Patent Description:
It is known to install a cable in a trench in a sea floor by using a boulder clearing apparatus to clear debris such as boulders from the region where the trench is to be formed, and then to tow a trenching plough by a ship to form a trench having sidewalls inclined relative to each other. After the cable is laid in the trench, a backfill apparatus is used to push spoil displaced by formation of the trench into the trench to bury the cable.

This known arrangement suffers from the disadvantage that several separate apparatus are required which significantly increases costs, and in order to bury a cable to a depth of <NUM> meters, the known cable plough operates at a pulling force of <NUM> tonnes and has a weight of <NUM> tonnes.

European Patent Application <CIT> discloses an apparatus for forming a trench and burying a cable in the trench in which certain parts of the apparatus are interchangeable in order to enable the apparatus to carry out boulder clearing, first pass trenching, full depth trenching and backfilling operations. However, this arrangement suffers from the drawback that a significant number of interchangeable components are required, and the apparatus must be retrieved to the surface in order to enable conversion between at least some of the different modes of the apparatus to take place.

Preferred embodiments of the present invention seek to overcome one or more of the above disadvantages of the prior art.

According to an aspect of the present invention, there is provided an apparatus as defined by claims <NUM>, <NUM> or <NUM>.

The sea floor engaging means may be adjustable between a first mode of said sea floor engaging means, in which the sea floor engaging means engages the sea floor, and a second mode of the sea floor engaging means, in which the sea floor engaging means engages the sea floor adjacent the trench and at at least one wall of the trench.

By providing sea floor engaging means adjustable between a first mode of said sea floor engaging means, in which the sea floor engaging means engages the sea floor, and a second mode of the sea floor engaging means, in which the sea floor engaging means engages the sea floor adjacent the trench and at at least one wall of the trench, this provides the advantage of improved control of the apparatus in the first and second modes of the apparatus, without the necessity of changing the sea floor engaging means. This in turn reduces the cost of components of the apparatus, while also reducing the cost of operation of the apparatus, by reducing the time during which the apparatus need to be recovered to the surface to exchange the sea floor engaging means.

The apparatus may further comprise trench cutting means supported by the body for cutting a trench in a sea floor.

The sea floor engaging means may comprise at least one skid.

At least one said skid may have a first portion for engaging the sea floor in said first and second modes, and a second portion, pivotable relative to said first portion, for engaging the sea floor in said first mode and engaging a wall of the trench in said second mode.

This provides the advantage of providing a lower cost, simplified construction of the skid, which is easy to adjust.

The height of the sea floor engaging means may be adjustable relative to the body.

This provides the advantage of enabling the depth of the trench cutting means to be adjusted.

The apparatus may further comprise material displacing means for displacing material on the sea floor as a result of movement of the apparatus along the trench, wherein the material displacing means is adjustable between a first mode of the material displacing means, in which material removed from the trench is displaced laterally away from the trench, and a second mode of the material displacing means, in which material adjacent the trench is displaced into the trench.

By providing material displacing means for displacing material on the sea floor as a result of movement of the apparatus along the trench, wherein the material displacing means is adjustable between a first mode of the material displacing means, in which material removed from the trench is displaced laterally away from the trench, and a second mode of the material displacing means, in which material adjacent the trench is displaced into the trench, this provides the advantage of enabling separate debris clearing and backfilling operations to be carried out by a single apparatus, thereby reducing component cost, and reducing the cost of operation of the apparatus, by while also reducing the cost of operation of the apparatus, by reducing the time during which the apparatus need to be recovered to the surface to exchange a material displacing means suitable for one of the first and second modes for a material displacing means suitable for the other of the first and second modes.

The material displacing means may comprise a plurality of first material displacement members pivotable between said first and second modes of the material displacement means.

The apparatus may further comprise restraining means for restraining outward pivoting of said first material displacement members relative to the body in said second mode of the material displacing means.

The apparatus may further comprise material displacing means for displacing material on the sea floor as a result of movement of the apparatus along the sea floor, wherein the material displacing means comprises a plurality of first material displacement members mounted to the body, and a plurality of second material displacement members mounted to the first material displacement members in a first mode of the material displacing means such that a lateral width of the apparatus in said first mode of the material displacing means is larger than the lateral with of the apparatus in a second mode of the material displacing means.

By providing material displacing means for displacing material on the sea floor as a result of movement of the apparatus along the sea floor, wherein the material displacing means comprises a plurality of first material displacement members mounted to the body, and a plurality of second material displacement members mounted to the first material displacement members in a first mode of the material displacing means such that a lateral width of the apparatus in said first mode of the material displacing means is larger than the lateral with of the apparatus in a second mode of the material displacing means, this provides the advantage of ensuring more efficient operation of the apparatus by enabling debris clearance and/or backfilling to be carried out over a wider path than is covered by a trenching operation, thereby reducing the tendency of large debris to be inserted into the trench in the backfilling operation. The apparatus also enables the width of the apparatus during deployment from the surface to be reduced, thereby making deployment from and recovery to the surface easier.

The apparatus may further comprise trench cutting means supported by the body for cutting a trench in the sea floor.

At least one said second material displacement member may be pivotably mounted to a respective said first material displacement member.

The material displacing means may further be adapted to displace material on the sea floor, forwards of the sea floor engaging means, laterally outwards of the apparatus.

This provides the advantage of further assisting the debris clearing operation.

The material displacing means may be adapted to displace material by means of at least one third material displacing member mounted to said body.

The third material displacing member may be removable.

A preferred embodiment of the invention will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawings, in which:.

Referring to <FIG>, <FIG> and <FIG>, a universal plough <NUM> for clearing debris such as boulders from a region of a sea floor where a trench is to be formed, and cutting part of the trench in a first pass, is shown in a debris clearing mode of the plough <NUM>. The plough <NUM> has a body <NUM> having a single point lift attachment <NUM> for connection to a lift wire (not shown) for enabling deployment of the plough <NUM> to the sea floor from a surface vessel (not shown), or recovery of the plough <NUM> from the sea floor to the surface vessel. The plough is controlled by means of electrical power supplied by means of an umbilical cable (not shown).

The body <NUM> supports trench cutting means in the form of a plough share <NUM> and a pair of fixed mouldboards <NUM> are located above the plough share <NUM> for displacing soil out of a trench formed by the plough share <NUM> as the plough <NUM> is towed forwards. The body <NUM> also supports sea floor engaging means in the form of a pair of front skids <NUM> pivotably mounted via links <NUM> to a beam <NUM>, which is in turn pivotably mounted to the front of the body <NUM>. Each of the front skids <NUM> can be raised and lowered relative to the body <NUM> by means of a respective hydraulic actuator <NUM>, and has a fixed first part <NUM>, and a second part <NUM> pivotably mounted to the first part <NUM>, the operation of which will be described in greater detail below with reference to <FIG> and <FIG> to <NUM>. A debris clearing member <NUM> is removably attached to the front skids <NUM>, and a towing cable <NUM> is attached to each end of the beam <NUM> to enable towing of the plough <NUM>.

Material displacing means includes first material displacement members in the form of a pair of pivotable mouldboards <NUM> pivotably mounted to the body <NUM> to the rear of the plough share <NUM> and the fixed mouldboards <NUM>, and second material displacement members in the form of a pair of mouldboard extensions <NUM> pivotably mounted to the pivotable mouldboards <NUM>. The pivotable mouldboards <NUM> are pivotable relative to the body <NUM> by means of hydraulic actuators <NUM>, and the mouldboard extensions <NUM> are pivotable relative to the pivotable mouldboards <NUM> by means of hydraulic actuators <NUM> (<FIG>). The body <NUM> is further supported on the sea floor by a pair of rear skids <NUM> (<FIG>). A pair of pivotable thrusters <NUM>, <NUM> enable control of the orientation of the plough <NUM> while it is supported by the lift wire before coming into contact with the sea bed.

The operation of the plough <NUM> in a debris clearing and first pass trenching mode will now be described.

Referring to <FIG>, in a launch/recovery configuration, the front skids <NUM> of the plough <NUM>, together with the debris clearing member <NUM>, are pivoted relative to the body <NUM> into a generally vertical orientation by means of hydraulic actuators <NUM> connected between the front skids <NUM> and the links <NUM>, to reduce the overall length of the plough <NUM>. The lateral width of the plough <NUM> is also reduced by pivoting the mouldboard extensions <NUM> by means of hydraulic actuators <NUM> to that the mouldboard extensions are arranged in an orientation 30A (<FIG>) generally parallel to a longitudinal axis <NUM> of the plough <NUM>.

The plough <NUM> is then lowered from the surface vessel to the seabed, and as it approaches the seabed, the front skids <NUM> together with debris clearing member <NUM> are lowered to a generally horizontal orientation as shown in <FIG> by means of the hydraulic actuators <NUM>. The mouldboard extensions <NUM> are also pivoted relative to the pivotable mouldboards <NUM> by means of hydraulic actuators <NUM> to take up the orientation 30B shown in <FIG>, so that a front surface <NUM> of each pivotable mouldboard <NUM> generally forms a continuous surface with a front surface <NUM> of the corresponding mouldboard extension <NUM>. The pivotable mouldboards are pivoted relative to the body <NUM> by means of hydraulic actuators <NUM> so that the pivotable mouldboards <NUM> and mouldboard extensions <NUM> are arranged at an angle α to the longitudinal axis <NUM>, as shown in <FIG>.

When the plough <NUM>, now in the configuration shown in <FIG>, rests on seabed <NUM>, the front skids <NUM> and debris clearing member <NUM> are raised relative to the plough share <NUM> by means of hydraulic actuators <NUM>, so that the plough share <NUM> penetrates the seabed <NUM> when the plough <NUM> is towed forwards, as shown in <FIG>.

The surface vessel (not shown) then tows the plough <NUM> via towing cable <NUM>, and debris located forwards of the front skids <NUM> is displaced out of the path of the front skids <NUM> by the debris clearing member <NUM>. In addition, debris is displaced laterally of the plough <NUM> by pivotable mouldboards <NUM> and mouldboard extensions <NUM> to form first debris heaps <NUM> on both sides of the plough <NUM>.

On completion of the first pass cutting of the trench by the plough <NUM> in the configuration shown in <FIG>, the plough <NUM> is raised from the seabed <NUM>, returned to its launch/recovery configuration shown in <FIG>, and is then recovered to the surface vessel where the debris clearing member <NUM> is removed from the front skids <NUM>. The mouldboard extensions <NUM> are either removed from the pivotable mouldboards <NUM> or are pivoted relative to the pivotable mouldboards <NUM> by means of hydraulic actuators <NUM> so that they are located behind the pivotable mouldboards <NUM>. The plough is then in the configuration shown in <FIG> and is returned to the seabed <NUM> to the trench formed in the first pass trenching operation described above.

As the plough approaches the seabed <NUM>, the front skids <NUM> are rotated to a generally horizontal orientation by means of the hydraulic actuators <NUM> to provide the configuration shown in <FIG>. The front skids <NUM> are then raised relative to the plough share <NUM> by means of hydraulic actuators <NUM> so that the plough share <NUM> can penetrate the seabed <NUM> to a greater depth than in the configuration shown in <FIG> to enable the plough <NUM> to operate in its full depth trenching mode as shown in <FIG> and <FIG>.

The operation of the plough <NUM> in a full depth trenching mode will now be described.

The plough <NUM> is towed by the surface vessel so that second pass cutting of the trench is carried out in which the plough <NUM> share cuts the trench to its full depth. Soil displaced from the trench by the plough share <NUM> is displaced laterally away from the trench by fixed mouldboards <NUM> and then by pivotable mouldboards <NUM> to form second debris heaps <NUM> (<FIG>) on both sides of the plough <NUM>. Because the mouldboard extensions <NUM> do not contribute to material displacement from the trench in the full depth trenching mode, the second debris heaps <NUM> are located laterally inwards of the first debris heaps <NUM>. At the same time, a cable (not shown) to be installed in the trench is guided into the trench via guide wheels <NUM>, <NUM>.

On completion of the full depth trenching process, the plough <NUM> is returned to its launch/recovery configuration as shown in <FIG> and then recovered to the surface vessel for reattachment of the mouldboard extensions <NUM>, if they have been removed for the full depth trenching mode, and for reconfiguration of the plough <NUM> to its backfilling mode as shown in <FIG>. The mouldboard extensions <NUM> are arranged so that the front surface <NUM> of each mouldboard extension <NUM> forms a generally continuous surface with the front surface <NUM> of the corresponding pivotable mouldboard <NUM>, and the pivotable mouldboards <NUM> are pivoted forwards of the body <NUM> by means of hydraulic actuators <NUM> so that the pivotable mouldboards <NUM> and mouldboard extensions <NUM> are arranged at an angle β to the longitudinal axis <NUM> of the plough <NUM>, to take up the orientation 28A as shown in <FIG>. The angle β shown in <FIG> is smaller than the angle α shown in <FIG>. Restraining members <NUM> prevent the pivotable mouldboards <NUM> from pivoting outwards relative to the body <NUM> beyond the orientation 28B shown in <FIG>.

The operation of the plough <NUM> in a backfilling mode will now be described.

The front skids <NUM> are pivoted to a generally vertical orientation as shown in <FIG> by means of hydraulic actuators <NUM> to place the plough in its launch/recovery configuration. The plough <NUM> is then returned to the seabed in its launch/recovery configuration as shown in <FIG>, and shortly before arrival at the seabed <NUM>, the front skids <NUM> are lowered to a generally horizontal orientation by means of the hydraulic actuators <NUM> to bring the plough <NUM> into a landing configuration. The second parts <NUM> of the front skids <NUM> are then pivoted relative to the first parts <NUM> to bring the front skids <NUM> into the configuration shown in <FIG>. The front skids <NUM> are then located in the top of the trench so that the first parts <NUM> engage the seabed <NUM> adjacent the trench and the second parts <NUM> engage the upper parts of the sidewalls of the trench to more reliably locate the skids <NUM> in engagement with the trench as the plough <NUM> is towed forwards.

The front skids <NUM> are then raised relative to the body <NUM> by means of hydraulic actuators <NUM> to bring the plough into the configuration shown in <FIG> so that the plough share <NUM> does not enter the trench to its full depth. The plough <NUM>, supported by the front skids <NUM> and rear skids <NUM>, is then towed along the trench containing the cable and the pivotable mouldboards <NUM> together with mouldboard extensions <NUM> displace relatively finer soil located in the second debris heaps <NUM> (<FIG>) into the trench to bury the cable in the trench, while leaving the first debris heaps <NUM>, containing relatively coarser soil, generally undisturbed, since the mouldboard extensions <NUM> extend laterally outwards from the plough <NUM> to a lesser extent in the backfilling mode of <FIG> than in the debris clearing mode of <FIG>, because the angle β is smaller than the angle α.

Claim 1:
An apparatus (<NUM>) for forming a trench in a sea floor and/or displacing material on the sea floor, the apparatus comprising:-
a body (<NUM>); and
sea floor engaging means mounted to the body for engaging the sea floor and supporting the body;
wherein the sea floor engaging means is adjustable between a first mode of said sea floor engaging means, in which the sea floor engaging means engages the sea floor, and a second mode of the sea floor engaging means, in which the sea floor engaging means engages the sea floor adjacent the trench and at at least one wall of the trench wherein the apparatus (<NUM>) is a plough (<NUM>) comprising a debris clearing member (<NUM>),
and wherein the sea floor engaging means comprises skids (<NUM>, <NUM>), wherein the front skids (<NUM>) of the plough (<NUM>), together with the debris clearing member (<NUM>), are pivotable relative to the body (<NUM>), by means of hydraulic actuators (<NUM>), between a generally horizontal orientation and a generally vertical orientation corresponding to a launch/recovery configuration in which the overall length of the apparatus (<NUM>) is reduced.