Shockload limiting system

Abstract

A shockload limiting system for limiting a shockload on a hoisting device during an installation procedure of an offshore load, the hoisting device comprising a hoisting device tip and a hoisting device line configured to be connected with a free end thereof to the load for hoisting the load, the shockload limiting system comprising: a motion compensation system for compensating vertical motions between the load and the hoisting device tip, the motion compensation system providing a first resilient connection between the hoisting device and the load, wherein the motion compensation system comprises a pre-tension device configured to provide a relatively low first stiffness to the first resilient connection; a sensor system configured to acquire first parameter data indicative of a vertical acceleration and / or vertical velocity of the load, the sensor system being configured to be operatively coupled to a control system configured for comparing the first parameter data to a predetermined first threshold value, and for generating a control command when an acquired first parameter value exceeds the predetermined first threshold value, wherein the shockload limiting system is configured to control the pre-tension device based on the control command.

Description

[0001] Title: Shockload limiting system

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a shockload limiting system and a method for limiting a shockload on a hoisting device during an installation procedure of an offshore load. The present invention further relates to a vessel comprising a hoisting device and the shockload limiting system.

[0004] The present invention yet further relates to a motion compensation system for compensating vertical motions between a hoisting device and a load hoisted by the hoisting device.

[0005] BACKGROUND OF THE INVENTION

[0006] Offshore structures are generally grounded to the seabed with large diameter piles or by jacket like structures supported by smaller diameter piles. The piles may be installed using hammers. The piles for jacket like structures may be installed through the legs of the structure, so called main piles, or may be installed adjacent to the structure and connected with pile sleeves, so called skirt piles, to the structure. Alternatively the piles can be preinstalled by piling through a seabed supported template or by other means. For placement onto the seabed, lifting equipment is used for being able to lift the pile. In order to insert these piles into the seabed, hydraulic impact hammers are typically used.

[0007] When placing the pile, or any other structure onto the seabed that is intended to be inserted into the seabed, there is often a risk for sudden loss of support capacity. Sudden loss of support capacity can occur after having transferred part of the hoisting device load to the ground or seabed. The sudden loss of support is often called a drop-fall or punch-through. Drop-fall or punch-through can happen at any time during installation and is caused by a loss in capacity of the supporting soil on which the pile is positioned. This can happen during the transfer of the load from the hoisting device to the ground or seabed, or even after transferring the full load towards the supporting soil. The loss of supporting capacity can happen directly or the soil can withstand the load put onto it for a certain time. The soil mechanics tend to be difficult to predict. When the load is connected to the hoisting device, the drop-fall or punch-through results in a shockload on the system. A sudden loss of supporting capacity can have detrimental effects on a hoisting device as well as on the structure supporting the hoisting device, e.g. a floating vessel or a bottom founded structure supported hoisting device, e.g. a jack-up rig. When there is a sudden loss of support, a pile or other foundation element will suddenly start to move with high accelerations resulting in high velocities. These large accelerations and / or velocities result in a large build-up of energy. When the foundation element is still connected to the hoisting device, for example a hoisting device, the hoisting device would need to resist this energy to stop the foundation element. The energy that needs to be incurred by the hoisting device is often considered as a DAF (Dynamic Amplification Factor) which is expressed as a factor on the weight to account for this energy.

[0008] The risk for the hoisting device and its supporting structure depends on the energy the system is able to build up and the stiffness of the hoisting system. The further the pile falls, typically the larger the speed, the greater the energy built up.

[0009] With the recent and expected further increase in size and weight of wind turbines and their foundation elements, the risks of a sudden load transfer from the soil to the hoisting system during installation of piles are also increasing. In the past, the weights of the items being installed were generally well within the capacity of the hoisting device. Therefore, the hoisting devices were able to withstand relatively large impact loads, or shockloads. If impact loads would increase, this would typically still be within the capacity of the hoisting device. With the current and expected future weights of the installation equipment and the foundation elements, the amount that needs to be invested just for the unpredictable and accidental shockload case would become excessively high.

[0010] SUMMARY OF THE INVENTION

[0011] It would be desirable to at least partially remove the above drawbacks, in particular to reduce a shockload on a hoisting device during a drop fall or punch through of a pile during installation thereof in a ground or seabed.

[0012] To better address one or more of these concerns, in a first aspect of the invention a shockload limiting system is provided for limiting a shockload on a hoisting device, in particular a crane, during an installation procedure of an offshore load, in particular during a drop fall or punch through of the offshore load, the hoisting device comprising a hoisting device tip and a hoisting device line configured to be connected with a free end thereof to the load for hoisting the load, the shockload limiting system comprising: - a motion compensation system for compensating vertical motions between the load and the hoisting device tip, the motion compensation system providing a first resilient connection between the hoisting device and the load, wherein the motion compensation system comprises a pre-tension device configured to provide a relatively low first stiffness to the first resilient connection,

[0013] - a sensor system configured to acquire first parameter data indicative of a vertical acceleration and / or vertical velocity of the load, the sensor system being configured to be operatively coupled to a control system configured for comparing the first parameter data to a predetermined first threshold value, and for generating a control command when an acquired first parameter value exceeds the predetermined first threshold value, wherein the shockload limiting system is configured to control the pre-tension device based on the control command.

[0014] Controlling the pre-tension device based on the control command that is based on a first parameter indicative of a vertical acceleration and / or vertical velocity of the load allows for a fast and reliable control of the shockload limiting system. When for example a drop fall or punch through of an offshore load such as a foundation pile occurs, this will cause an acceleration and / or increase in velocity of the offshore load. A first parameter indicative of said acceleration and / or vertical velocity is relatively easy and reliable to obtain, thereby providing an effective control for the shockload limiting system.

[0015] In an embodiment of the shockload limiting system, when the acquired first parameter value exceeds the predetermined first threshold value, the control command includes a disabling of the pre-tension device.

[0016] By disabling the pre-tension device, the pre-tension device is in fact isolated or shut off such that the initial relatively low first stiffness is greatly increased, in a sense becoming substantially infinite. When the pre-tension device would be enabled during the drop fall or punch through the offshore load would fall a first falling distance because of the relatively low first stiffness. The greater the first falling distance, the greater the possible build-up of energy and the corresponding shockload to the hoisting device. This first falling distance can be reduced by disabling the pre-tension device, thereby reducing the build-up of energy and the impact of the shockload on the hoisting device.

[0017] In an embodiment of the shockload limiting system, the shockload limiting system comprises a shock absorption device, wherein the shock absorption device is configured to provide a resilient connection between the hoisting device and the load, the resilient connection having a second stiffness and / or a damping coefficient, wherein the second stiffness is higher than the first stiffness, wherein during normal operation both the pretension device and the shock absorption device are active, and wherein when the acquired first parameter value exceeds the predetermined first threshold value the pre-tension device is disabled while the shock absorption device remains active.

[0018] In an embodiment of the shockload limiting system, the pre-tension device comprises an adjuster configured to adjust a pre-tension force of the first resilient connection.

[0019] In an embodiment of the shockload limiting system, the pre-tension device is configured for keeping the hoisting device line substantially taut while compensating relative vertical motions between the hoisting device tip and the load when the load is supported by the ground or seabed. This is for example beneficial during driving of the pile with the driving device or when disconnecting an installation tool from the load, because in case of a drop fall or punch through the falling load is stopped quicker.

[0020] A benefit of keeping the line substantially taut with the pre-tension device is that the risk related to human error can be reduced. There is in principle no need for the hoisting device operator to monitor and keep the rigging slack within a certain limit. This usually is a difficult task for the operator due to the large durations and vast number of operations.

[0021] In an embodiment of the system, the motion compensation device is provided in the hoisting device, e.g. in a winching unit of the hoisting device.

[0022] In an embodiment of the system, the motion compensation device is provided in the installation tool used to connect the hoisting device to the load.

[0023] In an embodiment of the shockload limiting system, the motion compensation device is configured to be suspended between the hoisting device tip and the load, the motion compensation device comprising

[0024] - a piston system comprising: o a main piston housing comprising:

[0025] ■ a first end having attachment means for releasable attachment to the hoisting device line or the load,

[0026] ■ a second end having an opening adapted to provide a fluid tight enclosure around a piston rod of a piston assembly, ■ an inner space divided by a slide-able first piston into a liquid filled first chamber and a second chamber, and

[0027] ■ a piston rod having at a first rod end attachment means for releasable attachment of the other of the hoisting device line or the load, and which is at a second rod end attached to the piston, and which stretches through the first chamber and further a distance out of the opening at said first end,

[0028] - the pre-tension device comprising: o a first accumulator comprising:

[0029] ■ an upper end,

[0030] ■ a lower end, and

[0031] ■ an inner space divided by a first separator into an upper chamber filled with a gas and a lower chamber filled with a liquid, the gas having a first gas pressure, a first liquid connection between the liquid filled first chamber of the main piston housing and the lower chamber of the first accumulator, a flow control member configured to be operatively coupled to the control system for receiving the control command, wherein the flow control member is configured to, based on receipt of the control command, control a flow resistance through the first liquid connection.

[0032] In an embodiment of the shockload limiting system, the sensor system comprises a flow sensor for sensing a flow velocity in the first liquid connection, wherein the flow velocity is indicative of the vertical acceleration and / velocity of the load.

[0033] In an embodiment of the shockload limiting system, the flow control member is a solenoid valve which, based on receipt of the control command, controls the flow resistance through the first liquid connection. In such an embodiment the control command is typically an electrical or digital control command.

[0034] In an embodiment of the shockload limiting system, the flow control member is a spring-loaded system, that based on a maximum flow allowed, stops the flow. This setup is, for example, commonly used for hose break valves or burst valves. In such an embodiment the control command is typically an analogue or mechanical control command.

[0035] In an embodiment of the shockload limiting system, the sensor system comprises at least one cylinder position sensor, where the cylinder position is used to calculate the vertical acceleration and / or vertical velocity of the cylinder and thus the load. In an embodiment of the shockload limiting system, the sensor system comprises at least one motion reference unit that is connected to the load, directly or indirectly via for example the installation tool, to determine the vertical acceleration and / or vertical velocity of the load.

[0036] In an embodiment of the shockload limiting system, the sensor system comprises a Total Station located on the vessel, to calculate the vertical acceleration and / or vertical velocity of the load.

[0037] In an embodiment of the shockload limiting system, the sensor system comprises a sensor for sensing the position of the piston rod, wherein the control system is configured to monitor the position of the piston rod. The control system may be operatively coupled to the hoisting device for controlling the pay out or pay in of the hoisting line based on the position of the piston rod. This way the likelihood is reduced of unintentionally reaching the end of the stroke of the piston rod, which could result in either a slack rigging when one side of the stroke is reached or a sudden transfer of load to the hoisting device on the opposite side of the stroke.

[0038] In an embodiment of the shockload limiting system, the sensor system comprises a combination of two or more of the afore mentioned sensor systems. Combining sensor systems provides redundancy.

[0039] In an embodiment of the shockload limiting system, the motion compensation device further and the shock absorption device are integrated, the shock absorption device comprising:

[0040] - a second accumulator comprising: o an upper end, o a lower end, and o an inner space divided by a second separator into an upper chamber filled with a gas and a lower chamber filled with a liquid, the gas having a second gas pressure, wherein the second gas pressure is higher than the first gas pressure,

[0041] - a second liquid connection between the liquid filled first chamber of the main piston housing and the lower chamber of the second accumulator.

[0042] In an embodiment of the system, the shock absorption device is integrated in the hoisting device. The shock absorption device may for example be integrated in the lower block, i.e. the crane block. In an embodiment of the system, the shock absorption device is located in the installation tool used to connect the hoisting device to the load.

[0043] In an embodiment of the shockload limiting system, the load comprises an installation tool and a pile, in particular a monopile for a wind turbine, wherein the installation tool is connected to an upper end of the pile.

[0044] In an embodiment of the shockload limiting system, the sensor system comprises a motion sensor for sensing a vertical motion of the load, wherein the vertical motion is indicative of the vertical acceleration and / or vertical velocity of the load, and wherein the control command comprises a digital command.

[0045] In an embodiment of the shockload limiting system, the installation tool is a driving device for driving the pile into the ground or seabed, wherein the driving device is configured to be operatively coupled to the control system for receiving the control command, the control command comprising a digital control command, wherein the driving device is configured to, based on receipt of the control command, stop driving of the pile into the ground or seabed.

[0046] The present invention is suitable for a ’passive’ shockload limiting system, e.g. a passive heave compensator comprising the pre-tension device, for an ‘active’ shockload limiting system, e.g. a winch of the hoisting system which controls the hoisting line tension, or for a combination of the passive and active system.

[0047] With an ‘active’ shockload limiting system, it is also possible to provide the option to lift an installation tool, e.g. a delicate driving device, upwards to compensate for vessel inclination caused by the driving device weight being transferred from the pile to the crane. Another benefit of an active shockload limiting system, for example comprising a controlled winch, is that after the offshore load has come to a standstill upon the occurrence of a dropfall, the offshore load can immediately be hoisted back up again.

[0048] In a second aspect of the invention a vessel is provided comprising a hoisting device and a shockload limiting system according to the first aspect of the invention.

[0049] In a third aspect the invention provides a motion compensation system for compensating vertical motions between a hoisting device and a load hoisted by the hoisting device, the motion compensation system comprising:

[0050] - a piston system comprising: o a main piston housing comprising: ■ a first end having attachment means for releasable attachment to the hoisting device line or the load,

[0051] ■ a second end having an opening adapted to provide a fluid tight enclosure around a piston rod of a piston assembly,

[0052] ■ an inner space divided by a slide-able first piston into a liquid filled first chamber and a second chamber, and

[0053] ■ a piston rod having at a first rod end attachment means for releasable attachment of the other of the hoisting device line or the load, and which is at a second rod end attached to the piston, and which stretches through the first chamber and further a distance out of the opening at said first end,

[0054] - a pre-tension device comprising: o a first accumulator comprising:

[0055] ■ an upper end,

[0056] ■ a lower end, and

[0057] ■ an inner space divided by a first separator into an upper chamber filled with a gas and a lower chamber filled with a liquid, the gas having a first gas pressure,

[0058] - a first liquid connection between the liquid filled first chamber of the main piston housing and the lower chamber of the first accumulator,

[0059] - a flow control member configured to be operatively coupled to the control system for receiving the control command, wherein the flow control member is configured to, based on receipt of the control command, control a flow resistance through the first liquid connection.

[0060] In an embodiment of the motion compensation system, the flow control member comprises a valve configured to shut off the first liquid connection based on receipt of the control command.

[0061] In an embodiment of the motion compensation system, comprising an integrated shock absorption device, the shock absorption device comprising

[0062] - a second accumulator comprising: o an upper end, o a lower end, and o an inner space divided by a second separator into an upper chamber filled with a gas and a lower chamber filled with a liquid, the gas having a second gas pressure, wherein the second gas pressure is higher than the first gas pressure, a second liquid connection between the liquid filled first chamber of the main piston housing and the lower chamber of the second accumulator.

[0063] The invention further provides a method for limiting a shockload on a hoisting device during hoisting of a load with the hoisting device, in particular in case of a dropfall of the load, the method comprising the steps of: a) positioning a hoisting device and a shockload limiting system according to the first aspect of the invention at an installation location, b) connecting the load to a hoisting device line of the hoisting device and suspending the load from the hoisting device line, c) acquiring first parameter data indicative of a vertical acceleration and / or vertical velocity of the load, d) comparing the first parameter data to a predetermined first threshold value, and generating a control command when an acquired first parameter value exceeds the predetermined first threshold value, e) controlling the pre-tension device based on the control command.

[0064] In an embodiment of the method, when the acquired first parameter value exceeds the predetermined first threshold value, the pre-tension device is controlled by disabling the pretension device.

[0065] In an embodiment of the method, the hoisting device is located on a floating vessel and the method is performed via the floating vessel. The method is highly beneficial to perform with a floating vessel, because the workability can be greatly increased.

[0066] In an embodiment of the method, the load comprises an installation tool and a pile, in particular a monopile for a wind turbine, wherein the installation tool is connected to an upper end of the pile, wherein the pile is in a vertical orientation and supported by the ground or seabed, and wherein the pre-tension device provides a first pre-tension force that corresponds to between 10 to 99 percent of a weight of the installation tool, preferably between 20 to 80 percent of the weight of the installation tool, more preferably between 40 to 70 percent of the weight of the installation tool, for keeping the hoisting device line substantially taut while compensating relative motions between the hoisting device tip and the load.

[0067] In an embodiment of the method, the installation tool is a lifting tool, and wherein the method comprises the step of disconnecting the lifting tool from the pile while the hoisting device line is kept substantially taut by the pre-tension device. When load transfer of the load from the hoisting device to the seabed is complete, in the prior art the connection between the hoisting device and the load, e.g. a foundation element, is slackened to allow for disconnection of the lifting tool that connects the rigging to the foundation element. This is done to guarantee that no pulling load is put onto the lifting tool while disconnecting. When installing from a floating vessel, a reason to slacken the connection, i.e. the hoisting line, can also be to prevent the introduction of dynamic loads caused by motions of the vessel. If not slackened, these dynamic loads can become very high as the relative motion of the vessel relative to the stiffness of the system can be very high.

[0068] However, if a slackened wire is used, the dynamic loading when a drop-fall or punch- though occurs is typically very high. This is mainly caused by the sudden stiffness change going from no stiffness at all when the wire is slack, to very stiff when the wire is tensioned in an instance. This effect is often referred to as a snap-load. To minimise the dynamic impact or snap-load, a passive heave compensator can be used. The passive heave compensator may be installed in the hoisting device, used in the rigging, or provided in the installation tool. A passive heave compensation system allows for a reduced stiffness, thus allowing for a larger braking distance and thus lower loading on the hoisting system. It should be noted however that the energy build-up is not limited in this configuration, only the braking distance is impacted. The energy build-up is even increased, because of the stroke of the passive heave compensator, i.e. the load ends lower because of the extended stroke. The same holds true if the heave compensation system is used to keep the rigging slack using a very soft stiffness setting to allow for vessel motions to occur, as a low stiffness still results in a larger distance travelled and would therefore not limit the loading sufficiently considering the growth in size and weights of the foundation elements seen in the industry today and likely in the future.

[0069] In an embodiment of the method, the installation tool is a driving device for driving the pile into the ground or seabed, and wherein the method comprises driving the pile into the ground or seabed with the driving device while the hoisting device line is kept substantially taut by the pre-tension device.

[0070] Following disconnection of the lifting tool, the foundation element generally needs to be brought into the soil using a driving device, typically a hydraulic hammer. When installing the driving device, the load of the driving device typically needs to be transferred onto the foundation element. As the load onto the soil is increased, the risk of punch / drop-fall is again apparent and can potentially happen at any time during the transfer. Following the transfer of the load of the driving weight onto the foundation element, the connection system between the driving system and the hoisting device, typically rigging, is slackened in the prior art. This is done to make sure that, during driving, the energy of the driving device is going toward the foundation element. The energy of a driving device, typically a hydraulic hammer, is normally detrimental to a hoisting device. To prevent this energy transfer to the hoisting device from happening, driving devices generally have a built in system that turns off the driving system when load is measured on the connection point(s) on top of the driving device.

[0071] During the driving process, drop fall can also happen as the foundation element is over and over brought to the a new depth having different properties and also because the driving process itself also generates downward energy into the pile which already generates a downward motion and thus energy. If during this process the foundation element punctures a stiff layer and enters a soft layer with too little stiffness to stop the foundation element, a drop fall can or will occur.

[0072] During driving, in order to keep snap loads from occurring and to guarantee the hammering energy is not transferred to the hoisting device, in the prior art the hoisting line needs to be slackened. This way the system allows for possible vessel motions and the expected stroke of the foundation element as a result of the driving process itself. As this slack of the wire allows for larger acceleration of the foundation element, now in tandem with the driving device on top of the foundation element, the larger the slack, the larger the possible build-up of energy.

[0073] One way to minimise the build-up of energy is therefore reducing the slack. This can be achieved by either limiting the energy generated by the driving system, thus reducing the expected stroke of the foundation element by the driving, or by reducing the allowed motions of the vessel. Reducing the allowed energy, the driving system is allowed to generate increases the duration of the driving process itself. Limiting the needed slack for allowing vessel motions would meaning reducing the environmental conditions in which one would be able to work. When considering one foundation element, this might be achievable, but considering the amounts of foundations installed in a typical wind turbine park, this would typically result in large weather downtime and thus limiting the amount of foundation elements that can be installed and / or limiting the period / season in which installation can commence.

[0074] Another option to minimise the impact on the hoisting device is to introduce a passive heave compensation system, for example in the hoisting device into the rigging or in the installation tool, or a combination thereof. This would allow for a larger braking distance to slow down the pile and thereby reduce the dynamic load introduced onto the hoisting device. With the current increase in weights however, this is quickly becoming insufficient. (Hydraulic) hammers are growing in size to proportions and resulting weights previously deemed impossible. The increased size is needed to generate sufficient energy to install ever growing foundation elements, especially monopiles. Also, the interface between the driving device and the foundations is growing in size to cope with the increase moments introduced by ever growing wind turbine sizes and peak power now hitting 20+ MW.

[0075] In an embodiment of the method, the control command comprises a digital control command, wherein, when the acquired first parameter value exceeds the predetermined first threshold value, the driving device stops driving of the pile into the ground or seabed upon receiving the control command. This prevents that the driving energy is transferred to the hoisting device.

[0076] In an embodiment of the method, the shockload limiting system comprises a shock absorption device, and wherein when the acquired first parameter value exceeds the predetermined first threshold value, the pre-tension device is disabled while the shock absorption device decelerates the load.

[0077] These and other aspects of the invention will be more readily appreciated as the same becomes better understood by reference to the following detailed description and considered in connection with the accompanying drawings in which like reference symbols designate like parts.

[0078] BRIEF DESCRIPTION OF THE FIGURES

[0079] Figure 1 schematically shows a perspective view of an installation vessel with a hoisting device hoisting a lifting tool that is connected to an upper end of a pile for installation in the seabed.

[0080] Figure 2 schematically shows a perspective view of the installation vessel of figure 1, wherein the hoisting device is hoisting a driving device connected to the upper end of the pile.

[0081] Figure 3 schematically shows a side view of the prior art.

[0082] Figure 4 schematically shows a side view of an embodiment of a shockload limiting system according to the present invention.

[0083] Figure 5 schematically shows an embodiment of a shockload limiting system according to the present invention.

[0084] Figures 6 to 8 schematically show different phases of an installation procedure of a load with the shockload limiting system as shown in figure 5. Figures 9 to 11 schematically show different phases of an installation procedure of a load with another embodiment of a shockload limiting system according to the invention.

[0085] Figure 12 schematically shows an embodiment of a shockload limiting system according to the invention comprising a motion compensation device with a pre-tension device.

[0086] DETAILED DESCRIPTION OF THE FIGURES

[0087] Figures 1 and 2 show a floating installation vessel 100; 101 , in particular a semisubmersible vessel. The invention is not limited to floating vessels and is also suitable for for example jack-ups. The vessel comprises a hoisting device 2 for hoisting a load 5. The hoisting device 2 can be for example a crane 3. Here the load 5 comprises an installation tool 66 and a foundation pile 67 for a wind turbine. In figure 1 the installation tool 66 is a lifting tool 74, in particular a flange mounted upending tool. In figure 2 the installation tool is a driving device 75 for driving the pile into the ground or seabed 23, such as for example a hammer. The installation tool is connected to an upper end 69 of the pile 68.

[0088] Figure 3 schematically shows the prior art, wherein a hoisting device line 8 of a hoisting device 2 is connected to an installation tool 66 via a passive heave compensator PHC. The pile is fully supported by the seabed which is not shown. The hoisting device line 8 between the passive heave compensator PHC and the installation tool 66 is slack 90. According to the prior art the line needs to be slack to for example disconnect the installation tool from the pile, or to drive the pile into the ground with a driving device. The slack allows for a large build-up of energy when the pile experiences a drop fall or punch through 6. The energy that is built up eventually ends up in the hoisting device 2 and the installation vessel and can have detrimental consequences, especially with the ever-increasing sizes of the (mono)piles.

[0089] Figure 4 schematically shows the hoisting device line 8 being connected to the installation tool 66 that is connected to an upper end 69 of the pile 67, via an embodiment of a shockload limiting system 1 according to a first aspect of the invention. The pile is supported by the seabed which is not shown in this figure. Contrary to figure 3 the hoisting device line 8 in figure 4 between the shockload limiting system 1 and the load 5 is substantially taut 22, i.e. substantially not slack. The shockload limiting system 1, schematically shown as a black rectangle in figure 4, can be connected to the hoisting device line 8 of the hoisting device 2 as shown in figures 1 and 2. The shockload limiting system 1 limits a shockload on a hoisting device 2 during an installation procedure, in particular during a drop fall or punch through, of an offshore load 5, here a pile for a wind turbine. The hoisting device 2 comprises a hoisting device tip 7 and a hoisting device line 8 configured to be connected with a free end 9 thereof to the load 5 for hoisting the load 5, here via the shockload limiting system 1.

[0090] Exemplary embodiments of the shockload limiting system 1 are shown in figures 5 to 12. The shockload limiting system 1 comprises a motion compensation system 10 for compensating vertical motions between the load 5 and the hoisting device tip 7. The vertical motions being for example induced by waves on the vessel 100. The motion compensation system 10 provides a first resilient connection 11 between the hoisting device 2 and the load 5 and is configured to be suspended between the hoisting device tip 7 and the load 5. The motion compensation system 10 comprises a pre-tension device 12 configured to provide a relatively low first stiffness 13 to the first resilient connection 11.

[0091] The shockload limiting system 1 comprises a sensor system 14 configured to acquire first parameter data indicative of a vertical acceleration and / or vertical velocity of the load 5. The sensor system 14 is configured to be operatively coupled to a control system 15 configured for comparing the first parameter data to a predetermined first threshold value, and for generating a control command when an acquired first parameter value exceeds the predetermined first threshold value. The shockload limiting system 1 is configured to control the pre-tension device 12 based on the control command. The control command can comprise a digital and / or analogue control command.

[0092] The pre-tension device 12 is configured for keeping the hoisting device line 8 substantially taut 22 while compensating relative motions between the hoisting device tip 7 and the load 5 when the load 5 is supported by the ground or seabed 23, as shown in figure 4. The pre-tension device 12 therefore provides a first pre-tension force that corresponds to between 10 to 99 percent of a weight of the installation tool, preferably between 20 to 80 percent of the weight of the installation tool, more preferably between 40 to 70 percent of the weight of the installation tool. This pre-tension, or first stiffness, keeps the hoisting device line 8 substantially taut 22 while compensating relative vertical motions between the hoisting device tip 7 and the load 5.

[0093] When the acquired first parameter value exceeds the predetermined first threshold value, the control command includes a disabling 16 of the pre-tension device 12. The disabling 16 is schematically shown in figures 8 and 11. The pre-tension device 12 is isolated. The load 5 remains connected to the hoisting device 2. The first parameter typically exceeds a predetermined first threshold value when the load 5 experiences a drop fall or punch through 6. By disabling 16 the pre-tension device 12 upon a detection of such drop fall or punch through 6 the falling distance of the load 5 can be reduced, thereby limiting the shockload on the hoisting device 2 and the vessel 100, 101.

[0094] When the installation tool is a driving device 75 for driving the pile into the ground or seabed 23, the driving device may be configured to be operatively coupled to the control system 15 for receiving the control command. In that case the control command comprises a digital control command. The driving device is then configured to, based on receipt of the control command, stop driving of the pile into the ground or seabed 23.

[0095] The shockload limiting system 1 may comprise a shock absorption device 17. The shock absorption device 17 is configured to provide a resilient connection 18 between the hoisting device 2 and the load 5. The resilient connection 18 has a second stiffness and / or a damping coefficient, wherein the second stiffness is higher than the first stiffness 13 provided by the pre-tension device 12. During normal operation both the pre-tension device 12 and the shock absorption device 17 are active. When the acquired first parameter value exceeds the predetermined first threshold value the pre-tension device 12 is disabled while the shock absorption device 17 remains active. So in case of a drop fall or punch through 6 the shock absorption device 17 will absorb at least a part of the shockload. Due to the higher second stiffness the falling distance will be less than if the pre-tension device 12 were to absorb the shockload. Subsequently the shock load on the hoisting device 2 and / or the vessel 100 will be lower.

[0096] The relatively low first stiffness 13 may for example provide a tension in the range of the rigging weight, e.g. 20 tonnes. The relatively high second stiffness is in the range of for example 1.1 times the static hook load. So when the load 5 is for example 2000 tonnes, the shock absorption device should start to decelerate the load 5 at a force corresponding to 2200 tonnes or more.

[0097] The pre-tension device 12 may comprise an adjuster 21 configured to adjust a pretension force of the first resilient connection 11. This can for example be done via controlling the first gas pressure P1 in the first accumulator 41. The upper chamber 46 of the first accumulator 41 may be connected to a gas reservoir 95 via which gas can be added to or removed from the upper chamber 46 for increasing or decreasing the first gas pressure P1. Also the shock absorption device 17 may have an adjuster, for example also in the form of a gas reservoir 96 that has a controllable fluid connection with the upper chamber 46 of the second accumulator 55.

[0098] Turning to the embodiment as shown in figures 5 to 8, the shockload limiting system 1 comprises the motion compensation device 10. The motion compensation system comprises a piston system 24 comprising a main piston housing 25.

[0099] The main piston housing 25 comprises a first end 26 having attachment means 27 for releasable attachment to the hoisting device line 8 or the load 5. A second end 28 of the main piston housing 25 has an opening 29 adapted to provide a fluid tight enclosure around a piston rod 30 of a piston assembly 31. An inner space 32 is divided by a slide-able first piston 33 into a liquid filled first chamber 34 and a second chamber 35. The second chamber 35 is typically filled with a gas. A piston rod 30 stretches through the first chamber 34 and further a distance out of the opening 29 at said first end 26. The piston rod 30 has at a first rod end 37 attachment means 38 for releasable attachment of the other of the hoisting device line 8 or the load 5. At a second rod end 39 the piston rod 30 is attached to the piston.

[0100] The pre-tension device 12 comprises a first accumulator 41. The first accumulator 41 comprises an upper end 42, a lower end 43, and an inner space 44. The inner space 44 is divided by a first separator 45 into an upper chamber 46 filled with a gas and a lower chamber 48 filled with a liquid. The gas in the upper chamber 46 has a first gas pressure P1.

[0101] In the shown embodiments the first separator 45 is a slide-able piston. The first separator 45 may also be for example a bladder or a membrane.

[0102] The motion compensation device 10 comprises a first liquid connection 51 between the liquid filled first chamber 34 of the main piston housing 25 and the lower chamber 48 of the first accumulator 41.

[0103] A flow control member 52 is operatively coupled to the control system 15 for receiving the control command. The flow control member 52 is configured to, based on receipt of the control command, control a flow resistance through the first liquid connection 51.

[0104] In the embodiment shown in figures 5 and 9 the sensor system 14 comprises a flow sensor 53 for sensing a flow velocity or flow rate in the first liquid connection 51. The flow sensor 53 can be a digital one, or an analogue one. The flow velocity or flow rate is indicative of the vertical acceleration and / vertical velocity of the load 5. A relatively simple embodiment can be provided by a flow control member 52 in the form of a valve 72 that shuts off the first liquid connection 51 based on receipt of the control command. The sensor system 14 and control system 15 can for example be integrated in a hose burst valve or flow fuse valve, providing an analogue embodiment. A digital embodiment can be provided by for example a solenoid valve which closes upon receiving an electric signal.

[0105] The sensor system 14 may instead or also comprise a motion sensor 70 for sensing a vertical motion of the load 5. The vertical motion is indicative of the vertical acceleration and / or vertical velocity of the load 5. When a motion sensor 70 is used the control command comprises a digital command.

[0106] The motion compensation device 10 and the shock absorption device 17 can be integrated in one unit. The shock absorption device 17 comprises a second accumulator 55. The second accumulator 55 comprises an upper end 56, a lower end 57, and an inner space 58. The inner space 58 is divided by a second separator 59 into an upper chamber 60 filled with a gas and a lower chamber 62 filled with a liquid. In the shown embodiments the second separator 59 is a slide-able piston. The second separator 59 may also be for example a bladder or a membrane.

[0107] In figure 5 there is substantially no liquid in the lower chamber 48, because the second separator 59 is in a position located at the lower end 57. The gas in the upper chamber 60 has a second gas pressure P2. The second gas pressure P2 is higher than the first gas pressure P1 of the upper chamber 46 of the first accumulator 41.

[0108] There is a second liquid connection between the liquid filled first chamber 34 of the main piston housing 25 and the lower chamber 48 of the second accumulator 55. The second liquid connection is intended to be always open, for absorbing shockloads or snap loads.

[0109] Figures 9 to 11 show an embodiment of a shockload limiting system 1, wherein a third accumulator 76 is provided. The third accumulator 76 comprises an upper end 77, a lower end 78, and an inner space 79. The inner space 79 is divided by a third separator 80 into an upper chamber 81 filled with a gas and a lower chamber 82 filled with a liquid. The gas having a third gas pressure P3, wherein the third gas pressure P3 is higher than the first gas pressure P1 and lower than the second gas pressure P2. There is a third liquid connection 83 between the liquid filled first chamber 34 of the main piston housing 25 and the lower chamber 82 of the third accumulator 76. The flow control member 52 is configured to, based on receipt of the control command, control a flow resistance through the third liquid connection 83, in particular to shut off the third liquid connection just as the first liquid connection.

[0110] With the third accumulator 76 and the third liquid connection 83 a further configuration of the shockload limiting system 1 can be obtained, as shown in particular in figure 10. In this configuration the load 5 is fully suspended by the hoisting device 2, for example during a horizontal pile lift. The weight of the load 5 is such that the first separator 45 in the first accumulator 41 is located in its upmost position, i.e. the first gas pressure P1 is too low to provide heave motion compensation. That is because the first gas pressure P1 is chosen such that the pre-tension device 12 is able to keep the hoisting line 8 taut when the load 5 is supported by the seabed 23, but not able to provide motion compensation when the load 5 is fully suspended. The third accumulator has a third gas pressure which is such that it can provide heave motion compensation during suspension of the load 5. The third separator 80 in the third accumulator 76 is shown as located substantially halfway the inner space 79.

[0111] In operation

[0112] During operation a method for limiting a shockload on a hoisting device 2 during hoisting of a load 5 with the hoisting device 2, in particular in case of a drop fall or punch through 6 of the load 5, comprises the steps of: a) positioning a hoisting device 2 and a shockload limiting system 1 according to the invention at an installation location, b) connecting the load 5 to a hoisting device line 8 of the hoisting device 2 and suspending the load 5 from the hoisting device line 8, c) acquiring first parameter data indicative of a vertical acceleration and / or vertical velocity of the load 5, d) comparing the first parameter data to a predetermined first threshold value, and generating a control command when an acquired first parameter value exceeds the predetermined first threshold value, e) controlling the pre-tension device 12 based on the control command.

[0113] When the acquired first parameter value exceeds the predetermined first threshold value, the pre-tension device 12 is controlled by disabling 16 the pre-tension device 12. This is schematically shown in figures 8 and 11 for the two embodiments of the shockload limiting system 1, wherein a valve 72 shuts of the first liquid connection 51 between the first accumulator 41 and the main piston housing 25.

[0114] When the installation tool 66 is a driving device 75 for driving the pile into the ground or seabed 23, the method comprises driving the pile into the ground or seabed 23 with the driving device 75 while the hoisting device line 8 is kept substantially taut 22 by the pretension device 12.

[0115] When the acquired first parameter value exceeds the predetermined first threshold value, the driving device may be configured to stop driving of the pile into the ground or seabed 23 upon receiving of the control command. In that case the control command comprise a digital command.

[0116] The hoisting device 2 may be located on a floating vessel such that the method is performed via the floating vessel.

[0117] Referring to figures 5 and 11 different situations are shown for when the load 5 comprises an installation tool 66 and a pile, in particular a monopile for a wind turbine. The installation tool 66 is connected to an upper end of the pile as shown for example in figures 1 and 2.

[0118] Figure 6 shows a stage of the installation procedure, wherein the installation tool 66 and the pile are fully suspended from the hoisting device 2, i.e. the pile has not yet touched the seabed 23. The first accumulator 41 is stroked in, i.e. the first separator 45 is located at the top of the inner space. The second separator of the second accumulator 55, is stroked out, i.e. the second separator is located at the bottom of the inner space. The stiffness and / or damping provided by the second gas pressure P2 in the upper chamber 46 of the second accumulator 55 is chosen such that the second separator remains at the bottom of the inner space while the load 5 is fully suspended. The second gas pressure is chosen such that in case of a drop fall or punch through 6 of the load 5 the second separator will be able to move upwards, as shown in figure 8 for this embodiment, and in figure 11 for another embodiment.

[0119] Figure 5 shows a step in the installation procedure, wherein the pile has touched the seabed 23 and the weight of the load 5 is being gradually transferred from the hoisting device 2, here the hoisting device 2, to the seabed 23. The piston rod 30 of the main piston housing 25 moves upwards while the first separator 45 in the inner space of the first accumulator 41 moves downwards, relative to the situation shown in figure 6. The pre-tension device is configured to provide a first range 92 of motion of the slide-able piston as shown in figure 5, whereas the shock absorption device is configured to provide a second range 91 of motion. Figure 9 shows a similar set down situation for another embodiment of a shockload limiting system 1 comprising a third accumulator 76.

[0120] Figure 7 shows a next step in the installation procedure, wherein the pile is in a vertical orientation and supported by the ground or seabed 23, in particular at a self-weight penetration depth. The pre-tension device 12 in the form of the first accumulator 41 provides a first pre-tension force that corresponds to between 10 to 99 percent of a weight of the installation tool 66, preferably between 20 to 80 percent of the weight of the installation tool 66, more preferably between 40 to 70 percent of the weight of the installation tool. This pretension force is high enough for keeping the hoisting device line 8 substantially taut 22, as shown in figure 4, while compensating relative vertical motions between the hoisting device tip 7 and the load 5. When compensating relative vertical motion between the hoisting device tip 7 and the load 5, the rod 30 of the main piston housing 25 is configured to move up and down as indicated by arrow 92, while the first separator 45 of the first accumulator 41 moves the opposite direction as indicated by arrow 93. Figure 5 also shows a first range of motion 92 for the pre-tension device 12, and a second range of motion 91 for the shock absorption device 17.

[0121] Figures 8 and 11 schematically show the situation in which a drop fall or punch through 6 of the pile occurs and the shockload limiting system 1 comprises a shock absorption device 17. The shock absorption device 17 may however also be omitted for the present invention. A vertical acceleration and / or vertical velocity exceeds a predetermined threshold value, e.g. zero. This causes a disabling 16, or shut down, of the pre-tension device 12, which is schematically shown by the cross X. The disabling 16 can for example be achieved via a valve 72 in the first liquid connection 51 that prevents a liquid flow between the first accumulator 41 and the main piston housing 25. The piston rod 30 in the main piston housing 25 moves down upon the drop fall, while the second separator in the second accumulator 55 moves up. So the pre-tension device 12 is shut down or disabled while the shock absorption device 17 decelerates the load 5.

[0122] Turning to figure 12, a schematic representation is shown of an embodiment of a shockload limiting system 1 according to the invention comprising a motion compensation device 10 with a pre-tension device 12. A hoisting device 2 is schematically shown which is provided on a floating vessel which is not shown. The hoisting device 2 comprises a hoisting device line 8 that is guided along a plurality of rollers. At one end the hoisting device line 8 is connected to a winch 84 that pays out or takes in the hoisting line 8. At a free end 9 the hoisting device line 8 is connected to the motion compensation device 10, which is in turn connected to a load 5. Here the load 5 is an installation tool 66 and a monopile 68 that is supported by the seabed 23. The pre-tension device 12 keeps the line substantially taut 22 while compensation vertical motions between a hoisting device tip 7 and the load 5. The pretension device 12 therefore provides a relatively low first stiffness 13.

[0123] A sensor system 14 comprises a motion sensor 70 that is provided on the load 5, here on the installation tool. The sensor system 14 is operatively connected to the control system 15. The control system 15 in turn is operatively connected to the motion compensation device 10. When a vertical acceleration and / or vertical velocity exceeds a predetermined threshold value, which is the case when a drop fall or punch through 6 occurs, the control system 15 receives the data from the sensor system 14 and sends a control command to the motion compensation device 10 for disabling 16 the pre-tension device 12. This way the pre-tension device 12 does not stroke out anymore and the load 5 is stopped earlier.

[0124] A shock absorption device 17 may be provided in addition to the motion compensation device 10. In the schematic embodiment shown in figure 12 the shock absorption device 17 is connected to a vertically movable roller 85. When the drop fall or punch through 6 of the pile occurs, a shock absorption device 17 absorbs the shockload via a resilient connection having a second stiffness. The movable roller will move upwards upon the shockload. The second stiffness is relatively high, in particular compared to the first stiffness 13 provided by the pretension device 12. The second stiffness is chosen such that is higher than the static hookload 5 when the load 5 would be fully suspended, i.e. not supported by the seabed 23. In addition, or instead, the shock absorption device 17 may comprise a damping member 86 having a damping coefficient for providing the resilient connection.

[0125] The shockload limiting system 1 may be a ‘passive’ system and / or an ‘active’ system. A passive system would for example be a passive heave compensator. An active system would for example be the winch 84 of the hoisting device 2, wherein the winch 84 is configured as pre-tension device for keeping the hoisting line substantially taut. In case of a dropfall or punch through of the offshore load, the winch is controlled by locking or braking the winch, i.e. disabling the pre-tension device. Said locking or braking of the winch causes an immediate increase in the stiffness between the hoisting device and the offshore load. Because of this immediate stiffness increase, the falling distance of the offshore load, and thereby the energy build-up, will be lower. As a result the shockload on the hoisting device is limited. It may also be possible to combine the ‘active’ system, e.g. the controllable winch 84, with a ‘passive’ system, e.g. the pre-tension device integrated in a passive motion compensation device, e.g. a passive heave compensator.

[0126] A controllable winch 84 being configured as a pre-tension device which can be disabled by locking or braking the winch 84 may also be combined with for example a spring and / or damper unit in the hoisting device 2, e.g. provided in the hoisting line. The spring and / or damper unit, i.e. a form of a shock absorption device, limits the shockload on the winch in case of a dropfall and locking of the winch 84. The spring then has a relatively high second stiffness.

[0127] As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. Further, the terms and phrases used herein are not intended to be limiting, but rather, to provide an understandable description of the invention.

[0128] The terms "a" or "an", as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms including and / or having, as used herein, are defined as comprising (i.e., open language, not excluding other elements or steps). Any reference signs in the claims should not be construed as limiting the scope of the claims or the invention.

[0129] The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

CLAIMS1. Shockload limiting system (1) for limiting a shockload on a hoisting device (2), in particular a crane (3), during an installation procedure of an offshore load (5), in particular during a drop fall or punch through of the offshore load, the hoisting device comprising a hoisting device tip (7) and a hoisting device line (8) configured to be connected with a free end (9) thereof to the load for hoisting the load, the shockload limiting system comprising: a motion compensation system (10) for compensating vertical motions between the load and the hoisting device tip, the motion compensation system providing a first resilient connection (11) between the hoisting device and the load, wherein the motion compensation system comprises a pre-tension device (12) configured to provide a relatively low first stiffness to the first resilient connection, a sensor system (14) configured to acquire first parameter data indicative of a vertical acceleration and / or vertical velocity of the load, the sensor system being configured to be operatively coupled to a control system (15) configured for comparing the first parameter data to a predetermined first threshold value, and for generating a control command when an acquired first parameter value exceeds the predetermined first threshold value, wherein the shockload limiting system is configured to control the pre-tension device based on the control command.

2. Shockload limiting system according to claim 1 , wherein, when the acquired first parameter value exceeds the predetermined first threshold value, the control command includes a disabling (16) of the pre-tension device.

3. Shockload limiting system according to claim 1 or 2, wherein the shockload limiting system comprises a shock absorption device (17), wherein the shock absorption device is configured to provide a resilient connection (18) between the hoisting device and the load, the resilient connection having a second stiffness and / or a damping coefficient, wherein the second stiffness is higher than the first stiffness, wherein during normal operation both the pre-tension device and the shock absorption device are active, and wherein when the acquired first parameter value exceeds the predetermined first threshold value the pre-tension device is disabled while the shock absorption device remains active.

4. Shockload limiting system according to any one of the preceding claims, wherein the pre-tension device comprises an adjuster (21) configured to adjust a pretension force of the first resilient connection.

5. Shockload limiting system according to any one of the preceding claims, wherein the pre-tension device is configured for keeping the hoisting device line substantially taut while compensating relative motions between the hoisting device tip and the load when the load is supported by the ground or seabed.

6. Shockload limiting system according to any one of the preceding claims, wherein the motion compensation device is configured to be suspended between the hoisting device tip and the load, the motion compensation device comprising a piston system (24) comprising: o a main piston housing (25) comprising:■ a first end (26) having attachment means (27) for releasable attachment to the hoisting device line or the load,■ a second end (28) having an opening (29) adapted to provide a fluid tight enclosure around a piston rod (30) of a piston assembly (31),■ an inner space (32) divided by a slide-able first piston (33) into a liquid filled first chamber (34) and a second chamber (35), and■ a piston rod (36) having at a first rod end (37) attachment means (38) for releasable attachment of the other of the hoisting device line or the load, and which is at a second rod end (39) attached to the piston, and which stretches through the first chamber and further a distance out of the opening at said first end, the pre-tension device comprising: o a first accumulator (41) comprising:■ an upper end (42),■ a lower end (43), and■ an inner space (44) divided by a first separator (45) into an upper chamber (46) filled with a gas and a lower chamber (48) filled with a liquid, the gas having a first gas pressure (P1), a first liquid connection (51) between the liquid filled first chamber of the main piston housing and the lower chamber of the first accumulator,a flow control member (52) configured to be operatively coupled to the control system for receiving the control command, wherein the flow control member is configured to, based on receipt of the control command, control a flow resistance through the first liquid connection.

7. Shockload limiting system according to the preceding claim, wherein the sensor system comprises a flow sensor (53) for sensing a flow velocity in the first liquid connection, wherein the flow velocity is indicative of the vertical acceleration and / velocity of the load.

8. Shockload limiting system according to claim 6 or 7, wherein the motion compensation device and the shock absorption device are integrated, the shock absorption device comprising: a second accumulator (55) comprising: o an upper end (56), o a lower end (57), and o an inner space (58) divided by a second separator (59) into an upper chamber (60) filled with a gas and a lower chamber (62) filled with a liquid, the gas having a second gas pressure (P2), wherein the second gas pressure is higher than the first gas pressure, a second liquid connection (65) between the liquid filled first chamber of the main piston housing and the lower chamber of the second accumulator.

9. Shockload limiting system according to any one of the preceding claims, wherein the load comprises an installation tool (66) and a pile (67), in particular a monopile(68) for a wind turbine, wherein the installation tool is connected to an upper end(69) of the pile.

10. Shockload limiting system according to any one of the preceding claims, wherein the sensor system comprises a motion sensor (70) for sensing a vertical motion of the load, wherein the vertical motion is indicative of the vertical acceleration and / or vertical velocity of the load, and wherein the control command comprises a digital command.

11. Shockload limiting system according to any one of the preceding claims, wherein the installation tool is a driving device (71) for driving the pile into the ground or seabed, wherein the driving device is configured to be operatively coupled to the control system for receiving the control command, the control commandcomprising a digital control command, wherein the driving device is configured to, based on receipt of the control command, stop driving of the pile into the ground or seabed.

12. Vessel (100) comprising a hoisting device and a shockload limiting system according to any one of the preceding claims.

13. Motion compensation system for compensating vertical motions between a hoisting device and a load hoisted by the hoisting device, the motion compensation system comprising: a piston system comprising: o a main piston housing comprising:■ a first end having attachment means for releasable attachment to the hoisting device line or the load,■ a second end having an opening adapted to provide a fluid tight enclosure around a piston rod of a piston assembly,■ an inner space divided by a slide-able first piston into a liquid filled first chamber and a second chamber, and■ a piston rod having at a first rod end attachment means for releasable attachment of the other of the hoisting device line or the load, and which is at a second rod end attached to the piston, and which stretches through the first chamber and further a distance out of the opening at said first end, a pre-tension device comprising: o a first accumulator comprising:■ an upper end,■ a lower end, and■ an inner space divided by a first separator into an upper chamber filled with a gas and a lower chamber filled with a liquid, the gas having a first gas pressure, a first liquid connection between the liquid filled first chamber of the main piston housing and the lower chamber of the first accumulator, a flow control member configured to be operatively coupled to the control system for receiving the control command, wherein the flow control member is configured to, based on receipt of the control command, control a flow resistance through the first liquid connection.

14. Motion compensation system according to claim 13, wherein the flow control member comprises a valve configured to shut off the first liquid connection based on receipt of the control command.

15. Motion compensation system according to claim 13 or 14, comprising an integrated shock absorption device, the shock absorption device comprising: a second accumulator comprising: o an upper end, o a lower end, and o an inner space divided by a second separator into an upper chamber filled with a gas and a lower chamber filled with a liquid, the gas having a second gas pressure, wherein the second gas pressure is higher than the first gas pressure, a second liquid connection between the liquid filled first chamber of the main piston housing and the lower chamber of the second accumulator.

16. Method for limiting a shockload on a hoisting device during hoisting of a load with the hoisting device, in particular in case of a dropfall or punch through of the load, the method comprising the steps of: a) positioning a hoisting device and a shockload limiting system according to any one of claims 1-11 at an installation location, b) connecting the load to a hoisting device line of the hoisting device and suspending the load from the hoisting device line, c) acquiring first parameter data indicative of a vertical acceleration and / or vertical velocity of the load, d) comparing the first parameter data to a predetermined first threshold value, and generating a control command when an acquired first parameter value exceeds the predetermined first threshold value, e) controlling the pre-tension device based on the control command.

17. Method according to claim 16, wherein, when the acquired first parameter value exceeds the predetermined first threshold value, the pre-tension device is controlled by disabling the pre-tension device.

18. Method according to claim 16 or 17, wherein the hoisting device is located on a floating vessel (101) and the method is performed via the floating vessel.

19. Method according to any one of claims 16-18, wherein the load comprises an installation tool and a pile, in particular a monopile for a wind turbine, wherein the installation tool is connected to an upper end of the pile, wherein the pile is in a vertical orientation and supported by the ground or seabed, and wherein the pretension device provides a first pre-tension force that corresponds to between 10 to 99 percent of a weight of the installation tool, preferably between 20 to 80 percent of the weight of the installation tool, more preferably between 40 to 70 percent of the weight of the installation tool, for keeping the hoisting device line substantially taut while compensating relative vertical motions between the hoisting device tip and the load.

20. Method according to the preceding claim, wherein the installation tool is a lifting tool (74), and wherein the method comprises the step of disconnecting the lifting tool from the pile while the hoisting device line is kept substantially taut by the pretension device.

21. Method according to claim 19, wherein the installation tool is a driving device (75) for driving the pile into the ground or seabed, and wherein the method comprises driving the pile into the ground or seabed with the driving device while the hoisting device line is kept substantially taut by the pre-tension device.

22. Method according to the preceding claim, wherein the control command comprises a digital control command, wherein, when the acquired first parameter value exceeds the predetermined first threshold value, the driving device stops driving of the pile into the ground or seabed upon receiving of the control command.

23. Method according to any one of claims 16-22, wherein the shockload limiting system comprises a shock absorption device, and wherein when the acquired first parameter value exceeds the predetermined first threshold value, the pre-tension device is disabled while the shock absorption device decelerates the load.

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