NO317430B1 - Procedure for use in offshore cargo transfer, float and hydraulic device for the same - Google Patents

Description

The invention relates to a float for offshore installation and removal of structural elements on or from a marine structure, a hydraulic device for use in a horizontal positioning system for holding a float in a target position within a horizontal limitation and relative to a marine structure, as well as an associated method for use in offshore cargo transfer, where a float is brought to a transfer point in the sea and cargo is transferred between the float and the transfer point, the float being horizontally positioned relative to a marine structure at the transfer point before and during the load transfer.

The invention relates to a float with adjustable buoyancy for offshore transport, installation and removal of structural elements. The invention has been particularly developed in connection with the need for assembly and disassembly of larger structural elements offshore, particularly in connection with the removal of existing fixed platform installations in the sea.

Basically, the float can have any shape that is adapted or suitable for offshore transport, installation and removal of structural elements. The float can thus, for example, be of the type shown in US patent no. 6,244,786 Bl, where a pillar-stabilized float is shown and described, or it can be a catamaran-like float, for example as shown in US patent no. .3,078,680. Other embodiments of suitable floaters can be found in EP 000 462 Al, FR 247 992, NO 160424, NO 171495 and NO 135056.

The floater will be used for the transport and installation (or removal) of larger structural elements (hereinafter referred to as "cargo") to (from) fixed structures or a floating structure (hereinafter referred to as "marine structures") offshore, in the open sea where the floater will be exposed to waves.

The load is preferably carried from the underside using beam elements (load transfer beams) that protrude from the float.

The weight of the cargo is transferred from the float to the marine structure by ballasting the float (filling ballast in the float's ballast tanks).

Removal of cargo (in most cases so-called topsides or similar structures) from marine structures is a reversed installation. The weight of the cargo is transferred from a marine structure to the float by deballasting the float (removal of ballast from ballast tanks). Various methods are known for vertical load transfer, movement compensation and load reduction.

Several load transfer systems are also known with features that enable movements of the float relative to the marine structure during the load transfer, thereby limiting the horizontal dynamic forces between the float and the marine structure. Fig. 1 shows an example of such a construction, where hinged beams are used.

GB 2 165 188 describes a float for the installation and removal of a platform deck, equipped with a horizontal positioning system consisting of hydraulic cylinders which are hinged at one end to the float and at the other end connected to the platform deck.

US 6 167 701 describes a hydraulic positioning system which is connected in parallel with several hydraulic accumulators, where these are dimensioned so that a combination of the accumulators gives a favorable spring characteristic.

The aforementioned methods for load transfer of large structural elements to/from marine structures will, however, be able to introduce very large dynamic horizontal loads from the float against the marine structure when such an operation is carried out offshore, in the open sea

(where the floater will be exposed to waves) if the floater is not designed for recording horizontal movements, particularly in wave frequency movements, relative to the marine structure during the load transfer. This could cause damage to the marine structure, particularly on old and corroded oil and gas platforms where the upper parts must be removed from the platform substructure ("jackets"). The horizontal dynamic load from the float can introduce a larger bending moment at the bottom of the substructure (which is attached to the seabed), larger shear forces in the substructure as well as larger horizontal forces at the point of contact between the platform's so-called top side and the load-bearing location on the load transfer beams.

Thus, according to the invention, a float is provided for offshore installation and removal of structural elements on or from a marine structure, including a horizontal positioning system for holding the float in a target position within a horizontal limitation, relative to the marine structure, which system includes a number of hydraulic jacks mounted on the float by means of gimbal suspension or similar devices which enable tilting of the jacks in vertical and horizontal planes, each hydraulic jack including a cylinder and a piston with a piston rod intended for connection with the marine structure, which piston is movable longitudinally in the cylinder . The floater according to the invention is characterized by the fact that the cylinder on each side of the aforementioned piston is hydraulically connected in parallel with at least three hydro-pneumatic accumulators with different gas pressure, the hydraulic accumulators being dimensioned in such a way that a combination of accumulators achieves a spring characteristic with high spring stiffness from a neutral position and up to a certain piston stroke, and a lower spring stiffness for larger piston strokes.

In one embodiment of the invention, the type and number of said accumulators are determined by the number of different spring characteristics to be achieved in the hydraulic jacks.

It is further according to the invention provided a hydraulic device for use in a horizontal positioning system for holding a float in a target position, within a horizontal limitation, relative to a marine structure, including a cylinder with two opposite ends; a piston which is movable in the longitudinal direction in the cylinder between the said two ends, which piston defines two opposite chambers in the cylinder, each of these chambers being hydraulically connected in parallel with a first hydro-pneumatic accumulator which has a first lower gas pressure; a second hydro-pneumatic accumulator having a second intermediate gas pressure; and a third hydro-pneumatic accumulator having a third higher gas pressure. The hydraulic device according to the invention is characterized by a piston rod connected to the piston and projecting from the cylinder at both its ends, and that the hydraulic accumulators are dimensioned in such a way that a combination of accumulators achieves a spring characteristic with high spring stiffness from a neutral position up to a certain piston stroke, and a lower spring stiffness with a larger piston stroke.

In one embodiment of the invention, a hydraulic pump with variable displacement volume is hydraulically connected to each of the aforementioned chambers in the cylinder.

In one embodiment, said hydraulic pump is reversible, with two opposite outlets/inlets, the pump is hydraulically connected to a respective one of said chambers in the cylinder through a line from a respective outlet (inlet), and two adjustable safety relief valves are connected between these lines .

In one embodiment, each of said lines includes a valve.

Furthermore, according to the invention, a hydraulic device is provided for use in a horizontal positioning system for holding a float in a target position within a horizontal limitation relative to a marine structure, including a cylinder with two opposite ends, a transverse wall in the cylinder between the said ends, whereby two chambers are formed in the cylinder, a respective piston which can be moved longitudinally in a respective chamber. The hydraulic device according to the invention is characterized by a piston rod connected to two pistons and protruding from the cylinder at both its ends, each piston forming two respective sub-chambers in the respective cylinder chambers, between the transverse wall and the respective piston and between the respective piston and a respective of the mentioned cylinder ends, each of the mentioned sub-chambers adjacent to the transverse wall being hydraulically connected in parallel with a first hydro-pneumatic accumulator which has a first lower gas pressure, a second hydro-pneumatic accumulator which has a second medium gas pressure, and a third hydro-pneumatic accumulator which has a third higher gas pressure, as the spring characteristic provided by the combination of the accumulators has a high spring stiffness from a neutral position up to a certain piston stroke, and a lower spring stiffness at greater piston stroke, as the two other sub-chambers are connected to each other via a fixed or adjustable flow restrictor.

In one embodiment, each of said cylinders forms a piston in a respective external chamber.

In one embodiment, the aforementioned external chambers are flow-connected to each other.

An embodiment of the hydraulic device is characterized in that the first hydro-pneumatic accumulator includes a first accumulator cylinder with two opposite first accumulator cylinder ends, a first accumulator piston which is movable in the longitudinal direction in the first accumulator cylinder and forms a first hydraulic chamber and a first gas chamber in the first accumulator cylinder, and an end stop in the first accumulator cylinder for the first accumulator piston, between said first accumulator cylinder ends, the second accumulator includes a second accumulator cylinder and a second accumulator piston which is movable in the longitudinal direction in the second accumulator cylinder and forms a second hydraulic chamber and a second gas chamber in the second accumulator cylinder, and that the third accumulator includes a third accumulator cylinder and a third accumulator piston which is movable in the longitudinal direction in the third accumulator cylinder and forms a third hydraulic chamber and a third gas chamber in the third accumulator cylinder, the dimensions and filling pressure being chosen in such a way as to achieve the above-mentioned spring characteristics.

Furthermore, according to the invention, a method has been developed for use in offshore load transfer, using a float and a hydraulic device as indicated above, where the float is brought to a transfer point in the sea and load is transferred between the transfer point and the float or vice versa, which float is positioned horizontally relative to a marine structure or cargo at the transfer point before and during the cargo transfer. The method according to the invention is characterized by the fact that the float is held in a target position within a horizontal limitation relative to the marine structure by means of the horizontal positioning system, the piston rod is connected to the marine structure or load, the horizontal movement of the load relative to the float is dampened by means of the spring characteristics in the hydraulic jacks after that the float has lifted the load from the marine structure.

In one embodiment of the method according to the invention, the load on the float is secured by closing shut-off valves against the hydraulic cylinder.

The hydraulic device according to the invention is advantageously used for dampening the horizontal movement of a load relative to a float and securing the load relative to the float.

A main purpose of the present invention is thus to be able to reduce the floater's horizontal movements as a result of waves, without thereby introducing greater dynamic horizontal loads on the marine structure, and to keep the vessel in a target position, within a horizontal limitation, relative to the marine structure. The purpose is to simplify the design of the load transfer system, to reduce the weight and costs of the load transfer system and to avoid collisions between floats and the marine structure during the preparations for and during the execution of the load transfer.

Another feature of the invention is that it will stabilize the load (removed from the marine structure) and secure the load horizontally (sea safety) relative to the float during so-called lift off (after the load transfer is complete).

Generally speaking, the inventive idea consists in using a float which is equipped with a horizontal positioning system. The system consists of at least three hydraulic jacks with drive and control systems and support structures. The jacks are mounted on the float using gimbal suspension, which enables the jacks to tilt in the vertical plane and in the horizontal plane. Pistons in the hydraulic jacks, or extension beams connected to the pistons, are connected to the load (or the marine structure). One or more hydraulic jacks regulate the longitudinal position and movements (chasing) of the float relative to the load (or the marine structure), and one or more hydraulic jacks regulate the transverse position and movements (swaying) of the float relative to the load (or the marine structure) . A minimum of two jacks control the orientation and yawing motion relative to the cargo (or the marine structure).

The horizontal movements of the float consist of wave frequency movement and low frequency movement. Stopping the low-frequency movement requires small forces compared to stopping the wave-frequency movement (the low-frequency forces will only amount to about 10% of the force needed to stop the wave-frequency movements). By eliminating the low frequency movements, the amplitude of the float's horizontal movements (oscillations) can be reduced by over 50%. The drive and control systems for the hydraulic jacks will be such that they virtually eliminate low-frequency movement and thus significantly reduce the float's horizontal movements, while allowing wave-frequency movements and avoiding a greater dynamic load from the float on the cargo or on the marine structure.

To enable this, each positioning system must first be activated, which means that it must be connected between the float and the cargo (or the marine structure), after which certain operating characteristics must be activated.

These characteristics of the horizontal positioning system will include one or more spring elements which will constantly attempt to pull the float back to its target position, with or without damping elements. The spring elements can be in the form of a linear or non-linear spring. The spring characteristic (force/deflection) can have different stiffness in different deflection ranges.

If a damping element is part of the system, such an element can have a speed-independent or speed-dependent force. A combination of these two dependencies will be able to contribute to the achievement of an optimal horizontal positioning system.

During operation, it may be necessary to make adjustments to the average float position relative to the load. It is therefore necessary to take measures to change the characteristic within the horizontal positioning system's operating area.

The maximum forces must also be limited, in order to prevent overloading of the system and the surrounding structures in emergency situations.

fig. 1 shows a known float with hinged beams,

fig. 2 shows a graph showing the spring characteristics of the new system,

fig. 3 shows a schematic top view of a U-shaped float,

fig. 4 shows a hydraulic system according to the invention,

fig. 5 shows a variant of the hydraulic system, with a special damping effect, and

The U-shaped float 1 in fig. 1 is provided with a number of hinged beams 2 for carrying a load 3. Another embodiment (not shown) is that the load is in the form of a superstructure placed on a tower on the seabed.

Hydrodynamic studies of how to reduce low-frequency movements of the float and at the same time allow larger high-frequency movements, show that a minimum requirement for the horizontal positioning system is that a spring characteristic with two different stiffness values in the deflection area is required. This is shown schematically in fig. 2. The first part of the characteristic (between the position —X] and the position +xi) has a "high" spring stiffness, while in other positions there is a significantly lower spring stiffness, with a distinct stiffness change in the position -Xi and + X\.

The purpose of the invention is to provide a system with the aforementioned properties and of the passive type.

Furthermore, the system must have integrated control features and a limitation of maximum forces.

An example of a positioning system according to the invention will be described below.

In fig. 3 shows a top view of a U-shaped float 1, which float 1 is placed around a load 3, which can for example be mounted on top of a marine structure, such as a tower or the like.

The floater 1 can make horizontal movements in three different directions (degrees of freedom). This concerns so-called chasing, swaying and gearing. The first two movements are linear movements, one in the longitudinal direction and the other in the float 1 lateral direction. The latter movement is a rotation about a vertical axis.

To reduce and control the three degrees of freedom for the horizontal movement, three individual horizontal positioning systems are required (as a minimum). These systems are designated as HPS 1, HPS 2 and HPS 3. HPS 1 is mounted in the longitudinal direction and affects the chasing motion, while HPS 2 and HPS 3 are mounted in the lateral direction and affects the yawing and yawing motions. These systems are also shown in fig-1-

Each HPS system has the same mode of operation, but the dimensioning and absolute values of the force-deflecting characteristics may differ.

In the following paragraphs, an HPS is described, and the work operation is also explained. Particular reference is made to flg. 4.

A hydraulic cylinder 5 with two piston rods 6 and 7 and with a piston 16 is connected to the float 1 by means of a gimbal suspension 8 (or another device that enables tilting of the hydraulic cylinder 5 horizontally and vertically), and the piston 7 is connected to the load 3 (or the marine structure). Other types of cylinders and fasteners can also be used. A variable volume hydraulic pump/motor 9 is used to transfer hydraulic oil from one side of the cylinder to the other side. This pump/motor is advantageously driven by an electric motor (m) and this combination is suitable for a 4-quadrant operation, which means that all power directions and speed directions are possible. By means of this arrangement, it is possible to move the piston rods 6, 7 in a controlled manner all the time.

Each cylinder side is connected to a set of (at least) three hydro-pneumatic accumulators 10, 11 and 12. The number of accumulators is related to the number of the different spring characteristics.

The accumulator 10 is a low-pressure piston accumulator with a built-in mechanical end stop 14.1 fig. 4, the low-pressure piston 15 is shifted to a position to abut against the mechanical end stop 14.

The accumulator 11 is used for a range from low to medium pressure and can be of the membrane type or the piston type. The accumulator 12 is for the range from medium pressure to high pressure and is of the piston type. These are preferred accumulator types. Other types can be used provided they have the same properties.

In the stationary state, the pressure on both sides of the cylinder 5 is the same, so that the cylinder's pulling or pushing force (F) is equal to zero. The accumulators 10, 11, 12 in the one in fig. state shown in 4, i.e. that the accumulator 10 is full (system against the limit stop 14), and that the accumulators 11 and 12 are completely empty (the gas pressure is greater than the oil pressure in the system).

Given that the piston 16 in the cylinder 5 is stationary in the middle position (as shown) and that this is the reference point x = 0, and given that the hydraulic motor 9 is inactive and that no movement of the float that generates a piston movement to the right occurs, the oil from the right chamber in the cylinder 5 will automatically be pressed into the accumulator 11 only. This is due to the fact that the pre-pressure in the accumulator 12 is much higher than the pre-pressure in the accumulator 11, and the fact that the accumulator 10 cannot absorb any oil, because the piston 15 is already in its end position.

With a movement of the piston 16 to the right, the left chamber in the cylinder 5 will increase in volume and the necessary volume of oil will flow from the accumulator 10. As a result of the characteristics of the accumulators, the pressure in the right chamber in the cylinder 5 will increase, while the pressure in the left chamber is reduced. Thereby, the force F on the piston rod 7 increases when the movement is to the right. Depending on the accumulator sizes and gas pre-pressures, it will be possible to obtain the desired spring stiffness in the first part of the deflection range (0 -X|). Outside this range, the force F will change from 0 to Fi.

After further deflection (x = xi), the pressure in the accumulator 11 will become practically the same as the pre-pressure in the accumulator 12 and now (at deflection x >Xi), the oil will flow into this latter accumulator i from the right cylinder chamber of the cylinder 5. The size of and the pre-pressure in the accumulator 12 is chosen so that the spring stiffness (force-deflection curve) will have a different, lower value than that in the area with small deflection (we speak here of "a" stiffness related to the accumulator 12).

After the maximum deflection is reached and the float 1 reverses its movement, i.e. the float moves in the opposite direction, the described sequence will be repeated in reverse order.

When the cylinder/piston combination reaches the starting position x = 0, the accumulators 11 and 12 arranged on the right side will be empty, and the accumulator 10 will be filled.

On the left side, the accumulators 11 and 12 will still be empty. The accumulator 10 will again be filled and the piston 15 will abut against the mechanical stopper.

Because the movement to the right continues (due to the floater's behavior in the sea), the procedure described above (for a movement to the right side) will be repeated identically on the left side.

The maximum stroke length in the cylinder 5 is greater than the maximum stroke length which the movements of the float will require.

With the help of the pump/motor 9, oil on one side of the system can be transferred to the other side, and in this way the position of the spring characteristic can be shifted to the desired degree, without the piston 16 reaching its end positions in the cylinder 5.

The diagram in fig. 4 also shows two (remotely) adjustable safety relief valves 17. These have several functions: 1. They limit the maximum forces in the cylinder 5, as the valves 17 are set to the desired high opening pressure. 2. They provide a "free float" or by-pass condition, in that the valves 17 are fully opened. 3. They enable a gradual transition from "free float" to "spring" operation, by controlled increase of the opening pressure.

The hydraulic elements 18 will include shut-off valves (manually or electrically operated) so that the cylinder state can be "frozen" when the system is out of operation.

Box 19 represents standard hydraulic equipment, which is used for filling the system, pressurizing the system, flushing, filtering and cooling. This is not described in more detail as this equipment does not constitute fundamental parts of the invention.

A solution with a specific spring characteristic, without a special damping effect, is described in front. If an additional damping effect is desired, a cylinder design can be used as shown in fig. 5. This design includes an "inner" cylinder 20 with two pistons 21 and 22 which are interconnected with the rod 31, as well as four oil chambers or sub-chambers 23,24,25 and 26. The two middle sub-chambers 24, 25 are connected by a hydraulic system with several hydro-pneumatic accumulators, as shown in fig. 4. An accumulator 28 is shown here only symbolically for each sub-chamber. The two outer sub-chambers 23 and 26 in the "inner" cylinder 20 are connected to each other via a fixed or (proportionally controlled) adjustable flow limiter 29. This serves as a damping element in the system. With the help of a suitable control algorithm and control system, the damping characteristic is "freely programmable".

In addition, there is an "outer" cylinder 30 which uses the same piston rod 31. The ends of the "inner" cylinder 20 form a piston that can move in the "outer" cylinder 30. The oil chambers 32, 33 in the "outer" cylinder 30 can be used as (extra) safety relief valves or for regulation purposes. In fig. 5, the two chambers 32 and 33 are flow connected with valves as shown.

An important advantage achieved with the invention is the possibility of dampening the relative movements between floats and load between the so-called lift off of the load from the marine structure and until this phase is finished (under the condition that the piston rod is connected to the load and not with the marine structure).

The horizontal movement of the structural element relative to the float will then be dampened by the spring characteristics of the hydraulic jacks. The construction element can then be attached to the float (sea safety) by closing the valves 18. When these valves are closed, possible high loads will be limited by the pressure relief valves 17.

Claims (13)

1. Float for offshore installation and removal of structural elements on or from a marine structure, including a horizontal positioning system for holding the float (1) in a target position within a horizontal constraint, relative to the marine structure (3), which system includes a number of hydraulic jacks ( HPS 1, 2, 3) mounted on the float using gimbal suspension (8) or similar devices which enable tilting of the jacks in the vertical and horizontal planes, as each hydraulic jack (HPS 1, 2,3) includes a cylinder (5) and a piston (16) with a piston rod (7) intended for connection with the marine structure, which piston (16) is movable in the longitudinal direction in the cylinder (5), characterized in that the cylinder (5) on each side of said piston (16) is hydraulically connected in parallel with at least three hydro-pneumatic accumulators (10,11,12) with different gas pressure, as the hydraulic accumulators are dimensioned in such a way that with a combination of accumulators o A spring characteristic with high spring stiffness is achieved from a neutral position up to a certain piston stroke, and a lower spring stiffness at greater piston stroke. 2. Floats according to claim 1, characterized in that the type and number of said accumulators (10,11,12) are determined by the number of different spring characteristics to be achieved in the hydraulic jacks (HPS 1, 2, 3). 3. Hydraulic device for use in a horizontal positioning system for holding a float in a target position, within a horizontal constraint, relative to a marine structure, comprising a cylinder (5) with two opposite ends; a piston (16) which is movable in the longitudinal direction in the cylinder (5) between the aforementioned two ends, which piston (16) defines two opposite chambers in the cylinder (5), each of these chambers being hydraulically connected in parallel with a first hydro-pneumatic accumulator (10) having a first lower gas pressure; a second hydro-pneumatic accumulator (11) having a second mean gas pressure; and a third hydro-pneumatic accumulator (12) which has a third higher gas pressure, characterized by the wooden piston rod (6, 7) connected to the piston (16) and projecting from the cylinder at both ends, and that the hydraulic accumulators are so dimensioned that a combination of accumulators achieves a spring characteristic with high spring stiffness from a neutral position up to a certain piston stroke, and a lower spring stiffness at greater piston stroke. 4. Hydraulic device according to claim 3, characterized by the hydraulic pump (9) with variable displacement volume and hydraulically connected to each of the aforementioned chambers in the cylinder (5). 5. Hydraulic device according to claim 4, characterized in that said hydraulic pump (9) is reversible, with two opposite outlets/inlets, that the pump (9) is hydraulically connected to a respective one of the said chambers in the cylinder (5) through a line from a respective outlet (inlet), and that two adjustable safety relief valves (17) are connected between these lines. 6. Hydraulic device according to claim 5, characterized by the valve (18) in each of the said lines. 7. Hydraulic device for use in a horizontal positioning system for holding a float in a target position within a horizontal limitation relative to a marine structure, comprising a cylinder (20) with two opposite ends, a transverse wall in the cylinder (5) between said ends, whereby the two chambers are formed in the cylinder (20), a respective piston (21,22) which can be moved longitudinally in a respective chamber, characterized by a piston rod (31) connected to two pistons (21, 22) and projecting from the cylinder (20) at both its ends, each piston (21,22) forming two respective sub-chambers (23, 24 and 25,26) in the respective cylinder chambers, between the transverse wall and the respective piston (21,22) and between the respective piston (21, 22) and a respective one of the aforementioned cylinder ends, each of the aforementioned sub-chambers (24, 25) adjacent to the transverse wall being hydraulically connected in parallel with a first hydro-pneumatic accumulator having a first lower gas pressure, a second hydro-pneumatic accumulator having a second medium gas pressure, and a third hydro-pneumatic accumulator having a third higher gas pressure, the spring characteristic provided by the combination of the accumulators (27 , 28) has a high spring stiffness from a neutral position up to a certain piston stroke, and a lower spring stiffness at larger piston strokes, as the other two sub-chambers (23,26) are connected to each other via a fixed or adjustable st escape limiter (29). 8. Hydraulic device according to claim 7, characterized in that each of said cylinders forms a piston in a respective external chamber (32, 33). 9. Hydraulic device according to claim 8, characterized in that the aforementioned external chambers (32,33) are interconnected by flow. 10. Hydraulic device according to one of claims 3-9, characterized in that the first hydro-pneumatic accumulator (10) includes a first accumulator cylinder with two opposite first accumulator cylinder ends, a first accumulator piston (15) which is movable in the longitudinal direction in the first accumulator cylinder and forms a first hydraulic chamber and a first gas chamber in the first accumulator cylinder, and an end stop (14) in the first accumulator cylinder for the first accumulator piston (15), between said first accumulator cylinder ends, the second accumulator (11) includes a second accumulator cylinder and a second accumulator piston which is movable in the longitudinal direction in the second accumulator cylinder and forms a second hydraulic chamber and a second gas chamber in the second accumulator cylinder, and that the third accumulator (12) includes a third accumulator cylinder and a third accumulator piston which is movable in the longitudinal direction in the third accumulator cylinder and forms a third hydraulic chamber and a third gas chamber in the third accumulator cylinder, the dimensions and filling pressure being chosen in such a way as to achieve the spring characteristics defined in claim 3. 11. Procedure for use in offshore cargo transfer, using a float as specified in claim 1 and a hydraulic device as specified in claim 3, where the float (1) is brought to a transfer point in the sea and cargo is transferred between the transfer point and the float or vice versa, whichever floats (1) is positioned horizontally relative to a marine structure or load (3) at the transfer point before and during the load transfer, characterized in that: - the float (1) is held in a target position within a horizontal limitation relative to the marine structure (3) using the horizontal positioning system , - the piston rod (7) is connected to the marine structure or load, - the horizontal movement of the load (3) relative to the float is dampened by means of the spring characteristics in the hydraulic jacks (HPS 1,2, 3) after the float (1) has lifted the load ( 3) from the marine structure. 12. Method according to claim 11, characterized in that the load (3) is secured on the float (1) by closing shut-off valves (18) against the hydraulic cylinder (5). 13. Use of a hydraulic device according to one of claims 3 - 8 for dampening the horizontal movement of a load (3) relative to a float (1) and securing the load (3) relative to the float (1).