HK1028265B - Jack-up platform locking apparatus - Google Patents

Description

Jack-up platform locking apparatus

Field and background of the invention

The present invention relates to the field of leg locking and support systems for jack-up platforms or jack-up rigs of the type used for the exploration and production of offshore hydrocarbons (oil and gas) and other uses. The oil and gas industry in the continental shelf domain has used offshore engineering platforms extensively for drilling, production, construction of oil and gas, pipeline pumping stations, worker accommodations and various services and workover operations.

Offshore fixed platforms intended to be set up at a location offshore are conventionally constructed onshore, transported by barge to a predetermined location offshore, launched and turned to an upright position and finally permanently fixed to the seabed. Various mobile marine engineering vessels have been developed to meet the needs of the offshore industry for facilities from which drilling, production or workover operations may be carried out, such vessels being generally maintained in a fixed position only while the operations are being carried out and moved to another location after the operations. A variety of mobile oceanographic engineering vessels have also been developed to meet the needs of the offshore industry, including semi-submersible and floating drilling vessels for deep water operations, spud barges for inland waters or estuaries, and jack-up platforms for shallow to medium water depths.

A typical jack-up offshore drilling rig or platform includes a barge hull and support legs operable to raise the hull above the water surface. The barge hull can be towed from one location to another as a floating vessel with the support legs lifted through the hull. After reaching the predetermined location, the support legs are extended downwardly through the barge hull using the lifting system until they contact the seabed, and the legs are continued to be pushed downwardly and into the seabed until their feet stand firmly on the seabed to form a firm foundation, after which continued jacking will raise the hull off the sea level to a height above the maximum wave height that can be expected during operation.

The lifting system of a jack-up rig typically has three or more legs, each leg consisting of one or more, but most often three, spars. One or more racks extend longitudinally along the length of the spar of each leg and are secured thereto and are driven by pinions attached to the hull, the pinions being powered by hydraulic, electrical or mechanical means in a manner well known to those skilled in the art. The pinions may be arranged with their teeth facing the centre of a truss leg formed by a plurality of spars, or the pinions may be arranged opposite each other so that a rack mounted on each side of the leg or leg spar engages each of the facing pinions. Multiple pinions are often stacked vertically to provide sufficient force to lift a predetermined load.

Such jack-up rigs are subjected to large environmental loads created by storms that exert wind forces on the platform and wind and wave forces on the legs of the platform. These forces, combined with the weight of the platform, result in a large interaction between the platform and the legs, which forces must act at the interface or connection of the legs to the hull. To increase the strength and rigidity of the leg-to-hull interface, jack-up rigs are typically provided with leg locking systems that are engaged after the platform is lifted to its desired position, or in some cases, when a storm is anticipated. Prior art leg locking systems typically include an elongated wedge that is surface shaped to mate with teeth on an elongated leg rack. The wedges are vertically arranged so as to be engaged with the teeth and then horizontally moved by means of hydraulic cylinders, screw jacks, electric motors, etc. until they are firmly engaged with the teeth on each of the girders of each leg. Various types of mechanical and hydraulic means can then be used to lock the wedges in the engaged position so that they lock the legs in place while increasing the rigidity of the elevated structure and isolating the pinion from stress loads caused by storm waves and the like.

The main problem with this prior art arrangement is that the toothed wedges must be properly vertically aligned with the teeth of the racks on the leg spar before the wedges can be engaged. The pinion enables the legs to be positioned vertically. However, due to the large legs, the teeth of the respective racks at the highest points of the three legs are slightly different from each other in vertical relation to the hull surface due to manufacturing tolerances, applied loads and the like. For a leg in a fixed position, it is not uncommon for the teeth of the rack at one highest point of the same leg to be vertically offset relative to the hull by plus/minus 1 to 3 inches within the 12 inch vertical dimension of a typical tooth. Accordingly, there is a need to provide a means for mating the wedges with the teeth of the leg rack with limited vertical adjustment of the individual wedges relative to the platform body to align the teeth of each wedge with the teeth of each leg rack before the teeth of the wedges matingly engage the teeth of the rack. Many prior art leg locking systems have this function by providing means for vertically adjusting the wedges relative to a wedge support housing or structure mounted on the hull of the drilling rig, after which the wedges are locked in their vertical position before the wedge teeth and rack teeth are brought into horizontal engagement. With such a system, if the vertical adjustment of the wedge is made imprecisely, this results in slight misalignment in the direction between the wedge teeth and the leg rack teeth, which can create stress concentrations between the partially engaged teeth, which can greatly reduce the effectiveness of the wedge.

Another problem with prior art leg locking devices is that they do not accommodate manufacturing tolerances of the leg rack teeth. The teeth of the support leg rack of most self-elevating drilling machines are cut by heavy steel plates through a profiling template or computer-controlled guide flame. The heat treatment after the cutting heat treatment causes the rack to warp, resulting in teeth of varying sizes, typically as much as 1/8 inches for a 12 inch tooth. Since in leg locking systems it is desirable to have a toothed wedge engage at least four teeth on each leg rack, the cumulative manufacturing tolerances on the four tooth lengths are sufficient to not properly match some of the teeth, which in turn can cause stress concentrations that do not achieve the desired even distribution of load forces across the engaged teeth.

Yet another problem with most prior art leg lock devices is that such devices may become jammed after exposure to storm loads, making it difficult to disengage the engaged teeth when the leg lock system is to be released.

In addition, some prior art systems rely on hydraulic pressure to maintain mating engagement of the wedges with the leg rack, which can risk disengaging the engaged teeth should the power on the platform be lost altogether.

Object of the Invention

It is therefore a primary object of the present invention to provide an improved jack-up platform locking apparatus which overcomes or reduces the inherent drawbacks of the prior art.

It is another object of the present invention to provide an improved jack-up platform locking apparatus which enables a jack-up platform to be securely and reliably engaged with legs, once engaged, to function independently of leg jacking mechanisms, and which is simple and reliable to operate and will not fail in the event of platform loss of power.

It is a further object of the present invention to provide a jack-up platform locking apparatus that vertically adjusts the wedges relative to the teeth of the rack in a manner that is simpler, more robust and more reliable than prior art systems.

It is a further object of the present invention to provide such a system wherein each cleat component has a plurality of relatively short vertically aligned cleat segments, each cleat segment preferably engaging no more than two consecutive teeth of a corresponding leg rack, to minimize the effects of tolerance variations in the flame cutting teeth of the leg rack.

It is a further object of the present invention to provide such a system which utilizes hydraulically actuated support wedges for horizontally and vertically positioning and supporting wedge segments in mating engagement with rack teeth. It also utilizes a self-locking horizontal screw mechanism to mechanically lock the support wedges and chock segments in an engaged position, thereby minimizing or eliminating the reliance on hydraulic pressure to maintain the system in the locked position.

A final object of the invention is to provide such a system in which the support wedges and wedge segments can be quickly and easily disengaged without the risk of seizure inherent in prior art systems.

Drawings

These and other objects and advantages of the present invention will become apparent from the following detailed description of a preferred embodiment thereof, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a plan view of a jack-up rig employing the leg locking system of the present invention showing three triangular cross-section jacking legs and the arrangement of the leg rack and pinion lift system for raising and lowering the legs relative to the rig body;

FIG. 2 is a partial elevation view of one of the spars of the jack-up rig of FIG. 1 showing the relative positions of the elongated rack, jack-up pinion and leg lock on the leg spar of the present invention;

FIG. 3 is a side view showing one half of one means of the leg locking system of the present invention engaged with rack teeth on one of the rails of one of the legs of the platform;

FIG. 4 is a side elevational view, partially in section, of the apparatus of FIG. 3 showing the toothed wedge segments and a supporting wedge for vertically and horizontally positioning and supporting the wedge segments, with the wedge segments shown in a retracted position not engaging the leg rack;

FIG. 5 is an enlarged detailed cross-sectional view taken along line 5-5 of FIG. 4 showing details of the guide for interconnecting the upper and lower toothed wedge segments;

FIG. 6 is a view similar to FIG. 4 but showing the toothed wedge extending to engage the rack teeth of the leg;

FIG. 7 is a partial view, partially in section, taken generally along line 7-7 of FIG. 3, showing details of the locking wedge and guide slide configuration for locking the center support wedge of the system into an engaged position;

FIG. 8 is a partial view, partially in section, taken generally along line 8-8 of FIG. 3, showing details of the hydraulic and mechanical system for positioning and locking a support wedge of the system into an extended (service) position;

FIG. 9 is a partial view, partially in cross-section, taken along line 9-9 of FIG. 3, showing details of the hydraulic system for one of the toothed wedge segments of the positioning system;

FIG. 10 is a front elevational view, partially in section, taken along line 10-10 of FIG. 6, showing additional details of the threaded wedge retaining device of FIGS. 8 and 9;

FIG. 11 is a fragmentary view taken along line 11-11 of FIG. 4 showing details of the gear configuration for the threaded wedge retaining device of FIGS. 8-10;

FIG. 12 is an elevational view similar to FIG. 6, but showing the components of the system provided that the teeth on the leg rack and the teeth on the chock segment are initially vertically offset, with the teeth of the leg rack initially being about 3 inches higher than the teeth of the corresponding chock;

FIG. 13 is a view similar to FIG. 12, but showing the components of the system provided that the teeth on the leg rack are initially about 3 inches lower than the teeth on the corresponding chock segment;

FIG. 14 is an exploded simplified view showing another guide for interconnecting the upper and lower toothed wedge segments and the intermediate support wedge of the system;

FIG. 15 is a view similar to FIG. 6 but showing the upper and lower toothed wedge segments provided with the reinforcing locking wedge and the intermediate support wedge;

fig. 16 is a view similar to fig. 6, but showing an alternative construction of the intermediate support wedge, in which the anti-rotation guide shown in fig. 3-6 is omitted.

Summary of The Invention

The leg locking system of the present invention uses a plurality of vertically aligned toothed wedge segments disposed longitudinally to each leg rack. The longitudinal dimension of each wedge segment is relatively short, preferably it engages the leg rack by no more than two teeth of the rack. The toothed wedge segments have upper and lower inclined bearing surfaces that consistently contact the wedges supporting the wedge segments. The support wedge allows horizontal and vertical adjustment of the wedge segments to correspond with the horizontal and vertical positions of the corresponding rack teeth to be engaged by the wedge. To move the rack wedge segments and their supporting wedges into alignment and mating engagement with the corresponding rack teeth, a double acting hydraulic cylinder is provided. In order to lock the engaged system in place without hydraulic pressure, a mechanical screw arrangement with self-locking threads is provided.

The use of a plurality of short independently adjustable rack wedge segments, each engaging preferably no more than two teeth of the leg rack, allows for four or more teeth of the leg rack to be engaged by the aligned plurality of rack wedge segments while limiting the effect of dimensional variations in the individual rack teeth. The use of a wedge that is horizontally and vertically adjustable and supports the wedge segments of the rack reduces the risk of parts seizing and locking due to loads experienced during use of the system, and reduces the force required to unlock the system and return the parts to the stowed position when it is desired to release the drill leg.

Detailed description of the invention

Fig. 1 illustrates in plan view a typical type of offshore jack-up platform that may advantageously employ the leg locking mechanism of the present invention. The platform 10 includes a floating barge hull that can be self-propelled or towed to a predetermined location. The hull is used to support and transport a plurality of platform legs 14. in the illustrated embodiment, the platform legs 14 comprise three triangular platform legs. The deck 16 of the platform is equipped with a set of offshore drilling and/or production equipment, such as a derrick, a drawworks, a pipe rack, a mud handling device, a dwelling for a drilling and production crew, a heliport, a crane, etc. At each of the three corners of the platform is mounted a shaft through the hull for guidingly receiving one of the platform legs 14. Each platform leg comprises three vertically extending spars 18 which are structurally tied together and joined together by suitably configured cross braces 20.

When the platform is moved from one location to another, the legs are in the raised position and are carried away. The legs may be segmented with the leg segments resting on deck, and when it is desired to lengthen the legs, the leg segments may be aligned and connected one after the other to the leg segments below.

After the platform has reached its intended operating position, the leg sections are ejected downwardly until they reach the seabed, allowing the hull to be raised above the water surface. Once the support on the bottom of each leg penetrates into the ground sufficiently to support the load, continued pushing of the leg means will raise the platform above the water surface to the required working height at which the hull is not affected by the largest storm waves that can be expected.

The invention is particularly applicable to a common leg lift mechanism known as a rack and pinion lift system. In this system, each spar of each leg includes a longitudinally extending double sided toothed rack 22 having a plurality of flame cutting teeth 24. Oppositely disposed pinions 26 are adapted to engage each side of each leg rack in mating engagement with the rack teeth. Hydraulic or electric drive mechanisms 27 mounted on the platform provide power to the pinions to rotate them in a predetermined direction, thereby raising or lowering the platform legs relative to the platform hull.

Once the platform reaches its predetermined height above the water surface, the operation of the pinion is stopped. Pinion drive systems are self-locking so that they can hold the platform in a predetermined raised position. A plurality of leg locks 28 in the present invention are also carried by the platform. Each device comprises two vertically aligned toothed wedge segments, each segment having two teeth shaped to conform to the teeth of the longitudinal leg rack. When the toothed wedge segments mate with and rigidly engage the leg rack as described below, they lock the legs against longitudinal movement relative to the platform hull while protecting the pinion from excessive loading, jamming, deformation, etc. caused by extreme conditions during a storm.

Referring now to fig. 4, a single leg lock 28 is shown in a partially cut-away front view opposite one side of a longitudinal leg rack 22. At least one such leg locking means is provided on each side of each longitudinal leg rack. Thus, a jack-up platform with three triangular legs would have eighteen such devices. The relative positions of which are assumed to be in the stored position (fig. 4) and the operative, locked position (fig. 6) are shown.

Each leg locking means comprises a rigid housing 36 mounted on the hull for suitably supporting and guiding the moving parts of the locking means. The upper and lower horizontal support surfaces 37, 39 and the rear wall 41 and opposing side wall portions (not shown) define a central opening in the housing 36 in which the movable components of the locking system are located.

These components include a first or upper wedge segment 30 having two teeth 34 and a second or lower wedge segment 32 having two teeth 34. The upper and lower wedge segments are separated by a central triangular support wedge 38. The support wedge 38 acts as a double-sided wedge engaging both a lower, uniformly shaped inclined surface 40 on wedge segment 30 and an upper inclined surface 42 on wedge segment 32. The upper and lower chock segments 30, 32 and the intermediate support wedge 38 are all made of high strength steel plate of suitable thickness so that they can withstand the heavy mechanical loads exerted on the locking system by the legs of the platform 10. The preferred slope between the inclined surfaces 40, 42 on the chock segments and the double support chock 38 is such that the chock and chock are substantially self-locking in the unloaded condition.

To slidably interconnect the upper and lower wedge segments 30, 32, anti-rotation guides may be provided. As shown in fig. 4 and 5, these means include a pair of elongated guides 43, one on each side of the upper and lower wedge segments 30, 32, and spanning the center wedge block 38. The shoulder 44 of each guide 43 has upper and lower inclined guide surfaces which engage and are guided by correspondingly shaped inclined guide grooves 45 on the wedge segments. Although not shown, the guide 43 is held against outward movement from the guide groove 45 by sliding engagement with a portion of the chock device housing. The guide 43 acts as a free wheel in the slot 45 so that when the chock segments 30, 32 are moved vertically towards or away from each other, the guide 43 will move horizontally as required to accommodate such vertical movement of the chock segments. The engagement of the guide surfaces on its shoulder 44 with the guide slots 45 provides additional moment locking for the chock segments to prevent any significant rotation of the chock segment relative to the other chock segment, providing additional rigidity and strength to the overall structure.

The chock segments 30, 32 are provided with upper and lower support by additional support wedges interposed between the chock segments and the device housing. The top surface of the upper cleat section 30 is defined by a downwardly sloping surface 46. Which engages a correspondingly shaped lower surface of a first or upper support wedge 48, which support wedge 48 is interposed between the upper surface of the wedge segments 30 and the upper horizontal support surface 37 which defines the top surface of the housing opening. An upwardly inclined surface 50 on the bottom surface of the lower chock segment 32 engages a second or lower support wedge 52 interposed between the bottom surface of the chock segment 32 and the lower horizontal support surface 39 of the housing 36. It is again emphasized that the slope between the wedges and the upper and lower support wedges is preferably such that the components are substantially self-locking in the unloaded condition, although any desired slope may be used.

It will be appreciated by those skilled in the art that the three support wedges 38, 48 and 52 may allow for vertical, horizontal adjustment and support of the wedge segments 30, 32. Wedge segments 30, 32 having oppositely inclined surfaces may also function as wedges between the opposite wedge surfaces on the support wedges 38, 48 and 52. As will be described more fully below, this configuration allows for substantially unrestricted horizontal and vertical adjustment of the chock segments 30, 32 within the system dimensional parameters, thereby ensuring an accurate fit between the teeth of the chock segments and the corresponding teeth of the leg rack 22. However, once the teeth of the wedge segments engage the teeth of the leg rack (fig. 6), and the wedges 38, 48, 52 contact their respective mating surfaces on the wedge segments and are held against movement longitudinally away from the leg rack 22, the entire system is rigidly and securely locked in place and the leg rack 22 cannot move vertically relative to the chock assembly until the wedges 38, 48, 52 are released.

To horizontally move the upper and lower wedge segments 30, 32 and the support wedges 48, 52 between the stowed and extended (operating) positions within the device housing 36, a positioning device is provided. In the preferred embodiment, the positioning device comprises two double acting hydraulic cylinders 53, 54, each having a piston end connected to one wedge section and a cylinder end connected to a box beam 57 forming part of the device housing (fig. 3, 9). The positioning means for moving the upper and lower support wedges 48, 52 horizontally within the housing includes a second pair of double acting hydraulic cylinders 55, 56, each having a cylinder end connected to the housing of the apparatus and a piston end connected to a respective one of the upper and lower wedges 48, 52 (fig. 3, 8). The double acting hydraulic cylinders 53, 54, 55, 56 are preferably slidably or pivotally mounted such that the chock segments and supporting wedges can be vertically adjusted up or down by at least three inches relative to the chock device housing without binding the cylinders. Hydraulic lines 58 supply pressurized hydraulic fluid to either end of the double acting hydraulic cylinder while draining hydraulic fluid from the other end of the cylinder, thereby enabling a piston (not shown) in the cylinder to move the attached chock segments or wedges horizontally toward or away from the leg rack 22. A conventional hydraulic power unit 60 has conventional control means (not shown) for selectively supplying pressurized hydraulic fluid to either side of each cylinder to effect the desired horizontal movement of the chock segments or wedges. For simplicity of illustration, all of the hydraulic lines are labeled "58" and only a single hydraulic power source 60 is shown. It will be appreciated, however, that separate hydraulic lines are required to supply each side of each double acting hydraulic cylinder and that one or more hydraulic power sources and associated control devices may be required in order to power and control each locking device 28 separately or to simultaneously control two or more devices as required. Of course, threaded, electrical, pneumatic, etc. positioning devices may be substituted for the hydraulic devices disclosed herein.

In order to selectively hold the three support wedges against horizontal movement out of the leg rack 22 once they have been extended into engagement, retaining means are provided. As shown in fig. 4 and 6, two elongated tubular spacers 60 are attached to and move horizontally with the upper and lower wedges 48, 52, respectively. In the case of the upper chock 48, the spacer 60 associated therewith is located between the rear face of the chock and a threaded female plate 62, the threaded female plate 62 being in threaded engagement with three elongated threaded rods 64 rotatably mounted in the chock device housing 36. A reversible hydraulic motor 66 drives a central gear 68 (fig. 11) which in turn drives three larger gears 70, one gear 70 on top of each screw 64 (fig. 11) to allow synchronous rotation of the three screws in either direction. Since the nut plate 62 is threadedly engaged with the three rods 64, rotation of these rods 64 in one direction will move the master plate 62, spacer 60 and upper wedge 48 horizontally toward the leg rack 22, while reverse rotation of the threaded rods will move the nut plate 62 horizontally away from the leg rack 22, thus moving the spacer 60 and wedge 48 horizontally away from the rack by the double acting hydraulic cylinder 55. Suitable means are provided for selectively supplying pressurized hydraulic fluid to the reversible hydraulic motor 66 to selectively rotate the screw 64 in either direction. Although not shown, such means may include hydraulic fluid lines extending between the reversible hydraulic motor 66 and the hydraulic power unit 60 and control devices (not shown) within the hydraulic power unit that may selectively supply pressurized hydraulic fluid to either side of the reversible hydraulic motor 66 as desired.

The same horizontal retention means is provided for the lower wedge 52.

The holding means for the double acting center support wedge 38 includes a fifth double acting hydraulic cylinder 72 (fig. 7) that powers a locking wedge 74 connected to its piston rod. The locking wedge 74 contacts a guide slide 76 secured to the device housing 36. Guide slide 76 has an inclined surface 78 that cooperates with an inclined surface 80 on wedge 74, while an opposite flat surface 82 on wedge 74 contacts a rear edge 84 of center support wedge 38 to retain wedge 38 in its operative extended or locked position. The respective inclinations on the guide slide 76 and the wedge 74 are sufficiently small to enable the wedge surface to be substantially self-locking. This means that when the system is in its extended locked state, minimal, if any, force is required by the hydraulic cylinder 72 to hold the wedge 74 in place. A suitable mechanical locking mechanism may also be used for such wedges. An alternative design is also possible for the retaining means, the required function being to support and lock the three supporting wedges in their operating position.

Figure 15 shows another embodiment of the leg lock arrangement of the present invention in which the upper and lower wedge segments 30, 32 are also provided with reinforced locking wedges. As shown, the upper locking wedge 86 is disposed between the back of the upper wedge section 30 and a guide slide 88 mounted on the device housing, while the lower locking wedge 90 is disposed between the back of the lower wedge section 32 and a guide block slide 92 in the device housing. Each additional locking wedge 86, 90 is driven by a cylinder (not shown) identical to the hydraulic cylinder previously described in connection with center locking wedge 74 (fig. 7). Locking wedges 86, 90 also operate in the same manner as described for center locking wedge 74. If a reinforcing locking wedge is provided for each of the upper and lower chock segments and the central support wedge 38, additional anti-rotation guides, such as elongated guides 43, provided for the chock segments may not generally be employed and, therefore, are not shown in FIG. 15.

Referring to fig. 14, another alternative embodiment of an anti-rotation guide for the upper and lower chock segments 30, 32 is shown. As shown in the exploded view, a vertical guide rod 94, preferably rectangular in cross-sectional shape, is slidably received in a uniformly shaped guide channel formed vertically through the body of the intermediate support wedge 38. Both the upper and lower ends of the guide rod 94 are slidably received in correspondingly shaped, generally vertical pockets 98, 100 formed in the body of the upper and lower wedge segments 30, 32, respectively. The clearance between the slip fit components preferably allows for appropriate independent adjustment of the upper and lower wedge segments 30, 32 and the center support wedge 38 relative to each other and to the teeth of the leg rack 22 to allow the teeth of the wedge segments to fully mate with the corresponding teeth on the leg rack while accommodating manufacturing tolerances of the rack teeth. However, the guide rods 94 ensure that the intermediate support wedge 38 moves horizontally with the upper and lower wedge segments 30, 32 and additionally acts as a torque lock, preventing any significant relative rotation of the wedge segments with respect to each other.

Referring to FIG. 16, another alternative structural shape for the upper and lower cleat segments 30, 32 and the central support cleat 38 is shown. Variations include providing opposing shoulders 106 and 108 on the double wedge 38 and on each of the upper and lower wedge segments 30, 32. These opposing shoulders can prevent the double wedge from moving toward the rear of the wedge segments so that the two wedge segments and the double wedge move as a unit as a whole. Preferably, however, the double wedges 38 are slightly smaller than the space between the two chock segments so that the double wedges and chock segments have limited freedom of movement laterally and vertically relative to each other. This enables the system to accommodate small differences in size between the two rack teeth that engage the upper chock segment 30 and the two rack teeth that engage the lower chock segment 32, thereby making the force distribution between the leg rack and the chock relatively equal. In the embodiment shown in fig. 16, the elongated guide 43 of fig. 3-6, the central vertical guide bar 94 of fig. 14, and the additional reinforcing locking wedge of fig. 15 are not present. Of course, the structure of FIG. 16 could employ any such additional anti-rotation device, if desired.

When the system is in its stowed position (fig. 4), the chock segments 30, 32 are centered within the opening in the housing 36. In this position, the upper shell surface 37 preferably has a clearance of at least about 3 inches from the top of the wedge segments 30 and the lower shell surface 39 preferably has a clearance of at least about 3 inches from the bottom of the wedge segments 32. As will be described in greater detail below, this will allow a total of about 6 inches of vertical adjustment (plus or minus about 3 inches from the center) to the wedge segments to accommodate misalignment between the wedge teeth 34 and the leg rack teeth 24. The longitudinal centerlines of wedge segments 30, 32 and wedges 38, 48, 52 are preferably substantially aligned with the longitudinal centerline of leg rack 22. The hydraulic cylinders 53, 54, 55, 56 are pressurized in one direction to hold the components in their retracted, positions, or to provide the chock segments with a mechanical locking mechanism, such as a fixed pin (not shown), so that the teeth of the chock segments cannot engage the leg rack teeth. When the components are in their stowed positions, it is preferable to provide means to maintain the hydraulic cylinders at a certain pressure if the hydraulic system is shut off. Such means may include control means (not shown) in the hydraulic power unit 60 capable of isolating the cylinders from their respective hydraulic lines to maintain the pressure on the respective sides of the cylinders at a suitable level to safely maintain these components in their retracted, stowed positions. An accumulator (not shown) may also be provided in the hydraulic system for this purpose. Hydraulic cylinder 72 and its associated wedge 74 are retracted to a parked off condition. The threaded masters 62 are retracted on their threaded shafts 64 to retract both the upper and lower support wedges 48, 52 and their associated spacers 60.

When engagement of the locking system is required, for example when a storm is anticipated, the three spars on each leg are preferably "wedged" one at a time. The spar to be wedged first is selected and the leg rack of that spar is aligned with the vertical position of the chock system by operating the pinion 26 to substantially align the teeth on the leg rack 22 for mating engagement with the teeth of the corresponding chock device on the chock segment. This may be done manually or preferably by means of a vertical alignment sensor 102 mounted on the platform hull. One such sensor may be provided for each leg of the platform and is preferably located on or near the spar of the leg that is to be wedged first. The elevation of the platform relative to the legs can be stopped by sensors of conventional construction at a preselected elevation at which point the teeth on the leg rack of the leg spar should be in substantial alignment for mating engagement with the teeth on the wedge segments of the two wedge means of that leg spar in the centered stowed position. Although any desired type of vertical alignment device or sensor may be used, a preferred type is a proximity sensor in which a proximity probe mounted on the hull senses the proximity of each tooth tip as it passes adjacent thereto, thereby enabling the number of tooth tips to be calculated and accumulated, thereby allowing the platform to be automatically raised to a preselected vertical position on the leg. The pinion may then be stopped at a point where a tooth tip substantially directly faces the proximity detector, thereby ensuring that additional rack teeth are substantially vertically aligned with the centrally located chock teeth of the chock assembly. Although substantial alignment is desired, the cleat device will be able to accommodate misalignments up to the design limit in the system, which in the preferred embodiment shown is plus or minus about 3 inches.

Once the legs have been properly positioned, the hydraulic cylinders 53 and 54 are supplied with pressurized fluid in one direction, causing the two wedge segments 30, 32 to move toward the leg rack until the teeth of the wedge segments engage the teeth of the leg rack. The double support wedge 38 will advance with the wedge segments 30, 32.

As the chock segments 30, 32 advance toward the rack teeth, they will move slightly downward in response to the ramp between the lower chock segment 32 and the lower support wedge 52. Once the chock teeth contact the rack teeth, continued urging of the hydraulic cylinders 53, 54 forcing the chock segments toward the rack movement causes the chock teeth to slide upwardly and inwardly on the inclined surfaces of the rack teeth 24 until a near perfect fit is achieved between the leg rack teeth 24 and the chock segment teeth 34. The feature of the two wedge segments 30, 32 being able to move somewhat independently of each other within the tolerance of the interconnecting guide means, if used, allows a more perfect fit of the wedge teeth to the leg rack teeth than would be possible with a single wedge segment having four teeth. The effect of manufacturing dimensional errors of flame cut rack teeth can thus be limited to a two tooth range rather than cumulatively over the entire vertical distance of four rack teeth.

With continued retention of the chock segments in close mating engagement with the rack teeth by the hydraulic cylinders 53, 54, the hydraulic cylinders 55, 56 are supplied with pressurized fluid in one direction to move the two support wedges 48, 52 into firm supporting engagement with the chock segments. This completes the basic alignment/engagement process.

With the components in their engaged positions, hydraulic cylinder 72 is pressurized in one direction to force intermediate locking wedge 74 against the inclined surface of guide slide 76 to lock intermediate support wedge 38 stably in place. Upper and lower locking wedges 86, 90 are similarly engaged if desired. Nut plate 62 on screw 64 is then brought into contact with hollow spacer 60 by hydraulic motor 66, which locks upper and lower support wedges 48, 52 firmly in place, preventing wedge segments 30, 32 from disengaging the leg rack teeth. The self-locking threads between the nut plate 62 and the screw 64 prevent disengagement until the motor 66 rotates the screw in the opposite direction. The pressure in the hydraulic cylinders 53, 54, 55 and 56 can then be released, since they now no longer perform any holding function. Although not absolutely necessary, it is desirable to maintain a pressure within hydraulic cylinder 72 and within the cylinders of upper and lower locking wedges 86 and 90, if used, that helps to hold the locking wedges in place. This can be achieved by locking the pressurized fluid in the cylinder by adjusting a control (not shown) in the hydraulic power unit 60, since very little pressure is required. Alternatively, a passive accumulator arrangement may be provided to maintain the pressure of the hydraulic cylinder locking the wedges so that disengagement does not occur even if all power from the hydraulic power unit 60 is interrupted. Alternatively, a mechanical locking device is used for this same purpose.

The steps described above should be performed sequentially for each cleat device on each spar of each platform leg to securely lock the platform legs in place.

Even if the wedge teeth and rack teeth of the first spar are substantially aligned under the control of the vertical alignment sensor, the wedge teeth and rack teeth on the other spars of the leg may still be somewhat misaligned due to manufacturing tolerances, stress deformations, etc. However, because each cleat device can accommodate the vertical misalignment between the teeth of its cleat segment and the corresponding leg rack teeth without being affected by the other cleat devices, a reliable and nearly perfect fit between the cleat teeth and the rack teeth on each cleat device can be ensured, as long as the total misalignment of the leg struts does not exceed the vertical design adjustment range of the device. Referring to fig. 11 and 12, there is shown the relative positions assumed by the wedge segments and wedges when offset upwardly (fig. 11) and downwardly (fig. 12) by no more than 3 inches to allow proper alignment with the teeth of the leg rack 22.

The foregoing disclosure and description of the preferred embodiments are illustrative and explanatory only, and various changes in the size, shape, materials and other details of construction and method of operation of the device may be made within the scope of the appended claims without departing from the basic spirit of the invention.

Claims (19)

1. A jack-up platform locking apparatus, the hull of such a platform including legs extending therethrough and a longitudinally extending rack on said legs, the rack having a plurality of longitudinally spaced rack teeth thereon engageable with and driven by a pinion gear on said hull, said locking apparatus comprising:

a cleat housing mounted on the hull;

a plurality of vertically aligned chock segments disposed within said housing, each of said chock segments having at least one tooth adapted to matingly engage with the teeth of said leg rack,

each of said wedge segments having inclined upper and lower bearing surfaces;

a plurality of supporting wedge means in said chock housing adapted to contact said upper and lower inclined support surfaces of said chock segments in unison for selectively supporting said chock segments in said chock housing;

positioning means for horizontally moving said chock segments and said supporting wedge means relative to said housing between a stored position in which said teeth of said chock segments are not engaged with said teeth of said rack and an operative position in which said teeth of said chock segments are engaged with said teeth of said leg rack; and

retaining means for selectively retaining said support wedge means in said engaged position.

2. The apparatus of claim 1 wherein each of said chock segments has no more than three teeth matingly engageable with said leg rack teeth.

3. The apparatus according to claim 2 wherein each of said wedge segments has two teeth.

4. The apparatus of claim 1, wherein the holding device is operable independently of the positioning device.

5. The apparatus according to claim 1 wherein said positioning means comprises a plurality of double acting hydraulic cylinders, each of said cylinders having one end attached to said chock housing and the other end attached to one of said chock segments or one of said support wedge means.

6. The apparatus of claim 1, wherein said support wedge means comprises upper, middle and lower support wedges, and wherein said retaining means comprises an adjustable threaded support member having self-locking threads for selectively locking at least said upper and lower support wedges in said operating position.

7. The apparatus according to claim 1 wherein said plurality of chock segments comprises first and second chock segments vertically aligned within said chock housing, wherein said wedge assembly comprises a first support wedge disposed above and adapted to contact the upper inclined support surface of said first chock segment, a second support wedge disposed below and adapted to contact the lower inclined support surface of said second chock segment, and an intermediate support wedge disposed between said first and second chock segments and adapted to contact the lower inclined support surface of said first chock segment and the upper inclined support surface of said second chock segment in unison.

8. The apparatus according to claim 7 wherein said retaining means further comprises a locking wedge selectively engageable with said intermediate support wedge to prevent horizontal movement of said intermediate support wedge away from said wedge teeth when said chock segments are in said operating position.

9. The apparatus of claim 8 further comprising a locking wedge selectively engageable with each of said upper and lower chock segments to prevent horizontal movement of said upper and lower chock segments away from said rack teeth when said chock segments are in said operating position.

10. The apparatus according to claim 7 further comprising anti-rotation guides interconnecting said first and second chock segments for preventing rotation of said chock segments relative to each other.

11. The apparatus according to claim 10 wherein said anti-rotation guide means comprises an elongated guide member having an upper inclined guide surface and a lower inclined guide surface thereon, said upper inclined surface adapted to engage a uniformly shaped inclined guide slot on said first chock segment and said lower inclined guide surface adapted to engage a uniformly shaped inclined guide slot on said second chock segment, whereby vertical movement of said chock segments relative to each other is accommodated by horizontal movement of said guide member while said chock segments remain substantially non-rotatable relative to each other as constrained.

12. The apparatus according to claim 10 wherein said anti-rotation guide means comprises an elongated guide rod disposed between and interconnecting said first and second chock segments, the upper end of said guide rod being adapted to be received in a uniformly shaped substantially vertical guide slot formed in said first chock segment and the lower end of said guide rod being adapted to be slidably received in a uniformly shaped substantially vertical guide slot formed in the body of said second chock segment, whereby vertical movement of said chock segments relative to each other is accommodated by sliding said guide rod in said guide slots while said first and second chock segments remain substantially rotationally fixed relative to each other due to constraint.

13. The apparatus according to claim 12, further comprising a guide slot formed through the body of said intermediate support wedge in substantial vertical alignment with said guide slots on said first and second chock segments, wherein said guide rod is slidably received through said guide slot in said intermediate support wedge.

14. An apparatus for elevating a hull of an offshore platform, comprising:

a toothed rack having a longitudinal axis and being longitudinally fixed to an upright leg extending through the hull;

a drive pinion gear mounted on the hull and drivingly engaged with the rack teeth;

means for rotating said pinion gear relative to said rack gear to move said rack gear along said longitudinal axis relative to the hull, thereby moving said hull up and down relative to said legs;

a locking mechanism for locking the leg against longitudinal movement relative to the hull, the locking mechanism comprising:

a housing mounted on the hull and having upper and lower support surfaces;

first and second vertically aligned wedge segments mounted within said housing between said upper and lower bearing surfaces,

said first chock segment including a plurality of teeth adapted for mating engagement with said rack teeth, an upper bearing surface inclined downwardly in a direction horizontally away from said chock teeth and a lower bearing surface inclined upwardly in a direction horizontally away from said chock teeth,

said second cleat segment including a plurality of teeth adapted for mating engagement with said rack teeth, an upper bearing surface sloping downwardly in a direction horizontally away from said cleat teeth, and a lower bearing surface sloping upwardly in a direction horizontally away from said cleat teeth;

a first support wedge disposed between and in conforming contact with said upper bearing surface of said first wedge segment and said upper bearing surface of said housing;

a second support wedge disposed between and in conforming contact with said lower support surface of said second wedge segment and said lower support surface of said housing;

a middle support wedge disposed between and in conforming contact with said lower support surface of said first wedge segment and said upper support surface of said second wedge segment;

positioning means for horizontally moving said first and second chock segments and first and second support wedges in said housing between a stowed position in which said teeth of said chock segments do not engage said teeth of said rack and an operative position in which said teeth of said chock segments engage said teeth of said rack; and

a retaining means independent of said positioning means for retaining said first and second support wedges and said intermediate support wedge in their operative positions, thereby retaining said first and second chock segments in their operative positions.

15. The apparatus of claim 14 wherein said positioning means comprises a plurality of double acting hydraulic cylinders, each of said cylinders having one end connected to said housing and the other end connected to one of said chock segments or one of said first and second support chocks.

16. The apparatus according to claim 14 wherein said retaining means includes threaded support means selectively engageable with said first and second support wedges for preventing movement of said first and second support wedges in said operative position horizontally away from said wedge segments.

17. The apparatus according to claim 16 wherein said retaining means further comprises a locking wedge selectively engageable with said intermediate support wedge to prevent movement of said intermediate wedge in a position horizontally away from said rack teeth when said chock segments are in said operating position.

18. The apparatus of claim 14 further comprising locking wedges selectively engageable with said first and second chock segments to prevent horizontal movement of said chock segments in a direction horizontally away from said rack teeth when said chock segments are in said operating position.

19. A method of locking the legs of a jack-up platform against vertical movement relative to the hull of said platform by wedging the teeth of a leg rack extending longitudinally of said legs, said method comprising:

providing a leg locking device on said hull, the device comprising: a cleat housing mounted on the hull; a plurality of vertically aligned chock segments disposed within said housing, each of said chock segments having at least one tooth adapted to matingly engage the teeth of said leg rack, and each of said chock segments having upper and lower inclined support surfaces; a plurality of support wedge means within said wedge housing adapted to contact said upper and lower inclined support surfaces of said wedge segments in unison for selectively supporting said wedge segments within said housing; positioning means for horizontally moving said chock segments and said support wedge means relative to said housing between a stored position in which said teeth of said chock segments are not engaged with said teeth of said rack and an operative position in which said teeth of said chock segments are engaged with said teeth of said rack; and a retaining device for selectively retaining said support wedge device in said workpiece position;

aligning the leg and the leg rack in a desired vertical position relative to the hull;

horizontally moving the wedge segments in the housing from the stowed position to a position where the teeth of the wedge segments engage corresponding teeth on the rack with the positioning device;

continuously forcing said chock segments into engagement with said rack teeth with said positioning means whereby said chock segments will move vertically and horizontally in response to being pushed by said positioning means forcing said rack teeth into maximum mating engagement with the teeth of said chock segments;

horizontally moving said support wedge assembly within said housing from said stowed position to an operative position contacting said support surface of said wedge segments with said positioning assembly, thereby supporting said wedge segments against vertical and horizontal movement relative to said rack;

holding said support wedge means with said retaining means against horizontal movement away from said leg rack thereby maintaining locking mating engagement of said teeth of said rack with said teeth of said wedge segments.