[0001] This disclosure relates generally to the field of movable cantilever load support devices. More particularly, the disclosure relates to cantilever load support devices that can move longitudinally and rotate on order to be able to position a supported load at any position within an arcuate section.

[0002] The present description is made in terms of supported loads such as mobile offshore drilling units. However, it should be clearly understood that devices according to the present disclosure are not limited to use with offshore drilling units.

[0003] Mobile offshore drilling units, for example, bottom supported "jackup" drilling units are known in the art to have a subterranean well drilling unit supported on a barge hull over an opening in the hull (or beyond the end of the hull) to a body of water below using a cantilever support. Cantilever supports known in the art are designed to "skid" or extend in one direction by using toothed racks formed into the cantilever side rails engaged with motor operated pinion gears attached to the barge hull or to the supported load (i.e., the drilling unit). During transport of the barge to a drilling location, the cantilever may be retracted so that the drilling unit is disposed within the exterior profile of the hull, so as to balance the buoyant load in the water. When the barge is positioned proximate the drilling location, the cantilever may be longitudinally extended so that the drilling unit is positioned over the body of water. Some barge hulls include an opening, such as a "C" shaped recess in the side of the hull to enable the drilling unit to be positioned over the water without unduly extending the cantilever. Other barge hulls may not have such opening; in such circumstances the cantilever may be extended such that the drilling unit is positioned beyond the edge of the hull and over the water.

[0004] One type of cantilever load support system known in the art may be configured to move in one direction, that is, to extend and retract longitudinally. Such cantilever support systems may further include a provision for moving the cantilever transversely to the longitudinal direction to more precisely position the drilling unit over the water. Other types of cantilever load supports may be disposed on arcuate tracks to enable rotation of the entire cantilever such that the load, e.g., the drilling unit, may be moved more readily in two directions for precise positioning over the water. The latter type of cantilever load support is known to occupy a relatively large portion of the deck space on the hull, thereby limiting the available space on the hull deck for storage of other materials and equipment. Other types of cantilever support systems provide separate apparatus to move the cantilever longitudinally and move it transversely along its entire length.

Brief Description of the Drawings

[0005] FIGS. 1, 2 and 3 show various views of a cantilever lateral skidding mechanism.

[0006] FIGS. 4 through 7 show various views of a cantilever longitudinal extension mechanism.

[0007] FIG. 8 shows a plan view of the cantilever in the longitudinally retracted position.

[0008] FIG. 9 shows a plan view of the cantilever in the longitudinally extended position and skidded in one direction.

[0009] FIG. 10 shows a drilling unit supported on the cantilever.

Detailed Description

[0010] A cantilever skidding according to the present disclosure may take the form of a pair of parallel, longitudinal rails either or each of the rails having a longitudinal extension mechanism coupled thereto. Each of the longitudinal rails may be supported by a rail support, e.g., in a guide plate, to transfer torque created by supporting a load at one end of the cantilever to a load support base, for example and without limitation a barge hull on a mobile offshore drilling unit. The longitudinal rails may be maintained at a fixed distance from each other by an end beam coupled between or proximate to respective longitudinal ends of each of the longitudinal rails. The longitudinal rails may each be on one lateral side of the cantilever in some embodiments. In some embodiments, the longitudinal rails may be on the bottom of the cantilever. [0011] In one embodiment, the longitudinal extension mechanism(s) may comprise a toothed rack coupled to one or each longitudinal rail. The toothed rack(s) on the one or each of the longitudinal rails may engage a respective drive unit, for example, at least one pinion gear driven by a motor, e.g., an electric, hydraulic or pneumatic motor. The drive unit(s) may be pivotally coupled to the load support base such that they can rotate and translate positionally about the load support base. Such rotational and translational movement of the drive unit(s) enables the entire cantilever to rotate about an axis proximate to the drive units (when the skidding mechanism is operated) and to be extended and retracted longitudinally by the drive units. In one embodiment, translational motion of the drive units may be obtained by forming an elongated slot in a load support surface into which a support pin for each drive unit is disposed. The elongated slot may be linear and oriented substantially transversely to a direction of the cantilever when the cantilever is rotationally oriented in a center of rotation (explained below). In some embodiments, the elongated slots may be arcuate. In such embodiments, the elongated slots enable the cantilever to rotate relative to the load support surface while maintaining full contact between the guide plates and the longitudinal rails as the cantilever is rotated.

[0012] FIG. 1 shows an example embodiment of a lateral skidding mechanism 10 that may be used with a cantilever according to the present disclosure. The lateral skidding mechanism 10 includes a skidding rack 12 having gear teeth 14 thereon. The skidding rack 12 may be positioned proximate a longitudinal end of the cantilever (see FIG. 8) when the cantilever (see FIG. 8) is longitudinally retracted, and may be coupled to one of the longitudinal rails 22 of the cantilever by a guide plate 16 that captively retains an upper surface of the longitudinal rail 22. The guide plate 16 may be coupled to or form part of a skidding gear frame 18. One or more pinion gears 20 may be rotationally affixed to the skidding gear frame 18. The pinion gear(s) 20 may be rotated by a motor (not shown for clarity), such as an electric motor, an hydraulic motor or a pneumatic motor. Operation of the motor (not shown) rotates the pinion gear(s) 20 thus causing longitudinal movement of the skidding mechanism 10 with respect to the skidding rack 12. Because one of the longitudinal rails 22 of the cantilever (FIG. 8) is captured within the guide plate 16, such movement of the skidding mechanism 10 causes corresponding movement of the rail 22 along the rack 12.

[0013] The described lateral skidding mechanism is only one example of such a mechanism. In other embodiments, the skidding gear frame 18 may be coupled to, for example, an hydraulic cylinder or a ram in an hydraulic cylinder with the opposite longitudinal end of such device coupled to the load support surface (see FIG. 10). In other embodiments, the skidding gear frame 18 may be coupled to a worm gear/ball nut combination, wherein an opposite end of such combination is coupled to the load support surface (see FIG. 10).

[0014] FIG. 2 shows an end view of the longitudinal rail 22 disposed in the guide plate

16 proximate the skidding rack 12. The longitudinal rail 22 may be coupled to a laterally adjacent longitudinal rail (see FIG. 8) at a fixed distance using an end rail 23 affixed to a longitudinal end of the longitudinal rail 22. Movement of the skidding mechanism 10 along the skidding rack 12 will thus cause corresponding movement of the longitudinal rail (FIG. 8) coupled to the skidding mechanism 10.

[0015] FIG. 3 shows a view of the longitudinal rail 22 coupled to the skidding mechanism 10 when the cantilever is moved by operating the skidding mechanism 10. It will be appreciated by those skilled in the art that movement of the skidding mechanism 10 wherein an opposed end of the cantilever (see FIG. 9) is in a substantially fixed position transverse to the longitudinal direction of the cantilever will result in relative rotation between the longitudinal rail 22 and the skidding mechanism 10. To accommodate such movement of the longitudinal rail 22 within the guide plate 16, inner surfaces of the guide plate 16 may be rounded to enable the longitudinal rail 22 to engage the guide plate 16 at any angle within a selected range of angles, while being retained within the guide plate 16. It will also be appreciated by those skilled in the art that as the skidding mechanism 10 is moved along the skidding rack 12, the angle subtended between the longitudinal rail 22 and the skidding rack 12 will change.

[0016] FIG. 4 shows an example of a longitudinal extension mechanism 30 for the cantilever. The longitudinal extension mechanism 30 may include a gear frame 31 that is coupled to a support structure such as the hull of a barge or floating vessel (H in FIG. 10). The gear frame 31 may be coupled to the support structure (H in FIG. 10) using a pin 36 that enables rotation of the gear frame 31 about the axis of the pin 36, as well as enabling translational movement of the pin 36 within a slot (not shown) in the support structure (H in FIG. 10). Thus, the longitudinal extension mechanism 30 may both rotate and translate so as to maintain contact with the longitudinal rail 22 as the cantilever is moved transversely by the skidding mechanism (10 in FIGS. 1-3). One or more pinion gears 34 may be affixed to the gear frame 31. The pinion gear(s) 34 may be rotated by a motor (not shown) such as an electric motor, an hydraulic motor or a pneumatic motor. The longitudinal rail 22 may be captively held by a guide plate 32 similar in structure to the guide plate used to hold the skidding rack (12 in FIGS. 1-3) in the skidding mechanism (10 in FIGS. 1-3). The gear frame 31 may be held in relative position with respect to the longitudinal rail 22 using guide rollers 38 mounted to the gear frame 31. FIG. 5 shows a rack 23 formed on or coupled to one side of the longitudinal rail 22 and having meshing teeth that contact the pinion gear(s) 34. When the pinion gear(s) 34 are rotated, the rack 23 and thus the longitudinal rail 22 will be moved longitudinally, that is, transversely to the guide plate 32 coupled to the gear frame 31.

[0017] FIG. 5 shows an oblique view of the longitudinal extension mechanism 30 and the longitudinal rail 22. FIG. 6 shows an oblique view of the longitudinal extension mechanism 30 when the longitudinal rail 22 is moved laterally by the skidding mechanism (10 in FIGS. 1-3) such that the gear frame 31 rotates about the pivot 36. FIG. 7 shows another view of the cantilever rail 22 engaged with the longitudinal extension mechanism 30 when the cantilever is laterally displaced by the skidding mechanism (10 in FIGS. 1-3).

[0018] The described longitudinal extension mechanism 30 explained with reference to

FIGS. 5 through 7 is only one example embodiment of such a longitudinal extension mechanism. In other embodiments, the gear frame 31 may be coupled to, for example, an hydraulic cylinder or a ram in an hydraulic cylinder with the opposite longitudinal end of such device coupled to the load support surface (e.g., barge hull H in FIG. 10). In other embodiments, the gear frame 31 may be coupled to a worm gear/ball nut combination, wherein an opposite end of such combination is coupled to the load support surface (FIG. 10). In other embodiments, the longitudinal rails 22 may be disposed on a bottom surface of the cantilever, wherein the cantilever is supported by, for example, a crane bearing to enable both longitudinal motion and rotation of the cantilever 50.

[0019] FIG. 8 shows a plan view of the cantilever 50 when it is fully longitudinally retracted and laterally centered. The skidding racks 12 and skidding gear frames 18 are shown wherein the skidding gear frames 18 are positioned such that the cantilever 50 is in its rotationally centered position. The cantilever 50, as explained above, may be made from two longitudinal rails 22 coupled at their respective longitudinal ends by end rails 23. The position of a supported load on the cantilever 50, such as a wellbore drilling unit, is shown at R.

[0020] FIG. 9 shows the cantilever 50 with its supported load R wherein the cantilever 50 is longitudinally extended, and is displaced laterally at one end so as to rotate about an axis A proximate a position between the two longitudinal extension mechanisms 30.

[0021] FIG. 10 shows an oblique view of a drilling unit D on a substructure S mounted on the cantilever system as explained with reference to FIGS. 1-9. In FIG. 10, the cantilever is longitudinally extended and is displaced laterally to the left hand side of the drawing (port side). As will be readily appreciated by those skilled in the art, the cantilever may be moved so that a center of the supported load (drilling unit D) may be positioned above any point within an area defined by an outer arc subtended by the cantilever when it is fully longitudinally extended and an inner arc subtended wherein the cantilever is longitudinally extended a minimum possible distance beyond the edge of the support structure, e.g., the barge hull H in FIG. 10.

[0022] A cantilever skidding system according to the various aspects of the present disclosure may enable a cantilever to be positioned precisely in two dimensions within a relatively large area using much simpler mechanisms for moving the cantilever longitudinally and transversely thereto. Further, an amount of deck space required to support the cantilever may be reduced for any given cantilever coverage area than conventional X-Y translational cantilever positioning mechanisms known in the art. While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.