Offshore structure, supporting member, skid shoe, method for moving a cantilever

Abstract

Method for moving a cantilever with respect to a deck of an offshore structure in longitudinal and rotational direction, around a predetermined virtual vertical axis, without providing a fixed vertical rotation shaft, comprising providing an offshore structure with a cantilever movable with respect to a deck of the offshore structure, providing cantilever rails on the bottom side of the cantilever and providing a supporting member or a skid shoe to support the cantilever on the deck, wherein the supporting member or the skid shoe has a top part configured for allowing the cantilever rail to have an angle deviating from the centerline of the skid shoe during rotation of the cantilever.

Claims

1. An offshore structure comprising: a platform having a deck with an X-direction corresponding to a centerline of the platform; a cantilever mountable on the deck and movable with respect to the deck of the platform; a skidding system that is arranged for supporting and moving the cantilever with respect to the deck, wherein the skidding system is arranged for translational movement of the cantilever along a longitudinal direction of the cantilever and for rotational movement of the cantilever around a vertical rotation axis; such that the cantilever is movable between a retracted position in which it substantially is above the deck, and an extended position in which it is substantially extended outside of the deck; wherein the skidding system comprises: a pair of longitudinal cantilever rails mounted to a bottom side of the cantilever, and a rotating system arranged to support and allow rotation of the cantilever with respect to the deck around the vertical axis; a supporting system arranged to support the cantilever on the deck mounted at a distance from the rotating system along the X-direction; supporting members arranged to engage the longitudinal cantilever rails with the rotating system or the supporting system; wherein the supporting system comprises at least one deck rail arranged in a Y-direction substantially transverse to the X-direction; and wherein the rotating system comprises at least two deck rails mounted in symmetrical fashion with respect to the X-direction and having an angle with respect to the Y-direction, and the at least one deck rail of the supporting system and/or the at least two deck rails of the rotating system are curved wherein the at least two deck rails of the rotating system are curved with respect to the vertical rotation axis and have a radius, wherein the at least one deck rail of the supporting system is either (a) curved with respect to the vertical rotation axis and has a radius, or (b) straight and has a distance with respect to the vertical rotation axis; and wherein the radius or distance of the at least one deck rail of the supporting system is larger than the radius of the at least two deck rails of the rotating system.

2. The offshore structure according to claim 1, wherein the angle is an oblique angle and is between approximately 0 degrees and approximately 90 degrees.

3. The offshore structure according to claim 1, wherein the at least one deck rail of the supporting system is mounted aft of the deck.

4. The offshore structure according to claim 1, wherein the supporting members comprise a top part and a bottom part wherein the top part and/or the bottom part are configured to allow rotational movement of the rail to which it is engaged, during rotation of the cantilever with respect to the deck.

5. The offshore structure according to claim 4, wherein the top part and/or bottom part comprises a guide element for receiving the rail, wherein the guide element has a width larger than a width of the cantilever rail, to allow for rotational movement of the rail.

6. The offshore structure according to claim 4, wherein the top part and/or bottom part comprises a guide element for receiving the rail, and wherein the guide element has curved or V-shaped guide walls to allow for rotational movement of the rail.

7. The offshore structure according to claim 1, wherein each supporting member is actuated by a skid unit comprising a rack and pinion system.

8. An offshore structure comprising: a platform having a deck with an X-direction corresponding to a centerline of the platform; a cantilever mountable on the deck and movable with respect to the deck of the platform; a skidding system that is arranged for supporting and moving the cantilever with respect to the deck, wherein the skidding system is arranged for translational movement of the cantilever along a longitudinal direction of the cantilever and for rotational movement of the cantilever around a vertical rotation axis; such that the cantilever is movable between a retracted position in which it substantially is above the deck, and an extended position in which it is substantially extended outside of the deck; wherein the skidding system comprises: a pair of longitudinal cantilever rails mounted to a bottom side of the cantilever, and a rotating system arranged to support and allow rotation of the cantilever with respect to the deck around the vertical axis; a supporting system arranged to support the cantilever on the deck mounted at a distance from the rotating system along the X-direction; supporting members arranged to engage the longitudinal cantilever rails with the rotating system or the supporting system; wherein the supporting system comprises at least one deck rail arranged in a Y-direction substantially transverse to the X-direction; and wherein the rotating system comprises at least two deck rails mounted in symmetrical fashion with respect to the X-direction and having an angle with respect to the Y-direction, and the at least one deck rail of the supporting system and/or the at least two deck rails of the rotating system are curved, wherein each of the supporting members arranged to engage with the supporting system and/or the rotating system comprises a bottom part for engagement with one of the deck rail(s) and a top part for engagement with one of the cantilever rails, wherein the top part and/or the bottom part are configured to allow off-centerline movement of one of the rails with respect to the centerline of the top part and/or the bottom part respectively and wherein the top part and/or the bottom part of each of the supporting members have an oblique angle with respect to each other.

9. An offshore structure comprising: a platform having a deck with an X-direction corresponding to a centerline of the platform; a cantilever mountable on the deck and movable with respect to the deck of the platform; a skidding system that is arranged for supporting and moving the cantilever with respect to the deck, wherein the skidding system is arranged for translational movement of the cantilever along a longitudinal direction of the cantilever and for rotational movement of the cantilever around a vertical rotation axis; such that the cantilever is movable between a retracted position in which it substantially is above the deck, and an extended position in which it is substantially extended outside of the deck; wherein the skidding system comprises: a pair of longitudinal cantilever rails mounted to a bottom side of the cantilever, and a rotating system arranged to support and allow rotation of the cantilever with respect to the deck around the vertical axis; a supporting system arranged to support the cantilever on the deck mounted at a distance from the rotating system along the X-direction; supporting members arranged to engage the longitudinal cantilever rails with the rotating system or the supporting system: wherein the supporting system comprises at least one deck rail arranged in a Y-direction substantially transverse to the X-direction; and wherein the rotating system comprises at least two deck rails mounted in symmetrical fashion with respect to the X-direction and having an angle with respect to the Y-direction, and the at least one deck rail of the supporting system and/or the at least two deck rails of the rotating system are curved, wherein each of the supporting members arranged to engage with the supporting system and/or the rotating system comprises a bottom part for engagement with one of the deck rail(s) and a top part for engagement with one of the cantilever rails, wherein the top part and/or the bottom part are configured to allow off-centerline movement of one of the rails with respect to the centerline of the top part and/or the bottom part respectively and wherein the bottom part has a curvature corresponding to a curvature of a deck rail on which it is engaged.

10. An offshore system comprising: a platform having a deck; a cantilever mountable on the deck and movable with respect to the deck of the platform; a skidding system that is arranged for supporting and moving the cantilever with respect to the deck, wherein the skidding system is arranged for translational movement of the cantilever along a longitudinal direction of the cantilever and for rotational movement of the cantilever around a vertical rotation axis, such that the cantilever is movable between a retracted position in which it substantially is above the deck, and an extended position in which it is substantially extended outside of the deck; wherein the skidding system comprises a pair of longitudinal cantilever rails mounted to a bottom side of the cantilever, and at least a pair of skid shoes mountable on the deck, wherein a top part of a skid shoe is arranged to receive and guide a cantilever rail; wherein the top part of the skid shoe is configured to allow the cantilever rail to have an angle deviating from a centerline of the skid shoe during rotation of the cantilever and wherein the top part of the skid shoe comprises adjustable guide walls to receive the cantilever rail therebetween and to allow rotational movement of the cantilever rail.

11. The offshore structure according to claim 10, wherein each skid shoe is fixedly mounted onto the deck of the platform.

12. The offshore structure according to claim 10, wherein the top part of each skid shoe has curved or V-shaped guide walls to receive the cantilever rail therebetween and to allow rotational movement of the cantilever rail.

13. The offshore structure according to claim 10, further comprising a deck rail configured in Y-direction of the deck with at least two supporting members arranged to engage the longitudinal cantilever rails with the deck rail.

14. The offshore structure according to claim 13, further comprising two skid shoes arranged at a distance from the deck rail, in the X-direction, and in symmetrical fashion with respect to each other about the X-direction.

15. A supporting member comprising a bottom part arranged to engage a curved deck rail and a top part arranged to engage a cantilever rail, wherein the top part and/or the bottom part are configured to allow rotational movement of the rail to which it is engaged during rotation of the cantilever rail with respect to the curved deck rail wherein the top part and/or bottom part comprises a guide element for receiving a rail, wherein the guide element has a width larger than a width of the rail, to allow for rotational movement of the rail, and wherein the top part and/or bottom part comprises a guide element for receiving the rail, the guide element has curved or V-shaped guide walls to allow for rotational movement of the rail.

16. The supporting member according to claim 15, wherein the top part and the bottom part are arranged to have an oblique angle with respect to each other.

17. The supporting member according to claim 16, for use in an offshore structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The invention will further be elucidated on the basis of exemplary embodiments which are represented in a drawing. The exemplary embodiments are given by way of non-limitative illustration.

(2) In the drawing:

(3) FIG. 1 shows a schematic top view of an offshore structure with cantilever and an embodiment of a skidding system with a fixed rotation shaft, with the cantilever in extended position;

(4) FIG. 2 shows a schematic top view of the embodiment of FIG. 1 with the cantilever in retracted position;

(5) FIG. 3 shows a schematic side view of an embodiment of an offshore structure with a skidding system with a fixed rotation shaft;

(6) FIG. 4 shows a schematic side view of an embodiment of an offshore structure with a skidding system with a fixed rotation shaft, mounted onto an elevated level;

(7) FIG. 5 shows a schematic top view of an embodiment of an offshore structure with a skidding system with a fixed rotation shaft with the cantilever in extended position;

(8) FIG. 6 shows a schematic top view of the offshore structure of FIG. 5 with the cantilever in longitudinal extended position;

(9) FIG. 7 shows a schematic cross-sectional view of the embodiment of FIG. 3 along the line A-A;

(10) FIG. 8 shows a schematic top view of an embodiment of an offshore structure with a skidding system with a virtual rotation axis with the cantilever in extended position;

(11) FIG. 9 shows a schematic top view of the offshore structure of FIG. 8 with the cantilever in longitudinal extended position;

(12) FIG. 10 shows a schematic side view of a supporting member;

(13) FIGS. 11a, 11b, 11c, 11d show a schematic side view (FIGS. 11a, 11b, 11c) of a deck rail being guided through a bottom part of a supporting member, as seen in the top view of FIG. 11d;

(14) FIG. 12a shows a schematic top view of an embodiment of a skidding system comprising two longitudinal cantilever rails and two forward positioned supporting members;

(15) FIG. 12b shows a schematic top view of an embodiment of a skidding system comprising two longitudinal cantilever rails with two forward positioned supporting members and a coupling member;

(16) FIG. 13a shows a detail of the forward supporting members of the embodiment of FIG. 12a having a fixed vertical rotation axis;

(17) FIG. 13b shows a detail of the forward supporting members with coupling member of the embodiment of FIG. 12b having a fixed vertical rotation axis;

(18) FIG. 13c shows an embodiment of supporting members with a floating rotation axis;

(19) FIG. 14 shows an embodiment of a supporting member of which a bottom part is engaged with a deck rail and a top part is engaged with a cantilever rail;

(20) FIG. 15 shows a schematic cross-sectional view of the rotating system of FIG. 16 along the line A-A;

(21) FIG. 16 shows a schematic top view of an offshore structure with an embodiment of a skidding system with the cantilever in a straight position, in which the centerline of the cantilever is aligned with the centerline of the platform, and in rotated position;

(22) FIG. 17 shows a side view of the offshore structure of FIG. 16;

(23) FIG. 18 shows a schematic top view of an aft side of the platform with the cantilever mounted thereon and an embodiment of a skidding system;

(24) FIG. 19a shows a schematic top view of an offshore structure with an embodiment of a skidding system with a curved aft deck rail and two curved forward deck rails around a virtual rotation axis, comprising skid units;

(25) FIG. 19b shows a schematic side view of the embodiment of FIG. 19b;

(26) FIG. 20a shows a schematic top view of an offshore structure with an embodiment of a skidding system with a curved aft deck rail and two curved forward deck rails around a rotation shaft with a coupling member, comprising skid units;

(27) FIG. 20b shows a schematic side view of the embodiment of FIG. 20b;

(28) FIG. 21 shows a schematic top view of a rack and pinion system as skid unit;

(29) FIGS. 22a and 22b show a schematic perspective side view and top view respectively of an embodiment of a forward curved deck rail with supporting member thereon and a portion of the cantilever rail;

(30) FIGS. 23a and 23b show a schematic perspective side view and top view respectively of an embodiment of an aft curved deck rail with a supporting member thereon and a portion of the cantilever rail;

(31) FIGS. 24a and 24b show a schematic top view and side view respectively of an embodiment of a skid shoe;

(32) FIGS. 25a, 25b, 25c show a schematic top view of a skid shoe having adjustable guide elements;

(33) FIG. 25d shows a schematic perspective view of the skid shoe of FIGS. 25a, 25b, 25c.

(34) It is noted that the figures are only schematic representations of embodiments of the invention that are given by way of non-limiting example.

(35) Various modifications, variations, and alternatives are possible, as well as various combinations of the features described. The specifications, drawings and examples are, accordingly, to be regarded in an illustrative sense rather than in a restrictive sense.

(36) In general, the skidding system 1 for moving a cantilever 2 with respect to a deck 3 of a platform 4, such as a vessel or a jack-up, comprises one or more guides on a deck 5, also called deck rails 6 for directing movement of supporting members 7 with respect to the deck 5. The deck rails 6 can be positioned on either side, forward or aft, of the point of rotation C of the cantilever 2. The cantilever 2 itself is at its bottom side provided with longitudinally extending guides or cantilever rails 8. In the embodiments shown here, the offshore structure 9 comprises a platform 4, a cantilever 2, and three or four legs 10 that are adjustable with respect to the platform 4 in a well-known manner.

(37) The centerline of the platform 4 vessel is the X-direction. The Y-direction is perpendicular to the X-direction in the horizontal plane. The rotation axis extends in a vertical Z-direction, perpendicular to the deck plane of the X- and Y-direction.

(38) Further, the skidding system 1 for moving a cantilever 2 with respect to a deck 5 may comprise one or more supporting members 7, also called skidboxes, each interacting with at least one of the longitudinal rails 8 and at least one of said deck rails 6. Each supporting member 7 or skidbox comprises: an top part arranged to allow the cantilever 2 to move along the longitudinal rails 8 and/or to hold the cantilever in position; and a bottom part arranged to move along the deck rails 6.

(39) In the embodiments of FIGS. 1 and 2, a curved aft deck rail 6 is provided, whereas in the embodiments of FIGS. 5 and 6 a straight aft deck rail 6 is provided.

(40) Further, the supporting member 7 comprises holding means or clamping means to hold said rail which it interacts with, e.g. guide elements, or means provided to the said rail or guide to hold the supporting members/skidboxes it interacts with.

(41) In the embodiment of FIGS. 1-7, a connecting beam 11 is provided between placed apart supporting members 7 at one end of the cantilever 2, here the forward end, for example between the aft supporting members or between the forward skidboxes. Advantageously, as here in FIGS. 1-7, the skidboxes 7 are arranged on both sides of the point of rotation C of the cantilever 2. By providing a connecting beam 11, the supporting members 7 may be kept aligned and at the same distance with respect to each other. The connecting beam 11 may also take up reaction forces and/or other loads.

(42) The rotating system 12, in the embodiments of FIGS. 1-7 comprising a connecting beam 11, may have a fixed rotation point or rotation axis C, wherein a pivoting structure, such as a bearing 13, may be fixed to the deck 5 positioned at the point of rotation of the cantilever, e.g. at the crossing of centerlines of the cantilever and the connecting beam, to keep the supporting members 7 aligned with respect to the deck rails 6.

(43) A holding member is arranged to allow at least one supporting member 7 to move along the deck rail and/or cantilever rail and to hold the supporting member 7 in place in case vertical pulling loads are exerted to the supporting member 7, e.g. when the cantilever 2 is in extended position. The supporting member 7 can be arranged between the deck rails, e.g. as a connecting beam 11 or provided on a connecting beam 11, as to align movement of the supporting member 7 in the direction of the deck rail. The deck rail may be provided at its upper end with a stop member to prevent the supporting member from vertically unlocking of the deck rail 6, e.g. an upside-down T-shaped construction. Instead, the supporting member may be movable arranged over the deck rail 6.

(44) As shown in FIGS. 1-7, the rotating system 12 may comprise a forward located yoke or connecting beam 11, which is mounted on a centrally located bearing 13 having a vertical rotation axis C, wherein the bearing is fixedly mounted on the deck 5, as in FIG. 3, or on an elevated level of the deck 5, as in FIG. 4, of the jack-up. In its neutral position the yoke 11 is oriented in a transverse direction, and it can be rotated to an angle from this neutral position, by a rotation of the central bearing 13. The bearing 13 is centrally located with respect to the width of the cantilever, meaning approximately on the centerline of the cantilever 2.

(45) The width of the yoke 11 may be about equal to the width between the outermost edges of the longitudinal rails 8 fitted at the bottom of the cantilever, at least is sufficiently wide such that the longitudinal cantilever rails 8 can be supported onto the yoke 11. The yoke 11 has supports, for example embodied as skid-pads, for example embodied as supporting members 7, at both ends, which support the longitudinal cantilever rails 8. The cantilever rails exert a load on the supports, and the yoke 11 transfers these vertical loads from the supports to the centrally located rotating bearing 13. Skid units or actuating units can be fitted to the yoke at both ends, in line with the supports: these facilitate the longitudinal movement of the cantilever 2, by skidding the longitudinal rails over the supports of the yoke 11. Longitudinal means here that the skidding movement is along the centerline L of the cantilever 2, which is typically perpendicular to the yoke, regardless of the direction of the yoke which can be at an angle from its neutral position, in case the yoke 11 is rotated on the central bearing 13.

(46) By providing the supporting members 7 on a connecting beam 11, such as a yoke, alignment between the supporting members 7 on both sides of the point of rotation C of the cantilever 2 can be provided. This connecting beam 11 can hold the supporting members 7 in an aligned position with respect to each other and can keep them at an approximately fixed distance corresponding with the distance between the centerlines of the cantilever rails 8.

(47) In the embodiments of FIGS. 1-7, there are at least two supporting members 7 placed on a transverse deck rail 6 which is fixedly mounted on the aft end of the jack-up's or vessels hull. These supporting members 7 in turn support the longitudinal rails 8 of the cantilever 2.

(48) When the supporting members 7 on the aft deck rail 6 shift in transverse direction, the cantilever 2 will turn around its point of rotation C.

(49) In case of a straight aft rail 6, see e.g. FIGS. 5 and 6, so-called psi-skidboxes can be used as supporting member 7 between the aft deck rail 6 and the cantilever rails 8. In case of a curved rail 6, as in FIGS. 1-2, with a large enough radius, standard GustoMSC skidboxes can be used as supporting member. When the radius of the curved aft deck rail is smaller than the curvature that can be handled by the conventional XY-skid box, the bottom part of the XY-skidbox can be arranged to hold a curved rail by providing guide members with a corresponding radius. Modified skidboxes can be provided with curved and/or V-shaped guides. Such curved and/or V-shaped guides can allow sufficient play between the guide and the respective rail for the modified skidbox to take a curved rail and/or a deviated rail.

(50) In an embodiment, as shown in FIG. 1 or FIG. 2, a cantilever 2 is pivotally mounted on a deck 5 of an offshore structure 9. The cantilever 2 can rotate about a fixed vertical rotation axis C. In this example the cantilever is connected to the deck via a centrally located bearing 13 providing for a fixed physical rotation shaft. The centrally located bearing 13 is centrally located with respect to the width of the cantilever, meaning approximately on the centerline of the cantilever, as e.g. shown in FIG. 7. FIG. 7 shows a yoke 11 connected to the centrally located bearing 13. The yoke 11 is provided with supporting members 7 bearing the cantilever rails 8 of the cantilever 2.

(51) The centrally located bearing 13 can also be situated at another deck level than the aft skid boxes or even on top of any construction or housing on deck, as for example shown in FIG. 4. Advantageously, to allow for a freely usable main deck below the cantilever, the skidding system is arranged such that the underside of the cantilever is situated at a level about 3 to 4 meters above the main deck, see e.g. FIG. 3 or FIG. 4.

(52) In an embodiment, the rotation point or yoke can also be movable in a transverse or longitudinal direction to extend the reach of the cantilever. This can be achieved by providing additional means such as one or more transverse and/or longitudinal rails on deck and skidboxes between the yoke support and the deck rail.

(53) In the embodiment, as shown in FIG. 1 or FIG. 2, the transverse aft skid rail has a curvature with a radius R1 equal to the distance from the rotation axis C formed by the centrally located rotation bearing 13. The sufficiently large distance between the aft rail and rotating point results in reduced (pulling) loads on the rotating point and respective skidboxes. When the rail has a sufficiently large radius, the curvature can be handled by conventional skid boxes.

(54) When the radius of the curved aft skid rail is smaller than the curvature that can be handled by the conventional XY skidbox, the bottom part of the XY-skidbox can be arranged to hold a curved rail by providing guide members with a corresponding curvature.

(55) The curved rail is especially advantageous for use on a ship shaped jack up, as shown in FIGS. 1 and 2. On a jack-up rig a straight rail located on the aft transom can be more preferable, see FIGS. 5 and 6. In this case the top parts of the skid boxes 7 cooperating with the cantilever rails 8 are arranged to allow the cantilever rail to have a negative or positive angle deviating from the centerline of the top part of the supporting member 7. Alternatively and/or additionally, instead of the top parts, the bottom parts of the skidboxes can be arranged to allow the transverse deck rails 6 to enter at an angle deviating from the centerline of the lower part of the supporting member. Also, both the top and bottom parts of the skidboxes 7 can be arranged to allow the respective cantilever rail 8 to adjust to an angle deviating from the respective centerlines. Also, both the top and bottom parts of the skidboxes can be arranged to allow the respective cantilever rail to adjust to an angle deviating from the respective transverse rail.

(56) In another embodiment, see FIGS. 8-9, the forward yoke may be omitted and two placed apart skidboxes 7 may be provided instead. These placed apart skidboxes are at a top side arranged to couple with the cantilever rails 8 and can be at a bottom part arranged to couple with a deck-rail or -rails. These deck-rail(s) may have a linear/straight configuration and may be oriented transverse with respect to the cantilever rails, or may be curved with an orientation substantially transverse to the cantilever rails as well. The curved rails preferably have a radius R1 with a center at a fixed rotation point C on the deck 5. Then, rotation of the cantilever around this rotation point may be facilitated. To accommodate reaction forces and other loads, a connecting beam may be provided between the two placed apart forward skid boxes, if necessary.

(57) When using two placed apart skidboxes at the forward end of the cantilever coupling with transverse deck rail or rails at the lower end and longitudinal cantilever rails at the upper end, the cantilever can rotate and translate without a fixed rotation point, i.e. a floating rotation point, as in FIGS. 8 and 9.

(58) By providing a rotation system with two placed apart supporting members, there is no fixed pivoting axis required, so contrary to the prior art, there is no single point on deck that needs to take up all the load. Instead, now there may be an even load distribution over the support elements, which improves the load transfer to the hull construction.

(59) Further, in some embodiments it may be advantageous to provide the underside of the cantilever relatively close to the deck, as to improve the stability of the vessel or jack-up during transit. By providing such a rotating system, a relatively low free height between deck and underside cantilever may be possible. Thereto, a supporting member with a relatively low height, see e.g. in FIG. 14, can be provided.

(60) When providing three or four supporting members as shown in e.g. FIG. 8 and FIG. 9, the cantilever may be rotated in the absence of a centrally located rotation point or rotation bearing, but with a floating rotation point instead. By providing here supporting members 7 according to the invention, with a top part having a guide element engaging the cantilever rail and a bottom part having a guide element engaging the deck rail, wherein the top part and/or the bottom part are configured to allow off-centerline movement of the rail engaged therein, rotational movement of the cantilever with respect to the deck can be facilitated. In an embodiment, the top part guide element and the bottom part guide element having an oblique angle with respect to each other, movement of the cantilever over these deck rails becomes possible with much simpler and lighter supporting members as opposed to the prior art supporting members. Contrary to the prior art supporting members that comprise a hinge between the top part and the bottom part such that, upon movement of the cantilever, the top part pivots with respect to the bottom part, providing for a complex and heavy supporting member. According to the invention, rotation of the cantilever can e.g. be achieved by moving the supporting members 7 on the aft deck rail over a different distance than the supporting members 7 on the forward deck rail. The top and/or bottom part of the supporting members are configures to allow off-centerline movement of the respective rail to the top and/or bottom part respectively. By allowing such off-centerline movement, rotation of the cantilever with respect to the deck can be obtained. The angles between the transverse rails on deck and the longitudinal rails of the cantilever are taken up by the supporting members 7, preferably the angle is equally divided over the respective supporting members 7. Active and/or passive controls can be used to control the supporting members 7.

(61) Since the cantilever has, in this embodiment of FIGS. 8-9, no fixed pivoting point, there is no predetermined rotation axis. Depending on the position of the cantilever, the position of the rotation axis can be different. The rotation axis can then be said to be floating.

(62) FIGS. 10 and 11 show a supporting member 7 allowing the cantilever rail 8 or a deck rail 6 to have a centerline deviating from the centerline of the top part 7a and the bottom part 7b. Typically, such a supporting member 7 has no pivoting mechanism and can rotate around a Z-axis transverse to the plane of the cantilever and/or deck rails. The Z-axis can typically be a vertical axis. By providing such a supporting member 7, rotating movement of the cantilever 2 can be accommodated on a straight aft transverse deck rail 6 and with straight longitudinal cantilever rails 8, or on a curved aft transverse deck rail 6 with straight longitudinal cantilever rails 8.

(63) The supporting members 7 can be arranged to allow a cantilever rail 8 to enter at a deviating angle by providing a curved guiding element 15 alongside at least one side, preferably alongside both sides, of the rail, each guiding member comprising an arc shape or e.g. a V-shape which is close to the rail at its middle and flaring further outwardly from the rail at its ends of the supporting member 7. The cylinders of the skid unit, connected thereto are suitably arranged to be able to push or pull the rail through the upper or bottom part of the supporting member 7 in a direction deviating from the centerline of the supporting member 7. The curved guide elements 15 can be provided on the top part of the supporting member 7 to guide the cantilever rail 8, and/or can be provided on the bottom part 7b of the supporting member to guide the deck rail 6. See FIG. 10 and FIGS. 11a, 11b, 11c, and 11d.

(64) Active or passive control may be provided to make sure the deviating angle between the two deck rail and cantilever rail is taken up by both the top part and the bottom part of the supporting member, preferably in an evenly distributed manner.

(65) By providing curved and/or V-shaped guides, sufficient play in the system can be allowed to have the supporting member rotating up to an angle of approximately 5 to 10 degrees, to one side, for example 7.5 degrees, with respect to a straight deck rail or straight cantilever rail. By providing such a guide element 15 both at the top part and at the bottom part of the supporting member 7, play is allowed to accommodate rotation with respect to the deck rail as well as with respect to the cantilever rail, allowing a maximum rotation of the cantilever with respect to the deck of for example 15 degrees, i.e. twice the 7.5 degree for each guiding element. In an embodiment, the upper and lower curved guiding member 15 may be coupled, e.g. hydraulically, to provide for rotation on the upper and lower guide member in the same direction.

(66) In another embodiment, FIG. 12a shows the longitudinal rails 8 on the bottom side of a cantilever 2 with two supporting members 7 placed apart at the forward end of the cantilever 2. FIG. 13a shows a detail of FIG. 12a with forward supporting members 7 with skid-units 16, i.e. actuating units, for actively moving the cantilever 2 in its longitudinal direction.

(67) FIG. 12b shows also the longitudinal rails 8 on the bottom side of a cantilever 2 with two supporting members 7 placed apart at the forward end of the cantilever 2, but with a connecting beam 11 between the two placed apart skidboxes/supporting members 7. FIG. 13b shows a detail of the skidboxes 7 with the connecting beam 11 and FIG. 15 shows a cross-section view thereof along the line A-A in FIG. 16. In the example of FIGS. 13a and 13b the cantilever 2 has a virtual rotation axis C which position is fixed with respect to the deck 5 of the vessel 4. The connecting beam 11 allows the skidboxes 7 to be placed apart and to take up loads. The connecting beam 11 can also be connected to the deck. The connecting beam can be connected to the deck at a fixed pivoting point. In this example the connecting beam is connected to the deck via a curved forward rail 17 having its center point C at the rotation point C of the cantilever 2. So, here the cantilever 2 has a rotation axis C fixed with respect to the vessel or jackup, as the cantilever 2 itself may also move in its longitudinal direction. However, by providing the placed apart skidboxes, the loads are divided and the pivoting shaft, such as a bearing 13 or the forward curved rail 17, does not have to take up all loads, thus allowing for a better load distribution to the deck and/or the hull of the vessel.

(68) As can be seen in FIGS. 13a and 13b, the guides between which the bottom part of the skidbox are arranged, are curved with a radius of a circle having its center point at the rotation point of the cantilever. Here, the supporting members have skid unit 16 at the top part, thus also providing actuation of the cantilever with respect to supporting member 7 (and vice versa).

(69) It will be appreciated that the supporting member shown in FIG. 15 may be used on the rotating system of FIG. 12a.

(70) FIG. 13c shows an example wherein the supporting members 7 are not placed on curved rails, but e.g. on straight longitudinal rails. Since the cantilever has no fixed pivoting point, there is no predetermined rotation axis, and depending on the position of the cantilever, the position of the rotation axis is thus different. The rotation axis can then be said to be floating.

(71) In an embodiment of the rotating system, shown e.g. in FIGS. 13a and 13b, there are two curved deck rails 6. Here, the radius R2 of the centerline of each curved deck rail 6 corresponds with the distance of the centerline of the deck rail to the point of rotation C of the cantilever. The deck rails 6 are positioned to both sides of the cantilever 2, such that the radial centerlines of the deck rails (at the middle of the deck rail) are in line with each other, crossing the point of rotation of the cantilever, and substantially perpendicular to the centerline of the vessel or jack-up. In this embodiment both deck rails may extend for at least 10 deg to both sides of their radial centerline.

(72) The deck rail 6 may have the form of an upside-down T-shaped track, with side walls fixed on the deck and top plates forming a slot along the centerline of the guide, as e.g. shown in FIG. 14. The deck rail 6 can have a bottom plate or can use the deck surface 5 as the bottom plate. Inside, the deck rail is preferably be provided with sliding elements, preferably sliding bearings. Sliding elements are provided at least at one side wall and the bottom surface. The top plates hold the supporting member 7 in place when pulling loads occur. By providing such a deck rail structure, the height of the supporting member 7 can remain relatively limited. Alternatively, the deck rail 6 can be embodied as a T-shaped rail over which the bottom part of the supporting member can hold or clamp.

(73) The supporting member 7 can have a compact construction, with a base plate 17 at its bottom part 7b which interacts with and is received by a recess provided by a deck rail 6, see FIG. 14. This base plate 17 extends under the top plates of the deck rail 6, such that the top plates can hold the supporting member in place. The base plate 17 can have the same curvature as the deck rail 6. On top of the base plate 17, the top part 7a of the supporting member 7 is provided, in this embodiment consisting of side walls 18 with top rims 19. Inside, this top part 7a has sliding elements, preferably sliding bearings. Sliding elements are provided at least at the side walls 18 and on the top surface of the base plate 17. The rims 19 partly enclose the rail 8 of the cantilever to hold the cantilever 2 in place in case of pulling loads.

(74) The longitudinal movement of the cantilever can be effectuated by the aft supporting members 7. The top part 7a of the forward supporting members 7 then allows a cantilever rail to move through.

(75) The supporting member 7 of FIG. 14 is a compact and passive version provided in/between the deck rail 6 at its bottom part 7b and holds the cantilever rails 8 on the top part 7a. As such, the supporting member 7 has a relatively low height, allowing for limited free height between deck 5 and cantilever 2. Here, the supporting member 7 itself is not actuated, and thus is following the movement induced by the actuated aft supporting members. The supporting member shown in FIG. 14 may e.g. be used in the rotating system of FIG. 13a, 13b or 13c.

(76) FIG. 16 and FIG. 17 show a general arrangement of a cantilever 2 with a rotating system on a vessel 4 having an aft deck rail 6 placed transverse at the aft end of the vessel 4 on which at least two supporting members 7 or skidboxes are placed. Here, a cantilever 2 is shown with a fixed rotation axis C at the position of the physical pivoting point. Advantageously, the pivoting point C is located on the centerline X of the vessel and on the centerline L of the cantilever. At the forward end, two curved deck rails 6 are provided in which the bottom part 7b of the supporting members 7 can be received. The top parts 7a of the supporting members 7 are clamped around and hold the rails 8 underneath the cantilever to allow movement of the cantilever 2 in longitudinal direction of the cantilever. The cantilever 2 can rotate around the fixed pivoting point that is fixed with respect to the deck 5.

(77) In another embodiment, it is also possible to use one supporting member 7 on the aft deck rail 6, providing sufficient load bearing capacity for the cantilever 2, or to use two or more skidboxes connected to each other to form a single part.

(78) In another embodiment, an additional reaction arm may be provided to counteract reaction forces (axial to the cantilever), e.g. by means of said pivoting point or an arm on said beam, the arm being arranged to transfer reaction forces to an additional (curved) guiding element fixed on deck. Instead of the fixed rotation axle, an alternative reaction arm can be provided to counteract the reaction forces. The reaction arm is fixed to the connecting beam and cooperates with an additional reaction arm fixed on deck. This way the reaction forces can be distributed over a larger area. The additional reaction arm can be curved, such that when the reaction arm follows this reaction arm, the connecting beam rotates around the desired point of rotation C of the cantilever 2. This way the fixed rotation axle is not needed.

(79) The connecting beam 11 may further be provided with additional arm(s), possibly integrated with the connecting beam construction, extending transversely with respect to the beam. One end of the arm may be connected to said beam 11 or directly to the supporting member 7 and the other end of the arm may be, e.g. slidably, connected to a rail of the cantilever at a distance from the supporting member, thereby arranged to keep the supporting member aligned to said rail of the cantilever while moving and to align the supporting member 7 with the deck rails for smooth operation.

(80) Further improvement of the alignment of the supporting members 7 to the cantilever rails 8 can be achieved by providing a fixed pivoting point at the point of rotation of the cantilever, as in the embodiments of FIGS. 1-7. The radial centerlines of the supporting members 7 coincide with the centerline of the connecting beam 11. The centerline of the connecting beam 11 crosses the centerline L of the cantilever 2 at its point of rotation C. At this position a fixed rotation axle or shaft, e.g. a bearing 13, can be provided between the connecting beam 11 and the deck 5. With a fixed rotation point C and the connecting beam 11, the supporting members 7 may be optimally aligned and positioned with respect to the cantilever rails 8.

(81) There may be no or limited vertical load on the fixed rotation point or axle, as the load of the cantilever 2 may be distributed over the supporting members 7. The fixed rotation axle 13 can counteract reaction forces (axial to the cantilever) caused by the skidding forces. These reaction forces can otherwise result in displacement or misalignment of the supporting members.

(82) As a result of the rotation of the cantilever 2, each supporting member 7 will be forced to follow the respective deck rail 6 and align with the respective cantilever rail 8. A relatively large force is transferred locally through the guiding parts of the supporting member 7. When the additional reaction arms are used, force is transferred through the connecting beam 11 or directly to the supporting member 7. At the position of the slidable connection of an arm to a cantilever rail, less force is needed to create sufficient moment to align the supporting member 7. Also, with such a reaction arm in place, movement of a cantilever rail 8 around the point of rotation C of the cantilever 2 may result in a more direct actuation of the supporting member 7. The rail pushes directly against the slidable connection, which directly acts on the connecting beam 11 or the supporting member 7 itself. Play between the guiding parts of the supporting member and rail does not have to be overcome first.

(83) Instead of the additional reaction arm, the cylinders of the skid unit or actuation unit of the supporting member, on the top part of the supporting member, can be locked and used as a lever to align the supporting member 7.

(84) A supporting member can also be specifically arranged for the purpose of the configuration shown in FIG. 18. The configuration of FIG. 18 shows a rotating system having two curved deck rails 6 that are arranged in symmetric fashion with respect to the X-direction of the platform and that have an oblique angle with respect to the Y-direction. The aft deck rail 6 is arranged substantially transverse to the X-direction and is curved having a radius of curvature R1 from the center of rotation C to the centerline of the deck rail 6. The pair of curved forward deck rails 6 have a radius of curvature R2, from the center of rotation C. The angle denotes the angular position of the radial centerline of a forward curved deck rail 6 (from the middle of the deck rail 6 through the point of rotation C of the cantilever) with respect to the Y-axis. In FIG. 18 both forward curved deck rails 6 are positioned forward of the (virtual) rotation point C of the cantilever 2. In this example the angle is approximately +30 degrees. The angular extent of the forward curved guide in this example is approximately 20 degrees (+/10 degrees relative to the radial centerline). More in general the angular extent of the forward curved guides can e.g. be between 10 and 45 degrees. The angle alpha can be between approximately 5 degrees and approximately 50 degrees, preferably between approximately 10 and approximately 45 degrees, or preferably around 30 degrees.

(85) To accommodate this configuration, the bottom part 7b of the supporting member 7, can have a centerline with a radius corresponding to R1 or R2 of the curved rail segment, and is arranged to travel along the curved deck rail 6. The top part 7a of supporting member 7 can be arranged to receive and hold a cantilever rail 8 and to allow the cantilever 2 to move through in the longitudinal direction of the cantilever 2.

(86) In FIG. 18 the cantilever 2 is shown in a position pivoted over an angle with respect to the X-direction.

(87) In the embodiments of FIGS. 19a, 19b, 20a, 20b, forward curved deck rails 6 under an oblique angle are provided and a curved aft deck rail 6. In the embodiment of FIG. 20a, 20b, further a connecting beam 11 is provided between the forward curved deck rails 6. The aft supporting members 7 are provided with skid-units 16. The skid units 16 at the top part 7a of the supporting member 7 effectuate the longitudinal movement of the cantilever 2. The skid units 16 at the bottom part of the supporting member 7 effectuate the transverse movement of the cantilever 2, at the location of the aft deck rails. This results in an augmented transverse shift at aft end of the cantilever extended over the stern of the vessel 4, while at the same time the transverse movement at the location where the jackhouses with legs 10 are located, is reduced. This reduction is dependent on the relative lengthwise location of the jackhouses 20 of the legs 10 between the aft deck rails and the forward located rotation bearing 13.

(88) Typically, the skid unit 16 comprises the parts for moving the rail. Thereto the skid unit 16 can include a yoke and (hydraulic) cylinders. The skid unit can be configured with hydraulic cylinders in combination with pin/hole connections with the holes in the rail or gripper systems clamping on the rail. Alternatively, or additionally, the skid unit 16 can have an associated rack and pinion system. The pinion can be part of the skid unit 16. The rack can be part of, or associated with, the respective rail. This rack and pinion system can be electric or hydraulic or air driven or any other power source.

(89) The top part 7a of the supporting member 7 can be configured with a skid unit 16 for actively effectuating longitudinal movement of the cantilever 2 with respect to the supporting member 7. This may reduce the required force which has to be delivered by the aft supporting member 7 and may improve smooth operation.

(90) Rotation of the cantilever 2 can be effectuated by moving the aft supporting members 7 in a transverse direction, i.e. in Y-direction. The aft supporting members 7 will then have to allow or actuate the rail 8 of the cantilever to move with respect to the supporting member 7. The transverse movement will turn the cantilever around the point of rotation. Each rail will push the respective forward supporting members to follow the respective guide.

(91) The top part 7a of an aft supporting member 7 can be configured with a skid unit 16 for actively effectuating movement of the cantilever. The top part can also be configured without skid unit. The movement of the cantilever may then have to be induced by other actuating means, such as the forward supporting members.

(92) The bottom part 7b of an aft supporting member can be configured with a skid unit for actively effectuating transverse movement of the supporting member 7 along the aft deck rail, resulting in the rotational (Psi-direction) movement of the cantilever 2.

(93) Optionally, the aft supporting members are provided with skid units. Optionally, the forward supporting members are provided without skid units.

(94) The bottom part 7b of the supporting member 7 can be provided with a skid unit 16 to actively move the supporting member 7 with respect to the deck rail 6. This may reduce the required force which has to be delivered by the aft supporting member and may improve smooth operation.

(95) The skid unit 16 at the top part of an aft supporting member effectuates the longitudinal movement of the cantilever, along the X-direction.

(96) The deck rails 6 can be equipped with guiding elements on the side walls to take up the reaction forces and associated friction which occurs when the cantilever pushes the supporting members along the deck rails, either in a forward or aft direction. These forces can vary par rail or per side, possibly resulting in misalignment of the supporting members.

(97) The transverse deck rail can be curved, e.g. having a radius of curvature corresponding to the distance between the transverse skid rail and the rotation axis of the cantilever. Conventional supporting members can be used on such curved rail if the radius of curvature is large enough. If the radius of curvature is smaller, modified supporting members can be used, arranged to receive curved rails with a smaller radius.

(98) The transverse skid rail can be straight. It will be appreciated that an angle between the transverse deck rail and the cantilever rails can vary depending on a rotation of the cantilever relative to the deck. Modified supporting members, according to the invention, can be used to take rails under such deviating angles (herein also referred to as psi-skidbox).

(99) The supporting member can be provided with curved and/or V-shaped guide elements for receiving a rail. Such curved and/or V-shaped guide elements can allow sufficient play between the deck rail and the respective rail for the supporting member to take a curved rail and/or a deviated rail.

(100) Alternatively, the forward curved guides 6 can be positioned aft of the (virtual) rotation point of the cantilever. This is for example shown in FIG. 19a in top plan view. FIG. 19b shows a side view of the construction in FIG. 19a. In this example the angle is approximately 30 degrees. The angular extent of the forward curved guide in this example is approximately 20 degrees (+/10 degrees relative to the radial centerline). More in general the angular extent of the forward curved guides can e.g. be between 10 and 45 degrees. The angle alpha can be between approximately 5 degrees and approximately 50 degrees, preferably between approximately 10 and approximately 45 degrees, or preferably around 30 degrees.

(101) FIG. 20a shows an example of a top plan view similar to that shown in FIG. 19a. FIG. 20b shows a side view of the construction in FIG. 20b. In this example the forward supporting members are connected through a connecting beam 11. It is noted that such connecting beam is also shown in FIG. 13b. In order to further improve the alignment or the supporting members, a rotation axle or shaft fixed to the deck can be provided. This fixed rotation axle and possibly an additional reaction arm can further assist in counteracting the reaction forces. The connecting beam 11 may further be provided with additional arm(s), to transfer the pushing force of the cantilever rail, which occurs when supporting members on the aft deck rail 6 move in transverse direction, directly to the supporting member 7.

(102) FIG. 21 shows an example of a skid unit 16 using a rack and pinion system. In this example both the transversal deck rail 6 and the cantilever deck rail 8 have a rack 21 associated therewith. The supporting member 7 has two skid units 16 attached thereto. The skid units 16 comprise pinions 22 cooperating with the respective racks 21. It will be appreciated that the rack and pinion systems can also be viewed in FIGS. 19a, 19b, 20a and 20b. In those examples each skid units 16 includes four pinions 22.

(103) FIG. 22a shows a first view of an example of a forward curved deck rail 6. The forward curved deck rail 6 is formed as a generally T-shaped rail. On top of the forward curved deck rail 6 is a forward supporting member 7. The forward supporting member 7 is provided with a bottom part 7b which is arranged to cooperate with the curved deck rail 6. The forward supporting member 7 comprises a bottom guide element 23 grips around a top portion of the forward curved deck rail 6 so as to prevent lifting the supporting member 7 off the deck rail 6. On top of the forward supporting member is a cantilever rail 8. The top part 7a of the forward supporting member 7 has a guide element 24 is arranged to receive and hold a cantilever rail 8 and allow the cantilever 2 to move through in the longitudinal direction of the cantilever 2. The forward supporting member 7 grips around a bottom portion of the cantilever rail 8 so as to prevent lifting the cantilever rail off the supporting member 8. FIG. 22b shows a second view of the example shown in FIG. 22a. The bottom guide element 23 and the top guide element 24 have an oblique angle with respect to each other allowing for longitudinal and angular movement of the cantilever with respect to the deck.

(104) The bottom part 7b, including the guiding element 23, can have a centerline with a radius corresponding to R2 of the curved rail segment 6, and arranged to travel along the curved deck rail. This bottom part 7b can have one or more curved guiding elements, with a curvature corresponding with R2, extending alongside at least one, in this example alongside both sides, of the rail 6. The top part 7a can be configured with a skid unit 16 for actively effectuating movement of the cantilever (not shown).

(105) FIG. 23a shows a first view of an example of an aft curved deck rail 6. The aft curved deck rail 6 is formed as a generally T-shaped rail. On top of the aft curved deck rail is an aft supporting member 7. The aft supporting member 7 is provided with a bottom part 7b having a guide element 23 which is arranged to cooperate with the curved deck rail 6. On top of the aft supporting member is a cantilever rail 8. The top part 7a of the aft supporting member 7 is arranged to receive and hold a cantilever rail 8 and allow the cantilever 2 to move through in the longitudinal direction of the cantilever. FIG. 23b shows a second view of the example shown in FIG. 23a.

(106) The bottom part 7b, including the guiding elements 23, can have a centerline with a radius corresponding to R1 of the curved guide or curved rail segment, and arranged to travel along the curved deck rail. This bottom part 7b can have one or more curved guiding members, with a curvature corresponding with R1, extending alongside at least one, in this example alongside both sides, of the rail or guide. When the radius R1 is sufficiently large, the bottom part can also have straight guiding elements 23. The upper and bottom part 7a, 7b can be configured with a skid unit for actively effectuating movement of the cantilever (not shown).

(107) It will be appreciated that in FIGS. 23a and 23b the supporting members 7 have eyes 25 to which the skid units can be attached (also see FIG. 21).

(108) It is also possible that the forward rotating system includes or consists of two skid shoes 26, see FIGS. 25a-25d. The two skid shoes 26 can be placed apart and fixed to the deck 5 at a distance corresponding with the distance between the cantilever rails 8. The skid shoes 26 therefore are immobile relative to the deck 5.

(109) The skid shoes 26 can be at an equal distance from the longitudinal centerline of the vessel or jackup 4. The centerline of the skid shoe 26 can be parallel to the centerline of the vessel or jack-up. Each skid shoe 26 is arranged to support a cantilever rail 8 and allow it to move through in a longitudinal direction. The skid shoes 26 can be combined with any aft supporting system described herein.

(110) FIGS. 24a and 24b show a top plan view and front view of an example of a skid shoe 26, respectively. The skid shoe 26 forms a guide element 24 as an upside down T-shaped track, with side walls 27 fixed to a bottom plate 28 or directly to the deck and top plates 29 forming a slot along the centerline of the shoe 26. This shoe is provided with sliding elements 30, such as sliding bearings, at least at one side wall 27 and the bottom surface 28.

(111) The forward skid shoes 26 are in a fixed position, which means the cantilever rails will move through the skid shoes but cannot move sideways at the position of the skid shoe, resulting in the cantilever 2 having an angle deviating from the centerline of the skid shoe 26. Therefore, the skid shoe 26 is arranged to prevent locking of the rail 8 in the skid shoe 26 due to skewing if the cantilever rail 8 deviates relative to the skid shoe center line. The skid shoe 26 can therefore be arranged to allow the cantilever rail 8 to have an angle deviating from the centerline of the skid shoe by providing sufficient play between rail 8 and guiding elements 15 and by providing a curved guiding element 15 alongside at least one side, preferably along both sides, as can be seen in FIG. 24a.

(112) FIGS. 25a, 25b, 25c and 25d show an example of a skid shoe including includes hinged guiding elements 15 for guiding the cantilever rail. In this example the skid shoe includes two opposed hinged guiding elements 15. It will be appreciated that it is also possible that the skid shoe includes a single hinged guiding element. The hinged guiding elements are arranged for rotation about a vertical axis. The hinged guiding elements can rotate in a plane parallel to the deck around a vertical rotation axis E.

(113) The hinged guiding element 15 provide a larger supporting surface along the longitudinal direction of the cantilever rail 8. When the cantilever rail makes an angle relative to the skid shoe center line, the hinged guiding elements will rotate to accommodate rotation of the cantilever rail. Thereby, sideways forces are transferred to the skid shoe (also) via the hinged guiding elements 15. As can be seen in FIG. 25d, the part of the skid shoe overhanging part of the cantilever rail so as to prevent uplifting of the cantilever rail is shorter than the hinged guiding elements in longitudinal direction of the cantilever rail. The angle can be between approximately 0 and approximately 20 degrees, preferably around 5 degrees.

(114) In another embodiment the rotation point E is close to the edge of the platform and/or the skidboxes are on an inwardly placed skidding beam.

(115) Instead of using skid boxes as supporting members for the cantilever also bogie wheels can be used. Bogie wheels, for example of the type with curved contact surfaces as described in WO98/31585, are especially suitable for curved rails. During transit the bogie wheels can be sea fastened.

(116) Herein, the invention is described with reference to specific examples of embodiments of the invention. It will, however, be evident that various modifications and changes may be made therein, without departing from the essence of the invention. For the purpose of clarity and a concise description features are described herein as part of the same or separate embodiments, however, alternative embodiments having combinations of all or some of the features described in these separate embodiments are also envisaged.

(117) For instance, it will be appreciated that any forward rotating system disclosed herein can be combined with any aft supporting system disclosed herein.

(118) For the purpose of clarity and a concise description features are described herein as part of the same or separate embodiments, however, it will be appreciated that the scope of the invention may include embodiments having combinations of all or some of the features described.

(119) The word comprising does not exclude the presence of other features or steps than those listed in a claim. Furthermore, the words a and an shall not be construed as limited to only one, but instead are used to mean at least one, and do not exclude a plurality. The mere fact that certain features are recited does not indicate that a combination of these features cannot be used to an advantage.

(120) Many variants will be apparent to the person skilled in the art. All variants are understood to be comprised within the scope of the invention.