Method for laying subaqueous cable, and subaqueous cable line

Abstract

This method for laying a subaqueous cable comprises a step for laying, on a seabed, a subaqueous cable loaded on a ship. The step for laying the subaqueous cable includes: a step for drawing out the subaqueous cable from the ship such that the subaqueous cable forms a water entry angle of 80°-90° with the water surface; and a step for disposing the drawn-out subaqueous cable onto a grounding point for the subaqueous cable by causing the same to pass through the inside of a guide pipe suspended from the ship into the water. The guide pipe is connected to a wire extending from the ship into the water without being connected to an excavator for excavating the seabed.

Description

Underwater cable laying method and underwater cable line

[0001] This disclosure relates to a method for laying an underwater cable and an underwater cable line. This application claims priority to Japanese Patent Application No. 2023-207668 filed on December 8, 2023, and incorporates the entire contents of said Japanese application by reference.

[0002] Patent Document 1 discloses a long object burial device that includes a vessel on the water, a conduit pipe placed underwater, and an burying machine placed on the bottom of the water. A long object such as a power cable is passed through the conduit pipe. The conduit pipe is connected to the burying machine. The burying machine excavates the bottom of the water to form a burial trench. The long object that has passed through the conduit pipe passes through the burying machine and is placed in the burial trench.

[0003] Japanese Patent Application Publication No. 08-246497

[0004] The disclosed method for laying a submarine cable comprises the steps of: laying a submarine cable on the water bottom mounted on a vessel; unwinding the submarine cable from the vessel so that its water entry angle with respect to the water surface is between 80° and 90°; and passing the unwinding submarine cable through a conduit suspended underwater from the vessel and placing it at the bottom of the cable. The conduit is connected to a wire extended from the vessel into the water without being connected to an excavator that excavates the water bottom.

[0005] FIG. 1 is a schematic diagram illustrating a method for laying a submarine cable according to a first embodiment. FIG. 2 is an enlarged view of region A in FIG. 1. FIG. 3 is a schematic perspective view showing a cylindrical cage member constituting a conduit used in the method for laying a submarine cable according to the first embodiment. FIG. 4 is a schematic front view of the cylindrical cage member shown in FIG. 3. FIG. 5 is a schematic top view of the cylindrical cage members shown in FIG. 3 arranged in series. FIG. 6 is a schematic diagram illustrating a ship's route in the method for laying a submarine cable according to the first embodiment. FIG. 7 is a schematic top view of a submarine cable line according to the first embodiment. FIG. 8 is a schematic top view of another example of a submarine cable line according to the first embodiment. FIG. 9 is a schematic diagram illustrating a method for laying a submarine cable according to a second embodiment. FIG. 10 is a schematic diagram illustrating a method for laying a submarine cable according to a third embodiment.

[0006] [Problem to be Solved by the Present Disclosure] In Patent Document 1, the long body is placed in the burial trench by passing through a conduit and an burial machine to which the conduit is connected in sequence. To prevent extreme bending stress from acting on the long body, the conduit is connected at an angle to the burial machine. This reduces the water entry angle of the long body relative to the water surface. The water entry angle is the angle between the long body and the water surface that is closer to the boat. Because the water entry angle is small, it is difficult to construct a line with a small bending radius when bending the long body for laying.

[0007] One object of the present disclosure is to provide a method for laying an underwater cable that allows for the construction of an underwater cable line having a bend with a small bending radius.

[0008] Effect of the Present Disclosure The method for laying an underwater cable according to the present disclosure makes it possible to construct an underwater cable line having a bend with a small bending radius.

[0009] <Description of Embodiments of the Present Disclosure> First, embodiments of the present disclosure will be listed and described.

[0010] (1) A method for laying a submarine cable according to one aspect of the present disclosure comprises the steps of: laying a submarine cable on the water bottom mounted on a vessel; unwinding the submarine cable from the vessel so that the cable's entry angle with respect to the water surface is between 80° and 90°; and passing the unwinding submarine cable through a conduit suspended underwater from the vessel and placing it at the bottom of the cable. The conduit is connected to a wire extended from the vessel into the water without being connected to an excavator that excavates the water bottom.

[0011] In the submarine cable laying method (1) above, since the conduit is not connected to the excavator, the water entry angle can be set to 80° or more. The water entry angle is the angle between the submarine cable and the water surface closer to the stern. A water entry angle of 80° or more allows the bottom landing point of the submarine cable to be closer to the stern. Therefore, the submarine cable laying method (1) above makes it easy to construct a submarine cable line with a bent section with a small bending radius. Therefore, the submarine cable laying method (1) above not only excels in laying workability but also facilitates cost reduction. A water entry angle of 90° or less allows the bending radius of the submarine cable to be equal to or greater than the allowable bending radius, and kinking of the submarine cable is less likely to occur. Furthermore, the submarine cable is less likely to come into contact with the stern when introduced to the water surface. Therefore, the submarine cable laying method (1) above makes it easy to lay the submarine cable.

[0012] (2) In the method of laying an underwater cable described above in (1), the conduit may be connected to the wire so that, when the ship is viewed from above, the distance between the stern and the bottom landing point is 20 m or less.

[0013] The above-mentioned method (2) for laying an underwater cable makes it easy to construct an underwater cable line having a bend with a small bending radius.

[0014] (3) The method for laying an underwater cable according to (1) or (2) above may further include a step of navigating the ship through a sea route with a turning radius of 50 m or less.

[0015] The above-mentioned method (3) for laying an underwater cable makes it easy to construct an underwater cable line having a bend with a small bending radius.

[0016] (4) In the method for laying a submarine cable according to any one of (1) to (3), the step of laying the submarine cable may further include a step of excavating the water bottom using the excavator suspended underwater from the ship. The step of placing the submarine cable places the submarine cable at the location excavated by the excavator. The excavator is equipped with a sand pump.

[0017] An excavator equipped with a sand pump can suck up sediment from the water bottom and discharge the sediment. Therefore, the submarine cable laying method of (4) above can continuously perform the steps of forming a trench by excavating the water bottom, laying the submarine cable at its landing point in the trench, and burying the laid submarine cable. That is, the submarine cable laying method of (4) above can excavate the water bottom to form a trench, lay the submarine cable at its landing point in the trench, and then bury the submarine cable at the landing point in the trench while laying it there.

[0018] (5) An underwater cable line according to one embodiment of the present disclosure includes an underwater cable laid on the bottom of the water, and the underwater cable has a bend with a bending radius of 50 m or less.

[0019] The underwater cable line of (5) above has a bend with a small bending radius, so that the length of the laid underwater cable can be shortened.

[0020] (6) In the underwater cable line of (5) above, the bent portion may bypass an obstacle.

[0021] The underwater cable line of (6) above has a bend with a small bending radius, making it easy to bypass obstacles.

[0022] <Details of the embodiments of the present disclosure> Embodiments of the submarine cable laying method and submarine cable line of the present disclosure will be described below with reference to the drawings. The shapes, sizes, and positional relationships shown in each figure are depicted for the purpose of clarity of explanation and do not necessarily represent the actual shapes, sizes, and positional relationships. The same symbols in the figures indicate the same items. Note that the present invention is not limited to the configurations shown in the embodiments, but is defined by the claims, and all modifications within the meaning and scope of the claims are intended to be included.

[0023] In the embodiments, the term "water" in the phrases "bottom of the water," "underwater," and "water surface" refers to the "sea," "lake," or "river." That is, the bottom of the water refers to the bottom of an ocean, lake, or river, "underwater" refers to the inside of an ocean, lake, or river, and the surface of the water refers to the surface of an ocean, lake, or river.

[0024] <<Embodiment 1>> [Method for laying a submarine cable] A method for laying a submarine cable according to embodiment 1 will be described with reference to Figures 1 to 6. The method for laying a submarine cable according to embodiment 1 involves laying a submarine cable 2 along the water bottom 90, electrically connecting land and surface facilities, land and underwater facilities, surface facilities to each other, underwater facilities to each other, or surface and underwater facilities. The method for laying a submarine cable according to embodiment 1 can be used to construct a submarine cable line equipped with a submarine cable 2 connecting these facilities. The land facility is, for example, a substation. The surface facility is, for example, an offshore plant or offshore power plant. The offshore power plant is, for example, equipped with an offshore wind turbine or a wave power generator. The offshore wind turbine is, for example, a bottom-mounted type whose foundation is fixed to the seabed, or a floating type whose foundation is moored above the sea. The underwater facility is, for example, an undersea power plant. The undersea power plant is, for example, equipped with a tidal power generator or an ocean current power generator. The submarine cable 2 can be a known submarine cable, for example, a known dynamic cable. The submarine cable laying method of Embodiment 1 comprises Step B, in which a submarine cable 2 carried on a ship 1 is laid on the water bottom 90. One of the features of the submarine cable laying method of Embodiment 1 is that Step B comprises Step B1, in which the submarine cable 2 is let out from the ship 1 so that the water entry angle θ of the submarine cable 2 relative to the water surface 92 is a specific angle, as shown in Figure 2. The submarine cable laying method of Embodiment 1 further comprises Step A, in which the ship 1 is navigated along a predetermined route 100, as shown in Figure 6.

[0025] [Step A] In step A, the ship 1 is navigated so as to include a route 100 with a turning radius R1 of 50 m or less, for example. A turning radius R1 of 50 m or less makes it easy to construct a submarine cable line 8 with a bent section 21 with a bending radius R2 of 50 m or less, as shown in FIG. 7 . The turning radius R1 may be 25 m or less or 10 m or less. The lower limit of the turning radius R1 is the allowable bending radius of the submarine cable 2. The lower limit of the turning radius R1 is, for example, 3 m. That is, the turning radius R1 is 3 m or more and 50 m or less, 3 m or more and 25 m or less, or 3 m or more and 10 m or less. Although not shown, the ship 1 may also be navigated so as to include at least one of a route with a turning radius R1 of more than 50 m and a straight route.

[0026] As shown in Figure 1, the ship 1 is equipped with a control room 11, a cable tank 12, a braking device 13, a guide 14, a first winch 15, and a first pulley 16. The control room 11 is a room where operation control of the ship 1, control of the braking device 13, monitoring of the bottom landing point (described later), and monitoring of the alignment of the conduit 5 are carried out. The control room 11 is also equipped with the equipment necessary for these controls. The cable tank 12 stores the underwater cable 2 in a wound state. The braking device 13 adjusts the payout speed of the underwater cable 2 wound around the cable tank 12, i.e., the running speed of the underwater cable 2. The guide 14 guides the paid-out underwater cable 2 to the water surface 92. The first winch 15 winds up the first wire 31 that suspends the conduit 5 (described later). The first pulley 16 guides the first wire 31 paid out from the first winch 15 toward the water surface 92. Although not shown in the figure, the ship 1 has a transceiver for the acoustic positioning device 61. The transceiver is pulled out from the ship 1 into the water 93. The transceiver transmits signals to a first transponder 611 and a second transponder 612 (described below), and receives signals from the first transponder 611 and the second transponder 612. The acoustic positioning device 61 can obtain the three-dimensional coordinates of the first transponder 611 and the second transponder 612 by transmitting and receiving signals.

[0027] [Step B] Step B is a step of laying the submarine cable 2 on the water bottom 90. Step B comprises step B1 of letting out the submarine cable 2 from the ship 1, and step B2 of placing the let-out submarine cable 2 at a bottom landing point. Step B may further comprise at least one of step B3 of monitoring the bottom landing point of the submarine cable 2 and step B4 of monitoring the alignment of the conduit 5.

[0028] (Step B1) In step B1, as shown in Figure 2, the submarine cable 2 is let out from the ship 1 so that the water entry angle θ of the submarine cable 2 relative to the water surface 92 is between 80° and 90°. The submarine cable 2 is let out from the stern. In Figure 1, the stern is to the left. That is, in Figure 1, the direction of travel of the ship 1 is to the right. These points are also true in Figures 9 and 10, which will be described later. The water entry angle θ is the angle between the submarine cable 2 and the water surface 92 that is closer to the stern. A water entry angle θ of 80° or more allows the bottom landing point of the submarine cable 2 to be closer to the stern. Therefore, as shown in Figure 7, it is easy to construct a submarine cable line 8 with a bent section 21 whose bending radius R2 is 50 m or less. A water entry angle θ of 90° or less allows the bending radius of the submarine cable 2 to be greater than the allowable bending radius, and makes the submarine cable 2 less likely to kink. In addition, the underwater cable 2 is less likely to come into contact with the stern of the ship. Therefore, the method for laying a submarine cable in this example makes it easy to lay the underwater cable 2. The water entry angle θ may be, for example, between 85° and 90°.

[0029] (Step B2) In step B2, as shown in Figure 1, the submarine cable 2 is placed at the bottom landing point by passing it through the inside of a conduit 5 placed underwater 93. The conduit 5 is suspended underwater 93 by being connected to a first wire 31 that is extended from the vessel 1 into the water 93. In this example, the conduit 5 is connected to the first wire 31 so that it is positioned forward of the direction of travel of the vessel 1 on the first wire 31, i.e., to the right of the page in Figure 1. By passing the submarine cable 2 through the inside of the conduit 5, the submarine cable 2 is less likely to bend to a degree that would cause damage during its movement to the water bottom 90. Furthermore, the submarine cable 2 is less likely to kink during its movement to the water bottom 90.

[0030] Unlike this example, if the conduit 5 is connected to the first wire 31 so as to be positioned rearward of the first wire 31 in the direction of travel of the ship 1, i.e., to the left of the paper surface in Figure 1, the following may occur: As the submarine cable 2 passes through the conduit 5, the submarine cable 2 comes into contact with the conduit 5, causing the conduit 5 to rotate around the first wire 31 as the center of rotation so that it is positioned forward of the first wire 31 in the direction of travel of the ship 1. The rotated conduit 5 rubs against the submarine cable 2, damaging the submarine cable 2.

[0031] In contrast, in this example, the conduit 5 is connected to the first wire 31 so as to be positioned forward of the first wire 31 in the direction of travel of the ship 1, so even if the conduit 5 comes into contact with the underwater cable 2 as it passes through the inside of the conduit 5, the conduit 5 is prevented from rotating around the first wire 31. This prevents the rotated conduit 5 from rubbing against the underwater cable 2, making it less likely that the underwater cable 2 will be damaged. Furthermore, preventing the conduit 5 from rotating helps to prevent the umbilical cable 4, which will be described later, from becoming tangled.

[0032] The conduit 5 is not connected to the excavator that excavates the water bottom 90. Because the conduit 5 is not connected to the excavator, the conduit 5 is likely to be positioned vertically. Therefore, the water entry angle θ is likely to be 80° or greater. Furthermore, when the ship 1 is viewed from above, the conduit 5 is likely to be suspended underwater 93 so that the distance L between the stern and the bottom landing point is short. In this example, the conduit 5 is connected to the first wire 31 so that the distance L is 20 m or less. Therefore, as shown in FIG. 7 , it is easy to construct a submarine cable line 8 having a bent portion 21 with a bending radius R2 of 50 m or less. The distance L may be 15 m or less or 10 m or less. The lower limit of the distance L is not particularly limited, but is, for example, 5 m. That is, the distance L is 5 m or more and 20 m or less, 5 m or more and 15 m or less, or 5 m or more and 10 m or less.

[0033] <Conduit> The conduit 5 includes a plurality of cylindrical cage-shaped members 5a. Each cylindrical cage-shaped member 5a is made of a metal such as steel. Each cylindrical cage-shaped member 5a may have a base made of a metal such as steel and a rust-preventive layer covering the surface of the base. The rust-preventive layer prevents the base from rusting. The plurality of cylindrical cage-shaped members 5a are arranged in series by a first wire 31. As shown in FIG. 3, each of the plurality of cylindrical cage-shaped members 5a has a through-hole 55a through which the first wire 31 shown in FIG. 1 is passed. The central axis of the through-hole 55a is parallel to the central axis of each of the plurality of cylindrical cage-shaped members 5a. As shown in FIG. 1, the first wire 31 has stopper portions 311 that abut or fix the plurality of cylindrical cage-shaped members 5a at intervals to position them. There are a plurality of stopper portions 311. The number of stopper portions 311 can be appropriately selected depending on the number of cylindrical cage-shaped members 5a. If there is only one stopper portion 311 and it is provided at the lower end of the first wire 31, the weight of all of the cylindrical cage-shaped members 5a needs to be supported by that single stopper portion 311. In contrast, if there are multiple stopper portions 311, each stopper portion 311 only needs to support the weight of the cylindrical cage-shaped members 5a disposed between the stopper portions 311, thereby reducing the load acting on each stopper portion 311. The number of stopper portions 311 can be set to a number that allows positioning of, for example, five cylindrical cage-shaped members 5a. In addition to the first wire 31, the umbilical cable 4 shown in FIG. 1 may be passed through the through hole 55a. The umbilical cable 4 is a bundle of cables that are connected to each of the camera 60, the first transponder 611, the second transponder 612 of the acoustic positioning device 61, and the altimeter 62 described below, and that supply power and send and receive signals.

[0034] As shown in Figure 3, each of the multiple cylindrical cage-shaped members 5a has a main body portion 50 configured to allow the underwater cable 2 to be passed through, and at least one protrusion portion 55 extending from the main body portion 50 in a direction away from the central axis of the main body portion 50.

[0035] The main body 50 of this example has a base 501 and a door 502. The base 501 of this example is a portion where an engaging protrusion 591 and an engaging recess 592 (described later) are connected, and the door 502 is a portion where the engaging protrusion 591 and the engaging recess 592 are not connected. The base 501 has an arc-shaped first base 511 (described later), an arc-shaped second base 521 (described later), and a plurality of rod-shaped portions 54 connecting the first base 511 and the second base 521. The door 502 is connected to the base 501 so as to be able to open and close the main body 50. The door 502 of this example has an arc-shaped first opening / closing portion 512 (described later), an arc-shaped second opening / closing portion 522 (described later), and a plurality of rod-shaped portions 54 connecting the first opening / closing portion 512 and the second opening / closing portion 522. The door portion 502 allows the tubular cage member 5a to be fitted from the side of the underwater cable 2. Therefore, the tubular cage member 5a can be placed in the water 93 by fitting it from the side of the underwater cable 2 on the ship 1 and dropping it into the water 93.

[0036] The number of protrusions 55 may be one or more. In this example, there are two protrusions 55. In this example, each protrusion 55 is formed of a plate-shaped member. A through hole 55a is provided in each protrusion 55. In this example, both protrusions 55 are connected by a rod-shaped connecting portion 55b. Each protrusion 55 has a first protrusion 581 connected to the base portion 501 of the main body 50 and a second protrusion 582 connected to the door portion 502. Since the first protrusion 581 is connected to the base portion 501 and the second protrusion 582 is connected to the door portion 502, opening and closing the door portion 502 allows the second protrusion 582 to open and close relative to the first protrusion 581. As shown by the solid lines in FIG. 4 , the first protrusion 581 and the second protrusion 582 have notches 581a and 582a that face each other when the door portion 502 is closed. A through-hole 55a is formed between the notches 581a and 582a. The two-dot chain line in Figure 4 indicates the state in which the door portion 502 is open. As the door portion 502 is opened or closed, the cylindrical cage-shaped member 5a can be fitted onto the first wire 31 from the side. In this example, the connecting portion 55b is connected to both first protrusions 581.

[0037] The main body 50 of this example has a first annular portion 51, a second annular portion 52, and a plurality of rod-shaped portions 54, which will be described later. The first annular portion 51 and the second annular portion 52 are arranged at intervals along the central axis of the main body 50. The central axis of the first annular portion 51 and the central axis of the second annular portion 52 are coaxial. The first annular portion 51 and the second annular portion 52 of this example have a circular ring shape. Unlike this example, the first annular portion 51 and the second annular portion 52 may have a rectangular ring shape.

[0038] The first annular portion 51 has a first base portion 511 and a first open-close portion 512. In this example, the first base portion 511 has an arc-shaped configuration. The first open-close portion 512 is connected to the first base portion 511 so as to freely open and close the inside and outside of the first annular portion 51. In this example, the first open-close portion 512 is connected to the first base portion 511 by a hinge 53. In this example, the first open-close portion 512 has an arc-shaped configuration. The second annular portion 52 has a second base portion 521 and a second open-close portion 522. In this example, the second base portion 521 has an arc-shaped configuration. The second open-close portion 522 is connected to the second base portion 521 so as to freely open and close the inside and outside of the second annular portion 52. In this example, the second open-close portion 522 is connected to the second base portion 521 by a hinge 53. In this example, the second open-close portion 522 has an arc-shaped configuration. The position of the first annular portion 51 around the central axis of the first open-close portion 512 and the position of the second annular portion 52 around the central axis of the second open-close portion 522 are the same. The hinge 53 connecting the second base portion 521 and the second open-close portion 522 has thin-walled portions at the ends of the second base portion 521 and the second open-close portion 522. A shaft hole is provided in each thin-walled portion. The hinge 53 is configured by overlapping the thin-walled portion of the second base portion 521 and the thin-walled portion of the second open-close portion 522 with each other, and passing the shaft portion through the shaft holes of the overlapped thin-walled portions. The same is true for the hinge 53 connecting the first base portion 511 and the first open-close portion 512.

[0039] The plurality of rod-shaped portions 54 connect the first annular portion 51 and the second annular portion 52. The number of rod-shaped portions 54 is not particularly limited and can be selected as appropriate. In this example, the number of rod-shaped portions 54 is six. One or more of the plurality of rod-shaped portions 54 connect the first base portion 511 and the second base portion 521. Furthermore, one or more of the plurality of rod-shaped portions 54 connect the first opening / closing portion 512 and the second opening / closing portion 522. In this example, three rod-shaped portions 54 connect the first base portion 511 and the second base portion 521. Furthermore, in this example, three rod-shaped portions 54 connect the first opening / closing portion 512 and the second opening / closing portion 522.

[0040] The two protrusions 55 are a first protrusion 56 extending from the first annular portion 51 in a direction away from the central axis of the first annular portion 51, and a second protrusion 57 extending from the second annular portion 52 in a direction away from the central axis of the second annular portion 52. The first protrusion 56 and the second protrusion 57 face each other. The first protrusion 56 and the second protrusion 57 have through holes 55a. The central axis of the through hole 55a of the first protrusion 56 is parallel to the central axis of the first annular portion 51. The central axis of the through hole 55a of the second protrusion 57 is parallel to the central axis of the second annular portion 52. The central axis of the through hole 55a of the first protrusion 56 and the central axis of the through hole 55a of the second protrusion 57 are coaxial. The first protrusion 56 and the second protrusion 57 have a first protrusion 581 and a second protrusion 582. The first protrusion 581 and the second protrusion 582 have a through hole 583 that communicates with each other when the door portion 502 is closed. A pin (not shown) is inserted into this through hole 583 to maintain the door portion 502 in a closed state. In this example, the first protrusion 581 and the second protrusion 582 have notches 581a and 582a at diagonal positions of the generally rectangular plate. As shown in FIG. 4 , the first protrusion 581 has the notch 581a at the upper right corner of the generally rectangular plate, and the second protrusion 582 has the notch 582a at the lower left corner of the generally rectangular plate. When the base portion 501 and the door portion 502 are closed, the notch 581a and the notch 582a face each other to form the through hole 55a.

[0041] Each of the multiple cylindrical cage members 5a may further include an engaging protrusion 591 and an engaging recess 592. The engaging protrusion 591 is connected to the first protrusion 56. The engaging protrusion 591 extends from the first protrusion 56 toward the opposite side of the second protrusion 57 along the central axis of the through hole 55a. The engaging recess 592 is connected to the second protrusion 57. The engaging recess 592 extends from the second protrusion 57 toward the opposite side of the first protrusion 56 along the central axis of the through hole 55a. The engaging recess 592 corresponds to the engaging protrusion 591. Of the three cylindrical cage members 5a arranged in series as shown in FIG. 5 , the central cylindrical cage member 5a is referred to as the first cylindrical cage member 5a, the right cylindrical cage member 5a is referred to as the second cylindrical cage member 5a, and the left cylindrical cage member 5a is referred to as the third cylindrical cage member 5a. The engagement recess 592 corresponds to the engagement protrusion 591, which means that the engagement protrusion 591 of the first cylindrical cage-shaped member 5a engages with the engagement recess 592 of the second cylindrical cage-shaped member 5a, and the engagement recess 592 of the first cylindrical cage-shaped member 5a engages with the engagement protrusion 591 of the third cylindrical cage-shaped member 5a.

[0042] As shown in FIG. 3 , the engaging protrusion 591 in this example is formed by a single protrusion connected to the tip of the rod-shaped portion connected to the first protrusion 581, and the engaging recess 592 in this example is formed by a bifurcated piece connected to the tip of the rod-shaped portion connected to the second protrusion 582. The rod-shaped portion connected to the first protrusion 581 and the rod-shaped portion connected to the second protrusion 582 may be formed by members independent of the connecting portion 55b, or may be formed by part of the connecting portion 55b. In the latter case, the rod-shaped portion connected to the first protrusion 581 and the rod-shaped portion connected to the second protrusion 582 may be formed by the connecting portion 55b that penetrates the first protrusion 581 and the second protrusion 582. In this case, the through holes of the first protrusion 581 and the second protrusion 582 and the connecting portion 55b may be fixed by welding or the like. As shown in Fig. 5, the first cylindrical cage member 5a and the second cylindrical cage member 5a are connected, and the first cylindrical cage member 5a and the third cylindrical cage member 5a are connected, by inserting the engaging protrusion 591, which is a protruding piece, into the engaging recess 592, which is a bifurcated piece. As shown in Fig. 3, the engaging protrusion 591 of this example has a through hole 591a, and the engaging recess 592 has a through hole 592a. The through holes 591a and 592a are arranged to communicate with each other when the engaging protrusion 591 is inserted into the engaging recess 592. The engagement between the engaging protrusion 591 and the engaging recess 592 is maintained by inserting a pin (not shown) through the through holes 591a and 592a.

[0043] (Step B3) In step B3, the bottom landing point of the submarine cable 2 is monitored using the image from the camera 60 and the position information of the first transponder 611 of the acoustic positioning device 61. The bottom landing point is the point of contact between the submarine cable 2 and the water bottom 90. When step B3 is included, step B2 involves placing the submarine cable 2 at the bottom landing point while monitoring the bottom landing point of the submarine cable 2. The camera 60 and the first transponder 611 are attached to the lower end of the conduit 5 or the first wire 31, which is located near the bottom landing point. The camera 60 and the first transponder 611 may be attached directly to the lower end of the conduit 5 or the first wire 31, or the camera 60 and the first transponder 611 may be attached to an attachment jig (not shown), and the attachment jig may be attached to the lower end of the conduit 5 or the first wire 31. In this example, the camera 60 and the first transponder 611 are attached to the cylindrical cage member 5a located closest to the bottom landing point.

[0044] The distance from the camera 60 to the bottom 90 can be calculated from the image of the water bottom 90 captured by the camera 60. The first transponder 611 can acquire three-dimensional positional information of the location where the first transponder 611 is attached. Therefore, the vertical distance and horizontal distance from the stern to the first transponder 611 can be calculated. The first transponder 611 is attached to the conduit 5 at the same height as the camera 60. By attaching the first transponder 611 at the same height as the camera 60, the vertical distance from the stern to the bottom landing point can be calculated, which is the sum of the vertical distance from the stern to the first transponder 611 and the distance from the first transponder 611 and the camera 60 to the water bottom 90.

[0045] The camera 60 and the first transponder 611 enable continuous monitoring of the bottom landing point. Monitoring the bottom landing point allows the submarine cable 2 to be laid at the designed position. Calculating the vertical distance from the stern to the bottom landing point allows the submarine cable 2 to be laid while ensuring that its residual tension is within the design range. Furthermore, the submarine cable 2 can be laid while ensuring that the bending radius of the submarine cable 2 at the bottom landing point is within the allowable range. Images captured by the camera 60 also allow for observation of any abnormalities in the appearance of the submarine cable 2. The camera 60 is attached to the tubular cage member 5a located closest to the bottom landing point, allowing for the distance H between the water bottom 90 and the tubular cage member 5a located closest to the bottom landing point to be calculated. Calculating the distance H allows for the three-dimensional coordinates of the lower end of the conduit 5 to be adjusted.

[0046] The submarine cable laying method of this example does not require the use of a remotely operated vehicle (ROV) because the landing point can be monitored using the camera 60 and the first transponder 611. ROVs are subject to limitations on the hydrological conditions under which they can be used. In hydrological conditions that preclude the use of ROVs, such as when the water current is fast, laying operations must wait. However, because the submarine cable laying method of this example does not use an ROV, there are fewer or no hydrological conditions limitations compared to when an ROV is used. In other words, the submarine cable laying method of this example can shorten or eliminate waiting times due to hydrological conditions. Furthermore, the submarine cable laying method of this example facilitates cost reduction by not using an ROV.

[0047] In step B3, the position information of the altimeter 62 may be further used to calculate the vertical distance from the stern to the bottom landing point. The altimeter 62 is attached to, for example, the lower end of the conduit 5 located near the bottom landing point.

[0048] (Step B4) In step B4, the alignment of the conduit 5 is monitored using position information from the first transponder 611 of the acoustic positioning device 61 and position information from the second transponder 612 of the acoustic positioning device 61. When step B4 is included, step B2 involves placing the submarine cable 2 at the bottom landing point while monitoring the alignment of the conduit 5. The second transponder 612 is attached to the upper end of the conduit 5 or the first wire 31 that is located underwater 93 near the water surface 92. The upper end of the first wire 31 is a point on the first wire 31 that is at the same height as the upper end of the conduit 5. The second transponder 612 may be attached directly to the upper end of the conduit 5 or the first wire 31, or the second transponder 612 may be attached to an attachment jig (not shown), and the attachment jig may be attached to the upper end of the conduit 5 or the first wire 31. In this example, the second transponder 612 is attached to the upper end of the cylindrical cage member 5a located closest to the water surface 92. By monitoring the alignment of the conduit 5, it is possible to monitor the alignment of the underwater cable 2 inside the conduit 5. Therefore, it is possible to determine whether or not a load due to excessive bending is acting on the underwater cable 2 inside the conduit 5.

[0049] [Submarine Cable Line] A submarine cable line 8 of embodiment 1 will be described with reference to Figures 7 and 8. The submarine cable line 8 of embodiment 1 comprises a submarine cable 2 laid on the water bottom 90. As shown in Figure 7, the submarine cable 2 in the submarine cable line 8 has a bent section 21 with a bending radius R2 of 50 m or less. The bending radius R2 may be 25 m or less or 10 m or less. The lower limit of the bending radius R2 is the allowable bending radius of the submarine cable 2. The lower limit of the bending radius R2 is, for example, 3 m. That is, the bending radius R2 is 3 m or more and 50 m or less, 3 m or more and 25 m or less, or 3 m or more and 10 m or less. Although not shown, the submarine cable 2 in the submarine cable line 8 may have a bent section with a bending radius greater than 50 m or a straight section. The bent section 21 may bypass an obstacle 80. The obstacle 80 may be a rock or an underwater structure, for example. The underwater structure is, for example, a support 85 of an offshore wind turbine.

[0050] Referring to Figure 8, an example of the submarine cable line 8 of this example including an underwater cable 2 connecting offshore wind turbines will be described. For ease of explanation, Figure 8 only shows the support columns 85 of the offshore wind turbines. Figure 8 shows an example in which multiple support columns 85 are fixed to the seabed 90 at predetermined intervals. For ease of explanation, Figure 8 shows a straight line passing through the centers of the multiple support columns 85 as a two-dot chain line.

[0051] The inlet 851 and outlet 852 for the submarine cable 2 on a support 85 may be located at a submerged position on the support 85. In this case, if the inlet 851 and outlet 852 are located on a straight line as indicated by the dashed two-dot line, the submarine cable 2 can be laid in a straight line, connecting the outlet 852 of one support 85 to the inlet 851 of the next support 85. In this case, the submarine cable line 8 includes a submarine cable 2 laid so that the outlet 852 of one support 85 and the inlet 851 of the next support 85 are connected in a straight line. This submarine cable line 8 has a short length of the submarine cable 2. Furthermore, the submarine cable laying method for constructing this submarine cable line 8 requires a small turning radius at the waypoint to lay the submarine cable 2, which connects the outlet 852 of one support 85 to the inlet 851 of the next support 85, making it easy to lay the submarine cable 2.

[0052] Because the inlets 851 and outlets 852 can be mechanically weak points in the event of a tidal current, the inlets 851 and outlets 852 are sometimes designed to face a specific direction relative to the main tidal current to maximize the lifespan of the struts 85. As a result, depending on the tidal current, the inlets 851 and outlets 852 of each strut 85 may be positioned off the dashed-two-dot line, and all of the inlets 851 and outlets 852 may be positioned in the same direction, as shown in Figure 8. In Figure 8, the inlets 851 are located below the plane of the page and the outlets 852 are located above the plane of the page. In this case, the submarine cable 2 cannot be laid in a straight line from the outlet 852 of one strut 85 to the inlet 851 of the next strut 85. In other words, the submarine cable 2 must be bent between the outlet 852 of one strut 85 and the inlet 851 of the next strut 85. When laid in this way, the submarine cable 8 has a bent section 21 between the exit 852 of one support 85 and the entrance 851 of the next support 85. The submarine cable 8 in this example has a bent section 21 with a bending radius R2 of 50 m or less, allowing the length of the submarine cable 2 to be relatively short. Therefore, the submarine cable laying method of this example for constructing the submarine cable 8 in this example makes it easy to lay the submarine cable 2.

[0053] Second Embodiment [Method for laying a submarine cable] A method for laying a submarine cable according to the second embodiment will be described with reference to Figure 9. The method for laying a submarine cable according to the second embodiment differs from the method for laying a submarine cable according to the first embodiment in that step B for laying the submarine cable 2 further includes step B5 for excavating the water bottom 90 using an excavator 7 suspended underwater 93 from the ship 1.

[0054] The excavator 7 is suspended by a second wire 32. The second wire 32 is an independent member from the first wire 31. Although not shown, the second wire 32 is wound around a second winch and guided toward the water surface 92 by a second pulley. The second wire 32 extends into the water 93 at a substantially right angle to the water surface 92. In other words, the water entry angle of the second wire 32 with respect to the water surface 92 is substantially 90°. In this example, the second wire 32 is spaced apart from the conduit 5 so as not to be connected to the conduit 5. The second wire 32 is positioned forward of the conduit 5 in the direction of travel of the ship 1. The excavator 7 is equipped with a sand pump. The excavator 7 equipped with a sand pump can suck up sediment from the water bottom 90 and discharge the sucked up sediment. Therefore, in this example, the method for laying a submarine cable can be performed in succession by excavating the water bottom 90 to form a trench 91, placing the submarine cable 2 at its landing point in the trench 91, and burying the placed submarine cable 2. In other words, in this example, the method for laying a submarine cable can be performed by excavating the water bottom 90 to form a trench 91, placing the submarine cable 2 at its landing point in the formed trench 91, and burying the submarine cable 2 while placing it at its landing point in the trench 91. In this example, the landing point of the submarine cable 2 is the point of contact between the submarine cable 2 and the bottom of the trench 91.

[0055] Third Embodiment [Method of laying a submarine cable] A method of laying a submarine cable according to the third embodiment will be described with reference to Figure 10. The method of laying a submarine cable according to the third embodiment differs from the method of laying a submarine cable according to the second embodiment in that a part of the conduit 5 is connected to the second wire 32 that suspends the excavator 7.

[0056] In this example, the conduit 5 is connected to the second wire 32 with a gap between its upper end and the second wire 32 halfway between its upper and lower ends. The conduit 5 and the second wire 32 are connected, for example, by a clip (not shown). Alternatively, the conduit 5 may have an openable / closable protrusion with a through-hole through which the second wire 32 passes, although this is not shown. The openable / closable protrusion is connected to the base 501 so as not to interfere with the opening and closing of the door 502 shown in Figures 3 and 4. The conduit 5 is not connected to the second wire 32 from its middle to its lower end. In this example, the submarine cable laying method easily brings the water entry angle θ of the submarine cable 2 closer to 90° because a portion of the conduit 5 is connected to the second wire 32. Furthermore, this submarine cable laying method easily reduces the distance L between the stern of the ship 1 (as viewed from above) and the bottom landing point to 20 m or less. Therefore, the method for laying an underwater cable in this example makes it easy to construct an underwater cable line 8 having a bent portion 21 with a bending radius R2 of 50 m or less.

[0057] DESCRIPTION OF SYMBOLS 1 Ship, 11 Control room, 12 Cable tank, 13 Brake device 14 Guide, 15 First winch, 16 First pulley 2 Underwater cable, 21 Bending portion 31 First wire, 311 Stopper portion, 32 Second wire 4 Umbilical cable 5 Conduit, 5a Cylindrical cage-shaped member, 50 Main body portion 501 Base portion, 502 Door portion 51 First annular portion, 511 First base portion, 512 First opening / closing portion 52 Second annular portion, 521 Second base portion, 522 Second opening / closing portion 53 Hinge, 54 Rod-shaped portion, 55 Protruding portion 55a Through hole, 55b Connecting portion, 56 First protruding portion, 57 Second protruding portion 581 First protruding piece, 581a Notch, 582 Second protruding piece, 582a Notch 583 Through hole, 591 Engaging protrusion, 591a Through hole 592 Engaging recess, 592a Through hole 60 Camera, 61 Acoustic positioning device 611 First transponder, 612 Second transponder, 62 Altimeter 7 Excavator 8 Underwater cable line, 80 Obstacle, 85 Support 851 Entrance, 852 Exit 90 Water bottom, 91 Groove, 92 Water surface, 93 Underwater 100 Route A Area, H, L Distance R1 Turning radius, R2 Bending radius, θ Water entry angle

Claims

1. A method for laying a submarine cable, comprising the step of laying a submarine cable mounted on a ship on the bottom of the water, the step of laying the submarine cable comprising the steps of: paying out the submarine cable from the ship so that the water entry angle of the submarine cable with respect to the water surface is between 80° and 90°; and passing the paid-out submarine cable through a conduit suspended underwater from the ship, and placing it at the point where the submarine cable hits the bottom, wherein the conduit is connected to a wire extended from the ship into the water, without being connected to an excavator that excavates the bottom of the water.

2. A method for laying an underwater cable as described in claim 1, wherein the conduit is connected to the wire so that the distance between the stern and the bottom landing point is 20 m or less when the ship is viewed from above.

3. A method for laying an underwater cable as claimed in claim 1 or 2, further comprising the step of navigating the ship in a sea route having a turning radius of 50 m or less.

4. A method for laying a submarine cable as claimed in any one of claims 1 to 3, wherein the step of laying the submarine cable further comprises the step of excavating the bottom of the water by the excavator suspended under the water from the ship, and the step of placing the submarine cable comprises placing the submarine cable at the location excavated by the excavator, and the excavator is equipped with a sand pump.

5. An underwater cable line comprising an underwater cable laid on the bottom of the water, the underwater cable having a bend with a bending radius of 50 m or less.

6. The underwater cable line according to claim 5, wherein the bent portion bypasses an obstacle.

Images