JPS5922443B2 - How to lay underwater cable - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for laying an underwater cable, and particularly to a method for laying a cable on the underwater bottom using a towing method.

In recent years, underwater cables have become larger, and even when laid on the seabed at a depth of about 300 m, large and heavy cables are often installed. It is desired that the cable be laid in a straight line without meandering.

However, conventionally, for example, as shown in Fig. 1, the tugboat 1
The cable 3 is simply fed out from a sheave 2 installed at the stern of the laying ship 1 which is being towed by a cable or an anchor, etc., while controlling the tension with a brake device 4 according to the speed of the laying ship 1. The tension of the cable 3 above, that is, the horizontal tension To at the bottom contact point, and the installation tension T, which approximates the sum of the weight W of the unit length of the cable 3 multiplied by the water depth, have a relationship of T'ThTo + wh. , this laying tension T is detected by a tension meter 5, and a water entry angle detector 6
By detecting the water entry angle θ of the cable 3 using However, in reality, due to the influence of tidal currents, loops and meandering tend to occur in the installed cable, so if To is set too large, it will not follow the undulations of the water bottom and will cause so-called bridge over. Therefore, vibration fatigue due to tidal currents is likely to occur in the cable at the location where this bridge over occurs.

For this reason, conventionally, as shown in FIG. 2, a towing wire 11 and A plurality of control rings 13 as shown in Fig. 3 are arranged along the control wire 12, and the cable 3 is guided by the control ring 13 and then entered into a burial device and buried in the excavated trench. A method of laying cables has been proposed that fixes the cables to the ground and eliminates the need to control the cable tension on board the ship.

In the case of such a conventional underwater cable installation method, the control rings 13 fixed to the traction wire 11 are aligned by the control wire 12, and the cable 3 is guided by the alignment guide rings 13 to the buried vessel 10. Since the cable is continuously supplied and laid on the water bottom one by one, if the shelf of the burial machine 10 can excavate the water bottom even slightly, the cable 3 can be laid on the water bottom without loops or meandering even under the influence of tidal currents. This means that it can be buried and laid.

However, it is necessary to adjust the number of control rings 13 arranged in accordance with changes in water depth, and in this case, the installation speed must be temporarily lowered or the ship must be stopped temporarily to adjust the number of control rings 13 arranged. Work hours are regulated on cross-country routes, and on routes with fast currents, the cable-laying vessel may be swept away by the current and deviate from the planned cable-laying route.

In addition, the structure that supports the entire length of the cable from the seabed to the laying ship with the control ring is limited to water depths of up to approximately 200 meters; at deeper water depths, the control ring becomes larger and heavier, causing problems such as becoming impractical. There are drawbacks.

The present invention is a novel invention that improves the conventional drawbacks as described above, and its purpose is to provide a method that can reliably and easily lay cables in a straight line along the undulations of the water bottom with simple operations. It is about providing.

Examples will be described in detail below. FIG. 4 is a detailed explanatory diagram of the present invention, and the same reference numerals as in FIGS. 1 and 2 indicate the same parts.

The control rings 13 are stacked along the traction wire 11 and the control wire 12 as shown in the figure, but the number of control rings 13 arranged is determined by a submerged sliding device (a submerged sliding device is a device consisting of a simple ring, frame, pipe, etc.). (including) 20 to a predetermined length, for example, approximately the average water depth of the laying sea area, and the traction wire 11 is connected to a winch 21 of the laying ship 1 so that the length in the water can be adjusted.

The cable 3 is fed out from the sheave 2 at the stern of the laying ship 1 while controlling the tension with a brake device 4. After the cable 3 that has been fed out reaches the end of the guide ring 13, it is fed out by the rail guide ring 13. It is guided to the bottom sliding device 20 and laid on the bottom of the water as the bottom sliding device 20 moves.

The underwater sliding device 20 includes an elevation angle detector 22 and a water depth detector 23
is provided so that the elevation angle α and the water depth as seen from the bottom sliding device 20 can be detected on the laying ship 1.

Furthermore, it is preferable to provide an underwater television camera 23 so as to monitor the guiding condition of the cable 3, and further to provide a rolling pitching detector 24 and a traveling distance detector 25.

As described above, a plurality of control rings 13 are installed at a predetermined length from the bottom sliding device 20, and the elevation angle α of the traction wire 11 viewed from the bottom sliding device 20 is within a certain range, for example, 20 to 40 degrees.
By adjusting the length of the traction wire 11 so that it falls within the range of , when the water depth is deep, the guiding ring 13 will not be arranged along the entire length between the laying ship 1 and the bottom sliding device 20. Even if the cable 3 is affected by tidal currents etc. in the part without the guide ring 13, it is guided to the bottom sliding device 20 in a state where the influence of the current etc. is blocked by the part with the guide ring 13. , and then passes through the inside of the bottom sliding device 20, comes out almost horizontally in contact with the bottom, and is laid.
No loops or meandering occur.

Moreover, since the cable tension at the underwater contact point is minimized, it is possible to prevent bridge over from occurring.

Furthermore, since the underwater sliding device 20 does not have a shelf like a buried vessel, the underwater sliding device 20 can be towed even in a hard rocky area where the geology of the underwater bottom is not suitable for excavation.

In addition, by adjusting the length of the tow wire 11 according to changes in water depth, there is no need to adjust the number of parapet guide rings arranged, and therefore there is no need to temporarily reduce the laying speed or temporarily stop the ship. Therefore, even if the work time is restricted on a route that crosses a channel, the installation work can be easily accomplished, and even on routes with fast currents, the installation work is speeded up, so there are no problems such as deviating from the planned installation route. It becomes something that does not occur.

As explained above, according to the present invention, it is only necessary to adjust the length of the traction wire according to the water depth, and there is no need to adjust the number of arrayed tank guide rings. Not only is it much shorter than the guide ring system, but the elevation angle of the towing wire is always within a certain range, so the cable lands diagonally on the seabed and does not form a loop, and the cable passes through the rail guide ring just before landing. This eliminates the occurrence of loops, which has the advantage of eliminating loops and kinks, which are the most important things to avoid in cables.

[Brief explanation of the drawing]

FIGS. 1 and 2 are explanatory diagrams of a conventional method of laying a submarine cable, FIG. 3 is a diagram of a working guide ring, and FIG. 4 is a diagram of a method of laying a submarine cable according to an embodiment of the present invention. be. 1 is a laying ship, 2 is a sheave, 3 is a cable, 4 is a brake device, 5 is a tension detector, 6 is an entry angle detector, 11 is a traction wire, 12 is a control wire, 13 is a control ring, 2
0 is an underwater sliding device, 21 is a winch, 22 is an elevation angle detector, and 23 is an underwater television camera.

Claims (1)

[Claims] 1. A plurality of rail guide rings are arranged to a predetermined length from the bottom sliding device along the traction wire and control wire between the laying ship and the bottom sliding device towed by the laying ship, and the bottom sliding device is towed by the laying ship. In order to keep the angle of elevation of the tow wire within a certain range when viewed from the device, the length of the underwater portion of the tow wire to which the control ring is not attached is adjusted to the water depth and ship speed without changing the number of guide rings arranged. A method for laying an underwater cable, which is characterized by adjusting accordingly.