NL2011872C2 - System and method for deploying/operating tool and heave compensation for same. - Google Patents

Description

SYSTEM AND METHOD FOR DEPLOYING/OPERATING TOOL AND HEAVE

COMPENSATION FOR SAME

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The invention relates to a system and method to deploy, adjust and operate a tool subsea in a location without direct vertical access. It further relates to motion compensation for stabilization of tools, equipment, and other objects hoisted, positioned and/or maneuvered by a hoisting system from a vessel or floating platform in an offshore environment, and more particularly, to passive heave compensation against wave-induced motion. 2. Description of the Related Art [0002] In offshore engineering, operations are conducted which require deployment and maneuvering of tools and equipment in subsea environments. Deployment and control of the tools, equipment, and other objects used in such operations are generally executed with the aid of Remotely Operated Vehicles (ROVs) such as the Magnum™ ROV provided by Oceaneering™ (Houston, TX), accordingly equipped with the necessary tool or equipment for a particular operation. However, use of ROVs presents drawbacks as the lifting capacity is limited. Also deployment, operation and retrieval of ROVs is weather sensitive and can be costly and complex.

[0003] Alternatively, hoisting systems on vessels or floating platforms can be used for deployment and control of a tool and/or equipment during an operation. A tool or piece of equipment is connected to the hoisting system for lifting or lowering to a desired depth or altitude.

[0004] The tool is generally connected to the hoisting system through a rigging arrangement that is designed to deploy the tool in the desired position. Adjusting the orientation of the tool relative to the vessel or platform cannot be done without retrieving the tool to the surface to adjust the rigging arrangement of the tool above water. Subsequent operations requiring different orientation of a tool can become very time consuming.

[0005] Further it is difficult to reach all target locations when a tool is connected to a hoisting system from a vessel or floating platform, particularly target locations which cannot be reached by direct vertical access, e.g. under an overhang, under the structure that operates the hoisting system, or within a subsea structure.

[0006] Further, precise operation and control of a tool or piece of equipment can be challenging in an offshore environment due to the wave-induced motion experienced by the vessel or floating platform from which the tool or equipment is hoisted.

BRIEF SUMMARY OF THE INVENTION

[0007] At least one of the indicated problems is solved or reduced by the method, system and/or device according to the appended claims.

[0008] In order to address one or more of the aforementioned problems, it is an object of the invention to provide a supporting module and/or a tool assembly for supporting and/or maneuvering a tool for and during conduction of an operation under water, wherein the supporting module is configured to allow operating a tool at a location without direct vertical access, such as under an overhang.

[0009] It is a further object of the invention to provide a hoisting system, a floating platform, such as a vessel, with a hoisting system and a tool assembly comprising the supporting module and tool, and/or methods to hoist and/or position and/or maneuver a load, tool, piece of equipment or other object or article, wherein the load supporting module is configured to allow operating a tool at a location without direct vertical access.

[0010] In order to address one or more of the aforementioned problems, it is a further object of the invention to provide a load supporting module and/or a load assembly for use in hoisting and/or positioning and/or maneuvering of loads, such as tools, equipment or other objects, wherein the load supporting module is configured to allow position a load in a location without direct vertical access, such as under an overhang.

[0011] It is a further object of the invention to provide a hoisting system, a floating platform, such as a vessel, with a hoisting system and a load assembly comprising the supporting module and load, and/or methods to hoist and/or position and/or maneuver a load, such as a tool, piece of equipment or other object or article, wherein the load supporting module is configured to allow operating the load in a location without direct vertical access.

[0012] In order to address one or more of the aforementioned problems, it is another object of the invention to provide a load supporting module and/or load assembly comprising the load supporting module for supporting, maneuvering and positioning a load for and during conduction of an operation, in which reliable passive heave compensation is provided in response to wave-induced motion.

[0013] In order to address one or more of the aforementioned problems, it is a further object of the invention to provide a load supporting module and/or load assembly for use in hoisting and maneuvering of loads such as tools, equipment or other objects, which load supporting module is configured to counteract wave-induced motion via heave compensation.

[0014] It is a further object of the invention to provide a hoisting system, a floating platform, such as a vessel, with a hoisting system and a tool assembly comprising the load support module and/or methods to hoist, position and/or maneuver a load, tool, piece of equipment or object, which load supporting module is configured to counteract wave-induced motion via passive heave compensation.

[0015] In an embodiment of the invention, a tool assembly is provided comprising a tool connected to an arm of a tool supporting module having a counterweighting element.

[0016] In a further embodiment of the invention, a load supporting module is provided for connection to a hoisting system and which module is configured to support a load, such as a tool, piece of equipment, other objects, and aid in control of the positioning of the object, the load supporting module being configured to provide heave compensation.

[0017] In a further embodiment of the invention a method of supporting and balancing a load, such as a tool, a piece of equipment, a device and/or an article, in an underwater environment, using a load supporting module configured to operate the tool in a location without direct vertical access and preferably suspended from a hoisting system on a floating device, such as a vessel.

[0018] In accordance with an embodiment of the invention a vessel is provided comprising at least one hoisting system for hoisting a load assembly having a load supporting module.

[0019] In another embodiment of the invention, a load assembly is provided comprising a load connected to a load supporting module, a counterweight, an arm, and at least one, preferably two surfaces extending from the arm along a horizontal plane.

[0020] In a further embodiment of the invention, a load supporting module is provided for connection to a hoisting system and which module is configured to support a load and aid in control of the positioning of the load, the load supporting module being configured to provide heave compensation.

[0021] In a further embodiment of the invention a method of supporting a load under sea level and in a location without direct vertical access using a load supporting module configured for heave compensation is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The features and advantages of the invention will be appreciated upon reference to the following drawings, in which:

Figure 1 shows schematically a cross-sectional side view of an embodiment of the invention;

Figure 2 shows a detailed view of an assembly comprising a tool support module and tool according to an embodiment of the invention;

Figures 3A-B show cross-sectional views of an assembly configured for passive heave compensation according to the invention;

Figure 4 shows another embodiment of a load supporting module according to the invention; and

Figure 5 shows schematically a view of operating the assembly in accordance with the invention.

Figure 6 shows another embodiment of a load support module according to the invention; and

Figure 7 shows an assembly configured for passive heave compensation according to the invention.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0023] Although the invention will be described with reference to the drawings, it will be clear that the invention encompasses more than the embodiments as shown in the drawings. The drawings illustrate exemplary embodiments only. In this application several advantages of the method, system and parts of the system are described. Any of these features, both explicit and implicit, can be combined with elements of the features of the methods and the system and each of the advantages can be the basis for a claim, in particular for a divisional application. The skilled person is aware of many embodiments for lifting and hoisting devices for offshore applications and can combine these with the invention.

[0024] According to a first set of aspects a method and system for operating a tool assembly having a tool on an arm suspended from a floating platform is provided. The tool can be suspended from the hoisting system. The tool is part of the tool assembly that also comprises the tool support module. The tool is mounted to a tool support module.

[0025] Maneuvering the tool in a location without direct vertical access, such as under an overhang, under water is difficult. The tool and/or the arm on which the tool is mounted can have considerable weight. Further reaching and maintaining a target position of the tool under the overhang can be difficult, especially if adjustment of the position and orientation of the tool under water is not possible. The stability of the tool is further decreased by the motion of the lifting system, which shifts the tool’s position. These difficulties have deterred the development of tools suitable for working under an overhang for suspension from a hoisting system on a vessel or floating platform.

[0026] Therefore, a need exists to provide a method, system, assembly, and module allowing efficient operation of a tool, piece of equipment and other devices and articles in a location without direct vertical access from a vessel or floating platform.

[0027] Referring to Fig. 1, a vessel 10 according to an embodiment of the invention is shown, the vessel 10 including a hoisting system 23 and an assembly 30 connected to the hoisting system 23 via an extension member 22.

[0028] Assembly 30 includes a load supporting module 30a and a tool 36, for instance a cutting tool, which is connected to, and supported by, the load supporting module 30a.

[0029] Hoisting system 23 includes boom 20 and the extension member 22 for hoisting a load from a suspension point 21. The hoisting system 23 is arranged for lifting, lowering and maneuvering a load, in the exemplary embodiment shown in Figure 1, the load hoisted by the hoisting system is tool assembly 30 consisting of tool support module 30a and cutting tool 36. The skilled person will be familiar with several hoisting systems and the details of the hoisting system are not subject of this application. Combinations with different hoisting systems, including e.g. winches or multiple cranes, in special cases cranes from multiple vessels, can be made.

[0030] The hoisting system 23 shown in the example is positioned on top of the deck of the vessel 10. It can also be positioned inside the hull of the vessel or on another area. In an alternative embodiment, a floating platform can be used to support the hoisting system 23.

[0031] The boom 20 of the hoisting system 23 extends outwardly during operation. Suspension point 21 is located outside, in generally adjacent relationship to the hull. The hoisting extension member allows lowering and lifting the assembly 30 into and out of the sea and can hold the support module 30 at a distance under the sea level 11. Extension member 22 can comprise a rope, wire, cable, chain or any other suitable structure of any suitable material for the hoisting of a load.

[0032] A hydrocarbon production platform 12 at sea is shown comprising a deck 13 supported by a frame 14, known in the art as a jacket, erected on the sea bed 15. The frame generally consists of interconnected tubular elements. In this example, the sea platform 12 is to be put out of order and needs to be removed. The method and vessel according to an embodiment of the invention can be used for removing the platform 12 or a part thereof by cutting a number of the tubular elements of jacket 14. The cutting tool 36 can be hoisted and positioned as necessary with respect to the jacket 14, even if direct vertical access to the jacket is prohibited by the deck 13. The tool 36 can further be moved within the structure of tubular elements if required.

[0033] It would be clear that the removal of a sea platform 12 is just one of the possible examples for which the invention can be used. The invention can also be applied to other offshore operations including construction, maintenance, inspection and repair work. The tool of the assembly can be an inspection tool, for instance a camera or sampling tool, or a tool for different operations, for instance drilling or digging. The tool can further be applied to any type of structures under water which require removal, such as pipelines, wreckage or debris.

[0034] The tool supporting module 30a comprises an arm 32, a rigid element 31, and a counterweighting element 34. Tool 36 is connected to the load supporting module 30a at or near a terminus 37 of arm 32. In the example depicted in Fig. 1, the tool 36 comprises a cutting tool. Clearly other loads or tools can be connected to and/or supported by the arm 32.

[0035] The load supporting module 30a is connected to the hoisting system via a connection device 39 comprising a rigid element 31 and a connection point 33. The connection device 39 can comprise suitable means for allowing to connect an extension member 22 to the load support module 30a. The connection between extension member 22 and rigid arm 31 may comprise a detachable or adjustable connection or may be an integral connection.

[0036] Providing a rigid element 31 as part of the connection device 39 between the assembly 30 and the extension member 22 of the hoisting system 23 provides rigidity and stability to the connection, which aids in the controllability of the position and orientation of assembly 30. Specifically the rigid element provides a pendulum effect as described in more detail with reference to Fig. 5. It further makes it possible to connect a drive between vertical extension member 22 and horizontal member 32, as shown in figure 2. Rigid element 31 may be omitted, in which case the assembly 30 can be directly connected to the extension member 22.

[0037] Connection point 33 is provided at a lower terminus of the rigid member 31 and comprises a hinge having a pivot axis (in Fig.l out of the drawing) for pivoting of the arm 32 and arm 35 according to arrow 38. The connection point 33 / hinge can comprise suitable bearings or other suitable pivoting mechanisms. Preferably a low-friction bearing is used.

[0038] It should be noted that in other, less preferred, embodiments the extension member 22 can be directly connected to the arms 32,35 forming a connection point 33. A similar hinging function will be achieved as the arms 32,35 will be able to hinge according to arrow 38 around the connection point 33.

[0039] Arm 32 and arm 35 are preferably connected to each other. In an embodiment the arms 32,35 are an integral arm. The connection of arms 32 and 35 over the hinge at connection point 33 will result in movement of both arms 32 and 35 in the same direction around connection point 33.

[0040] The counterweighting element 34 is configured to provide a weight, which will move a centre of gravity of the arms 32,35, load 36 closer to the connection point 33. A counterweighting element 34 according to the invention is a counterweighting element that significantly shifts the centre of gravity of the assembly 30 / module 30a.

[0041] The counterweighting element 34 is positioned such that the centre of gravitation of the tool assembly 30 moves closer to the connection point 33 than it would be without the counterweighting element 34. This will result in lowering the necessary force for hinging arms 32,35 according to arrow 38. This will reduce the size of the necessary drive for setting an angle between the rigid arm 31 and the arms 32,35.

[0042] The counterweighting element 34 and arm 35 are preferably free hanging arms. The counterweighting element 34 and arm 35 could have a combined weight higher than the weight of the arm 32.

[0043] Preferably the assembly 30 is balanced so that its centre of gravity is located at connection point 33. The counterweighing element allows balancing the weights and moments of loads on the opposite sides of hinge at connection point 33, which includes, at least the arm 32 and the cutting tool 36. When the centre of gravity is precisely in the rotation axis of connection point 33, it will allow to position the assembly 30 in any angle to the vertical in an balanced equilibrium.

[0044] Clearly ‘opposite’ sides of the arm incorporates not only polar opposite positions, but also other angles are possible.

[0045] In use, the arms 32,35 each extend away from the connection point 33 resulting in opposite moments of gravitational force around the connection point. Of the tool assembly 30 arm 35 and counterweighting element 34 provide one moment of gravitational forces around connection point 33, whereas all other elements of the tool assembly 30, including e.g. tool 36, provide for the opposite moment. The opposite moments are preferably balanced, however a certain unbalance can be accommodated by the drives in the system to prevent the tool from rotating. The ratio between the moments should preferably be between 0.8 and 1.2, more preferably between 0.9 and 1.1, most preferably between 0.95 and 1.05.

[0046] The load supporting module 30a and cutting tool 36 are arranged so that the centre of gravity 33 of the portion of assembly 30 that is hingebly attached to the connection point 33, including the arms 32,35, load 36 and counterweighting element 34, is located at the general intersection between the axis 42 containing the hoisting extension member 22 and a central axis 41 of arm 32. In other embodiments the centre of gravity can be positioned above or below the longitudinal axis.

[0047] In this application ‘balanced arm’ or ‘balanced state’ will refer to the hingebly attached portion of tool assembly 30 to the connection point 33 having a centre of gravity close to, preferably in, the connection point 33.

[0048] In a balanced state the arm can be positioned in any position in an equilibrium. In another embodiment the centre of gravity of the hingebly attached portion of tool assembly 30 to connection point 33 is positioned under the arm 32. This will provide a stable equilibrium: rotating the balanced arms and loads having a centre of gravity under the connection 33 will result in elevation of the centre of gravity point. The balanced arm will be biased back to the horizontal position. Accordingly the tool support module 30a will, if suspended from a hoisting system 20 hold the arm 32 in a generally horizontal position under the influence of gravity. A drive, such as a thruster or cylinder can be provided to position the arm in a different orientation.

[0049] Arm 32 and/or arm 35 can be buoyant. This will lower the weight of the support module 30 in the water.

[0050] Counterweighting element 34 may be connected to connection point 33 via an arm 35, which is preferably shorter than arm 32 which allows the end of arm 32 to extend away from the vessel 10 while the counterweighting element 34 is held between the hull and connection 33. Preferably the arm 32 extends multiple times the length of arm 35 from connection 33 which will allow the terminus of the arm of 32 to extend in a location without direct vertical access such as under the outline of a deck 13 (as illustrated in figure 1).

Further, by shortening the arm 35, the inertia of the support module 30a is lowered.

[0051] In an embodiment, one or more propulsion devices and/or one or more drives can be provided in the assembly 30 in order to actively control positioning and orientation of the assembly and especially the tool 36. The propulsion device, may comprise, for example, thrusters.

[0052] In an embodiment the tool 36 positioned near or at the terminus 37 of arm 32 away from the connection 33 is a cutter as shown in Fig. 2. It will be clear to the skilled person that this cutter can comprise hydraulically activated blades in between which an element of jacket 14 can be held and cut when driving the hydraulics. Other types of cutters or other types of tools can also be connected to arm 32. Although shown with the tool 36 provided at the end of arm 32, it will be clear that the tool can also be positioned closer to the connection 33.

[0053] Figure 2 shows a detailed view of an assembly 100 that can be connected to a hoisting system of a vessel, floating platform, or aerial vehicle.

[0054] As shown in Fig. 1 the tool assembly 100 is suitable to be held under water / below sea level 11. Clearly the tool assembly 100 could be suitable for operating in other fluids, including gasses.

[0055] Tool support assembly 100 comprises a connection device comprising rigid element 101 and connection 102 having a hinge. Rigid element 101 is arranged to extend upwardly and can be connected to a part of the hoisting system, e.g. supported by a floating device such as a vessel. Near an end of rigid element 101 a connection 102 is provided that allows pivoting of arms 103 and 104 around a generally horizontal axis 99. The arms 103 and 104 support counterweight 105 and suitable drives, tools and further connections.

[0056] The counterweight 105 significantly shifts the centre of gravity of the tool support assembly 100 towards the connection 102. Preferably the total weight of the assembly 100, including arms and supported elements, is balanced such that a centre of gravity of a pivotably attached portion of the assembly 100 is preferably in or close to the connection 102, such as below the connection 102. The pivotably attached portion comprises generally the complete assembly 100 except for the connection device including connection 102 and the rigid element 101 that is directly suspended from the hoisting system attached thereto. It can further be noted that since the rigid element 101 is positioned above the connection 102, the rigid element does not influence the centre of gravity of the assembly 100.

[0057] In Fig. 2 arms 104 are connected to two optionally separated counterweighting elements 105. The arms 104 and counterweights 105 are arranged such that pivoting 98 about axis 99 is allowed over large angles, e.g angles over 45 degrees. In the shown embodiment the arms 103,104 can pivot over 80 degrees, even 90 degrees, in the counter clockwise direction, wherein the counterweights 105 move upward and arm 103 with tool 109 moves downward.

In such state the counterweights 105 are positioned on opposite sides of rigid element 101.

[0058] In some embodiments lifting and lowering the support assembly 100 comprises bringing the arms 103-104 in a generally (close to) upright position, wherein the counterweight is held on opposite side of the rigid element 101. In such an upright position friction during lifting or lowering can be reduced and the tool assembly 100 can be moved easier through the wave zone. A suitable drive can be provided to allow bringing the arms to the generally (close to) upright position.

[0059] Arm 103 extends away from connection 102. The arm 103 allows positioning a tool 119 in a location without direct vertical access when the tool assembly 100 is suspended from a hoisting system or other lifting system from a vessel or another floating platform.

[0060] Connections 111, 112 connect a controlled hydraulic cylinder 110 to arm 103 and rigid element 101 respectively. The hydraulic cylinder 110 can be driven to configure an angle between rigid element 101 and arm 103. As arms 103,104 are balanced, the moment needed for moving arm 103 to pivot is relatively low and a relatively small hydraulic cylinder is needed. This is weight and cost efficient and lowers maintenance costs.

[0061] One or two thrusters 130, 131, illustrated schematically, can be provided. Thruster 131 is provided further away from connection 102 than connection 111 on arm 103. Thruster 130 can be provided on a counterweight 105, in an alternative embodiment the thruster itself can act as the counterweight. The one or more thrusters 130,131 or any other kind of drive can be controlled to counteract weathervaning according to arrow 120 of the support assembly 100. The thrusters 130,131 can counteract weathervaning and control the direction of extension of the arm 105 without adjusting the position of the vessel at the surface. The thrusters 130,131 can provide a yawing moment to counter act the rotation around hoisting wire 22. Suitable electric and control lines can be connected to the thrusters 130, 131 via the hoisting system to the vessel 10 for providing power and control respectively.

[0062] To reduce weathervaning as a result of water flows, the drag of the counterweighting element and the arm+tool is preferably designed to be about equal.

[0063] Even more remote from connection 102, a bearing 106 is provided which allows rotation according to arrow 123 as a result of a suitable driver (not shown). The bearing 106 and suitable drive allow for rotation 123 of the parts connected to arm 103. The rotation 123 is a rotation around the length of the arm 103 as shown by axis 97.

[0064] As the parts located distal with respect to bearing 106 are gravity balanced, preferably with a centre of gravity along the axis 97 of arm 103, rotation 123 of the parts connected to arm 103 does not change the centre of gravity of the load support module.

[0065] Further a connection 107 is provided further away from bearing 106. In the position illustrated in figure 2, connection 107 has a vertical pivoting axis 96 that allows pivoting according to arrow 124 using a suitable drive such as a cylinder 114. The drive 114 will allow positioning of the tool 109. A hinging movement 124 of distal parts from connection 107 could cause a minor shift of the centre of gravity, but generally the centre of gravity is maintained close to the preferably balanced state.

[0066] Connected to the connection 107 is a tool holder 108 embodied as a fork-like structure. The tool holder 108 is pivotally connected over a pivoting axis 118 with tool 109. The pivoting axis 118 allows pivoting according to arrow 125 of the tool 109 for positioning the tool for cutting the jacket 14.

[0067] Connection 107, tool holder 108 and bearing 106 allow positioning the tool 109 in a desired position, e.g. onto jackets 14 positioned under an overhang such as a platform 13. Positioning and maneuvering the load support assembly 100 is part of the operation method according to the invention.

[0068] Suitable drivers and hydraulics can be used for accurately positioning and maneuvering the tool, wherein such drives allow rotation The balance of the arm is generally maintained by keeping the centre of gravity close to the equilibrium point or by activating the drives to accommodate an unbalance. Clearly other kinds of connections and hinges on arm 103 can be used for positioning and maneuvering the tool 109, but the principle shown allows accurate adjustment of the position of the tool around all three major axes 96,97 and 99.

[0069] According to an embodiment the invention provides for a load support assembly that positions the load in a vertical direction using the hoisting system suspending the support assembly as a general positioning device, while using a suitable drive and connection on arm 103, such as pivoting axis 118, for final and more exact positioning of the tool 109. Such a two stepped vertical position control results in a more accurate and simpler design for vertical position control.

[0070] Although an arm 103 connected to the hoisting system via connection 102 is provided, the connection 102 e.g. in combination with cylinder 110, is not used for active vertical position control.

[0071] During operation a remote control can be used to position the tool 109. In operation a remote vehicle having cameras can be used to overview the operation under water and to provide feedback to the operator. In other embodiments GPS sensor or other position sensors are used to measure the position and to provide a computer processor with input for the relative position of the tool. This will allow automatic guiding of the support arm 30 to use the tool 109 at a desired, e.g. a programmed, position. In an embodiment, the positions for operating the tool 109 are programmed into a memory and the support arm 30 and tool 109 are automatically guided from position to position according to the programmed memory.

This will further reduce the time for executing an operation. A camera can also be positioned on the tool or the support arm.

[0072] In the embodiment shown in Figs. 1 and 2 tool 109 is a cutter or shear. The cutter is shown only schematically. The cutter comprises knives 119 that can be hydraulically driven to cut an element of jacket 14 between the knives. Hydraulics are not shown. The skilled person will be aware of suitable ways for hydraulically driving the cutter 119. Known cutters suitable for cutting jackets have a significant weight. As a result of using the counterweighting elements 130 such a cutting tool can now be used on an arm that can extend under an overhang.

[0073] The support module 30a or the tool assembly 100 according to the invention comprises a balanced arm 103,104, wherein one arm 103 extends away from a connection having the tool 109 and the counter arm 104 is connected to counterweights. The centre of gravity will be moved significantly by the counterweighting elements towards the connection 102, preferably in or close to, preferably under, the connection 102. The position of the centre gravity is also maintained during operation and maneuvering using the positioning drive and connections 107,105,108.

[0074] In some embodiments a drive can be provided for driving the counterweight elements 105, or a part thereof, to correct for shifts of the centre of gravity during operation. When a shift of the centre of gravity is experienced, either because of a different tool or as a result of operation, a suitable drive can drive to counterweights to compensate for the shift of centre of gravity and shift the centre of gravity back to position close to equilibrium connection 102 or in the vertical axis or plane of the equilibrium connection. The moment of the counterweighting element 105 with respect to the connection 102 can be changed e.g. by adding or reducing the weight or by adjusting the distance to the connection 102 [0075] In an embodiment different tools instead of cutter 109 can be mounted onto the arm 103 of the support module, having a different weight, resulting in a shift of the centre of gravity. To adjust for the different weight, the counterweighting elements 105 can be adjusted.

[0076] As a result of the gravity balanced arms 103,104 cylinder 110 can be a relatively small cylinder reducing weight and cost. The forces to be absorbed and overcome by cylinder 110 are relatively small.

[0077] Cylinder 110 can be operated in different modes:

Dampened state;

Locked state;

Open state allowing free movement.

[0078] In a locked state cylinder 110 is actively controlled in a predetermined position to maintain or bring about a change in the angle between arm 103 and rigid element 101 according to arrow 121. The cylinder 110 can be controlled to provide a bias ‘back’ to the default position of arm 102 perpendicular to the rigid element 101.

[0079] In another mode cylinder 110 is in a dampened mode, in which arm 103 is allowed to hinge 121 around connection 102 but the hinging movement is dampened. This can e.g. be accomplished by throttling the hydraulic supply to the cylinder. This mode can also be used to create a certain resistance which allows movement of the drive only when a certain load or force is exceeded.

[0080] In a further operational mode the hydraulic cylinder 110 is not locked. In this mode the arms 103 and 104 can pivot freely around connection 102. Such a mode is, for example, beneficial when cutter 119 is engaged on jackets 14 and free motion of the support assembly 100 can be allowed to prevent damage.

[0081] To operate the tool, the assembly formed by the tool and supporting module is lowered to the work area. During lowering of the tool the drives on the load support module 100 are locked. For example the cylinder 110 can be locked in a position wherein the arm 103 and rigid element 101 are locked at about 90 degrees. In the example depicted in Fig. 2, cutting tool 109 is deployed to an area in the periphery of a target object 126 to be cut.

During lowering of the assembly to the target area any associated hydraulic cylinders can be set to a locked state, so that the components of the assembly remain static during deployment.

[0082] The submerged tool is re-orientated as necessary to a desired position and orientation with respect to a target object. The tool’s position and orientation can be manipulated along the three major axes with the aid of drives such as hydraulic cylinders. The cutting tool 109 is orientated with respect to the target object 126 to be cut in accordance with the desired cutting angle. In the depicted example, the target object 126 is part of a jacket. The cutting angle can be a predetermined cutting angle based on an programmed operation outline, or it can be determined in real-time, in situ with the aid of optical sensors.

[0083] The position of the arm 103 along a rotational direction indicated by arrow 120 can be controlled via the rigid element 101. The positioning and orientation of the tool while submerged is effected with the aid of the hydraulic cylinders, which are actuated accordingly and ultimately set in a locked state when the desired position is attained. In the depicted example, a hydraulic cylinder 110 can actuate rotation of the arm 103 supporting the tool about an axis 99 along a direction indicated by arrow 121. The tool can be further rotated about an axis 118 as indicated by arrow 125. The tool holder 108 can be rotated about axis 107 in a direction indicated by arrow 124. The tool holder 108 and tool 109 may be jointly rotated about axis 97 at a connection 106 in a rotation direction indicated by arrow 123. The orientation of the cutting tool may be continuously or intermittently readjusted as necessary.

[0084] After the tool attains the desired orientation it can be actuated in order to engage and cut the target object. Once the cutting tool 109 has engaged the target object 126 with the knives 119, any hydraulic cylinders enabling a rigid position of the tool may be released to an open state so that the tool is disconnected from the motions of the vessel during operation. By setting the hydraulic cylinders to an open state the points of movement of the tool controlled by the hydraulic cylinders become free. It is desirable to release the hydraulic cylinders whenever the tool is engaged, as opposed to maintaining a locked state, in order to avoid damage to the cutting blades due to movements of the lifting system being transferred to the stationary tool.. Operation of the tool is not negatively impacted by the release of the hydraulic cylinders once the target object has been engaged by the tool since the strength of the engagement is such that it cannot generally be disrupted by the expected wave-induced motions transferred to the assembly.

[0085] Accordingly the assembly 100 can be first positioned at a first position for operating the tool and subsequently be moved to a second position. The repositioning is possible under water, saving time to raise, adjust the orientation of the tool, and again lower the assembly 100. For repositioning the drives are returned from an open state to a locked state, which will allow repositioning the load to a desired second operating position.

[0086] Although ‘balanced arm’ is used herein, the centre of gravity is not necessarily exactly positioned at the equilibrium connection 102. Advantages according to the invention are already achieved when a counterweight is used to compensate partially for the weight of the opposite arm and tools. By providing the counterweighting element 105, the cylinder 110 can be reduced in size with respect to the cylinder that would be needed if no counterweight is present. Another advantage of drive 110 is that the position of the tool can be adjusted without retrieving the tool to the surface, thereby saving costly operational time.

[0087] The tool assembly 100 is preferably arranged to provide a stable, balanced position, in particular a configuration that is biased to a balanced position wherein the arms extend horizontally. By providing a bias, which in some embodiments is provided by drives, the assembly is returned to a default position, such as the horizontal position. In an embodiment cylinder 110 is driven to return the arms and accordingly assembly 100 to a horizontal position.

[0088] According to a further set of aspects, the invention relates to heave compensation methods and systems comprising an assembly of a tool mounted on an arm. The method and assembly comprise hoisting the tool from a floating platform in the sea.

[0089] Wave-induced motion of a vessel or floating platform can be divided into several general components including heave, roll, and pitch. The heave component is that motion which causes vertical displacement of the vessel or floating platform. It is well known in the art to employ motion compensation systems in order to reduce the effect of wave-induced motion of the vessel or floating platform on a load being maneuvered by a hoisting system.

By using motion compensation, the workability of a tool can be improved, and the weather window, i.e. the range of weather conditions within which the tool can be effectively operated, is expanded as the system becomes more resilient to movement.

[0090] Heave compensation systems generally fall into two main categories, namely, active and passive heave compensation. A combination of both active and passive compensation elements is also possible. Active motion compensation or semi-active motion compensation systems are often employed systems. However, there are drawbacks associated with active and semi-active heave compensation systems, including the need for control systems for actively counterbalancing the wave-induced motion, and the need for an external power supply. These elements increase the complexity and fallibility of the system. In contrast, fully passive heave compensation systems require no external power supply and counterbalance an induced motion through the mechanical absorption and/or transmission of the force associated with the motion. However, known passive compensation systems rely on shock absorbing elements, which are not suitable for use during prolonged periods of time as they are susceptible to performance deterioration. Therefore, a need exists for a heave compensation system for providing heave compensation to tools, equipment and other objects subject to wave-induced motions of a vessel or floating platform, which is simple and reliable. Moreover, a need exists for methods and systems to control and maneuver a tool or piece of equipment during subsea operations which are resilient to wave-induced motion.

[0091] Although Fig. 3A and 3B introduce the passive heave compensation system that is not shown in the earlier embodiments, it will be clear that the basic configuration of the balanced arm of figures 1-2 is generally applicable too to the load assembly 60 shown in figures 3a/3b and, for clarity, won’t be repeated here. The basic idea of the heave compensation system is to reduce the motions on one side of the connection point, more precisely the side holding the load. The part on the other side of the connection point, with the counterweight, is allowed to move more. The heave compensation system will work when the horizontal surface on the side of the connection point where the load is connected is larger than the horizontal surface on the side of the counterweight. The heave compensation can therefore be achieved by either adding surface on the load side, or decreasing the surface on the counterweight side, for instance by designing the shape of the counterweight such that horizontal surface is reduced. Fig. 3A shows, partially in perspective, an equilibrium position of a load assembly 60 including load support module 60a and a supported element 66. Load support arm 60a is suspended from a hoisting wire 50. The load support module 60a comprises a connection device having rigid element 61 and connection 62. Further load support module 60a comprises arms 63,64 and counterweighting element 65. The load support module 60a and supported element 66 are generally balanced around connection 62 formed by a hinge having an axis in the horizontal plane (in Fig. 3a perpendicular to the plane of the paper).

[0092] Counterweight 65 is positioned at a predetermined length away from connection 62 over arm 64 resulting in the centre of gravity of the load support assembly 60 being closer to the connection 62.

[0093] Supported element 66 is a load and can comprise a tool. The supported element 66 may comprise a tool, a piece of equipment, a load, or any other element which may require hoisting. In a preferred embodiment, the supported element 66 comprises a cutter, such as those for use in cutting a jacket of a platform or pipes. Supported element 66 can comprise drives and other suitable means for positioning the tool, moving the tool with respect to the arm 63.

[0094] Further, in this embodiment, two heave compensating plates 68 and 69 extend outwardly from the arm 63. The plates extend a long a substantially horizontal plane. The plates 68,69 are part of a passive heave compensation system 67. While in this exemplary embodiment the plates are depicted as two separate plates for clarity purposes, it will be understood that the plates may alternatively comprise a single, integral structure extending along opposite directions as shown in Fig.4.

[0095] The counterweight 65 is arranged such that the centre of gravity of the complete assembly 60 is located closer to the connection 62 than without the counterweight. Preferably the counterweight brings the centre of gravity of the assembly 60 to the connection 62, below or above. The result is a balanced assembly 60 having its centre of gravity located at connection 62.

[0096] During operation of the assembly 60, e.g. during cutting, wave-induced motions experienced by the vessel can be transferred to the tool 66, which will affect its precision and workability. A heaving motion of the vessel is transferred via the hoisting wire to the assembly 60. Heaving will cause connection 62 to be displaced in the vertical direction 70.

[0097] The assembly is configured so that transfer of wave-induced heaving motion from connection 62 to supported object 66 is attenuated. This objective is achieved by way of passive heave compensation. The passive heave compensation device 67 is arranged to dampen or reduce the heaving of the support module and in particular a tool connected to an arm 63 of the support module 60. In particular the upward and downward heaving is passively compensated. The passive heave compensation device 67 comprises an increased horizontal surface area that attenuates any vertical movement. The horizontal surface area can be formed by wings, sails and/or one or more plates 68,69. Alternatively the surface can be made up from many, much smaller parts.

[0098] Plates 68,69 extend generally in a horizontal plane. The plates are arranged to provide resistance by mobilizing the mass of water above or below it if the plates move upward or downward. This “added mass” resistance is used to the dampen the heaving in vertical direction.

[0099] In the exemplary embodiment of Fig. 3a, the passive heave compensation device comprises a resistance surface area, such as two plates 68, 69 which are located on each side of the arm and along a substantially horizontal plane. In order to counteract the wave-induced motion, passive heave compensation device 67 is provided extending from arm 63 of the support module 60a and are configured to counteract the heaving motions of the vessel by attenuating transfer of wave-induced heaving motion from connection 62 to tool 66.

[0100] The two plates will provide resistance against this upward/downward movement. The magnitude of the resistance against motion along each vertical direction is generally directly proportional to the surface area of the plates facing that direction. The plates will dampen the vertical movement of the arm. Since the resistance to displacement of the assembly 60 is to an extent proportional to the surface area of the two plates 68, 69, the dimensions of the two plates may be selected in accordance with a desired resistance effect, or by extension, with a desired heave compensation effect at tool 36, with larger plates providing increased resistance to motion.

[0101] In figure 3B the situation is shown wherein, as a result of the heaving, hoisting wire and consequently connection 62, are moved downwardly by a distance indicated by arrow 70, for example over a length in the order of lm. In dotted lines the original position of connection 62 is shown in figure 3b.

[0102] The result of vertical friction of the heave compensation system 67 is that at the position of the arm connected to the plates 68,69 the heaving motion is dampened, shown by arrow 71, to less than the distance 70. This can be for example in the order of 50 cm or less. This reduction in motion can be enough to deploy, set and operate the tool in weather conditions that would not allow operating a tool without heave compensation.

[0103] Since the heaving motion of connection 62 is attenuated as it is along the arm 63 to the supported object 66, a sudden, significant displacement of the supported object 66 is prevented. Thus, the supported object 66 will experience only a fraction, such as less than 30 cm, or none, of the heaving motion induced at connection 62. The workability of the tool and the precision of the operation, which are susceptible to the motion, are improved as compared to other forms of operating the tool.

[0104] This is highly advantageous in a variety of scenarios. For example, the load support module can be used to support a tool, as it executes an action in a subsea environment. The workability of the tool and the precision of the action, which are susceptible to the motion, can thus be increased as compared to other forms of operating the tool.

[0105] The two resistance plates may be of any suitable material and thickness that will provide a desired level of resistance. The two plates 68, 69 may be connected to arm 63 by way of an adjustable connection. Alternatively the two resistance plates may be integrally formed with arm 63. The two plates may be located at any area between remote end of arm 64 and the remote end of arm 63. In an embodiment, the two plates are located between the connection 62 and a distal terminus near the tool 66 with respect to the connection 62. The plates may be statically placed along the arm or may be arranged for dynamic control and displacement thereof moving connection 75 away or closer to connection 62.

[0106] A skilled man can calculate surface area of the heave compensation plates 68 and 69 connected to arm 63 at connection point 75 that results in a certain compensation of the heaving motion 70 at the location of the supported element 66.

[0107] Basically a ratio between the vertical movement 71 and vertical movement 70 is to be equal to the ratio between distance on the one hand between connection 62 to the supported element 66 and on the other hand between connection 62 and the connection 75. As a result the supported element can be held in position with a tolerance of several centimetres despite the heaving motion 70 of the vessel. The resistance to displacement of the assembly 30 is to an extent proportional to the surface area of the two plates 68, 69. Thus, the dimensions of the two plates may be selected in accordance with a desired resistance effect, or by extension, with a desired heave compensation effect at supported object 36, with larger plates providing increased resistance to motion.

[0108] In an embodiment the surface area of the plates 68,69 of the heave compensation system 67 can be operated, e.g. by moving the plates partially over each other. This will allow enlarging or reducing the horizontal surface area of the plates, resulting in control of the heave compensation. Preferably the movement of the plates extends in the direction of the surface area of the plates, which movement can be provided by a relatively small drive. The enlarging and reducing of the surface area allows enlarging or reducing of the vertical friction, e.g. dependent on the amount of heaving. An active feedback loop can be used to control the surface area.

[0109] In another embodiment, a single plate or multiple plates can be used. The single plate can be positioned below or over the arm 63.

[0110] In an alternative embodiment a mechanism for reducing and enlarging the surface area of the two plates is provided in order to facilitate deployment and retrieval (lifting and lowering) of the assembly or load supporting module and/or to reduce and enlarge the frictional force countering the heaving.

[0111] In an example, the surface area of the plates is about 5-6m .The plates 68 and 69 of the passive heave compensation system 67 are connected to the arm at about 50-80% of the length of the arm resulting in the balance heave compensation according to figure 3B during 1 meter heaving.

[0112] Counterweight 65 will, as a result of the heaving motion, move according to arrow 72 over a larger distance than the heaving motion itself.

[0113] Additionally to the passive heave compensation system, the respective drives of the arm, including cylinder 110, but also a suitable drive, such as a winch, for pivoting the tool or cutter 109 around axis 118 can be used to actively compensate for the vertical heaving and possibly for other heaving motions.

[0114] In an embodiment cylinder 110 is operated in use during heave compensation of a balanced arm in a dampened state. This will allow the arm 63,64 with load 66 to hinge around connection 62, but the hinging is dampened. In a further embodiment the dampening of the cylinder 110 can be controlled, e.g. using a feedback loop based upon the observations of suitable sensors, such as position sensors of the load 66. A suitable controller can be connected to the sensors and to a throttle of the cylinder 110 for controlling the throttle as a result of the observations.

[0115] Figure 4 shows a further embodiment, wherein a heave compensation system 160 comprises a horizontal plate 173 connected closer to connection 162 with arm 163. The single plate 173 functions similar to the passive heave device 67 of Figs 3a and 3b.

[0116] In the embodiment according to Fig. 4 a traditional drive 172 allowing telescopic extension of the arm 163 in a direction away from connection 162 according to arrow 172 is provided in order to compensate for the pivoting around connection 162 resulting from passive heave compensation system 160. A tool 166 is provided at a distal end of the arm with respect to the connection point. During heaving and the resultant pivoting of arm 163 around connection 162, the tool 166 will move toward the connection point in the horizontal plane. This moving will be larger for more heaving. The horizontal shift can be compensated by telescopic extension of the arm 163.

[0117] It is noted that as the position of the tool 166 is adjusted, the centre of gravity of the load supporting arm will change. The heave compensation device, in particular the location of the plates, may require adjustment thereto.

[0118] Figure 4 further shows an extension and reduction of the length of arm 164 in direction 174 using a suitable drive (not shown) allowing to change the length of arm 164, and thereby the distance of the counterweights 165 with respect to connection 162 in order to compensate for possible shifts of centre of rotation, resulting in a change of moment of gravitational force around connection 162.

[0119] In some embodiments a drive can be provided for driving the counterweights, or a part thereof to correct for shifts of centre of gravity. When the shift of the centre of gravity is experienced, the suitable drive can drive to counterweights to compensate for the shift of centre of gravity and shift the centre of gravity back to position close to the equilibrium connection or in the plane of the equilibrium connection.

[0120] In a further embodiment, the counterweight is arranged for dynamic adjustment of the weight. This can be achieved, for example, by providing a water-based counterweight which can release or absorb water as necessary to reach a desired weight.

[0121] Figure 5 shows a pendulum action of the load support module 150. In case of a pendulum motion of the load support module 150, the rigid element 151 is not extending vertically anymore. As connection point 159 to the hoisting wire (or block) is located at a distance from hinge 156 gravitation action is affected, resulting in a ‘back to default’ movement according to arrow 158, wherein default is a generally vertical extending rigid element 151 and horizontal load support module 150. The rigid element 151 provides a pendulum effect.

[0122] Alternatively the load supporting module 150 can be used to support and handle a piece of equipment, or any other object such as a tool such as cutter 166. The load may be hoisted over the load supporting module 150 by the hoisting system from a floating vessel.

[0123] Fig. 6 shows an assembly 180 according to an embodiment of the invention, comprising an arm 192 connected to a counterweight 188 at a connection point 186 for supporting a load 190 at a connection 194. The assembly may be connected to a hoisting system via an optional rigid element 204.The load may comprise a tool, a piece of equipment, or any other type of load, such as a camera. The stability of the load 190 is maintained via heave compensation system including plates 196, 198, which allows more controlled positioning of the load.

[0124] Fig. 7 shows a load support module 200 in accordance with a further embodiment of the invention. The load support module 200 is configured for supporting and providing passive heave compensation to a load at a connection point 214. The load support module 200 comprises counterweight 206 and plates 210, 212, arm 208 and may be connected to a hoisting system via an optional rigid element 204. The load may comprise a tool, a piece of equipment, or any other type of load, such as a camera.

[0125] In a further embodiment, the arm is shaped in a plate-like fashion in order to increase the resistance surface area. This is advantageous because it augments the heave compensation provided by the plates. Further, increasing a surface area of the arm decreases the resistance surface area that must be provided by the plates. That is, the plates can have a smaller surface area.

[0126] In an embodiment the arm is not straight. The arm, in particular the arm connected to the tool can be a bended arm.

[0127] In an embodiment a 3D sensor or camera may be provided along the support or tool in order to capture imagery of an area, such as a work area. This is advantageous as it can increase the precision of the work performed and to receive instant feedback of the effect of the operation being conducted.

[0128] Further modifications in addition to those described above may be made to the structures and techniques described herein without departing from the spirit and scope of the invention. Accordingly, although specific embodiments have been described, these are examples only and are not limiting upon the scope of the invention. CLAUSES: 1. Underwater load supporting module for connection to a hoisting system, comprising: at least an arm configured for connection to engaging a load, at least a counterweighting element arranged to counterweight the arm and/or the load, wherein the arm and the counterweighting element are connected to a connection device to be connected to the hoisting system. 2. Underwater load supporting module according to clause 1, wherein the connection device comprises a hinge, wherein the arm and the counterweighting element are arranged to hinge about the hinge. 3. Underwater load supporting module according to clause 1 or 2, wherein the counterweighting element is arranged to position a centre of gravity of the load and load supporting module significantly closer to, preferably at, the connection device, preferably the hinge. 4. Underwater load supporting module according to any of the preceding clauses, wherein the arm is arranged to detachably mount a load near a terminus of the arm, remote from the connection device. 5. Underwater load supporting module according to any of the previous clauses, wherein the connection device comprises a rigid element extending from a connection point, the rigid element arranged to be connected to the hoisting system. 6. Underwater load supporting module according to clause 5, wherein a drive connects the arm with the rigid element, the drive arranged for controlling the orientation of the arm with respect to the rigid element. 7. Underwater load supporting module according to clause 6, wherein the drive is a hydraulic cylinder. 8. Underwater load supporting module according to any of the previous clauses, wherein the arm comprises one or more drives for positioning the load, wherein the drives are preferably arranged to control the orientation of the load about at least two major axes. 9. Underwater load supporting module according to clause 8, wherein the arm and drives are arranged such that driving the one or more drives generally maintains the position of the centre of gravity of the underwater load supporting module and load. 10. Underwater load supporting module according to any of the previous clauses, comprising a drive, such as a thruster, arranged to control rotation of the load support module around a vertical axis. 11. Underwater load supporting module according to any of the previous clauses, further comprising a heave compensation system that is arranged to dampen resultant heaving movement of the arm. 12. Underwater load supporting module according to clause 11, wherein the heave compensation system comprises a difference in the horizontal surface area on either side of the connection point causing a difference in acceleration in vertical direction. 13. Underwater load supporting module according to clause 11 or 12, wherein the heave compensation system comprises at least one wing extending in laterally opposite directions from the arm. 14. Underwater load supporting module according to any of the clauses 11-13, wherein the heave compensation system is arranged to balance attenuation of the arm such that the load is held generally in position during heaving. 15. Underwater load supporting module according to any of the previous clauses, comprising one or more centre of gravity adjusting devices, such as drives, for moving a centre of gravity of load supporting module and load. 16. Assembly for connection to a hoisting system comprising a load supporting module according to any of the clauses 1-15, and a load. 17. Assembly according to clause 16, wherein the load is a tool. 18. Assembly according to clause 17, wherein the tool is a cutter, preferably a hydraulic cutter. 19. Hoisting system comprising the load supporting module according to any of the clauses 1-15, and an extension member; the load supporting module being connected to an extension member of the hoisting system. 20. Floating platform, such as a vessel comprising a hoisting system according to clause 19. 21. Method of hoisting a load under water from a floating platform, such as a vessel, comprising a hoisting system, comprising: providing an arm; connecting the load to the arm; providing a counterweighting element connected to the arm, the counterweighting element shifting the centre of gravity of arm and load towards a connection point, and hoisting the arm at the connection point. 22. Method according to clause 21, wherein the load is a tool and the method comprises operating the tool in a first location under water. 23. Method according to clause 22, wherein the method comprises moving the tool under water to a further location and operating the tool in the further location. 24. Method according to any of the clauses 21 - 23, wherein the method further comprises providing drives to control the position of the load, and adjusting the position of the load under water, by operating the drives. 25. Method according to any of the clauses 21 - 24, wherein the method comprises lowering or raising the load in the water, wherein, at least during lowering, drives for moving the load on the arm are in a locked state. 26. Method according to any of the clauses 21 - 25, wherein the load is a tool and the method further comprises engaging a jacket under water and wherein during operation of the tool hydraulic drives are operated in an unlocked (open) state to disconnect motions of the floating platform and the tool. 27. Method according to any of the clauses 21-26, further comprising providing on the arm, between the load and the connection point, at least one heave compensation element extending horizontally from the arm, and reducing the heaving motion of the load using the heave compensation element. 28. Method according to clause 27, wherein the method further comprises balancing the heave compensation, for example in function of the surface of the heave compensation element and the distance from the connection point, to hold the load substantially in a predetermined position.

Claims (28)

An underwater module for supporting a load that can be connected to a hoisting system, comprising: - at least one arm adapted to grip a load, - at least one counterweight adapted to provide a counterweight against the arm and / or the load, wherein the arm and the counterweight are connected to a connecting device that can be connected to the hoisting system. An underwater module for supporting a load according to claim 1, wherein the connecting device comprises a hinge, the arm and the counterweight being adapted to rotate around the hinge An underwater module for supporting a load according to claim 1 or 2, wherein the counterweight is arranged around a center of gravity of the load and of the module for supporting the load considerably closer to, preferably on, the connecting device, preferably the hinge , to lay. An underwater module for supporting a load according to any one of the preceding claims, wherein the arm is adapted to be releasably coupled to a load near an end of the arm, distant from the connecting device. An underwater module for supporting a load as claimed in any one of the preceding claims, wherein the connecting device comprises a rigid element extending from a connecting point, the rigid element being adapted to be connected to the hoisting system. An underwater module for supporting a load according to claim 5, wherein the arm is connected to the rigid element via a drive, the drive being adapted to control the orientation of the arm relative to the rigid element. An underwater module for supporting a load according to claim 6, wherein the drive is a hydraulic cylinder. 8. Underwater module for supporting a load according to one of the preceding claims, wherein the arm comprises one or more drives for positioning the load, wherein the drives are preferably adapted to orient the load relative to at least two arrange main axes. 9. Underwater module for supporting a load according to claim 8, wherein the arm and drives are arranged such that driving the one or more drives essentially leads to the position of the center of gravity of the load and the underwater module for supporting a load . An underwater module for supporting a load according to any one of the preceding claims, comprising a drive, such as a weir, adapted to control rotation of the module for supporting a load around a vertical axis. An underwater module for supporting a load according to any one of the preceding claims, further comprising a swell-compensation system that is adapted to damp a movement of the arm as a result of swell. An underwater load support module according to claim 11, wherein the swell compensation system comprises a difference of surface area in the horizontal plane on either side of the connection point, the difference in surface area leading to a difference in the acceleration in the vertical direction. An underwater module for supporting a load according to claim 11 or 12, wherein the swell compensation system comprises at least one wing that extends on either side of the arm in the lateral direction. An underwater module for supporting a load according to any one of claims 11-13, wherein the swell compensation system is arranged to balance damping of the movement of the arm such that the load is substantially held in position during swell. An underwater module for supporting a load according to any one of the preceding claims, comprising one or more center of gravity adjustment units, such as drives, for displacing a center of gravity of the module for supporting a load. An assembly for being connected to a hoisting system comprising a module for supporting a load according to any of claims 1-15, and a load. The assembly of claim 16, wherein the load is a tool. An assembly according to claim 17, wherein the tool is a cutting means, preferably a hydraulic cutting means. A hoisting system comprising the module for supporting a load according to one of claims 1-15, and a hoisting element, such as a cable, wherein the module for supporting a load is connected to the hoisting element of the hoisting system. A floating platform, such as a vessel, comprising a hoisting system according to claim 19. A method for hoisting a load under water from a floating platform provided with a hoisting system, comprising: - providing an arm; - connecting the load to the arm; - providing a counterweight connected to the arm, wherein the counterweight shifts the center of gravity of the arm and load towards a connecting point; and - hoisting the arm at the connecting point. The method of claim 21, wherein the load is a tool and wherein the method comprises performing an operation with the tool at a first location under water. The method of claim 22, wherein the method comprises moving the tool underwater to another location and performing a treatment at the other location with the tool. The method of any one of claims 21 to 23, wherein the method further comprises providing drives for controlling the position of the load and adjusting the position of the load under water by turning on drives. The method of claim 24, wherein the method comprises moving the load down or up in the water, wherein, at least during the down movement, drives for moving the load have been brought into a locked state. A method according to any one of claims 21-25, wherein the load is a tool and wherein the method further comprises engaging an underwater element (jacket) and wherein hydraulic drives are in an unlocked (open) state during the operation of the tool to disconnect movements of the floating platform from the tool. A method according to any of claims 21-26, further comprising - providing on the arm, between load and connection point, at least one swell-compensation element that extends horizontally from the arm, and - reducing the swell movement of the load using the swell compensation element. A method according to claim 27, wherein the method further comprises balancing the swell compensation, for example as a function of the surface of the surface of the swell compensation element and the distance to the connection point, about the load substantially in a predetermined position to keep.