US 3778854 A
The apparatus includes a spar buoy comprised of an elongated column mounting a platform at its upper end, the platform carrying a helicopter pad and a movable boom for assisting the mooring of tankers to the buoy and off-loading oil to the tanker. The platform includes a ballast system providing an adjustable counterweight to the movement of the boom. The buoy is anchored and oil lines from production or control platforms or underwater oil storage tanks extend upwardly through the buoy to the boom for delivering oil to an awaiting tanker. The buoy has an anchoring collar located therealong in a manner to limit the tilt angle of the buoy within a predetermined angle and to limit the lateral excursion of the lower end of the buoy through which the oil receiving lines pass to within a specified range. The buoy is constructed to obtain a long natural period whereby the amplitude of vertical movement due to excitation forces caused by wave action is reduced.
Description (OCR text may contain errors)
United States Patent [191 Chow MOORING AND OIL TRANSFER APPARATUS  Inventor: Philip Y. Chow, Orinda, Calif.
 Assignee: Santa Fe International Corporation, Los Angeles, Calif.
 Filed: Mar. 16, 1971  Appl. No.: 124,738
 US. Cl. 9/8 P  Int. Cl... B63b 35/44, B65d 87/08, E02d 17/00  Field of Search 9/8 P; 114/0.5 T; 137/615, 236; 212/48, 49
[5 6] References Cited UNlTED STATES PATENTS 3,360.810 l/l968 Busking 9/8 P 3,411,303 11/1968 Bates et a1. 137/236 X 3,620,181 11/1971 Naczkowski 9/8 P 3 414,918 12/1968 Petrie et al...... 9/8 P 3,407,416 10/1968 Brickhouse 9/8 P 3,500,783 3/1970 Johnson et a1. 9/8 P 3,434,422 3/1969 Manning 9/8 P X 2,857,021 10/1958 Kinsman 212/49 X 3,340,907 9/1967 Bily 212/48 X Primary ExaminerMilton Buchler Assistant ExaminerGregory W. O'Connor Attorney-LeBlanc & Shur 5 7 ABSTRACT The apparatus includes a spar buoy comprised of an elongated column mounting a platform at its upper end, the platform carrying a helicopter pad and a movable boom for assisting the mooring of tankers to the buoy and off-loading oil to the tanker. The platform includes a ballast system providing an adjustable counterweight to the movement of the boom. The buoy is anchored and oil lines from production or control platfonns or underwater oil storage tanks extend upwardly through the buoy to the boom for delivering oil to an awaiting tanker. The buoy has an anchoring collar located therealong in a manner to limit the tilt angle of the buoy within a predetermined angle and to limit the lateral excursion of the lower end of the buoy through which the oil receiving lines pass to within a specified range. The buoy is constructed to obtain a long natural period whereby the amplitude of vertical movement due to excitation forces caused by wave action is reduced.
13 Claims, 8 Drawing Figures PATENTEU DEC 1 8 I975 SHEET 10F 4 INVENTOR PHILIP Y. CHOW BY 45mm Q ATTO RN EYS n u n n n n mooRm's FORCE FM H6 8 CB (CENTER OF BUOYANCY) CG(CE NTER OF GRAVITY) MAX.. ALLOWED PAIENIEDBEc 1a 1915 SEE! 3 0F 4 MOORING AND OIL TRANSFER APPARATUS The present invention relates to an apparatus useful in the offshore environment for transferring fluid minerals, particularly oil, from an underwater location to an awaiting tanker and the like and particularly relates to a floating spar type buoy utilized for the transfer of fluid minerals from production platforms or underwater well heads to tankers moored to the buoy. The present invention also relates to a spar type buoy for fluid mineral transfer operations which is particularly useful in offshore areas commonly subject to severe weather conditions.
Fluid minerals, such as oil and gas, hereinafter collectively referred to as oil, are currently being produced in an ever increasing number of subaqueous regions throughout the world. Many problems are, however, associated with offshore oil producing sites, not the least of which is the problem of handling and conveying oil from a well head to a shore facility for refining. it is customary, in many offshore oil producing installations, to lay pipelines between the producing wells and a nearby shore facility whereby the oil may be pumped directly from the wells through the pipelines to the shore facility. Underwater pipelines, however, are difficult and expensive to lay and become increasingly impractical and uneconomical as a method of marine oil transport where production sites are located great distances from the shore facility and also wherein the depth of water in which the pipe must be laid becomes excessive.
Attention in recent years has therefore been directed to apparatus for accumulating the oil from the wells in large quantities at the production site with subsequent deliver to a shore facility being provided by tankers or barges plying between production sites and the shore facility. One such system currently in use provides for the submergence of a large capacity hemispherical steel tank and the pinning of the tank to the sea bottom. Oil lines from the producing well heads are then laid and oil flows directly from the producing wells into the submerged tank. Underwater storage facilities, such as the foregoing, have many advantages in comparison with surface floating storage tanks or dummy tankers in that such surface floating storage facilities are continuously subject to wind and wave action which causes excessive motion of such facilities whereby operations are greatly inhibited. Accordingly, significant attention has recently been directed to the employment of underwater storage tanks as a method of accumulating oil at the offshore production site for subsequent delivery to tankers or barges. This has been particularly true wherein the offshore producing site is located large distances from the nearest shore facility whereby economics simply prohibit the laying of pipeline directly from the producing well to such shore facility.
There remains, however, the problem of transferring oil from a storage facility located at the production site to the awaiting tanker. A system has been developed for accomplishing this and includes a buoy anchored to the sea bottom and having oil lines in communication with the storage facility. Particularly, the buoy has mooring facilities whereby tankers can moor directly to the buoy in a manner to be rotatable about the buoy. The bow ofthe tanker thus always faces in the direction of the oncoming wind and waves and oil is transferred to the tanker from the storage facility via oil lines communicating with the tanker through the buoy. In utilizing this system, however, small boats or launches are normally employed to carry the mooring and oil transfer lines between the tanker and the buoy. Under severe weather conditions, for example, in seas having 7 or 8 foot waves or greater, such small boat operations become particularly hazardous and, as a result, the tankers must lie to and wait until calmer weather conditions prevail before mooring and oil transferring operations can be accomplished. Thus, in areas of the world for example, the North Sea, where severe weather conditions are more common than not, the foregoing described oil transfer system cannot practically and economically be employed.
The present invention provides a mooring and oil loading buoy for use in transferring oil from storage facilities at an offshore production site which minimizes the above discussed and other shortcomings of prior oil transfer systems and provides various advantages in construction, mode of operation and result over such prior systems. Generally, this is accomplished by providing an elongated spar type buoy mounting a platform at its upper end which, in normal operating conditions, is spaced above the waterline a height greater than the height of the maximum anticipated wave at the producing site. The platform carries a helicopter pad and a movable boom which, in turn, carries mooring lines and oil loading lines. The buoy is anchored, preferably by an 8 point mooring system, and oil lines f r o m the'bilayb'dihifiu'mififln oilstora ge facility, preferably underwater storage tanks such as described and illustrated in US. Pat. No. 3,467,118. The oil lines are secured along the sea bottom and are directed upwardly through the spar type buoy to the platform and outwardly along the boom for transfer of oil to an awaiting tanker in a manner to be described. It is a significant feature of the present invention that the spar type buoy hereof obtains a long period in heave whereby the amplitude of its vertical movement is considerably reduced and resonance with wave action is avoided. Moreover, the long heave period reduces the possibility of fouling or otherwise breaking the anchor chains and oil lines extending upwardly from the seabed to the buoy. ln utilizing the mooring and oil loading buoy hereof, personnel are transported to the buoy by helicopter and the platform is thereafter rotated such that the boom extends toward the tanker which approaches from the leeward. Lead lines are dropped from the boom and the tanker removes the mooring lines from their stowed position on the boom and the same are secured to the tanker. Oil loading arms are carried by the boom and are then coupled to the tanker. Upon completion of loading, the oil loading lines and mooring lines are detached from the tanker and the tanker backs away from the buoy. In a preferred form of the present invention, the boom is pivoted for movement about a horizontal axis. In another form hereof, the boom is longitudinally extensible and retractable. In both forms, the platform carries water ballast tanks on the opposite sides of the buoy from the boom whereby the movement of the boom can be counterbalanced by selective ballasting and deballasting of the ballast chamber on the platform.
In a further form hereof, water ballast lines are also connected between the tanker and the buoy prior to commencing the oil loading operation. The oil is then flowed through the buoy into the tanker to displace the ballast water in the oil storage compartments of the tanker for return via the water ballast lines through the buoy to the on-site production platform for separation. This oil-water ballast transfer constitutes a closed system which substantially reduces or eliminates pollution of the surrounding water. In providing a spar type buoy for accomplishing the foregoing, particularly under severe weather and sea conditions, it is desirable to accurately locate the anchoring collar along the length of the buoy for optimization of two countervailing re quirements. It is essential to the proper operation of the mooring and loading buoy hereof that the tilt angle of the buoy, that is its inclination from a true vertical when the tanker is moored thereto, is maintained within a predetermined angle, for example, on the order of 4 or Conflicting with that requirement is the necessity to maintain lateral movement of the base of the buoy within a predetermined radius to preclude fouling and/or breaking of the anchor lines and the oil hoses extending from the pipeline manifold along the seabed to the lower end of the buoy. That is to say, the lateral excursion of the lower end of the buoy must be maintained within predetermined limits. The location of the anchoring collar along the length of the spar buoy is also a factor in providing the buoy with a long period in heave. Thus, its location is critical and the present invention provides for locating the collar along the buoy in a manner providing the foregoing desired motion characteristics.
Accordingly, it is a primary object of the present invention to provide a novel mooring and oil loading buoy for transferring oil from an offshore production facility to an awaiting tanker.
It is another object of the present invention to provide a mooring and oil loading buoy having a long period in heave and which buoy thus obtains a minimum amplitude of vertical movement in heave due to exitation forces caused by wave action.
It is still another object of the present invention to provide a mooring and oil loading buoy wherein the maximum angle of tilt of the buoy from the true vertical and the maximum lateral excursion of the base of the buoy are maintained within predetermined limits.
It is a further object of the present invention to provide a mooring and oil loading buoy having a platform mounting a helicopter pad whereby the prior necessity of utilizing small boats or launches for accomplishing an oil transfer operation is entirely eliminated.
It is a still further object of the present invention to provide a mooring and oil loading buoy particularly useful for transferring oil under severe weather conditions from an offshore storage facility and an awaiting tanker.
It is a related object of the present invention to provide a mooring and oil loading buoy wherein the anchoring collar for the buoy is located along the buoy in a manner to limit the tilt angle of the buoy within a predetermined angle and to limit the lateral excursion of the lower end of the buoy through which the oil receiving lines pass to within a specified limit while simultaneously permitting the buoy to obtain long natural periods in heave wherein the amplitude of vertical movement due to excitation forces caused by wave action is reduced.
It is a still further object of the present invention to provide a mooring and oil loading buoy wherein a water ballast system is employed to maintain the buoy in a substantially vertical position throughout the entire mooring and oil transferring operation.
These and further objects and advantages of the present invention will become more apparent upon reference to the following specification, appended claims and drawings wherein:
FIG. 1 is a side elevational view of a mooring and oil transfer apparatus constructed in accordance with the present invention;
FIG. 2 is a plan view thereof;
FIGS. 3, 4 and 5 are cross sectional views thereof taken generally about on lines 3-3, 44 and 5-5 in FIG. 1;
FIG. 6 is a view similar to FIG. 1 illustrating a further form of the invention hereof;
FIG. 7 is a plan view thereof; and
FIG. 8 is a fragmentary schematic illustration of the lower portion of an apparatus constructed in accordance with the present invention and illustrating various parameters considered in providing the mooring and oil transfer apparatus hereof.
Referring now to the drawings, particularly to FIG. 1, there is illustrated a mooring and oil transfer apparatus constructed in accordance with the present invention and comprising an elongated spar-type buoy, generally indicated 10, floating substantially vertically in an aqueous medium, the waterline and sea bottom of which is indicated at WL and 12, respectively. A tanker T is schematically illustrated in position moored to buoy 10 for receiving oil from underwater storage tanks or production platforms, not shown, and for discharging ballast water from its oil storage tanks to a production platform via lines extending therefrom and coupled to the tanker through the buoy. Particularly, such lines extend from the storage tanks or platforms as applicable along sea bottom 12 and are suitably secured thereto by means not shown. Portions of these lines terminate in a manifold 14 to which is connected one or more flexible hose lines 16 and 17 connected at their opposite ends to connections 18 provided at the lower end of buoy l0. Buoy 10 includes a pair of central concentric vertically extending pipes 19 and 20 for respectively transferring the oil from the flexible hose line or lines 16 to the upper end of the buoy and for de livering ballast water from the tanker to the production platform for scrubbing. Suitable connections are provided with concentric pipes 19 and 20 wherein the former terminates at the upper end of the buoy in a pair of oil pipelines 21 straddling a ballast water pipeline 22 (FIG. 3). The pipelines 21 and 22 are carried through suitable pivotal connections by a boom 24 and terminate in a loading arm 25 for delivering oil to and transferring ballast water from the awaiting tanker T.
The buoy 10 includes a stepped vertically extending column 26 which may be formed of steel or prestressed concrete, the lower end 27 of which below anchoring collar 28 is formed of heavy concrete for ballast purposes. A fender system 32 is disposed about the smaller diameter upper portion of the column 26 adjacent the waterline and provides a docking area for small boats, launches and the like, as desired.
On the upper end of column 26, there is rotatably mounted a platform 34. Boom 24 is carried by platform 34 for pivotal movement about a horizontal axis between the positions illustrated. Particularly, a mast 36 is supported atop platform 34 and carries the usual pulleys over which lines 38 are reeved for pivoting boom 24 between various inclined positions. Winches 39 or the like (FIG. 3) are provided on platform 34 for the purpose of raising and lowering boom 24. Also supported on the upper deck of platform 34 and on the side thereof remote from boom 24 is a heliport deck 40 capable of handling helicopter landings and takeoffs for reasons amplified hereinbelow. As illustrated in FIGS. 1 and 3, the platform 34 includes a pair of superposed decks, the upper deck providing quarters and offices for operation of the transfer buoy as below amplified and the lower deck, illustrated in FIG. 3, providing machinery spaces. Also, one or more ballast tanks 42 are provided platform 34 on the end thereof remote from boom 24. A ballast line 44 extends from ballast tanks 42 through a suitable ballast pump 43 into the column 26 terminating at an opening 45 located below the waterline.
Platform 34 is suitably mounted on bearings located on column 26 for rotation about a vertical axis coincident with the axis of column 26. A circular rack 46 (FIG. 4) extends about an upper end portion of column 26 and a plurality of hydraulically driven pinions 48 are carried by a short columnar portion 49 depending from and fixed to platform 34, the pinions 48 engaging rack 46 to pivot platform 34 about the vertical axis of column 26. The short columnar portion 49 forms the upper end portion-of the column 26. The buoy is anchored, preferably utilizing an 8 point anchoring system, by a plurality of anchor chains 50 connected at one end to tensioning devices Slwithin the column, the chains 50 extending through openings in the anchoring collar 28 and carrying anchors at their opposite ends for embedment in seabottom 12. Thus, buoy is restrained from substantial lateral movement and vertical heaving motions, as well as from rotation or twisting about its vertical axis.
In use, buoy 10 is situated as described in an oil producing field and is generally left unmanned except for periodic maintenance as necessary and desired. When it is desired to load oil collected in underwater storage tanks or in storage tanks located about the production platform to an awaiting tanker, personnel for operating the buoy and effecting such oil transfer are transferred to buoy 10 by helicopter, the latter landing on the helicopter pad 40. As will be appreciated from the description hereinbelow, it is important that the buoy have minimum motion, i.e., minimum response to wind and wave action, in order to facilitate helicopter operations for the transfer of personnel to and from the buoy. After operating personnel are landed on platform 34, the drive motors for pinions 48 are activated and the platform is rotated such that the boom extends in a downwind direction toward the awaiting tanker T. Under most conditions, the tanker I approaches the buoy from the leeward. The booth, at this point, is in the inclined position illustrated in FIG. 1. Mooring lines 52 carried along the underside of boom 24 are dropped to the tanker and secured. The boom 24 is then lowered and the loading arms are extended and connected to the tanker manifolds. It will be appreciated that the lowering of boom 24 as well as the mooring of the tanker to the buoy exerts a tilting force on the buoy in the direction of the tanker. To counteract and offset at least a portion of this force, the ballast tanks 42 are ballasted with sea water through operation of pump 43. Oil transfer operations can thus be effected with the tanker moored to the buoy. In those systems wherein the water ballast carried by the tanker is to be purged, the water ballast is transferred through the buoy to the production platform via the water transfer line 20. When oil transfer operations are completed, the loading arms are disconnected from the tanker manifolds and the mooring lines are let go, whereupon they return to a stored position on the underside of the boom 24. The boom 24 can then be raised to the inclined position illustrated in FIG. 1 and tanker T backed away from the buoy. The ballast compartments 42 are deballasted and the buoy is returned to its normal floating position with the boom 24 inclined and the loading arms retracted as illustrated in FIG. I. The personnel on the platform can then be removed by helicopter.
In a preferred form of the present invention, and for operation particulary in about 400 feet of water, the length of the buoy from its lower end to the waterline is preferably about 320 feet, with the exposed portion of the buoy from the waterline to the underside of the platform extending approximately 63 feet above the waterline. The diameter of the lower portion of the column is about 45 feet and the diameter of the upper portion is about 34 feet. The heavy concrete ballast utilized at the lower end of the column extends from the lower end upwardly a distance of about 73 feet and in this configuration of the buoy as utilized in a depth of 400 feet of water, the anchoring collar is located a distance of 90 feet above the lower end of the buoy which fulfills the criteria set forth therefor as described hereinafter. The total dry weight of the buoy is about 15,000 tons and the column, with the foregoing configuration, obtains a natural heave period of about 25 seconds.
Referring now to FIGS. 6-7, there is illustrated a further form of oil transfer buoy 69 constructed in accordance with the present invention comprised of an elongated vertically extending buoy formed similarly as the buoy of the first embodiment and having a concrete lower ballast portion 70, an anchoring collar 72 for securing the ends of anchor chains 74, a stepped column forming the body of the buoy, and a rotatable platform 76 at the upper end of the buoy and well above the mean waterline indicated WL. The platform is similarly rotatably mounted on the column as in the first embodiment utilizing a pinion drive mechanism. In this form, the platform carries an extensible and retractable boom 78. Particularly, boom 78 is mounted for longitudinal sliding movement along guides provided on an elongated cantilivered portion of the platform. Suitably powered mechanisms, not shown, for extending and retracting the boom 78 are provided. The boom 78 carries flexible oil transfer lines 80 which extend into the central portion of the buoy. The flexible lines 80 are doubled back on themselves to positions where they are secured along the inner wall of the buoy and extend downwardly terminating in a central connection 82 at the lower end of the buoy. The doubled hose portion is provided with stabilizing guides 84 whereby the forces generated by the oil flow through the flexible hose lines are controlled and do not move or otherwise affect the flexible hose within the column. As in the previous embodiment, a water ballast tank 86 is carried on the platform on the side thereof remote from extensible boom 78. Suitable ballast lines and connections, similar to those provided in the previously described embodiment, are provided between the water ballast compartment and a water inlet below the waterline WL and including pumps, not shown, for ballasting and deballasting the compartments. Buoy 69 includes a helicopter pad 88 carried by platform 76 on the side thereof remote from boom 78.
In utilizing this form of buoy, personnel are transported to the buoy 69 by helicopter. The boom 78 is then extended as illustrated. Simultaneously, the buoy is ballasted to counterbalance the boom extension. Anchor lines, carried in a stowed position along the underside of boom 78, are then disposed over the bow of the approaching tanker, the mooring lines thus connecting between the tanker and a mooring collar 90 carried by the rotatable column portion of the buoy. Thus, the mooring force acts directly on the spar buoy a slight distance above the waterline. The transfer lines are then connected with the tanker manifolds and oil flows from the underwater storage or production platform through the flexible hose lines in the buoy to the tanker. Upon completion of oil transfer operations, the oil lines and mooring lines are disconnected, and the tanker backs away from the buoy. The boom is retracted and the ballasted compartment 86 is emptied. Operating personnel are then transferred by helicopter from the buoy to either the tanker or other facilities in the immediate area.
The present oil transfer system is particularly adapted for operation in heavy sea conditions and in sea conditions wherein the use of small boats or launches is precluded. In order to operate effectively in high seas, the tilt angle of the buoy, that is its inclination from the true vertical both prior to and after a tanker is moored thereto, must be maintained within a predetermined angle, on the order of 4 or 5. A countervailing constraint is the necessity to maintain the lateral movement of the base of the buoy within a predetermined radius to preclude fouling and/or breaking or kinking of the hose lines connecting between the anchored oil transfer manifold and the lower end of the buoy. That is to say, the lateral excursion of thelower end of the buoy, which is a combination of both horizontal linear movement of the buoy and the horizontal movement contributed by tilting of the buoy, must be maintained within predetermined limits. A third constraint is the necessity to preclude motion amplification of the buoy in response to wind and wave action thereon and hence to provide the buoy with a long natural period in heave. Since the anchor collar is the pivot for the buoy and is the only fixed constraint, its location along the length of the buoy is critical in providing the buoy with the desired motion characteristics. It will be appreciated that as the location of the collar is moved upwardly along the length of the buoy, the tilting moment provided the buoy by the tanker decreases since the tiiting moment provided by the mooring force multiplied by the moment arm decreases the closer the collar is located to the point of application of the mooring force. However, as the collar moves upwardly, the contribution to the lateral excursion of the lower end of the buoy by tilting action of the buoy increases beyond permissible limits above a certain point. Should the collar be located toward the lower end of the buoy, the angle of tilt of the buoy increases although the lateral displacement of the lower end of the buoy decreases.
Referring now to FIG. 8, it can be established that wherever the anchor collar is located along the buoy (the extreme ends of the buoy excepted), the tilt angle of the buoy can be represented by 0 tan Fm Ym/Fcb( Yb- Yg) where Fm denotes the mooring force, Ym denotes the moment arm between the point of application of the mooring force and the anchoring collar, Fcb denotes the restoring force at the center of buoyancy of the buoy, and Yb- Yg represents the difference in distances between the anchoring collar and the center of buoyancy and the anchoring collar and the center of gravity of the buoy. Since the denominator of the formula is essentially constant for small angles of 0, the latter angle varies substantially directly with the lever arm Ym. it can also be demonstrated that the lateral displacement A of the base of the buoy contributed by the tilt angle is essentially constant for any location of the anchor collar along the height of the buoy inwardly of its ends, except close to the ends.
In applying the foregoing, it is desirable to limit the maximum horizontal excursion of the base within a circle having a diameter twice the distance of the base of the buoy from the sea bottom. Further, for the protection of the oil hoses between the manifold and the buoy, it can be assumed that the maximum lateral displacement of the collar under the mooring force is a fraction K of the distance Y+ D where l is the distance from the base of the buoy to the anchoring collar and D is the distance between the lower end of the buoy and the sea bottom. This particular parameter is assured by selectively pretensioning the anchor chains by operation of the tensioning devices 51. Accordingly, the relationship It (Y+ D) equals D A can be solved for Y with the result that Thus, where the region in which the buoy is to be used is known, and where the maximum tilt angle and maximum lateral displacement of the base of the buoy are chosen to satisfy the foregoing described criteria, the optimum location of the collar along the buoy can be calculated. If the tilt angle is excessive (i.e., greater than, for example, 5, it can be reduced by adjusting Fcb, Fcg and Yb-Yg.
The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the fore going description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
What is claimed and desired to be secured by United States Letters Patent is:
l. A mooring and oil transfer apparatus comprising an elongated columnar member having a central axis and adapted to float in a substantially vertical position with a major portion thereof submerged below the water surface, a platform located at the upper end of said member, the upper portion of said member above the water surface rotatably carrying said platform, drive means carried by said apparatus for rotating said platform relative to said buoy and about its substantially vertical axis, said platform carrying a boom movable between first and second positions along a common radius substantially emanating from said axis, oil transfer and mooring lines carried by said boom, at least one oil transfer line extending through said columnar member from its lower end to said platform in communication with the oil transfer line carried by said boom, said boom in said first position carrying said oil transfer and mooring lines in a stowed position with said tip portion in said first position thereof, said boom in said second position locating said tip portion in said second position thereof radially outwardly of said tip portion in its first position for locating the oil transfer and mooring lines adjacent an awaiting tanker, at least one ballast compartment carried by said buoy on the side thereof remote from the tip portion of said boom, and means for selectively ballasting and deballasting said compartment to counterbalance said member when the boom is moved between said first and second positions.
2. Apparatus according to claim 1 wherein said boom is pivotal about an axis substantially normal to the axis of said elongated member.
3. Apparatus according to claim 1 wherein said boom is extensible and retractable in the direction of the axis of the boom.
4. Apparatus according to claim 1 wherein said platform includes spaces for quartering personnel.
5. Apparatus according to claim 1 including means for anchoring said member, said anchoring means being located intermediate the ends thereof.
6. Apparatus according to claim 5 wherein said anchoring means includes a collar disposed about said member adjacent the lower end thereof and anchor lines coupled to said collar.
7. Apparatus according to claim 6 wherein said anchoring means includes a plurality of anchor lines coupled to said member, and means carried by said member for selectively tensioning said anchor lines to limit the lateral excursion of said buoy when anchored.
8. Apparatus according to claim 1 including a mooring swivel disposed about said member below said platform for permitting movement of the tanker about the member.
9. Apparatus according to claim 1 including at least one water ballast line extending through the buoy and from the lower end to its platform, said water ballast line being carried by the boom for communication with the awaiting tanker for transfer of water ballast from the tanker through said member.
10. Apparatus according to claim 1 wherein said member is formed at least partially of concrete, the major portion thereof being located adjacent the lower end of said member.
11. Apparatus according to claim 1 having a natural period in heave greater than 20 seconds.
12. A method of fabricating a buoy comprising the steps of constructing an elongated generally columnar shaped member adapted to float in the water with the axis thereof substantially vertical, rotatably mounting a platform adjacent the upper end of said buoy, mounting a boom on said platform for movement between first and second positions and disposing anchor line securement means at a location along the length of said columnar member in accordance with the following formula:
where Y= the distance from the base of the buoy to the anchor line securement means;
D= the distance between the lower end of the buoy and the sea bottom;
K= maximum lateral displacement of the anchor line securement means under a given mooring force and which is a fraction of Y D; and
0 tilt angle of the buoy from true vertical, whereby the buoy is maintained within a predetermined angle of inclination from the vertical and lower end of the buoy within a selected magnitude of displacement from a predetermined position of the buoy when in the floating position.
13. A method of transferring petroleum products from underwater storage tanks through a transfer buoy to a tanker wherein the buoy has a rotatable platform carrying a boom and a helicopter pad comprising the steps of: transporting men by helicopter to the buoy, swivelling the boom toward the tanker before mooring the tanker to the buoy, mooring the tanker to the buoy, displacing the tip portion of the boom outwardly along a radius between first and second positions to lie in said second position in close juxtaposition with the tanker, coupling an oil transfer line between the buoy and the tanker and ballasting the buoy on the side thereof remote from the tip portion to compensate for buoy inclination due to outward displacement of the tip portion and the mooring forces acting on the buoy from the tanker.
"H050 UNITED STATES PATENT OFFICE Q CERTIFICATE OF CORRECTION Patent No. 3,778,854 Dated December 18, 1973 Inventor(s) ilip CHOW It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
Col. 5, line 54, "tanker I" should read -tanker T--. 01. 8, line 46, "5," should read --5)--,
C01. 9, Claim 9, line 47, "the" should read -its--; same line "its" should read --the--.
' i v Signed and sealed this 21st day oi Hay 197b,.
EDWARD EQJELLT JHMLJH. G MARSHALL DANDY Attesting Officer Commissioner of Patents