NL2033203B1

NL2033203B1 - Vessel having in-line cable laying devices

Info

Publication number: NL2033203B1
Application number: NL2033203A
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 first cable laying and/or trenching tool, wherein the first cable laying and/or trenching tool comprises an 5 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 first 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, characterised in that the boom section is mounted rotatably around an axis substantially transverse to a movement 10 direction defined by the hull, and that the vessel comprises a second cable laying and/or trenching tool, wherein the second cable laying and/or trenching tool comprises a second tool section configured to be moved over the seabed during movement of the vessel to perform cable laying and/or trenching operations in the seabed, wherein the first cable laying and/or trenching tool and the second cable laying and/or trenching tool are, in the movement 15 direction, positioned behind each other for in-line operation of the respective tool sections in the seabed. + fig 1

Description

P35775NLO0/MBA

Title: Vessel having in-line cable laying devices

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 first cable laying and/or trenching tool, wherein the first 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 first 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 an axis substantially transverse, e.g. perpendicular, to a movement direction defined by the hull.

The vessel comprises a second cable laying and/or trenching tool, wherein the second cable laying and/or trenching tool comprises a second tool section configured to be moved over the seabed during movement of the vessel to perform cable laying and/or trenching operations in the seabed, wherein the first cable laying and/or trenching tool and the second cable laying and/or trenching tool are, in the movement direction, positioned behind each other for in-line operation of the respective tool sections in the seabed.

The cable lay vessel is able to lay a cable in the seabed under varying seabed conditions, as the first tool section and the second tool section allow for subsequent trenching and/or cable laying operations using different tools from a single vessel. The first tool section and the second tool section may comprise mutually different tools. However, the respective tool sections may also comprise the same tools, which allows e.g. to dig a trench in two steps.

Further, as the first tool section is rotatable around an axis transverse to the movement direction, the first tool section may follow the hull over the seabed during movement of the vessel, such that the first tool section and the section tool section can operate in-line.

As the first tool section and the second tool section are positioned behind each other, the respective tool sections may each follow the movement of the hull naturally, instead of relying on the pipeline or cable to control movement of the tool.

By having a first tool section and a second tool section, the cable lay vessel may be used in varying soil conditions, such as with layered soil structures.

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

This way, the tool section may be moved around the axis, independently of sideways and upwards movements of the hull, thus less dependent on 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, a substantially horizontal axis, e.g. a horizontal axis, or a combination thereof.

The tool sections 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 sections are moved over the seabed to perform operations in the seabed. By having an elongate boom section, the first tool section may be moved over the seabed relatively precisely compared to tool moved by towing cables. Further, the first tool section may be partially suspended in the elongate boom section to reduce weight load of the tool section on the seabed. The second tool section may be attached like the first tool section, e.g. via an elongate boom section, or in another way, e.g. be suspended via cables. The second cable laying and/or trenching tool is in use moved over the seabed via the respective attachment, e.g. by an elongate boom section or towed by the cables.

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

The tool sections may, for example with the respective elongate boom section, be movable between at least one operation position, in which the respective 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 boom section may be configured to move the first tool section between the operation position and the storage position.

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 first tool section. For example, a single hinge may be provided that is rotatable around the axis, or multiple hinges such that the boom is rotatable around multiple axes. The rotatable mount may, in use, be arranged above the water level, but may alternatively be protrude into the water.

The first 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.

The first cable laying and/or trenching tool and the second cable laying and/or trenching tool are, in the movement direction, positioned behind each other for in-line operation of the respective tool sections in the seabed. The cable laying and/or trenching tools may be mounted to the hull behind each other, and for example each be arranged on the same side of the vessel. Alternatively, the tools may be arranged on different sides of the vessel and be provided with a positioning mechanism, such as a boom or cable, to position the first tool section and the second tool section behind each other. As such, during movement of the vessel in the movement direction, the first tool section and the second tool section are positioned in-line on or near the seabed for in-line operation by trenching and/or laying a cable in the seabed.

In an embodiment, the second cable laying and/or trenching tool comprises a second 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 respective lower end, wherein the second tool section is attached to the respective lower end, and wherein the second boom is mounted rotatably around an axis substantially transverse, e.g. perpendicular, to the movement direction. This way, the second boom section may advantageously support the second tool section. Additionally, the second boom section may, for example, be controlled similar to the first boom section.

In an embodiment, the first elongate boom section and/or the second elongate boom section may be rotatably mounted around two axes substantially transverse, e.g. perpendicular, to the movement direction. This allows movement of the respective tool with respect to the hull, such that the respective tool may be moved to perform cable laying and/or 5 trenching operations even during sideways and upwards movements of the hull, for example due to wave motion. The movement direction may be determined by the 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 respective tool may be rotatably mounted over two axes substantially perpendicular to the movement direction, for example a substantially vertical axis and a substantially horizontal axis.

Between the first tool section and the hull and/or between the second tool section and the hull, a sag controller and/or a swing controller may be arranged, which form at least one additional connection between the respective tool and the hull. The sag controller and the swing controller may both be connected at the respective boom section and/or at the respective tool section, or at mutually different connection locations. The sag controller and the swing controller allow for movement of the respective boom section, but may limit and/or damp movement of the respective boom section around the two axes, for example limit within predetermined boundaries. 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 is very suited for varying soil conditions, such as with layered soil structures.

Further, an existing pipe or cable may not be required for alignment of the tool, such that the vessel may advantageously lay sensitive pipelines and cables, for example, power cables, telecom cables, electrical cables, optic cables, flowlines and/or umbilicals.

The sag controller and the swing controller may comprise actuators having a variable length, for example 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 respective 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 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 and in-line operation can be performed. However, larger changes in the movement direction may also be transferred to the respective 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 respective 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 respective tool section during operations of the respective tool section. The sag controller may suspend the respective tool section and/or the boom section to the hull. The downward pressure exerted by the respective tool section may be adjustable. In particular, sag controller may be configured to exert an upward tension to the respective boom and/or the tool section, for example such that at least 50%, such as at least 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 respective tool section on the seabed, pipeline and/or cable to at most 50%, such as at most 25% of the weight of the respective 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 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 arranged to keep the respective 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 respective 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 respective tool section during operations. The pulling device may comprise a tension cable attached to the respective tool section, for example the respective 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 respective tool. The steering mechanism may be an active steering mechanism configured to actively influence movement of the respective 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 first and/or second 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 respective tool section may be attached to be movable along a longitudinal direction of the respective 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 respective boom section between the hull mount and the lower end.

In an embodiment, the vessel comprises a selection mechanism, operatively connected to the first cable laying and/or trenching tool and/or the second cable laying and/or trenching tool, and configured to selectively raise or lower one of the first cable laying and/or trenching tool or the second cable laying and/or trenching tool for selective operation the second cable laying and/or trenching tool or the first cable laying and/or trenching tool in the seabed, respectively. The respective cable laying and/or trenching tool may be raised completely out of the seabed, for example above a water level, or partially.

The selection mechanism may be configured to selectively move the first tool section and the second tool section between a respective storage position and a respective operation position.

The first tool section may be provided with a first sag controller and the second tool section may be provided with a second sag controller, wherein the selection mechanism is configured to activate the first sag controller and the second sag controller to move the respective tool sections into the storage position or the operation position.

By having a selection mechanism, operation of one or both of the tool sections may be selected, such that the tools can be selected to match the seabed conditions.

In a further embodiment, the selection mechanism is configured to selectively raise or lower one of the first cable laying and/or trenching tool or the second cable laying and/or trenching tool while the cable laying and/or trenching tools remain positioned in-line. For example, the tool section may comprise an operation member for performing operations in the seabed and a support member for support of the operation member in the seabed. The operation member may for example be a cutting member for cutting a trench or a laying member for laying a cable. The operation member may be vertically movable with respect to the support member. The selection mechanism may be configured to move the operation member with respect to the support member to selectively raise or lower the operation member in or out of the seabed. In this way, it is possible to switch without having to re-align the first and second tool section with each other.

In an embodiment, the first cable laying and/or trenching tool is a cable laying tool, and the second cable laying and/or trenching tool is a trenching tool, or vice versa. For example, the first cable laying and/or trenching tool comprises a vertical injector and the second cable laying and/or trenching tool comprises a soil cutter, such as a chain cutter. This combination has proven to be an advantageous solution for laying cables or pipelines in seabeds with varying compositions, for example with a soft upper layer and or alternating hard and soft sails.

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 sag controller is configured to control sinking of the vertical injector and/or the soil cutter into the seabed.

In an embodiment, the first tool section and/or the second tool section is rotatably mounted to the respective elongate boom section to be rotatable around a substantially vertical axis. This way, the respective tool section is movable with respect to the respective boom and may rotate in response to changes in the movement directions, i.e. when the hull follows a curved trajectory. As such, the respective 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 first cable laying and/or trenching tool and/or the second cable laying and/or trenching tool comprises a steering mechanism arranged between the respective elongate boom section and the first and/or second tool section, configured to control sideways movement of the respective tool section by influencing rotation of the respective tool section with respect to the respective 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 respective 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.

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.

The steering mechanism may be an active steering mechanism, configured to actively change a rotation of the tool section. 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.

In an embodiment, the first tool section and/or the second tool section is rotatably mounted to the respective 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 respective 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 respective 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 respective tool section, for example between the tool section and the respective boom section and/or between the respective 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 respective 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 respective 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 respective 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 of the first cable laying and/or trenching tool and/or of the second trenching tool 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 respective boom section in a longitudinal direction. By having a boom section that is movable ina longitudinal direction thereof, wave motion may be accommodated by movement in the longitudinal direction of the boom section. This way, the respective toal 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 respective 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 respective tool section may remain on the seabed, while the hull may move along the respective boom section, e.g. during waves.

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

In an embodiment, the elongate boom section of the first cable laying and/or trenching tool and/or the second trenching tool comprises a boom cable support extending through the upper end and the lower end, wherein the respective 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 respective cable laying and/or trenching tool is provided with a transition guide configured 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 respective tool and may, for example, comprise a cable reel and/or a cable buffer.

When the respective 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 the seabed, comprising the steps of: - providing a vessel comprising a hull and a first cable laying and/or trenching tool, wherein the first 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 a hull of the vessel at a distance from the lower end and a first tool section; - 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 first tool section, wherein the boom section, during movement of the vessel, is rotatable around an axis substantially transverse to the movement direction, and that the method further comprises the steps of, during movement: - moving a second cable laying and/or trenching tool comprising a second tool section over the seabed while performing cable laying and/or trenching operations in the seabed with the second tool section, wherein, during movement of the vessel, the first tool section and the second tool section are positioned behind each other for in-line operation of the respective tool sections in the seabed.

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 first cable laying and/or trenching tool and/or the second 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 respective vertical injector and/or the respective 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 comprise 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 further comprises the step of, during operations, controlling sideways movement of the first and/or second tool section by rotating the respective tool section with respect to the elongate boom section around a substantially vertical axis.

In an embodiment, the method further comprises the steps of

- determining a seabed condition; - selecting sequential or individual operation of the first tool section and the second tool section in dependence of the determined seabed condition; and - raising and/or lowering the first cable laying and/or trenching tool or the second cable laying and/or trenching tool based on the selected individual or sequential operation. The seabed condition may comprise, for example soil type, depth, or other parameters.

In an embodiment, the elongate boom section of the first cable laying and/or trenching tool and/or the second cable laying and/or trenching tool is rotatably mounted to the hull via longitudinal guide that is rotatable with respect to the hull, wherein the longitudinal guide allows movement of the boom in a longitudinal direction of the boom section, further comprising the step of, during operations, controlling a longitudinal movement of the respective boom with respect to the longitudinal guide, for example wherein the longitudinal controller comprises a cable-pulley mechanism.

In an embodiment, the first cable laying and/or trenching tool is a cable laying tool and wherein the second cable laying and/or trenching tool is a trench cutter, wherein a trench in dug by the trench cutter, and wherein a cable is laid in the trench by the cable laying tool during a single movement of the vessel in the movement direction by in-line operation of the first tool section and the second tool section.

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

Figure 2 schematically depicts a top view of the vessel according to the embodiment of Fig. 1;

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

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

Figure 5 schematically depicts a top view of the vessel according to Fig. 1; wherein the tools are following a relatively curved trajectory;

Figure BA schematically depicts a side view of the vessel of Fig. 1, wherein the tool sections are arranged in a storage position;

Figure 6B schematically depicts a side view of the vessel of Fig. 1, wherein the tool sections are arranged in an operation position; and

Figure 7 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 1 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 first cable laying and/or trenching tool 11.

The first 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 first cable laying and/or trenching tool 11 further comprises a first 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 second cable laying and/or trenching tool 12, which comprises a second tool section 3’ to be moved over the seabed during movement of the vessel 10 to perform cable laying and/or trenching operations in the seabed. The second cable laying and/or trenching tool 12 comprises a second 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 respective lower end 21’. A second tool section 3’ is attached to the second lower end 21’, and the second boom section 2’ is mounted rotatably around two axes Y’, Z’ substantially transverse to the movement direction

X.

The first cable laying and/or trenching tool 11 and the second cable laying and/or trenching tool 12 are, in the movement direction X, positioned behind each other for in-line operation of the respective tool sections 3, 3’ in the seabed 98.

The vessel 1 comprises a selection mechanism 7, operatively connected to the first cable laying and/or trenching tool 11 and to the second cable laying and/or trenching tool 12, but may also be operatively be coupled to one of the tools 11, 12. The selection mechanism 7 is configured to selectively raise or lower one of the tools 11, 12 for selective operation the second cable laying and/or trenching tool 12 or the first cable laying and/or trenching tool 11 in the seabed. The selection mechanism 7 is configured to selectively raise or lower one of the tools 11, 12 while the trenching tools 11, 12 remain positioned in-line.

The first cable laying and/or trenching tool 11 is a cable laying tool, in particular a vertical injector, and the second cable laying and/or trenching tool 12 is a trenching tool, in particular soil cutter.

The first tool section 3 and the second tool section 3’ are rotatably mounted to the respective elongate boom section 2, 2’ to be rotatable around a substantially vertical axis z, z’ and around a substantially horizontal axis y, y’. However, one of the tool sections 3, 3’, or none may be rotatably mounted around one or more axes, as shown in the embodiment of

Fig. 7.

The vessel 1 comprises two sag controllers 4, 4’, arranged between the respective tools 11, 12 and the hull 10 and partially suspending the tool sections 3, 3’ and the boom sections 2, 2’ to the hull to control sinking of the respective tool sections 3, 3’ into the seabed 98 by reducing weight load, i.e. downward pressure, for each of the tool sections 3, 3' on the sea bed during operations to at most 50%, such as at most 25% of the weight of the tool section 3, 3’. The sag controllers 4, 4’ are configured to exert an upward tension to the boom sections 2, 2’ and/or the tool sections 3, 3’, such that at least 50%, such as at least 75% of the weight of the tools 11, 12 is carried by the respective sag controllers 4, 4’, that, in this embodiment each comprise a crane, but may additionally or alternatively comprise other lifting devices, such as an a-frame, arranged to lift at least one of the tools 11, 12 during operations on the seabed with that respective one of the tools 11, 12.

The sag controllers 4, 4’ are configured to hold the tool sections 3, 3’ at a continuous predetermined tension and the cranes each comprise a continuous tension (CT) winch.

Additionally or alternatively, the sag controllers 4, 4’ may be arranged to hold the respective tool sections 3, 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 at least one of the sag controllers is configured to determine the desired trench depth in dependence on the measured and/or provided seabed depth.

The vessel 1 further comprises two swing controllers 5, 5’, arranged between the cable laying and/or trenching tools 11, 12 and the hull 10 and configured to control sideways movement of the tools with respect to the hull 10, in particular to reduce the sideways movement of the respective tool section 3, 3’ during operations of that tool section 3, 3’ by pulling and/or pushing the respective tool 11, 12 sideways, i.e. in y or y’ direction, with respect to the movement direction X. The swing controllers 5, 5’ are configured to hold the tool sections at a continuous predetermined tension and each comprise a continuous tension (CT) winch.

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

A first one 23 of the longitudinal guides 23, 23’ comprise 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. However, one or both of the longitudinal guides 23, 23" may be provided with a longitudinal controller 24, 24’.

The sag controllers 4, 4’ and the swing controllers 5, 5’ are spaced apart over a distance in the movement direction X, and comprise adjustable tension cables 41, 41°, 33,

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 cables 41, 41’ are attached between the crane 4 and lifting eyes that forms the sag controller connections on the tools 11, 12. The adjustable tension cables 33, 33’ are attached between the respective winches 5, 5’ and pulling eyes that form the swing controller connections on the tools 11, 12.

The tool sections 3, 3’ are each, with the respective boom sections 2, 2’, movable between at least one operation position, as depicted in Fig. 6B, in which the respective tool section 3, 3’ is arranged on the seabed 98 to perform operations in the seabed, and a storage position, as depicted in Fig. 8A, in which the respective tool section 3, 3’ is positioned higher compared to the operation position, i.e. above the water level, such as on the hull 10.

The elongate boom sections 2, 2’ are rotatably mounted to the hull 10, via hinges 23, 23’ that are each rotatable around two axis, Y, Zand Y, Z', respectively. The hinges 22, 22° are positioned on the hull 10 and each support one of the cable laying and/or trenching tools 11,12.

The tool sections 3, 3’ are attached to the respective lower ends 21, 21°, by means of two hinges, and are partially suspended in the elongate boom sections 2, 2’. During movement of vessel 1 in the direction X, each elongate boom section 2, 2’ transfers the movement of the vessel in the movement direction X towards the respective tool sections 3, 3. The elongate boom sections comprise 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 3’ comprising a soil cutter, in particular a chain cutter, for digging a trench in a seabed 98. The tool sections 3, 3’ are partially suspended in the elongate boom section 2, 2’ 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 38, 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 sections 3 3’, are each rotatably mounted to the elongate boom section to be rotatable around a substantially vertical axis z, z'. The swing controllers each comprise a steering mechanism 31, 31’ arranged between the elongate boom section 2, 2’ and the tool section 3, 3’, configured to control sideways movement of the respective tool, in particular the tool section 3, 3’, by influencing rotation of the tool section with respect to the elongate boom section 2, 2’ around the substantially vertical axis z, z.

The swing controllers are configured to control sideways movement of the respective tool 11, 12 and to reduce the sideways movement of the respective tool section 3, 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 mechanisms 31, 31’ are passive steering mechanisms configured to passively influence movement of the tool section 3 by damping a swing movement thereof.

The steering mechanisms 31, 31’ are arranged around the substantially vertical axis z,

Z' to control rotation of the tool section 3 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, 31’ may actively control sideways movement by rotating the tool section 3 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 sections are each rotatably mounted to the elongate boom sections 2, 2’ to be rotatable around a substantially horizontal axis y, y’.

As shown in fig. 1, 3, the first boom section 2 comprises a boom cable support 61 extending between the upper end 22 and the lower end 21. The first tool section 3 comprises atool cable support 682 extending through the first tool section 3 to 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 99 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 64 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 81, and the cable entrance 65 has a funnel shape.

The vessel 1 comprises skewing mechanisms 32, 32’, one arranged at the first tool section 3 and at the second 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 32’ 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, 33’ arranged between the tool section 3, 3’ and the swing controller 5, 5, and the swing controller 5, 5" may be configured to adapt a length of the respective tensioning element 33, 33’ in dependence of the skew of the tool section.

The vessel 1 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 first 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.

Simultaneously, the second cable laying and/or trenching tool 12 is moved over the seabed 98 in front of the first tool section 11, while performing cable laying and/or trenching operations in the seabed with the second tool section 3’ in-line with the first tool section 3.

Sinking of the tool 12 into the seabed during operations is controlled with the sag controller 4’, and sideways movement of the tool 12 with respect to the hull is controlled with the swing controller 5’.

This way, a trench in dug by the trench cutter 12, and a cable 99 is laid in the trench by the cable laying tool 11 during a single movement of the vessel in the movement direction by in-line operation of the first tool section 3 and the second tool section 3’.

Further, sideways movement of the tool sections 3, 3’ may be controlled by rotating the tool sections 3, 3’ with the steering mechanisms 31, 31’, and a skew of the tool sections 3, 3’ may be controlled with the skewing mechanisms 32, 32’. Movements of the hull 10, for example due to waves, may be accommodated by movement of the boom section 2, 2’ in the longitudinal directions L, L’ thereof, through longitudinal guides 23, 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.

The tool sections 3, 3’ remain at least partially suspended in the elongate boom section 2, 2’ in case a relatively soft soil is encountered, whereby sinking of the tool 11, 12 is controlled by the respective sag controller 4, 4’. When the movement direction X of the vessel 1 changes, the boom sections 2, 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 sections 3, 3’. However, larger changes in the movement direction may also be transferred to the tool sections 3, 3’ with the swing controllers 4, 4’ in order to follow a trajectory of the vessel 1.

As aresult, the tools 11, 12 may be moved over the seabed 98 like self-propelled or pulled tools, while remaining attached to the hull 10 via the boom sections 2, 2’ to support the tool sections 3, 3’, such that a support area on the seabed, pipe and/or cable can be reduced.

During operations, a seabed condition, such as a harder or softer soil may be determined. In dependence of the determined seabed condition, sequential or individual operation of the first tool section 11 and the second tool section 12 may be selected.

The first cable laying and/or trenching tool 11 and/or the second cable laying and/or trenching tool 12 may be raised or lowered during cable laying and/or trenching operations with one of the tools 11, 12, based on the selected individual or sequential operation. The seabed condition may comprise, for example soil type, depth, or other parameters.

For example, in case a relatively soft soil is encountered, the second tool section 3’ may be arranged in the storage position, and the first tool section 3 may be arranged in the operation position with the selection mechanism.

In case a relatively hard soil is encountered, the second tool section 3’ may also be arranged in the operation position to dig a trench, in which a cable may be laid subsequently using the first tool section 3.

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 (99), comprising a hull (10) and a first cable laying and/or trenching tool (11), wherein the first cable laying and/or trenching tool comprising: an elongated boom portion (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 first tool portion (3) attached to the lower end for movement over the seabed during movement of the vessel to perform cable laying and/or trenching operations in the seabed, the boom portion being rotatably mounted about a substantially transverse to a axis of movement determined by the hull, and wherein the vessel comprises: a second cable laying and/or trenching tool (12), wherein the second cable laying and/or trenching tool comprises a second tool section (3') designed to be moved over the seabed during movement of the vessel to carry out cable laying and/or trenching operations in the seabed, with the first cable laying and/or trenching tool (11) and the second cable laying and/or trenching tool (12) positioned aft in the direction of movement (X) are positioned together for in-line operation of the respective tool sections in the seabed.

Cable laying vessel according to claim 1, wherein the second cable laying and/or trenching tool (12) comprises a second elongated boom portion (2%) extending between a lower end (21°) and an upper end (22) and rotatably attached to the hull at a distance from the respective lower end, wherein the second tool portion (3) is attached to the respective lower end (21°), and wherein the second boom portion (2') is mounted rotatably about an axis substantially transverse to the direction of movement .

Cable laying vessel according to claim 1 or 2, wherein the vessel comprises a selection mechanism (7), operatively connected to the first cable laying and/or trenching tool (11) and/or the second cable laying and/or trenching tool (12), and arranged to selectively raise or lower one of the first cable laying and/or trenching tools (11) and/or the second cable laying and/or trenching tools (12) for selective operation of, respectively, the second cable laying and/or trenching tools and /or the first cable laying and/or trenching tool in the seabed.

4. Cable laying vessel according to claim 3, wherein the selection mechanism is designed to selectively raise or lower one of the first cable laying and/or trenching tools and/or the second cable laying and/or trenching tools, whereby the cable laying and/or trenching tools are inserted into line remain positioned.

Cable laying vessel according to any one of claims 1 to 4, wherein the first cable laying and/or trenching tool (11) is a cable laying tool, and wherein the second cable laying and/or trenching tool (12) is a trenching tool, or vice versa, for example wherein the first cable laying and/or trenching tool comprises a vertical injector and wherein the second cable laying and/or trenching tool comprises a bottom cutter.

Cable laying vessel according to any one of claims 1-5, wherein the first tool section (3) and/or the second tool section (3°) is rotatably attached to the respective boom section (2, 2} to be rotatable around a substantially vertical axis (z, z').

Cable laying vessel according to claim 6, wherein the first cable laying and/or trenching tool and/or the second cable laying and/or trenching tool comprises a steering mechanism (31) arranged between the respective elongated boom section (2, 2°) and the first and/or the second tool portion (3, 3'), adapted to control lateral movement of the respective tool portion (3, 3') about the substantially vertical axis (z, z').

Cable laying vessel according to any one of the preceding claims, wherein the first tool section and/or the second tool section (3, 3) is rotatably attached to the respective boom section to be rotatable about a substantially horizontal axis (y, y'), for example wherein the vessel comprises a tilt mechanism (32, 33) arranged near the tool section, such as between the respective tool section and the respective boom section and/or between the respective tool section and the hull, wherein the tilt mechanism is adapted to control an tilt position of the tool section around an essentially horizontal axis (vy, ¥)-

Cable laying vessel according to any one of the preceding claims, wherein the elongated boom part (2) of the first cable laying and/or trenching tool and/or the elongated boom part (2'} of the second cable laying and/or trenching tool is rotatably attached to the fuselage (10) via a longitudinal guide (23, 23') rotatable relative to the fuselage, the longitudinal guide allowing movement of the respective boom section in a longitudinal direction (L, L') of the respective boom section.

Cable laying vessel according to claim 9, wherein the length guide comprises a length adjuster (24) designed to regulate longitudinal movement of the boom section relative to the length guide.

11. Method for laying a cable in a seabed, comprising the steps of: - providing a vessel comprising a first cable laying and/or trenching tool, wherein the first cable laying and/or trenching tool comprises an elongated boom section 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 first tool portion; — moving the vessel in a direction of movement 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 first tool section, the boom section being rotatable during movement of the vessel is around an axis substantially transverse to the direction of movement, and that the method further comprises the steps of, during movement: or trenching operations in the seabed with the second tool section, wherein, during movement of the vessel, the first tool section and the second tool section are positioned one behind the other for in-line operation of the respective tool sections in the seabed.

The method of claim 11, further comprising the step of, during operations, controlling lateral movement of the first and/or second tool portion by rotating the respective tool portion relative to the elongated boom about a substantially vertical axis.

13. Method according to claim 11 or 12, further comprising the steps of: - determining seabed condition; — selecting sequential or individual operation of the first tool section and the second tool section depending on the determined seabed condition; and — raising and/or lowering the first cable laying and/or trenching tool or the second cable laying and/or trenching tool based on the selected individual or sequential operation.

14. Method according to any one of claims 11-13, wherein the elongated boom part of the first cable laying and/or trenching tool and/or the second cable laying and/or trenching tool is rotatably attached to the hull via a longitudinal guide that is rotatable relative to the hull, wherein the longitudinal guide allows movement of the boom in a longitudinal direction thereof, further comprising the step of, during operation, controlling a longitudinal movement of the respective boom portion relative to the longitudinal guide, for example wherein the length adjuster comprises a cable-pulley mechanism.

15. Method for laying a cable in a seabed according to any one of claims 11-14, wherein the first cable laying and/or trenching tool is a cable laying tool and wherein the second cable laying and/or trenching tool is a trencher, wherein a trench is dug by the trencher, and wherein a cable is laid in the trench by the cable laying tool during a single movement of the vessel in the direction of movement by in-line operation of the first tool part and the second tool part.

A method for laying a cable in a seabed according to any one of claims 11-15, wherein a water depth is less than 15 meters.