DEVICE FOR INTRODUCING AN elongated object into a trench

Description

[0001] The present invention relates to an apparatus for inserting an elongate object into a trench in floor of a body of water, and relates particularly, but not exclusively, to an apparatus for burying power cables in the seabed in shallow water.

[0002] Apparatus for burying power cables in the seabed in shallow water close to beaches are known in which location of the cable at the bottom of a trench formed by the apparatus is assisted by water pumps which displace water into the trench, to fluidise debris or slurry in the trench to facilitate movement of the cable to the bottom of the trench. However, such known apparatus suffers from the drawback that the water pumps use considerable amounts of energy, and it is not possible to operate the water pumps when the water has depth insufficient depth to fully submerge the pumps.

[0003] US4787777 discloses a device for producing an underwater channel that uses a flushing device.

[0004] US4037422 discloses an apparatus for entrenching an elongated structure which comprises fluid jets.

[0005] WO99 / 54556 discloses a vehicle for laying an elongate product which comprises jets of water.

[0006] US5639185 is directed to an underwater trenching system with cutting blades.

[0007] Preferred embodiments of the present disclosure seek to overcome one or more of the above disadvantages.

[0008] The invention is as claimed in the claims.

[0009] By providing gas directing means for directing at least one gas into the trench, as set out in claim 1, this provides the advantage that debris can be displaced from the trench in shallower water than is the case with known apparatus, and less energy is consumed than in the case of known apparatus.

[0010] The gas directing means may be adapted to introduce at least one gas into water in a lower portion of the trench.

[0011] This provides the advantage of maximising the effect of lift generated by the gas on debris or slurry in the trench.

[0012] The gas directing means may comprise at least one first conduit having at least one aperture for directing gas therethrough into water in the trench.

[0013] At least one said first conduit may have a plurality of apertures for directing gas therethrough into water in the trench.

[0014] This provides the advantage of assisting in fluidisation of debris or slurry in the trench.

[0015] The gas directing means may comprise at least one second conduit having at least one inlet and at least one outlet, and at least one said first conduit may be adapted to introduce at least one gas into water in said second conduit.

[0016] This provides the advantage of enabling the gas introduced into water in the second conduit to reduce the density of water in the second conduit, thereby causing more dense water in the trench surrounding the second conduit, together with debris, to enter at least one inlet and to displace water and debris out of at least one said outlet.

[0017] At least one said outlet may be adapted to output material out of the trench.

[0018] The gas directing means may be movable between a storage condition and a working condition.

[0019] This provides the advantage of making the apparatus more compact for transport purposes.

[0020] The apparatus may further comprise gas supply means for supplying at least one gas to the gas directing means.

[0021] The gas supply means may comprise air compressor means.

[0022] This provides the advantage of enabling ambient air to be used to displace the debris or slurry in the trench.

[0023] The gas supply means may comprise at least one container of compressed gas.

[0024] This provides the advantage of increasing the range of depth over which the apparatus can operate.

[0025] The apparatus as set out in claim 1 further comprises object engaging means for engaging the object into the trench and the gas directing means are mounted to the object engaging means.

[0026] This provides the advantage of enabling more compact construction of the apparatus when the gas directing means is in its stowed condition.

[0027] A preferred embodiment will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawings, in which:- Figure 1 is a side view of an apparatus embodying the disclosure operating in water of a first depth; Figure 2 is a front view of the apparatus of Figure 1; Figure 3 is a side view of the apparatus of Figure 1 operating in water of a second depth; Figure 4 is a front view of the apparatus of Figure 3; Figure 5 is a side view of the apparatus of Figure 1 operating in water of a third depth; Figure 6 is a front view of the apparatus of Figure 5; Figure 7 is a perspective view of an eductor unit of the apparatus of Figures 1 to 6; Figure 8 is a side view of the eductor unit of Figure 7; and Figure 9 is a part cross-sectional view along the line A-A in Figure 8.

[0028] Referring to Figures 1 to 6, an apparatus 2 for burying a power cable 4 in the seabed 6 in shallow water, for example near to a beach, has a body 8 for supporting the cable 4 and trench cutting means in the form of a chain cutter 10 pivotably mounted to the body 8 for forming a trench 12 in the seabed 6. Moving means in the form of a pair of tracks 14 enables the apparatus 2 to move relative to the seabed 6 to enable the chain cutter 10 to form the trench 12 in the seabed 6. A cable engaging means in the form of a depressor arm 16 is pivotably mounted to a rear part 18 of the body 8 and is adapted to engage the cable 4 to urge the cable 4 to the bottom of the trench 12.

[0029] Gas directing means in the form of an air eduction system 20 is mounted to the depressor arm 16 and comprises a pair of eductor units 22, shown in greater detail in Figures 7 to 9. Each eductor unit 22 is pivotably mounted to a respective side of the depressor arm 16, so that the depressor arm 16 and eductor units 22 can be pivoted between a storage condition and a working condition.

[0030] As shown in greater detail in Figures 7 to 9, each eductor unit 22 has a pair of elongate first conduits 24 which extend from an air inlet 26 at the upper part of the eductor unit 22 to apertures 28 at a lower part of the eductor unit 22, and a second conduit 30 having an inlet 32 at its lower end and an outlet 34 at its upper end. The outlet 34 is arranged to direct material out of the trench 12. Each first conduit 24 also has apertures 36 arranged along its length which act as air jet nozzles to enable fluidisation of debris or slurry in the trench 12 to assist in location of the cable 4 at the bottom of the trench 12 by the depressor arm 16. By introducing compressed air through apertures 28 into the lower end of the second conduit 30, the density of water in the second conduit 30 is reduced, as a result of which more dense water surrounding the second conduit 30 enters the second conduit 30 via inlet 32 to draw debris in the trench 12 into the inlet 32 of the second conduit 30 and displace it out of the trench 12 via the outlet 34 of the second conduit 30.

[0031] A first support member in the form of a lightweight tower 38 extends upwards from the body 8, and a second support member in the form of a floating pontoon 40 is slidably mounted to the tower 38. The floating pontoon 40 is provided with buoyancy blocks 42 to ensure that it floats on the surface of the water and slides along the tower 38 as the position of the surface of the water changes relative to the tower 38. Gas supply means in the form of one or more electrically or hydraulically operable air compressors 44 is mounted to the floating pontoon 40 and receives and compresses ambient air above the surface of the water, and feeds the compressed air via a conduit (not shown) to the air eduction system 20. The floating pontoon 40 can freely move up and down the tower 38 so that it floats on the surface of the water. A remote hydraulic intervention panel is also supported on the floating pontoon 40 to allow functions of the apparatus 2 to be performed from the surface, for example in the event of a failure of the apparatus 2. A tank of compressed air (not shown) can also be mounted directly on the apparatus 2, to enable operation of the apparatus 2 in deeper water.

[0032] It will be appreciated by persons skilled in the art that the above embodiment has been described by way of example only and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the disclosure as defined by the appended claims.

Claims

1. An apparatus (2) for inserting an elongate object (4) into a trench in a floor (6) of a body of water, the apparatus (2) comprising:- a body for supporting an elongate object (4); trench forming means for forming a trench in the floor (6) of the body of water for receiving the elongate object (4); moving means for moving the apparatus (2) relative to the floor (6) of the body of water to enable the trench forming means to form the trench; and gas directing means (22) for directing at least one gas intc water in the trench; characterised in that the apparatus further comprises object engaging means (16) for engaging an object for urging the object into the trench; wherein the gas directing means is mounted to the object engaging means.

2. An apparatus (2) according to claim 1, wherein the gas directing means is adapted to introduce at least one gas into water in a lower portion of the trench.

3. An apparatus (2) according to claim 1 or 2, wherein the gas directing means comprises at least one first conduit (24) having at least one aperture (28) for directing gas therethrough into water in the trench.

4. An apparatus (2) according to claim 3, wherein at least one said first conduit (24) has a plurality of apertures (28) for directing gas therethrough into water in the trench.

5. An apparatus (2) according to claim 3 or 4, wherein the gas directing means comprises at least one second conduit (30) having at least one inlet (32) and at least one outlet (34), and at least one said first conduit (24) is adapted to introduce at least one gas into water in said second conduit (30).

6. An apparatus (2) according to claim 5, wherein at least one said outlet (34) is adapted to output material out of the trench.

7. An apparatus (2) according to any one of the preceding claims, wherein the gas directing means is movable between a storage condition and a working condition.

8. An apparatus (2) according to any one of the preceding claims, further comprising gas supply means for supplying at least one gas to the gas directing means.

9. An apparatus (2) according to claim 8, wherein the gas supply means comprises air compressor means.

10. An apparatus (2) according to claim 8 or 9, wherein the gas supply means comprises at least one container of compressed gas.