US 3894504 A
A monopod drilling platform having cylindrical structural column extending vertically between a drilling deck and a submerged base in which a concentric sleeve surrounds the column and is rotatably supported from outside of the sleeve, the sleeve having ice cutter arms projecting radially from the outer surface thereof. Both axial thrust and centering of the sleeve are provided by a plurality of rollers mounted around the outside of the sleeve, the roller engaging a conical surface projecting outwardly from the sleeve. The rollers are individually adjustable and removable without interrupting rotation of the sleeve by drive means mounted on the deck.
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Description (OCR text may contain errors)
United States Patent July 15, 1975 Smith l l ICE CUTTER FOR MONOPOI) DRILLING L TFORM Primary E.taminerTrygve M. Blix A Assistant E.t'aminerStuart M. Goldstein  Inventor: Charles Glenddlfi Cdhf' Attorney Agent, or Firm-Christie, Parker & Hale  Assignees Sea-Log Corporation, Pasadena.
Calif  ABSTRACT  Filed; Apr. 8, 1974 A monopod drilling platform having cylindrical structural column extending vertically between a drilling [Z1] Appl- N05 459,029 deck and a submerged base in which a concentric sleeve surrounds the column and is rotatably sup- 52 5 3 114 2; 4 299/24 ported from outside of the sleeve the sleeve having 51 Int. ct .i B63!) 35/12 ice Cutter firms Projecting radially from the Outer WP  Field of Search H H4/5 D4UU4142; face thereof. Both axial thrust and centering of the 61/465 1 R; 299/24 25 sleeve are provided by 11 plurality of rollers mounted around the outside of the sleeve. the roller engaging a  References Cited conical surface projecting outwardly from the sleeve UNITED STATES PATENTS The rollers are individually adjustable and removable without interrupting rotation of the sleeve by drive 3669.052 (1/l972 Schlrtzlnger l 14/42 means mounted On the deck 3,696,624 lU/l972 Bennett w. ll4/42 1759046 9/1973 Anders .7 l l4/4l 8 Claims. 6 Drawing Figures :r c: u c u a 8 u u a a n a a PATENTH] JUL 1 5 I975 SHEET ICE CUTTER FOR MONOPOD DRILLING PLATFORM FIELD OF THE INVENTION This invention relates to drilling platforms for operation in arctic waters, and more particularly, is concerned with an ice cutting mechanism for a monopodtype structure.
BACKGROUND OF THE INVENTION With the discovery of oil in the arctic regions of the world, there has developed a need for a drilling platform capable of operating in icy waters. The forces created by lateral and vertical movement of ice floes can damage or overturn an offshore drilling platform. Various types of mechanisms have heretofore been proposed for cutting, melting, or otherwise diverting the ice from imposing destructive forces on the supporting structure of off-shore drilling platforms. See, for example, US. Pat. No. 3,669,052.
Such prior art systems have included the use of high speed rotating cutters for comminuting the ice as it moves toward the platform supports. Generally the cutters have been spaced about the supporting structure so as to operate effectively with ice movement from any direction. Some designs include cutters which rotate concentrically around the vertical axis of the supporting structure. However, concentrically operated cutters have presented problems in effectively supporting and driving the concentric cutters so as to withstand the forces and transmit the power required. For example, it has been necessary to adjust the vertical position of the cutters to accommodate different levels and thicknesses of ice. Such arrangements have been practical only where the supporting columns are relatively small in diameter.
The present invention provides an improved ice cutting apparatus for operation with a monopod-type structure, in which all drilling takes place through a central opening in a single column that also provides structural support for the drilling deck and associated superstructure above the water from a submerged base. Such a column is, of necessity, of relatively large diameter, presenting unique problems in rotatably supporting thereon a concentric cutter strong enough and driven with sufficient torque to handle heavy ice floes.
SUMMARY OF THE INVENTION In brief, the present invention provides an ice cutting mechanism for a monopod platform in which the cutters are mounted as radial arms on a sleeve that is concentric with the supporting column. The sleeve may extend substantially the full length of the column but is supported at either end on a plurality of rollers which engage a conical surface projecting from the outside of the sleeve. The rollers are individually mounted and adjustable to align the sleeve concentrically with the supporting column. In one embodiment, the rollers with their mounting structure are positioned inside a housing beneath the deck for protection from the elements.
In an alternative embodiment the rollers are located adjacent the lower end of the sleeve and mounted on the lower hull structure below the water. The rollers are individually adjustable to equalize the load on each bearing, and are individually replaceable to permit maintenance and individual replacement to go forward without interruption of the cutter drive mechanism.
DESCRIPTION OF THE DRAWINGS For a better understanding of the invention. reference should be made to the accompanying drawings, wherein:
FIG. I is an elevational view of a monopod drilling structure incorporating the features of the present invention;
FIG. 2 is a sectional view taken substantially on a line 22 of FIG. 1;
FIG. 3 is a partial sectional view taken on a line 3-3 of FIG. 2;
FIG. 4 is a detailed sectional view of the supporting roller assembly;
FIG. 5 is a sectional view taken substantially on a line 5-5 of FIG. 4; and
FIG. 6 is a detailed sectional view of an alternative embodiment.
DETAILED DESCRIPTION Referring to the drawings in detail, the numeral l0 indicates generally the base of a drilling platform. The base is in the form of a hull constructed of bulkheads and outer plates, providing a substantially watertight structure which may be ballasted to rest on the sea bottom at the drilling location or which may be sufficiently buoyant to float beneath the surface as a semisubmersible. A superstructure 12 providing an upper drilling deck I4 is supported above the water surface from the base I0 by a single vertical column indicated generally at 16. Drilling is accomplished from the drilling deck 14 down through the column and base into the sea floor by means of conventional drilling equipment including a drilling derrick 18 mounted on the drilling deck 14. As shown in the cross-sectional view of FIG. 2, the column consists of an outer stationary cylindrical shell 20 which is rigidly attached at its lower end to the bottom of the base 10. Inside the column 20 is a cylindrical casing 22 through which access to the ocean floor from the drilling deck is provided. The opening through the casing is referred to as the "moon pool" The casing 22 is preferably offset from the outer stationary cylinder 20 to provide a larger working space for men and equipment between the drilling deck and the subsurface base.
Surrounding the outside of the cylinder 20 and concentric therewith, is a cylindrical sleeve 24. The sleeve 24 is rotatably supported and driven from the upper superstructure 12 to permit continuous rotation of the sleeve 24 around the outside of the cylinder 20. Individual cutter arms 26 are secured to the outer surface of the sleeve 24. The cutter arms are positioned around the complete circumference of the sleeve 24 and are positioned vertically substantially the full length of the column 16.
The cutter sleeve 24 is rotatably supported at its upper end by means of a segmented collar 30. The segmented collar provides a conical supporting surface 32 extending continuously and completely around the top of the sleeve. The axis of revolution of the conical surface is coaxial with that of the cylinder 20, the conical surface extending at an acute angle upwardly and outwardly from the sleeve. A plurality of roller assemblies 34 are mounted on supporting members 36 attached to and extending downwardly from the structure supporting the drilling deck 14. Details of the roller assembly are described below in connection with FIGS. 4 and 5. While as few as three roller assemblies would permit balanced support, because of the large load and to provide sufficient margin of safety, typically ninety or more roller assemblies spaced at a foot or less apart are provided.
The roller assemblies 34 include rollers which engage the conical surface 32. The rollers, by having their roll axes intersecting the axis of rotation of the cutter sleeve at the same acute angle as the conical surface 32, both support the weight of the sleeve and center the sleeve about its axis of rotation. Rotation is imparted to the cutter sleeve 24 by means of a segmented ring gear 40 attached to the outer circumference of the cutter sleeve just below the upper end thereof. The ring gear in turn is engaged by one or more drive assemblies, each including an engine 42 connected through a clutch 44 to a gearbox 46, all of which is mounted on a lower deck 48 within the upper housing 12 of the drilling platform. The gearbox 46 drives a pinion gear 50 that is in driving engagement with the ring gear 40. A number of such engine and gearbox drives may be angularly spaced about the periphery of the ring gear 40, permitting the amount of horsepower driving the cutter sleeve to be varied according to the load conditions by increasing or decreasing the number of engines operat- Referring to FIGS. 4 and in detail, the roller support assembly is shown in more detail. The collar 30 is made up of a plurality of abutting sectors having an inner cylindrical surface which engages the outer surface of the upper end of the cutter sleeve 24. The collar sectors are held in place by screws 52 which extend through flange portions of the collar sectors and threadedly engage the cutter sleeve. The abutting collar sectors provide a continuous annular conical surface 32 extending completely around the cutter sleeve 24. Each roller assembly 34 including a supporting bracket 54 which is bolted to the supporting members 36 by removable bolts (not shown). Each bracket 54 has a lower flange 56 through which extends a threaded opening 58. The axis of the opening 58 extends substantially perpendicular to the conical surface 32. An adjustable support and guide member 60 threadedly engages the opening 58. The axial position of the member 60 can be changed by screwing it in and out of the opening 58. A lockscrew 62 extends through a selected one of a plurality of notches 63 positioned around the outer periphery of the adjusting member 60. The screw 62 threadedly engages the flange 56.
A yoke 64 has an integral supporting shaft 66 journaled for rotation in a bore 68 extending through the adjusting member 60. Axial position of the yoke 64 is made adjustable by spring means positioned between the yoke 64 and the adjusting member 60. The spring is preferably in the form of at least one pair of dished spring washers 70, commonly referred to as Belleville" washers.
The yoke supports a shaft 72 on which is journaled a roller 74 by means of a pair of tapered roller bearings 76. Shaft 72 is held in place on the yoke by means of a flange 78 at one end and a nut 80 which threadedly engages the other end. The yoke 64 is provided with a lug 82 on one side which engages a slot 84 formed adjacent the upper end of the supporting bracket 54. The
lug 84 prevents any rotation of the roller assembly about the axis of the supporting shaft 66.
In a typical installation the cutter sleeve may have an outer diameter of the order of 20 feet, for example, thus the supporting column may have a circumference of 65 feet or greater. As many as ninety roller assemblies may be positioned around the circumference of the collar to share the load of the cutter sleeve. By way of example only, the vertical load imposed by the rotating cutter assembly on the supporting rollers may be in the order of 400 tons. Each of the rollers can be adjusted so as to distribute the load substantially equally among all of the rollers. However, it is possible for the cutter sleeve to be operated with one or more of the rollers not taking any of the load. Thus, extremely high reliability is achieved since, if any one of the roller assemblies fails, it can be removed and replaced without interrupting the operation of the cutters. A defective roller assembly can be easily removed by removing the adjusting member 60. The roller assembly 34 can then be cocked to one side and lifted out of opening 58, permitting a new assembly to be inserted in its place. The location of the roller assemblies within the upper housing 12 makes them readily accessible during operation.
The angle of the rollers is such that they are capable of resisting not only vertical forces due to the weight or other axial thrust loads on the cutter sleeve, but also the rollers resist radial forces on the sleeve and act to center the sleeve in concentric position with respect to the supporting cylindrical structure 20. However, it is preferable to provide a nylon or other suitable bearing material in the annular space between the inside of the cutter sleeve 24 and outside of the cylinder 20 adjacent the upper end of the sleeve. The nylon bearing includes a base member secured to the cylindrical member 20 with a nylon facing 92 spaced from the inside wall of the cutter sleeve 24. The nylon bearing may either be in the form of a continuous ring or in the form of angularly spaced individual segments positioned around the circumference of the cylindrical member 20. The nylon bearing is provided only as a safety feature and normally would not be under radial load.
In addition, a nylon bearing 96 is provided as a spacer between the cylindrical member and the sleeve at the lower end of a cutter sleeve 24 for transferring a por tion of the lateral loads from the sleeve to the supporting column.
An alternative embodiment is shown in FIG. 6 in which the bearing support and drive for the sleeve 24 are located at the lower end of the sleeve. The motors for driving the sleeves are located within the lower hull 10. Output drive shaft, such as indicated at 100, passes through a plate 102 within the lower hull 10 through a suitable bearing 104. The upper end of each shaft terminates in a pinion gear 106 which engages a ring gear 108 extending around the outside of the lower end of the sleeve 24. A plurality of drive shafts 100 and pinion gears 106 are positioned at circumferentially spaced points around the ring gear 108.
The bearing support assembly for the sleeve 24 includes a base plate 110 which is supported from the plate 102 by an outer support plate 112 and a plurality of radially extending plates, one of which is indicated at 114. A plurality of roller assemblies, one of which is indicated at 116, similar to the roller assembly 34 described above, are individually supported from the top of the plate by an adjustable mounting assembly indicated generally at 118. p
The adjustable mounting assembly 118 includes a base 120 which is bolted or otherwise secured to the top of the plate 110. A hinge plate 122 is pivotally joined to the base 120 by a hinge pin 124. The outer end of the hinge plate 122 is adjustably supported from the base 120 by an arm 125 pivotally joined to the base 120 by a hinge pin 126. The outer end of the arm is threaded, as indicated at 128. A coupling unit has a sleeve portion which slips over the threaded end of the arm 124 and is held between two nuts 132 and 134 which engage the threaded end 128 of the arm 124 and clamp the sleeve portion of the coupling unit. The outer end of the hinge plate 122 in turn is pivotally connected to the coupling unit 130 by a pin 136. Thus by adjusting the nuts 132 and 134, the angle of the hinge plate 122 relative to the base 120 can be varied.
The roller assembly 116 includes a roller 138 which is in rolling with a conical surface 140 provided by a support bracket 142 which extends around the periphery of the sleeve 24.
The roller assembly 116 includes one or more pairs of dished spring elements 144 which are placed under compression by the load of the sleeve 24. The load is equalized among a plurality of roller assemblies by a threaded guide member 146 which engages a threaded opening in the hinge plate 122. Rotation of the threaded guide member by a detent knob 148 moves the roller assembly 116 in a direction perpendicular to the conical surface 140. The detent knob 148 is locked in position by a detent member 150 which is anchored to a shaft 152 by a clamping screw 154. The shaft 152 also passes through a flange 156 integral with the roller assembly 116 so as to keep the roller assembly in proper alignment. An indexing plate is held between the lower end of the spring elements and the knob 148 to provide an indication of the degree to which the spring elements are compressed by adjust ment of the knob 148. This permits each roller assembly 116 to be adjusted to equalize the load on each assembly.
Individual roller assemblies 116 can be removed by loosening the knob 148 until the load on the roller is relieved. The pin 136 is then withdrawn, allowing the hinge plate 122 to be backed off sufficiently for the roller assembly to be lifted from the threaded guide member 146. A shroud 158 may be provided which surrounds the roller assembly 116 to prevent pieces from a broken bearing falling into the gears.
The entire roller assembly is positioned in the watertight lower hull 10. the sleeve 24 extends down through the top of the hull through a suitable seal (not shown) to prevent water from entering around the outside of the sleeve.
What is claimed is:
1. A drilling platform for operation in arctic waters comprising:
a work platform positioned above the water, subsurface support means including a vertically extending cylindrical member on which the working platform is supported, and ice cutting means mounted on the cylindrical member, the ice cutting means including a concentric sleeve extending around the cylindrical member, bearing means rotatably supporting the sleeve on the cylindrical member, a plurality of radially projecting cutter arms mounted on the sleeve, drive means for rotating the sleeve about the cylindrical member. the bearing means comprising a plurality of rollers spaced around the outer circumference of the sleeve, and means individually supporting the rollers in fixed relation to the sub-surface support means with the axes of the rollers extending radially of the sleeve at an acute angle to the axis of the rotation of the sleeve, the sleeve having a conical surface extending outwardly of the sleeve at said acute angle and in contact with said rollers.
2. Apparatus of claim 1 wherein each individual roller supporting means includes spring means for yieldably supporting the associated roller along an axis perpendicular to the conical surface.
3. Apparatus of claim 2 wherein each individual roller supporting means is detachable.
4. Apparatus of claim 1 wherein the drive means includes a ring gear extending around the outside of the sleeve, and a plurality of drive units supported from the working platform and spaced around the periphery of the ring gear, each drive unit having a pinion engaging the ring gear to drive the ring gear and sleeve.
5. in a drilling platform having a lower submerged hull, an upper deck structure, and at least one cylindrical supporting column extending vertically between the lower hull and upper deck structure, ice cutting apparatus comprising a tubular sleeve concentrically positioned on the supporting column, the upper end extending up to the deck structure and the lower end extending down to the hull, annular bearing means between the column and inside of the sleeve adjacent the lower end of the sleeve, and thrust bearing means extending around the outside of the upper end of the sleeve, support means rigidly secured to the upper deck structure extending under the thrust bearing means for supporting the thrust bearing means from the deck structure, and means extending radially from the sleeve above the thrust bearing means for transferring the weight of the sleeve to the thrust bearing means, a plurality of ice cutters projecting from the sleeve below the thrust bearing, and drive means supported from the upper deck and engaging the sleeve in driving relationship.
6. In a drilling platform having a lower submerged hull, an upper deck structure, and at least one cylindrical supporting column extending vertically between the lower and upper hulls, ice cutting apparatus comprising a tubular sleeve concentrically positioned on the supporting column, annular bearing means between the column and inside of the sleeve adjacent the lower end of the sleeve, and thrust bearing means extending around the outside of the upper end of the sleeve, support means secured to the upper deck structure extending under the means for supporting the thrust bearing means, and means extending radially from the sleeve above the thrust bearing means for transferring the weight of the sleeve to the thrust bearing means, a plurality of ice cutters projecting from the sleeve below the thrust bearing, and drive means supported from the upper deck and engaging the sleeve in driving relationship, the thwst bearing means including a plurality of rollers spaced around the outer circumference of the sleeve, and means individually supporting the rollers in fixed relation to the support means with the axes of the rollers extending radially of the sleeve at an acute angle to the axis of rotation of the sleeve, the sleeve having 3 ,894,504 7 8 a conical surface extending outwardly of the sleeve at pendicular to the conical surface. said acute angle and in contact with said rollers.
7. Apparatus of claim 6 wherein each individual roller supporting means includes spring means for yieldably supporting the associated roller along an axis per- 8. Apparatus of claim 7 wherein each individual roller supporting means is detachable.