US3517910A

US3517910A - Elevating assembly for an offshore platform

Info

Publication number: US3517910A
Application number: US663330A
Authority: US
Inventors: John R Sutton; William G Newman
Original assignee: Individual
Current assignee: Individual
Priority date: 1967-08-25
Filing date: 1967-08-25
Publication date: 1970-06-30
Anticipated expiration: 1987-06-30

Description

June 30, 1970 3,517,910 ELEVATING ASSEMBLY FOR AN OFFSHORE FLATFORM Filed Aug. 25, 1967 J. R. SUTTON ET AL 4 Sheets-Sheet l INVENTORS.

m N m N M swm mm A M 6 M A. N H Q i J W KM 0 BY 6m ELEVATING ASSEMBLY FOR AN OFFSHORE PLATFORM Filed Aug. 25, 1967 June 30, 1970 SUTTQN ET AL 4 Sheets-Sheet i3 E [WW/l,

FIG. 5

FIG. 4

(Q R m E N W0 IT T U S R N H O J 5% WILLIAM G. NEWMAN 0 U f M ATTORNEYS June ,30, 1970 J,R.su1 -TN ET AL 3,517,910

E m 9 1 2 L. u A d e l 1 F FIG. 3

. INVENTORS JOHN R. -SUTTON WILLIAM G. NEWMAN ATTORNEYS,

June 30, 1970 J. R..su1"roN ET AL ELEVATING ASSEMBLY FOR AN OFFSHORE PLATFORM Filed Aug. 25, 1967 4 Sheets-Sheet 4 FIG. 7

INVENTORS JOHN R. SUTTON I WILLIAM G. NEWMAN BY 1 I I (Om w, im am ATTORNEYS,

United States Patent Oifice 3,517,910 Patented June 30, 1970 3,517,910 ELEVATING ASSEMBLY FOR AN OFFSHORE PLATFORM John R. Sutton, 1189 Calder Ave., Beaumont, Tex. 77701, and William G. Newman, Troy, Mich.; said Newman assignor to said Sutton Filed Aug. 25, 1967, Ser. No. 663,330

Im. on. B66f 7/14 US. Cl. 254-92 12 Claims ABSTRACT OF THE DISCLOSURE lectively engaged with other engaging means spaced vertically along the one leg to secure the yoke and deck independently against vertical motion. At least one extensible jack positioned between the yoke and the deck includes a protective outer tube telescopingly receiving an inner stress tube. A threaded rod of the ball screw type, supported for rotation concentrically within the outer tube, extends partially into the inner tube. Nut means threadably engaged with the threaded rod is fixedly secured to an adjacent end of the inner tube. Motor means selectively rotates the threaded rod in opposite directions to extend and retract the inner tube relative to the outer tube. The remote ends of the inner and outer tubes are respectively connected to the deck and yoke by joints which permit pivotal motion of the jack to accommodate flexural distortions of the leg, yoke and deck during operation.

BACKGROUND OF THE INVENTION This invention relates to an elevating assembly for an elevating platform of the type used for supporting equipment at a variable elevated level such as for example a tower for supporting geophysical, radio, radar or nuclear equipment. In particular, but not exclusivley, the invention relates to an offshore platform for performing off-shore marine operations such as underwater drilling operations.

In performing offshore marine operations in continental shelf areas or the like, it is sometimes advantageous to use an offshore platform of the so-called jack up type for supporting oil drilling and like equipment. Such jack up platforms usually comprise a horizontal deck supported on a plurality of legs which rest on the seabed at their lower ends and which extend vertically and slidably through the deck. Extensible jacks may be secured to one side of the deck. The remote end of each jack is usually provided with means for selective locking engagement with at least one leg. Similarly, the deck is also provided with means for selective locking engagement to the legs. By engaging the remote ends of the jacks with the leg and disengaging the deck then causing linear movement of the jacks, the deck may be moved vertically along the legs. Representative examples of such offshore platforms are disclosed in Us. Pats. Nos. 3,082, 607, 3,245,658 and 3,282,565 issued to the present applicant.

Although elevating platforms of the type described are generally satisfactory, certain serious disadvantages may be encountered during conditions of operational use. For example, in such previous structures the jack has sometimes comprised a deck-mounted motor driving a threaded collar. A rod extends through and is threadedly engaged with the collar, with the rod being adapted at a remote end thereof for locking engagement with the leg. In such a structure, protection of the working parts from the uniquely corrosive local environment is sometimes provided by a flexible sleeve, extending about the threaded rod. However, the corrosive effects of sea Water spray and wave action in the particular environment of an otfshore platform are frequently such as to cause destruction of the sleeve, thus exposing the threaded elongate member to the same elements, with the result that it becomes corroded and the jack becomes unserviceable.

Another disadvantage arising with prior structures of the type described is that the jack elements are sometimes rigidly connected at their extremities to the leg and deck. This may result in the usual lateral and torsional deformation of the legs, encountered operationally during use of an offshore platform, causing lateral binding pressure between the threaded rod and the motor driven collar sufficient to impair the ability of the jack to perform its function.

This difficulty has been compounded by the current practice of using elevating jacks functioning in compression during periods of deck elevation as such operation in compression increases the likelihood of lateral compressive buckling loading of the working parts, also leading to jamming thereof and like disadvantageous consequences.

SUMMARY OF INVENTION It is therefore a general object of the invention to provide an elevating assembly for an offshore platform intended to obviate or minimize problems of the type previously described.

It is a particular object of the invention to provide an elevating assembly for an offshore platform wherein various working members causing highly efficient elevation and lowering of the platform are effectively and lastingly protected against the adverse effects of a corrosive external environment.

It is a further object of the invention to provide an elevating assembly for an oifshore platform wherein lateral and torsional deformation of various portions of the platform commonly encountered during use thereof, does not cause any impairment of the operating ability of the elevating assembly.

One preferred embodiment of the invention intended to accomplish at least some of the foregoing objects is intended for use in conjunction with an offshore platform of the type including a generally horizontal deck supported on a plurality of ground engaging, generally vertical legs extending slidably through the deck. The invention includes a plurality of elevating assemblies each one of which is connected to a separate one of the legs. Each elevating assembly includes yoke means connected with the one leg for vertical sliding motion therealong, the yoke means being spaced vertically from the deck. The yoke means may be selcetively locked against movement along the one leg by second engaging means fixed to the yoke means, which is selectively engageable "with one at a time of a plurality of first engaging means spaced at vertical intervals along the leg. Similarly the deck may also be selectively locked against movement along the one leg by third engaging means connected with the deck and selectively engageable one at a time of the first engaging means. At least one extensible jack is positioned between the yoke means and the deck. The jack includes an outer protective tube telescopingly receiving an inner stress tube. An elongate threaded ball screw member supported by bearings for rotation concentrically within the outer tube extends partially into the inner tube. Ball nut means engaging the threaded ball screw member, by balls interposed between the ball screw and the ball nut means, is fixedly secured to an adjacent end of the inner tube. Motor means connected with the ball screw member may be selectively operated to rotate the ball screw member in opposite directions to cause outward and inward telescoping of the inner tube relative to the outer tube. By looking the yoke means to the leg by operation of the second engaging means and freeing the deck for motion by release of the third engaging means, the motor means may be selectively operated to retract and extend the jack to cause motion of the deck along the leg in opposite directions. By enclosing all the moving elements of the jack within rugged tubes, lasting and efficient protection against the harsh external conditions particularly encountered in the environment of an offshore platform is provided.

The remote ends of the jack are connected to the yoke means and the deck by pivotal joint means which permit relative pivotal motion between the jack and the deck and the jack and the yoke means, thus advantageously preventing binding of the working parts of the jack during elevation and lowering of the deck.

In more detail, in the preferred embodiment the yoke means is positioned above the deck with the outer tube secured to the deck and the upper end of the inner tube secured to the yoke means.

In an alternative embodiment of the invention the yoke means is positioned below the deck with the outer tube connected with the yoke means and the inner tube connected with the deck.

THE DRAWINGS A preferred embodiment of the invention is illustrated in the accompanying drawings in which:

FIG. 1 is a side view of a portion of an offshore plat form provided with elevating assemblies constructed according to the preferred embodiment of the invention;

FIG. 2 is a simplified cross-sectional view of a portion of the offshore platform shown in FIG. 1 taken along the lines 22 therein with two of the elevating assemblies removed for clarity;

FIG. 3 is a perspective view partially in section of one of the elevating assemblies according to the preferred embodiment shown in FIG. 1.

FIG. 4 is a cross-sectional side view of a portion of the elevating assembly shown in FIG. 2 taken along the lines 44 therein;

FIG. 5 is a cross-section side view of a first alternative embodiment of a pivoted joint forming a part of the elevating assembly shown in FIG. 3;

FIG. 6 is a side view partially in section of a second alternative embodiment of the elevating assembly; and

FIG. 7 is an enlarged view partially in section of a portion of the elevating assembly shown in FIG. 6.

DETAILED DESCRIPTION FIG. 1 of the drawings shows a typical offshore platform of the type with which an elevating assembly constructed in accordance with a preferred embodiment of the invention is intented to be used. The platform includes a generally horizontal deck 2 supported above the surface of a body of water by a plurality of vertically extending legs 4 extending slidably through the deck 2 and having their lower ends resting on the bed of the body of water. Each of the legs 4 (FIG. 2) comprises three, separate tubular legs 6 distributed equally about the surface of a hypothetical circle and rigidly connected together in spaced relation by bracing members 8. It will be appreciated that the legs 4 may be fabricated in other conventional configurations and additionally the tubular legs 6 may be of round, square, triangular, polygonal or other desired shape. For raising and lowering the deck 2 relative to the legs 4, a plurality of elevating assemblies 10 are provided.

Each elevating assembly 10 (FIG. 3) in the preferred embodiment of the present invention includes an L- shaped yoke member 16 (sometimes referred to as a saddle) extending about a major portion of the circumference of one leg 6 and slidable vertically therealong. Each leg 6 is further provided with two vertically extending, radially projecting rectangular tracks 18 pro vided with a plurality of vertically spaced recesses 20, though the number of tracks 18 per leg 6 may be varied if desired. The yoke 16 may be selectively locked immovably to the leg 6 by two upper plunger units v22 secured to the underside of the yoke 16, each of which is selectively engageable with one at a time of the recesses 26. Similarly, the deck 2 may also be selectively secured immovably to the leg against vertical motion by two lower plunger units 26 secured to the underside of the deck 2.

The elevating jacks 28, 30 and 32 are conventional jacks of the type having telescoping tubes protecting a central threaded member which is driven by an electric motor to advance a ball nut longitudinally along the threaded member. The jacks are available commercially from Beaver Precision Products, Clawson, Mich.

The three identical elevating

jacks

28, 30 and 32 are positioned between and secured to the deck 2 and the yoke 16. Each jack (FIG. 4) includes a protective outer tube 34 connected with the deck 2 and a load-carrying inner stress tube 36 connected with the yoke 16. The inner tube 36 may be extended and contracted relative to the outer tube 34 by the action of a selectively operable, reversible motor 38 drivingly connected with a threaded member 40 of the ball screw type, hereinafter sometimes referred to as the ball screw, which is concentrically positioned within the tubes and is drivingly connected to the inner tube 36 by a ball nut 42. The threads of the member 40 are formed for rolling action therein of balls 43 of the nut 42, as shown in FIG. 4.

In operation, with the

jacks

28, 30 and 32 in an initial fully retracted position and the plungers 26 extended to secure the deck to the leg (as shown in FIG. 3), the upper plunger units 22 are selectively retracted to free the yoke 16 for vertical motion along the leg 6. The jacks are then extended by operation of the motors 38 until, with the jacks in a nearly fully extended position, the upper plunger units 22 are aligned with the then most closely adjacent pockets 20. The upper plunger units 22 are then extended to lock the yoke 16 to the leg. The lower plunger units 26 are then retracted to free the deck for vertical motion along the leg. The

jacks

28, 30 and 32 are then retracted by operation of the motors 38 in a reverse sense, with the result that the deck 2 is moved upwardly along the leg 6 toward the now stationary yoke 16 with the jacks functioning in tension. When the jacks are nearly fully retracted, the lower plunger units 26 are aligned with the then most closely adjacent recesses 20 in the tracks 18, after which the lower plunger units 26' are extended to secure the deck to the leg in its elevated position. Lowering of the deck occurs in reverse sequence to that described.

Suitable power and control equipment (not shown or claimed) may be utilized for effecting synchronous and sequential operation of the various separate elevating assemblies 10 supported on the deck 2 and of the various jacks and upper and lower plunger units included in the several elevating assemblies.

It will be appreciated that the provision of elevating jacks including the

concentric tubes

34 and 36 extending about and totally enclosing the operating members, namely the ball screw 40 and the ball nuts 42, protects the latter at all times from the deleterious effects of corrosive sea water and spray, abrasive saind granules suspended in the sea water, the clogging effect of marine sea organisms and the like, such effects being associated particularly with the unique environmental conditions encountered during the use of offshore platforms.

In another aspect of the invention the jacks at their upper and lower points of connection to the yoke 16 and deck 2 are provided with upper and lower

pivotal connections

43 and 44 respectively (to be described). The

pivotal connections

43, 44 ensure that each jack may align itself between the yoke and deck in such a manner as to maintain concentricity of the inner and

outer tubes

36, 34, the ball screw 40 and the ball nut 42, despite the torsional and fiexural deformations of the deck, leg and saddle structure usually occurring in the use of offshore platforms.

Additionally, the use of jacks functioning in tension during the deck elevating period provides a straightening effect for ensuring concentric alignment of the moving parts of the jack. In this way, binding and jamming between the working parts which might otherwise seriously reduce the elevating efiiciency and operational life of the jacks, is effectively minimized.

Referring in more detail to FIG. 2, each previously mentioned leg 6 extends through a circular aperture 45 in the yoke 16 and a corresponding opening in the deck 2 slidably and snugly extending about a major portion of the periphery of the leg. Adjacent holes 45 are joined by edges 46 spaced sufiiciently from the adjacent bracing members 8 to avoid interference therewith during vertical movement of the deck. About each leg 6 and spaced above the deck 2 is one of a plurality of the previously mentioned yokes 16. Each yoke 16 comprises an L-shaped, horizontally disposed plate-like member of generally uniform thickness provided with a central aperture 47 configured to extend slidably and snugly about a major portion of the leg 6, and to avoid interference with the adjacent bracing members 8.

The deck 2 and the yokes 16 are also provided with vertically extending

recesses

48 and 49, respectively, configured to extend slidably and snugly about the tracks 18. It will be appreciated that the tracks 18 cooperating with the correspondingly configured recesses 48 and 49 of the deck and yoke prevent rotational relative motion between the deck and the yoke and each leg 6 while permitting relative vertical sliding motion therebetween.

Although the invention is disclosed as including a leg provided with two tracks 18 and three elevating jacks, it will be understood that the number of tracks and jacks provided at each leg may be varied if this is desired.

Secured to the underside of the yoke 16 are the two previously mentioned upper plunger units 22 each supported from an adjacent portion of the yoke 16 by a bracket 50. Each upper plunger unit 22 includes a horizontally disposed, linearly acting plunger 52 having a forward end 54 adapted to enter and be snugly received within an adjacent one of the previously mentioned recesses 20 in the adjacent track 18. The plunger 52 is moved linearly into and out of locking engagement with the adjacent track 18 by a motor 56 forming a portion of the plunger unit 22. The motor 56 in the preferred embodiment comprises a conventional expansible chamber, hydraulic ram. However, it will be appreciated that other forms of axially acting motors such as for example linearly acting electromechanical actuators or pneumatic actuators may be utilized if so desired. As illustrated in FIG. 3, the plungers 52 on the upper plunger units 22 are shown released from the tracks 18 so that the yoke 16 is free to move relative to the leg 6.

To secure the deck 2 to the leg 6 plunger units, the previously mentioned lower plunger units 26 are provided, secured to the underside of the deck 2 by brackets 60. The lower plunger units 26, which are similar in construction and operation to the previously described upper plunger unit 22, are shown in FIG. 3 to be in an engaged position with the tracks 18 to secure the deck against motion relative to the legs 6.

The previously mentioned jack 28 is positioned angularly intermediate the tracks 18 relative to the leg 6, while the other two

jacks

30 and 32 are positioned on opposite sides of the tracks 18 from the central jack 28. Other arrangements for differing numbers of jacks may be provided.

Each of the

jacks

28, 30 and 32 (FIG. 4) includes a vertically extending, hollow, generally cylindrical, lower housing 70' having a closed lower end 72 and an open upper end 74. The closed lower end 72 of the housing is connected to the deck by the lower mounting 44 (to be described hereinafter).'-Fixedly secured to the upper end 74 of the lower housing 70 and concentric therewith is the previously mentioned upwardly extending cylindrical outer tube 34 which has an open upper end 78 provided with a radially inwardly extending lip 80. Mounted con centrically within and spaced radially from the outer tube 34 is the previously mentioned inner tube 36 which extends axially outwardly of the outer tube 34 through the opening 78. The upper end of the inner tube 36 is connected to the yoke means 16 by the upper joint 43 (to be described hereinafter).

Extension and contraction of the inner tube 36 is effected by the previously mentioned elongate ball screw 40 which is positioned concentrically within the outer protective tube 34 and has its upper portion extending into the inner tube 36. The ball screw 40 includes a lower portion extending into the lower housing 70'. The lower portion of the ball screw 40 is supported by a conventional, self-aligning, radical thrust bearing 86 and extends therethrough. The bearing 86 is of the type permitting rotary motion of the ball screw 40' about its central vertical axis, but preventing axial motion of the ball screw 40 in either direction relative to the housing 70 and outer tube 34. The lowermost end of the ball screw 42 projects downwardly a short distance below the bearing 86 and is received within a slip-spline driving sleeve 90. The sleeve 90 is drivingly connected through

bevel gears

94 and 96 to a driving shaft 98 extending radially into the lower housing and forming part of the previously mentioned motor 38 secured to the exterior of the housing 70. The motor 38 in the preferred embodiment comprises a selectively operable, reversible, hydraulic rotary motor, but alternative forms of motor such as for example electric or pneumatic motors may be employed if so desired. The motor 38 may be selectively operated in forward and reverse directions to rotate the ball screw 40 in opposite directions via the

gear train

94, 96 and the sleeve 90. Additional gearing (not shown) may be incorporated as a part of the motor 38 to enable the latter to provide the necessary torques and speeds required for elevating the immense loads encountered during elevation of the deck and for lowering thereof at a te strained rate. A spring-loaded disc brake 39 which may be included in the motor assembly 38 is included in the drive train to lock the ball screw 40 against rotation and is released automatically by an electrical solenoid 41 (FIG. 4) actuated concurrently with the motor 38, thus providing for fail safe locking of the jack.

To enable the rotary motion of the ball screw 40 to be converted into corresponding axial motion of the inner tube 36, the previously mentioned ball nut 42 is fixedly secured to the lower end of the inner tube 36 and extends about the ball screw 40 in threaded engagement therewith. As the advantagesof. ball nuts and their constructionand operation are'generally well known, further description of the present ball screw 40 and ball nut 42 will not be given except to say that it may be of the type disclosed, for example, in U.S. Pat. No. 2,932,209.

To provide a limit stop for overrunning of the ball nut 42, a projecting collar 100 is fixedly secured to the upper end of the ball screw 40. Downward travel of the nut 42 is limited by engagement with a corresponding lower projecting collar adjacent the lower end of the ball screw 40. Suitable limit switches (not shown) may also be provided to terminate operation of the motor before the ball nut 42 comes into abutting engagement with either of the just described points of abutment at its extreme limits of movement.

The range of motion of the ball nut 42 along the ball screw 40 is sutficient to move the lower end of the inner tube 36 from a fully retracted position closely above the lower end of the outer tube 34 to a fully extended position closely below the upper end of the outer tube 34.

Further protection against the ingress of damaging outside elements such as sea spray is provided by a resilient annular seal 92 abutting the outer surface of the inner tube 36 secured to the interior of the outer tube 34 and the lip 80 subjacent thereto.

It will be appreciated that the arrangement described protects the working elements of the jack, particularly the ball screw 40 and the ball nut 42, entirely from the effects of Wind, wave action, spray and sea water outside the

tubes

34 and 36, and furthermore that such protection is substantially unaffected during long periods of use. In this manner, disadvantages associated with the corrosive action of such elements acting directly on the working parts are entirely obviated, thereby providing enhanced working life and unimpaired working eiiiciency during extended periods of time under the particularly harsh environmental conditions uniquely encountered in the use of offshore platforms.

The previously mentioned

joints

43 and 44 at the upper and lower ends, respectively, of each of the elevating

jacks

28, 30 and 32 in the preferred embodiment comprise gimbal joints. Each gimbal joint 44 includes a horizontally disposed, first circular shaft 110 supported in spaced relation parallel to and above the adjacent deck 2 by a supporting bracket 112 fixed to the deck 2 and supporting the ends of the shaft 110 for rotation about the axis thereof. Fixedly secured to the shaft 110 adjacent the midpoint thereof and extending perpendicularly to the shaft 110 in opposite directions is a second circular shaft 114. A yoke 116 having spaced depending legs 118 rotatably secured about the opposed ends of the shaft 114 is fixedly secured to the lower end of the housing 70. It will be appreciated that the arrangement defines a gimbal jointpermitting pivotal motion of the lower housing 70 about two mutually, perpendicularly disposed,

horizontal axes. The upper gimbal joint 43 is similar in construction to the lower gimbal joint 44.

The provision of the gimbal joints 43 and 44 ensures that relative horizontal movement of the upper end of the jack relative to the lower end thereof, caused by flexural or torsional deformation of either the leg 6 or of the deck 2 or of the yoke 16 (frequently encountered during use), is compensated for by permitting the jack as a whole to align itself linearly between its upper and lower points of connection. Such linear alignment is additionally particularly facilitated by utilizing jacks which during periods of elevation of the deck are functioning in tension, thereby enhancing the straightening effect. In this manner, concentricity of the ball screw 40, the ball nut 42, the inner tube 36 and the outer tube 34 is maintained, thereby minimizing or avoiding potential binding of the working elements that might otherwise occur. In this manner, jamming of the extensible jack working elements is advantageously minimized, thereby maintaining operating efficiency and working life of the jacks.

An alternative form of pivotal joint is shown in FIG. 5. The joint shown in FIG. 5 includes an axially, downwardly extending shaft 120 fixedly secured to the lower end of the housing 70 and received within a ball member 122 forming part of a ball and socket joint supported in a ball housing 124 fixedly secured to the surface of the deck. A splined collar 126 fixed about the shaft 120 above the ball member 122 engages corresponding keyed portions 128 on the interior of the housing to prevent relative rotation between the housing 70 and the deck about the vertical axis of the jack. A resilient sleeve 130 extends between the exterior of the housing 116 and the lower end of the housing to prevent the ingress of contaminating fluids such as sea water, and of dirt. A similar upper ball joint may be provided for the upper end of the inner tube connected to the saddle.

It will be appreciated that elevating sequence described earlier for the preferred embodiment utilizes operating jacks which act in tension during the actual process of elevation of the deck 2 relative to the leg.

An alternative embodiment of the invention intended to function with the jacks acting in compression during periods of elevation of the deck is shown in FIGS. 6 and 7. In this embodiment, the leg 6 is provided with only a single track 18 having the previously mentioned recesses 20.

Two jacks 140, of the type previously described for the first preferred embodiment, have the upper ends of their respective inner tubes 36 fixedly secured to the underside of the deck 2 adjacent and on opposite sides of the track 18 (FIG. 6). An upper plunger unit 22, of the type previously described, for selectively securing the deck 2 to the track 18, is secured to the deck 2 by a depending bracket 142. The lower housings 70 of the two jacks are connected by a central housing 144 extending between the jacks and maintaining the outer tubes 34 thereof in parallel relation. The housing 144 extends toward the leg 6 and extends slidably and snugly about a major portion of the circumference of the leg 6 and the track 18 and is vertically slidable therealong. The housing 144 further includes and supports a lower plunger unit 26, of the type previously described, for fixedly securing the lower housing unit 144 to the track 18.

Mounted on the exterior of the housing 144 is a motor 148 having a shaft 150 (FIG. 7) extending radially into the interior of the housing 124. The shaft 150 has fixedly secured to its inward extremity a bevel gear 152. Two aligned, rotatably mounted shafts 154 supported on interior portions of the housing 144 and extending perpendicularly outwardly from the shaft 150 in opposite directions are provided at their mutually adjacent extremities with bevel gears .156 in meshing engagement with the bevel gear 152. At their outward extremities each of the shafts 154 has fixedly secured thereto another bevel gear 158 meshingly engaging one of the previously mentioned bevel gears 94 drivingly connected with the ball screw members 40 of the jacks. As the shafts 154 are rotated in opposite direction utilizing the gearing described, it is necessary to have the two ball screws 40 provided with opposite hand of thread in order that operation of the motor 158 in one direction extends the two jacks concurrently in the same direction. Reverse operation of the motor 158 similarly retracts the two jacks 140 concurrently.

Operation of the alternative embodiment of the invention shown in FIGS. 6 and 7 is generally similar to that described for the first embodiment with the exception that the jacks 140 are acting in compression during elevation of the deck 2. With the jacks initially in the position shown in FIG. 6, and with the lower plunger unit 32 engaged to secure the lower housing 144 to the track 18, the upper plunger unit 22 is then released to free the deck 2 for movement relative to the leg. The motor 148 is then operated to extend the inner tubes outwardly of the outer tubes so that the deck is elevated relative to the leg. With the tubes in an almost fully extended condition, the upper plunger unit 22 is aligned with the then most closely adjacent recess 20 in the track .18 and the plunger unit 22 engaged to lock the deck 2 to the leg. The lower plunger unit 26 is then released to free the lower housing 144 for motion relative to the leg 6. The motor 148 is then operated in reverse sense to retract the jacks until, in a nearly fully retracted position thereof, the lower plunger 26 is aligned with the then most closely adjacent recess 20 in the track 18. The lower plunger unit 26 is then engaged to lock the lower housing unit 144 to the leg and the process may be repeated for further subsequent elevation of the deck. Lowering of the deck occurs in reverse sequence.

In constructing an elevating assembly for an offshore platform according to the present invention, certain important operational advantages are provided.

A particularly significant advantage is provided by enclosingthe working elements of the jacks, namely the ball screw members and the ball nuts entirely within rigid rugged tubes, thus protecting the working elements from the deleterious effects of sea water corrosion and the like. Such protection ensures that operation 'of the jacks can continue unimpaired for extended periods of time in most severe environmental conditions.

Another significant advantage is provided by the pivotal joints provided at the upper and lower ends of the jacks for connecting them to the yoke and deck. Such pivotal connection ensures that the jacks may align themselves to compensate for flexural or torsional deformations of the surrounding structure in such a manner as to maintain concentricity of the various jack members. Such maintained concentricity (which is assisted by operating the jacks in tension during deck elevation in the first preferred embodiment) prevents binding or jamming of the various jack parts, resulting from objectionable buckling, couple or moment forces which might otherwise reduce the efficiency and operating life of the jacks.

Although the invention is described in reference to certain preferred embodiments, it will be apparent to those skilled in the art that additions, deletions, modifications, substitutions and other changes not specifically described and illustrated in the preferred embodiment may be made within the purview of the appended claims.

What is claimed is:

1. In an offshore platform of the type including a generally horizontal deck supported on a plurality of ground engaging, generally vertical legs extending slidably through the deck the legs being adapted for selective connection to the deck, at least one elevating assembly connected with at least one of the legs for raising and lowering the deck relative to the one leg, said elevating assembly comprismg:

yoke means connected with the leg for vertical sliding motion relative thereto, said yoke means being adapted for selective fixed connection to the leg,

at least one extensible jack positioned between said yoke means and the deck, said jack including:

an outer tube,

an inner tube telescopingly received within said outer tube and extending axially outwardly at one thereof,

an axially extending threaded member having a ball receiving groove and positioned concentrically within said outer tube and extending partially into said inner tube,

bearing means connected with said outer tube adjacent another end thereof for supporting said threaded member for rotary motion, said hearing means preventing axial movement of said threaded member relative to said outer tube,

motor means connected with said threaded member for selectively rotating said threaded member in opposite directions,

means for locking the threaded member against rotation,

nut means having balls threadedly engaging said threaded member, said nut means fixedly secured to an adjacent one end of said inner tube, said nut means causing relative extending and contracting movement of said inner tube relative to said outer tube upon rotation of said threaded member in opposite directions by said motor means,

first joint means for connecting said yoke means to said other end of one of said inner and outer tubes, said first joint means preventing axial movement of said one of said inner and outer tubes relative to said yoke means but permitting pivotal movement relative thereto, and

second joint means for connecting the deck to said other end of the other of said inner and outer tubes, said second joint means preventing axial movement of said other tube relative to the deck, but permitting pivotal motion relative thereto.

2. An elevating assembly as defined in claim 1 wherein, said yoke means is spaced vertically above the deck, said outer tube being secured to the deck, and said inner tube being secured to said yoke means.

3. An elevating assembly as defined in claim 2 wherein. said nut means comprises a ball nut and said threaded member comprises a ball screw engaging said ball nut.

4. An elevating assembly as defined in claim 3 wherein said first and second joint means each comprise ball and socket joints.

5. An elevating assembly as defined in claim 3 wherein said first and second joint means each comprises gimbal joints.

6. An elevating assembly as defined in claim 3 further including,

automatic locking means connected with said ball screw member for preventing rotation thereof, said locking means being connected with said motor means for automatically releasing said locking means only during operation of said motor means.

7. An elevating assembly as defined in claim 3 further including,

a plurality of vertically spaced recesses in the leg,

and

first and second motors respectively secured to the deck and said yoke means having plungers movable selectively into locking engagement with one at a time of said recesses in said leg.

8. An elevating assembly as defined in claim 7 wherein said motor means includes a first bevel gear fixedly connected to said threaded member,

a second bevel gear meshingly engaged with said first bevel gear,

a shaft fixedly connected with said second bevel gear,

and

a reversible, selectively operable motor drivingly connected with said shaft.

9. The elevating assembly as defined in claim 3 wherein said ball nut means includes,

a housing extending peripherally about said ball screw member,

said housing including a threaded track, and

a plurality of ball members interposed between corresponding ball track portions of said ball screw member and said ball nut housing.

10. An elevating assembly as defined in claim 1 wherein, said yoke means is spaced vertically below the deck, said outer tube being connected with said yoke means, and said inner tube being connected with the deck.

11. An elevating assembly as defined in claim 10 further including,

at least two said jacks,

said motor means including an engine,

a driving shaft driven by said engine,

two driven shafts,

means for drivingly connecting each of said driven shafts concurrently and separately with said driving shaft; and

means for drivingly connecting said ball screw members of said two jacks with one each of said two driven shafts.

12. In an offshore platform of the type including a generally horizontal deck supported on a plurality of ground engaging, generally vertical legs extending slidably through the deck, the legs being adapted for selective 1 1 connection to the deck, at least one elevating assembly connected with at least one of the legs for raising and lowering the deck relative to the one leg, said elevating assembly comprising: an extensible jack mounted between the one leg and the deck, said jack including an upright housing, a threaded member having a ball-receiving helical groove extending at its lower end into said housing and with the upper end of said threaded member projecting above the housing, means in the housing journaling the threaded member for rotation while holding said member against axial movement relative to the housing, a drive motor at one side of the housing having means in the housing operatively connecting the motor with the threaded member, said motor including means for locking the threaded member against rotation when not operated by the motor, a ball nut mounted on the threaded member, and a sleeve connected with the nut and extending therefrom over the upper end portion of the threaded member for connecting the nut with the one leg.

References Cited UNITED STATES PATENTS ROBERT C. RIORDON, Primary Examiner D. R. MELTON, Assistant Examiner US. Cl. X.R. 254106