NL2033202B1

NL2033202B1 - Vessel with steerable cable laying device

Info

Publication number: NL2033202B1
Application number: NL2033202A
Authority: NL
Inventors: Van Bruggen Richard; Roelf Van Baalen Lennart
Original assignee: N Sea Group B V
Priority date: 2022-09-30
Filing date: 2022-09-30
Publication date: 2024-04-08

Abstract

Cable lay vessel for laying a cable in a seabed comprising a hull and a cable laying and/or trenching tool, wherein the cable laying and/or trenching tool comprises an elongate boom 5 section that extends between a lower end and an upper end; and that is rotatably mounted to the hull at a distance from the lower end; and a tool section attached to the lower end to be moved over the seabed during movement of the vessel to perform cable laying and/or trenching operations in the seabed, wherein the boom section is mounted rotatably around two axes substantially transverse to a movement direction defined by the hull, and that the 10 vessel comprises a sag controller, arranged between the cable laying and/or trenching tool and the hull and configured to control sinking of the tool section into the seabed by reducing weight load of the tool on the sea bed during operations; and a swing controller, arranged between the cable laying and/or trenching tool and the hull and configured to control sideways movement of the tool section during operations with respect to the hull. 15 + fig 1A

Description

P35774NL00/MBA

Title: Vessel with steerable cable laying device

Field of the invention

The present invention relates to a cable lay vessel for laying a cable in a seabed, comprising a hull and a cable laying and/or trenching tool. The present invention further provides a method for laying a cable in a seabed.

Background of the invention

At present, various types of cable laying tools are known, such as water jets or vertical injectors, plows, cutter heads, scoops or clam shell diggers. These tools are usually either self-propelled or pulled over the seabed like a sled by means of a cable.

However, currently known methods create a relatively wide disturbance of the soil, i.e. the seabed, that may affect the ecology of the waterway. In order to preserve the ecology, it is desirable to keep the width of a strip that is dug in as narrow as possible, i.e. to reduce the area of the tool section that touches the soil.

US7637696 discloses an underwater trenching system for evacuating sediment with limited disturbance of the soil. The system comprises an elongate boom section that is mounted on a side of a barge and that is propelled by the barge along a waterway. On a lower end of the boom, a trenching unit is provided comprising jets that blast away sediment from the soil to bury a pre-laid pipeline.

The trenching tool is lowered on the pipeline to be buried, and remains aligned thereon by means of roller guides that roll along the pipe. A burial depth can be selected by mounting height of the rollers prior to lowering the trenching unit into water, such that a deeper trench is dug when the tool is allowed to sink further along the pipe.

A disadvantage of the known tool is that is that it relies on the pipe for height adjustment of the trench. This poses a relatively large load on the underlying surface, i.e. on the pipe. Further, horizontal alignment of the tool requires relatively precise positioning of the barge with respect to the pipe. Misalignment and/or movements of the barge, for example due to waves or currents, causes a horizontal load on the pipe. Due to the vertical and horizontal loads, the tool is not suitable for burying more sensitive pipelines and/or cables, such as power cables, as these loads may induce cable failure.

A further disadvantage of all currently known cable laying tools is that they are relatively dependent on the conditions of the soil. The tool may not or limitedly be suitable for seabeds having varying soil conditions. For example, a lower speed of the barge is necessary when a denser soil, e.g. clay instead of sand, is present, reducing operational efficiency.

Also, in a relatively soft seabed, the vertical position of the tool may be reduced due to sinking of the tool into the seabed, whereas in a harder seabed, a less deep trench may result. The inventor acknowledges that to reduce sinking of the tool into the seabed, support surfaces for supporting the cable laying tool on the seabed may conventionally be provided, but such surfaces would increase the area of the tool section touching the seabed.

In particular, none of the currently known tools are suitable for laying cables in seabeds consisting of a layered soil structure, such as a seabed with a hard lower layer and a relatively soft upper layer. As a result, it may be necessary to perform multiple passes to get the trench to the desired depth along the whole trajectory of the cable or pipeline.

Object of the invention

It is therefore an object of the invention to overcome the above-mentioned drawbacks, or at least to provide an alternative cable lay vessel.

Detailed description

The present invention provides, according to a first aspect, a cable lay vessel for laying a cable in a seabed comprising a hull and a cable laying and/or trenching tool, wherein the cable laying and/or trenching tool comprises: - an elongate boom section that extends between a lower end and an upper end; and that is rotatably mounted to the hull at a distance from the lower end; and - a tool section attached to the lower end to be moved over the seabed during movement of the vessel to perform cable laying and/or trenching operations in the seabed, wherein the boom section is mounted rotatably around two axes substantially transverse, e.g. perpendicular, to a movement direction defined by the vessel. The vessel comprises a sag controller, arranged between the cable laying and/or trenching tool and the hull and configured to control sinking of the tool section into the seabed by reducing weight load of the tool section on the sea bed during operations; and a swing controller, arranged between the cable laying and/or trenching tool and the hull and configured to control sideways movement of the tool during operations with respect to the hull.

The present cable lay vessel is able to handle a cable or pipeline relatively carefully by reducing the loads on a cable to be laid, as the boom section is rotatable around two axes, allowing movement of the tool with respect to the hull. Further, movement of the tool is controlled with respect to the hull, instead of relying on the pipeline or cable to control movement of the tool.

By controlling movement of the tool during operations with respect to the hull, movement dependency on soil conditions is reduced, such that sinking of the tool into the seabed and unevenness of the trench depth may be avoided. Therewith, the cable lay vessel may be used in varying soil conditions, such as with layered soil structures.

As an existing pipe or cable is not required for alignment of the tool, the invention may provide for a cable lay vessel suitable for laying sensitive pipelines and cables, for example, power cables, telecom cables, electrical cables, optic cables, flowlines and/or umbilicals.

Further, the tool is rotatably mounted to the hull via the boom section over two axes transverse to the movement direction, for example perpendicular to the movement direction.

This way, the tool may be moved independently of sideways and upwards movements of the hull, independent of wave motion. The movement direction may be determined by the hull of the vessel. The movement direction may be a main direction of motion of the vessel, i.e. to follow a desired trajectory and may, e.g. when moving forward in a straight line, be aligned with the longitudinal axis of the hull. The tool may be rotatably mounted over a substantially vertical axis, e.g. a vertical axis, and a substantially horizontal axis, e.g. a horizontal axis, or a combination thereof.

The tool may serve various purposes for laying a cable and/or pipeline, for example to dig a trench in the seabed and/or to lay a cable in the seabed. Generally, the tool section is moved over the seabed to perform operations in the seabed. By having an elongate boom section, the tool section may be moved over the seabed relatively precisely compared to tool moved by towing cables. Further, the tool section may be partially suspended in the elongate boom section to reduce weight load of the tool section on the seabed.

The tool section may for example comprise a chain cutter, a wheel cutter, a suction cutter head and/or a high pressure water cutter.

The tool section may, with the elongate boom section, be movable between at least one operation position, in which the tool section is arranged to perform operations in the seabed, e.g. on the seabed, and a storage position, in which the tool section is positioned higher compared to the operation position, e.g. above the water level.

The elongate boom section is rotatably mounted to the hull at a distance from the lower end, for example nearby the upper end, e.g. either directly via a hinge positioned on the hull or by means of a hinge positioned on a support positioned sideways with respect to the hull, and forms the support for the cable laying and/or trenching tool. For example, a single hinge may be provided that is rotatable around two axis, or two hinges that are rotatable around a single axis but are attached to each other at an angle. The rotatable mount may, in use, be arranged above the water level, but may alternatively be protrude into the water.

The tool section is attached to the lower end, e.g. either integrally or by means of one or more hinges, and may be partially suspended in the elongate boom section. The elongate boom section may transfer movement of the vessel in the movement direction towards the tool section. The elongate boom section may be arranged to transfer both pulling and pushing forces between the hull and the tool section. For example, the boom section may be relatively stiff and may for example be embodied as a tube. The elongate boom section may comprise a metallic material, for example steel.

During operations, the lower end is positioned lower than the upper end, for example near the seabed, whereas the upper end may be positioned near or above the hull.

Between the cable laying and/or trenching tool and the hull, a sag controller and a swing controller are arranged, which form at least one additional connection between the tool and the hull. The sag controller and the swing controller may both be connected at the boom section and/or at the tool section, or at mutually different connection locations. The sag controller and the swing controller allow for movement of the boom section, but may limit and/or damp movement of the boom section around the two axes, for example limit within predetermined boundaries. The sag controller and the swing controller may comprise actuators having a variable length, for example as adjustable tension cables arranged between the tool and the hull.

The swing controller may be connected to the hull at a swing controller connection, and the sag controller may be connected to the hull at a sag controller connection. The swing controller connection and the sag controller connection may be spaced apart over a distance, e.g. a distance in the movement direction of the vessel.

In case a relatively soft soil is encountered, the tool section may remain at least partially suspended in the elongate boom section, whereby sinking of the tool is controlled by the sag controller. Further, when the movement direction of the vessel changes, the boom section may first rotate with respect to the hull, such that small changes, for example due to waves, do not directly influence an operation direction of the tool section. However, larger changes in the movement direction may also be transferred to the tool section in order to follow a trajectory of the vessel.

As a result, the tool may be moved over the seabed like a self-propelled or pulled tool, while the tool remains attached to the hull via the boom section to support the tool section, such that an area of a support surface of the tool section on the seabed, pipe and/or cable can be reduced. The support surface may for example be shaped relatively narrow, for example as a ski.

The sag controller may be configured to reduce the downward pressure exerted by the tool section during operations of the tool section. The sag controller may suspend the tool section and/or the boom section to the hull. The downward pressure exerted by the tool section may be adjustable. In particular, sag controller may be configured to exert an upward tension to the boom section and/or the tool section, for example such that at least 50%, such as atleast 75% of the weight of the tool is carried by the sag controller. For example, the sag controller may be configured to reduce a downward pressure exerted by the tool section on the seabed, pipeline and/or cable to at most 50%, such as at most 25% of the weight of the tool section. By having a small downward pressure, the tool section may remain on the seabed, while sinking of the tool into the seabed may be avoided.

The sag controller may comprise a crane or another lifting device, for example a land crane or a-frame, arranged to lift the tool during operations on the seabed. The lifting device 5 may comprise a lifting wire attached to the tool section, for example the tool section may comprise a lifting eye attached to the lifting wire.

The sag controller may be arranged to hold the tool section at a desired trench depth.

The vessel may comprise a depth sensor arranged to measure a depth of the seabed and/or a depth mapper arranged to provide a depth of the seabed, wherein the sag controller is configured to determine the desired trench depth in dependence on the measured and/or provided seabed depth. Additionally or alternatively, the sag controller may be configured to hold the tool section at a continuous predetermined tension and, for example, comprise a continuous tension (CT) winch.

The swing controller may be configured to reduce the sideways movement of the tool section during operations of the tool section. The swing controller may pull and/or push the tool sideways with respect to the movement direction.

The swing controller may be arranged to keep the tool section at a predetermined distance to the hull perpendicular to the movement direction. Additionally or alternatively, the swing controller may be configured to hold the tool section at a continuous predetermined tension and, for example, comprise a continuous tension (CT) winch.

The swing controller may comprise a winch or other pulling device, arranged to pull the tool section during operations. The pulling device may comprise a tension cable attached to the tool section, for example the tool section may comprise a pulling eye attached to the tension cable.

Additionally or alternatively, the swing controller may comprise a steering mechanism configured to control sideways movement of the tool. The steering mechanism may be an active steering mechanism configured to actively influence movement of the tool section, i.e. by inducing a swing movement thereof, or a passive steering mechanism configured to passively influence movement of the tool section, i.e. by damping a swing movement thereof.

The swing controller may for example be configured to reduce the sideways movement of the tool section to at most 45 degrees, for example at most 25 degrees, with respect to the movement direction of the hull.

The elongate boom section may be mounted to the hull via the one or more hinges at a fixed position on the boom section, or in a longitudinally movably fashion, such that the longitudinal position of the elongate boom with respect to the rotatable mount is variable, e.g. a distance between the hull mount and the lower end of the boom section is variable.

Additionally or alternatively, the tool section may be attached to be movable along a longitudinal direction of the boom section and/or the elongate boom section may be telescopically. The swing and/or sag controller may be configured to vary a length of the boom section between the hull mount and the lower end.

In an embodiment, the tool section is rotatably mounted to the elongate boom section to be rotatable around a substantially vertical axis. This way, the tool section is movable with respect to the elongate boom section and may rotate in response to changes in the movement directions, i.e. when the hull follows a curved trajectory. This way, the tool section may more precisely follow the curved trajectory and sideways forces on the tool section and elongate boom section during curves are reduced.

In an embodiment, the swing controller comprises a steering mechanism to control sideways movement of the tool section by influencing rotation of the tool section with respect to the elongate boom section around the substantially vertical axis.

The steering mechanism may be arranged around the substantially vertical axis to control rotation of the tool section, for example on the substantially vertical axis. The steering mechanism may control sideways movement by rotating the entire tool section or a part thereof, such that movement of the hull in the movement direction causes a sideways movement of the tool section. The steering mechanism may be configured to rotate the tool section in the seabed.

The steering mechanism may comprise an actuator, for example an hydraulic actuator, such as an hydraulic cylinder or two hydraulic cylinders positioned opposite to each other around the hinge. Alternatively, pneumatic or electric actuators may be provided, such as an pneumatic cylinder or electric motor.

By actively steering the rotation of the tool section with respect to the elongate boom section, a trajectory followed by the tool section on the seabed may be steered more precisely. This allows to lay a cable according to a desired trajectory relatively precisely, even when no pipeline or cable is already present at the seabed for alignment of the tool.

The steering mechanism may comprise a damper, for example an hydraulic damper such as an hydraulic cylinder or two hydraulic cylinders positioned opposite to each other around the hinge. Alternatively, pneumatic or electric dampers may be provided, such as an pneumatic cylinder or electric motor.

By passively steering the rotation of the tool section with respect to the elongate boom section, a trajectory followed by the tool section on the seabed may be relatively curved while limiting disturbances due to waves or varying soil hardness that could result in rotation of the tool section around the substantially vertical axis.

In an embodiment, the tool section is rotatably mounted to the elongate boom section to be rotatable around a substantially horizontal axis. As such, movements of the elongate boom section due to movement of the hull, e.g. due to wave motion, may occur while the tool section remains on the seabed. This way, the tool section can relatively precisely lay a cable and/or dig a trench at a desired depth. Furthermore, the tool section may more precisely follow the shape of the seabed by rotating around a horizontal axis.

In an embodiment, the vessel comprises a skewing mechanism arranged at the tool section, for example between the tool section and the boom section and/or between the tool section and the hull, wherein the skewing mechanism is configured to control a skew of the tool section around the substantially horizontal axis. For certain tools, a specific skew with respect to the seabed may be advantageous for efficient cable laying and/or trenching.

The skewing mechanism may be arranged around the substantially horizontal axis to control rotation of the tool section, for example on the substantially horizontal axis. The skewing mechanism may control skewing movement by rotating the entire tool section or a part thereof, such that movement of the hull in the movement direction causes a desired skew of the tool section of the part thereof. The steering mechanism may be configured to skew the tool section in the seabed.

The skewing mechanism may comprise an actuator, for example an hydraulic actuator, such as an hydraulic cylinder or two hydraulic cylinders positioned opposite to each other around the hinge. Alternatively, pneumatic or electric actuators may be provided, such as an pneumatic cylinder or electric motor.

In an embodiment, the skewing mechanism comprises a tensioning element arranged between the tool section and the swing controller, and the swing controller is configured to adapt a length of the tensioning element in dependence of the skew of the tool section. This way, the skew of the tool section may be determined by the swing controller by keeping the tensioning element at a length for pulling the tool section over the seabed.

In an embodiment, the boom section is rotatably mounted to the hull via a longitudinal guide that is rotatable with respect to the hull, and the longitudinal guide allows movement of the boom section in a longitudinal direction of the boom section. By having a boom section that is movable in a longitudinal direction thereof, wave motion may be accommodated by movement in the longitudinal direction of the boom section. This way, the tool section may remain on the seabed during motion of the hull, for example roll and pitch motion due to waves. The longitudinal guide may for example comprise a sleeve that at least partially surrounds the boom section, wherein the sleeve is rotatably mounted to the hull.

In particular, roll motion of the hull could result in a downward force exerted via the boom section that pushes the tool section into the seabed, when the boom section is not mounted via a longitudinal guide. Such a force potentially damages the tool section and could result in the tool getting stuck in the seabed. By having a longitudinal guide, the tool section may remain on the seabed, while the hull may move along the boom section, e.g. during waves.

In a further embodiment, the longitudinal guide comprises a longitudinal controller configured to control longitudinal movement of the boom section with respect to the longitudinal guide. The longitudinal controller may be configured to damp motion of the boom section along the longitudinal direction. This way, relatively large motion of the hull in the movement direction may be transferred to the tool section, whereas smaller motions, e.g. waves, may be absorbed by longitudinal motion of the boom section.

In an embodiment, the tool section comprises a vertical injector and/or a soil cutter, and the sag controller is configured to control sinking of the vertical injector and/or the soil cutter into the seabed. A vertical injector and a soil cutter, such as a chain cutter, are found to be very suitable for laying a cable using the vessel or method according to the invention.

Further, a vertical injector and soil cutter may require feed lines, such as high- pressure water lines. By having an elongate boom section, feed lines may be integrated therein for protection during operations. The vessel may comprise a feed source, such as a water pressure source, connected to the tool section via feed lines. The feed source may be adjustable in dependence of seabed conditions. In particular, a water pressure may be adjustable in dependence of soil density.

In particular the tool, e.g. a vertical injector, may be configured to dig a trench and subsequently lay a cable and/or pipe in the trench. Due to the elongate boom section the cable and/or pipe to be laid may be supported by the elongate beam between the hull and the tool section, such that catenaries therein and associated chances of damage are reduced.

In an embodiment, the boom section comprises a boom cable support extending between the upper end and the lower end, wherein the tool section comprises a tool cable support extending through the tool section to the seabed, wherein the vessel further comprises a cable feed mechanism configured to feed a cable to the boom cable support and thereby defines a cable route between the feed mechanism and the seabed.

In an embodiment, the boom cable support comprises a cable entrance for feeding the cable from the cable feed mechanism into the boom cable support, wherein the cable entrance has a funnel shape. It has been found that this way, the boom section may move while still providing advantageous support to a cable with the funnel.

In an embodiment, the cable laying and/or trenching tool is provided with a transition guide to support a cable between the boom cable support and the tool cable support, such that the cable route is supported to be free of catenaries.

The cable feed mechanism may be configured to feed a cable and/or pipe to be laid into the seabed towards the boom cable support of the tool and may, for example, comprise a cable reel and/or a cable buffer.

When the tool section is rotatably mounted to the elongate boom section to be rotatable around a substantially horizontal axis, the transition guide may be rotatable and/or have an adjustable length to allow for rotation of the tool section. The transition guide may be flexible or extendible.

In an embodiment, the vessel is a shallow water vessel, for example wherein the vessel is suited for performing cable laying and/or trenching operations when a water depth is less than 15 meters, such as less than 10 meters, e.g. 5 meters or less.

Advantageously, the cable lay vessel according to the present invention allows to perform cable laying and/or trenching operations in relatively shallow waters. The cable lay vessel may be configured to allow falling dry of the vessel during low tide. This way, the cable laying and/or trenching operations may be performed relatively efficiently in shallow waters.

According to another aspect, the invention provides a method for laying a cable in a seabed, comprising the steps of: - providing a vessel having a cable laying and/or trenching tool comprising an elongate boom section that extends between a lower end and an upper end; and that is rotatably mounted to a hull of the vessel at a distance from the lower end; and a tool section attached to the lower end - moving the vessel in a movement direction and moving the cable laying and/or trenching tool over the seabed while performing cable laying and/or trenching operations in the seabed with the tool section, wherein, the boom section, during movement of the vessel, is rotatable around two axes substantially transverse to the movement direction, and that the method further comprises the steps of, during movement: - controlling sinking of the tool into the seabed during operations with a sag controller mounted between the hull and the trenching tool by reducing weight load of the tool on the sea bed during operations; and - controlling sideways movement of the tool during operations with respect to the hull with a swing controller mounted between the hull and the trenching tool.

The method may, for example, be carried out using a vessel according to one of the embodiments described herein. Using the method, the same or similar benefits may be achieved as disclosed herein for the vessel.

In an embodiment, the cable laying and/or trenching tool comprises a vertical injector and/or a soil cutter. The step of performing cable laying and/or trenching operations in the seabed may be performed using the vertical injector and/or the soil cutter.

In an embodiment, during operations, the method comprises the step of feeding the cable laying and/or trenching tool using a feed source, such as a water pressure source, of the vessel. The method may further comprising the steps of determining a seabed condition and adjusting the feed source, for example a pressure thereof, to the seabed condition.

In an embodiment, the method comprises the step of, during operations, controlling sideways movement of the tool section by rotating the tool section with respect to the elongate boom section around a substantially vertical axis.

The method may further comprise the step of, during operations, controlling a skew of the tool section by rotating the tool section with respect to the elongate boom section around a substantially horizontal axis.

In an embodiment, the boom section is rotatably mounted to the hull via longitudinal guide that allows movement of the boom section in a longitudinal direction of the boom section, further comprising the step of, during operations, controlling a longitudinal movement of the boom section with respect to the longitudinal guide, for example wherein the longitudinal controller comprises a cable-pulley mechanism.

Advantageously, with the method, a trench is dug and a cable is laid during a single movement of the vessel in the movement direction. This way, the invention allows for very efficient cable laying using a fraction of time that was conventionally required.

Further, the method according to the invention is well suited for usage in shallow waters, for example wherein cable laying and/or trenching operations are performed when a water depth is less than 15 meters, such as less than 10 meters, e.g. 5 meters or less.

In an embodiment, the method comprises the steps of: - halting cable laying and/or trenching operations in the seabed with the tool section, e.g. when the water depth decreases; - optionally, placing the tool section in a storage position; - letting the vessel fall dry; and - resuming cable laying and/or trenching operations in the seabed with the tool section operations, e.g. when the water depth increases again.

Advantageously, the method allows falling dry of the vessel during low tide. This way, the cable laying and/or trenching operations may be performed relatively efficiently in shallow waters. In some embodiments the vessel may remain at the same location to resume operations at the same location after low tide.

Brief description of drawings

Further characteristics of the invention will be explained below, with reference to embodiments, which are displayed in the appended drawings, in which:

Figure 1A schematically depicts an embodiment of a cable lay vessel according to an embodiment of the present invention;

Figure 1B schematically depicts a top view of the vessel according to the embodiment of Fig. 1A;

Figure 2A schematically depicts an embodiment of a cable lay vessel, wherein the tool section is performing cable laying and trenching operations in the seabed;

Figure 2B schematically depicts the cable lay vessel of Fig. 2A, wherein the tool section is arranged in a storage position;

Figure 3 schematically depicts an embodiment of a tool section comprising a vertical injector,

Figure 4 schematically depicts an embodiment of a tool section comprising a ski cutter;

Figure 5 schematically depicts a cable lay vessel according to another embodiment of the present invention, wherein the cable laying and trenching tools are performing operations in the seabed;

Figure 6 schematically depicts a top view of the vessel according to the embodiment of Fig. 5;

Figure 7 schematically depicts a top view of the vessel according to Fig. 5; wherein the tools are following a relatively curved trajectory;

Figure 8A schematically depicts a side view of the vessel of Fig. 5, wherein the tool sections are arranged in a storage position;

Figure 8B schematically depicts a side view of the vessel of Fig. 5, wherein the tool sections are arranged in an operation position; and

Figure 9 schematically depicts a side view of a vessel according to another embodiment of the invention.

Throughout the figures, the same reference numerals are used to refer to corresponding components or to components that have a corresponding function.

Detailed description of embodiments

Figure 1A schematically depicts an embodiment of a cable lay vessel 1 according to an embodiment of the present invention. The vessel 1 comprises a hull 10 and a cable laying and/or trenching tool 11.

The cable laying and/or trenching tool 11 comprises an elongate boom section 2 that extends between a lower end 21 and an upper end 22; and that is rotatably mounted to the hull 10 nearby the upper end 22, at a distance from the lower end 21.

The cable laying and/or trenching 11 further comprises a tool section 3 attached to the lower 21 end to be moved over the seabed 98 during movement of the vessel 1 to perform cable 99 laying and/or trenching operations in the seabed.

The boom section 2 is mounted at a starboard side of the vessel 1 and is mounted rotatably around two axes Y, Z substantially transverse to a movement direction X which is a main direction of motion of the vessel 1. When travelling forward in a straight line, the movement direction X is defined by the shape of the hull 10 and aligned with the longitudinal axis of the hull 10. A thruster arrangement in or at the hull 10 may also define the movement direction X.

The vessel 1 comprises a sag controller 4, arranged between the cable laying and/or trenching tool 11 and the hull 10 and partially suspends the tool section 3 and the boom section 2 to the hull to control sinking of the tool section 3 into the seabed 98 by reducing weight load, i.e. downward pressure, of the tool section 3 on the sea bed during operations to at most 50%, such as at most 25% of the weight of the tool section 3. The sag controller 4 is configured to exert an upward tension to the boom section 2 and/or the tool section 3, such that at least 50%, such as at least 75% of the weight of the tool 11 is carried by the sag controller 4, that, in this embodiment comprises a crane, but may additionally or alternatively comprise other lifting devices, such as an a-frame, arranged to lift the tool 11 during operations on the seabed.

The sag controller 4 is configured to hold the tool section at a continuous predetermined tension and the crane comprise a continuous tension (CT) winch. Additionally or alternatively, the sag controller 4 may be arranged to hold the tool section 3 at a desired trench depth. The vessel 1 comprises a depth sensor arranged to measure a depth of the seabed and a depth mapper arranged to provide a depth of the seabed, wherein the sag controller is configured to determine the desired trench depth in dependence on the measured and/or provided seabed depth.

The vessel 1 further comprises a swing controller 5, arranged between the cable laying and/or trenching tool 11 and the hull 10 and configured to control sideways movement of the tool with respect to the hull 10, in particular to reduce the sideways movement of the tool section during operations of the tool section by pulling and/or pushing the tool 11 sideways, i.e. in y direction, with respect to the movement direction X. The swing controller 5 is configured to hold the tool section at a continuous predetermined tension and comprises a continuous tension (CT) winch.

The boom section 2 is rotatably mounted to the hull 10 via a longitudinal guide 23 that is rotatable with respect to the hull, and the longitudinal guide 23 allows movement of the boom section 2 in a longitudinal direction L of the boom section such that the longitudinal position of the elongate boom along its longitudinal axis L, with respect to the rotatable mount, is variable, e.g. a distance between the hull mount and the lower end of the boom section is variable. The one or more hinges that are rotatable around the axis Y, Z, comprise the longitudinal guide 23. The longitudinal guide 23 comprises a sleeve that at least partially surrounds the boom section 2, wherein the sleeve is rotatably mounted to the hull 10.

The longitudinal guide 23 comprises a longitudinal controller 24 configured to control longitudinal movement of the boom section 2 with respect to the longitudinal guide 23 by damping motion of the boom section 2 along the longitudinal direction L.

The sag controller 4 and the swing controller 5 are spaced apart over a distance in the movement direction X, and comprise an adjustable tension cable 41, 33, respectively provided on a crane or continuous tension winch, and that each form an additional connection between the tool 11 and the hull 10. The adjustable tension cable 41 is attached between the crane 4 and lifting eye 35 that forms the sag controller connection. The adjustable tension cable 33 is attached between the winch 5 and pulling eye 34 that forms the swing controller connection.

The tool section 1 is, with the elongate boom section 2, movable between at least one operation position, as depicted in Fig. 2A, in which the tool section 3 is arranged on the seabed 98 to perform operations in the seabed, and a storage position, as depicted in Fig. 2B, in which the tool section is positioned higher compared to the operation position, i.e. above the water level, such as on the hull 10.

The elongate boom section 2 is rotatably mounted to the hull 10, via a hinge 22 that is rotatable around two axis, X,Y. The hinge 22 is positioned on the hull 10 and supports the cable laying and/or trenching tool.

The tool section 3 is attached to the lower end 21, by means of two hinges, and is partially suspended in the elongate boom section 2. During movement of vessel 1 in the direction X, the elongate boom section transfers the movement of the vessel in the movement direction X towards the tool section 3. The elongate boom section comprises a metallic material, in this embodiment steel, that is relatively stiff and is embodied as a tube.

Figure 3 schematically depicts an embodiment of a tool section 3 comprising a vertical injector for combined digging of a trench and laying a cable and/or a pipeline; and figure 4 schematically depicts an embodiment of a tool section comprising a soil cutter, in particular a chain cutter, for digging a trench in a seabed. The tool sections 3 are partially suspended in the elongate boom section to reduce weight load of the tool section on the seabed 98.

The vertical injector 3 comprises high-pressure nozzles 36, in this embodiment water nozzles, to dig a trench by flushing soil away, and a tool cable support 62, to guide a cable 99 into the seabed 98. Nozzles 36 are connected to a high-pressure feed source, such as a water pressure source, via feed lines 37, such as high-pressure water lines, integrated in the boom section 2. A water pressure of the feed source, and the nozzles 36, is adjustable in dependence of soil density.

The soil cutter 3 comprises a cutting member 38, such as a chain saw, supported on the seabed 98 by a support member provided with a support surface 39. The tool section is supported via the boom section 2 and the sag controller 4, such that the support member 39 is shaped relatively narrow, in particular as a ski.

The tool section 3 is rotatably mounted to the elongate boom section to be rotatable around a substantially vertical axis z. The swing controller comprises a steering mechanism 31 arranged between the elongate boom section 2 and the tool section 3, configured to control sideways movement of the tool, in particular the tool section 3, by influencing rotation of the tool section with respect to the elongate boom section 2 around the substantially vertical axis z.

The swing controller is configured to control sideways movement of the tool 11 and to reduce the sideways movement of the tool section 3 to at most 45 degrees, for example at most 25 degrees, with respect to the movement direction X of the hull 10. The steering mechanism 31 is a passive steering mechanism configured to passively influence movement of the tool section 3 by damping a swing movement thereof.

The steering mechanism 31 is arranged around the substantially vertical axis z to control rotation of the tool section 3, externally, as in Fig. 3, or integrated in the hinge as in

Fig. 4. The steering mechanism 31 in Fig. 3 comprises two hydraulic dampers positioned opposite to each other around the hinge. Additionally or alternatively, by having actuable hydraulic cylinders, the steering mechanism 31 may actively control sideways movement by rotating the tool section 3, such that movement of the hull 10 in the movement direction X causes a sideways movement of the tool section upon rotation.

The tool section 3 is rotatably mounted to the elongate boom section 2 to be rotatable around a substantially horizontal axis y.

As shown in fig. 1A, 1B, 2A, 2B and 3, the boom section 2 comprises a boom cable support 61 extending between the upper end 22 and the lower end 21. The tool section comprises a tool cable support 62 extending through the tool section 3 and the seabed 98.

The vessel 10 further comprises a cable feed mechanism having a cable reel 64 and a cable buffer 63, configured to feed a cable to the boom cable support 61, and which thereby defines a cable route between the feed mechanism and the seabed 98. The cable laying and/or trenching tool 3 is provided with a transition guide 64 to support a cable 99 between the boom cable support 61 and the tool cable support 62, such that the cable route is supported to be free of catenaries. The transition guide 645 is rotatable and flexible.

The boom cable support 61 comprises a cable entrance 85 for feeding the cable 99 from the cable feed mechanism into the boom cable support 61, and the cable entrance 65 has afunnel shape.

The vessel 1 comprises a skewing mechanism 32 arranged at the tool section 3. In

Fig. 3, the skewing mechanism 32 is an hydraulic cylinder arranged between the tool section 3 and the boom section 2. In Fig. 4, the skewing mechanism comprises a hydraulic cylinder arranged between the cutting member 38 and the support member 39. However, other configurations may also be possible, e.g. both embodiments may be combined. The skewing mechanism may also comprise the tensioning element 33 arranged between the tool section 3 and the swing controller 5, and the swing controller 5 may be configured to adapt a length of the tensioning element 33 in dependence of the skew of the tool section.

The vessel is a shallow water vessel suited for performing cable laying and/or trenching operations when a water depth is less than 15 meters, in particular less than 10 meters, more in particular 5 meters or less.

In use, the vessel 1 may be moved in a movement direction X and, thereby, the cable laying and/or trenching tool 11 is moved over the seabed 98 while performing cable laying and/or trenching operations in the seabed with the tool section 3, whereby sinking of the tool 11 into the seabed during operations is controlled with the sag controller 4, and sideways movement of the tool 11 with respect to the hull is controlled with the swing controller 5.

Further, sideways movement of the tool section 3 may be controlled by rotating the tool section 3 with the steering mechanism 31, and a skew of the tool section 3 may be controlled with the skewing mechanism 32. Movements of the hull 10, for example due to waves, may be accommodated by movement of the boom section 5 in the longitudinal direction L thereof, through longitudinal guide 23.

The cable laying and/or trenching operations may be performed when a water depth is less than 15 meters, in particular less than 10 meters, more in particular 5 meters or less. The cable laying and/or trenching operations in the seabed may be temporarily halted, and optionally, the tool section 3 may be positioned in a storage position. The vessel 10 may fall dry, and when the water depth is sufficient, cable laying and/or trenching operations in the seabed may be resumed.

In case a relatively soft soil is encountered, the tool section 3 remains at least partially suspended in the elongate boom section 2, whereby sinking of the tool is controlled by the sag controller 4. When the movement direction X of the vessel 1 changes, the boom section 2 may first rotate with respect to the hull, such that small changes, for example due to waves, do not directly influence an operation direction of the tool section 3. However, larger changes in the movement direction may also be transferred to the tool section 3 with the swing controller 4 in order to follow a trajectory of the vessel.

As a result, the tool 11 may be moved over the seabed 98 like a self-propelled or pulled tool, while the tool remains attached to the hull 10 via the boom section 2 to support the tool section 3, such that a support area on the seabed, pipe and/or cable can be reduced.

Advantageously, the vessel is provided with two cable laying and/or trenching tools, as depicted in the embodiments of Fig. 8, 7, 8A, 8B and 9. This way, a trench is dug and a cable may be laid during a single movement of the vessel 1 in the movement direction X.

Claims

CONCLUSIONS

1. Cable laying vessel (1) for laying a cable (99) in a seabed, comprising a hull (10) and a cable laying and/or trenching tool (11), wherein the cable laying and/or trenching tool comprises: an elongated boom section (2) extending between a lower end (21) and an upper end (22); and which is rotatably attached to the hull at a distance from the lower end; and a tool portion (3) attached to the lower end to be moved over the seabed during movement of the vessel to perform cable laying and/or trenching operations in the seabed, the boom being rotatably mounted about two axes (Y, Z) which extend essentially transversely to a direction of movement (X) determined by the hull, and wherein the vessel comprises: a bag regulator (4), arranged between the cable laying and/or trenching tool and the hull and adapted to sink the tool part (3) in the seabed by reducing the weight load of the tools on the seabed during operations; and a slew controller (5) disposed between the cable laying and/or trenching tool and the hull and adapted to control lateral movement of the tool portion (3) relative to the hull during operations.

A cable-laying vessel according to claim 1, wherein the tool portion (3) is rotatably attached to the elongate boom (2) to be rotatable about a substantially vertical axis (z).

A cable-laying vessel according to claim 2, wherein the slew controller comprises a steering mechanism (31) for controlling lateral movement of the tool section by influencing rotation of the tool section relative to the elongated boom about the substantially vertical axis (z).

Cable laying vessel according to any one of the preceding claims, wherein the tool portion (3) is rotatably attached to the elongated boom (2) to be rotatable about a substantially horizontal axis (y).

Cable laying vessel according to claim 4, wherein the vessel comprises a tilt mechanism (32, 33) arranged near the tool part, for example between the tool part and the boom and/or between the tool part and the hull, wherein the tilt mechanism (32, 33) is arranged to control an inclination of the tool part about the substantially horizontal axis (y).

Cable laying vessel according to claim 5, wherein the tilt mechanism (32, 33) comprises a tensioning element (33) arranged between the tool part (3) and the swivel controller (5), and wherein the swivel controller is adapted to adjust a length of the tensioning element depending on an inclination of the tool part.

Cable laying vessel according to any one of the preceding claims, wherein the boom portion (2) is rotatably attached to the hull via a longitudinal guide (23) rotatable relative to the hull, the longitudinal guide allowing movement of the boom in a longitudinal direction (L ) of the tree section.

Cable laying vessel according to claim 7, wherein the longitudinal guide comprises a length regulator (24) adapted to regulate movement of the boom in the longitudinal direction relative to the longitudinal guide.

9. Cable laying vessel according to any of the preceding claims, wherein the tool part comprises a vertical injector and/or a bottom cutter, wherein the bag controller is designed to control the sinking of the vertical injector and/or the bottom cutter into the seabed.

Cable laying vessel according to any one of the preceding claims, wherein the boom section comprises a boom cable support (61) extending between the upper end and the lower end (21), the tool section comprising a tool cable support (82) extending between the tool section towards the seabed , and wherein the vessel further comprises a cable entry mechanism (83) adapted to introduce a cable into the boom cable support and thereby determine a cable route between the entry mechanism and the seabed, and wherein the cable laying and/or trenching tool is provided with a transition guide (64 ) arranged to support a cable between the boom cable support (61) and the tool cable support (62), so that the cable route is supported to be free of catenaries.

11. Method for laying a cable in a seabed, comprising the steps of:

- providing a vessel (1) comprising a cable laying and/or trenching tool comprising an elongated boom portion (2) extending between a lower end and an upper end; and rotatably attached to a hull (10) of the vessel at a distance from the lower end; and a tool portion (3) attached to the lower end; — moving the vessel in a direction of movement (X) and moving the cable laying and/or trenching tool over the seabed while carrying out cable laying and/or trenching operations in the seabed with the tool part, the boom part, during movement of the vessel , is rotatable about two axes (Y, Z) substantially transverse to the direction of movement, and that the method further comprises the steps of, during movement: — controlling sinking of the tool section (3) into the seabed during operations with a bag regulator (4) secured between the hull and the cable laying and/or trenching tool by reducing weight loading of the tool on the seabed during operations; and — controlling lateral movement of the tool section (3) during operations relative to the hull with a swing controller (5) mounted between the hull and the cable laying and/or trenching tool.

The method of claim 11, further comprising the steps of, during operations, controlling lateral movement of the tool portion by rotating the tool portion relative to the elongated boom about a substantially vertical axis (z).

Method according to claim 11 or 12, further comprising the step of, during operations, controlling an inclination of the tool part by rotating the tool part relative to the elongated boom part about a substantially horizontal axis (y).

A method according to any one of claims 11 to 13, wherein the boom section is rotatably attached to the hull via a longitudinal guide (23) allowing movement of the boom section in a longitudinal direction of the boom section, further comprising the step of, during operations, controlling a longitudinal movement of the boom part relative to the longitudinal guide, for example by means of a length adjuster (24) that comprises a cable-pulley mechanism.

A method of laying a cable in a seabed according to any one of claims 10-14, wherein a trench is dug and a cable is laid in a single movement of the vessel in the direction of movement.

A method for laying a cable in a seabed according to any one of claims 10-15, wherein a water depth is less than 15 meters.