynamic subsea cable 10, the configuration, from the floating offshore structure to the TDP 50 has been illustrated twice in figure 1. The first configuration, indicated by arrow 12, is the dynamic subsea cable 10 at a start of life configuration, when the cable 10 has just been initially installed. The second configuration, indicated by arrow 14, is the dynamic subsea cable 10 at a later time, for example at an end-of-life configuration. For example, marine growth on the initial installation, the first configuration 12, may cause the hog bend 18, or sag bend 19, or both, to lower, sink down a distance 16 or 17, so that the dynamic subsea cable 10 is in the second configuration 14. This change in configuration changes how the dynamic subsea cable 10 bends close to the TDP 50. The change in configuration and behaviour of the subsea cable 10 changes the curvature close to the TDP, the curvature between the tether clamp 20 and the TDP 50.
[0047] Figure 2 illustrates how the dynamic subsea cable 10 bends close to the TDP 50 in the first configuration 12, i.e. just after the initial installation of cable 10. A tether 100 connects the cable 10, via a tether clamp 20, to the seabed 2, via a tether base 30. As time progresses there is less uplift pulling the cable 10 up to the floating offshore structure 40, for example due to marine growth on the cable 10, or on ancillaries such as buoyancy modules. With time, for example with increase of marine growth, the configuration of the cable 10 changes and the cable 10 bends sharper near the TDP 50. This may damage and shorten the life of the cable. The second configuration may start when the cable 10 has marine growth, for example when the cable 10, or ancillaries, has at least 30 mm marine growth in a radial direction from the outer side of the cable 10. Figure 3 illustrates how toP398009.W0.01
[0048] 7
[0049] reduce the sharp bend so that the dynamic subsea cable 10 doesn’t bend too much close to the TDP 50 in the second configuration 14, for example at a configuration 14 that lasts to the end of life for the cable 10. A tether 100 connects the cable 10, via a tether clamp 20, to the seabed 2, via a tether base 30. The tether 100 in figure 3 is longer than the tether 100 in figure 2 and this gives a softer bend of the cable 10 close to the TDP 50. The details of the tether line 100 is not illustrated in figures 1 to 3 and may instead be taken from figures 4 to 7.
[0050] Embodiments of the tether 100 are illustrated in figures 4 to 7. The tether 100 comprises three connection lines 110, 120, 130. There may be more than only three connection lines, for example four or five connection lines. However, there is at least three connection lines 110, 120, 130. The first connection line 110 is between a tether clamp 20 and an intermediate connection point 200. The tether clamp 20 is connected to the dynamic subsea cable 10. The intermediate connection point 200 is part of the tether 100. The second connection line 120 is between a tether base 30 and the intermediate connection point 200. The tether base 30 is located at the seabed 2. As best taken from figure 7, the first connection line 110 and the second connection line 120 are initially load bearing. The third connection line 130 is between the intermediate connection point 200 and the tether clamp 20 or the tether base 30 as illustrated in figure 7. The third connection line 130 has a longer length than the first or second connection lines 110, 120 that the third connection line 130 is parallel with. The first connection line 110 and the second connection line 120 are initially load bearing. The first connection line 110 or the second connection line 120 is configured to be disconnected such that the third connection line 130 becomes load bearing together with the remaining connected first or second connection line 110, 120, respectively. In figure 7 the second connection line 120 is configured to be disconnected, for example cut. When disconnected, then the third connection line 130 together with the first connection line 110 become load bearing. Hereby the tether 100 becomes longer and the change from the first configuration 12 as illustrated in figures 1 and 2 to the second configuration 14 as illustrated in figures 1 and 3 are made. This provides a reduced curvature of the dynamic subsea cable 10 between the tether clamp 20 and the TDP 50, i.e. a less sharp bend of the dynamic subsea cable 10 close to the TDP 50. Thereby the life of the cable 10 is extended. The tether 100 with the connection lines 110, 120, 130 is easy to apply and install to existing tethering systems.P398009.W0.01
[0051] 8
[0052] Figure 7 illustrates that the first connection line 110 is connected to the tether clamp 20 and that the second and third connection lines 120, 130 are connected to the tether base 30. However, the first and third connection lines 110, 130 may be connected to the tether clamp 20 and the second connection line 120 may be connected to the tether base 30, as illustrated in figure 8. This also applies to the embodiments of the tether 100 illustrated in figures 4 to 6. In figures 4 to 6 the top of the tether 100 may be connected to a tether clamp 20 on the dynamic subsea cable 10 and the bottom of the tether 100 may be connected to a tether base 30 on the seabed 2. However, it may be the other way around, the top of the tether 100 may be connected to a tether base 30 on the seabed 2 and the bottom of the tether 100 may be connected to a tether clamp 20 on the dynamic subsea cable 10.
[0053] Turning to figures 4 and 5, an embodiment of the tether 100 is illustrated where the intermediate connection point 200 may comprise a plate 210, for example a metal plate. The plate 210 may be a delta-plate. The plate 210 may comprise openings for each connection line. The first connection line 110 may extend from the plate 210 to a tether clamp 20, or a tether base 30. The tether clamp 20 and tether base 30 are not illustrated in the figures 4 to 6, but the tether clamp 20 would be at the top in the drawings and the tether base 30 at the bottom of the drawings, alternative the tether base 30 would be at the top in the drawings and the tether clamp would be at the bottom of the drawings 4 to 6. The second connection line 120 may extend from the plate 210 to a tether base 30, or a tether clamp 20. The third connection line 130 may extend from the plate 210 to the tether base 30, or the tether clamp 20. The third connection line 130 may extend from the plate 210 to the second connection line 120, such that when the second connection line 120 is cut or disconnected, then the overall length of the tether 100 is longer than when the first and second connection lines are load bearing. The connection of each connection line to the plate 210 may allow one, two, or three rotational degrees of freedom. Figures 4 and 5 illustrated two rotational degrees of freedom for each connection line 110, 120, 130.
[0054] Turning to figure 6, an embodiment of the tether 100 is illustrated where the intermediate connection point 200 may be the branch point in a Y-shaped tether. In figure 6 the Y is upside down. The Y shape consists of the leg, the first connection line 110, and the two arms, the second and third connection lines 120, 130. The end of each connection line may comprise an attachment means, such as for example a loop. The Y-shaped tether 100 may comprise two tether lines, where one part ofP398009.W0.01
[0055] 9
[0056] each tether line forms the second and third connection lines 120 130, respectively, and another part of each tether lines form together the first connection line 110. In other words, the first connection line 110 may be made up from parts of the two tether lines. One tether line is first load bearing, and when disconnected, then the other tether line becomes load bearing.
[0057] According to one embodiment, the tether 100 may comprise one or more visible marking 122, 132. The second connection line 120 may comprise a visible marking 122 indicating the connection line to cut, or indicating where to cut, or both. The visible marking may indicate where to disconnect. The disconnection may be made by cutting the connection line. The third connection line 130 may comprise a visible marking 132 indicating that the third connection line must not be cut or disconnected.
[0058] According to one embodiment, the connection of the tether 100 to the tether base 30 on the seabed 2 may be flexible. The tether base 30 may comprise a connection point 32 for one or more of the connection lines 120, 130. As illustrated in figures 7 and 8, the connection point 32 may be configured to swivel with two or three rotational degrees of freedom, Rx, Ry, Rz. This allows the tether 100 to connect to the tether base 30 without any friction or wear between the tether line 100 and the connection point 32 as the dynamic subsea cable moves.
[0059] According to one embodiment, a method of changing a configuration of a dynamic subsea cable 10 is disclosed. The steps are illustrated in figure 9, but the steps may be taken in any order as long as it makes technical sense, for example the first three steps of providing connection lines may be taken in any order, or simultaneously, or a combination thereof. The method comprises providing 310 a first connection line 110 between a tether clamp 20 and an intermediate connection point 200, the tether clamp 20 being connected to the dynamic subsea cable 10; providing 320 a second connection line 120 between a tether base 30 and the intermediate connection point 200, the tether base 30 being located at the seabed 2, and the first and second connection lines being initially load bearing; providing 320 a third connection line 130 between the intermediate connection point 200 and the tether clamp 20 or the tether base 30, the third connection line 130 having a longer length than the first or second connection lines 110, 120 parallel to the third connection line 130; and disconnecting 340 one of the first or second connection lines 110, 120 such that the third connection line 130 becomes load bearing together with the remaining connected first or second connection line 110, 120, respectively.P398009.W0.01
[0060] 10
[0061] As explained above, and with reference to the figures, this allows tether 100 to be made longer to soften the bend of the dynamic subsea cable 10 close to the TDP 50.
[0062] According to one embodiment, the method may further comprise checking 330 the curvature, or the cable configuration, of a hog bend 18, or a sag bend 19, or both, of the dynamic subsea cable 10 to decide when to disconnect. The hog bend 18 of the dynamic subsea cable 10 may be the first bend after the tether clamp 20. The hog bend 18 may extend up towards the sea surface 4 and then back down towards the seabed 2, as illustrated in figure 1. The sag bend 19 may follow the hog bend 18 and may extend down towards the seabed 2 and then back up towards the sea surface 4. The checking may be made by physically looking at the hog bend 18, or the sag bend 19, or both, or by measuring positions or relative positions of one or more sensors along the dynamic subsea cable 10. The checking may comprises determining if the hog bend 18 of the dynamic subsea cable 10 has sunk deeper than a predetermined amount to decide when to disconnect. Such a predetermined amount may be the distance illustrated in figure 1 by one or both of arrows 16 and 17. Correspondingly, the checking may comprises determining if the sag bend 19 of the dynamic subsea cable 10 has sunk deeper than a predetermined amount to decide when to disconnect.
[0063] According to one embodiment, the method may further comprise checking if marine growth thickness on the dynamic subsea cable 10, or on any ancillaries, is more than a predetermined amount to decide when to disconnect. If the marine growth is, for example, 10, 20, 30, or 40 cm in the radial direction from the centre, or outside, of the dynamic subsea cable 10, then the disconnection may be made to make the tether 100 longer and thereby change the configuration of the dynamic subsea cable 10. Checking the marine growth may be made by physically looking at the hog bend 18, or the sag bend 19, or both, or by measuring positions or relative positions of one or more sensors along the dynamic subsea cable 10.
[0064] According to one embodiment, the disconnecting of one of the first or second connection lines 110, 120 may comprise finding a visible marking 112, 122 on the first or second connection lines 110, 120. The visible marking may indicate one, or both, of: which connection line to disconnect and where to disconnect. The marking may indicate which one of the connection lines should be disconnected. The marking may indicate where to disconnect, for example where to cut or uncouple. The marking may be a combination of these two. The marking may be a bright marking, or a reflective marking, or a text marking, or any combination of the three. The visibleP398009.W0.01
[0065] 11
[0066] marking may be where not to disconnect, such that an error of disconnecting the wrong connection line does not occur. If a plate 210 is used at the intermediate connection point 200, then the plate 210 may care the visible marking to indicate where to disconnect. For example, the visible marking may indicate what bolt or clamp to remove.
[0067] According to one embodiment, the disconnecting may be done by cutting the first or second connection lines 110, 120 with a tool operated by a remotely operated vehicle, ROV. An ROV may go subsea and use a cutter to disconnect the first or second connection lines 110, 120. If a plate 210 is used at the intermediate connection point 200, then the ROV may comprise a tool for removing a bolt or clamp to disconnect the first or second connection lines 110, 120.
[0068] According to one embodiment, the third connection line 130 may comprise different properties than at least the connection line 110 or 120 to be disconnected. In this way the tether 100 may have a different overall property in the second configuration that lasts to the end of life for the cable 10. This is further described herein.
[0069] According to one embodiment, the intermediate connection point 200 may be the branch point in a Y-shaped tether. This is best illustrated in figure 6 where the Y is upside down. The Y shape consists of the leg and the two arms, each forming one of the three connection lines. This is further described herein.
[0070] According to one embodiment, the method may further comprise providing one or more additional connection lines parallel to one, or both, of the first connection line 110 and the second connection line 120. This is further described herein, for example with a fourth and fifth connection line.
[0071] According to one embodiment, a system tethering a dynamic subsea cable 10 to the seabed 2, where the system is configured to change a configuration of the dynamic subsea cable 10, is disclosed. The system comprises a first connection line 110 between a tether clamp 20 and an intermediate connection point 200, the tether clamp 20 being connected to the dynamic subsea cable 10; a second connection line 120 between a tether base 30 and the intermediate connection point 200, the tether base 30 being located at the seabed 2. The first connection line 110 and the second connection line 120 are initially load bearing. The system comprises further a third connection line 130 between the intermediate connection point 200 and the tether clamp 20 or the tether base 30, wherein the third connection line 130 has a longer length than the first or second connection lines 110, 120 parallel to the thirdP398009.W0.01
[0072] 12
[0073] connection line 130; and the first connection line 110 or the second connection line 120 being configured to be disconnected such that the third connection line 130 becomes load bearing together with the remaining connected first or second connection line 110, 120, respectively. As described herein, this allows a tether 100 comprising the connection lines 110, 120, 130 to be made longer by disconnecting, for example cutting, the connection line that is in parallel with the third connection line 130. Such a lengthening changes the configuration of the dynamic subsea cable 10 and gives a softer bend of the cable 10 close to the TDP 50.
[0074] According to one embodiment, the configuration of the first connection line 110 or the second connection line 120 to be disconnected may comprise a visible marking 112, 122 on the first or second connection lines 110, 120 indicating one, or both, of: which connection line to disconnect and where to disconnect. A visible marking aids the disconnection. For example, when using an ROV to disconnect the first or second connection lines 110, 120, that is parallel with the third connection line 130, then the operator of the ROV gets a confirmation that the correct connection line is disconnected.
[0075] According to one embodiment, the third connection line 130 may comprise different properties than at least the connection line 110 or 120 to be disconnected. For example, the different properties may be different fibres, different internal structure, different flexibility. The third connection line may age differently than the first or second connection lines. The third connection line may be a different kind of tether line, for example if the first and second connection lines are ropes, then the third connection line may be a wire. The tether 100 comprises the connection lines 110, 120, 130. Each connection line may be a flexible line, for example a rope, a chain, or a wire.
[0076] According to one embodiment, the intermediate connection point 200 may be the branch point in a Y-shaped tether. An end of each connection line may be connected to each other at the intermediate connection point 200. As described herein, two tethers may be used to form the three connection lines. The two tethers may be lined together for a part to form together the first connection line 110, and the two remaining prats of the two tethers may form the second and third connection lines 120, 130, respectively.
[0077] According to one embodiment, the intermediate connection point 200 may comprise a plate 210. The plate 210 may comprise attachment means for each connection line 110, 120, 130. An end of each connection line may be connected toP398009.W0.01
[0078] 13
[0079] the plate 210. The intermediate connection point 200 as described herein may be between the tether clamp 20 and the tether base 30.
[0080] According to one embodiment, a connection point 32, for one or more of the connection lines 120, 130, on the tether base 30 may be configured to swivel with two or three rotational degrees of freedom, Rx, Ry, Rz. The tether base 30, or the tether 100, may comprise the connection point 32 that may swivel.
[0081] According to one embodiment, the system may further comprise one or more of the following: the touch down point, TDP, 50 for the dynamic subsea cable 10 on the seabed 2; the tether clamp 20; the tether base 30; a floating offshore structure 40; and the dynamic subsea cable 10 extending from the TDP 50 to the floating offshore structure 40. The floating offshore structure 40 may comprise a renewable energy device. The renewable energy device being one or more of windmill, solar power, and wave energy.
[0082] According to one embodiment, the system and method may comprise one or more additional connection lines parallel to one, or both, of the first connection line (110) and the second connection line (120). The tether 100 may comprise four or five connection lines. The fourth connection line may be parallel with the first connection line 110, such that the four connection lines form a X-shaped tether. The two arms of the X may connect to the tether clamp 20, and the two legs of the X may connect to the tether base 30. Alternatively, the fourth connection line may be parallel with the second and third connection lines 120, 130. The fifth connection line may be parallel with the fourth, third, and second connection lines. For example, the fourth connection line may be arranged correspondingly and parallel to the third connection line 130 in the embodiments illustrated by figures 4 to 8. For example, the fifth connection line may be arranged correspondingly and parallel to the third and fourth connection line 130 in the embodiments illustrated by figures 4 to 8. For example, the fourth connection line may be arranged correspondingly and parallel to the first connection line 110 in the embodiments illustrated by figures 4 to 8. Such embodiments with further connection lines would allow to further subsequent change, reduce, the curvature of the dynamic subsea cable 10 between the tether clamp 20 and the TDP 50.
[0083] According to one embodiment, a floating offshore structure 40 producing electric energy transported in a dynamic subsea cable 10 is disclosed. The dynamic subsea cable 10 is suspended in a configuration between the floatingP398009.W0.01
[0084] 14
[0085] offshore structure 40 and a touch down point 50, TDP, on the seabed 2. A change of configuration from a first configuration at a start-of-life, when the cable 10 is initially installed, to a second configuration for an end-of-life, the configuration the cable 10 has to the end-of-life, can be made by lengthening the tether for cable 10. The lengthening may be made disconnecting the connection line that is parallel to the longer connection line, as described herein. This gives the cable 10 a larger curvature close to the TDP 50. The change to the second configuration may be made when the dynamic subsea cable 10 has a predetermined amount of marine growth, for example at least 30mm marine growth thickness.
[0086] It will be apparent to those skilled in the art that various modifications and variations can be made to the mooring line, the mooring system for an offshore structure, and the method of installing an anchor member with such a mooring line. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed mooring line, mooring 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
P398009.W0.0115Claims1 Method of changing a configuration of a dynamic subsea cable (10), the method comprising:providing (310) a first connection line (110) between a tether clamp (20) and an intermediate connection point (200), the tether clamp (20) being connected to the dynamic subsea cable (10);providing (320) a second connection line (120) between a tether base (30) and the intermediate connection point (200), the tether base (30) being located at the seabed (2), and the first and second connection lines being initially load bearing; providing (320) a third connection line (130) between the intermediate connection point (200) and the tether clamp (20) or the tether base (30), the third connection line (130) having a longer length than the first or second connection line (110, 120) parallel to the third connection line (130); anddisconnecting (340) one of the first or second connection lines (110, 120) such that the third connection line (130) becomes load bearing together with the remaining connected first or second connection line (110, 120), respectively.2 The method according to claim 1, further comprising:checking (330) the curvature of a hog bend (18), or a sag bend (19), or both, of the dynamic subsea cable (10) to decide when to disconnect.3 The method according to claim 2, wherein the checking comprises determining if the hog bend (18), or the sag bend (19), or both, of the dynamic subsea cable (10) has sunk deeper than a predetermined amount to decide when to disconnect.4 The method according to claim 1, further comprising:checking (330) if marine growth thickness on the dynamic subsea cable (10), or attached ancillaries, is more than a predetermined amount to decide when to disconnect.5 The method according to any one of the preceding claims, wherein the disconnecting comprises finding a visible marking (122, 132) on the first or secondP398009.W0.0116connection lines (110, 120), the visible marking indicating one, or both, of: which connection line to disconnect and where to disconnect.6 The method according to any one of the preceding claims, wherein the disconnecting is done by cutting the first or second connection lines (110, 120) with a tool operated by a remotely operated vehicle, ROV.7 The method according to any one of the preceding claims, wherein the third connection line (130) comprises different properties than at least the connection line (110 or 120) to be disconnected.8 The method according to any one of the preceding claims, wherein the intermediate connection point (200) is the branch point in a Y-shaped tether.9 The method according to any one of the preceding claims, the method further comprising providing one or more additional connection lines parallel to one, or both, of the first connection line (110) and the second connection line (120).10 A system tethering a dynamic subsea cable (10) to the seabed (2), the system being configured to change a configuration of the dynamic subsea cable (10), the system comprising:a first connection line (110) between a tether clamp (20) and an intermediate connection point (200), the tether clamp (20) being connected to the dynamic subsea cable (10);a second connection line (120) between a tether base (30) and the intermediate connection point (200), the tether base (30) being located at the seabed (2);wherein the first connection line (110) and the second connection line (120) are initially load bearing;a third connection line (130) between the intermediate connection point (200) and the tether clamp (20) or the tether base (30), wherein the third connection line (130) has a longer length than the first or second connection line (110, 120) parallel to the third connection line (130); andthe first connection line (110) or the second connection line (120) being configured to be disconnected such that the third connection line (130) becomesP398009.W0.0117load bearing together with the remaining connected first or second connection line (110, 120), respectively.11 The system according to claim 10, wherein the configuration of the first connection line (110) or the second connection line (120) to be disconnected comprises a visible marking (112, 122) on the first or second connection lines (110, 120) indicating one, or both, of: which connection line to disconnect and where to disconnect.12 The system according to claim 10 or 11, wherein the third connection line (130) comprises different properties than at least the connection line (110 or 120) to be disconnected.13 The system according to any one of the claims 10 to 12, wherein the intermediate connection point (200) is the branch point in a Y-shaped tether.14 The system according to any one of the preceding claims 10 to 13, further comprising one or more additional connection lines parallel to one, or both, of the first connection line (110) and the second connection line (120).15 The system according to any one of the preceding claims 10 to 14, further comprising a touch down point, TDP, (50) for the dynamic subsea cable (10) on the seabed (2); the tether clamp (20); the tether base (30); a floating offshore structure (40); the dynamic subsea cable (10) extending from the TDP (50) to the floating offshore structure (40); and the floating offshore structure (40) comprising a renewable energy device.16 The system or method according to any one of the preceding claims, wherein the intermediate connection point (200) comprises a plate (210), the plate (210) comprises attachment means for each connection line (110, 120, 130).17 The system or method according to any one of the preceding claims, wherein a connection point (32) for one or more of the connection lines (120, 130) on the tether base (30) is configured to swivel with two or three rotational degrees of freedom.