US3771481A - Single column semisubmersible drilling vessel - Google Patents

Single column semisubmersible drilling vessel Download PDF

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US3771481A
US3771481A US00139765A US3771481DA US3771481A US 3771481 A US3771481 A US 3771481A US 00139765 A US00139765 A US 00139765A US 3771481D A US3771481D A US 3771481DA US 3771481 A US3771481 A US 3771481A
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vessel
draft
columns
platform
central column
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US00139765A
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Y Goren
S Lloyd
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Santa Fe International Corp
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Santa Fe International Corp
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
    • B63B35/00—Vessels or similar floating structures specially adapted for specific purposes and not otherwise provided for
    • B63B35/44—Floating buildings, stores, drilling platforms, or workshops, e.g. carrying water-oil separating devices
    • B63B35/4413—Floating drilling platforms, e.g. carrying water-oil separating devices
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
    • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
    • B63B1/00—Hydrodynamic or hydrostatic features of hulls or of hydrofoils
    • B63B1/02—Hydrodynamic or hydrostatic features of hulls or of hydrofoils deriving lift mainly from water displacement
    • B63B1/10—Hydrodynamic or hydrostatic features of hulls or of hydrofoils deriving lift mainly from water displacement with multiple hulls
    • B63B1/107—Semi-submersibles; Small waterline area multiple hull vessels and the like, e.g. SWATH

Definitions

  • a central column supports a working platform in spaced relation above the hulls.
  • the hulls buoyantly support the vessel in a low draft condition with the hulls having freeboard.
  • the hulls and outboard columns have ballast compartments for ballasting and deballasting the vessel to respectively submerge the hulls, outboard columns, and a portion of the central column to provide a high draft condition with the mean waterline located intermediate the height of the central column and between the platform and the upper ends of the outboard columns, and return the vessel to a low draft condition.
  • the outboard columns provide stability to the vessel during the initial portion of its transition from the low draft condition to the high draft condition and in the final portion of its transition from the high to the low draft condition. Stability in the high draft condition is predominantly provided by locating the center of gravity below the center of buoyancy. Drilling operations in the high draft condition are effected through the central column which also provides decks for mud handling, storage, etc.
  • This invention relates to a variable draft vessel and particularly relates to a variable draft deep water drilling vessel having twin hulls and a single central column mounting a drill platform.
  • An early method of offshore drilling provides for the erection of a self-contained fixed platform which is supported by pilin gs driven into the sea floor and has a drilling rig, auxiliary equipment and crews quarters located on the platform.
  • a tender or derrick barge is brought to dismantle and remove the drilling equipment and, in the case of a dry hole, the entire selfcontained platform is dismantled and removed.
  • a variation of the foregoing method provides a somewhat smaller platform similarly erected on piles and having a drilling rig located thereon while the auxiliaries, equipment and crew are located in a tender tied alongside.
  • the platform is likewise either left for oil production or is dismantled and removed in the case of a dry hole.
  • the latter two methods are largely applied for production drilling and not exploratory.
  • Another method employs a selfelevating barge which is towed to .the drilling site and provided with columns or legs which are then lowered and embedded in the sea floor. The barge is then jacked up so as to clear the water surface and serves as a platform on which the drilling rig, crew, and auxiliary equipment are subsequently positioned for drilling operation.
  • a fixed platform is generally erected for continuing oil production and the selfelevating barge is towed to another drilling site.
  • Deep water exploratory drilling is usually accomplished by means of surface floating drilling vessels which are either towed or self-propelled to the drilling site and are self-contained in that the drilling rig, auxiliary equipment and crews quarters form an integral part of the vessel.
  • These floating drilling vessels are anchored over the drilling site and are normally provided with a central opening through which the drilling rig is operated. Drilling operations from these floating vessels are, however, highly restricted by sea state conditions, since excessive vessel motion in heave, pitch and roll can and does damage the drilling equipment, as well as aggravate the problem of maintaining the vessel anchored directly over the drilling site.
  • the stability and motion characteristics of such a single-hulled drilling vessel are accordingly not conductive to efficient oil drilling operations.
  • a twin hulled or catamaran type oil drilling vessel has been constructed; however, while that vessel affords greater stability than a single-hulled vessel, it involves substantial problems which include excessive vessel motion due to wave action, no substantial motion minimizing characteristics, overstability including a low natural period and resultant snapping action which tosses personnel about and may endanger the drill string and other equipment. Accordingly, while these vessels are not geographically limited to offshore drilling operations, they are limited to use in restricted or calm waters.
  • Deep water exploratory drilling operations have also employed semisubmersible platforms, which, like the floating vessels, are completely self-contained.
  • the platform is supported by a plurality of structural members including stabilizing columns joined at their lower ends to a base flotation structure which, when in unballasted condition, floats the entire structure above the surface of the water in a low draft condition with the base structure having freeboard.
  • the columns are spaced from one another and are usually arranged substantially symmetrically about the outboard extremities of the platform.
  • the base flotation structure is ballasted to submerge the same and portions of the columns whereupon the vessel obtains a high draft condition.
  • the drilling platform is maintained above water in the high draft condition by the displacement of the submerged portions of the columns and the residual displacement of the base structure. Platform stability about pitch and roll axes is provided by the righting moments generated by the waterplane areas of the columns located outboard of the center of the platform.
  • the stabilizing columns form substantially symmetrical equilateral polygons with the columns located at the apices of the respective polygons which are normally square or triangular in shape.
  • the equilateral symmetrical polygonal arrangement provides substantially identical righting moments about the roll and pitch axes, as well as any intermediate axes, regardless of wave direction.
  • Another form of similar semisubmersible vessel includes a plurality of stabilizing columns interconnected adjacent their upper ends so that only the columns float in the water, with the columns again being arranged in a symmetrical equilateral polygon.
  • a variable draft drilling vessel which has achieved adequate stability for well drilling operations in a high draft condition and which has eliminated the serious disadvantage of very low mobility between drilling sites common to prior semisubmersible platforms, has been constructed and utilized.
  • Such vessel is described and illustrated in US. patent application Ser. No. 766,662 filed Sept. 4, 1968 as a continuation-in-part of application Ser. No. 666,395 filed Sept. 8, 1967, now abandoned, both of which applications are of common assignee herewith.
  • that vessel is characterized by a pair of hulls in spaced sideby-side substantially parallel relation one to the other with each hull mounting a plurality of upstanding columns supporting a drilling platform at their upper ends.
  • Particular features of that vessel include high mobility between drilling sites, adequate stability in the high draft condition over the drilling site, and vessel motion minimizing characteristics whereby the vessel is substantially non-responsive to excitation forces caused by wind and wave action. This vessel has performed successfully in various drilling areas throughout the world.
  • FIG. 1 is a perspective view of a twin hull variable draft vessel constructed in accordance with the principles of the present invention and illustrated in a high draft condition;
  • FIG. 2 is a side elevational view thereof
  • FIG. 3 is an end elevational view thereof
  • FIG. 4 is a horizontal cross sectional view thereof taken generally about on line 4-4 in FIG. 2;
  • FIG. 5 is a cross sectional view of the platform taken generally about on line 55 in FIG. 2 and illustrating its general arrangement;
  • FIG. 6 is an enlarged vertical cross sectional view of the central column
  • FIGS. 7, 8 and 9 are cross sectional views thereof taken generally about on lines 77, 8-8, and 9-9 in FIG. 6;
  • FIG. 10 is a schematic view of one of the hulls of the vessel illustrating a ballast system therefor;
  • FIG. 11 is a perspective view of another embodiment of a twin hull variable draft vessel constructed in accordance with the principles of the present invention arid illustrated in a low draft towing condition;
  • FIG. 12 is a perspective view of the vessel illustrated in FIG. 11 in a high draft drilling condition
  • FIG. 13 is a side elevational view thereof
  • FIG. 14 is an end elevational view thereof.
  • FIG. 15 is a horizontal cross sectional view thereof taken generally about on line 15-15 in FIG. 14.
  • variable draft vessel comprising a pair of transversely spaced, elongated hulls 12 extending in parallel relation one to the other and providing sufficient displacement to support vessel 10 in a low draft floating condition with the hulls having freeboard indicated atfin FIG. 2.
  • I-Iulls 12 are substantially identical one with the other, each hull having a substantially rectangular cross section as illustrated in FIG. 3.
  • Each hull 12 has designed hydrostatic properties and hydrodynamic characteristics, including being streamlined for minimum resistance to motion through the water.
  • Each hull has a bow 14, a sterrn 16 and a midbody therebetween.
  • Hulls 12 are substantially streamlined in shape to minimize resistance to movement through the water when vessel 10 is entirely supported by hulls 12 in the low draft condition with the hulls having freeboard f as illustrated in FIG. 2.
  • Suitable longitudinally spaced box-like trusses 18 extend between the hulls 12 in overlying relation thereto and between the end pairs of columns 26 to be described. Trusses 18 provide structural connections for maintaining the hulls in spaced substantially parallel relation one to the other.
  • a platform or main deck 20 is supported in spaced relation above hulls 12 by a vertically extending central column 24, the lateral extremities of platform 20 being cantilevered from column 24.
  • the upper end of central column 24 is secured to platform 20 and its lower end is spaced above hulls 12, the column 24 being supported thereat by box like structural elements 28 having generally rectangular cross sections and which extend diagonally inwardly and upwardly from hulls 12 to the underside of column 24.
  • elements 28 provide structural interconnection between column 24 and hulls 12 with column 24 located centrally of the vessel, i.e., the vertical axis of column 24 lies medially between hulls l2 and substantially medially of the opposite ends of vessel 10.
  • central column 24 includes an enlarged diameter portion 30 which forms the lower end or base of column 24.
  • Column 24 has a central shaft 32 extending coaxially therewith for its full length.
  • a drilling derrick or mast 38 is carried on deck 20 centrally of the vessel 10 whereby a marine riser, not shown, can extend from derrick 38 through central shaft 32 of column 24 and between hulls 12 for conducting drilling operations as set forth more particularly hereinafter.
  • the central column 24 comprises a plurality of decks at the various elevations thereof, the upper decks including a spider deck 40 and storage decks 42 for storing drilling supplies.
  • the lower diametrically enlarged portion 30 of column 24 provides a mud system deck 44.
  • the mud system deck houses mud pumps, mud mixing pumps, reserve mud tanks, etc.
  • personnel and freight elevators 46 and 48 respectively are provided for access to each of these decks.
  • Deck 20 is circular in plan view at its forward and aft ends as illustrated in FIG. 4 with its sides terminating coincident with chord lines of the circle circumscribing the fore and aft deck ends.
  • Deck 20 includes a Texas deck comprising a plurality of deck houses 50 for housing machinery 51, crews quarters 53, various auxiliary equipment, etc.
  • a plurality of pipe racks 55 are provided deck 20 for storing drill pipe.
  • an upper deck is provided and includes a deck house 52 for housing various offices and additional auxiliary equipment, deck house 52 being located adjacent the forward portion of the vessel.
  • a helideck 54 is provided above deck house 52.
  • the drilling equipment on deck 20 preferably includes an automatic drill pipe racking mechanism, generally indicated 56, for lifting the pipe from its storage area to a vertical position within the drilling mast for connection in the drill string.
  • a pair of cranes 58 are mounted on opposite sides of vessel 10 and may be of any conventional design, including the usual booms 60 and operating cabs 62. Cranes 58 may have any desired capacity, for example, 100 tons. Preferably, the cranes are mounted on pedestals 64.
  • columns 26 are disposed along the outboard sides of hulls 12 such that the cen troids of the cross-sectional areas thereof lie outboard of the centerlines of the associated hulls. In this man ner, the columns develop larger moments of inertia of the waterplane areas about the roll and pitch axes to provide stability to the vessel during its transition between high and low draft conditions as set forth hereinafter than would be the case were the columns 26 disposed along the centerlines of the hulls.
  • Columns 26 upstand from hulls 12 a predetermined height depending upon the predicted characteristics of the vessel when the vessel makes the transition between low and high draft conditions, also as set forth more particularly hereinafter.
  • each hull 12 is provided with a layer of very dense concrete along its bottom.
  • the concrete has a very high specific gravity on the order of 3.5 or 4 and comprises permanent ballast for the vessel in addition to the water ballast utilized as described hereinafter to vary the draft of the vessel between low and high draft conditions.
  • hulls 12 are each divided into a plurality of compartments forming ballast chambers for varying the draft of the vessel.
  • the columns 26 are divided into a plurality of compartments 72 (FIG. 3) forming ballast chambers and the ballast chambers 70 and 72 are selectively and independently ballasted and deballasted whereby the draft of the vessel can be altered between high and low draft conditions with the deck 20 remaining substantially level at each vessel draft.
  • the ballast chambers may also be utilized to correct the trim of the vessel about both roll and pitch axes during submergence to and retention of the vessel in the high draft condition.
  • ballasting and deballasting operations can be conducted when the vessel lies in thehigh draft condition to change the natural period of the vessel in heave, pitch and roll, as I desired.
  • the starboard hull and ballast system therefor are illustrated and it will be understood that the port hull is similarly arranged and ballasted but is of opposite hand.
  • the ballast chambers 72 in the transitional columns 26 carried by each hull 12 are not illustrated although the ballast connections for such chambers 72 are illustrated.
  • Ballast chambers 70 and 72 are selectively and independently ballasted and deballasted whereby the vessel may be partially submerged, i.e., within a range between high and low draft conditions as herein set forth,
  • a plurality of conduits 74 extend from a centrally located pump room P in each of the hulls in opposite longitudinal directions to the several ballast chambers 70 in the hulls.
  • a plurality of conduits 76 also extend from the pump room in each hull to the ballast chambers 72 in columns 26.
  • a pair of conduits 78 extend aft from pump room P and terminate in a pair of compartments 80 which may be employed as supplemental ballast compartments or as compartments containing drilling water. While not a part of the ballasting system per se, a pair of bilge water conduits 82 extend fore and aft from pump room P into bilges of the hulls and are in communication with the ballast pumps in a manner to be described.
  • the pump room is provided with a sea suction inlet indicated at 84 and an overboard discharge indicated at 86 controlled by suitable power-operated gate valves 88 and 90, respectively, the hull sides being indicated by the dashed lines in FIG. 10.
  • a pair of pumps 92 and 94 are provided to suction sea water through inlet 84, past valve 88, through pumps 92 and 94 via conduits 96 and 98, respectively, past check valves 100 and 102, respectively, and into a conduit 104 communicating with a main ballast conduit 106.
  • ballast conduits 74 and 76 Opposite ends of main conduit 106 communicate with fore and aft ballast conduits 74 and 76 through suitable selectively opened power-operated valves 108, ballast conduits 74 being arranged in parallel at opposite ends of main conduit 106.
  • valves 88, 100 and102 open, the ballast compartments in each hull, as well as the three illustrated ballast compartment in each of the columns 26 on each hull, may be ballasted with sea water by selective operation of valves 108.
  • no more than two compartments are ballasted at a any one time to facilitate maintenance of the vessel at an even keel when ballasting to the high draft condition.
  • valve 88 To refloat vessel with the hulls 12 having freeboard, valve 88 is closed and valves 90, 108 and 110 are opened. Pumps 92 and 94 operate to pump water in the same direction as before and, accordingly, suction main conduit 106 through conduit 112. By selective operation of valves 108, ballast water from the ballast compartments can be discharged through conduit 104, open valve 90, and outlet 86. Preferably, no more than two ballast compartments are deballasted at any one time and this permits maintenance of the vessel at an even keel when deballasting to the low draft condition.
  • Conduit 114 connects the port and starboard pump rooms and communicates with ballast conduit 106.
  • ballast conduit 106 By activating the appropriate valves, including ,valve 116 in conduit 114, ballast can be transferred from one hull to the other.
  • the ballasting system can be controlled by opening valve 116 and controlling the ballast system with the pumps in the other hull.
  • ballast/drilling water conduits 78 are also con nected in parallel to the aft end of main conduit 106 through suitable valves 118 similar to valves 108
  • the ballast/drilling compartments can be ballasted, deballasted and selectively ballasted and deballasted similarly as compartments 70 and 72 by selected operation of valves 118 and the aforementioned valves 88, and 110.
  • a fresh water intake or filling conduit 120 communicating with deck 20 via an uptake conduit 122, and a fresh water suction conduit 124, communicating with the ships service fresh water pump 126, each communicate with a fresh water compartment 128 located aft of the pumproom on the inboard side of the hull.
  • a conduit 129 communicates between fresh water pump 126 and deck 20 via uptake conduit 130.
  • a pair of fuel oil suction conduits 132 communicate with fuel oil tank 134 located forward of the pumproom on the inboard side of the hull and provides fuel oil to the machinery deck via an uptake conduit 136 by means of fuel pump 138.
  • Drill water is pumped from the aft drilling water compartment 140 and the ballast/drilling compartments 80 via conduits 142 and 78, 144, respectively, into a main drill water conduit 146 by a pump 148 which delivers the drill water via suitable valve 150 to deck 20 via an uptake conduit 152.
  • a drill water conduit 154 communicates with the forward drilling water compartment 156 and provides drill water to deck 20 via pump 148 and conduit 152.
  • Suitable valves 158 are provided in conduits 142 and 144 and these together with valve 156 in conduit 154 are selectively operable to fill and suction compartments 80, 1'40 and 156, whereby drill water may be transferred to and from the drilling rig and may be employed for the purposes of ballasting and deballasting the vessel.
  • columns 26 extend upwardly from hulls 12 a predetermined height effective to provide righting moments during transition of the vessel between high and low draft conditions and particularly at vessel drafts wherein the center of buoyancy lies below and at an elevation common with the center of gravity of the vessel.
  • columns 26 are effective upon submersion of hulls 12 to provide righting moments about roll and pitch axes to maintain vessel stability as its draft is increased from the low draft condition.
  • Motion minimizing characteristics are those vessel characteristics which minimize vessel motion due to excitation forces caused by wind and wave action, and are provided the vessel in the high draft condition by specifically designing the cross sectional area and configuration of said columns, distributing the weight of the vessel and formulating the geometry of the submerged portions of the vessel in the high draft condition such that the vessel obtains a natural period in heave, pitch and roll outside the range of periods of anticipated waves and reduced area at the mean waterline;
  • Low draft condition is that draft wherein the vessel floats with its hulls having freeboard;
  • High draft condition is that draft wherein the vessel floats with the mean waterline located intermediate the deck 20 and the upper ends of columns 26 and is the draft at which drilling operations are conducted;
  • Near low draft range is that range of vessel drafts in which the center of buoyancy lies below the center of gravity of the vessel and in which the mean waterline lies coincident with or above the upper surface of the hulls; and
  • Near high draft range is that range of vessel drafts wherein the center
  • the center of buoyancy lies below the center of gravity of the vessel in the low draft condition and through the near low draft range.
  • the centers of buoyancy and gravity move relative to the vessel toward one another.
  • Such movement continues through a vessel elevation whereat they pass one another, i.e., the vessel draft leaves near low draft range and enters the near high draft range.
  • Columns 26 are'located and provide waterplane areas throughout such increase in vessel draft in the near low draft range such'that they generate righting moments sufficient to provide stability to the vessel.
  • GM the metacentric height
  • KB and KG are the vertical heights of the center of buoyancy and the center of gravity respectively above the lower extremity of the vessel (defined by a plane containing the lower surfaces of the hulls)
  • BM is the metacentric radius UV (1 being the transverse or longitudinal moment of inertia of the waterline and V being the displaced volume to the waterline in question);
  • the enlarged diameter lower end portion 30 of central column 24 is located to raise the center of buoyancy as the vessel draft increases through the near high draft range to the high draft condition.
  • This enlarged portion 30 becomes effective after the center of buoyancy shifts above the center of gravity, i.e., after the pendulum type stability is obtained.
  • columns 26 are terminated at their upper ends well below the location of the mean waterline when the vessel lies in the high draft condition. More particularly, columns 26 terminate at their upper ends at an elevation coincident with the mean waterline when the vessel obtains a draft in the near high draft range wherein sufficient pendulum stability is afforded the vessel to maintain the vessel stability required.
  • Columns 26 are thus effective to provide vessel righting moments about the roll and pitch axes at least at vessel drafts wherein the center of buoyancy is spaced below the center of gravity and wherein the centers of buoyancy and gravity lie at a common elevation, i.e., throughout the near low draft range. Vessel stability in the near high draft range and in the high draft condition is thus provided by the large righting moment generated by the location of the center of gravity below the center of buoyancy with lesser and minimum contribution to stability afforded by the central column.
  • the columns 26 provide the sole stability to the vessel (from the low draft condition through the near low draft range) and a draft wherein the vessel obtains stability comprised predominantly of the pendulum type" stability (i.e., the c.g. located below c.b.) with minimum stability contribution from the waterplane area of the central column (i.e., through the near high draft range and in the high draft condition), the upper portions of columns 26 are formed to gradually decrease in cross sectional area toward deck 20.
  • the pendulum type stability i.e., the c.g. located below c.b.
  • This decrease in cross sectional area commences at an elevation above hulls 12 substantially coincident with the mean waterline at a vessel draft wherein the effects of the position of the center of buoyancy in relation to the center of gravity and the waterplane area of the central column combine to afford the vessel adequate stability while in the fully loaded condition.
  • the upper inside faces 27 of columns 26 are tapered outwardly and upwardly to form truncated wedges and the cross sectional area of the columns accordingly gradually decreases in a direction toward deck 20.
  • columns 26 are elongated in the direction of the axes of the hulls and that his affords greater righting moments as the vessel draft changes than would be the case of the columns were circular wherein the centroid of the columns would lie closer to the axis of inclination of the vessel. Also, in the high draft condition, the columns 26 are fully submerged and the mean waterline is located intermediate the upper ends of columns 26 and the underside of deck 20.
  • pairs of mooring pulleys 180 are mounted about and at the upper end of column 24.
  • Anchor lines 182 are received through the pulleys and are reeved over double drum winches 184 located on deck below the spider deck (FIG. 6).
  • Each pair of anchor lines 182 extends through sh'eeves 184a located at the upper end of column 24 and through a fairleader 185 located at the top of columns '26.
  • the anchor lines carry anchors, not shown, at an 8 point mooring system for maintaining vessel 10 in position over the drill site.
  • a pair of dynamic positioning and propulsion thrusters 186 are secured adjacent opposite ends of each of hulls 12. The thrusters are fully rotatable 360 and are utilized to accurately maintain the vessel in position over the drill site.
  • Control of the thrusters is provided from signalling devices which may comprise either an acoustical system utilizing transponders located on the ocean floor or from tension indicators on the anchor lines, neither of which are described or illustrated in detail herein.
  • dynamic thrusters vessel except as herein noted and comprising a pair of transversely spaced elongated hulls 212 supporting a main deck 220 in spaced relation above the hulls by a plurality of supports 222 and a vertically extending central column 224.
  • Hulls 212 and central column 224 are identical in construction with the hulls l2 and column 24, respectively, described in the previous embodiment.
  • Hulls 212 are connected one to the other by box-like trusses 218 and trusses 228 converge upwardly from hulls 212 for supporting column 224 similarly as in the prior embodiment.
  • Deck 220 includes a plurality of deck houses 250 for housing machinery, crews quarters and various auxiliary equipment, etc.
  • Pipe racks 251 are provided on deck 220 for storing drilling pipe.
  • a deck house 252 housing various offices and additional auxiliary equipment is carried on deck 220, a helideck 254 being provided above deck house 252.
  • the drilling equipment on deck 220 includes the automatic drill pipe racking mechanism 256 and cranes 258 including booms and cabs 260 and 262, respectively, the cranes being mounted on pedestals 264.
  • deck 220 is generally rectangular in plan form and is supported not only by central column 224 but also by a plurality of supports 222.
  • supports 222 comprise elongated structural elements extending vertically between deck 220 and hulls 212 adjacent the outboard sides thereof. As illustrated, three support elements 222 are provided in longitudinally spaced positions along the lateral extremity of each of the hulls and provide structural support for deck 220 adjacent its outer extremeties.
  • each column upstands from each of hulls 212 adjacent the outboard sides thereof in longitudinal spaced relation one to the other.
  • each column encompasses or fully encloses a lower portion of the associated upstanding structural element 222.
  • the central supports 222 bisect the intermediate columns 226 on each hull while the columns 226 at opposite ends of the hulls are located with respect to the associated support elements 222 such that major portions of the columns lie fore and aft respectively of the associated fore and aft elements 222.
  • the upper ends of columns 226 are formed to gradually decrease in cross sectional area toward deck 220.
  • This decrease in cross sectional area commences at an elevation above hulls 212 similarly as described with respect to the previous embodiment and is provided by tapering the inside faces of the columns outwardly and upwardly to form truncated wedges.
  • the upper edges of the columns are tapered in a fore and aft direction and this provides for a further gradual transition in vessel draft between the two types of stability provided the vessel at drafts respectively in the near low draft range and in the near high draft range and in the high draft condition as previously set forth.
  • the longitudinally outboard portions of the upper ends of the columns located at opposite ends of the hulls are tapered gradually away from the vessels transverse centerline as indicated at 266.
  • the upper ends of the intermediate columns 226 on each hull taper gradually toward the associated support element 222.
  • the vessels of the two specific embodiments herein set forth are similar in all other respects. It will, however, be appreciated that the waterplane areas of the upper portions of support members 222 are substantially insignificant in terms of the righting moments produced thereby in comparison with the righting moment produced by the pendulum type" stability obtained in the near high draft range and in the high draft vessel condition.
  • FIGS. 1-10 The operation of a vessel constructed in accordance with the present invention will now be described and is written, for brevity and except as otherwise indicated, with respect to the preferred embodiment hereof illustrated in FIGS. 1-10, it being appreciated that the description applies also to the embodiment illustrated in FIGS. 11-15.
  • the vessel 10 can be towed between drilling sites at speeds on the order of 8 knots providing the present vessel with significant mobility between drilling sites.
  • the hulls 12 have a displacement when deballasted to support the entire weight of the vessel in the low draft floating condition with the hulls 12 having freeboard.
  • the vessel 10 has the righting stability and roll angle characteristic of a twin hulled vessel.
  • the support bracing interconnecting the hulls is located adjacent the top surface of the hulls and hence above the waterline, whereby the bracing does not present a frontal area to the water to offer resistance to passage therethrough.
  • twin hulls 12 displace water and the hydrodynamic characteristics of the hulls, particularly their substantially streamlined bows, as well as the absence of support structure in contact with the water, minimizes resistance to passage through the water and permits the towing of the vessel at significantly higher speeds than heretofore possible with prior semisubmersible platforms (the vessels disclosed in applications Ser. Nos. 766,662 and 705,175 excepted).
  • the mooring system and propulsion thrusters are activated to locate and maintain the vessel over the drill site.
  • the anchors and anchor lines are deployed to maintain the vessel directly over the drilling site.
  • the hulls 12 are then ballasted to submerge the .hulls below the waterline-As the vessel is ballasted and the hulls submerged, and the vessel draft increases through the near low draft range, the moment of inertia of the waterplane areas of the columns 26 maintain the vessel stable as the centers of buoyancy and gravity shift relative to the vessel toward one another from an initial location in the low draft condition wherein the c.b. is below the c.g.
  • the c.b. and the c.g. shift past one another with the c.b. being then located above the c.g.
  • stability is obtained by virtue of the righting moments provided by columns 26.
  • the center of buoyancy particularly due to the lower enlargement of the central column, rises substantially above the center of gravity of the vessel, whereupon stability is increasingly obtained by the increasingly large righting moment provided by locating the c.g.
  • the vessel obtains pendulum stability.
  • This latter type of stability becomes predominant relative to the righting moments provided by the columns 26 and sufficient, as the draft increases, to maintain vessel stability in the high draft condition.
  • the upper portions of the columns 26 decrease in cross sectional area whereby their contribution to vessel stability gradually diminishes and becomes zero when the vessel obtains a draft wherein the mean waterline is located above the upper ends of columns 26.
  • the ideal high draft condition of the vessel is obtained at a draft wherein the mean waterline lies substantially medially of the upper ends of columns 26 and the underside of deck 20. Furthermore, in the high draft condition, the distance from the upper ends of columns 26 to the underside of deck 20 exceeds the height of the maximum anticipated wave from crest to trough. It will be appreciated that as the draft of the vessel increases, and where anchors are employed, the anchor lines are maintained at a predetermined tension by operation of the winches to maintain the vessel over the drilling site.
  • the vessel is configured such that the undamped natural periods of the vessel in heave, pitch and roll in the high draft condition are beyond the peak periods encountered in virtually all se'as where drilling operations are presently performed or may possibly be performed in the future.
  • the fully damped natural periods of the vessel will, of course, put such periods well beyond the peak periods of seas in virtually any part of the world.
  • the undamped natural periods are predicted as follows: heave about 28 seconds; pitch or roll about 51 seconds.
  • Drilling operations are conducted in the high draft condition of the vessel as illustrated in FIG. 2.
  • the marine riser and drill string are disposed through the shaft 32 of central column 24.
  • the vessel may be maintained on station over the drill site by operation of the dynamic thrusters 186 or alternately tensioning or releasing the anchor lines as necessary and applicable.
  • vessel 10 is deballasted to obtain the low draft condition.
  • the ballast compartments are pumped to evacuate the water therein as hereinbefore described.
  • the vessel draft decreases through the near high draft range with the c.b. and c.g. moving toward one another, the c.b. being initially above the c.g. in the high draft condition.
  • the vessel draft decreases, its stability decreases to a limited extent due to such movement of c.b. and c.g.
  • c.g. pass one another and the vessel enters the near low draft range with c.g. above c.b. In this latter range, stability is provided solely by the righting moments generated by columns 26 until the hulls 12 emerge whereupon the stability is that characteristic of a twin hulled vessel.
  • the illustrative preferred embodiment of a vessel constructed according to the present invention has an overall length of 360 ft. at hulls 12 with each hull having a beamof 55 ft. and inside spacing of 40 ft. from each other, providing an overall vessel beam of 150 ft.
  • the depth of the deck above the bottom of the hulls is 175 ft.
  • the depth of the hulls is ft. and the height of the columns 26 from the upper surface of the hulls is 80 ft.
  • the columns 26 have a length in the longitudinal direction of 45 ft. and a width of 25 ft., the outboard sides thereof forming continuations of the outboard sides of the associated hulls.
  • the waterline In the low draft condition, the waterline lies approximately 5 ft. below the upper surfaces of hulls 12. In the high draft condition, the waterline lies approximately 40 ft. below the underside of deck 20, i.e., about 35 ft. above the upper ends of columns 26. It will be appreciated that in the high draft condition of the vessel, the mean waterline is located such that the maximum anticipated wave does not act either against deck 20 or the upper ends of columns 26.
  • the deck 20 has an overall length of about 214 ft. and a width of 174 ft.
  • Central column 24 has an overall height of 108 ft. and a diameter of 52 ft.
  • the enlarged lower end portion 30 of column 24 has a diameter of 80 ft.
  • the shaft 32 through central column 24 has a diameter of 18 ft.
  • the lower end of column 24 tapers upwardly from its 52 ft. diameter to an 80 ft. diameter at the enlarged lower portion 30 through a distance of 8 ft.
  • the enlarged portion 30 extends vertically therefrom a distance of 30 ft.
  • a variable draft vessel comprising:
  • flotation members a pair of elongated flotation members disposed in spacedv side-by-side substantially parallel relation one to the other, said flotation members having a combined displacement sufficient to float the vessel in a low draft condition with the flotation members having freeboard and constituting substantially the entirety of the flotational support for said vessel in said low draft condition;
  • said elements including a central, substantially vertically disposed, column and a plurality of stabilizing members spaced laterally outwardly of said central column and one from the other;
  • means for ballasting and deballasting the vessel to respectively submerge the flotation members, stabilizing members and a portion of said central column thereby to provide a high draft floating condition with the water line located intermediate the height of said central column and to return the vessel to the low draft condition, said members being located and having waterplane areas sufficient to provide stability to the vessel during at least a portion of its transition between low and high draft conditions, the displacement of the submerged flotation members, stabilizing members and said portion of the central column being sufficient to maintain the vessel buoyant in the high draft condition;
  • stabilizing members comprise columns upstanding from said flotation members, the upper end of said central column being connected to said platform with its lower end lying at an elevation lower than the upper ends of said stabilizing columns, the upper ends of said stabilzing columns being fixed a predetermined like distance below said platform in both said high and low draft conditions of said vessel.
  • said stabilizing members comprise columns upstanding from said flotation members, the upper end of' said central column being connected to said platform and its lower end lying at an elevation lower than the upper ends of said columns, said connecting means including supports extending from the upper ends of said columns to said platform, the combined waterplane area of said supports being small in comparison with the waterplane area of said central column when said vessel lies in the high draft condition.
  • ballasting and deballasting means includes at least two ballast compartments in each of said members, said two ballast compartments being horizontally spaced one from the other, means for selectively ballasting and deballasting said two compartments in each said member to alter the natural period of said vessel.
  • said flotation members comprise hulls substantially rectangular in cross section and having a greater width than depth, and means connected to said hulls adjacent the upper surfaces thereof and extending transversely of said vessel for maintaining the hulls in spaced substantially parallel relation one to the other.
  • sta bilizing members comprise columns upstanding from said flotation members, the cross-sectional area of the stabilizing columns at an elevation above said flotation members and also containing a portion of said central column decreasing in a direction toward said platform, the upper end of said central column being connected to said platform and its lower end lying at an elevation lower than the upper ends of said stabilizing columns, the center of gravity of the vessel being located above its center of buoyancy in the low draft condition and below the center of buoyancy in the high draft condition, the stabilizing members upstanding from said flotation members a distance sufflcient to provide water plane areas during transition between the low and high draft conditions for vessel drafts between a draft wherein the mean waterline lies at substantially a common elevation with the lower ends of the columns and an intermediate vessel draft whereat the center of buoyancy and the center of gravity lie substantially at a common elevation, said central column having a diametrically enlarged portion adjacent its lower end and at an elevation corresponding to the elevation at which the columns decrease in cross-sectional area, said platform
  • GM is the metacentric height
  • KB and KG are the vertical heights of the center of buoyancy and center of gravity respectively above the lower extremity of the vessel and BM is the metacentric radius
  • the vessel being configured such that in the low draft floating condition a positive valued GM is obtained comprising the sum of a positive valued BM and a negative valued (KB-KG)
  • the vessel being configured such that in the high draft floating condition a positive valued GM is obtained comprising the sum of a positive valued BM and a positive valued (KB-KG).
  • a variable draft vessel comprising:
  • said elements including a central substantially vertically disposed column and a plurality of stabilizing members spaced laterally outwardly of said central column and one from the other;
  • said stabilizing members and a portion of said central column thereby to provide a high draft floating condition with the mean waterline in the high draft condition located intermediate the height of said central column and to return the vessel to a low draft floating condition with the base structure having freeboard, said members being located and having waterplane areas sufficient to provide stability to the vessel during at least a portion of its transition between said low and high draft conditions, the displacement of said base structure, said stabilizing members and said portion of the central column being sufficient to maintain the vessel buoyant in the high draft floating condition;
  • the vessel being configured such that in the low draft floating condition its center of gravity is located above its center of buoyancy and, in the high draft condition its center of buoyancy is located above its center of gravity;
  • said vessel according to claim 20 wherein said base structure includes a pair of elongated flotation members disposed in spaced side-by-side substantially parallel relation one to the other, said stabilizing means comprising a plurality of columns upstanding from said flotation members.

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  • Engineering & Computer Science (AREA)
  • Combustion & Propulsion (AREA)
  • Ocean & Marine Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Structural Engineering (AREA)
  • Civil Engineering (AREA)
  • Architecture (AREA)
  • Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • Earth Drilling (AREA)
  • Moulding By Coating Moulds (AREA)
  • Wind Motors (AREA)
US00139765A 1971-05-03 1971-05-03 Single column semisubmersible drilling vessel Expired - Lifetime US3771481A (en)

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US13976571A 1971-05-03 1971-05-03

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US (1) US3771481A (enExample)
JP (1) JPS5543959B1 (enExample)
CA (1) CA939918A (enExample)
ES (1) ES400241A1 (enExample)
FR (1) FR2135542B1 (enExample)
GB (1) GB1371147A (enExample)
IT (1) IT948383B (enExample)
NL (1) NL7203124A (enExample)
NO (1) NO138555C (enExample)

Cited By (25)

* Cited by examiner, † Cited by third party
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US3919957A (en) * 1974-04-15 1975-11-18 Offshore Co Floating structure and method of recovering anchors therefor
US3974792A (en) * 1975-01-03 1976-08-17 Earl & Wright Semi-submersible, directionally controlled drilling unit
US4015552A (en) * 1975-08-25 1977-04-05 Korkut Mehmet D Semi-submersible drill barge
US4109479A (en) * 1976-10-19 1978-08-29 Societe Nationale Elf Aquitaine (Production) Method and apparatus for tensioning anchor lines
US4168673A (en) * 1976-01-26 1979-09-25 Preussag Aktiengessellschaft Floating island for extracting or processing gas
US4281615A (en) * 1977-10-31 1981-08-04 Sedco, Inc. Self-propelled semi-submersible service vessel
US4457250A (en) * 1981-05-21 1984-07-03 Mitsui Engineering & Shipbuilding Co., Ltd. Floating-type offshore structure
US4471708A (en) * 1977-10-31 1984-09-18 Sedco, Inc. Self-propelled semi-submersible service vessel
WO1985003050A1 (en) * 1983-12-30 1985-07-18 William Bennet Semi-submersible vessel
GB2153749A (en) * 1984-02-13 1985-08-29 Robin Shipyard Stabilized jack-up mobile offshore drilling platform
US4580517A (en) * 1983-03-04 1986-04-08 Gotaverken Arendal Ab Vessel having parallel hulls with 360 degree rotatable thrusters
WO2000013964A1 (en) * 1998-09-04 2000-03-16 Halliburton Energy Services, Inc. Brine-based drilling fluids for ballast tank storage
WO2003002404A1 (en) * 2001-06-27 2003-01-09 Moss Maritime As Substructure for a floating offshore platform
US20040040487A1 (en) * 2000-10-06 2004-03-04 Per Herbert Kristensen Platform structure
US6869251B2 (en) 1999-04-30 2005-03-22 Abb Lummus Global, Inc. Marine buoy for offshore support
US20100314121A1 (en) * 2007-06-26 2010-12-16 Soerenson Bjoern Bro Well apparatus
US20110209655A1 (en) * 2010-02-18 2011-09-01 Geir Lasse Kjersem Float structure for storing liquids
US8733472B2 (en) 2010-09-13 2014-05-27 Christopher Magnuson Multi-operational multi-drilling system
US8770131B2 (en) 2010-11-24 2014-07-08 Floatec, Llc Spar hull centerwell arrangement
US9446825B1 (en) 2013-12-10 2016-09-20 Hugh Francis Gallagher Self-propelled, catamaran-type, dual-application, semisubmersible ship with hydrodynamic hulls and columns
CN109178236A (zh) * 2018-08-21 2019-01-11 广州中船文冲船坞有限公司 船舶抗拍击箱体及其安装工艺
WO2019171089A1 (en) * 2018-03-08 2019-09-12 Etme: Peppas Kai Synergates E.E. Floating platform for maritime surveillance
CN114735152A (zh) * 2022-04-19 2022-07-12 中国舰船研究设计中心 一种基于面元法的全附体舰船不沉性计算方法
US20230138893A1 (en) * 2020-04-16 2023-05-04 Tzong In Yeh Paddle
US12172737B2 (en) 2022-06-11 2024-12-24 Hugh Francis Gallagher Semi-autonomous immersible waterborne dock enclosure

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* Cited by examiner, † Cited by third party
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FR2540065B1 (fr) * 1983-02-01 1993-03-26 Creusot Loire Structure flottante et lestee, maintenue sur son site en mer ouverte
FR2541333A1 (fr) * 1983-02-21 1984-08-24 Fayren J Pont flottant perfectionne
DE3306057A1 (de) * 1983-02-22 1984-08-23 Blohm + Voss Ag, 2000 Hamburg Einrichtung fuer einen halbtaucher zur begrenzung einer durch eine leckage verursachten trimmlage
DE3321618A1 (de) * 1983-06-15 1984-12-20 Blohm + Voss Ag, 2000 Hamburg Einrichtung fuer ein als halbtaucher wirksames arbeitsgeraet
GB2147549A (en) * 1983-10-20 1985-05-15 Earl & Wright Ltd Minimum heave offshore structure
CN101786490B (zh) * 2009-01-22 2012-10-10 海洋能源科技股份有限公司 半潜装置
CN104015893B (zh) * 2014-05-23 2017-01-11 上海船舶研究设计院 一种增强半潜运输船稳性的装置及其工作方法

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US2946566A (en) * 1956-08-31 1960-07-26 Charles T Samuelson Subaqueous drilling apparatus
US3490406A (en) * 1968-08-23 1970-01-20 Offshore Co Stabilized column platform

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* Cited by examiner, † Cited by third party
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US2946566A (en) * 1956-08-31 1960-07-26 Charles T Samuelson Subaqueous drilling apparatus
US3490406A (en) * 1968-08-23 1970-01-20 Offshore Co Stabilized column platform

Cited By (39)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3919957A (en) * 1974-04-15 1975-11-18 Offshore Co Floating structure and method of recovering anchors therefor
US3974792A (en) * 1975-01-03 1976-08-17 Earl & Wright Semi-submersible, directionally controlled drilling unit
US4015552A (en) * 1975-08-25 1977-04-05 Korkut Mehmet D Semi-submersible drill barge
US4168673A (en) * 1976-01-26 1979-09-25 Preussag Aktiengessellschaft Floating island for extracting or processing gas
US4109479A (en) * 1976-10-19 1978-08-29 Societe Nationale Elf Aquitaine (Production) Method and apparatus for tensioning anchor lines
US4281615A (en) * 1977-10-31 1981-08-04 Sedco, Inc. Self-propelled semi-submersible service vessel
US4471708A (en) * 1977-10-31 1984-09-18 Sedco, Inc. Self-propelled semi-submersible service vessel
US4457250A (en) * 1981-05-21 1984-07-03 Mitsui Engineering & Shipbuilding Co., Ltd. Floating-type offshore structure
US4580517A (en) * 1983-03-04 1986-04-08 Gotaverken Arendal Ab Vessel having parallel hulls with 360 degree rotatable thrusters
WO1985003050A1 (en) * 1983-12-30 1985-07-18 William Bennet Semi-submersible vessel
US4646672A (en) * 1983-12-30 1987-03-03 William Bennett Semi-subersible vessel
AU581871B2 (en) * 1983-12-30 1989-03-09 William Bennet Semi-submersible vessel
GB2153749A (en) * 1984-02-13 1985-08-29 Robin Shipyard Stabilized jack-up mobile offshore drilling platform
WO2000013964A1 (en) * 1998-09-04 2000-03-16 Halliburton Energy Services, Inc. Brine-based drilling fluids for ballast tank storage
US6315061B1 (en) 1998-09-04 2001-11-13 Halliburton Energy Services, Inc. Brine-based drilling fluids for ballast tank storage
US6869251B2 (en) 1999-04-30 2005-03-22 Abb Lummus Global, Inc. Marine buoy for offshore support
US7117810B2 (en) * 2000-10-06 2006-10-10 Moss Maritime As Platform structure
US20040040487A1 (en) * 2000-10-06 2004-03-04 Per Herbert Kristensen Platform structure
WO2003002404A1 (en) * 2001-06-27 2003-01-09 Moss Maritime As Substructure for a floating offshore platform
US20100314121A1 (en) * 2007-06-26 2010-12-16 Soerenson Bjoern Bro Well apparatus
US8511385B2 (en) * 2007-06-26 2013-08-20 Agility Projects As Well apparatus
US20110209655A1 (en) * 2010-02-18 2011-09-01 Geir Lasse Kjersem Float structure for storing liquids
US8453588B2 (en) * 2010-02-18 2013-06-04 Luno, Mehr & Glever-Enger Marin AS Float structure for storing liquids
NO335841B1 (no) * 2010-02-18 2015-03-02 Lund Mohr & Giæver Enger Marin As Flyterkonstruksjon for lagring av væsker så som hydrokarboner.
US8733472B2 (en) 2010-09-13 2014-05-27 Christopher Magnuson Multi-operational multi-drilling system
US9051782B2 (en) 2010-09-13 2015-06-09 Christopher Magnuson Multi-operational multi-drilling system
US8770131B2 (en) 2010-11-24 2014-07-08 Floatec, Llc Spar hull centerwell arrangement
US9446825B1 (en) 2013-12-10 2016-09-20 Hugh Francis Gallagher Self-propelled, catamaran-type, dual-application, semisubmersible ship with hydrodynamic hulls and columns
WO2019171089A1 (en) * 2018-03-08 2019-09-12 Etme: Peppas Kai Synergates E.E. Floating platform for maritime surveillance
AU2019229775B2 (en) * 2018-03-08 2021-06-24 Etme: Peppas Kai Synergates E.E. Floating platform for maritime surveillance
JP2021518823A (ja) * 2018-03-08 2021-08-05 イーティーエムイー：ペッパス カイ シナーゲイツ イー．イー． 海洋監視用浮体
US11254399B2 (en) * 2018-03-08 2022-02-22 Etme: Peppas Kai Synergates E.E. Floating platform for maritime surveillance
CN109178236A (zh) * 2018-08-21 2019-01-11 广州中船文冲船坞有限公司 船舶抗拍击箱体及其安装工艺
CN109178236B (zh) * 2018-08-21 2019-10-15 广州中船文冲船坞有限公司 船舶抗拍击箱体及其安装工艺
US20230138893A1 (en) * 2020-04-16 2023-05-04 Tzong In Yeh Paddle
US11801927B2 (en) * 2020-04-16 2023-10-31 Tzong In Yeh Paddle
CN114735152A (zh) * 2022-04-19 2022-07-12 中国舰船研究设计中心 一种基于面元法的全附体舰船不沉性计算方法
CN114735152B (zh) * 2022-04-19 2023-12-01 中国舰船研究设计中心 一种基于面元法的全附体舰船不沉性计算方法
US12172737B2 (en) 2022-06-11 2024-12-24 Hugh Francis Gallagher Semi-autonomous immersible waterborne dock enclosure

Also Published As

Publication number Publication date
CA939918A (en) 1974-01-15
IT948383B (it) 1973-05-30
FR2135542A1 (enExample) 1972-12-22
DE2206929B2 (de) 1977-02-17
FR2135542B1 (enExample) 1973-06-29
DE2206929A1 (de) 1972-11-23
GB1371147A (en) 1974-10-23
NL7203124A (enExample) 1972-11-07
NO138555C (no) 1980-10-13
NO138555B (no) 1978-06-19
JPS5543959B1 (enExample) 1980-11-10
ES400241A1 (es) 1975-07-01

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