FIELD OF THE INVENTION

The invention relates to a combination of a heavy lift vessel and a floating appendage structure for the installation and/or removal of large offshore structures.

BACKGROUND OF THE INVENTION

General market

Currently the largest crane capacity is limited to approximately 10.000mT per crane. For a dual crane construction vessel the current maximum capacity is 20.000mT. When considering the reach required for lifting, this capacity is decreased. There is a general need for solutions that can remove and install larger topsides and possibly jackets or other types supporting structures such as gravity based structures in one piece. An installation and/or removal in one piece results in a smaller risk for the operator, in a reduced environmental impact and in an overall reduction of cost.

Larger loads can be lifted by a vessel (or a barge) which is positioned underneath the loads using buoyancy as the lifting force. However, the majority of platforms / jacket designs prevent the vessel to be positioned directly underneath the load because the jacket or other support construction is located there. Hence a different type of hull shape is required for the lifting vessel, such as a dual hull or a U-shaped type lifting vessels. Over the course of time several options have been developed. Some of these are already in use, such as the Pioneering Spirit operated by Allseas and the Versatruss operated by Versabar. These solutions are known to have high operational costs (OPEX) and also require a high initial investment (CAPEX).

Single lift dedicated vessels

The construction of a large (double) hull that is capable of lifting large offshore platforms (i.e. Pioneering Spirit) has a high initial cost and results in a high OPEX. Although the need was seen by Allseas to include an alternative operational mode in the vessel (i.e. a pipelay mode for laying pipelines on the seabed) the added vessel and equipment are always present and idle when not in use. This all adds to the operational cost (OPEX) of the vessel, also during the alternative use (of pipelay mode). Another drawback of the Pioneering Spirit and other lifting vessels is the limited capability of varying the draught of the vessel. The underside of a top side or module support frame (MSF) is generally the preferred location where the topside should be engaged for an installation procedure or a removal procedure in one piece. The underside of an installed topside on a jacket is generally positioned quite high above the water level in order to keep the topside out of reach of the waves in case of a storm. However, when transferred to shore, the preferred height of a topside which is to be scrapped is quite low, so the workers can easily and safely reach the topside. Therefore, at some point in time - preferably as soon as possible - it is desired to lower the topside during a removal operation. The desire to lower the topside also applies when a topside is scrapped directly from a removal vessel or barge.

For an installation procedure, the same may apply, but in an opposite sequence. It may be preferable to build the topside at a low location and to install the topside quite high on the jacket. The Pioneering Spirit is not capable of varying its height in order to change the level of the topside, or only to a very limited extent.

Other solutions are also known in this field. For instance, various parties have conceived a dedicated U shape vessel. For instance the MPU heavy Heavy Lifter of MPU Offshore Lift ASA is a purpose built vessel which was only intended for the lift of (large) offshore platforms. Although fabrication had started, this was halted at an early stage and the project was eventually completely stopped. In general, lifting operations of heavy structures offshore are quite rare and these vessels remain idle for a large part of the time. This results in a need to earn back a large initial investment in a limited number of offshore operations, driving up the costs. Also, most designs require accommodation, propulsion and other equipment to be incorporated in the single purpose vessel. This further increases the initial investment.

Floating appendage structures in combination with an existing vessel

Appendages (also called floating appendage structures) to existing vessels to perform single lifts have also been conceived and circumvent the drawbacks of dedicated vessels as outlined above. One proposed solution (Global Maritime, GM-Lift Decommissioning and Installation Vessel ) as presented in W00160688A1 uses a combination of a semi- submersible vessel and an floating appendage structure which are coupled to one another. The floating appendage structure has a U-shape, when seen in top view. The GM lifter is considered to form the closest prior art for the present invention. In the GM-Lift Decommissioning and Installation Vessel as presented in W00160688A1 , the coupling between the (main) semi-submersible vessel and the floating appendage structure comprises a right and a left connection at deck level and a right and left connection at the level of the floater (and possibly over the complete height).

A drawback of this solution is that the coupling between the floating appendage structure and the heavy lift vessel is put under heavy loads during operation. These large environmental loads (mainly hogging and sagging) will result in large bending moments in the combination. These bending moments need to be carried by the coupling.

The large loads necessitate extensive stiffening of both the main vessel and the floating appendage structure near the coupling. This in turn renders the ships relatively heavy, complex and expensive to build. A hinged coupling (moment free) would reduce the loads, but introduces the challenge of having to cope with relative motions between the two vessels. Relative motions are generally undesirable.

A further disadvantage of the GM-Lift Decommissioning and Installation Vessel is that a transfer operation of a topside from the GM-Lift Decommissioning and Installation Vessel to a barge or vice versa is quite difficult. This is related to the U-shape, which prevents a barge from traversing the GM-Lift Decommissioning and Installation Vessel.

It is noted that if in the GM-Lift Decommissioning and Installation Vessel the coupling breaks when the floating appendage structure carries a topside, this will almost certainly result in the loss of both the floating appendage structure and the topside itself. Most likely it will also result in the loss of the main vessel. In fact it is questionable whether the kind of coupling as envisaged in the GM-Lift Decommissioning and Installation Vessel can be constructed sufficiently strong for such a combination to be seaworthy. The GM-Lift

Decommissioning and Installation Vessel was never built and it may have been that the decision to cancel this project was related to the uncertainties surrounding the strength of the coupling and its technical feasibility and the associated risks and costs. Summarizing, the GM-Lift Decommissioning and Installation Vessel has a questionable technical feasibility.

Appendage structures are also known in pipe-laying vessels, such as those disclosed in US3924415A and US3854297A. In US3924415A, an appendage is disclosed which is hingedly attached to a pipe-laying vessel. The appendage can be partly sunk, to change its orientation with respect to the vessel. This provides a gradual transition for a pipe that is payed out from the vessel. In US3854297A, an appendage structure is disclosed which comprises two parts, one of which is suspended from an A-frame and is hingedly attached to a vessel, and one part which has a variable buoyancy and is hingedly attached to the other part. This achieves the same result as the appendage of US3924415A, although there are two hinge points along the pipeline instead of one. This allows for a better support of the pipe that is payed out from the vessel. Both appendages described above are used in pipe laying and would not be suitable for installing large structures such as topsides, jackets and gravity based structures.

One key difference between pipe laying and installation of large structures such as topsides, jackets and gravity based structures is that the latter operation generally demands a level support of the load. In contrast, pipe laying operations require a support under an angle from the horizontal, due to the tendency of the pipe to follow an S-curve once it is payed out from the stern of the vessel.

Transfer of the lifted structure to and from a barge

During an offshore installation or removal operation, the structure, e.g. the topside, is typically transferred from a barge to the lifting vessel or vice versa. For a removal operation, the topside is typically transferred from the lifting vessel to a barge. All of the proposed solutions above display a restricted access of a barge underneath the structure which is lifted by the lifting vessel. This prevents the structure from being positioned in the most favourable position on the barge (lengthwise): centrally where the centre of buoyancy relatively lines up with the platform's centre of gravity as to minimise ballasting and thus maximise barge capacity.

Conversely, the load needs to be positioned eccentrically on the barge, i.e. near the front end or rear end of the barge. This creates large longitudinal bending moments on the vessel or barge. The eccentric position necessitates the use of large barges or purpose-built barges with large section moduli and resulting large barge depth to withstand the loads exerted.

Beside technical drawbacks, this adds to both the CAPEX and OPEX of the complete system as the added barge(s) need to be earned back by the same operations, as typically no such barges are required in the market for any other kind of operation. OBJECT OF THE INVENTION

It is an object of the invention to provide a method of performing a heavy offshore lift operation, typically greater than the crane lifting capacity at reach of the vessel, in particular for the installation or removal of a topside or part thereof or other heavy structure at sea, which requires a limited financial investment (CAPEX) and results in relatively small operational expenses (OPEX). It is an object to keep the operational expenses relatively small both in use and in idle mode.

It is a further object of the invention to provide a combination of a main vessel and one or more floating appendage structures for carrying out the method.

SUMMARY OF THE INVENTION

In order to achieve at least one object, the invention provides a combination of a heavy lift vessel and an floating appendage structure which are interconnected by a hinge having a horizontal hinge axis, wherein:

the heavy lift vessel comprises:

o at least one crane comprising a crane boom, wherein the heavy lift vessel is configured to carry out heavy lift operations by itself, i.e. without the floating appendage structure,

o at least one vessel hinge assembly,

the floating appendage structure is configured to lift a heavy structure at sea and comprises:

o a hull,

o at least one appendage hinge assembly configured to be connected to the vessel hinge assembly and to form the hinge therewith,

o at least one crane line connector mounted to the hull,

wherein the heavy lift vessel and the floating appendage structure are interconnected via the hinge, wherein the hinge allows a rotation of the floating appendage structure relative to the heavy lift vessel about the hinge axis, and

wherein a crane line suspension point of the at least one crane boom is positioned above the floating appendage structure, wherein the at least one crane is connected to the floating appendage structure, wherein at least one first crane line extends from the first crane line connector to the crane line suspension point of the at least one crane, wherein the floating appendage structure is a semi-submersible vessel, comprising:

- one or more floaters,

- multiple columns which extend upward from the at least one floater over a vertical distance and define open areas between the columns, and

- ballasting tanks which can be filled and emptied for varying the draught of the floating appendage structure,

wherein the combination comprises a passageway between the columns of the floating appendage structure and the heavy lift vessel or between the columns of the floating appendage structure,

wherein the passageway is constructed to position a barge, or substructure in said passageway between said columns when said columns intersect the waterline for:

1 ) transfer of the topside from the floating appendage structure to the barge or substructure, and/or

2) for transfer of the topside from the barge or substructure to the floating appendage structure, and/or

3) for lifting the substructure or a portion of the substructure.

The combination according to the invention provides the capability of lifting operations of very heavy loads for relatively low capital costs, both CAPEX and OPEX. Also, use can be made of an already existing heavy lift vessel which only needs to be converted to a limited extent by adding a part of a hinge to the heavy lift vessel. A functionality similar to that of the bow section of the Pioneering Spirit can be achieved and possibly superseded by a suitable vessel by appending the floating appendage structure to said vessel. This provides great flexibility and a significant cost reduction when compared to the Pioneering Spirit and other vessels of similar functionality. A floating appendage structure in the form of a semi- submersible vessel was found to provide excellent characteristics during transfer operations at sea and in short transit. When ballasted to a draught in which the columns are in the water line, the floating appendage structure displays very calm behaviour.

The skilled person will understand that if the vessel rolls, the hinge axis will not be horizontal. Horizontal in this context is intended to refer to the reference frame of the heavy lift vessel itself.

As disclosed above, the combination comprises a passageway between the columns of the floating appendage structure and the heavy lift vessel or between the columns of the floating appendage structure. Providing a passageway allows favourable positioning of the floating appendage structure and makes float over operations for removal of topsides and other structures and installation of topside and other structures relatively easy.

In an embodiment, the passageway is configured for positioning:

- a barge, jacket or gravity based structure in said passageway and underneath a heavy structure carried by the appendage vessel, and/or

- a combination of a barge, jacket or gravity based structure on the one hand and a heavy structure which is carried by the barge, jacket or gravity based structure on the other hand and which extends upwards higher than the floating appendage structure in said passageway prior to transfer of said heavy structure to the floating appendage structure.

In an embodiment, the at least one crane line is under pretension and exerts an upward force on the floating appendage structure, wherein the crane line under pretension limits the freedom of movement of the floating appendage structure relative to the heavy lift vessel. This is a very effective alternative to the rigid connection on the GM lift

Decommissioning and Installation Vessel. The alternative according to the invention is technically feasible, which is uncertain for the rigid connection of the GM lift Decommissioning and Installation Vessel.

In an embodiment, the pretension causes the heavy lift vessel and the floating appendage structure to move in tandem, with motion characteristics resembling the motion characteristics of a single rigid vessel. With relatively simple and cost-effective means, a very large rigid vessel is mimicked with the combination according to the invention.

In an embodiment, the heavy lift vessel comprises:

a first crane and

a second crane positioned at a distance from the first crane,

wherein the floating appendage structure comprises:

a first crane line connector which is positioned on a first side of the hull of the floating appendage structure, and

a second crane line connector which is positioned on a second side of the floating appendage structure, and

wherein a first crane line is connected to the crane line suspension point of the first crane and to the first crane line connector and a second crane line is connected to the crane line suspension point of the second crane and the second crane line connector. The first crane and the second crane provide added stability and rigidity to the overall combination.

In an embodiment, the first crane is positioned on the right side of the heavy lift vessel and the first crane line connector is positioned on a right side of the floating appendage structure, and wherein the second crane is positioned on the left side of the heavy lift vessel and the second crane line connector is positioned on a left side of the floating appendage structure. This configuration has a generally longitudinal arrangement. It was found that this configuration has relatively little low drag forces during transit. Furthermore, use can be made of an already existing heavy lift vessel.

In an embodiment, when seen in top view the first and second crane define a crane axis, wherein the crane axis extends parallel to the hinge axis.

In an embodiment, when seen in top view the first and second crane are positioned on a same side or end of the heavy lift vessel as the vessel hinge part, said side or end being the right side, the left side the bow or the stern of the heavy lift vessel.

In an embodiment, the vessel hinge assembly comprises a first vessel hinge part and a second vessel hinge part which are positioned at a distance from one another, and wherein the appendage hinge assembly comprises a first appendage hinge part associated with the first vessel hinge part and a second appendage hinge part associated with the first vessel hinge part .

In an embodiment, the heavy lift vessel is a semi-submersible vessel, comprising:

- one or more floaters, in particular a right floater and a left floater,

a deck structure,

multiple columns which extend upward over a vertical distance from the at least one floater and which interconnect the floater with the deck structure, wherein the columns define open areas between the columns,

a ballasting system for varying the draught of the heavy lift vessel.

Heavy lift vessels in the form of a semisubmersible vessel have the advantage of being less sensitive to waves when the columns are positioned in the water line. The columns have a relatively small water piercing surface area, which results in very calm behavior. In an embodiment, when seen in top view the floating appendage structure has a right floater and a left floater. This has the benefit of low drag forces during transit mode.

In an embodiment, when seen in side view the at least one crane line, in particular the first crane line and the second crane line, extend under an angle of less than 35 degrees to the vertical, in particular less than 20 degrees. In this way, horizontal forces between the heavy lift vessel and the floating appendage structure and the offlead load on the crane are limited.

In an embodiment, the first vessel hinge part is connected to a first column of the heavy lift vessel and the second vessel hinge part is connected to a second, different column of the heavy lift vessel. It was found that this has the benefit of a very strong and rigid hinge.

In an embodiment, the first vessel hinge part and the second vessel hinge part are connected to respectively a first side of the first column and to a second side of the second column, wherein the first side and second side face one another.

In an embodiment, the floating appendage structure, when seen in top view, has a U- shape, H-shape or W-shape, the U-shape, H-shape, extended H-shape or W-shape having a right elongate part and a left elongate part and a cross-connection, the W-shape or extended H-shape further having an additional support element. The additional support element may be attached to a central floater of the floating appendage structure or to a transverse structure between the floaters.

In an embodiment, the floating appendage structure comprises an opening between the floaters at one end, and a transverse structure between the floaters at the opposite end, wherein the transverse structure is located higher than the floaters but lower than the upper ends of the columns of the floating appendage structure, and in particular about halfway the height of the columns of the floating appendage structure.

In an embodiment, the columns of the floating appendage structure define a passageway which traverses the floating appendage structure.

In top view, the passageway may extend between a row of right columns and a row of left columns of the appendage structure. The passageway may extend in a longitudinal direction of the floating appendage structure. The passageway may in top view extend longitudinally on either side of a longitudinal midplane of the floating appendage structure. The passageway may extend from a first opening located between a front right column and a front left column of the floating appendage structure and a second opening located between a rear right column and a rear left column of the floating appendage structure.

In an embodiment, a barge or combination of barges can move completely through said passageway, thereby traversing the floating appendage structure when the floating appendage structure is ballasted at a deep draught. In an alternative embodiment, the barge or combination of barges cannot move completely through said passageway, but only enter the passageway from one end of the floating appendage structure. Entry into the passageway from the other side may be blocked by the transverse structure, for example because the transverse structure is positioned just below, just above or at the level of the water line under any or all draught conditions of the floating appendage structure. In other words, the passageway may have a dead end in some embodiments.

The passageway extends in the longitudinal direction of the floating appendage structure and makes it easy to position a topside or other heavy structure centrally on the barge. The barge can travel into the passageway and be positioned with its center of buoyancy directly underneath the center of gravity of the topside.

In an embodiment, the vessel hinge assembly comprises a first hole and a second hole which are aligned, wherein the appendage hinge assembly comprises a first pin which is inserted in the first hole and a second pin which is inserted in the second hole. It was found that this type of hinge is very strong and reliable, which is essential for this application.

In an embodiment, the first pin and second pin are rigidly interconnected by a beam or truss construction.

In an embodiment, the first vessel hinge part and the second vessel hinge part each comprise a flat plate which positioned with one of the main faces thereof against a column and welded to a column at least at the circumference thereof, wherein the plate comprises the hole.

In an embodiment, the appendage hinge assembly is connected to the rest of the floating appendage structure via an open truss frame. This further limits the water piercing surface of the floating appendage structure when positioned with the columns in the water line. This further reduces motions of the floating appendage structure as a result of waves. In an embodiment, the vessel hinge assembly is provided above the floater of the heavy lift vessel. This reduces drag, and make it possible to position the hinge above the floaters of the floating appendage structure.

In an embodiment, the vessel hinge assembly is provided at the level of the columns of the heavy lift vessel.

In an alternative embodiment, the vessel hinge assembly is provided at the level of the deck structure of the heavy lift vessel.

In an embodiment, the floating appendage structure does not comprise: a propulsion system, a living quarters or a helicopter deck. In this way the floating appendage structure remains cost-effective.

In an embodiment, the columns of the floating appendage structure have a smaller water piercing surface than the columns of the heavy lift vessel. This reduces the motions of the floating appendage structure.

In an embodiment, one or more columns of the floating appendage structure are formed entirely or partially as a truss structure.

In an embodiment, one or more columns of the floating appendage structure comprise an upper part having a greater water piercing surface than a lower part of the column, wherein in particular the upper part is formed as a closed box and the lower part is formed as a truss structure.

In an embodiment, the upper ends of the columns of the floating appendage structure are interconnected by one or more beams which extend lengthwise of the floating appendage structure.

In an embodiment, the first crane line connector and the second crane line connector define a connector axis which extends parallel to the hinge axis and in particular parallel to the crane axis.

In an embodiment, when seen in top view the at least one crane line connector is positioned at a distance from the hinge axis which is greater than 35 percent, in particular greater than 45 percent of a distance from the hinge axis to the opposite side or end of the floating appendage structure. In an embodiment, the vessel hinge assembly is located at the bow or stern of the heavy lift vessel, and wherein the hinge axis extends orthogonal to a main longitudinal direction of the heavy lift vessel.

In an embodiment, the vessel hinge assembly is located at the right or left side of the heavy lift vessel and wherein the hinge axis extends parallel to a main longitudinal direction of the heavy lift vessel.

In an embodiment, the floating appendage structure comprises a plurality of cross- beams which rest on the upper end of the columns or on longitudinal beams which rest on the columns of the floating appendage structure, wherein the cross-beams extend over the open lifting area from a right side of the floating appendage structure to a left side of the floating appendage structure.

In an embodiment, the floating appendage structure comprises a hydraulic lift system configured to raise the cross-beams relative to the at least one hull of the floating appendage structure.

The present invention also relates to a method of lifting a heavy structure at sea, the method comprising:

providing the combination of the heavy lift vessel and the floating appendage structure according to any of the preceding embodiments,

positioning a heavy structure such as a topside on the floating appendage structure,

putting the at least one crane line under pre-tension,

wherein the at least one crane line under pretension limits the freedom of movement of the floating appendage structure relative to the heavy lift vessel, wherein the at least one crane line under pretension causes the heavy lift vessel and the floating appendage structure to move in tandem, with motion characteristics resembling the motion characteristics of a single rigid vessel..

The method provides substantially the same advantages as the combination.

In an embodiment of the method, when seen in top view at least one barge is positioned in a passageway between the columns of the floating appendage structure and the heavy lift vessel or between the columns of the floating appendage structure, in particular between the right columns and the left columns of the floating appendage structure under the heavy structure, and wherein the heavy structure is transferred from the barge onto the floating appendage structure or from the floating appendage structure to the barge.

In an embodiment of the method:

- a topside is lifted from a jacket or other substructure by positioning a U-shaped, H-shaped, extended H-shaped or W-shaped part of the floating appendage structure around the jacket or other substructure and by subsequently deballasting the heavy lift vessel and the floating appendage structure together, thereby lifting the topside from the jacket or jacket, or

a topside is installed onto a jacket by carrying the topside with the floating appendage structure and by positioning the U-shaped, H-shaped, extended H- shaped or W-shaped part of the floating appendage structure around the jacket or other substructure, and subsequently ballasting the heavy lift vessel and the floating appendage structure, thereby lowering the heavy lift vessel, floating appendage structure and the topside and placing the topside onto the jacket or other substructure.

In an embodiment of the method, the floating appendage structure comprises a hydraulic lift system configured to raise the cross-beams relative to the at least one hull of the floating appendage structure, wherein for making the initial contact between the floating appendage structure and the heavy structure which is to be lifted the hydraulic system raises the cross-beams relative to the hull.

In an embodiment of the method:

a topside or other heavy structure is transferred from a barge to the floating appendage structure, and wherein:

o the topside or other heavy structure is positioned centrally on the barge, o the floating appendage structure is ballasted to a deep draught,

o the barge including the topside or other heavy structure is positioned in the U- shaped, H-shaped, extended H-shaped or W-shaped part of the floating appendage structure, and

o the floating appendage structure is deballasted, thereby decreasing the

draught of the floating appendage structure, wherein the floating appendage structure lifts the topside or other heavy structure from the barge,

- a topside or other heavy structure is transferred from the floating appendage structure to at least one barge or vessel, wherein: o the topside or other heavy structure is positioned on the floating appendage structure,

o optionally the floating appendage structure including the topside or other heavy structure is pre-ballasted to a deeper draught,

o the barge is positioned in the U-shaped, H-shaped, extended h-shaped or W- shaped part of the floating appendage structure, and

o the floating appendage structure is ballasted, thereby increasing the draught of the floating appendage structure, wherein the floating appendage structure is lowered and places the topside or other heavy structure on the barge.

In an embodiment, the method comprises the subsequent steps of :

ballasting the combination which carries the heavy structure until the columns pierce the water line,

uncoupling the floating appendage structure from the heavy lift vessel, positioning at least one barge in the passageway of the floating appendage structure

further ballast the floating appendage structure until the heavy structure is positioned on the at least one barge.

In an embodiment, the method comprises the steps of:

providing the combination of the heavy lift vessel and the floating appendage structure according to any of the preceding device claims,

putting the at least one crane line under pre-tension,

wherein the at least one crane line under pretension limits the freedom of movement of the floating appendage structure relative to the heavy lift vessel,

wherein the at least one crane line under pretension causes the heavy lift vessel and the floating appendage structure to move in tandem, with motion characteristics resembling the motion characteristics of a single rigid vessel,

wherein a part of the jacket, gravity based structure or other substructure is positioned in the passageway,

wherein the floating appendage structure is connected to the jacket, gravity based structure or other substructure,

wherein:

the jacket, gravity based structure or other substructure is raised by deballasting the heavy lift vessel and the floating appendage structure together, thereby raising the jacket, gravity based structure or other substructure, or the jacket, gravity based structure or other substructure is lowered by ballasting the heavy lift vessel and the floating appendage structure together, thereby lowering the jacket, gravity based structure or other substructure.

The present invention further relates to a floating appendage structure configured to lift a heavy structure at sea, the floating appendage structure comprising:

a hull,

at least one appendage hinge assembly configured to be connected to a vessel hinge part of a heavy lift vessel and to form a hinge therewith,

at least one crane line connector mounted to the hull,

wherein the floating appendage structure is configured to be interconnected via the hinge to the heavy lift vessel, wherein the hinge allows a rotation of the floating appendage structure relative to the heavy lift vessel about the hinge axis,

wherein the floating appendage structure is a semi-submersible vessel, comprising:

- one or more floaters,

- multiple columns which extend upward from the at least one floater over a vertical distance and define open areas between the columns, and

- ballasting tanks which can be filled and emptied for varying the draught of the floating appendage structure,

wherein the combination comprises a passageway between the columns of the floating appendage structure and the heavy lift vessel or between the columns of the floating appendage structure,

wherein the passageway is constructed to position a barge or substructure in said passageway between said columns when said columns intersect the waterline for:

1 ) transfer of the topside from the floating appendage structure to the barge or substructure, and/or

2) for transfer of the topside from the barge or substructure to the floating appendage structure, and/or

3) for lifting the substructure or a portion of the substructure.

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. SHORT DESCRIPTION OF THE FIGURES

Figure 1 shows an isometric view of the combination according to the invention.

Figure 2 shows a top view of the combination according to the invention.

Figure 3 shows a side view of the combination according to the invention.

Figure 4 shows a rear or front view of the combination according to the invention.

Figure 5 shows an isometric view of the combination according to the invention carrying a topside.

Figure 6 shows a top view of the combination according to the invention carrying a topside.

Figure 7 shows a side view of the combination according to the invention carrying a topside.

Figure 8 shows a front view of the combination according to the invention carrying a topside.

Figure 9A shows an isometric view of the floating appendage structure.

Figure 9B shows a further isometric view of the floating appendage structure.

Figure 9A shows yet a further isometric view of the floating appendage structure.

Figure 10A shows an isometric view of the hinge.

Figure 10B shows they another isometric view of the hinge, with the rest of the heavy lift vessel and the appendage vessel left out.

Figure 11 shows a top view of the hinge.

Figure 12A shows an isometric view of a part of the hinge.

Figure 12B shows another isometric view of a part of the hinge.

Figure 12C shows a top view of a part of the hinge.

Figure 13A shows an isometric view of the installation or removal of a topside from a substructure.

Figure 13B shows an isometric view of the uncoupled floating appendage structure carrying a topside.

Figure 14 shows a front view of the uncoupled floating appendage structure carrying a topside.

Figure 15 shows a side view of the uncoupled floating appendage structure carrying a topside.

Figure 16 shows a top view of the uncoupled floating appendage structure carrying a topside.

Figure 17 shows the same view as figure 13B, but with two barges positioned under the topside and under the cross-beams.

Figure 18 shows a side view associated with figure 17. Figure 19 shows a top view associated with figure 17 and 18.

Figure 20 shows a front view associated with figure 17 - 19.

Figure 21 shows an isometric view of the floating appendage structure with two barges.

Figure 22 shows a front view of the floating appendage structure with two barges.

Figure 23 shows a side view of the floating appendage structure with two barges.

Figure 24A shows a top view of another embodiment of the invention.

Figure 24B shows a top view of yet another embodiment of the invention.

Figure 25 shows a front view of the embodiment of figure 24.

Figure 26 shows a top view of yet another embodiment of the invention

Figure 27 shows a top view of again another embodiment of the invention.

Figure 28 shows a top view of an embodiment of the invention wherein the floating appendage structure has a W-shape.

Figure 29 shows a top view of an embodiment of the invention wherein the floating appendage structure has a J-shape.

Figure 30A shows the floating appendage structure supporting a gravity based structure.

Figure 30B shows the floating appendage structure supporting part of a jacket.

Figure 30C shows a detail view of the attachment of the jacket to the floating appendage structure.

DETAILED DESCRIPTION OF THE FIGURES

Turning to figures 1 - 4, a combination 10 of a heavy lift vessel 12 and a floating appendage structure 14 is provided. The heavy lift vessel 12 and the floating appendage structure 14 are interconnected via a hinge which will be discussed further below.

The heavy lift vessel 12 is a semi-submersible vessel, comprising one or more floaters, in particular a right floater 56A and a left floater 56B and a deck structure 57. The heavy lift vessel 12 comprises multiple columns 58 which extend upward over a vertical distance from the at least one floater and which interconnect the floaters with the deck structure. The columns 58 are arranged in a right row 61 A and a left row 61 B.

The columns define open areas 59 between the columns. The columns have a lower water piercing surface than the combined floaters. The heavy lift vessel comprises a ballasting system for varying the draught of the heavy lift vessel. Such ballasting systems are known per se for semi-submersible vessels. The heavy lift vessel 12 comprises at least one crane 15. In the embodiment of figures 1 - 4 the heavy lift vessel comprises two cranes, a first crane 15A and a second crane 15B. The second crane 15B is positioned at a distance from the first crane. The cranes have a rotatable turret which allows rotation of the crane about a respective vertical axis.

However, as will be discussed further below in principle the invention is also possible with only a single crane 15.

Each crane 15A, 15B comprises a crane boom 20. The heavy lift vessel is configured to carry out heavy lift operations by itself, namely with the cranes 15A, 15B, and without the floating appendage structure 14. The heavy lift vessel comprises accommodation 31 , a helicopter deck 32, propulsion 33, and may comprise further equipment.

The floating appendage structure 14 is configured to lift a heavy structure at sea and comprises a hull 22. The floating appendage structure 14 and in particular the hull 22 thereof may be of a semi-submersible type.

The floating appendage structure 14 is a semi-submersible vessel, comprising one or more floaters, in this case a right floater 60A and a left floater 60B. The floating appendage structure 14 comprises multiple columns 62 which extend upward from the at least one floater over a vertical distance and define open areas 63 between the columns, and ballasting tanks which can be filled and emptied for varying the draught of the floating appendage structure.

The left floater 60B of the appendage structure may be aligned or substantially aligned with the left floater 56B of the heavy lift vessel, and the right floater 60A of the appendage structure may be aligned or substantially aligned with the right floater 56A of the heavy lift vessel. This reduces drag in transit. If the heavy lift vessel is relatively wide, it also provides a relatively broad passageway 77, which is discussed in more detail below.

The upper ends 90 of the columns 62 of the floating appendage structure are interconnected by one or more beams 92A, 92B which extend lengthwise of the floating appendage structure. The floating appendage structure does not have a“real” deck structure, because a central part is open for carrying out lifting operations.

The pumps for the ballasting tanks and other equipment on board may be temporarily removable in order to lower the Capex. The columns 62 of the floating appendage structure 14 have a smaller water piercing surface than the columns of the heavy lift vessel. This improves the lift characteristics. For the stability, the floating appendage structure 14 benefits from the stability of the heavy lift vessel when coupled to the heavy lift vessel.

The floating appendage structure 14 does not comprise: a propulsion system, a living quarters or a helicopter deck. The floating appendage structure 14 relies on the heavy lift vessel for these aspects, which keeps the floating appendage structure 14 cost-effective

The floating appendage structure 14, when seen in top view, has a U-shape having a right elongate part formed by the right floater and a left elongate part formed by the left floater and a cross-connection which will be discussed later. In an alternative embodiment, the floating appendage structure 14 may have an H-shape, extended H-shape or W-shape.

The floating appendage structure comprises an opening 70 between the floaters at one end 72, and a transverse structure 74 between the floaters at the opposite end. The opening 70 is large enough such that a barge, jacket of gravity based structure fits through it.

The floating appendage structure does not have a transverse connection at the level of the upper ends of the columns 62. This provides a passageway 77 for a barge to travel through when the floating appendage structure is ballasted at a deep draught. The floating appendage structure may also have a transverse connection at any level of the columns, such that the barge can only enter the passageway 77 from one side of the floating appendage structure. A jacket or gravity based structure can also be accommodated in the passageway.

The floating appendage structure 14 comprises at least one crane line connector 24A, 24B is mounted to the hull 22. The first crane line connector 24A is positioned on a first side of the hull (in this case the right side) of the floating appendage structure and the second crane line connector 24B is positioned on a second side of the floating appendage structure (in this case the left side).

The first crane line connector 24A and the second crane line connector 24B define a connector axis 93 which extends parallel to the hinge axis and in particular parallel to the crane axis 17, see fig. 2. When seen in top view the at least one crane line connector 24A, 24B is positioned at a first distance D1 from the hinge axis 45 which is greater than 35 percent, in particular greater than 45 percent, of a second distance D2 between the hinge axis 45 to the opposite end 95 of the floating appendage structure 14.

One or more columns 62 of the floating appendage structure 14 may be formed entirely or partially as a truss structure.

Alternatively or additionally, one or more columns 62 of the floating appendage structure 14 may comprise an upper part having a greater water piercing surface than a lower part of the column, wherein in particular the upper part is formed as a closed box and the lower part is formed as a truss structure.

A crane line suspension point 26A, 26B of the at least one crane boom is positioned above the floating appendage structure. The at least one crane is connected to the floating appendage structure via at least one crane line 28A, 28B. Figure 1 - 4 show that each crane 15A, 15B is connected to the floating appendage structure via multiple crane lines.

The at least one first crane line 28A extends from the first crane line connector 24A to the crane line suspension point 26A, of the first crane. The at least one second crane line 28B extends from the second crane line connector 24B to the crane line suspension point 26B of the second crane 15B.

When seen in side view the at least one crane line, in particular the first crane line 28A and the second crane line 28B, extend(s) under an angle a of less than 35 degrees to the vertical 19, in particular less than 20 degrees.

The first crane 15A is positioned on the right side of the heavy lift vessel and the first crane line connector 24A is positioned on a right side of the floating appendage structure. The second crane 15B is positioned on the left side of the heavy lift vessel and the second crane line connector 24B is positioned on a left side of the floating appendage structure.

When seen in top view the first and second crane 15A, 15B define a crane axis 17.

Turning to figs. 5 - 8, the same combination 10 is shown, but this time carrying a topside 30. It will be clear for the skilled person that the combination 10 can lift a topside 30, but also other types of heavy structures, such as a jacket, a gravity based structure, a vessel, or another type of heavy structure which is to be lifted. The jacket or gravity based structure can be lifted from a seabed and also lowered onto a seabed. The word seabed in this context is to be interpreted broadly and can also be the bottom of a harbor, lakebed, concrete slab on which a jacket is positioned, or a template, fundament or other kind of support structure on a bottom of a body of water.

In use, the at least one crane line 28A, 28B is under pretension and exerts an upward force on the floating appendage structure 14. The crane line(s) 28A, 28B under pretension limits the freedom of movement of the floating appendage structure 14 relative to the heavy lift vessel 12.

The pretension causes the heavy lift vessel and the floating appendage structure to move in tandem, with motion characteristics resembling the motion characteristics of a single rigid vessel. The skilled person will understand that in practice, some movement may occur between the floating appendage structure and the heavy lift vessel. The skilled person will understand that a single rigid vessel also deforms somewhat under the influence of the forces of wind and waves. Therefore, absolute rigidity does not occur.

Turning to figs. 9A, 9B, 9C, the floating appendage structure comprises a plurality of cross-beams 100 which rest on the upper ends 76 of the columns or on the longitudinal beams 92A, 92B which rest on the columns 62 of the floating appendage structure. The cross-beams 100 extend over the open lifting area 102 from a right side of the floating appendage structure to a left side of the floating appendage structure.

The floating appendage structure comprises a hydraulic lift system 104 configured to raise the cross-beams 100, i.e. move the cross-beams up or down, relative to the at least one hull 22 (and relative to the columns 62) of the floating appendage structure. See the arrow 105 in figures 9B and 9C.

T urning to figs. 10A - 12C, the hinge 40 is shown in further detail. The hinge 40 comprises a part on the side of the floating appendage structure 14. This part is called the appendage hinge assembly 42 and is configured to be connected to the vessel hinge assembly 44 and to form the hinge 40 therewith.

The hinge 40 has a horizontal hinge axis 45. The heavy lift vessel 12 and the floating appendage structure 14 are interconnected via the hinge 40. The hinge allows a rotation of the floating appendage structure 14 relative to the heavy lift vessel 12 about the hinge axis 45. The crane axis 17 extends parallel to the hinge axis 45.

The first and second crane 15A, 15B are positioned on a same end 48 of the heavy lift vessel 12 as the vessel hinge assembly 44, said end being the stern of the heavy lift vessel. It is noted that a heavy lift vessel often moves backwards, wherein the stern becomes the bow. For a heavy lift vessel, the stern and bow may be exchangeable.

The hinge axis 45 extends orthogonal to a main longitudinal direction 99 of the heavy lift vessel.

The vessel hinge assembly 44 comprises a first vessel hinge part 50A and a second vessel hinge part 50B which are positioned at a distance from one another. The first vessel hinge part 50A is connected to a first column 58.1 of the heavy lift vessel and the second vessel hinge part is connected to a second, different column 58.2 of the heavy lift vessel. The columns are numbered 58.1-58.8, the uneven columns 58.1 , 58.3, 58.5, 58.7 being located on the right side and the even columns 58.2, 58.4, 58.6, 58.8 being located on the left side.

The first vessel hinge part 50A and the second vessel hinge part 50B are connected to respectively a first side 59.1 of the first column 58.1 and to a second side 59.2 of the second column 58.2, wherein the first side and second side face one another.

The vessel hinge assembly 44 is provided above the floaters of the heavy lift vessel 12. In the shown embodiment, the vessel hinge assembly 44 is provided at the level of the columns 58 of the heavy lift vessel 12. Alternatively, the vessel hinge assembly 44 may be provided at the level of the deck structure of the heavy lift vessel.

The appendage hinge assembly 42 comprises a first appendage hinge part 51 A associated with the first vessel hinge part 50A and a second appendage hinge part 51 B associated with the first vessel hinge part 50B.

The transverse structure 74 may be located higher than the floaters but lower than the upper ends 76 of the columns 62 of the floating appendage structure, and in particular about halfway the height of the columns of the floating appendage structure. The transverse structure then restricts entry into the passageway 77 from one side of the floating appendage structure. The transverse structure 74 provides rigidity to the floating appendage structure and interconnects the floaters 60A, 60B. The transverse structure 74 also serves as a base frame which connects the appendage hinge assembly 42 to the floaters 60A, 60B.

Alternatively, the transverse structure 74 may be located at the level of the floaters as indicated in the embodiment of figs. 4 and 8. However, this is not preferred, because at this level, the transverse structure 74 creates drag in transit mode. On the other hand, this allows a barge to enter into the passageway 77 from both sides of the floating appendage structure when it is ballasted to a deep draught.

The vessel hinge assembly 44 comprises a first hole 80A and a second hole 80B which are aligned. The appendage hinge assembly 42 comprises a first pin 82A which is inserted in the first hole and a second pin 82B which is inserted in the second hole. The appendage hinge assembly 42 comprises a hydraulic system 47 (indicated in dashed lines in fig. 12B) for moving the pins 2A, 82B along the hinge axis from an inward to an outward position and vice versa as indicated with arrow 83. This allows coupling and uncoupling of the floating appendage structure. The inward position allows coupling and uncoupling. In the outward position of the pins, the floating appendage structure and the heavy lift vessel are coupled.

The first pin 82A and second pin 82B are rigidly interconnected by a beam 85 or truss construction in order to take bending moments, notwithstanding the capability of inward and outward movement of the pins.

The first vessel hinge part 50A and the second vessel hinge part 50B each comprise a flat plate 88A, 88B which is positioned with one of the main faces thereof against a column 58 and welded to a column at least at the circumference 89 thereof, wherein the plate comprises the hole 80.

The appendage hinge assembly 42 is connected to the rest of the floating appendage structure via the transverse structure 74 which in this embodiment has the form of an open truss frame.

Turning to figures 13A-23, the columns 62 of the floating appendage structure 14 define a passageway 77 which traverses the floating appendage structure.

In top view, the passageway may extend between the row 61 A of right columns and the row 61 B of left columns of the appendage structure. The passageway may extend in a longitudinal direction of the floating appendage structure. The passageway may be located centrally and in top view extend longitudinally on either side of a longitudinal midplane of the floating appendage structure.

The passageway 77 may have a width of at least 50 percent of the width of the appendage structure. The passageway may have a width of at least 50 percent of the width of the heavy lift vessel. The passageway may be at least 10 meters wide.

The passageway extends from a first opening 78 located between a front right column 62.5 and a front left column 62.6 of the floating appendage structure 14 and a second opening 79 located between a rear right column 62.1 and a rear left column 62.2 of the floating appendage structure.

In one embodiment of the passageway, a barge or combination of barges can move completely through said passageway, thereby traversing the floating appendage structure when the floating appendage structure is ballasted at a deep draught.

The skilled person will understand that when the appendage structure is coupled to the heavy lift vessel, the passageway may be blocked on one side by the heavy lift vessel. Also, in some embodiments the presence of the passageway may be dependent on the draught of the appendage structure. At some, relatively shallow, draughts the transverse structure 74 and/or the appendage hinge assembly 42 may be positioned just below, at or above the waterline and block the passageway on one side. Therefore, in that case in order for the passageway to be accessible from both ends of the floating appendage structure, the appendage structure will need to be positioned at a deep draught, allowing a barge to float over the appendage hinge assembly 42. When the appendage structure is at its deepest draught, the passageway may have a clearance (or draught) to the appendage hinge assembly 42 or to the transverse structure of several meters, e.g. 1-10 meters. Alternatively, the passageway may always be a dead end, irrespective of the draught of the floating appendage structure. A barge or combination of barges can then enter the passageway from one side of the floating appendage structure only.

Turning to figures 24A, 24B, and 25, an alternative embodiment is shown, wherein the vessel hinge assembly is located at the right or left side of the heavy lift vessel and wherein the hinge axis 45 extends parallel to a main longitudinal direction 99 of the heavy lift vessel. The combination 10 moves in the transport direction T, but may also move in the opposite direction. In these embodiments, when seen in top view, the first and second crane 15A, 15B are positioned on a same side of the heavy lift vessel as the hinge axis, said side being the right side. Obviously the side can also be the left side. The opening 70 of the floating appendage structure is oriented in the same direction as the bow 110 of the heavy lift vessel.

In the embodiment of fig. 24A, the heavy lift vessel comprises two cranes. In the embodiment of fig. 24B, the heavy lift vessel comprises a single crane 15. The appendage hinge assembly 42 of the hinge 40 is connected to the floater

Turning to fig. 26, in a variant, the floating appendage structure is asymmetric and has an L-shape instead of a U-shape, H-shape, extended H-shape or W-shape. The floating appendage structure has only a single floater. This embodiment may require two cranes 15A, 15B.

Turning to fig. 27, the single crane 15 may also be used in a longitudinal configuration, i.e. wherein the crane 15 and the floating appendage structure 14 are positioned at the bow 110 or stern of the heavy lift vessel 12.

In the embodiment of fig. 28, the floating appendage structure has an additional support element (60C), yielding a W-shape. A floating appendage structure having an H- shape may also include an additional support element (60C), forming an extended H-shape comprising an H with an extension from the horizontal line connecting the two vertical lines of the H, with the additional support element (60C) forming the extension.

In the embodiment of fig. 29, a floating appendage structure comprising a single floater is shown, including an additional support element (60C). This embodiment has a J- shape.

The skilled person will recognize that in the embodiments of figures 24A, 24B, 25, 26, 28 and 29 the passageway 77 is also present. In figure 28, for example, the passageway is located between the floaters of the floating appendage structure from the opening 70 up to the additional support element 60C. Over the length of the additional support element 60C, the passageway is split in two passageway parts, with the two passageway parts located between a floater of the floating appendage structure and the additional support element (60C). Turning to figs. 30A and 30B, the floating appendage structure is seen supporting a substructure, wherein the substructure is a gravity based structure 140 (fig. 30A) or a jacket 150 (fig. 30B). The gravity based structure is supported by cables 130 that are connected to the cross beams 100 and the substructure. The substructure is accommodated in the passageway 77, while part of the substructure extends below the floating appendage structure. The jacket may be supported in a similar way as the gravity based structure in fig. 30A, or by different means.

In fig. 30B, only the top portion 151 of the jacket is supported by the floating appendage structure. The bottom portion 152 of the jacket rests on the seabed. It will be obvious to the skilled person that the entire jacket may be lifted instead of the top portion only. Similarly, it will be obvious to the skilled person that a portion of a gravity based structure or other substructure may be lifted instead of the entire substructure. The term “portion” in this context is obviously not intended to refer to a very small part of a jacket, gravity based structure or other substructure, such as a single beam. Instead, the term portion in this document is intended to mean a significant part of the substructure, more in particular a portion which is large enough to extend to underneath the floating appendage structure when carried by the floating appendage structure. This will be generally be a portion which is at least 20 percent, more in particular at least 30 percent, of the total gross tonnage of the substructure,.

Fig. 30C shows a detail view of the attachment of the jacket 150 to the cross-beams 100. Collars 160 are welded to the legs 155 of the jacket. The collars 160 comprise castellation 165 to increase the weld length when compared to simple tubular collars. The cross-beams 100 comprise support elements 101 that engage with the collars 160 to support the jacket 150.

Operation

In operation, the method of lifting a heavy structure 30 comprises:

providing the combination 10 of the heavy lift vessel 12 and the floating appendage structure according to any of the preceding embodiments, positioning a heavy structure 30 such as a topside on the floating appendage structure,

putting the at least one crane line 28 under pre-tension,

wherein the at least one crane line under pretension limits the freedom of movement of the floating appendage structure relative to the heavy lift vessel. The at least one crane line 28 under pretension may cause the heavy lift vessel 12 and the floating appendage 14 structure to move in tandem, with motion characteristics resembling the motion characteristics of a single rigid vessel.

Turning to figures 17-23, when seen in top view at least one barge 120 is positioned between the right floater 60A and the left floater 60B of the floating appendage structure under the heavy structure and under the cross-beams 100. The heavy structure 30 or other heavy structure including the cross beams 100 is transferred from the barge 120 onto the floating appendage structure 14 or from the floating appendage structure 14 to the barge 120.

The topside 30 or other heavy structure is positioned centrally on the barge. In top view the centre of gravity of the topside is close to the centre of buoyancy of the barge. This improves the stability and makes it possible to use a smaller, simpler and more cost-effective barge.

Removal of a topside

When removing a topside, the topside 30 will initially be present on a jacket or other substructure at sea.

The combination 10 travels to the location of the topside. The cross-beams 100 are installed on the floating appendage structure 14. The U-shaped part, H-shaped part, extended H-shaped part, L-shaped part, W-shaped part or J-shaped part of the floating appendage structure 14 is positioned around the jacket or other substructure. See figure 13A, where the substructure is a gravity based structure. By subsequently deballasting the heavy lift vessel 12 and the floating appendage structure 14 together, thereby lifting the topside from the jacket or other substructure. The cross-beams engage the topside 30 and lift the topside 30 from the substructure.

The floating appendage structure comprises a hydraulic lift system 104 configured to raise the cross-beams 100 relative to the at least one hull 22 of the floating appendage structure. The hydraulic system 104 raises the cross-beams 100 relative to the hull 22 for making the initial contact between the floating appendage structure and the heavy structure which is to be lifted. The hydraulic system 104 obviously havs a limited stroke. After the initial contact, the ballast tanks are emptied, thereby raising the heavy lift vessel 12, the floating appendage structure and the topside 30 further. The combination 10 then travels to an inshore location. Here the conditions (wave, wind) are more benign. Here, the topside or other heavy structure is transferred from the floating appendage structure to at least one barge or vessel.

The floating appendage structure 14 may be uncoupled from the heavy lift vessel 12. Next, the floating appendage structure 14 including the topside 30 or other heavy structure is ballasted to a shallow draught. One or more barges 120 is positioned under the topside and under the cross-beams 100. The barge can travel through the passageway 77.

Next, the floating appendage structure 14 is ballasted, thereby increasing the draught of the floating appendage structure. The floating appendage structure is lowered and the topside 30 or other heavy structure including the cross-beams 100 is placed on the barge 120. Scrapping may then take place from the barge. This obviates the need for an extra transfer operation, or the need for a reinforced quayside or the need for a deep draught quayside.

Alternatively, the topside or other heavy structure may be transferred from the barge to a location on shore.

Installation of a topside

When installing a topside 30, the topside 30 is generally built on shore and first transferred from shore to a barge 120.

Next, the topside 30 needs to be first transferred from the barge 120 to the floating appendage structure 14. In this procedure, the cross-beams are connected to the topside 30 on the barge. The cross-beams 100 may be moved underneath the topside 30 by a translational movement. Next, the floating appendage structure 14 is ballasted to a deep draught. In this stage the floating appendage structure 14 may be uncoupled from the heavy lift vessel 12.

Next, the barge 120 including the topside 30 or other heavy structure is positioned in the U-shaped part of the floating appendage structure. The cross-beams 100 are already present and connected to the topside 30. Next, the floating appendage structure 14 is deballasted, thereby decreasing the draught of the floating appendage structure, wherein the floating appendage structure lifts the topside or other heavy structure including the crossbeams 100 from the barge 120. Next, the floating appendage structure 14 including the topside 30 is coupled to the heavy lift vessel 12 at the hinge 40. Next the combination 10 travels to the target location where a substructure, e.g. a jacket has previously been installed. During the travel, the crane lines 28 are pretensioned, thereby providing rigidity and stability to the floating appendage structure 14.

Next, the topside is transferred to the substructure. In this step, the topside 30 is installed onto a jacket by carrying the topside 30 with the floating appendage structure 14 and by positioning the U-shaped part, H-shaped part, extended H-shaped part, L-shaped part, W- shaped part or J-shaped part of the floating appendage structure 14 around the jacket or other substructure. See figure 13A. Subsequently the heavy lift vessel 12 and the floating appendage structure 14 are ballasted, thereby lowering the heavy lift vessel, floating appendage structure 14 and the topside 30 and placing the topside onto the jacket or other substructure.

Next, the cross-beams 100 are removed from the installed topside. The cross-beams may be withdrawn by a translational movement. The heavy lift vessel and floating appendage structure 14 then move away from the target location and travel back to an inshore location.

After an installation of removal operation, the floating appendage structure is uncoupled at an inshore location, and the heavy lift vessel is directly ready to perform an entirely different operation on its own, without the floating appendage structure. The floating appendage structure can remain in an inshore location to wait for a next operation.

The heavy lift vessel is only needed for the duration of the sailing and for the transfer operations.

Lifting of a substructure

When removing a substructure such as a jacket 150 or a gravity based structure 140, the floating appendage structure is positioned such that the substructure is accommodated in the passageway 77. The substructure is connected to the cross-beams 100 by cables 130. In order to raise the substructure, de draught of the floating appendage structure may be subsequently reduced by deballasting. Alternatively or additionally to deballasting the floating appendage structure, the cables 130 may be used to hoist the substructure by shortening their length between their attachment point 135 to the substructure and the cross-beams 100, for example by using winches mounted on the cross-beams or elsewhere on the floating appendage structure, or by using strandjacks. Installation of a substructure may be performed by positioning the floating appendage structure supporting the substructure over an intended installation location. Subsequently, the floating appendage structure may be ballasted to a deeper draught to lower the substructure onto the intended installation location. Additionally or alternatively to ballasting the floating appendage structure, the cables 130 may be used to lower the substructure by increasing their length between their attachment point 135 to the substructure and the cross-beams 100, for example by using winches mounted on the cross-beams or elsewhere on the floating appendage structure, or by using strandjacks.

Further general aspects

Typically the heavy lift vessel will be capable of lift operations in excess of 15.000 mT. However, smaller sizes are in principle also possible.

The columns of the heavy lift vessel may be closed. It is also possible that one or more of the columns of the heavy lift vessel are closed, whereas one or more other columns of the heavy lift vessel are open, and have a smaller water piercing surface.

The columns of the heavy lift vessel may be embodied in the form of truss structures.

The deck structure of the heavy lift vessel will typically be closed and may provide buoyancy. A deck structure with buoyancy can be combined with columns in the form of truss structures.

In principle no heave compensation systems are needed for the crane lines.

A closed column combines both functionalities in a single structure. This potentially results in a weight saving, but is more difficult to tune/adapt for different

conditions/requirements.

The present disclosure relates to the following clauses:

1 . Combination (10) of a heavy lift vessel (12) and an floating appendage structure (14) which are interconnected by a hinge (40) having a horizontal hinge axis (45), wherein: the heavy lift vessel comprises:

o at least one crane (15; 15A.15B) comprising a crane boom (20), wherein the heavy lift vessel is configured to carry out heavy lift operations by itself, i.e. without the floating appendage structure, o at least one vessel hinge assembly (44),

the floating appendage structure is configured to lift a heavy structure at sea and comprises:

o a hull (22),

o at least one appendage hinge assembly (42) configured to be connected to the vessel hinge assembly and to form the hinge (40) therewith,

o at least one crane line connector (24) mounted to the hull,

wherein the heavy lift vessel and the floating appendage structure are interconnected via the hinge, wherein the hinge allows a rotation of the floating appendage structure relative to the heavy lift vessel about the hinge axis, and

wherein a crane line suspension point (26) of the at least one crane boom is positioned above the floating appendage structure, wherein the at least one crane is connected to the floating appendage structure, wherein at least one first crane line (28) extends from the first crane line connector to the crane line suspension point of the at least one crane. Combination according to clause 1 , wherein the at least one crane line is under pretension and exerts an upward force on the floating appendage structure,

wherein the crane line under pretension limits the freedom of movement of the floating appendage structure relative to the heavy lift vessel. Combination according to clause 1 , wherein the pretension causes the heavy lift vessel and the floating appendage structure to move in tandem, with motion characteristics resembling the motion characteristics of a single rigid vessel. Combination according to clause 1 , wherein the heavy lift vessel comprises:

a first crane (15A) and

a second crane (15B) positioned at a distance from the first crane,

wherein the floating appendage structure comprises:

a first crane line connector which is positioned on a first side of the hull of the floating appendage structure, and

a second crane line connector which is positioned on a second side of the floating appendage structure, and

wherein a first crane line is connected to the crane line suspension point of the first crane and to the first crane line connector and a second crane line is connected to the crane line suspension point of the second crane and the second crane line connector. Combination according to any of the preceding clauses, wherein the first crane is positioned on the right side of the heavy lift vessel and the first crane line connector is positioned on a right side of the floating appendages structure , and wherein the second crane is positioned on the left side of the heavy lift vessel and the second crane line connector is positioned on a left side of the floating appendage structure. Combination according to any of the preceding clauses 4-5, wherein when seen in top view the first and second crane define a crane axis (17), wherein the crane axis extends parallel to the hinge axis. Combination according to any of the preceding clauses 4-6, wherein when seen in top view the first and second crane are positioned on a same side or end of the heavy lift vessel as the vessel hinge assembly, said side or end being the right side, the left side the bow or the stern of the heavy lift vessel. Combination according to any of the preceding clauses, wherein the vessel hinge assembly comprises a first vessel hinge part (50A) and a second vessel hinge part (50B) which are positioned at a distance from one another, and wherein the appendage hinge assembly comprises a first appendage hinge part associated with the first vessel hinge part and a second appendage hinge part associated with the second vessel hinge part. Combination according to any of the preceding clauses, wherein the heavy lift vessel is a semi-submersible vessel, comprising:

one or more floaters, in particular a right floater (56A) and a left floater (56B), a deck structure (57),

multiple columns (58) which extend upward over a vertical distance from the at least one floater and which interconnect the floater with the deck structure, wherein the columns define open areas between the columns,

- a ballasting system for varying the draught of the heavy lift vessel. Combination according to any of the preceding clauses, wherein the floating appendage structure is a semi-submersible vessel, comprising:

one or more floaters,

multiple columns which extend upward from the at least one floater over a vertical distance and define open areas between the columns, and ballasting tanks which can be filled and emptied for varying the draught of the floating appendage structure.

1 1. Combination according to clause 10, wherein the combination comprises a

passageway (77) between the columns of the floating appendage structure and the heavy lift vessel or between the columns of the floating appendage structure, wherein the passageway is constructed to position a barge or jacket in said passageway between said columns when said columns intersect the waterline for transfer of the heavy structure from the floating appendage structure to the barge or to the jacket and/or for transfer of the heavy structure from the barge or jacket to the floating appendage structure.

12. Combination according to any of the preceding clauses, wherein when seen in top view the floating appendage structure has a right floater (60A) and a left floater (60B).

13. Combination according to any of the preceding clauses, wherein when seen in side view the at least one crane line, in particular the first crane line and the second crane line, extend(s) under an angle of less than 35 degrees to the vertical, in particular less than 20 degrees.

14. Combination according to any of the preceding clauses, wherein the first vessel hinge part is connected to a first column of the heavy lift vessel and the second vessel hinge part is connected to a second, different column of the heavy lift vessel.

15. Combination according to the preceding clause, wherein the first vessel hinge part (50A) and the second vessel hinge part (50B) are connected to respectively a first side of the first column and to a second side of the second column, wherein the first side and second side face one another.

16. Combination according to any of the preceding clauses, wherein the floating

appendage structure, when seen in top view, has a U-shape or H-shape, the U-shape or H-shape, having a right elongate part and a left elongate part and a cross- connection.

17. Combination according to any of the preceding clauses, wherein the floating

appendage structure comprises an opening between the floaters at one end, and a transverse structure between the floaters at the opposite end, wherein the transverse structure is located higher than the floaters but lower than the upper ends of the columns of the floating appendage structure, and in particular about halfway the height of the columns of the floating appendage structure.

18. Combination according to any of the preceding clauses, wherein the columns of the floating appendage structure define a passageway (77) which traverses the floating appendage structure, the passageway extending from a first opening located between a front right column and a front left column of the floating appendage structure and a second opening located between a rear right column and a rear left column of the floating appendage structure, wherein a barge or combination of barges can move completely through said passageway, thereby traversing the floating appendage structure when the floating appendage structure is ballasted at a deep draft.

19. Combination according to any of the preceding clauses, wherein the vessel hinge assembly comprises a first hole (80A) and a second hole (80B) which are aligned, wherein the appendage hinge assembly comprises a first pin (82A) which is inserted in the first hole and a second pin (82B) which is inserted in the second hole.

20. Combination according to the preceding clause, wherein the first pin and second pin are rigidly interconnected by a beam or truss construction.

21. Combination according to the preceding clause, wherein the first vessel hinge part and the second vessel hinge part each comprise a flat plate which positioned with one of the main faces thereof against a column and welded to a column at least at the circumference thereof, wherein the plate comprises the hole .

22. Combination according to any of the preceding clauses, wherein the appendage hinge assembly is connected to the rest of the floating appendage structure via an open truss frame .

23. Combination according to any of the preceding clauses, wherein the vessel hinge assembly is provided above the floater of the heavy lift vessel.

24. Combination according to any of the preceding clauses, wherein the vessel hinge assembly is provided at the level of the columns of the heavy lift vessel. 25. Combination according to any of the preceding clauses, wherein the vessel hinge assembly is provided at the level of the deck structure of the heavy lift vessel.

26. Combination according to any of the preceding clauses, wherein the floating

appendage structure does not comprise: a propulsion system, a living quarters or a helicopter deck.

27. Combination according to any of the preceding clauses, wherein the columns of the floating appendage structure have a smaller water piercing surface than the columns of the heavy lift vessel.

28. Combination according to the preceding clause, wherein one or more columns of the floating appendage structure, are formed entirely or partially as a truss structure.

29. Combination according to the preceding clause, wherein one or more columns of the floating appendage structure comprise an upper part having a greater water piercing surface than a lower part of the column, wherein in particular the upper part is formed as a closed box and the lower part is formed as a truss structure.

30. Combination according to any of the preceding clauses, wherein upper ends of the columns of the floating appendage structure are interconnected by one or more beams which extend lengthwise of the floating appendage structure.

31. Combination according to any of the preceding clauses, wherein the first crane line connector and the second crane line connector define a connector axis which extends parallel to the hinge axis and in particular parallel to the crane axis.

32. Combination according to any of the preceding clauses, wherein when seen in top view the at least one crane line connector is positioned at a distance from the hinge axis which is greater than 35 percent, in particular greater than 45 percent of a distance from the hinge axis to the opposite side or end of the floating appendage structure.

33. Combination according to any of the preceding clauses, wherein the vessel hinge assembly is located at the bow or stern of the heavy lift vessel, and wherein the hinge axis extends orthogonal to a main longitudinal direction of the heavy lift vessel. 34. Combination according to any of the preceding clauses, wherein the vessel hinge assembly is located at the right or left side of the heavy lift vessel and wherein the hinge axis extends parallel to a main longitudinal direction of the heavy lift vessel.

35. Combination according to any of the preceding clauses, wherein the floating

appendage structure comprises a plurality of cross-beams which rest on the upper end of the columns or on longitudinal beams which rest on the columns of the floating appendage structure, wherein the cross-beams extend over the open lifting area from a right side of the floating appendage structure to a left side of the floating appendage structure.

36. Combination according to any of the preceding clauses, wherein the floating

appendage structure comprises a hydraulic lift system configured to raise the crossbeams relative to the at least one hull of the floating appendage structure.

37. Method of lifting a heavy structure at sea, the method comprising:

providing the combination of the heavy lift vessel and the floating appendage structure according to any of the preceding clauses,

positioning a heavy structure such as a topside on the floating appendage structure,

putting the at least one crane line under pre-tension,

wherein the at least one crane line under pretension limits the freedom of movement of the floating appendage structure relative to the heavy lift vessel.

38. Method according to any of the preceding clause, wherein the at least one crane line under pretension causes the heavy lift vessel and the floating appendage structure to move in tandem, with motion characteristics resembling the motion characteristics of a single rigid vessel.

39. Method according to any of the preceding method clauses, wherein when seen in top view at least one barge is positioned between the right floater and the left floater of the floating appendage structure under the heavy structure, and wherein the heavy structure is transferred from the barge onto the floating appendage structure or from the floating appendage structure to the barge.

40. Method according to any of the preceding method clauses, wherein: a topside is lifted from a jacket or other substructure by positioning the U-shaped part of the floating appendage structure around the jacket or other substructure and by subsequently deballasting the heavy lift vessel and the floating appendage structure together, thereby lifting the topside from the jacket or other substructure, or

- a topside is installed onto a jacket by carrying the topside with the floating

appendage structure and by positioning the U-shape of the floating appendage structure around the jacket or other substructure, and subsequently ballasting the heavy lift vessel and the floating appendage structure, thereby lowering the heavy lift vessel, floating appendage structure and the topside and placing the topside onto the jacket or other substructure.

41. Method according to any of the preceding method clauses, wherein the floating

appendage structure comprises a hydraulic lift system configured to raise the cross- beams relative to the at least one hull of the floating appendage structure, wherein for making the initial contact between the floating appendage structure and the heavy structure which is to be lifted the hydraulic system raises the cross-beams relative to the hull.

42. Method according to any of the preceding method clauses, wherein:

a topside or other heavy structure is transferred from a barge to the floating appendage structure, and wherein:

o the topside or other heavy structure is positioned centrally on the barge, o the floating appendage structure is ballasted to a deep draft,

o the barge including the topside or other heavy structure is positioned in the U- shaped part of the floating appendage structure, and

o the floating appendage structure is deballasted, thereby decreasing the

draught of the floating appendage structure, wherein the floating appendage structure lifts the topside or other heavy structure from the barge,

- a topside or other heavy structure is transferred from the floating appendage

structure to at least one barge or vessel, wherein:

o the topside or other heavy structure is positioned on the floating appendage structure,

o the floating appendage structure including the topside or other heavy structure is ballasted to a shallow draught,

o the barge is positioned in the U-shaped part of the floating appendage

structure, and o the floating appendage structure is ballasted, thereby increasing the draught of the floating appendage structure, wherein the floating appendage structure is lowered and places the topside or other heavy structure on the barge.

43. Method according to any of the preceding method clauses, comprising the subsequent steps of :

ballasting the combination which carries the heavy structure until the columns pierce the water line,

uncoupling the floating appendage structure from the heavy lift vessel, positioning at least one barge in the passageway of the floating appendage structure

further ballast the floating appendage structure until the heavy structure is positioned on the at least one barge.

44. Floating appendage structure configured to lift a heavy structure at sea, the floating appendage structure comprising:

a hull ,

at least one appendage hinge assembly configured to be connected to a vessel hinge part of a heavy lift vessel and to form a hinge therewith,

at least one crane line connector mounted to the hull,

wherein the floating appendage structure is configured to be interconnected via the hinge to the heavy lift vessel, wherein the hinge allows a rotation of the floating appendage structure relative to the heavy lift vessel about the hinge axis.

45. Floating appendage structure according to clause 44, wherein the combination

comprises a passageway (77) between the columns of the floating appendage structure and the heavy lift vessel or between the columns of the floating appendage structure, wherein the passageway is constructed to position a barge or jacket in said passageway between said columns when said columns intersect the waterline for transfer of the heavy structure from the floating appendage structure to the barge or to a jacket and/or for transfer of the heavy structure from the barge or jacket to the floating appendage structure.

46. Floating appendage structure according to clause 44 or 45, further comprising any of the features of the dependent clauses 2-35 insofar as related to the floating appendage structure. 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.

White lines between text paragraphs in the text above indicate that the technical features presented in the paragraph may be considered independent from technical features discussed in a preceding paragraph or in a subsequent paragraph.