Method of simultaneously laying a plurality of elongate flexible members on the seabed

Abstract

A method for simultaneously laying three or more slender flexible members on the seabed from an installation vessel comprises: a) advancing all individual slender flexible members to a first position and gathering them together at that position to form a group of slender flexible members; b) advancing the group of slender flexible members from the first position to a second position located at a first distance from the first position, while twisting the group of slender flexible members at least one turn in a first direction between the first position and the second position to obtain a section of the slender flexible member group twisted in the first direction; c) binding together at least a portion of the section of the slender flexible member group twisted in the first direction at the second position; d) advancing the group of slender flexible members from the first position to the second position, while twisting the group of slender flexible members at least two turns in a second direction opposite to the first direction between the first position and the second position to obtain the slender flexible member twisted in the first direction A step of obtaining a second directionally twisted elongated flexible member group section following a flexible member group section, e) binding together at least a portion of the second directionally twisted elongated flexible member group section at the second location, and repeating steps a) to e) until the entire length of the elongated flexible members is laid on the seabed in an alternately twisted form.

Description

Technology Field

[0001] The present disclosure generally relates to laying slender, flexible members, such as power cables, on the seabed from an installed vessel. Background Technology

[0002] Subsea cables can be installed from marine vessels such as cable layers or barges. Typically, submarine cables are fed from a drum or turntable to the seabed through a curved chute or laying wheel installed on the vessel. Thus, the submarine cable bends while lying on the chute. When the submarine cable comes into contact with the seabed, it bends in a direction generally opposite to that on the chute or laying wheel.

[0003] Recently, power cable systems are beginning to be designed to feature three direct current (DC) submarine power cables connecting two points of a power generation system: one for the positive pole, one for the negative pole, and one for redundancy purposes. These cable systems may also include submarine fiber optic cables extending outward along the length of the submarine power cables. This introduces new installation complexity compared to cable systems with two high-voltage direct current (HVDC) cables and one fiber optic cable, particularly considering the advantage that installing all submarine cables connecting two points simultaneously reduces installation time, thereby mitigating risks associated with changing weather conditions at sea and the associated costs. Another advantage is that less seabed disturbance is required, as only one trench or burial campaign is needed instead of two separate trenches; this implies a smaller environmental impact and reduced influence on benthic organisms.

[0004] The conventional simultaneous installation of multiple cables can be carried out by bundling all submarine cables together and lowering them underwater. When cables are arranged in a flat configuration—that is, placed side by side on a single plane—there are problems with lowering them because it is difficult to maintain catenary stability. Cables with lower specific gravity tend to deviate from alignment with other cables, which can pose a risk of damaging the fiber optic cables. In a trilobate configuration, if one power cable is positioned above the others, the cable bundle bends over the chute and at the touchdown point. This results in a mismatch in the length of the power cables. The inner power cable(s) are compressed along the curve formed by the bundle, while the outer cable(s) are extended. If the bundle is tightly bound, this can induce significant compressive and tensile forces on the individual cables within the bundle and introduce greater complexity during the installation process.

[0005] In light of the foregoing description, the objective of the present invention is to provide a method for simultaneously laying three or more slender flexible members on the seabed from an installation vessel, thereby solving or at least mitigating the problems of the prior art.

[0006] Accordingly, a method for simultaneously laying three or more slender flexible members on the seabed from an installation vessel is provided, the method comprising: a) advancing all individual slender flexible members to a first position and gathering them together at that position to form a group of slender flexible members; b) advancing the group of slender flexible members from the first position to a second position located at a first distance from the first position, while twisting the group of slender flexible members at least one turn in a first direction between the first position and the second position to obtain a section of the group of slender flexible members twisted in the first direction; c) binding together at least a portion of the section of the group of slender flexible members twisted in the first direction at the second position; d) advancing the group of slender flexible members from the first position to the second position, while twisting the group of slender flexible members at least two turns in a second direction opposite to the first direction between the first position and the second position, so as to the first direction A step of obtaining a second directionally twisted slender flexible member group section following a twisted slender flexible member group section, e) a step of binding together at least a portion of the second directionally twisted slender flexible member group section at the second location, and a step of repeating steps a) to e) until the entire length of the slender flexible members is laid on the seabed in an alternately twisted form.

[0007] The method enables the transfer of multiple slender flexible members from an installation vessel to the seabed in a stable “bundle” configuration, allowing for installation / post-installation protection without causing complexity to the trenching / installation tool. Due to the alternating SZ or ZS twist of the group of slender flexible members, relative axial movement between individual slender flexible members may be limited.

[0008] According to one example, one of the slender flexible members may have a lower proportion than other slender flexible members.

[0009] According to one embodiment, in steps b) and d), a group of slender flexible members is advanced toward the stern of the installed vessel.

[0010] According to one embodiment, the first distance is equal to or greater than the length of one catenary of a group of slender flexible members extending from the installation vessel toward the seabed. The catenary length refers to the length of the catenary that the group of slender flexible members follows from the exit point of the installation vessel to the touchdown point of the seabed. Accordingly, in this example, the length of each section of the slender member group twisted in the first / second direction is equal to or greater than the catenary length, and thus each is aggregated by its end points being joined in steps c) and e).

[0011] If the first distance is equal to or greater than a single catenary length, the binding of the group of slender flexible members may be for a limited length, e.g., less than half of the first length, along a section of the group of slender flexible members twisted in the first / second direction. For example, if the laying depth is 30 m and the catenary length is 45-50 m, the binding may be for a distance of 2-5 m or less than 10 m along a section of the group of slender flexible members twisted in the first / second direction. If the first distance is shorter than the catenary length, continuous binding may be desirable to obtain a stable bundle of the group of slender flexible members.

[0012] According to one embodiment, the installation vessel comprises N spaced-apart rotating station units arranged on a deck, a first rotating station among the rotating station units is located at a first position, and the other N-1 rotating station units are arranged between the first position and the second position, and a group of slender flexible members is advanced through the rotating station units, and the group of slender flexible members is twisted by 1 / N rotation at each rotating station unit.

[0013] According to one embodiment, N=3.

[0014] Alternatively, N can be greater than 3 depending on how many twists are to be made at each rotating device station.

[0015] N rotating device stations can be distributed back and forth on the deck at equal distances between each pair of adjacent rotating device stations.

[0016] According to one example, N rotating device stations are configured to be movable on a track or similar to move together with a group of slender flexible members, thereby assisting in the rotation of the group of slender flexible members.

[0017] According to one embodiment, the installation vessel includes ray tensioners that advance individual elongated flexible members toward a first position.

[0018] According to one embodiment, each layer tensioner advances each of the individual elongated flexible members toward a first position.

[0019] According to one embodiment, among the slender flexible members, the first and second slender flexible members are DC cables, and among the slender flexible members, the third slender flexible member is a metal return cable. The metal return cable may have a lower specific gravity than the first and second slender flexible members.

[0020] According to one embodiment, the installation vessel is a cable laying vessel.

[0021] According to one embodiment, step a) comprises advancing an optical fiber cable having an outer diameter smaller than that of slender flexible members to a first position, where the optical fiber cable is grouped with the slender flexible members, and the optical fiber cable grouped with the slender flexible members undergoes steps a) through e) and repetitions thereof.

[0022] According to one embodiment, step a) comprises advancing an optical fiber cable having an outer diameter smaller than that of the elongated flexible members to any one of N rotating device stations, such as a second, third, or Nth rotating device station, which is after the first position and before the second position, where the optical fiber cable is grouped with a group of elongated flexible members. Thus, the optical fiber cable is grouped with a group of elongated flexible members at a point subsequent to the first rotating device station. Thus, the optical fiber cable is not twisted as much as the group of elongated flexible members.

[0023] According to one embodiment, there are three slender flexible members, and in step a), the three individual slender flexible members are grouped into a trilobate configuration.

[0024] In general, all terms used in the claims shall be interpreted according to their ordinary meaning in the art, unless otherwise expressly specified herein. All references to “element, device, component, means, etc.” shall be publicly interpreted as referring to at least one instance of the element, device, component, means, etc., unless explicitly stated otherwise. Brief explanation of the drawing

[0025] Now, specific embodiments of the concept of the present invention will be described, by way of example, with reference to the accompanying drawings, where: FIG. 1 is a plan view illustrating an example of a back deck of an installed vessel; FIG. 2 is a plan view of a back deck having slender flexible members extending along the back deck; FIGS. 3a through 3f illustrate cross-sections at different locations along the length of elongated flexible members as they extend over the back deck; FIG. 4 schematically illustrates an example of a rotating device station (S) on a back deck; Figure 5 is a flowchart of a method for simultaneously laying three or more slender flexible members on the seabed from an installation vessel. Specific details for implementing the invention

[0026] Now, the concept of the invention will be explained more fully below with reference to the accompanying drawings, in which exemplary embodiments are illustrated. However, the concept of the invention may be embodied in many different forms and should not be interpreted as being limited to the embodiments described herein; rather, these embodiments are provided as examples to ensure that the disclosure is thorough and complete and to fully convey the scope of the concept of the invention to those skilled in the art. Similar numbers refer to similar elements throughout the description.

[0027] Figure 1 is a plan view of the back deck (3) of the installed vessel (1).

[0028] The installation vessel (1) can be, for example, a cable laying vessel or a cable laying barge.

[0029] The installation vessel (1) is equipped with a chute or a lay wheel (7). The chute or lay wheel (7) may be provided at the stern (5) of the installation vessel (1).

[0030] The installation vessel (1) is configured to simultaneously lay three or more slender flexible members on the seabed via a chute or a ray wheel (7). The slender flexible members may be power cables, flexible pipelines, flexible umbilicals, or communication cables.

[0031] In the case of a power cable, the first and second slender flexible members among the slender flexible members may be DC cables such as HVDC cables, for example, and the third slender flexible member among the three slender flexible members may be a metal return cable.

[0032] In the example described herein, three slender flexible members are simultaneously laid on the seabed from the installation vessel (1). Additionally, a fiber optic cable may be laid on the seabed together with the slender flexible members.

[0033] The installed vessel (1) may be equipped with a plurality of lay tensioners or tensioning devices (T1-T3). The lay tensioners (T1-T3) may be placed on the back deck (3). For example, each lay tensioner (T1-T3) may be one of a track tensioner or a capstan wheel.

[0034] According to the example, the number of lay tensioners (T1-T3) is three, that is, one for each slender flexible member. In other examples, the number of lay tensioners for advancing three slender flexible members may be fewer, or there may be more than three lay tensioners when more than three slender flexible members are installed simultaneously. For example, two slender flexible members may be arranged in a piggybacked configuration in some examples and may be advanced along the back deck by a single lay tensioner (T1, T2, T3), for example by a twin cable / product tensioning device. In this case, fewer lay tensioners may be required than the number of slender flexible members to be installed simultaneously.

[0035] The installation vessel (1) may additionally be equipped with a plurality of rotating device stations (S1-SN). The rotating device stations (S1-SN) are placed on the back deck (3).

[0036] The rotating device stations (S1-SN) are arranged sequentially with respect to the ray tensioners (T1-T3) in a direction toward the rear (5), that is, in the rear direction. The rotating device stations (S1-SN) are arranged sequentially between the ray tensioners (T1-T3) and the chute or ray wheel (7) of the installation vessel (1).

[0037] The rotating device stations (S1-SN) can be arranged in a line with each other.

[0038] The rotating device station (S1-SN) can be arranged in line with the chute or ray wheel (7).

[0039] The rotating device station (S1-SN) may be arranged to move in line with the chute or ray wheel (7) during laying.

[0040] The rotating device station (S1-SN) and the chute or ray wheel (7) can be aligned with each other, that is, they can be arranged in a straight line in a direction toward the rear (5).

[0041] According to the example, the number (N) of the rotating device stations (S1-SN) is 3, but more generally, N can be 3 or more.

[0042] For example, if the number of slender flexible members is 3, N=3. According to some embodiments, N = the number of slender flexible members laid simultaneously in groups from the installation vessel (1). The number (N) of the rotation device stations (S1-SN) generally depends on the amount of twisting that must be performed at each station to achieve at least a complete rotation of the group of slender flexible members before they are laid from the installation vessel (1). This may vary depending on the available space on the installation vessel (1), the design of the slender flexible members, and the available equipment provided on board the installation vessel (1).

[0043] A first rotating device station (S1) is positioned at a first location on the back deck (3). The first rotating device station (S1) is positioned closest to the line tensioners (T1-T3) of all rotating device stations (S1-SN).

[0044] The distance between any pair of adjacent rotating device stations (S1-SN) may be the same. Thus, for example, the distance between the first rotating device station (S1) and the second rotating device station (S2) closest to the Ray tensioner (T1-T3) may be D, and the distance between the second rotating device station (S2) and the third rotating device station (SN) may also be D. In general, the distance between any pair of adjacent rotating device stations Sn and Sn+1 may be D.

[0045] The installation vessel (1) is equipped with a machine (M) positioned on the back deck (3). The machine (M) may be a wrapping machine, a strapping machine, or a bundling machine. The machine (M) is positioned at a second location on the back deck (3).

[0046] A second position may be placed at a first distance (L) from the first position. According to one example, the first distance (L) may be equal to, approximately equal to, or greater than the length of a catenary of a group of slender flexible members extending from the installation vessel (1) toward the seabed during installation. Here, "approximately equal" means a range of 90% to 110% of the catenary length.

[0047] The machine (M) can be arranged in line with the turning device station (S1-SN). The machine (M) can be arranged between the Nth turning device station (SN) closest to the chute or ray wheel (7) and the stern (5). The turning device station (S1-SN), the machine (M), and the chute or ray wheel (7) form a line for laying slender flexible members on the seabed.

[0048] The installation vessel (1) may include one or more storage units, such as a cable drum, a turntable, or a cable carousel, for storing slender flexible members to be laid on the seabed. The slender flexible members are supplied from one or more storage units to a rotating device station (S1-SN) by a cable tensioner (T1-T3) as described in more detail herein.

[0049] Referring to FIGS. 2 to 5, a method for simultaneously laying three or more elongated flexible members (A, B, C) on the seabed from an installation vessel (1) will now be described.

[0050] In step a), all individual slender flexible members (ACs) are moved to a first position, and at that position they are gathered together to form a group of slender flexible members (ACs).

[0051] The slender flexible members (AC) can be advanced by the Lay tensioners (T1-T3). For example, each slender flexible member (AC) can be advanced to a first position by each Lay tensioner (T1-T3).

[0052] A group of slender flexible members may be positioned flat before reaching the first rotating device station (S1), as illustrated at position P1 in FIG. 3a. A group of slender flexible members may be positioned in a trilobate configuration before reaching the first rotating device station (S1). This may be accomplished, for example, by guiding one of the slender flexible members (AC) in a flat form onto two other slender flexible members (AC) so that the slender flexible member (AC) can be lifted onto two slender flexible members (AC) or naturally provided by the positioning of the lay tensioner. For example, to raise the slender flexible member (AC) above the other slender flexible members (AC), one lay tensioner may be provided in a position raised relative to the others.

[0053] In step b), the group (15) of the elongated flexible members (AC) is advanced from the first position to the second position. At the same time, the group (15) of the elongated flexible members is rotated at least once between the first position and the second position and twisted in the first direction, so that a section (21) of the elongated flexible member group twisted in the first direction is obtained.

[0054] Twisting can be performed by a rotating device station (S1-SN). Each rotating device station (S1-SN) provides partial twisting of a group (15) of slender flexible members (AC), causing the group (15) of slender flexible members (AC) to rotate by at least one full rotation between a first position and a second position, i.e., between the first rotating device station (S1) and the machine (M).

[0055] In the examples of FIGS. 2 to 3e, a group (15) of slender flexible members (AC) is advanced through a rotating device station (S1-SN) and twisted by 1 / 3 turn or 120° at each rotating device station (S1-SN).

[0056] As illustrated in FIG. 4, in one exemplary embodiment, each rotary device station (S1-SN) may include a stand or platform (16) mounted on a back deck (3) and a roller or group of rollers (17) that facilitates the advancement of a group (15) of elongated flexible members (AC) across the rotary device station (S1-SN). The roller (17) may be a single roller, or the group of rollers may include a pair of rollers, or multiple / more than two rollers in a horizontal or inclined configuration. The roller or group of rollers (17) may be active or passive. Additionally, each rotary device station (S1-SN) may include an actuator or actuators (19) configured to operate the elongated flexible members (AC). The actuator or actuators (19) may be hydraulic, mechanical, and / or electric. An actuator or actuators (19) is configured to change the position of elongated flexible members (AC) on, for example, a roller or a group of rollers (17) to obtain partial twisting of a group (15) of elongated flexible members (AC) on a rotating device station (S1-SN). In the example of FIG. 4, the left actuator (19) can be raised or lowered and has a manipulator (19a) that can change direction to engage with the leftmost elongated flexible member (B). Similarly, the right actuator (19) can be raised or lowered and has a manipulator (19b) that can change direction to engage with the rightmost elongated flexible member (C). Thus, the configuration of the three elongated flexible members (AC) can be changed. In the example of FIG. 4, the group of slender flexible members (AC) can be reconfigured from the trilobate configuration shown in FIG. 3b at position P2 of FIG. 2 prior to the first rotating device station (S1) to the trilobate configuration shown in FIG. 3c at position P3 after the first rotating device station (S1).

[0057] At each of the remaining rotary device stations (S2-SN), as shown in the positions (P4-P5) of FIG. 2 and FIG. 3d-3e respectively, the group (15) is advanced through these rotary device stations (S2-SN) and thereby provides partial twisting of the group (15) of slender flexible members (AC), so the actuator(s) and manipulator change the position of the group (15) of slender flexible members (AC).

[0058] When the group (15) of slender flexible members (AC) reaches the machine (M), that is, when the group (15) is advanced by a first distance (L) from the first position to the second position, the group (15) of slender flexible members (AC) is rotated, for example, by one full rotation or more than one full rotation.

[0059] In step c), at least a portion of the slender flexible member group section (21) twisted in the first direction is bound at a second position shown at position P6 in FIGS. 2 and FIGS. 3f. The machine (M) binds, bundles, wraps, or straps at least a portion of the slender flexible member group section (21) twisted in the first direction so that the group (15) maintains integrity. The binding may be achieved using, for example, a silo wrap / high-strength cling film, an elastic strapping band, or a thread such as a polymer thread.

[0060] The binding may be performed continuously along the entire length of the slender flexible member group section (21) twisted in the first direction, or only at a limited distance along the slender flexible member group section (21) twisted in the first direction. FIG. 2 illustrates an example in which the binding (25) is performed continuously.

[0061] In step d), the group (15) of slender flexible members (AC) is advanced from the first position to the second position, while the group (15) of slender flexible members is twisted in the second direction opposite to the first direction by at least two turns between the first position and the second position. The first turn returns the group (15) of slender flexible members to its natural state or original zero position, and the second turn twists it by one turn past the original zero position. Thus, following the slender flexible member group section (21) twisted in the first direction, a slender flexible member group section (23) twisted in the second direction is obtained. At this time, the leading end of the slender flexible member group section (23) twisted in the second direction reaches the second position and the machine (M) around the time the trailing end of the slender flexible member group section (21) twisted in the first direction moves away from the chute or ray wheel (7).

[0062] In step e), at least a portion of the slender flexible member group section (23) twisted in the second direction is joined together at the second position. The machine (M) joins, wraps, or straps at least a portion of the slender flexible member group section (23) twisted in the second direction so that the group (15) maintains integrity. The joining may be achieved using, for example, a silo wrap / high-strength cling film, an elastic strapping band, or a thread such as a polymer thread.

[0063] The binding can be performed continuously along the entire length of the slender flexible member group section (23) twisted in the second direction, or only at a limited distance along the slender flexible member group section (23) twisted in the second direction.

[0064] Steps a) through e) are repeated until the entire length of the slender flexible members is laid on the seabed in a twisted form, that is, in an alternating SZ or ZS form.

[0065] In one example, step a) involves advancing an optical fiber cable having an outer diameter smaller than that of a slender flexible member (AC) to a first position where it is grouped with the slender flexible member (AC). The optical fiber cable grouped with the slender flexible members then undergoes steps a) through e), that is, the optical fiber cable is also twisted by a turning device station (S1-SN) and bound together with the group of slender flexible members (AC) by a machine (M) at a second position. Thus, the optical fiber cable is also twisted with the slender flexible member (AC) in a first direction for a first length (L), and then twisted with the slender flexible member (AC) in a second direction for a first length (L). Steps a) through e) are also repeated until the entire length of the slender flexible member (AC) is reached in this example, and the optical fiber cable is laid on the seabed in a twisted form.

[0066] In one example, the optical fiber cable is advanced immediately before the second position, that is, after the final turning station, and is coupled with a group of slender flexible members (15) after the final turning station. In this case, the optical fiber cable is not twisted with the slender flexible members.

[0067] The concept of the present invention has been described above with reference to a few examples. However, as will be readily recognized by those skilled in the art, other embodiments other than those disclosed above are equally possible within the scope of the concept of the present invention as defined by the appended claims.

Claims

Claim 1 A method for simultaneously laying three or more slender flexible members (A, B, C) on the seabed from an installation vessel (1), wherein the method comprises: a) advancing all individual slender flexible members (A, B, C) to a first position and gathering them together at that position to form a group (15) of slender flexible members (A, B, C); b) advancing the group (15) of slender flexible members (A, B, C) from the first position to a second position located at a first distance (L) from the first position, while twisting the group (15) of slender flexible members (A, B, C) at least one turn in a first direction between the first position and the second position to obtain a slender flexible member group section (21) twisted in the first direction; c) binding together at least a portion of the slender flexible member group section (21) twisted in the first direction at the second position. d) advancing a group (15) of slender flexible members (A, B, C) from a first position to a second position, while twisting the group (15) of slender flexible members (A, B, C) at least two turns in a second direction opposite to the first direction between the first position and the second position to obtain a slender flexible member group section (23) twisted in a second direction following a slender flexible member group section (21) twisted in the first direction; e) binding together at least a portion of the slender flexible member group section (23) twisted in the second direction at the second position; and repeating steps a) to e) until the entire length of the slender flexible members (A, B, C) is laid on the seabed in an alternately twisted form. A method for the simultaneous laying of slender flexible members. Claim 2 A method for the simultaneous laying of slender flexible members according to claim 1, wherein in steps b) and d), a group (15) of slender flexible members (A, B, C) is advanced toward the stern (5) of the installed vessel (1). Claim 3 A method for the simultaneous laying of slender flexible members according to claim 1 or 2, wherein the first distance (L) is equal to or greater than the length of one catenary of a group (15) of slender flexible members (A, B, C) extending from the installation vessel (1) toward the seabed. Claim 4 A method for the simultaneous laying of slender flexible members according to any one of claims 1 to 3, wherein the installation vessel comprises N spaced-apart rotating device stations (S1, S2, SN) arranged on a deck (3), wherein the first rotating device station (S1) among the rotating device stations is located at the first position, and the other N-1 rotating device stations (S2, SN) are arranged between the first position and the second position, and a group (15) of slender flexible members (A, B, C) is advanced through the rotating device stations (S1, S2, SN), and the group (15) of slender flexible members (A, B, C) is twisted by 1 / N rotation at each rotating device station (S1, S2, SN). Claim 5 In paragraph 4, a method for the simultaneous laying of slender flexible members with N=3. Claim 6 A method for the simultaneous laying of slender flexible members, wherein, in any one of claims 1 to 5, the installation vessel (1) comprises lay tensioners (T1, T2, T3) that advance individual slender flexible members (A, B, C) toward the first position. Claim 7 A method for the simultaneous laying of slender flexible members, wherein, in any one of claims 1 to 6, each lathe tensioner (T1, T2, T3) advances each slender flexible member among the individual slender flexible members (A, B, C) toward the first position. Claim 8 A method for the simultaneous laying of slender flexible members, wherein, in any one of claims 1 to 7, the slender flexible members (A, B, C) are power cables. Claim 9 A method for the simultaneous installation of slender flexible members according to claim 8, wherein the first and second slender flexible members among the slender flexible members (A, B, C) are DC cables, and the third slender flexible member among the slender flexible members (A, B, C) is a metal return cable. Claim 10 A method for simultaneously laying slender flexible members, wherein, in any one of claims 1 to 9, the installation vessel (1) is a cable laying vessel. Claim 11 A method for the simultaneous laying of slender flexible members according to any one of claims 1 to 10, wherein step a) comprises advancing an optical fiber cable having an outer diameter smaller than that of the slender flexible members (A, B, C) to the first position to be grouped with the slender flexible members (A, B, C), and the optical fiber cable grouped with the slender flexible members (A, B, C) undergoes steps a) to e) and the repetition thereof. Claim 12 A method for the simultaneous laying of slender flexible members, wherein, in any one of claims 1 to 11, the slender flexible members (A, B, C) are three in number, and in step a), the three individual slender flexible members (A, B, C) are grouped into a trifoil configuration.

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