Abstract
A floatable structure is described having a hull and a deck. The floatable structure further includes a mooring system for mooring a second floating structure at a mooring position relative to the floatable structure. The mooring system brings the second floating structure down in the water from an initial floating draft to a larger mooring draft to reduce motions of the second floating structure relative to the floatable structure. A method for mooring a second floating structure using the mooring system is also described.
Claims
1. A floatable structure that is floating on water of jacked-up out of the water, comprising a hull provided with a deck and a mooring system attached to the floatable structure and configured to moor a second floating structure at a mooring position relative to the floatable structure, wherein the mooring system is configured to bring the second floating structure down in the water from an initial floating draft to a larger mooring draft to reduce motions of the second floating structure relative to the floatable structure, wherein the mooring system is configured to pull the second floating structure down in the water from the floating draft to the larger mooring draft and thereto comprises a pull-down support structure attached to the hull of the floatable structure and extending over some length into the water to a depth below the second floating structure, and at least one tension cable extending between the pull-down support structure and the second floating structure to be moored.
2. The floatable structure according to claim 1, wherein the mooring system configured to pull the second floating structure down comprises said at least one tension cable extending between the pull-down support structure and corners of the second floating structure to be moored.
3. The floatable structure according to claim 1, wherein the mooring position is underneath the floatable structure.
4. The floatable structure according to claim 1, wherein the mooring position is along a side of the floatable structure.
5. The floatable structure according to claim 1, wherein the mooring system comprises the pull-down support structure and the at least one tension cable extends between the second floating structure to be moored to a sheave provided at a lower part of the pull-down support structure and from there to a winch provided at a higher part of the pull-down support structure.
6. The floatable structure according to claim 5, wherein the higher part of the pull-down support structure is above the water line.
7. The floatable structure according to claim 1, wherein the mooring system comprises the pull-down support structure and the support structure is formed by at least one elongated support member attached to a side of the floatable structure and extending over some length into the water to a depth below the second floating structure, wherein the at least one elongated support member preferably extends vertically, and the number of elongated support members is at least two, and more preferably at least three.
8. The floatable structure according to claim 7, further comprising guiding means connected to the hull of the floatable, and configured to rigidly hold an elongated support member in a support position.
9. The floatable structure according to claim 8, wherein the guiding means are hingedly connected to the hull of the floatable structure.
10. The floatable structure according to claim 8, wherein the guiding means are configured to hold the elongated support member and move the same between different vertical positions, preferably by comprising a jacking system.
11. The floatable structure according to claim 7, wherein the at least one elongated support member takes support on or in an underwater bottom.
12. The floatable structure according to claim 1, wherein the floatable structure comprises a jack-up platform comprising a number of vertical legs that connect to a working deck through jacking systems, each jacking system being configured to move a leg between a lower position, in which the leg takes support on an underwater bottom and the hull is jacked-up out of the water, and a higher position, in which the leg is free from the underwater bottom and the hull is floating on the water, wherein the mooring system comprises one leggy of the jack-up platform.
13. The floatable structure according to claim 12, wherein the mooring system comprises the support structure and said support structure is formed by one or more legs of the jack-up platform.
14. The floatable structure according to claim 12, wherein the legs of the jack-up platform are in the lower position.
15. The floatable structure according to claim 12, wherein the mooring position is along a side of the jack-up platform between two legs, and the mooring system comprises a tension cable for each of said legs.
16. The floatable structure according to claim 12, wherein the lower part of the leg comprises a transversely enlarged foot support of the leg.
17. The floatable structure according to claim 16, wherein the transversely enlarged foot support is extendable in the transverse direction, which extension is provided with the sheave.
18. The floatable structure according to claim 12, wherein the higher part of the leg is below the jacking system of the leg and optionally above the water line.
19. A method for mooring a second floating structure at a mooring position relative to a floatable structure in accordance with claim 1, the method comprising: bringing the second floating structure down in the water with the mooring system of the floatable structure from an initial floating draft to a larger mooring draft to reduce motions of the second floating structure relative to the floatable structure, wherein the mooring system pulls the second floating structure down in the water from the floating draft to the larger mooring draft.
20. The method according to claim 19, wherein the mooring system pulls the second floating structure down by tensioning at least one tension cable that extends between a pull-down support structure extending over some length into the water to a depth below the second floating structure and attached to the hull of the floatable structure, and the second floating structure to be moored.
21. The method according to claim 19, wherein the floatable structure comprises a jack-up platform, the method comprising the steps of: moving the legs of the jack-up platform from a higher position, in which the legs are free from an underwater bottom and the hull is floating on the water, to a lower position, in which the legs take support on the underwater bottom and the hull is jacked-up out of the water; providing at least one tension cable that extends between a leg of the jack-up platform in the jacked-up state and the second floating structure to be moored, and pulling the second floating structure down in the water from a floating draft to a larger mooring draft by making use of said leg; and mooring the second floating structure against the jack-up platform.
22. The method according to claim 19, wherein the mooring system comprises the pull-down support structure and the support structure is formed by the at least one elongated support member attached to the side of the floatable structure, the method further comprising providing at least one tension cable that extends between the at least one elongated support member and the second floating structure to be moored, and pulling the second floating structure down in the water from a floating draft to a larger mooring draft by making use of said support member; and mooring the second floating structure against the at least one elongated support member.
23. The floatable structure according to claim 1, wherein the floatable structure comprises a jack-up platform comprising a number of vertical legs that connect to a working deck through jacking systems, each jacking system being configured to move a leg between a lower position, in which the leg takes support on an underwater bottom and the hull is jacked-up out of the water, and a higher position, in which the leg is free from the underwater bottom and the hull is floating on the water, wherein the mooring system comprises two legs of the jack-up platform.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The invention will now be elucidated with reference to the following figures, without however being limited thereto. In the figures:
(2) FIG. 1 represents a schematic perspective rear view of a jack-up platform against which a floating vessel is moored in accordance with an embodiment of the invention;
(3) FIG. 2 represents a schematic perspective front view of the jack-up platform shown in the embodiment of FIG. 1;
(4) FIG. 3 represents a schematic side view of the jack-up platform shown in the embodiment of FIG. 1;
(5) FIG. 4 represents a schematic perspective view of a jack-up platform underneath which a floating vessel is moored in accordance with yet another embodiment of the invention;
(6) FIG. 5 represents a schematic perspective view of yet another embodiment of the jack-up platform;
(7) FIG. 6 represents a schematic perspective view of a jack-up platform against which a floating vessel is moored in accordance with yet another embodiment of the invention;
(8) FIG. 7 represents a schematic side view of the jack-up platform shown in the embodiment of FIG. 6;
(9) FIG. 8 represents a schematic side view of an embodiment of the jack-up platform showing foldable enlarged feet of the legs;
(10) FIG. 9 represents a schematic perspective view of a jack-up platform against which a floating vessel is moored in accordance with yet another embodiment of the invention;
(11) FIG. 10 represents a schematic perspective view of a jack-up platform against which a floating vessel is moored in accordance with yet another embodiment of the invention;
(12) FIG. 11 shows a schematic side view of a mono-hull floating structure comprising a pull-down support structure according to an embodiment of the invention;
(13) FIG. 12 shows a schematic side view of a jack-up platform comprising its legs as a pull-down support structure according to another embodiment of the invention; and finally
(14) FIG. 13 represents a schematic perspective view of a jack-up platform provided with a push-down support structure according to yet another embodiment of the invention.
DESCRIPTION OF THE INVENTION
(15) With reference to FIG. 11, a schematic side view of a mono-hull floating structure 1-1 is shown, illustrating the principle idea of the invention. The mono-hull floating structure 1-1 comprising a pull-down support structure 4-1 which may be embodied as one or more elongated support members that extend into the water to a depth below the bottom of a second floating structure 5-1 to be stably moored. Tension cables 46-1 extend from a lower position of the pull-down support structure 4-1 towards corner parts of the second floating structure 5-1. The tension cables 46-1 are tensioned, for instance by winches (not shown) provided on the pull-down support structure 4-1 and/or on the floating structure 5-1, which brings the second floating structure 5-1 from a floating draft to an increased mooring draft, as shown in FIG. 11. This effectively stabilizes the floating structure 5-1 with respect to horizontal and vertical motions.
(16) According to another embodiment of the invention, as shown in FIG. 12, a second floating barge 5-2 is connected to a jack-up platform 1-2 standing on its legs 12 through tension cables 46-2. The tension cables 46-2 extend from a lower position of the legs 12 towards corner parts of the second floating structure 5-2. The tension cables 46-2 are tensioned, for instance by winches (not shown) provided on the legs 12 of the jack-up platform 1-2 or otherwise and/or on the floating structure 5-2, which brings the second floating structure 5-2 from a floating draft to an increased mooring draft, as shown in FIG. 12. This effectively stabilizes the floating structure 5-2 with respect to horizontal and vertical motions. An additional push-down or pull-down support structure 4-2 may be present at a side of the jack-up platform 1-2. As also shown, a tug 9-1 is connected to the second floating structure 5-2 by a pulling wire 9-2, and is thrusted in the direction 9-3 to keep a relatively constant distance from the second floating structure 5-2 to the jack-up platform 1-2.
(17) With reference to FIG. 13, yet anther embodiment is shown in which use is made of a push-down support structure 90 connected to a side of a jack-up platform 1-3. The mooring system in this embodiment is configured to push the second floating structure 5-3 down in the water from the floating draft to the larger mooring draft. To this end, the push-down support structure 90 is attached to the hull of the jack-up platform 1-3 through a steel leg structure 90-1, which may be embodied as the elongated support members 4-1 of FIG. 11, to which steel leg structure 90-1 is movably connected a guiding device 90-2 that may be moved up and down in a vertical direction. Each guiding device 90-2 carries pushing members 90-3 that are at least movable in the vertical direction and contact a top or deck surface of the second floating structure 5-3, as shown.
(18) Some more specific examples of embodiments according to the invention will now be given.
(19) With reference to FIG. 1, a jack-up vessel or platform 1 in accordance with an embodiment of the invention comprises a hull 10, a horizontal working deck 11 and a number of vertically extending legs 12 that connect to the working deck 11 through a jacking system 13, provided on corners of the hull 10. Each jacking system 13 is configured to move a leg 12 between a higher position, in which the leg 12 is free from an underwater bottom 2 and the hull 10 is floating on the water 3, and a lower position, shown in FIGS. 1 and 2. In the lower position of the legs 12, each leg 12 takes support on or in the underwater bottom 2 and the hull 10 is jacked out of the water over some distance between a bottom of the hull 10 and the water surface 30. The legs 12 shown are of lattice type and at a bottom side provided with shoes or spud cans 120. The legs 12 may be embodied differently however, and may for instance comprise solid legs, optionally without shoes 120.
(20) The jack-up platform 1 further comprises a mooring system (4a, 4b). The mooring system (4a, 4b) is configured to moor a floating vessel 5 at a mooring side 15 of the jack-up platform 1. In the shown embodiment, the mooring system (4a, 4b) comprises means 4a for stabilizing the floating vessel 5 in a vertical and horizontal direction, and optional additional means 4b for stabilizing the floating vessel 5. The stabilizing means 4a comprise a number of tension cables 46 that extend between a leg 12 of the jack-up platform 1 in the jacked-up state and the floating vessel 5 to be moored. Each tension cable 46 is configured to pull the floating vessel 5 down in the water from a floating draft to a larger mooring draft by making use of said leg 12. In the embodiment shown in FIG. 1, the mooring position is along a side 15 of the jack-up platform 1 between two legs 12 positioned at that side 15, and the mooring system (4a, 4b) comprises a system of tension cables 46 for each of said legs 12.
(21) As shown, the tension cables 46 extend between each leg 12 of the jack-up platform 1 and are attached to four corners of the floating vessel 5. The tension cables 46 in particular extend between the floating vessel 5 to be moored to a sheave 48 provided at a lower part of each leg 12 of the jack-up platform 1 and from there to a winch 49 provided at a higher part of the leg 12, or close to the leg 12 at a part of the hull 10 of the jack-up platform. Each winch 49 is configured to pull at each cable 46 to pull down the floating vessel 5 to a mooring draft. Each winch 46 may be positioned in any suitable position of the jack-up platform 1 or mooring system (4a, 4b).
(22) The mooring system (4a, 4b) further comprises means 4b for stabilizing the floating vessel 5 in an optional manner. These means 4b comprise in the embodiment shown in FIGS. 1-3, three elongated support members in the form of lattice or other elongated support members of triangular or other cross-section shape 40, and guiding means, which could come in the form of a jacking system 41, rigidly connected to the hull 10 of the jack-up platform 1 along a line extending parallel to the mooring side 15 of the hull 10. The connection may be welded, or may be embodied by any other suitable way of connection. Each guiding means 41 in operation holds an elongated support member 40 and is able to move the elongated support member 40 up and down between different vertical positions, as schematically shown by the arrows 43 in FIG. 1. Each guiding means 41 is configured to rigidly hold an elongated support member 40 in a support position, shown in FIGS. 1 and 2, in which each elongated support member 40 (or at least some of these legs 40) is within reach of a hull part 50 of the floating vessel 5 to be supported when the hull 10 is jacked out of the water 3 over the distance and the jack-up platform 1 rests on its legs 12. In the support position, each elongated support member 40 is jacked down sufficiently to be able to support said hull part 50 of the floating vessel 5, moored against the jack-up platform 1. In the support position, each elongated support member 40 thereto extends into the water 3 over a distance (see FIG. 2) that reaches sufficiently deep to enable supporting the hull part 50 of the floating vessel 5 in mooring position. An outer end of each elongated support member 40 is hanging freely in the water 3.
(23) In the mooring position of the floating vessel 5, the connection between the floating vessel or barge 5 and the elongated support members 40 may be accomplished by using conventional mooring lines 51 and winches 52, provided on the floating vessel 5. The winches could also be provided on the jack-up vessel 1, or be integrated in one or more of the elongated support members 40. The winches 52 are configured to take in a length of mooring line 51, thereby bringing the vessel 5 closer to the elongated support members 40 as shown in FIG. 1, until the hull part 50 contacts the elongated support members 40. Paying out a length of mooring line 51 may remove the floating vessel 5 from the mooring side 15 of the jack-up platform. To prevent peak loads on the elongated support members 40 from occurring, shock dampers may be incorporated in between each elongated support member 40 and the hull part 50 of the floating vessel 5, such as the fenders 54.
(24) The jack-up platform 1 may further comprise a lifting device 6, a boom 60 of which is pivotably provided around a lifting device base 61, supported on the working deck 11 of the jack-up platform 1.
(25) In another embodiment, the guiding means 41 are provided with an optional hinge point on the side of the hull 10, and the elongated support members 40 positioned on deck separately from the guiding means 41. The elongated support members 40 may then be taken up by the lifting device 6 and inserted in the guiding means 41, and brought overboard.
(26) In the embodiment shown in FIG. 4, the mooring position of the floating vessel 5 is underneath the jack-up platform 1 in jacked-up state. In this embodiment, the means 4b for stabilizing the floating vessel 5 may be omitted. This function is indeed taken over by the tension cables 46 that extend between all legs 12 of the jack-up platform 1 and the floating vessel 5, in particular its four corners. The floating vessel 5 in this embodiment is positioned about centrally between the legs 12 of the jack-up platform 1, although this may also be a off-center position, if desired.
(27) FIG. 5 shows yet another embodiment of the invention. Here, a jack-up platform is provided having the same features as the embodiment shown in FIGS. 1-3, but having the three elongated support members 40, in the support position, extend into the underwater bottom 2 over some distance to take support in the underwater bottom 2. In this embodiment, forces exerted by the moored vessel 5 on the elongated support members 40 are not only absorbed by the guiding means 41 and led into the hull 10 of the jack-up platform 1, but are also absorbed by their fixation into the underwater bottom 2. In order to facilitate penetration of the elongated support members 40 into the underwater bottom 2, the elongated support members 40 may at a bottom side thereof be provided with pointed end parts 45.
(28) Yet another embodiment of the invention is shown in FIGS. 6 and 7. Here, a jack-up platform is provided having the same features as the embodiment shown in FIGS. 1-3, but having the three elongated support members 40, in the support position, extend into an enlarged foot section or shoe 120 of each vertical leg 12 of the jack-up vessel or platform 1. In the support position of the elongated support members 40, each elongated support member 40 at the mooring side 15 of the jack-up vessel or platform 1 then takes support in its corresponding spud leg shoe 120, provided on the mooring side 15. In this embodiment, forces exerted by the moored vessel 5 on the tension cables 46 and the elongated support members 40 are not only absorbed by the legs 12 and the guiding means 41 and led into the hull 10 of the jack-up platform 1, but are also absorbed by their fixation into the shoes 120. The connection between a lower part of the elongated support members 40 and the shoes 120 may be permanent, for instance by welding, or may be detachable, for instance by providing the shoes 120 with holes into which a lower part of each elongated support member 40 may be received and, optionally, secured. This embodiment has the additional advantage of not having to rely on the, sometimes uncertain or variable, properties and cohesion of the underwater bottom 2.
(29) As shown in the embodiment of FIGS. 6 and 7, the jack-up platform 1 may have legs 12, a lower part of which may comprise a transversely enlarged foot support 120, provided with enlargements 120a. This allows orienting the tension cables 46 about vertically, which may be optimal from a force transmission point of view.
(30) As schematically shown in FIG. 8, the transversely enlarged foot support 120 may comprise extendable parts 120a in the transverse direction, wherein the extendable parts 120a may be foldable around a hinge 120b from an inward position to a folded out position, shown in FIG. 8. The extension is preferably provided with the sheave 48, such that the tension cable 46 may be oriented about vertically between the extension 120a and its attachment point 57 on the floating vessel 5.
(31) FIG. 9 yet shows another embodiment of the jack-up platform 1 and mooring system 4. In the embodiment shown, the jack-up platform 1 further comprises a connecting structure, comprising a steel brace or beam 90, that is configured to connect the elongated support members 40 with a vertical spud leg 12 of the jack-up platform 1. The sheaves 48 are in this embodiment connected to the structure. The connecting structure connects with each spud leg 12 through guides 91 that are provided on each end of the brace or beam 90. The guides 91 allow the elongated support members 40 to be moved between different vertical positions, relative to the spud legs 12 of the jack-up platform 1. In this embodiment, forces exerted by the moored vessel 5 on the elongated support members 40 are not only absorbed by the guiding means 41 and led into the hull 10 of the jack-up platform 1, but are also absorbed by the spud legs 12 on the mooring side 15, or alternatively, on spud legs provided on another side than the mooring side 15. The forces are transmitted to said spud legs 12 through the connecting structure. The connecting structure shown has one brace 90 but may also comprise a plurality of braces, provided on different heights (vertical levels).
(32) As shown in FIG. 10, another embodiment comprises a jack-up platform 1 wherein the guiding means actually comprise the vertical spud legs 12 provided at the mooring side 15 of the jack-up platform 1, and its corresponding jacking system 13. The elongated elongated support members 40 in this embodiment extend vertically along the mooring side spud legs 12 in the support position. They are attached to the mooring side spud legs 12 through elongated support member guides 47 that are fixedly provided on each end of each elongated support member 40. The sheaves 48 and winches 49 are in this embodiment connected to the elongated support members 40. An upper and a lower elongated support member gliding guide 47 of a elongated support member 40 are provided around a spud leg 12 such that they allow the elongated support member 40 to be moved between different vertical positions, relative to the spud leg 12 of the jack-up platform 1. At least an upper or a lower elongated support member guide 47 (or both) may be fixed onto the leg 12 in the support position of the elongated support member 40. In this embodiment, forces exerted by the moored vessel 5 on the elongated support members 40 are not absorbed by the guiding means 41 and led into the hull 10 of the jack-up platform 1. Instead, they are absorbed by the jacking system 13 of the spud legs 12 at the mooring side 15. This may be a practical solution, as long as the expected mooring forces do not increase to levels such that the integrity of the spud legs 12 system may be compromised.
(33) The invented jack-up platform 1 may be used advantageously for mooring a floating vessel 5 against it. An assembly of the invented jack-up platform 1 and such a floating vessel 5 represents a relatively stable assembly, due to the stabilizing effect of the spud legs 12 and the mooring system (4a, 4b) on the assembly (1, 5).
(34) The assembly (1, 5) of a floating vessel 5 moored against a jack-up platform 1 under the intervention of the mooring system (4a, 4b), allows to safely lift an object, such as a wind turbine blade 7 (see FIG. 2) from the deck 55 of the moored floating vessel 5. Other systems may in addition be used to safely lift-off an object. Another benefit of the invented mooring system is that the floating vessel is kept positioned in the horizontal direction as close as possible to the jack-up platform 1 and its lifting device to maximize the lifting device's efficiency. Having the invented mooring system on the lifting device vessel means it can be used with all different kinds of floating vessels without being forced to adapt the latter. The lifted object may be provided on the working deck 11 of the jack-up platform 1 or on another substrate, such as a foundation element of a wind turbine (not shown) provided in the underwater bottom 2. It is without saying that other objects may be lifted such as a monopile, a transition piece, wind turbine components and other objects that are used in installing wind turbines offshore.
(35) The assembly (1,5) may further be used to safely transfer cargo, goods and personnel from the floating vessel 5 to the jack-up platform 1, and vice versa.
(36) The invention is not limited to the above described embodiments and also comprises modifications thereof, to the extent that these fall within the scope of the claims appended below.
