Underwater cable laying method and underwater cable line

Abstract

A method for laying a submarine cable comprises the steps of: laying a submarine cable on the water bottom mounted on a vessel. The step of laying the submarine cable comprises the steps of: paying out the submarine cable from the vessel so that the submarine cable has an entry angle of 80° to 90° relative to the water surface; and passing the paid-out 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.

Description

[Technical Field]

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

[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 that is reeled out from the vessel 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. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 08-246497 Summary of the Invention

[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. [Brief explanation of the drawings]

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

[0006] [Problem to be solved by this disclosure] In Patent Document 1, the long body is placed in the burial trench by passing through a conduit and an burial machine connected to the conduit 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] An 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] [Effects of this disclosure] The method for laying an underwater cable disclosed herein 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 embodiment 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 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.

[0011] In the submarine cable laying method (1) above, since the conduit is not connected to the excavator, the water entry angle can be 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 submarine cable to land closer to the stern. Therefore, the submarine cable laying method (1) above makes it easy to construct a submarine cable line with a bend with a small bending radius. Therefore, the submarine cable laying method (1) above not only excels in laying workability but also helps reduce costs. A water entry angle of 90° or less allows the bend radius of the submarine cable to be 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 it is introduced to the water surface. Therefore, the submarine cable laying method (1) above makes it easy to lay a 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 described in (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. In other words, the submarine cable laying method described in (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 in (6) above has bends with small bending radii, making it easy to bypass obstacles.

[0022] Details of the embodiments of the present disclosure The following describes embodiments of the disclosed underwater cable laying method and underwater cable line with reference to the drawings. The shapes, sizes, and positional relationships shown in the drawings are for the purpose of clarity and do not necessarily represent the actual shapes, sizes, and positional relationships. The same reference numerals in the drawings indicate the same objects. 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] First Embodiment [Underwater cable laying method] A method for laying an underwater cable according to the first embodiment will be described with reference to Figures 1 to 6. The method for laying an underwater cable according to the first embodiment involves laying an underwater cable 2 along the water bottom 90, electrically connecting land and underwater facilities, land and underwater facilities, surface facilities, underwater facilities, or surface and underwater facilities. The method for laying an underwater cable according to the first embodiment can be used to construct an underwater cable line equipped with an underwater cable 2 connecting these facilities. The land facility is, for example, a substation. The underwater facility is, for example, an offshore plant or an offshore power plant. The offshore power plant is equipped with, for example, an offshore wind turbine or a wave power generator. The offshore wind turbine is 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, a subsea power plant. The subsea power plant is equipped with, for example, a tidal power generator or an ocean current power generator. The subsea cable 2 can be a known underwater cable, such as a known dynamic cable. The submarine cable laying method of embodiment 1 comprises step B of laying a submarine cable 2 carried on a ship 1 on the water bottom 90. One of the features of the submarine cable laying method of embodiment 1 is that step B1 includes step B1 of paying out the submarine cable 2 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 of sailing the ship 1 along a predetermined route 100, as shown in Figure 6.

[0025] [Process A] In step A, the ship 1 is navigated along a route 100 with a turning radius R1 of 50 m or less, for example. A turning radius R1 of 50 m or less facilitates the construction of a submarine cable line 8 having 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 along a route with a turning radius R1 of more than 50 m and / or a straight route.

[0026] As shown in Figure 1, the vessel 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 vessel 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 reeled-up underwater cable 2. The braking device 13 adjusts the payout speed of the underwater cable 2 reeled up in the cable tank 12, i.e., the running speed of the underwater cable 2. The guide 14 guides the reeled-out underwater cable 2 to the water surface 92. The first winch 15 reel-up the first wire 31 that suspends the conduit 5 (described later). The first pulley 16 guides the first wire 31 reeled 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, which will be described later, 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] [Process B] Step B is a step of laying the submarine cable 2 on the seabed 90. Step B1 involves paying out the submarine cable 2 from the ship 1, and Step B2 involves placing the paid-out submarine cable 2 at a bottom landing point. Step B may further include 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] (Process B1) In step B1, as shown in Figure 2, the submarine cable 2 is let out from the vessel 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 vessel 1 is to the right. These points are also the same 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 kinking of the submarine cable 2 is less likely to occur. In addition, the submarine cable 2 is less likely to come into contact with the stern. Therefore, the method for laying a submarine cable in this example makes it easy to lay the submarine cable 2. The water entry angle θ may be, for example, between 85° and 90°.

[0029] (Process B2) In step B2, as shown in Figure 1, the submarine cable 2 is laid at its bottom landing point by passing it through 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. In this example, the conduit 5 is connected to the first wire 31 so that it is positioned forward of the vessel 1's direction of travel on the first wire 31, i.e., to the right of the page in Figure 1. By passing the submarine cable 2 through 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 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, it is easy for the conduit 5 to be positioned vertically. This makes it easy for the water entry angle θ to be 80° or greater. Furthermore, when the ship 1 is viewed from above, the conduit 5 is easily suspended underwater 93 so that the distance L between the stern and the bottom 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 Figure 7, it is easy to construct an underwater 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] 〈Decoration conduit〉 The conduit 5 includes multiple cage-shaped members 5a. Each cage-shaped member 5a is made of a metal such as steel. Each 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 cage-shaped members 5a are arranged in series by a first wire 31. As shown in FIG. 3, each cage-shaped member 5a has a through-hole 55a through which the first wire 31 shown in FIG. 1 passes. The central axis of the through-hole 55a is parallel to the central axis of each cage-shaped member 5a. As shown in FIG. 1, the first wire 31 has stopper portions 311 that position the cage-shaped members 5a by abutting or fixing them at intervals. There are multiple stopper portions 311. The number of stopper portions 311 can be selected appropriately depending on the number of cage-shaped members 5a. If there were only one stopper portion 311 provided at the lower end of the first wire 31, the weight of all the cylindrical cage members 5a would need to be supported by that single stopper portion 311. In contrast, by providing multiple stopper portions 311, each stopper portion 311 only needs to support the weight of the cylindrical cage members 5a located between them, thereby reducing the load acting on each stopper portion 311. The number of stopper portions 311 can be set to a number that allows the positioning of, for example, five cylindrical cage 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 connected to the camera 60, the first transponder 611 and second transponder 612 of the acoustic positioning device 61, and the altimeter 62 (described later) for supplying power and transmitting and receiving 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, 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 inside and outside of the main body 50. The door 502 of this example has an arc-shaped first opening and closing portion 512 (described later), an arc-shaped second opening and closing portion 522, and a plurality of rod-shaped portions 54 connecting the first opening and closing portion 512 and the second opening and 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 made of a plate-like 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 FIG. 4 indicates the state in which the door portion 502 is open. As the door portion 502 is opened or closed, the cylindrical cage 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 are circular annular in shape. Unlike this example, the first annular portion 51 and the second annular portion 52 may be rectangular annular in shape.

[0038] The first annular portion 51 has a first base portion 511 and a first opening / closing portion 512. In this example, the first base portion 511 has an arc-like shape. The first opening / closing 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 opening / closing portion 512 is connected to the first base portion 511 by a hinge 53. In this example, the first opening / closing portion 512 has an arc-like shape. The second annular portion 52 has a second base portion 521 and a second opening / closing portion 522. In this example, the second base portion 521 has an arc-like shape. The second opening / closing 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 opening / closing portion 522 is connected to the second base portion 521 by a hinge 53. In this example, the second opening / closing portion 522 has an arc-like shape. 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 protruding piece 581 and the second protruding piece 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 protruding piece 581 and the second protruding piece 582 have notches 581a and 582a formed at diagonal positions of the substantially rectangular plate. As shown in FIG. 4, the first protruding piece 581 has the notch 581a formed in the upper right corner of the substantially rectangular plate, and the second protruding piece 582 has the notch 582a formed in the lower left corner of the substantially 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 corresponding to the engagement protrusion 591 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 a 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 a 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 a member independent of the connecting portion 55b, or may be formed by a 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] (Process 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 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 bottom 90.

[0045] The camera 60 and the first transponder 611 allow for 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 element 5a located closest to the bottom landing point, allowing for calculation of the distance H between the water bottom 90 and the tubular cage element 5a located closest to the bottom landing point. Calculating the distance H allows for adjustment of the three-dimensional coordinates of the lower end of the conduit 5.

[0046] The submarine cable laying method of this example does not require the use of an ROV (Remotely Operated Vehicle) 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 make an ROV unusable, such as when the water current is fast, laying operations must be put on hold. 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, by not using an ROV, the submarine cable laying method of this example can easily achieve low costs.

[0047] In step B3, position information of the altimeter 62 may be further used to determine 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] (Process 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, which 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 the underwater cable 2 inside the conduit 5 is being subjected to loads such as excessive bending.

[0049] [Underwater cable line] A submarine cable line 8 of the first embodiment will be described with reference to Figures 7 and 8. The submarine cable line 8 of the first embodiment comprises a submarine cable 2 laid on the seabed 90. As shown in Figure 7, the submarine cable 2 in the submarine cable line 8 has bent sections 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 bent sections with a bending radius exceeding 50 m or may have straight sections. The bent sections 21 may bypass an obstacle 80. The obstacle 80 may be a rock or an underwater structure. The underwater structure is, for example, a support 85 of an offshore wind turbine.

[0050] Referring to Figure 8, an example will be described in which the submarine cable line 8 of this example includes an underwater cable 2 connecting offshore wind turbines. 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 dash-dot-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 has the submarine cable 2 laid so that it connects the outlet 852 of one support 85 to the inlet 851 of the next support 85 in a straight line. With this submarine cable line 8, the length of the submarine cable 2 is short. 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 support struts 85. As a result, depending on the tidal current, the inlets 851 and outlets 852 of each support strut 85 may be positioned off the two-dot chain 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 support strut 85 to the inlet 851 of the next support strut 85. In other words, the submarine cable 2 must be bent between the outlet 852 of one support strut 85 and the inlet 851 of the next support strut 85. When laid in this way, the submarine cable line 8 has a submarine cable 2 laid so that it has a bend between the exit 852 of one support 85 and the entrance 851 of the next support 85. The submarine cable line 8 in this example has a bend 21 with a bending radius R2 of 50 m or less, which allows 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 line 8 in this example makes it easy to lay the submarine cable 2.

[0053] Second Embodiment [Underwater cable laying method] The method for laying a submarine cable of embodiment 2 will be described with reference to Figure 9. The method for laying a submarine cable of embodiment 2 differs from the method for laying a submarine cable of embodiment 1 in that step B of laying the submarine cable 2 further includes step B5 of excavating the water bottom 90 with an excavator 7 suspended into the water 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 nearly 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 continuously perform the steps of forming a trench 91 by excavating the water bottom 90, placing the submarine cable 2 in the trench 91 at its landing point, and burying the placed submarine cable 2. In other words, in this example, the method for laying a submarine cable can excavate the water bottom 90 to form a trench 91, while placing the submarine cable 2 at its landing point in the formed trench 91, and then 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 [Underwater cable laying method] The method for laying an underwater cable of the third embodiment will be described with reference to Figure 10. The method for laying an underwater cable of the third embodiment differs from the method for laying an underwater cable of 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 at intervals from its upper end to midway 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 midway point to its lower end. In this submarine cable laying method, a portion of the conduit 5 is connected to the second wire 32, making it easy to bring the water entry angle θ of the submarine cable 2 close to 90°. Furthermore, this submarine cable laying method makes it easy to keep 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. [Explanation of symbols]

[0057] 1. Ship, 11. Control room, 12. Cable tank, 13. Brake equipment 14 Guide, 15 First winch, 16 First winch 2 underwater cable, 21 bend 31 first wire, 311 stopper portion, 32 second wire 4 umbilical cables 5: Conduit, 5a: Cylindrical cage member, 50: Main body 501 base part, 502 door part 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 protrusion 55a through hole, 55b connecting portion, 56 first protrusion, 57 second protrusion 581 first protrusion, 581a notch, 582 second protrusion, 582a notch 583 Through hole, 591 Engagement protrusion, 591a Through hole 592 engagement recess, 592a through hole 60 Camera, 61 Acoustic positioning device 611 First transponder, 612 Second transponder, 62 Altimeter 7. Excavator 8 underwater cable tracks, 80 obstacles, 85 supports 851 entrance, 852 exit 90 Bottom, 91 Groove, 92 Surface, 93 Underwater 100 routes 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 steps of laying a submarine cable on the bottom of the water carried by a ship, the method comprising the steps of: The step of laying the underwater cable comprises: forming a trench by excavating the bottom of the water with an excavator suspended underwater from the vessel; paying out the underwater cable from the ship so that the angle of entry of the underwater cable with respect to the water surface is between 80° and 90°; and a step of passing the unwound underwater cable through a conduit suspended from the vessel into the water and placing the cable at a bottom landing point, The step of placing the underwater cable at the bottom landing point includes placing the underwater cable in the trench; the conduit is not connected to the excavator but is connected to a wire extending from the vessel into the water; the excavator is equipped with a sand pump; How to lay underwater cables.

2. 2. The method for laying an underwater cable according to 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. 3. The method for laying an underwater cable according to claim 1, further comprising the step of navigating the ship in a seaway having a turning radius of 50 m or less.

4. An underwater cable is provided in a groove formed in the bottom of the water, The underwater cable is a cable connecting land facilities and surface facilities, land facilities and underwater facilities, surface facilities and surface facilities, underwater facilities and underwater facilities, or surface facilities and underwater facilities, which are arranged at intervals, and has a bend between these facilities with a bending radius of 50 m or less. Underwater cable line.

5. The underwater cable line according to claim 4 , wherein the bend bypasses an obstacle.

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