The vehicle 1 further comprises a cutter assembly 8 for forming a trench in the seabed, which in turn comprises a plurality of rotatable cutters 9, arranged substantially side by side (in a radial direction) and staggered (in axial direction), and is pivotable about an axis extending substantially transversely to the tracks 4 and hence to the direction of movement of the vehicle 1. The cutter assembly 8 is further connected to the frame 3 by means of a pair of hydraulic cylinders 10, with which the cutter assembly 8 can be moved between an extended position (
Claws 13 for grasping and guiding the cable 2 are mounted on the bottom side of the frame 3 and in between the tracks 4 (
A cable guide 15 is releasably connected to the vehicle 1 on or near its aft end. As shown in
At its bottom side, the guide 15 is provided with a keel 23, preferably having a width less than or equal to the width of the cutters 9. Also, the guide 15 comprises a locating aid, such as a beacon, transponder or reflector, preferably placed inside one of the tubes 16.
Finally, the vehicle 1 comprises an arm 24 mounted on the frame 3, which is extendable alongside and over the guide 15 and which comprises on its distal end a claw 25, similar to the claws 13 on the lower side of the frame 3.
Installing a cable by means the vehicle 1 and guide 15 according to the present invention may comprise the steps of:
lowering the vehicle 1 carrying the guide 15 from a surface vessel, such as a sub-sea support vessel or a cable laying vessel, and positioning the vehicle 1, by means of cables or thrusters (not shown) with the opened claws 13 over the pre-laid cable 2,
closing the claws 13, thus grasping and slightly lifting the cable 2,
activating and lowering the cutters 9,
moving the vehicle 1 along the cable 2 to form the beginning of a trench and positioning, by means of the parallelogram 19 and the arm 20, the cable guide 15 with respect to the trench and placing the keel 23 in the trench, and
grasping the cable 2 by means of the arm 24 and lifting it into the guide 15.
Trenching is performed by continuously moving the vehicle 1 along the cable 2, forming a trench and sliding the cable 2 laterally over the seabed and into the trench, all simultaneously. The keel 23 under the guide 15 facilitates (passively) maintaining proper alignment with the trench. If required, the guide 15 may be positioned actively by means of the parallelogram 19 and the arm 20.
If the installation of the cable 2 must be interrupted, e.g. because of weather conditions or a malfunction of the vehicle 1 or the surface vessel from which the vehicle 1 is operated, the vehicle 1 according to the present invention is disconnected from the guide 15 and hoisted. The guide 15 is left in place, maintaining the cable 2 in its position and stabilising the trench. When the weather has improved or the malfunction has been repaired, installation is resumed by lowering the vehicle 1 to the location of the guide 15 and over the cable 2, reconnecting the vehicle 1 and the guide 15, grasping the cable 2 by means of the guide claws 13, following the trench in reverse direction thus lifting a section of the cable from the trench, activating and lowering the cutters 9, and resuming installation.
The vehicle and guide according to the present invention facilitate installing a cable in a ground formation, in particular in a seabed, as well as interrupting installation. As the guide comprises substantially no components that must be coupled to an external power source, reconnecting the vehicle and the guide is relatively straightforward.
The invention is not restricted to the above-described embodiments, which can be varied in a number of ways within the scope of the claims. For instance, the vehicle and/or the guide may be provided with means to actively urge the cable into the trench. Also, the cutter assembly may comprise or consist of jets.
Number | Date | Country | Kind |
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06113314.6 | Apr 2006 | EP | regional |