EP1517831B1

EP1517831B1 - Multi-purpose heavy lift vessel

Info

Publication number: EP1517831B1
Application number: EP03741655A
Authority: EP
Inventors: Zweitze Bouwe Gall; Wilhelmus Coenradus Johannes Jozephus Woldring; Johan Albert Commandeur
Original assignee: IHC Gusto Engineering BV
Current assignee: IHC Gusto Engineering BV
Priority date: 2002-06-28
Filing date: 2003-06-27
Publication date: 2006-01-11
Anticipated expiration: 2023-06-27
Also published as: WO2004002814A1; EP1517831A1; DK1517831T3; AU2003280201A1; NO20050462L

Abstract

The invention relates to a lifting vessel (1) comprising a first and second hull (2,3) located side by side at a predetermined distance, at least one u-shaped lifting portal (8,9) comprising two vertical legs (33, 34) supported on a respective hull and a transverse leg (14) interconnecting the vertical legs, and connection means (12, 36, 37) for attaching a structure to the transverse leg. Each hull comprises along its length direction a number of ballast (16, 17, 18, 19) tanks at least partially located above water level (W). Each ballast tank comprises an outflow opening (45) above water level, a closure member (20, 46) for closing the ballast outflow and a releasable locking device (21, 48, 51) for maintaining the closure member in a closed position, wherein the locking devices (21, 48, 51) are each connected to a control unit (22) for releasing the locking devices.

Description

The invention relates to a lifting vessel comprising a first and second hull located side by side at a predetermined distance, at least one u-shaped lifting portal comprising two vertical legs supported on a respective hull and a transverse leg interconnecting the vertical legs, and connection means for attaching a structure to the transverse leg.
Such a vessel is known, for instance the "Ostrea" which was used in the eighties for construction of bridges in the Netherlands (Oosterschelde dam) for lifting and transporting heavy concrete pillars, partially submerged below water, and suspended from the transverse leg by cables. The concrete pillars were attached to the lifting frame at a dock and were suspended under controlled onshore conditions. Both hulls were connected at the front to form a U-shaped construction, which has a U-shaped water line. The sea going stability of the known lifting vessel construction is relatively small and the lifting capacity is relatively limited.
It is an object of the present invention to provide a vessel, which can lift heavy structures, such as topsides of oilrigs or spar buoys, which may have a weight of several thousand tons, under seagoing conditions.
It is another purpose of the present invention to provide a lifting vessel with a relatively simple lifting system which allows rapid and controlled lifting of heavy loads under seagoing conditions.
Hereto the vessel according to the present invention is characterised in that each hull comprises along its length direction a number of ballast tanks at least partially located above water level, each ballast tank comprising an outflow opening above water level, a closure member for closing the outflow opening and a releasable locking device for maintaining the closure member in a closed position, wherein the locking devices are each connected to a control unit for releasing the locking devices.
After connection of a load to the portal crane of the vessel, the ballast tanks can be rapidly emptied such that the vessel is raised, and the structure is lifted. The lifting speed may be for instance 15 m per minute, such that within 10 s a lifting distance about 2,5 m is reached. This allows lifting of heavy structures, such as an oil production platform topside, within an average wave period. The rapid lifting speed ensures that in a short time a sufficient distance between the lifted structure and its support, which in many cases will be resting on the seabed, is obtained such that a risk of collision due to wave-induced motions of the vessel is prevented.
The ballast tanks are distributed along the length of the hulls and allow controlled deballasting without trim or listing upon lifting of the load. The number of ballast tanks will be equal at portside and starboard, and the combined center of gravity of the tanks will lie substantially midship. The control unit can actuate release of the locking devices of the closure members (watertight hatches) of the ballast tanks that are situated at the same longitudinal position, at the same moment to prevent listing. The deballasting of the tanks in the length direction may also occur simultaneously to prevent trimming during lifting.
The lifting system according to the present invention allows for rapid lifting under naturally damped conditions. In the first phase of the lifting after opening of the ballast tanks, the lifting accelerations will be high, allowing a rapid separation of the structure to be lifted from the support structure from which it is separated. At the end of the lifting cycle, most of the water having flowed out, the accelerations will have decreased to nearly zero, such that up-swinging of the load and undesired tension in the support cables is prevented. The outflow characteristics of the water from the ballast tanks may be modified by the internal form of the ballast tanks (e.g. a sloping bottom) or via flow restrictions in the outflow opening of the ballast tanks, or via controlled opening of the closure members.
In order to compensate while lifting a structure which has a center of gravity which is not aligned with the center of buoyancy of the vessel, one ore more tanks may not be emptied upon lifting, or some tanks may be left empty upon filling of the ballast tanks, or again alternatively, the timing of the opening sequence of the ballast tanks may be controlled, such that the vessel before, during and after the lifting operation is maintained in a state without trim or list.
The locking device may be formed by hydraulic cylinders or explosive bolts, or any other controlled opening device for releasing of the hatches. Each ballast tank may be connected to a water inflow duct. The tanks may be filled via the inflow duct at the desired rate, which may be relatively slow. In one embodiment, each tank is provided with a valve, which may be closed to selectively fill some tanks while leaving others completely or partially empty for compensating for an offset in the center of gravity of the object to be lifted.
When opening the ballast tanks, a large amount of water flows into the sea close to the hull, for instance 40,000 tons, which may cause bubble formation (aeration) due to the impact of the ballast water on the water surface. To prevent negative effects of aeration on the buoyancy of the vessel, with consequent risk of listing during lifting, an outflow guiding structure may be placed near the outflow openings extending transversely to the wall of the hull for transporting the ballast water away from the hull. The outflow guiding structures may be formed by gutters or tubes extending beyond the hull for controlling the outflow and for placing the impact position of the ballast water on the water surface at the position away from the hull.
During lifting, the hulls of the vessel will be subject to repulsive forces, which may be taken up by the vertical legs of the portal crane structure. For providing stiffness to the vessel and for taking up separation forces between the two hulls caused by lifting operations, the vertical legs on each side of the hull comprise a connecting plate which extends alongside of the hull for transmitting transverse forces from the hull to the vertical legs. In this way, the U-shaped lifting frame contributes to the mechanical stiffness of the vessel of the present invention.
The hulls of the vessel may be interconnected at the fore end or at the aft end via one or more transverse beams located above water level. These anti-splitting/torsion beams absorb the torsion forces created by the relative motion between the two hulls due to wave-induced motions. Besides, the anti-splitting/torsion beams will help to counteract separation forces caused by lifting. By placing the transverse beams above the waterline, symmetry in buoyancy is provided between the fore and after part of the vessel and water resistance during sailing is reduced while seagoing stability is improved. On top of the transverse beams, accommodation facilities and life support systems can be positioned.
The structures to be lifted will be suspended from lifting cables of a lifting device placed on the transverse leg. The horizontal position of the lifting devices, which may comprise a trolley, may be varied. The lifting cables provide a natural damping of the heavy weight suspended therefrom by the relatively long length and the inherent elasticity of the cables in view of the pendulum movement of the load suspended from the cables. The main lifting operation will be performed by the gravity-induced deballasting whereas the lifting cables may be operated to fine tune the position of the lifted structure relative to the lifting frame.
On each cable a gripping arm may be provided which has attachment members which may be displaceable in length direction of the vessel for fine tuning the position of the lifted structure in order to optimize the position of the center gravity with respect to the center of buoyancy of the vessel.
An embodiment of a lifting vessel according to the present invention will be described in detail with reference to the accompanying drawings. In the drawings:

Fig. 1 shows a schematic perspective view of the lifting vessel according to the present invention;
Fig. 2 shows a schematic frontal view of the vessel of Fig. 1;
Fig. 3 shows a schematic layout of the ballast tanks;
Fig. 4 shows simultaneous opening of two adjacent ballast tanks;
Fig. 5 shows a ballast tank with a sloping bottom with a hinging cover, opening either at the top or at the bottom;
Fig. 6 shows schematically the outflow guiding structure of the present invention;
Fig. 7 shows a top view of a gripper arm of the present invention; and
Fig. 8 shows a partly cut-away perspective view of a lower part of the vertical legs.

Fig. 1 shows a lifting vessel 1 according to the present invention. The vessel 1 has is self-propelled and dynamically positioned. The offshore construction market experiences a need for the installation and commissioning of vertically anchored floating or guyed platforms in deep water as well as the de-commissioning and removal of existing platforms in shallow to medium water depths. The multi-purpose heavy lift vessel 1 of the present can operate on a worldwide basis to transport and install complete platform topside in one piece from shore to the desired location, where its lifting capability effectuates the installation on a supporting floating structure in the single lifting operation. Likewise, the removal of topsides in a single lift and transport to a shore base, the construction facility can be executed with the same vessel.
The vessel 1 is a catamaran type structure with two parallel hulls 2, 3. The hulls define an opening 4 therebetween, which extends from the fore part 5 of the vessel 1 to the aft part 6. If so desired, the part 6 can function as fore part and part 5 as aft part. The hulls 2, 3 are interconnected via an anti-splitting/torsion beam 7 at the aft part 6 and by two portal crane structures S, 9. The portal crane structures 8, 9 are provided with hoists 12, 13 movable in a transverse direction indicated by the arrow A along transverse legs 14, 15 of portal crane structures 8, 9. On the deck of the vessel, a number of ballast tanks 16, 17, 18, 19 is situated. Each ballast tank has an outflow opening closeable via a watertight hatch 20, which is closed by a releasable locking device 21. The locking devices 21 are controlled by a control unit 22 for a controlled opening of the hatches 20. The locking devices 21 are connected to the control unit 22 via schematically indicated data transmission lines 30, 31, which may be cables, optical fibers or a radiographical or acoustical transmission means. On each vessel, a pump 24 and a water supply duct 25 may be provided with outlets 26, 27 connecting to each ballast tanks 16, 17, 18, 19. The ballast tanks 16-19 may be opened or closed at the top. The symmetric layout of the vessel ensures that no trim and/or list occurs when lifting a heavy load. As the two hulls 2, 3 are interconnected via the portal cranes 8, 9 and the transverse anti-splitting/torsion beam 7, the torsion forces created by the relative motion between the two hulls 2, 3, due to wave-induced motion and separation forces, caused by the lifting operations, will be taken up by the portal cranes 8, 9 and the transverse beam 7. As the beam 7 is placed above the waterline, symmetry in buoyancy between the fore part 5 and the aft part 6 of the vessel is maintained and water resistance during sailing is decreased.
As can be seen from Fig. 2, portal crane 8 is provided with two vertical legs 33, 34, which may have a height of for instance 80 meters. Two hoists 12, 12' can move along transverse leg 14 and each hoist comprise a winch 35, a lifting cable 36 and lifting arm 37. Upon lifting of a top structure 40 having support legs 39, supporting it on a jacket which rests in the seabed, the vessel 1 is sailed over the top structure, while one or more of the ballast tanks 16-19 on each hull 2, 3 are filled with water. The lifting arms 37 are lowered from cable 36 and are engaged with legs 39 of top structure 40 via a clamping mechanism. Thereafter, the legs 39 are disconnected from the support jacket by known separation techniques, such as cutting or blow torching. With the winches 35 in a fixed position, the hatches 20 of the ballast tanks, which are located above water level W, are opened such that a rapid outflow of ballast water from the tanks is effected. Special care is taken that the timing of the opening of the ballast tanks for the hulls 2, 3 occurs simultaneously such that no listing or trimming occurs during the lifting operation. Within 10 seconds a lifting height of 2.5 meters can be reached during which the cables 36 perform no active lifting function. In the lifted position, such as shown in Fig. 2, the top structure 40 remains suspended from the cables 36 which provide a damping horizontal pendulum motion in view of their long length dampening the wave-induced motions of the structure 40. With the top structure 40 in the position as shown in Fig. 2, the vessel can sail to a docking position or to a position of transfer of the complete top structure 40. When offloading the structure 40, the winches 12 are operated to lower the structure 40 to a position in which the lifting arms 37 can be disengaged. The winches 35 maybe laid out only for lowering the load 40, but can, if so desired be also tailored to raise the load.
Via hoists 12 carrying the lifting arms 37, the center of gravity of the structure 40 is positioned in vertical line with the center of buoyancy of the vessel 1. This can be effected by placing the hoists 12 in their desired position along transverse arm 14 and by positioning the lifting arms 37 in the proper transverse position. When no load 40 is lifted, the hoists 12 can be skidded out of the way to a non-operative position. As shown in Fig. 2, during transportation, hydraulic dampers 41 may be extended to provide a horizontal damping force upon impact with the vertical legs 33, 34. The dampers 41 may be extended such as to resiliently engage with legs 33, 34 to reduce the stroke of the load 40, and to reduce the forces on the load.
As is shown in Fig. 3, the locking device 21 of each ballast tank 16, 17 is controlled via the control unit 22. Via control unit 22, the hatches 20, 20' of ballast tanks on hulls 2, 3, which are located at the same longitudinal position, can be opened in synchronism to prevent listing and heeling upon outflow of the contents. Furthermore, control unit 22 can open all ballast tanks 16-19 simultaneously or can provide for a timing difference between opening of ballast tanks 16-19 to compensate for an offset in the center of gravity of the load 40 from the center of buoyancy of the vessel 1.
For filling the ballast tanks 16-19, seawater is supplied via pump 24 through duct 25. Duct 25 may be provided for each ballast tank 16-19 with a valve 42, which may be controlled by the control unit 22. Opening or closing of the valves 42 allows for selectively filling the ballast tanks and leaving same ballast tanks fully or partly filled with ballast water. Hereby, the position of the vessel 1 in the water before, during and after release of the ballast water can be adjusted such as to achieve a position without trim and without list at all times.
Fig. 4 shows a detail of two ballast tanks 43, 44, each having an outflow opening 45 which is closed by a watertight hatch 46. The hatch 46 can hinge around hinges 47 at the lower end of the hatch 46. A hydraulic cylinder 48, operated via the control unit 22, can interlock with an eye 49 on the tanks 43, 44, such as to maintain the hatch 46 in a closed position. Retracting cylinder 48 causes the water pressure to open the hatch 46 such that a rapid outflow of ballast water from tanks is obtained.
As shown in Fig. 5, the bottom 50 of ballast tank 43 may be sloping downwardly towards the outflow opening 45 for providing a specific water outflow pattern and, hence, a desired lifting characteristics. For the tank 44 in an alternative embodiment, the hatch 46' hinges at the top part of the ballast tank 44. A hydraulic cylinder 51 can be applied to control the degree of opening of the hatch 46' and, hence, the outflow pattern and thereby the lifting characteristics of the vessel. Cylinder 51 may again be operated via control unit 22.
Fig. 6 schematically shows outflow guiding structures 53, 54 connected to the outflow openings of the ballast tanks 16-19. The outflow guiding structures in this case are formed by tubes, which extend transversely from the vessel to guide the water from the ballast tanks to a position at the distance from the hull 3. Hereby, the point of impact of the water from the ballast tanks with the water surface will be remote from the vessel, such that aeration and bubble forming will not negatively impact on the buoyancy of the vessel.
Fig. 7 schematically shows the lifting arm 37 for attaching to a structure 40. The lifting arm 37 may comprise a number of brackets 55, which can be clampingly engaged with the support frame or legs 39 of the top structure. The brackets may be slidable along a frame 56 to adjust the longitudinal position of the load 40 carried by the vessel 1 and/or to position the brackets with respect to the legs 39 of the load 40. The points of attachments 57 at which the cables 36 are connected are located on the centerline of the brackets 55 such that no moments are exerted on the support legs 39 upon lifting of the structure 40.
Finally, Fig. 8 shows the lower part of vertical leg 33, which is connected to the hull 2 along the vertical walls of said hull 2 via connecting plates 61, 62 on each side of the hull 2. Hereby, a stiffening force is provided by the portals 8, 9 on the hulls 2, 3 counteracting the splitting forces caused by the lifting operations and providing stiffness and torsion resistance to the combined hulls 2, 3.
The vessel according to the present invention provides for station keeping through a dynamic position system, which saves time by eliminating the need to run anchorlines on location. One complete cycle of docking the vessel 1 at the offshore location, lowering and connecting the lifting arms 37, lifting the vessel by de-ballasting of the ballast tanks 16-19 and securing the top structure can be executed within a 24-hour period. The vessel according to the present invention may as a non-limiting example have a lifting capacity of 18,000 tons and can lift loads of dimensions of 85 meters (L) x 60 meters (W) x 80 meters (H).

Claims

Lifting vessel (1) comprising a first and second hull (2, 3) located side by side at a predetermined distance, at least one u-shaped lifting portal (8, 9) comprising two vertical legs (33, 34) supported on a respective hull and a transverse leg (14) interconnecting the vertical legs, and connection means (12, 36, 37) for attaching a structure to the transverse leg, characterised in that each hull comprises along its length direction a number of ballast tanks (16, 17, 18, 19) at least partially located above water level (W), each ballast tank comprising an outflow opening (45) above water level, a closure member (20, 46) for closing the outflow opening and a releasable locking device (21, 48, 51) for maintaining the closure member in a closed position, wherein the locking devices (21, 48, 51) are each connected to a control unit (22) for releasing the locking devices.
Lifting vessel (1) according to claim 1, wherein the control unit (22) is adapted to open the closure members (20, 46) at a predetermined longitudinal position on each hull (2, 3) in synchronism.
Vessel (1) according to claim 1 or 2, the vessel comprising a pump (24) and a duct (25) connected to the pump and to each ballast tank (16, 17, 18, 19), wherein the duct (25) comprises for each tank (16, 17, 18, 19) a valve (42), which can be opened and closed by a control unit for selectively filling the ballast tanks.
Vessel (1) according to any of the preceding claims, wherein between 5 and 500 ballast tanks are provided on each hull, having a volume of between 10 and 8,000 m³.
Vessel (1) according to any of the preceding claims, wherein each outflow opening (45, 50) is placed near the side of the hull (2, 3), wherein an outflow guiding structure (53, 54) is placed near the outflow opening extending transversely to the side of the hull, for transporting the ballast water away from the hull.
Vessel (1) according to any of the preceding claims, wherein the vertical legs (33, 34) comprise on each side of the hull a connecting plate (61, 62) extending alongside of the hull (2, 3) for transmitting transverse forces from the hull to the vertical legs.
Vessel (1) according to any of the preceding claims, wherein the hulls (2, 3) are interconnected at the rear and/or at the front via one or more transverse beams (7), located above water level (W).
Vessel (1) according to any of the preceding claims, wherein at least one lifting cable (36) and a lifting device (12, 12') is placed on the transverse leg (14).
Vessel (1) according to claim 8, a gripping arm (37) being provided on each cable (36), having attachment members (55) displaceable in a length direction of the vessel for connecting to a structure to be lifted.