NZ195172A

NZ195172A - Offshore mooring terminal with fluid transfer apparatus from seabed pipeline

Info

Publication number: NZ195172A
Application number: NZ19517280A
Authority: NZ
Inventors: J M Kentosh
Original assignee: Amtel Inc
Priority date: 1980-10-07
Filing date: 1980-10-07
Publication date: 1984-03-30

Description

<div class="application article clearfix" id="description"> IUKM !>. .0 NEW ZEALAND 19517 l'V,': 00 Priority D est 4 a): .. Compile Specification Filed: I'JP.'Ji0. \ Cfass: & ?;'JP.Q.. .rt ■ ■ ■ ■ ^ Omar 1984 Pubkcatjon Date: ... ^ ,.&?h P.O. Journal, &o: V PATENTS ACT 195 3 Insert number of Provisional Specification(s) (if anv) and date(s) of fi ling; otherwise leave blank. Insert Title of Invention. Number: Date: COMPLETE SPECIFICATION MOORING INSTALLATION Insert full name, Z/WE AMTEL> INC., a corporation organized and in- full street address corporated in the State of Delaware, of 40 and nationality of Westminister Street, Providence, Rhode Island, (each) applicant. 02903, United States of America. hereby declare the invention for which -i/we pray that a patent may be granted to o*e/us and the method by which it is to be performed, to be particularly described in and by the following statement:- I ndicate if following page is numbered '1(a)' - 1 - 1.5.80 19517: BACKGROUND OF THE INVENTION Oil or other fluid cargo can be transferred between an undersea pipeline and a vessel, through a single point mooring terminal that includes a buoy floating, at 5 the surface of the sea and anchored in place by several catenary chains. The buoy serves as a transfer structure, and is coupled by a hose or pipe to the undersea pipeline and by another hose or pipe to a floating vessel. '.'In some applications, it has been found useful to permanent-10 ly moor a storage vessel to the buoy. A variety of mooring structures have been utilized to connect the buoy, or transfer structure, to a permanently moored vessel.4 One type of mooring terminal, such as that shown in U. S. * patent 3,335,690 by Busking, utilizes a beam rigidly-15 fixed to the vessel and to a rotatable portion of the transfer structure. In this type of terminal, the buoyancy of the vessel supports the transfer structure, and a nonrotatable portion of the transfer structure holds the vessel .in approximate location by means of chains that ex-2 0 end from the transfer structure to the sea floor. Thp trans fer structure can lie out of the water to facilitate access to a swivel unit, or product distribution unit (PDU), on the transfer structure, which is a device that typically requires maintenance, to facilitate such maintenance. However 25 as is pointed out in "The Advantages of the Single Buoy Stor age System (SBS)" by Sagot and Van Heijst in a paper given at '* v. /V. fiflS I* -2- \Q( // the fifth annual Offshore Technology Conference held in-Houston, Texas April 29-May 2, 1973, there are several disadvantages in this rigid mooring approach. These disadvantages include the fact that the transfer structure is subject to high pitch motions and the hose that extends down to the sea base is subjected to wave motions that can damage it. Also, the beam which holds the transfer structure must be very strong in order to hold the transfer structure a considerable distance away from the vessel to avoid the chains hitting the vessel. A mooring installation of the type which utilized a transfer structure rigidly connected to an end of a vessel, but which a-voided many of the disadvantages of prior art installations of this type, would be of considerable value. invention, an offshore terminal is provided, of the type which includes a dedicated vessel substantially fixed to a transfer structure located at or near the sea surface-and anchored to the sea floor, which provides high reliability and ruggedness while utilizing an economy of structure. A mooring beam structure holds the transfer structure close to an end of the vessel to minimize pitching forces that must be transmitted from the vessel to the transfer structure A transfer structure held to the sea floor by lines such as catenary SUMMARY OF THE IIIVEMTION In accordance with one embodiment of the present -3- v 195172 chains, has a lower end located at an underwater depth which is at least about the same as the adjacent epd of the vessel, to avoid the possibility that the catenary chains v/ill hit the vessel. The transfer structure extends from the under-5 water lower end to an upper end which is above the water line, and which is hollow to receive the pipe and hose structure that extends upwardly from the seabed, to protect the hose structure from surface waves. A swivel unit or product- distribution unit (PDU) lies at the top of the transfer structure, 10 ' and is separately rotatably mounted on the transfer structure and separately connected to the vessel to rotate with it, to avoid the transmittal of large mooring forces through the PDU or the pipes that connect it to the'vessel. The mooring structure can include a wide and tall box b^arn 15 having upper and lower plates that have ends formed in curves that mate with the extreme end of the vessel to fit closely thereabout for joining thereto. The novel features of the invention are set forth with particularity in the appended claims. The in-2 0 vention will be best understood from the following description when read in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a partial side elevation view of an 2 5 offshore terminal system constructed in accordance jw-i-tfh thn present invention. -4- 195172 •) Figure 2 is a view taken on the line 2-2 of Figure 1. Figure 3 is a partially sectional view of a portion of the system of Figure 1. Figure 4 is a partial perspective view of a portion of the system of Figure 3. Figure 5 is a partial side elevation view of an offshore terminal system constructed in accordance with .another embodiment of the invention. Figure 1 illustrates an offshore terminal system 10 of 4 a type which includes a transfer structure 12 which lies at the 14 such as a hose structure to at least one pipeline 16 near the sea floor 20. The pipeline 16, which is tied to a base 13 lying at the sea floor may,' for example, extend to a hydrocarbon well from which oil is received for delivery by way of a conduit that includes the hose structure 14 through the' transfer structure 12 to a vessel 22. The vessel 22 is a dedicated vessel for storage of the oil or other cargo, until it can be transferred to a tanker. A group of lines 24 which may be loose or aatenary chains, serve as anchor means to hold the transfer structure 12 from drifting far from a position over the base 18, while permitting some vertical and horizontal movement. The vessel 2 2 is a seaworthy structure, such DESCRIPTION OF THE PREFERRED EMBODIMENTS surface of the sea and is connected by an underwater flexible conduit -5- 19517: as a tanker or barge, that includes a buoyant elongated hull 22H having bow and stern ends, and which can be towed or self-propelled to the installation and there withstand heavy seas. A mooring structure 26 is provided 5 to substantially permanently connect the vessel 22 to the WW transfer st®c ture 12, to keep them close together, but without hitting each other during violent storms. The transfer structure 12 is constructed to permit the vessel to drift about a vertical axis 28 at the center of the in-10 stallation under the influence of currents, winds, and waves. As is also shown in Figure 3, the transfer-structure 12 includes a nonrotatable portion or flrame 30 4 that is anchored through the catenary lines 24 to the 0 15 sea floor, and also includes a rotatable portion or frame 32 that can rotate without limit about the vertical axis 28 together with the vessel 22. The largely nonrotatable frame 30 can turn to some extent, but is prevented from unlimited rotation about a vertical "axis by the caten-20 ary lines 24. The rotatable frame 32 is fixed to- the mooring structure 26 to move and rotate with the vessel, and is rotatably coupled through bearings- 3 6 to the nonrotatable or stationary frame 30 of the transfer structure- In addition, a fluid swivel unit or product 25 distribution unit (PDU) 38 is provided which has a stationary portion 40 fixed to the nonrotatable frame 30, and a turning portion 42 which rotates about the vertical -6- 195112 axis 23 and which is coupled to the hose structure 14 that extends down to the sea floor and also to a pipe 44-that extends to the vessel. The PDU 38 is of a type that can separately transfer two fluids, and includes another join*-at 46 that separately rotatably connects a pipe 4 8 to the vessel. The mooring structure 26 has an inner end 26i fixed to the vessel and an outer end 26o fixed to the rotatable portion 32 of the transfer structure, so that the mooring structure prevents free pivoting of the transfer structure about a horizontal axis with respect to the vessel. The bearings 36 prevent relative vertical movement of the transfer structure portions 30, 32. As a result, 4 the vessel 22 supplies the buoyancy required to hold the transfer structure 12 together with the weight of the chains 2 4 thereon, at the sea surface and with its rotation axis 2 8 in a largely vertical orientation, while the transfer structure 12 holds the vessel 22 from drifting far away from a position over the sea floor base 18. It can be appreciated that the rigid connection provided by the mooring structure 26 can result in considerable vertical movement of the transfer structure 12 during pitching of the vessel 22 in rough seas. However, the flexible connection of the transfer structure to the sea bottom through the lines 24 and the hose structure 14, permits such movement. The vessel 2 2 is much larger than the transfer 195172 structure 12, since a typical use of the vessel is to store large quantities of oil or other cargo while awaiting arrival of a tanker, and the vessel is typically highly buoyant. Accordingly, a transfer structure 12 can.be utilized which is negatively buoyant, especially when weighted by the chains 24 that 4s, a large float or buoyancy chainber does not have, to be utilized. The PDU 38 is a part of the system which normally requires considerable maintenance. Access to the PDU is. enhanced by mounting it so it lies above the sea surface, which also protects the PDU from damage toy waves and corrosion. The level of the sea surface changes with the amount of oil or other cargo stored in the vessel, with the line 50 indicating the relative water level at 100% * 4 ballast when the vessel 22 is filled with cargo, the line 0 52- indicating the water level at 60% ballast of the vessel, and the line 54 indicating the water level at 2 0% ballast. The vessel is always maintained above 20% ballast, since a lower level of ballast is dangerous in that it could result in capsizing of the vessel. In fact, where all of the cargo is to be pumped out, water is normally admitted to provide the necessary ballast. An average ballast condition is halfway between the safety borderline at 20% ballast and the maximum oil load at 100% ballast, which is the 50% ballast condition indicated by line 52. The description of the mooring terminal herein, refers to the 60% ballast condition where the condition is not otherwise described. Throuah- 195172 out the range of operation between the levels 50 and 54, the PDU 38 is above water level. The system is designed to prevent the possibility that any of the catenary chains 24 will hit the bottom of 5 the vessel 22, which could cause wear and possibly also damage to the hull. Although the chains normally extend in a primarily downward direction from the transfer structure, it is possible for them to extend at a relatively low incline, as when docking a tanker alongside th.a ves-10 sel 22, when forward surge of the vessel 22 may occur and a chain may extend at an incline of only about 30° from the horizontal. In one typical system, the chains normally ex-tend from the transfer structure at a downward angl$ of about 50° to 60° from the horizontal under quiescent condi-15 ' tions. It is estimated that the chains will extend $t an angle of about 35° from the horizontal perhaps once or twice a week during the life of the system, and that if the chains then struck the vessel they would abrade or otherwise damage it sufficiently in a few years to require 20 repairs. It is also estimated that the chains would extend at an angle of about 30° perhaps once a year, and that it is unlikely there then would be damage or sufficient wearing to require repairs over the total life of perhaps- 20 years of the installation. One design ap-25 proach is to avoid the likelihood of any chain-to-vessel contact during the life of the installation. To prevent interference between the chain and vessel, the transfer structure 12 is constructed with a -9- L J 1951 considerable height, and with the lower end of the transfer structure substantially no higher than the bottom 22B of the vessel at the end nearest the transfer structure. The nonrotatable portion 30 of the transfer structure 5 includes a platform or chain holder 56 at the bottom thereof, which is connected to the upper ends of the catenary lines 24. In the system of Figure 3 the bottom of the platform 56 is slightly lower than the bottom 22B of the vessel end. 10 By locating the transfer structure 12 so itr lower end is substantially no higher ;than the bottom of the adjacent vessel end, to avoid interference between the catenary chains and the vessel, it is possible to locate the transfer structure 12 very close to the vessel 22. 15 As shown in Figure 1, the distance S between the end of the vessel hull 2 2H and the transfer structure at the axis of rotation 28 thereof, is much less than the height H of the vessel, it preferably being less than half of the vessel height. This close mooring has several advan-20 tages, including the fact that the required bending strength of the mooring structure 26 is much less than would be required if the transfer structure were held t a considerable distance away from the vessel, so that the cross sectional area and length of the mooring structure 25 2 6 are only moderate. The close proximity also somewhat reduces the amount of pitching notion of the transfer structure 12 which results when the vessel pitches, and -10- 195172 also brings the PDU 38 closer to the vessel so access thereto is somewhat easier. In Figure 1, a large vessel is shown, wherein the transfer structure 12 does not extend up to the upper deck of the vessel, and a staircase 60 and walkway 62 are provided to enable personnel to reach the PDU 38 for maintenance. the transfer structure has the advantage of keeping the PDU 38 out of the water so it is easily accessibly* for maintenance while also keeping the lower end of the•structure deeply enough submerged in the water to avoid interference between the catenary chains and the vessel. This construction also enables protection of the hose structure 14 from surface waves. The nonrotatable portion 30 of the transfer structure includes an elongated hollow riser frame or riser 7 0 having a height which is a plurality of times greater than its outside diameter, and the platform 56 is fixed to the lower end of the riser frame 70. By extending the upper ends of the hose structure 14 through the hollow riser frame 70, the upper end of the hose structure 14 is safeguarded from wave action. It may. be noted that the upper end of the hose structure 14 may include rigid pipes, but their reliability is considerably enhanced by having them surrounded by the riser frame 7 0 at the location where they are subjected to surface waves. As discussed above, the considerable height of -11- The mooring structure 26 which holds the transfer structure 12 to the vessel, is formed to facilitate it construction and secure attachment to the complexly curved end of the vessel. As shown in Figure 4, the mooring structure 26 is largely in the form of a box beam, and has'upper and lower plates 74, 76 and a pair of side plates 73, 80. All of the plates have outer ends securely joined, as by welding, to the rotatable frame 32 of- the transfer structure and have inner ends designed to be joined, as by welding, to the vessel 22. The inner ends 74i, 76i of the upper and lower plates, as well as of the side plates, are curved to closely mate with the portion of the vessel end against which they lie and to which they are to be welded. The upper and lower plates can be initially formed with an approximate curvature to fit against vessels of approxj.- 4 mate size, and actual mating can be accomplished by further cutting away of small portions of the plate inner • ends to provide a good mating fit. As shown in Figure 2, the upper and lower plates are designed to be mounted on the extreme end of the vessel, and to extend on either side of the longitudinal center plane 82 of the vessel. This construction of the mooring structure 2 6 enables a relatively short box beam structure to be utilized, which can be securely held to the vessel to support the transfer structure against large forces in all directions. The fact that the mooring ^structure 26 holds only a transfer structure portion that lies at " i v>% a- low level, and that is very close to the vessel, allows the mooring '^tructure inner end 26i to lie below water level at least at 60% vessel buoyancy, and actually at all safe buoyancy conditions from 2 0% to 100% buoyancy. This avoids the need for beams connected to the' top and bottom of the hull that would be subjected to wave action and corrosion which would greatly increase the weight and cost of the structure. - 1.2 - 195172 1951 It may he noted that the mooring structrue 2& only attaches to the rotatable frame 32 which lies at the lower portion of the transfer structure. The rotatable portion 42 of the PDU 38 is separately connected to the vessel by the heavy duty pipe 44, so that the PDU is separately held to the vessel to rotate therewith. By vertically spacing the PDU from the rotatable frame 32 arrd separately connecting it to the vessel, the PDU is isolated from heavy forces that may be transmitted between the rotatable frame 32 and vessel and which could cause bending and damage to the PDU if allowed to pass therethrough-Figure 5 illustrates an offshore terminal 90 which includes a somewhat smaller tanker vessel 9 2 and a transfer structure 94 which extends up to the uppejr deck of the vessel to facilitate maintenance and the con- • nection of pipes 93 of the conduits that carry oil from the seabed to the vessel. A walkway 95 extends from the vessel to the transfer structure, and leads to a circular walkway 97 that is fixed to the nonrotatable portion of the transfer structure. The transfer structure 94 is similar to the transfer structure 12 of Figure 3. However, a platform 96 at the bottom of the transfer structure, which connects to chains 24 extending down to t.he sea bottom, lies at a height slightly above the bottom 92B of the"adjacent bow end of the vessel. As Mentioned above, the catenary chains such as 2 4 normally do not extend at an angle A of less than about 3 0° from the horizontal even during forward surge of the vessel. Thus, by locating the portion 9fi of the transfer structure which holds 1951V2 imaginary line 100 extending at a downward angel of 30° liec below the vessel bottom 92B, interference between the chains 24 and the vessel, is avoided. The mooring structure 102 which cpnnects the transfer structure to the 5 vessel, is positioned so that the upper plate 104 thereof is welded to the vessel hull at the sane level as a deck 106 of the vessel. The lower plate 103 of the mooring" structure is similarly located sp that it is at the same level as an internal bracing plate 110 of the vessel. 10 This permits moc-ing loads to be transferred to braced locations on the vessel where the loads can be best withstood. The offshore terminal can be constructed with many variations. While heavy chains extending in loose catenary 15 curves are widely accepted to serve as the anchor lines' that extend to the sea bed, it is possible to use light f;tretchable (e.g. Nylon) and largely taut lines. In another aspect of the invention, an advantage of using a tra^^rST structure fixed closely to a dedicated vessel is that the vestel (which would have 20 considerable spare buoyancy), can support the transfer structure and the weight of heavy chains that anchor it. It should be noted, however, that the transfer structure itself raay-be constructed to be somewhat positively buoyant. In still another aspect of the invention, the hose structure or flexible 'conduit, 25 which extends from the sea bed to the transfer structure can include ^^^'"^^vlong length of flexible pipe which has less flexibility than a'common hose, but may be of lower cost. It is even possible "2 FEB/981 to: use pivotally connected lengths'of hard pipe between the v>sea floor and the transfer structure. In still another aspect 30 of the invention, it is noted that it is possible to mount the PDU, or fluid swivel, or an overhanging beam extending from the ship, by mounting the rotatable portion of the PDU to the ship -14- and coupling the nonrotatable portion of the PDU to the ji©a—~~ rotatable portion of the PDU to prevent relative rotation- * i_ JL JL w ^ Thus, the invention provides an offshore terminal of the type which includes a transfer structure rigid-.5 ly moored to an end of the vessel, wherein a relatively snail and easily attached mooring structure can be utilized to hold the transfer structure to a dedicated vessel, and good protection is provided for" the conduit that extends from the sea bottom to the vessel by way of the 10 transfer structure. This is accomplished by utilizing a transfer structure which is held close to the vessel end such as within a distance less than the height of the vessel hull, and by mounting the transfer structure so its lower end is substantially no higher than the 1 5 bottom of the adjacent vessel end to prevent interference between a catenary chain and the vessel. The flexible * underwater conduit, which may include a hose or a moderately flexible pipe along most of its length, and which also may include lengths of hard piping, includes a length that extends 20 through a hollow portion of the transfer structure which extends from below the water surface to above it, to protect the conduit from surface wave action. The mooring structure can include upper and lower plates with inner ends curved to mate with the vessel, and which are attached to the 25 extreme end of the vessel. Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art and consequently, it is intended that 30 the claims be interpreted to cover such modificati^ffl^wand equivalents. JyV OrA l-*"2 FEBl9$f'\ -is- V. „"' X> ;• l\'CO . , </div>

Claims

<div class="application article clearfix printTableText" id="claims"> WHAT WE CLAIM IS: 195172 1 1. In an offshore terminal which includes a base 2 at the sea bottom, a transfer structure at the sea surface, ^ 3 a vessel of greater positive buoyancy than the positive 4 or negative buoyancy of said transfer structure; and at least 5 one fluid conduit extending up from near the sea bottom and 6 through said transfer structure to said vessel, and wherein 7 said transfer structure includes a substantially nonrotatable 8 portion which is of a height much less than the depth of 9 the sea thereunder and which is held in general location sub- 10 stantially only .by a plurality of flexible chain means extending 11 in loose curves to the sea floor, and said transfer'structure 12 also includes a rotatable portion which can rotate about a 13 substantially vertical axis on said nonrotatable portion', 14 the improvement comprising: 15 a mooring structure coupling said transfer 16 structure to an end portion of said vessel, said mooring 17 structure having first and second ends substantially fixed 18 respectively to said vessel and to said rotatable portion 19 of said transfer structure; 20 said mooring structure holding said transfer structure 21 so the distance between said vertical axis thereof and 22 the adjacent end of said vessel, is less than the height 23 of the hull of said vessel, and said transfer structure is 2 4 positioned so the lower end of sai.d nonrotatable portion 25 of said transfer structure lies substantially no higher than the adjacent end of said vessel, to preve®^%he loose 26 * •' ^ 2 7 chain means from striking the vessel. /v (if 2 £5 ■: c '•« -16- Yi I x-s /> 1S5172 1 2. The improvement described in Claim 1 wherein: 2 the lower end of said transfer structure lies 3 at a level wherein an imaginary line extending at a 30° 4 downward incline towards said vessel, from the bottom 5 of said transfer structure where it receives a chain means 6 which is closest to said vessel, does not ineract said 7 vessel. 1 3. The improvement described in Claim 1 wherein: 2 said nonrotatable portion of said transfer structure 3 includes a wide underwater chain holder which is connected 4 to said chain means, and lies underwater at all buoyancy 5 conditions of the vessel from 100% buoyancy to 20% 6 buoyancy and also includes a tall hollow upstanding riser # 7 having a lower end fixed to said chain holder and an upper 8 end lying above the water at all buoyancy conditions of the 9 vessel from 100% buoyancy to 20% buoyancy; 10 said rotatable portion of said transfer structure 11includes a frame yjjsittCftng surrounding the lower end portion 12 Utfty of said riser and rotatablfc connected thereto. 4. The improvement described.in Claim 3 wherein: 2 ^ swivel unit lies at the top of said riser, 3 so it is always out of the water, and said fluid conduit extends ^4 through said riser so it is protected from waves at 5 all buoyancy conditions of the vessel. i* -17- //' 195172 1 5. An off.shore terminal for connection to a 2 pipeline lying at or near the sea floor, comprising: 3 a transfer structure lying at the sea surface, 4 said transfer structure having a nonrotatable portion of a 5 height less than the depth of the sea thereat, a rotatable 6 portion, and bearings rotatably connecting said portions 7 and permitting said rotatable portion to rotate about a 8 substantially vertical axis with respect to the nonrotatable 9 portion while preventing unlimited vertical motion of said 10 portions relative to each other; 11 anchor means having an upper .end connected to the nonrotatable portion ^of the transfer struc£j»ie and a 13 lower end anchored to the sea floor, for limiting drifting 4 14 of the transfer structure without closely confining it 15 . in orientation or location; 16 a vessel having bow and stern ends; 17 fluid conduit means extending upwardly from said 18 pipeline near the sea floor through said transfer structure 19 to said vessel; and 20 a mooring structure having an outer end lying 21 beyond an end of the vessel and rigidly fixed to said ^^22 rotatable portionof said transfer structure, and having 2 3 an opposite inner end fixed to said vessel; 24 said transfer structure having a lower end below 25 water level and an upper end above water level, and the ^^26 portions of said fluid conduit which lie immediately below 27 and above the sea surface being surrounded by said transfer 2 8 structure. 195172 6. The offshore terminal described in Claim 5 wherein: 2 1 said transfer structure includes an elongated hollow 3 nonrotatable riser frame having a height which is a plurality 4 of times greater than its outside diameter, and a platform 5 fixed to the lower end of said frame, said anchor means 6 comprising flexible chain means and said platform connected 7 to said chain means; 8 said transfer structure also includes a rotatable 9 frame disposed about the lower end portion of said hollow 10 nonrotatable riser frame and connected by at least one 11 bearing to said hollow frame, said rotatable frame fixed 12 to said mooring structure; and ^^13 said transfer structure also includes a product 14 distribution unit lying at the top of said hollow non- 15 rotatable frame, and at least one length of fluid con'duit 16 extending through said hollow frame to said product distribution 17 unit. 1 7. An offshore terminal for connection to a 2 pipeline lying at or near the sea floor, comprising: 3 a transfer structure lying near the sea sur- 4 face, said transfer structure having a nonrotatable 5 portion and having a rotatable portion rotatable about 6 a substantially vertical axis with respect to the non- 7 rotatable portion; 8 andhor means having an upper end connected 9 to the nonrotatable portion of the transfer structure 10 and a lower end anchored to the sea floor; 11 a vessel having bow and stern ends; 12 fluid conduit means extending upwar 13 said pipeline near the sea floor through said 14 structure to said vessel; and ^ 195172 15 a mooring structure having an outer end lying 1»6 heyond an end of the vessel and rigidly fixed to said 17 rotatable portion of said transfer structure, and having 18 an opposite inner end fixed to said vessel; 19 ' said mooring structure including upper and lower 20 plates, each plate having an inner end which is curved 21 to mate with the hull of said vessel and which.extends 22 on either side of the longitudinal center plane of 'the 23 vessel. 1 8. An offshore terminal for connection to a pipeline 2 lying at or near the sea floor, comprising: 3 a transfer structure lying near the sea surface, 4 said transfer structure having a nonrotatable frame and 5 having a rotatable frame rotatable about a substantially 6 vertical axis with respect to the nonrotatable frame but 7 said rotatable. frame prevented from vertical movement 8 with respect to the nonrotatable frame; 9 anchor means having an upper end connected to 10 the nonrotatable frame of the transfer structure and a 11 lower end anchored to the sea floor, for permitting tilting 12 and drifting of the transfer structure while limiting drifting 13 thereof away from a predetermined location; 14 a vessel having bow and stern ends; 15 fluid conduit means extending from said pipeline 16 through sa'id transfer structure to said vessel; and 17 a rigid mooring structure having an outer end lying 18 beyond an end of the vessel and rig-idly fixed to said 19 rotatable frame of said transfer structure, and having an 20 opposite inner end fixed to said vessel; ' i • ' j -20- 195172 .21~ « , said transfer structure also including a product 22 distribution unit spaced above said rotatable frame, 2 3 said unit having a stationary portion connected to 24 said nonrotatable frame so it-avoids rotation as said 25 frame does, and a turning portion connected by said fluid 26 conduit to said vessel to rotate with it. 1 9. The offshore terirJ nal described in Claim 8 wherein: 2 said anchor means includes a plurality of catenary 3 chains extending between said nonrotatable frame and 4 the sea floor; and 5 the lowest portion of said transfer structure which 6 engages any of said chains, lies a sufficient depth under 7 the sea surface, that an imaginary line extending at a 8 downward incline of 30° from said lowest portion does not * 9 ' intercept the hull of said vessel. 1 10. An offshore terminal for installation in,a 2 sea, comprising: 3 a vessel (22) having a hull (22H) with opposite 4 ends; 5 a mooring structure (26) having an inner end fixed 6 to an end of said vessel and an outer end; 7 a transfer structure (12) having a rotatable 8 frame (32-) fixed to the outer end of said mooring structrue 9 so its axis of rotation lies closer to the vessel than the 10 height of the vessel, a nonrotatable portion (30), and 11 bearings (36) rotatably connecting the rotatable frame to the 12 nonrotatable portion, said nonrotatable fr^^^tl^dinq a hollow „ jrO. Y\ -21- • * * / • 195172 riser (70) having a lower end which is always underwater and an upper end which is always above the sea surface, for all safe buoyancy conditions of the vessel; a plurality of lines (24) having lower ends anchored to the sea bottom, and having upper ends connected to the bottom of the nonrotatable portion of the transfer structure at & level low enough to prevent hitting of the vessel despite closeness of the transfer structure to the vessel; a fluid conduit (14) extending generally upwardly from near the sea bottom, and through said riser to the upper end thereof; a product distribution unit (38) mounted at least as high as the top of said riser and connected to said fluid conduit; and a pipe (44) connecting said unit to said vessel. ll. An offshore terminal for connection to a pipeline \ying at or near the sea floor, comprising: a structure lyin^s^t the sea surface, said transfer structure having a nonrotatable portion of a height which is much less than the de^\J:h of the sea thereat, a rotatable portion, and bearings roS^tably connecting said portions to permit rotation of the rb^atable portion about a substantially vertical axis with inspect to the nonrotatable portions while substantially prev^ting relative vertical movement of said portions; -22- V '*pe*isci - :• v * 12 . ^3 ( - • 14 15 16 17 18 19 20 21 22 23 — ,I.P24 25 2G 27 28 29 V)4W 1 -■«■<** 2 3 4 5 X V O X « te at least one flexible line having an upper end connec^Qd to the nonrotatable portion of the transfer. structure'Vnd a lower end anchored to the sea floor; a Vessel having bow and stern ends; a flin^l conduit means extending upwardly•from said pipeline nea^he sea floor through said transfer structure to said ve^el, for carrying fluid between them; and a mooring stricture having an outer end.lying beyond an end of the vesse\ and rigidly fixed to said rotatable portion of said tranVier structure, and having an opposite inner end fixed to said vessel, said mooring structure holding said transfer Structure so that said vertical axis is closer to the nearest vessel end than the height of the vessel, and at a lev^L wherein the, lowest point where said flexible line is"Vield by 'said structure, lies at an underwater level at wl^ch an imaginary line extending at a 30° downward incline^Vtherefron towards said vessel does not intersect said vessel tt, 3% The terminal described in Claim^""wherein: the inner end of said mooring structure is fixed to said vessel at a level low enough that the height of said inner end is below the waterline at 60% ballast .of the vessel. An offshore terminal substantially as herein described with reference to Figs- 1-4. ^4- An offshore terminal substantially as herein described with reference to Fig. 5. ? A J.- t: "2FEB198I i ft "*2 : ( \ HARDiE & CO. ^ -t> Patent Attorneys for .-,0 - -23- ^ C the Applicant(s). </div>