NL2013539B1

NL2013539B1 - Lifting device for lifting an upper part of a sea platform.

Info

Publication number: NL2013539B1
Application number: NL2013539A
Authority: NL
Inventors: Cornelius Van Grieken Gerardus; Johannes Rutten Timotheus
Original assignee: Heerema Marine Contractors Nl
Priority date: 2014-09-26
Filing date: 2014-09-26
Publication date: 2016-09-29

Abstract

The invention relates to a lifting device (10) for lifting a sea platform (200), the sea platform comprising a support structure and a top side, the lifting device being constructed to be positioned on a lifting vessel (100), the lifting device comprising: a base frame (12) constructed to rest on the lifting vessel, a console frame (14) connected to the base frame via a flexible connection system, a suspension system (18) connected to the console frame and comprising a leg connector (20) which is constructed to be connected to a leg of the sea platform, wherein the suspension system is constructed to allow freedom of movement of the leg connector relative to the console frame, wherein the flexible connection system (16) forms a flexible connection between the console frame (14) and the base frame (12) and allows a limited movement of the console frame.

Description

Title: Lifting device for lifting an upper part of a sea platform FIELD OF THE INVENTION

The present invention relates to a lifting device for lifting a sea platform, in particular an upper part of a sea platform. The present invention relates to a lifting vessel comprising the lifting device and to a method of lifting a sea platform, in particular an upper part of a sea platform.

BACKGROUND OF THE INVENTION

The transport of large parts of a sea platform, such as a support structure or a top side as a whole, is required during both the removal and installation thereof. There is a desire to transport the topside or supporting structure as a complete part to limit offshore installation work.

Typically, existing sea platforms have a certain economical or technical life span after which they need to be removed. The removal generally comprises a lift operation and a transport operation. This is a complex and expensive operation for several reasons. One reason is the shear size and weight of sea platforms. Only very large lifting vessels are capable of lifting such a platform in a single lift or in a limited number of lifts.

Another reason is the fact that a lifting vessel moves under influence of waves, wind and current. The sea platform generally is stationary or substantially stationary because it rests on the sea bottom or is limited in its motions in another way. The lifting vessel therefore moves with respect to the sea platform which makes it difficult to connect to the sea platform and to carry out the lifting operation. There generally is a risk of collision between the lifting vessel and the sea platform. A number of heavy lift systems have been developed so far. One known concept is to use large cranes on a semi-submersible vessel. This solution is known from existing heavy lift vessels such as Hermod, Balder and Thialf. These vessels can lift an upper part of a sea platform from a lower part and subsequently place the upper part on a barge. It was found that this is a rather complex operation which requires calm weather. The lift capacity is also limited.

Another concept is disclosed in US2013/0045056. A lifting vessel has two arms and a number of lifting devices on these arms. It was recognized that the lifting device of US2013/0045056 allows only a limited freedom of movement of the lifting vessel relative to the sea platform. This narrows a window of opportunity in which the weather is sufficiently calm for the operation to be carried out in many locations.

Further, known lifting systems rely on an accurately pre-calculated COG. If the position of the COG is found to be other than expected during lift operations, a compensation system is required to cope with the difference in load distribution between the connection points.

Another lifting vessel system is being developed under the name Pieter Schelte by the company Allseas, a description of which can be found on www.allseas.com. It was recognized that this system requires large actuators to compensate for the relative movements between the sea platform and the lifting vessel. The large actuators are complex and require much maintenance. Moreover, during the actual lifting operation the actuators are actively controlled which requires much energy to keep the movements of the sea platform within the prescribed limits.

OBJECT OF THE INVENTION

It is an object of the invention to provide an alternative lifting device, lifting method and a lifting vessel comprising such a lifting device.

It is another object of the invention to provide a relatively simple lifting device, lifting method and a lifting vessel comprising such a lifting device.

It is another object of the invention to provide a lifting device which combines safety with a possibility to vary the stiffness between the lifting vessel and the sea platform during the lifting operation..

It is another object of the invention to provide a lifting device, lifting method and lifting vessel which requires less energy for maintaining a position of the upper part of the sea platform during lift and subsequent transport, in particular by using passive control where possible.

THE INVENTION

In order to achieve at least one of the objectives, the invention provides a lifting device for lifting a sea platform, in particular an upper part of a sea platform, the sea platform comprising a support structure and a top side, the lifting device being constructed to be positioned on a lifting vessel, the lifting device comprising: a base frame constructed to rest on the lifting vessel, at least one console frame connected to the base frame via a flexible connection system, a suspension system connected to the console frame and comprising a leg connector which is constructed to be connected to a leg of the sea platform, wherein the suspension system is constructed to allow freedom of movement of the leg connector relative to the console frame, wherein the flexible connection system forms a flexible connection between the console frame and the base frame and allows a limited movement of the console frame relative to the base frame.

In an embodiment, the flexible connection system comprises an actuation system which extends between the base frame and the console frame and which is configured to exert a force on the console frame, wherein the force is adjustable in order to vary the load-displacement relationship of the flexible connection system.

With the actuation system, the stiffness of the flexible connection system can be tuned, even during a lifting operation.

In an embodiment, the flexible connection system comprises resilient members which allow the console frame to be displaced relative to the base frame over a limited angle by deformation of the resilient members.

The resilient members allow the sea platform to be lifted in a passive mode, without applying external energy during the lift.

In an embodiment, the resilient members are configured to deform under shear stress.

In an embodiment, a load - displacement relationship between the base frame and the console frame as defined by the flexible connection system is adjustable: - by varying the number and/or position of the resilient members, and - by adjusting the actuation system .

This provides a combined advantage of a passive system which can also be easily tuned, even during the lifting operation.

In an embodiment, the resilient members and the actuation system act in parallel on the console frame, and wherein the actuation system is configured to apply an adjustable force on the console frame when the console frame is in a neutral position in which the resilient members are not under tension.

In an embodiment, the resilient members and the actuation system act in parallel on the console frame, and wherein the actuation system is configured to have an adjustable stiffness range.

In an embodiment, the actuation system comprises at least one cylinder, in particular a hydraulic cylinder, and a pump to control a pressure in the cylinder. This provides the benefit of an effective and simple adjusting capability of the stiffness of the actuation system.

In an embodiment, the actuation system comprises at least one accumulator configured to let the cylinder act as a spring. This allows the actuation system to also be used in a passive mode, i.e. both the resilient member and the actuation system can be operated passively, without applying external energy.

In an embodiment, the force exerted by the actuation system on the console frame is dependent on the displacement of the console frame relative to the base frame.

In an embodiment, the flexible connection system further comprises connection beams, wherein the base frame comprises deck beams, and wherein the resilient members are positioned between the connection beams and the deck beams and interconnect the connection beams and the deck beams. This was fund to be a simple arrangement.

In an embodiment, the connection beams extend parallel to the deck beams of a deck part of the base frame.

In an embodiment, the flexible connection system acts on the deck part of the base frame and on an upper part of the console frame. The upper part of the console frame may extend to above the deck of the lifting vessel and may be easy to connect to for the flexible connection system

In an embodiment, the lifting device comprises a horizontal restraining system for limiting a horizontal movement of the legs, wherein the suspension system is configured to exert a vertical force on the legs via the leg connector, and wherein the horizontal restraining system is configured to exert a horizontal force on the leg. The horizontal restraining system allows a split in the forces on the legs. The vertical forces are applied via the suspension system and the leg connectors and the vertical forces are applied to the legs via a different route.

In an embodiment, the horizontal restraining system comprises at least at least two horizontal restrainers which are constructed to limit the horizontal movement of the leg in an X-direction and an Y-direction, wherein the X-direction is a longitudinal direction of a lifting vessel and the Y-direction is the transverse direction of the lifting vessel. This is an effective way of restraining the horizontal movements along both the X-axis and the Y-axis.

In an embodiment, the horizontal restrainers are positioned substantially at a vertical distance above the leg connector, in particular above a deck part of the base frame, and are directed at a part of the leg which is substantially closer to the top side of the sea platform than a part of the leg on which the leg connector acts, and wherein said vertical distance is in particular greater than 2 meter. This effectively limits the bending moments in the legs and prevents damage to the legs.

In an embodiment, in top view the horizontal restrainers extend at an angle a of between 70 and 110 degrees relative to one another.

In an embodiment, the horizontal restrainers comprise hydraulic cylinders. In an embodiment, each horizontal restrainers is configured to act as a spring, in particular with an adjustable spring constant (or stiffness). This allows tuning of the horizontal restrainers according to specific requirements in an effective way.

In an embodiment, a load - displacement relationship of the horizontal restrainers is adjustable, in particular independently for each of the two horizontal restrainers.

In an embodiment, the horizontal restrainers are configured to operate in a passive mode without applying external energy.

In an embodiment, distal ends of the horizontal restrainers are positioned higher than a deck part of the base frame and wherein the leg connector is positioned lower than the deck part.

In an embodiment, the lifting device is configured to exert vertical forces on the legs via the suspension system and the leg connectors and wherein the lifting device is configured to exert horizontal forces on the legs via the horizontal restraining system and the leg connectors, wherein the suspension system and the horizontal restraining system are constructed to substantially prevent horizontal forces to be exerted onto the legs via the suspension system. This prevents large bending moments in the leg.

In an embodiment, the at least two horizontal restrainers are connected at one end to respective restraining support positions on the base frame and are configured to be connected at an opposite end to the leg, directly or indirectly via a collar which is attached to the leg.

In an embodiment, the base frame defines a number of pivot points, and wherein the console frame is connected to the base frame via the pivot points in order to make a pivoting movement about the pivot points relative to the base frame. The pivoting movement was found to be a very practical way of allowing some relative movement between the lifted upper part of the sea platform and the lifting vessel.

In an embodiment, the console frame comprises a console having an outer support, the console frame further comprising at least one upper connection point on which the flexible connection system acts, and wherein the suspension system comprises : at least one pivotable beam connected to the console frame via a hinging connection which allows the pivotable beam to pivot relative to the console frame between a lower position and an upper position, wherein in the lower position the pivotable beam engages the outer support of the console and is supported by the console frame, and wherein in the upper position the pivotable beam is positioned at a distance above the outer support and is allowed to pivot over an angle β, - a pivotable beam actuator for pivoting the pivotable beam between the upper position and the lower position, and - at least one pendulum arm connected at an upper end thereof to a protruding end of the pivotable beam via a pendulum hinge, - the at least one leg connector constructed to be connected to the leg, wherein the at least one leg connector is attached to a lower end of the at least one pendulum arm via a leg connector hinge.

The pendulum arms offer a natural relative movement between the lifting vessel and the upper part of the sea platform, in particular during the stage in which the lifting vessel is connected to the sea platform but has not lifted the upper part of the sea platform yet.

In an embodiment, the base frame has a deck part and a side part which extends downwards from the deck part, wherein the pivot points are provided on the side part and located lower than the deck part. In an embodiment, the deck part comprises the deck beams.

In an embodiment, the lifting device comprises two console frames and two pivotable beams, wherein each console frame is configured to support an associated pivotable beam via its outer support, and wherein each pivotable beam supports a pendulum arm, wherein the leg connector is supported on each side by the lower end of a pendulum arm.

In an embodiment, the at least one pendulum hinge between the pendulum arms and the pivotable beams and the at least one leg connector hinge between the at least one pendulum arm and the at least one leg connector are gimbal hinges which allow rotation about three independent axis of the pendulum arms relative to pivotable beams and of the leg connectors relative to the pendulum arms.

In an embodiment, the base frame is configured to be positioned on a lifting arm of a lifting vessel, wherein the pivot points are positioned at a distance below the deck part and wherein in particular the deck part and the side part extend at an angle of 90 degrees relative to one another.

In an embodiment, the console extends outwardly from the base over a horizontal distance.

In an embodiment, the leg connectors have an abutment surface at an upper side thereof and are constructed to slide relative to the legs in order to exert a vertical force onto the legs, in particular via the abutment surface and via a collar which is attached to the leg above a position where the leg connectors are engaged with the leg.

In an embodiment, the pivotable beams pivot about a horizontal axis, and wherein the console frame pivots about a horizontal axis.

In an embodiment, the lifting device can be switched between a: a free-moving mode, in which the at least one pivotable beam is in the upper position at a distance of the associated outer support and has a freedom of movement up and down relative to the outer support, wherein the at least one pendulum arm has a freedom of movement in at least two, in particular three degrees of freedom relative to the associated pivotable beam and wherein the leg connector has a freedom of movement in at least two, in particular three degrees of freedom relative to the at least one pendulum arm to which it is connected, and wherein the horizontal restrainers are freely movable, a supporting mode, in which the pivotable beams are in the lower position and rest on the outer supports, wherein the at least one pendulum arm has a freedom of movement in at least two, in particular three degrees of freedom relative to the associated pivotable beam and wherein the leg connector has a freedom of movement in at least two, in particular three degrees of freedom relative to the at least one pendulum arm to which it is connected, and wherein the horizontal restrainers substantially fixate a higher position of the leg in an X-direction and Y-direction relative to the base frame.

The lifting device may be operated passively, i.e. without applying substantial energy, in both the free moving mode and the supporting mode.

In an embodiment, the lifting device comprises a positioning system for positioning the leg connectors relative to the legs in at least two, and in particular three dimensions. This allows a fast and reliable positioning relative to the legs.

In an embodiment, the leg connector comprises: - a leg contact member constructed to extend substantially around a leg of the sea platform, the leg contact member defining a upper abutment surface configured to abut a lower abutment surface of a collar, - a vertical post extending upwardly from the leg contact member and comprising mounting positions for the at least two vertical restrainers, the mounting positions being provided at a vertical distance above the lower abutment surface of the collar.

The vertical post allows the horizontal restrainers to be directed at a higher position than the position of the leg connectors. In an embodiment, the vertical post is telescoping in order to adjust a height thereof.

The present invention further relates to a lifting vessel comprising a hull and two arms which define a docking bay between them, wherein on each arm a plurality of lifting devices according to the invention are positioned, wherein the suspension systems extend into the docking bay.

In an embodiment of the lifting vessel, the lifting arms are movable relative to the hull and wherein an angle γ between the lifting arms can be varied, and wherein in particular two parallel tracks are provided on the deck of the hull, wherein each lifting arms rest on said tracks via at least two movable carriages, one carriage for each track, and wherein both the distance and the angle between the arms can be varied by moving said carriages.

In an embodiment of the lifting vessel, each lifting arm comprises a skidding system extending along a longitudinal direction of the lifting arm, the skidding system being constructed for skidding the lifting devices relative to the lifting arms.

The present invention further relates to a method for lifting a sea platform, in particular an upper part of the sea platform, which sea platform comprises a support structure and a top side, the method comprising: providing the lifting vessel according to any the invention, and positioning the lifting devices on the lifting arms in a required position to engage the legs of the sea platform, and pivoting the pivotable beams of the lifting devices to the upper position, positioning the lifting vessel near the sea platform, wherein the sea platform is positioned in the docking bay between the lifting arms, repositioning the lifting arms of the vessel in order to extend parallel to one side of the sea platform and parallel to an opposite side of the sea platform, engaging the leg connectors of the lifting devices with the legs of the sea platform, and connecting the horizontal restrainers to the legs of the sea platform, cutting the legs of the support structure under the leg connectors, thereby dividing the sea platform in an upper part and a lower part deballasting the lifting vessel, wherein the pivotable beams pivot from the upper position to the lower position and engage the outer supports, and lifting the upper part sea platform from the lower part, and moving the combination of the lifting vessel and sea platform away from the substructure.

The sea platform may have a row of legs on each side and the lifting arms may be positioned parallel to the rows of the legs on both sides of the sea platform.

In an embodiment of method, the flexible connection systems of the lifting device are tuned during the lift.

In an embodiment of method, prior to making contact between the lifting vessel and the sea platform, the flexible connection systems are tuned to achieve a specific stiffness range according to the specific expected loads by removing or adding or replacing resilient blocks and/or pre-tensioning the actuation system at a predetermined level.

In an embodiment of method, the stiffness range of the individual flexible connection systems of the lifting devices are individually tuned and differ from one another in order to allow the flexible connection systems to accommodate to differing forces experienced by each connection point during lifting operation.

One of the main benefits of this is that it accommodates for incorrect calculations in the centre of gravity of the sea platform. This may lead to an uneven distribution of the forces on the different lifting devices, and to a non-vertical orientation of the lifted sea platform. By tuning the different flexible connection systems individually, the forces may be redistributed and/or the lifting vessel may be turned upright. This advantage may be combined with the passive character of the lifting device, i.e. once tuned, no more energy may be required for the lifting devices to continue the lifting operation.

In an embodiment of method, the upper part of the sea platform is lifted from the lower part of the sea platform in a single lift.

In an embodiment, the method comprises a step of connecting collars to the legs of the sea platform, wherein the leg connectors engage the collars during the lifting step and exert the lift force on the sea platform via the collars.

In an embodiment of method, the collars are attached to the legs above the position where the leg connectors engage the legs.

In an embodiment, the method comprises: - engaging the legs with the leg connectors, moving the leg connectors upwardly against collars on the legs, by pivoting the pivotable beams upwards, wherein the lifting devices of the lifting vessel are brought in a free-moving mode, in which the leg connectors are relatively free to move relative to the base frame, and in which the horizontal restrainers are free to moving and do not support the legs, after engaging with the legs, switching to a supporting mode by de-ballasting the lifting vessel, wherein the pivotable beams are moved to the lower position and engage the outer supports, wherein the at least one pendulum arm has a freedom of movement in at least two, and wherein the horizontal restrainers support the legs in the horizontal X-direction and Y-direction, and in particular act as a spring.

In an embodiment, initially the lifting arms are oriented in a diverging arrangement, and wherein after engagement of the lifting devices with the legs which are closest to a blind end of the docking bay the lifting arms are pivoted to a parallel orientation about said legs, wherein subsequently the lifting devices engage one by one with the legs starting from said first leg and going in the direction of free ends of the lifting arms by rotating the arms in a more parallel orientation about the first leg.

In an embodiment of method, an operator who controls the lifting arms controls the subsequent contacting of the leg connectors by only moving one point of each lifting arm, in particular by moving a single carriage.

In an embodiment of method, a blind end of the docking bay is engaged with the platform, in particular via fenders.

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.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1A shows a top view of a lifting vessel according to the invention.

Figure 1B shows a top view of a lifting vessel according to the invention with diverging lifting arms.

Figure 2 shows a side view of a lifting vessel according to the invention.

Figure 3 shows a front view of a lifting vessel according to the invention.

Figure 4 shows an isometric view of a lifting vessel according to the invention.

Figure 5 shows an isometric view of a lifting device according to the invention.

Figure 6 shows a top view of a lifting device according to the invention.

Figure 7 shows a sectional side view of a lifting device according to the invention along the lines A-A in figure 6.

Figure 8 shows a sectional side view of a lifting device according to the invention along the lines B-B in figure 6.

Figure 9 shows a partial and enlarged sectional side view of a lifting device according to the invention along the lines B-B in figure 6.

Figure 10 shows a top view of a horizontal restraining system according to the invention.

Figure 11 shows a side view of a horizontal restraining system according to the invention.

Figure 12 shows an isometric view of a horizontal restraining system according to the invention.

Figures 13A -13F show different stages of the lifting device in the lifting operation.

Figures 14A -13D show different stages of the lifting vessel in the lifting operation.

Figure 15 shows a isometric view of a sea platform.

Figures 16A and 16B show further options for tuning the lifting devices. DETAILED DESCRIPTION OF THE FIGURES The lifting vessel and sea platform

With reference to figures 1A, 1B, 2, 3 and 4 a lifting vessel 100 comprises a hull 101 and two arms 102 which define a docking bay 103 between them. The arms protrude to the rear or to the front of the hull. The vessel may comprise a ballasting system 107 with which the draft of the vessel can be varied. The hull may comprise a wide section 120 which supports the arms and a narrow section 121 which protrudes away from the docking bay.

The arms rest on the deck 122 of the vessel. The arms 102 may protrude over distance of between 10 and 40 meter.

On each arm 102 a plurality of lifting devices 10 according to the invention are positioned, The suspension systems 18 (further discussed below) extend into the docking bay. The vessel may comprise propulsion system but may also be a towed barge.

The lifting arms 102 are movable relative to the hull 101. An angle y between the lifting arms can be varied, see in particular fig. 1B. Two parallel tracks 106A, 106B are provided on the deck 122 of the hull. Each lifting arms 102 rest on said tracks via at least two movable carriages 108, wherein one carriage per lifting arm is provided for each track. Both the distance 124 and the angle γ between the lifting arms can be varied by moving said carriages 108 over the tracks .

Each lifting arm comprises a skidding system 110 which extending along a longitudinal direction of the lifting arm. The skidding system is constructed in order to move the lifting devices 10 relative to the lifting arms. Each arm may 102 comprise four lifting devices 10, but a different number is also possible.

With reference to figure 15, the sea platform 200 is shown. The sea platform comprises a support structure 206 and a top side 206. The support structure is often referred to as a jacket and comprises legs 210. The support structure is generally positioned on the seabed via pods 208 and comprises many beams 212, generally made of steel. The beams generally extend horizontally and diagonally and interconnect the legs 210.

With “X” the position in which the sea platform is divided in an upper part 214 and a lower part 215 is indicated. The upper part 214 is the part which is lifted with the present invention. The upper part 214 comprises the top side and a portion of the jacket. Such sea platforms have a life span of 20 - 50 years after which they generally need to be dismantled.

The lifting device

With reference to figures 5, 6, 7, 8 and 9, a lifting device 10 is shown for lifting an upper part 214 of a sea platform.

The lifting device is constructed to be positioned on the lifting vessel 100 more in particular on the legs 102 of the lifting vessel. The lifting device comprises a base frame 12 which is constructed to rest on the lifting vessel.

The base frame 12 is configured to be positioned on a lifting arm 102 of a lifting vessel. The base frame 12 comprises a deck part 32 and a side part 33. The deck part and the side part may be connected to one another via a hinge 41. A relatively small section 37 of the side part 33 may rest on the deck as well. The side part 33 which extends downwards from the deck part, wherein the pivot points 70 are provided on the side part. The pivot points 70 are positioned at a distance 49 below the deck part 32. The deck part and the side part (apart from the deck section 37 thereof) typically extend at an angle of 90 degrees relative to one another.

The deck part 32 comprises deck beams 30 which are interconnected via transverse beams 36.

The lifting device further comprises at least one console frame 14 and a flexible connection system 16, further elucidated below. The console frame 14 defines a console which extends outwardly from the base over a horizontal distance 47.

The lifting device further comprise a suspension system 18 which is connected to the console frame 14 and comprises a leg connector 20 which is constructed to be connected to a leg 210 of the sea platform. The suspension system is constructed to allow freedom of movement of the leg connector 20 relative to the console frame 14.

The flexible connection system 16 forms a flexible connection between the console frame 14 and the base frame 12 and allows a limited movement of the console frame relative to the base frame. As will be discussed further below, this is necessary to prevent excessive forces on the sea platform during transport.

The base frame 12 defines a number of pivot points 70, and the console frame 14 is connected to the base frame via the pivot points in order to make a pivoting movement about the pivot points relative to the base frame.

The console frame 14 comprises a console 72 having an outer support 73. The console frame 14 further comprises at least one upper connection point 74 on which the flexible connection system 16 acts.

The suspension system 18 comprises at least one pivotable beam 75 which is connected to the console frame via a hinging connection 76 which allows the pivotable beam 75 to pivot relative to the console frame between a lower position and an upper position.

In the lower position the pivotable beam engages the outer support 73 of the console 72 and is supported by the console frame 14. In the upper position the pivotable beam is positioned at a distance above the outer support and is allowed to pivot over an angle β, in order to allow the upper part of the sea platform to move in a vertical direction relative to the lifting vessel.

The suspension system 18 further comprises a pivotable beam actuator 83 (see figure 8) for pivoting the pivotable beam between the upper position and the lower position. This pivotable beam actuator 83 is a hydraulic cylinder and extends between the console and a point on the pivotable beam.

The suspension system 18 further comprises at least one pendulum arm 77 connected at an upper end 78 thereof to a protruding end 79 of the pivotable beam via a pendulum hinge 80. The suspension system 18 further comprises the at least one leg connector 20 constructed to be connected to the leg, wherein the at least one leg connector is attached to a lower end 81 of the at least one pendulum arm via a leg connector hinge 82.

The suspension system 18 is capable of switching between a supporting mode and a free-moving mode as will be discussed below.

The lifting device may comprise two console frames 14 and two pivotable beams 75, wherein each console frame is configured to support an associated pivotable beam via its outer support, and wherein each pivotable beam supports a pendulum arm 18, wherein the leg connector 20 is supported on two opposite sides by the lower end of a pendulum arm.

The at least one pendulum hinge 80 between the pendulum arms and the pivotable beams and the at least one leg connector hinge 82 between the at least one pendulum arm and the at least one leg connector are gimbal hinges which allow rotation about three independent axis of the pendulum arms 77 relative to the pivotable beams 75 and of the leg connectors 20 relative to the pendulum arms 77.

The pivotable beams 75 pivot about a horizontal axis, and the console frame also pivots about a horizontal axis.

The flexible connection system

The flexible connection system acts on the deck part 32 of the base frame and on an upper part 34 of the console frame 14.

The flexible connection system 16 comprises an actuation system 22 which extends between the base frame 12 and the console frame 14. The flexible connection system comprises connection beams 26 which extend horizontally from an upper part of the console frame. The connection beams 26 may be connected to the console frame via hinges 39. The hinges 39 have a horizontal hinge axis and allow the console frame 4 to pivot while the connection beams 26 stay substantially horizontal.

The connection beams 26 extend parallel to the deck beams 30 of a deck part 32 of the base frame.

The flexible connection system 16 comprises resilient members 28 which allow the console frame 14 to be displaced relative to the base frame 12 over a limited angle by deformation of the resilient members. The displacement may be a pivotal movement about the pivot points 70. The resilient members are configured to deform under shear stress, and may be rubber blocks. The rubber blocks are placed between the connection beams 26 and the deck beams 30 and deform when the connection beam displace relative to the deck beams. The resilient members interconnect the connection beams and the deck beams

The flexible connection system 16 is configured to exert a force on the console frame. Therefore depends on the displacement of the console frame relative to the base frame. A load-displacement relationship of the flexible connection system is variable.

The resilient members 28 and the actuation system 22 act in parallel on the console frame, i.e. their forces are added to form a combined (horizontal) force on the console frame via the connection beams.

The load - displacement relationship, or ‘stiffness’ between the base frame 12 and the console frame 14 as defined by the flexible connection system 16 is adjustable in two ways: 1) by varying the number and/or position of the resilient members 28, and 2) by adjusting the actuation system 22.

These options provide better fine tuning capabilities. The stiffness of the connection between the lifting vessel and the leg 210 can be controlled more accurately, is more robust, and is able to compensate for varying load distributions. More-over the stiffness can be modified after the lifting operation has begun and the lifting devices are under a load.

If the hydraulics fail, the resilient members still are able to hold the load.

The hydraulic system can be smaller in comparison with a system without the resilient members. The hydraulic system can be also be simpler in comparison with a system without the resilient members.

The actuation system 22 may be adjusted to apply an adjustable force on the console frame when the console frame is in a neutral position 29 in which the resilient members are not under tension. Therefore, when the resilient member do not exert any force on the console frame the actuation system may exert a force on the console frame (via the connection beams)

Typically the actuation system 22 comprises at least one cylinder 24, in particular a hydraulic cylinder, and a pump to control a pressure in the cylinder. The pressure may be adjustable according to the requirements. This provides a wide range of available load -displacement relationships

The actuation system 22 may comprise at least one accumulator which is configured to let the cylinder act as a spring, having a spring constant. The force exerted by the actuation system on the console frame via the connection beams is dependent on the displacement of the console frame relative to the base frame.

The actuation system 22 is configured to operate in a passive mode, without applying external energy. This provides a benefit over known systems that much less energy is required during transport of the sea platform.

The horizontal restrainers

With reference to figures 10, 11 and 12, if large bending moments occur in the legs 210, the legs may break. In the lifting device, large bending moments in the legs 201 are therefore to be avoided. To this end, the lifting device 10 comprises a horizontal restraining system 40 for limiting a horizontal movement of the legs 210. The suspension system 18 is configured to exert a vertical force on the legs via the leg connector 20, and the horizontal restraining system 40 is configured to exert a horizontal force on the leg.

The horizontal restraining system 40 comprises at least at least two horizontal restrainers 42A, 42B (also generally indicated with 42). These are constructed to limit the horizontal movement of the leg 210 in an X-direction and an Y-direction. The X-direction is a longitudinal direction of a lifting vessel and the Y-direction is the transverse direction of the lifting vessel.

The at least two horizontal restrainers 42A, 42B are connected at one end to respective restraining support positions 46A, 46B on the base frame and are configured to be connected at an opposite end to the leg 210, directly or indirectly via a collar 60 which is attached to the leg. The horizontal restrainers 42 are positioned at a vertical distance 130 above the leg connector 20, and in particular above a deck part 32 of the base frame. The horizontal restrainers are directed at a part 68 of the leg which is substantially closer to the top side of the sea platform than a part 69 of the leg on which the leg connector acts. Said vertical distance 130 may in particular be greater than 2 meter, but may be larger for instance 5 meter. Each horizontal restrainer 42A, 42B comprises a hydraulic cylinders 43A, 43B.

The distal ends 44A, 44B of the horizontal restrainers are positioned higher than a deck part 32 of the base frame and wherein the leg connector 20 is positioned lower than the deck part.

In top view the horizontal restrainers extend at an angle a of between 70 and 110 degrees relative to one another, see figure 10.

Each horizontal restrainers may be configured to act as a spring, in particular with an adjustable spring constant which is adjusted a single time prior to the operation. Typically the horizontal restrainers are configured to operate in a passive mode without applying external energy during the lifting operation.

However, it is also possible to actively monitor the pressure in the cylinder during the lifting and transport operation and to continuously adjust the pressure in the cylinder. A load - displacement relationship of the horizontal restrainers is adjustable by changing the pressure in the cylinder, in particular independently for each of the two horizontal restrainers.

The lifting device 10 is configured to exert vertical forces on the legs via the suspension system 18 and the leg connectors 20. The lifting device is configured to exert horizontal forces on the legs 210 via the horizontal restraining system 40 and the leg connectors. The suspension system 18 and the horizontal restraining system 40 are constructed to substantially prevent horizontal forces to be exerted onto the legs via the suspension system. This advantageously prevents large moments from occurring in the legs 210.

The leg connectors 20 have an abutment surface 52 at an upper side thereof and are constructed to slide relative to the legs in order to exert a vertical force onto the legs via the abutment surface and via a collar 60 which is attached to the leg above a position where the leg connectors are engaged with the leg. The leg connectors therefore are not gripping devices.

The lifting device can be switched between a: 1) a free-moving mode, in which the at least one pivotable beam 75 is in the upper position at a distance of the associated outer support and has a freedom of movement up and down relative to the outer support. The at least one pendulum arm has a freedom of movement in at least two, in particular three degrees of freedom relative to the associated pivotable beam 75 and the leg connector 20 has a freedom of movement in at least two, in particular three degrees of freedom relative to the at least one pendulum arm to which it is connected. The horizontal restrainers are freely movable. 2) a supporting mode, in which the pivotable beams are in the lower position and rest on the outer supports, wherein the at least one pendulum arm has a freedom of movement in at least two, in particular three degrees of freedom relative to the associated pivotable beam and wherein the leg connector has a freedom of movement in at least two, in particular three degrees of freedom relative to the at least one pendulum arm to which it is connected, and wherein the horizontal restrainers substantially fixate a higher position of the leg in an X-direction and Y-direction relative to the base frame.

The free moving mode is used during the connection phase wherein a connection between the lifting vessel and the sea platform has already been made but wherein the lifting vessel moves relative to the sea platform. The supporting mode is used during the lifting operation and the subsequent transport to shore.

The lifting device may comprise a positioning system for positioning the leg connectors relative to the legs in at least two, and in particular three dimensions.

The leg connector 20 comprises a leg contact member 50 constructed to extend substantially around a leg of the sea platform. The leg contact member 50 has doors 135 which open up to allow the leg 210 to move within the leg contact member. When the doors 135 close again, the leg contact member forms an annular shape around the leg. The leg contact member defines an upper abutment surface 52 configured to abut a lower abutment surface 62 of a collar 60.

The leg connector 20 further comprises a vertical post 54 extending upwardly from the leg contact member 50 and comprising mounting positions 56 for the at least two vertical restrainers, the mounting positions being provided at a vertical distance above the lower abutment surface 61 of the collar.

As is shown in figures 11 and 12, the vertical post is telescoping in order to adjust a height thereof.

Turning to figure 16, it may be required to provide further tuning of the lifting device, in particular to a collar position on the legs which is deviant from a target position thereof. To this end, shim plates (or resilient elements) 150 may be provided on the outer support in order to raise the position of the outer support 73, thereby raising the lower position of the pivotable beams 75 and consequently the lifting position of the leg connectors. The elements 150 are shown in foreground mode, because otherwise they would be concealed.

Turning to figure 16B, same or similar shim plates (or resilient elements) 152 may be provided on the upper abutment surface 52 of the leg connectors 20. This provide another option of tuning to deviant collar positions.

Operation

The operation of the entire system is discussed with reference to figures 13A - 13F and figures 14A - 14D.

Turning in particular to Fig. 14A, the lifting vessel according to the invention is provided, and the lifting devices 10 are positioned on the lifting arms 102 in the required position to engage the legs 210 of the sea platform. The lifting devices 10 may be skidded over the skidding system 110.

The lifting vessel is positioned near the sea platform 200, and the sea platform is positioned in the docking bay 103 between the lifting arms. The method comprises a step of connecting collars 60 to the legs of the sea platform prior to the lifting operation itself. The leg connectors 20 engage the collars during the lifting step and exert the lift force on the sea platform via the collars. The collars 60 are attached to the legs above the position where the leg connectors engage the legs.

The lifting arms may each diverge over an angle of 1 - 20 degrees to facilitate the positioning operation (shown in fig. 1B). After engagement of the lifting devices 10 with the legs 210A (see fig,. 14B) which are closest to a blind end 105 of the docking bay 103, the lifting arms 102 may be pivoted to a parallel orientation about said legs, wherein subsequently the lifting devices engage one by one with the legs starting from said first leg and going in the direction of free ends 116 of the lifting arms by rotating the arms in a more parallel orientation about the first leg. An operator who controls the lifting arms 102 may control the subsequent contacting of the leg connectors by only moving one point of each lifting arm, in particular by moving a single carriage 108 of each lifting arm.

Turning to figure 14B, the lifting arms 102 are positioned parallel to one another, at a greater distance than a width of the sea platform. The lifting arms of the vessel extend parallel to a row of legs on one side of the sea platform and parallel to a row of legs on an opposite side of the sea platform. A blind end 105 of the docking bay is engaged with the platform, in particular via fenders.

Turning to figure 14C, at one side of the sea platform the lifting devices 10 engage the legs 210. As is shown in figure 13A, in this phase the pivotable beams 75 of the lifting devices are in the lower position. The doors 135 of the leg connectors 20 are being closed around the leg 210.

Turning to figure 13B, the leg connectors 20 of the lifting devices 10 are engaged with the legs 210 of the sea platform, and the doors 135 are closed.

Turning to figure 13C, the horizontal restrainers 42 are connected to the mounting positions on the vertical post of the leg connector. In an alternative embodiment, the horizontal restrainers may be connected directly to the leg or to a separate collar which is provided on the leg above the collar 60.

Turning to figure 14D, the other lifting arm 102 is also positioned relative to the sea platform. The lifting devices 10 on this lifting arm also engage the respective legs 210 according to the process shown in figures 13A, 13B and 13C.

Turning to figure 13D, the pivotable beams 75 are pivoted upwards by the actuator 83 (not shown in figure 13D because the actuator 83 is underneath and partially inside the pivotable beam 75). The abutment surface 52 of the leg connector engages the abutment surface 61 of the collar 60.

Turning to figure 13E, the pivotable beams have been pivoted upwards. The lifting device is now in the free-moving mode. The lifting vessel can be moved relative to the sea platform under the influence of wind and waves over a certain distance in X, Y and Z direction. There is also freedom of rotation of the lifting vessel relative to the sea platform about three axes X, Y and Z over limited angles, i.e. a freedom in yaw, pitch and heave over limited angles.

The at least one pivotable beam is in the upper position at a distance of the associated outer support and has a freedom of movement up and down relative to the outer support. The at least one pendulum arm has a freedom of movement in at least two, in particular three degrees of freedom relative to the associated pivotable beam and the leg connector has a freedom of movement in at least two, in particular three degrees of freedom relative to the at least one pendulum arm to which it is connected.

The horizontal restrainers 42 are in a free moving mode, i.e. they are not under pressure.

Subsequently the legs 210 are cut underneath the leg connectors 20. The upper 214 part of the sea platform is now loose from the lower part 215 , but still rests on the lower part. It is possible that temporary flanges are created on the legs below the position where the leg connectors engage the legs. The temporary flanges allow the legs to be cut but still held together by a bolt which interconnects the flanges. In this embodiment, after the stage shown in figure 13E the legs 210 are not cut (they have already been cut) but the bolts are removed.

Turning to figure 13F, the ballasting system of the lifting vessel is emptied and the pivotable beams 75 return and come to rest again on the outer supports. Now the actual lifting operation begins and the full weight of the upper part of the sea platform is carried by the lifting devices and ultimately the lifting vessel. A large upward force is exerted via the suspension system and the leg connectors onto the legs 210. The upper part of the sea platform is lifted from the lower part of the sea platform in a single lift. The horizontal restrainers 42 are activated and act as a spring. The horizontal restrainers 42 exert a horizontal force on the vertical posts when the vertical posts move in an X-direction or Y-direction. The force exerted by the restrainers brings the leg 210 back to its neutral position. The horizontal restrainers can both push and pull the leg 210.

The lifting devices 10 are now in the supporting mode. Some movement of the upper part relative to the lifting vessel is allowed via the flexible connection system, but not much.

The at least one pendulum arm on its own still has a freedom of movement in at least two, in particular three degrees of freedom relative to the associated pivotable beam. The leg connector has a freedom of movement in at least two, in particular three degrees of freedom relative to the at least one pendulum arm to which it is connected.

However, there is no vertical freedom of movement anymore between the leg and the console frame 14, because the leg 210 rests on the leg connector 20 and the pivotable beams rest on the outer supports. Further, there is very limited freedom of movement in a horizontal direction, because the horizontal restrainers substantially fixate a higher position of the leg in an X-direction and Y-direction relative to the base frame.

There still is some freedom of movement between the upper part and the lifting vessel because the console frame 14 and the base frame move relative to one another via the flexible connection system 16 as is discussed above. The console frame 14 may pivot relative to the base frame over a limited angle. This prevents excessive forces on the legs 210 which could otherwise lead to damage or even collapse of one of the legs.

The combination of the lifting vessel and sea platform is subsequently moved away from the lower part, i.e. the substructure and may be towed to a port or sail under its own propulsion system.

Prior to making contact between the lifting vessel and the sea platform, the flexible connection systems 16 may be tuned to the specific expected loads by removing or adding or replacing resilient blocks and/or pre-tensioning the actuation system at a predetermined level. The deformation (bending and torsion) of the lifting arms 102 under the load may be taken into account, and result in different tuning settings for each lifting device 10 depending on the position on the lifting arms 102.

During the lifting operation, further tuning may be performed by adjusting the actuation system. The resilient members will generally not be changed under load.

All this time, the lifting device may be operated passively for the lift itself. The tuning requires energy, but the lift itself and the compensation of the relative movements between the upper part and the lifting vessel does not require energy.

The lifting procedure may also be reversed, i.e. lifting vessel may also be used to place an upper part of a sea platform onto a lower part.

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.

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. It will be recognized that a specific embodiment as claimed may not achieve all of the stated objects.

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

A lifting device (10) for lifting a sea platform (200), in particular an upper part of the sea platform, wherein the sea platform comprises a support structure (205) and a top side (206), wherein the lifting device is constructed to be positioned on a lifting vessel (100), the lifting device comprising: a base frame (12) constructed to rest on the lifting vessel, at least one projecting frame (14) passing through a flexible connecting system (16) ) is connected to the base frame, a suspension system (18) connected to the cantilever frame and comprising a leg connector (20) constructed to be connected to a leg (210) of the sea platform, the suspension system being constructed to create freedom of movement of the leg connector relative to the projecting frame (14), the flexible connection system (16) forming a flexible connection between the projecting frame (14) and the base frame (12) and a bar allows movement of the projecting frame relative to the base frame.

A lifting device according to claim 1, wherein the flexible connection system comprises an actuator system (22) extending between the base frame and the projecting frame and which is adapted to exert a force on the projecting frame, the force being adjustable to reduce the load - to vary the displacement relationship of the flexible connection system (16).

A lifting device according to claim 1 or 2, wherein the flexible connection system (16) comprises resilient members (28) that allow the projecting frame to be displaced by a limited angle with respect to the base frame by deformation of the resilient members.

4. Lifting device as claimed in claim 2, wherein the resilient members are adapted to deform under shear stress.

Lifting device according to claim 3 or 4, wherein a load-displacement relationship between the base frame and the projecting frame as defined by the flexible connection system (16) is adjustable: by varying the number and / or the position of the resilient members (28), and by adjusting the actuator system (22).

Lifting device according to any of claims 3-5, wherein the resilient members (28) and the actuator system (22) act in parallel on the projecting frame, and wherein the actuator system is adapted to exert an adjustable force on the projecting frame when the projecting frame is in a neutral position (29) in which the resilient members are not under tension.

The lifting device of any one of claims 3-6, wherein the resilient members (28) and the actuator system (22) operate in parallel on the projecting frame, and wherein the actuator system is arranged to have an adjustable stiffness range.

A lifting device according to any of claims 2-7, wherein the actuator system comprises at least one cylinder (24), in particular a hydraulic cylinder, and a pump for controlling a pressure in the cylinder.

9. Lifting device as claimed in claim 7, wherein the actuator system comprises at least one accumulator which is adapted to make the cylinder act as a spring.

10. Lifting device as claimed in any of the claims 2-9, wherein the force exerted by the actuator system on the projecting frame is dependent on the displacement of the projecting frame relative to the base frame.

11. Lifting device as claimed in any of the claims 2-10, wherein the actuator system is adapted to operate in a passive mode during a lifting operation without supplying external energy.

12. Lifting device according to one of the preceding claims, wherein the flexible connecting system (16) further comprises connecting beams (26), wherein the base frame comprises deck beams (30), and wherein the resilient members (28) are positioned between the connecting beams and the deck beams and connect the connecting beams and the deck beams together.

The lifting device of claim 12, wherein the connecting beams (26) extend parallel to the deck beams (30) of a deck portion (32) of the base frame.

A lifting device according to any of claims 7-13, wherein the flexible connection system acts on the deck portion of the base frame and on an upper portion (34) of the projecting frame (14).

Lifting device according to one of the preceding claims, comprising a horizontal restriction system (40) for restricting a horizontal movement of the legs (210), wherein the suspension system (18) is adapted to exert a vertical force via the leg connector (20). exerting the legs, and wherein the horizontal restraint system is adapted to exert a horizontal force on the leg.

The lifting device of claim 15, wherein the horizontal restraint system comprises at least two horizontal restraints (42A, 42B) that are constructed to limit the horizontal movement of the leg (210) in an X direction and in a Y direction, wherein the X direction is a longitudinal direction of a lifting vessel and wherein the Y direction is a transverse direction of the lifting vessel.

17. Lifting device according to claim 16, wherein the horizontal limiters are positioned substantially at a vertical distance above the leg connector (20), in particular above a deck portion (32) of the base frame, and are directed to a portion (68) of the leg that is substantially closer to the top side (206) of the sea platform than a part (69) of the leg on which the leg connector acts, and wherein said vertical distance is in particular greater than 2 meters.

18. Lifting device as claimed in any of the claims 116 or 17, wherein, in top view, the horizontal limiters extend with respect to each other at an angle α that lies between 70 and 110 degrees.

A lifting device according to any of claims 16-18, wherein the horizontal limiters comprise hydraulic cylinders (43A, 43B).

20. Lifting device as claimed in any of the claims 14-19, wherein each horizontal limiter is adapted to act as a spring, in particular as a spring with an adjustable spring constant.

21. Lifting device as claimed in any of the claims 14-20, wherein a load displacement installation of the horizontal limiters is adjustable, in particular independently for each of the horizontal limiters.

A lifting device according to any of claims 14-21, wherein the horizontal limiters are adapted to operate in a passive mode without supplying external energy.

The lifting device of any one of claims 14-22, wherein far-flung ends (44A, 44B) of the horizontal limiters are positioned higher than a deck portion (32) of the base frame and wherein the leg connector (20) is positioned lower than the deck portion.

A lifting device according to any of claims 14-23, wherein the lifting device is adapted to exert vertical forces on the legs via the suspension system and the leg connectors and wherein the lifting device is adapted to exert horizontal forces on the legs via the horizontal restriction system and the leg connector, wherein the suspension system (18) and the horizontal restriction system (40) are arranged to substantially prevent horizontal forces from being exerted on the legs via the suspension system.

A lifting device according to any of claims 14-23, wherein the at least two horizontal limiters are connected at one end thereof to respective restriction support positions (46A, 46B) on the base frame and are adapted to be connected to the opposite end leg (210), directly or indirectly via a collar (60) attached to the leg.

A lifting device according to any of the preceding claims, wherein the base frame defines a number of pivot points (70), and wherein the projecting frame is connected via the pivot points to the base frame to make a pivotal movement about the pivot points and relative to the base frame.

A lifting device according to any one of the preceding claims, wherein the projecting frame comprises a projection (72) with an outer support (73), the projecting frame (14) further comprising at least one upper connection point (74) at which the flexible connection system ( 16), and wherein the suspension system (18) comprises: at least one pivotable beam (75) that is connected via a hinged connection (76) to the projecting frame that allows the pivotable beam to pivot relative to the projecting frame and between a lower position and an upper position, wherein in the lower position the pivotable bar touches the outer support (73) of the projecting frame (72) and is supported by the projecting frame (14) and wherein in the upper position workable beam is positioned at a distance above the outer support and can pivot through an angle β, a pivotable beam actuator (83) for pivoting the pivotable beam between the upper position and the lower position, and at least one pendulum arm (77) connected at an upper end (78) thereof and via a pendulum hinge (80) to a projecting end (79) of the pivotable beam, the at least one leg connector ( 20) configured to be connected to the leg, the at least one leg connector being connected via a leg connector hinge (82) to the lower end (81) of the at least one pendulum arm.

A lifting device according to any preceding claim, wherein the base frame has a deck portion (32) and a side portion (33) extending downwardly from the deck portion, the pivot points (70) being provided on the side portion and positioned lower then the deck portion (32).

A lifting device according to any one of the preceding claims, wherein the deck portion comprises the deck beams (30).

A lifting device according to any one of the preceding claims, comprising two projecting frames (14) and two pivotable beams (75), wherein each projecting frame is adapted to support an associated pivotable beam via an outer support thereof, and wherein each pivotable beam supports a pendulum arm (18), the leg connector (20) being supported on each side by the lower end of a pendulum arm.

A lifting device according to any preceding claim, wherein the at least one pendulum hinge (80) between the pendulum arms and the pivotable beams and the at least one connector hinge (82) between the at least one pendulum arm and the at least one leg connector are ball hinges allowing rotation about three independent axes of the pendulum arms relative to the pivotable beams and of the leg connectors relative to the pendulum arms

A lifting device according to any one of the preceding claims, wherein the base frame is adapted to be positioned on a lifting arm (102) of a lifting vessel, the pivot points (70) being positioned at a distance (49) below the deck section and wherein in the in particular the deck part and the side part extend at an angle of 90 degrees with respect to each other.

33. Lifting device according to one of the preceding claims, wherein the projection extends outwards from the base over a horizontal distance (47).

A lifting device according to any one of the preceding claims, wherein the leg connectors have a contact surface (52) at an upper side thereof and are adapted to slide relative to the legs to exert a vertical force on the legs via the contact surface and via a collar (60) connected to the leg above a position where the leg connectors engage the leg.

A lifting device according to any one of the preceding claims, wherein the pivotable beams pivot about a horizontal axis, and wherein the projecting frame pivots about a horizontal axis.

36. Lifting device as claimed in any of the foregoing claims, wherein the lifting direction can be switched between: free-moving mode, in which the at least one pivotable beam is located in the upper position at a distance from the associated outer support and a freedom of movement has upwards and downwards with respect to the outer support, wherein the at least one pendulum arm has a freedom of movement in at least two, in particular three, degrees of freedom relative to the pivotable beam associated therewith, and wherein the leg connector has a freedom of movement has in at least two, in particular three degrees of freedom, relative to the at least one pendulum arm to which it is connected, and wherein the horizontal limiters are freely movable, a support mode in which the pivotable beams are in the lower position and rest on the outer supports, the at least one pendulum arm having freedom of movement in at least two, in particular three, degrees of freedom relative to the pivotable beam associated therewith, and wherein the leg connector has freedom of movement in at least two, in particular three, degrees of freedom relative to the at least one pendulum arm to which it is connected, and wherein the horizontal limiters substantially fix an elevated position of the leg in an X direction and a Y direction relative to the base frame.

A lifting device as claimed in any one of the preceding claims, comprising a positioning system for positioning the leg connectors with respect to the legs in at least two, and in particular three, dimensions.

A lifting device according to any preceding claim, wherein the leg connector (20) comprises: a leg contact member (50) adapted to extend substantially around a leg of the sea platform, the leg contact member having an upper contact surface ( 52) defines that is adapted to engage on a lower contact surface (62) of a collar (60), a vertical upright (54) that extends upwardly from the leg contact member (50) and includes mounting positions (56) for the at least two vertical limiters, the mounting positions being provided at a vertical distance above the lower contact surface (61) of the collar.

The lifting device of claim 38, wherein the vertical upright is telescoping to adjust a height thereof.

A lifting vessel (100) comprising a hull (101) and two arms (102) defining a docking station (103) therebetween, wherein on each arm a plurality of lifting devices (10) according to claim 1 are positioned, wherein the suspension systems (18) are located extend into the docking station.

A lifting vessel according to any one of the preceding lifting vessel claims, wherein the lifting arms are movable relative to the hull and wherein an angle γ between the lifting arms can be varied, and wherein in particular two parallel tracks (106A, 106B) are provided on the deck of the hull, wherein each lifting arm rests on said tracks via at least two movable carriages (108), a carriage for each track, and wherein both the distance and the angle between the arms can be varied by moving said carriages.

A lifting vessel as claimed in any one of the preceding lifting vessel claims, wherein each lifting arm has a sliding system (110) extending in a longitudinal direction of the lifting arm, the sliding system being adapted to slide the lifting devices (10) relative to the lifting arms.

43. Method for lifting a sea platform (200), in particular an upper part (204) of the sea platform, wherein the sea platform has a support structure (205) and a top side (206), the method comprises: - providing the lifting vessel according to any of claims 1 to 38, and positioning the lifting devices (10) on the lifting arms (102) in a position required to accommodate the legs (210) of the sea platform to grab, and pivot, the pivotable beams of the lifting devices to the upper position, positioning the lifting vessel near the sea platform (200), the sea platform being positioned between the lifting arms in the docking station (103) repositioning the lifting arms of the vessel so as to extend it parallel to one side of the sea platform and parallel to the opposite side of the sea platform, engaging the leg connectors (20) of the lifting devices (10) on the p legs (210) of the sea platform, and connecting the horizontal limiters to the legs of the sea platform, cutting the legs of the support structure under the leg connectors, the sea platform in an upper part (214) and a lower portion (215) is divided, unbalancing the lifting vessel, wherein the pivotable beams pivot from the upper position to the lower position and engage the outer supports, and wherein the upper part of the sea platform is lifted from the lower part, and moving the combination of the lifting vessel and the sea platform away from the substructure.

A method according to any of the preceding method claim, wherein the flexible connection systems (22) of the lifting device are tuned during lifting.

A method according to any of the preceding method claims, wherein prior to making contact between the lifting vessel and the sea platform, the flexible connection systems (16) are tuned to achieve a specific stiffness range according to the specific expected loads for removing, adding or moving resilient blocks and / or applying bias to a predetermined level on the actuator system.

A method according to any one of the preceding method claims, wherein the rigidity range of the individual flexible connection systems (16) of the lifting vessels is individually tuned and differs from each other in order to realize that the flexible connection systems (16) can accommodate different forces that each connection point ( 210) is encountered during a lifting operation.

A method according to any one of the preceding method claims, wherein the upper portion of the sea platform is lifted from the lower portion of the sea platform in a single lifting movement.

A method according to any of the preceding method claims, comprising a step of connecting collars (60) to the legs of the sea platform, wherein the leg connectors engage on the collars during the lifting step and exert the lifting force on the sea via the collars -platform.

A method according to any of the preceding method claims, wherein the collars are connected to the legs above the position where the leg connectors engage on the legs.

A method according to any of the preceding method claims, comprising: engaging the leg connectors (20) on the legs (210), moving the leg connectors upwards against the collars (60) on the legs, by lifting them upwards to pivot the pivotable beams, wherein the lifting devices (10) of the lifting vessel are brought into a free-moving mode, wherein the leg connectors are relatively free to move relative to the base frame, and wherein the horizontal limiters are free to move and the legs (210) do not support, after engaging the leg connectors (20) on the legs, switching to a support mode by unbalancing the lifting vessel, the pivoting beams being moved to the lower position and engaging the outer supports , wherein the at least one pendulum arm has freedom of movement in at least two directions, and wherein the horizontal restraints have the legs in the horizontal X direction and Y direction g support, and in particular act as a spring.

A method according to any of the preceding method claims, wherein the lifting arms are initially oriented in a diverging arrangement, and wherein after engaging the lifting device (10) with the legs closest to a blind end (105) of the docking station are, the lifting arms are pivoted to a parallel orientation with respect to said legs, the lifting devices subsequently moving one by one into engagement with the said first legs and moving in the direction of free ends (116) of the lifting arms by rotating from the arms around the first leg to a more parallel orientation.

A method according to any one of the preceding method claims, wherein an operator controlling the lift arms controls successive contact of the leg connectors by moving only a single point of each lift arm, in particular by moving a single carriage (108).

A method according to any of the preceding method claims, wherein a blind end of the docking station engages the platform, in particular via fenders.

54. A method according to any of the preceding method claims, wherein the cutting of the legs takes place prior to contacting the lifting vessel with the sea platform, and wherein temporary connections are made after cutting, the temporary connections being subsequently removed during the lifting operation.