US3837380A

US3837380A - Marine loading/unloading system

Info

Publication number: US3837380A
Application number: US00237755A
Authority: US
Inventors: R Davies
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-03-29
Filing date: 1972-03-24
Publication date: 1974-09-24
Anticipated expiration: 1991-09-24
Also published as: IT955151B; FR2155190A5; BE781378A; FR2155742A5; JPS5233873B1; DE2215279A1; NL7204109A

Abstract

Marine loading or unloading system for fluids, particularly for tanker loading in deep water, have a sea-bed pipe line joined to a sea-bed anchor to which directly or indirectly a ship for loading or unloading is moored. A conduit proceeds from the seabed anchor to the ship and includes rigid pipe lengths joined by pivoting joints of which at least one is a universal joint. In one embodiment of system shown, the conduit proceeds as a jointed rigid pipe substantially vertically from the anchor to a captive buoy to which the ship is moored and whence the conduit is conventional hose or the like; in another embodiment, the ship is moored direct to the sea bed anchor and the conduit proceeds as a jointed rigid pipe to a free-floating buoy or capture device. Novel universal joints and swivel bearing constructions for under-water applications are shown, and also a novel variable-buoyancy capture device.

Description

United States Patent [111 3,837,380 Davies Sept. 24, 1974 [54] MARINE LOADlNG/UNLOADING SYSTEM Primary Examiner-Houston S. Bell, Jr. [76] Inventor: Robert Henry Davies, Anfield, Mill Attorney A or Flrm"cushman Darby &

Ln., Herne, England Cushman [22] Filed: Mar. 24, 1972 57] ABSTRACT 21] Appl. No.: 237,755

Marine loading or unloading system for fluids, particularly for tanker loading in deep water, have a sea-bed [30] Fore'gn Apphcatlo Prlorlty Data pipe line joined to a sea-bed anchor to which directly Mar. 1971 Great Britain U 80 6/71 or indirectly a ship for loading or unloading is moored. 1971 Great Britain 5 A conduit proceeds from the seabed anchor to the Feb. 2, 1972 Great Britain 4994/72 shipand includes rigid pipe lengths joined by pivoting joints of which at least one is a universal joint. In one embodiment of system shown, the conduit [52] Cl 141/279 0 2 6 proceeds as a jointed rigid pipe substantially vertically [51 I t Cl 5 3/30 from the anchor to a captive buoy to which the ship is d 279 moored and whence the conduit is conventional hose le 0 227 137/236 or the like; in another embodiment, the ship is moored 166/6} 9/8 i 230 289/272 direct to the sea bed anchor and the conduit proceeds as a jointed rigid pipe to a free-floating buoy or 56] R f Ct d capture device. Novel universal joints and swivel e erences I e bearing constructions for under-water applications are UNITED STATES PATENTS shown, and also a novel variable-buoyancy capture 3,452,787 7/1969 Bily 141/388 device.

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v sum 11m 15 I MARINE LOADING/UNLOADING SYSTEM FIELD OF THE INVENTION The invention relates to marine loading and unloading systems for fluids, particularly oil and natural gases. It is concerned specially with deep-water loading stations at which ships are loaded with such fluids from a pipeline on the sea bed.

BACKGROUND OF THE INVENTION There have been many proposals for provision of marine loading stations. Common features are: a pipeline on the sea bed, a base point from which a conduit starts a rise towards the sea surface, some sort of buoy either supporting or marking the conduit, and lastly pivotal flexibility in the conduit, at least whenever the mooring position of the ship to be loaded or unloaded is not substantially uniquely fixed (contrast, for this last feature, US. Pat. No. 3,236,267).

Now obviously the fixing of the availability of the conduit end to the ship in a unique position substantially cuts down the availability of the station, because wind or sea conditions may make the position or the approach to the position impracticable.

So further developments concentrated on providing flexibility in the conduit beyond the base point. There were two relevant main lines of development. Either (a) a flexible hose was attached between the base point and a buoy substantially vertically above it (British Pat. Nos. 978,038, 1,051,934) or (b) a conduit rose obliquely, and went laterally as well as upwardly; in the latter case the conduit would be a flexible hose (British Pat. No. 1,238,542) or hingedly linked rigid pipes (British Pat. No. 1,053,741). Both these lines of development have disadvantages, and the proposals of the present invention are applicable to dealing with the disadvantages of both.

When stations were of the type designated (b) above,

, and the conduit was a flexible hose, or when they were of the type (a), the main problem was the wear imposed on the hose by its being driven by wind and sea, secondarily the difficulty of resisting high water pressures at and near the sea bed (a considerable portion of the conduit could lie at some depth in type (b), since it rose only gradually); these were to some extent overcome by providing pivoted links between rigid pipes (British Pat. No. 1,053,741), but this brought the disadvantage that because the joints were each pivotable about only parallel and single axes, there was a sacrifice of adaptability: there was only a restricted range of directions of approach to the mooring available to the ship, and the ship was moored (in e.g., US. Pat. No. 3,236,266) using an anchor block on the sea bed pipe line but different from that from which the conduit started to rise so that any movement of the ship about its moorings tended to cause the mooring line to interfere with the conduit and the resulting stresses in the conduit created a risk of damage and consequent pollution; thus the ship had also to be moored by its stem to be prevented from swinging with changes of weather.

Difficulties have also arisen at the place where the ship is to pick up the conduit. The weight of large diameter pipe is considerable. To provide for lifting it up to the freeboard of the ship, and to allow for the change in that freeboard as the ship is loaded or unloaded, it has been proposed (British Pat. No. 1,157,532) to provide a capture buoy of variable buoyancy which, however, because of the lack of lateral flexibility in the conduit cannot be left exposed to surface waves and wind, but when out of use must be sunk to the sea bed. It has also been proposed (British Pat. No. 808,675) to provide a rigid lifting gantry pivotable on the sea bed; this also must essentially be submerged when not in use, is only applicable in shallow water stations, and its pivot is rigid so that when the gantry is projecting from the surface the pivot is subjected to considerable strain as a result of wind or sea action.

SUMMARY OF THE INVENTION The disadvantages lie in the difficulty of designating and using hoses (at least of large diameter) so as to work under high pressures and to withstand wear due to flexing, and in the case of jointed rigid pipes, to provide the right sort of flexibility in the conduit as a whole (to allow a moored ship to move about its mooring while loading or unloading), and to allow the conduit to trail freely under the influence of wind or sea.

The present invention provides a marine loading/unloading system in which a conduit between the sea-bed and a ship includes rigid pipe lengths joined by a universal joint; and the ship is moored (directly or indirectly) to the sea bed anchor from which the conduit rises.

In one embodiment of the present invention there is provided a marine loading/unloading station for tankers including a floating buoy anchored by a mooring line to an anchor on the sea bed, a submarine pipeline secured to the anchor, a plurality of rigid pipe lengths connecting the buoy to the submarine pipe line and a connecting member joining two of the rigid pipe lengths so that one of the two rigid pipe lengths can pivot relative to the other rigid pipe length about any axis, the total length of the rigid pipe lengths being greater than the length of the mooring line between the anchor and the floating buoy.

In contrast to the situation designated (a) above, this enables a substantially vertically extending conduit between the sea bed anchor and a mooring buoy to be constructed of any practicable diameter while resisting the pressures found at deep water stations, and to resist the wear imposed by the continual agitation of the mooring buoy by wind and sea.

In another embodiment of the present invention there is provided a marine loading/unloading system including a plurality of rigid pipe lengths connected together by means of a plurality of pivotal joints to form an articulated rigid wall pipeline connected to a submarine pipeline at a seabed anchor, means for mooring to the anchor, a tanker to be connected to said articulated pipeline, said mooring means being arranged to restrain the tanker within a distance from the anchor less than the maximum length of said articulated pipeline. Buoyant means may be secured to the articulated pipeline to maintain it in a required depth range.

Taking the situation (b), the invention allows for the replacement of the flexible hose by the more advantageous and adaptable jointed rigid pipe lengths, without however any sacrifice of flexibility or of availability of the station in any wind or sea direction. Because the conduit is able to trail freely in the water in any direction, the ship may be moored to a point the same as that from which the conduit rises and may pick up the mooring from any direction and swing, while moored, in any direction.

A particular form of embodiment of the invention uses an underwater slewing anchor having mooring means for a ship and the conduit both secured for rotation together about a vertical axis through the anchor.

Whereas slewing underwater anchors or buoys are known, where a conduit is mounted on a turntable construction on the anchor or buoy, it has never been possible before the present proposal to allow the mooring means to have a permanently buoyant pick-up, free to move under the influence of wind and sea, and to use these means to rotate the slewing anchor to the appropriate direction. When a ship is attached to the mooring means, the effect is that the conduit is directed, underwater, generally towards the ship wherever she may be lying relative to the anchor.

The invention provides also a pick-up buoy of variable buoyancy which, however, is never as a whole negative. That is to say, the buoy has an upper buoyant position and a lower buoyant position, and is adjustable as to the level at which it floats between those levels by adjustment of the buoyancy of a lower buoyancy chamber; but an upper buoyancy chamber is always sufficiently buoyant, when on the surface of the water, to maintain the buoy as a whole projecting from the surface of the water. This is very advantageous from the point of view of case of pick-up, avoidance of high water pressure and avoidance of adhesion to the sea bed (which would particularly occur in deep-sea positions); and can be permitted only because of the flexibility and resistance to flexing wear of the conduit to which it is attached.

Also according to the invention, universal joints for underwater pipes are provided. These allow for the pipe sections to pivot abut one or more of three mutually orthogonal axes (i.e., axes in three spatial dimensions which intersect at a single point).

In a preferred form of universal joint two substantially U-shaped pipes are interconnected by means of a spherical member, swivel connectors being provided for each connection to the pipe lengths. Swivel connectors are also provided for each connection of the U- shaped pipes to the spherical member so that the U- shaped pipes are rotatable relative to the spherical member, about respective, mutually perpendicular axis.

Particular provision must be made in underwater pivoting or universal joints to resist flexural wear and to remain leakproof even after considerable such wear and under high water pressures. It is found according to the invention that a particularly effective bearing for such joints is a non-rolling load bearing element having radially inner and outer frusto-conical surfaces, which converge in the same direction and are preferably parallel, engaging respectively two relatively movable surfaces constrained to move respectively with the pipes, the bearing elements being slidable relative to at least one of the said relatively movable surfaces.

One preferred form of pipe joint has a bearing element having parallel, frusto-conical inner and outer surfaces disposed so that movement apart of the pipe ends tends to compress the element between relatively movable surfaces they engage.

In another preferred form of pipe joint according to the invention, particularly suitable for large diameter pipes such as are used in marine loading arms and oil tanker unloading buoys, one pipe end has two radially outward frusto-conical surfaces associated with it, tapering in opposite directions (e.g., away from each other), and the other pipe end has two flanges each having a radially inward frusto-conical surface located radially outwardly of (and preferably parallel to) one of the said frusto-conical surfaces on the said one pipe end, these two bearing elements having frusto-conical inner and outer surfaces, being respectively mounted radially between the pairs of radially outward and inward frusto-conical surfaces. Packing glands may be provided adjacent the bearing elements between relatively movable, e.g., cylindrical, surfaces of parts of the pipe ends and the flanges.

DESCRIPTION OF THE DRAWINGS AND OF PREFERRED EMBODIMENTS In the drawings:

FIG. 1 shows diagrammatically, in elevation, a first embodiment of the invention, this being in the type of loading/unloading station in which the flexible conduit rises substantially vertically from the sea bed anchor FIGS. 2 and 3 are elevations of a universal joint, taken at right angles to each other, FIG. 3 being taken in the direction of the arrow Ill, FIG. 2

FIG. 4 is an elevation of a sea-bed portion of the embodiment FIG. 5 is a diagrammatic view on the arrow V, FIG. 6, of a second form of universal joint FIG. 6 is a view on the arrow VI, FIG. 5, of the second form,

FIG. 7 shows diagrammatically, in elevation, a second embodiment of the invention, this being in the type of loading/unloading station in which the flexible conduit rises generally obliquely from the sea bed anchor FIG. 8 is a plan view of the second embodiment FIGS. 9 and 10 are elevations of the sea-bed portion of the second embodiment taken at right angles to each other FIG. 11 is a, plan view of the sea bed portion of the second embodiment FIG. 12 is a diagrammatical cross section, on a larger scale, of part of the sea bed anchor of the second embodiment FIG. 13 is an elevation of an upper portion of the second embodiment FIG. 14 is an elevation of a capture buoy FIG. 15 is a part elevation taken at right angles to FIG. 14

FIG. 16 is an elevation similar to FIG. 14 but showing the buoy with a connection to a ship FIG. 17 is a cross-section of part of the connection FIG. 18 is a plan view of a part of the second embodiment FIG. 19 shows a third embodiment, of the same type as the second FIG. 20 shows in diametrical cross-section crosssection a first embodiment of pipe swivel construction FIG. 21 is a part diametrical section, part elevation of a second embodiment of pipe swivel construction and FIG. 22 shows in diametrical cross section on a larger scale the second embodiment of pipe swivel construction.

Referring to FIGS. 1 to 6 a marine loading/unloading station includes a mooring buoy 2 at sea level'to which a tanker can be connected by means a conventional hose line 3. The tanker is also moored to the buoy. The buoy 2 is shown in three alternative positions A, B and C for the sake of illustrating the effect of wind or sea. A first rigid pipe length is connected between the buoy 2 and a first universal joint 4. The joint 4 is in turn connected by means of a rigid pipe length 5 to a second universal joint 6. The joint 6 is connected by means of a rigid pipe length and a single axis swivel connector 27 in a horizontal axis and a single axis swivel connector 28 on a vertical axis to a seabed manifold generally indicated 8. An adjustable link 9 connects the manifold 8 to a submarine pipe line 10 which is connected to the shore, well head or other storage area. The seabed manifold 8 is anchored to the seabed by means of an anchore 11. The position A of the buoy 2 is that in which the buoy is vertically over the point of connection of the pipe length to the manifold 8. The positions B and C are respective positions to which the buoy 2 can be displaced from the position A. The buoy 2 is anchored by means of chains 7 to the anchor 11.

In all positions of the buoy the conduit portion 1 formed by the rigid pipe lengths 5 and their joints extends generally vertically. But because the chains 7 are shorter than the total length of the pipe lengths 5, and because of the lengths of the individual

rigid pipe lengths

3, 5 and 7 being such that they are never parallel to one another, there are two possible configurations of the pipe lengths in any plane. Alternative positions in the plane of the paper are shown in FIG. 1. The effect of the vertical axis connector 28 is to allow the lower joint 4 to adopt any position on a circle lying in the surface of a sphere centered on the swivel connector 27, and of radius approximately equal to the length ofthe lower pipe length 5. Thus the conduit as a whole, while being made up of rigid pipe lengths, does not have to withstand any bending stresses.

Referring to FIGS. 2 and 3 of the universal joint 4 consists of two substantially

U-shaped pipes

12 and 13 interconnected by means of a spherical member 14. The

pipes

12 and 13 respectively include right angle pipe bends 15 and 16 each rigidly secured to one limb of the U by means of a connection 17. The pipe bends 15 and 16 are respectively connected to the length from buoy 2 extending toward joint 4 and pipe length 5 by means of single axis joints 18 and 19. These swivel joints I8 and 19 are constructed, preferably in a manner that will be described later, so as to withstand submarine conditions and allow the pipe bends l5 and 16, respectively, to rotate relative to the pipe lengths 5 about their common axes. at the joint. The spherical member 14 is provided with two short connecting

pipes

20 and 21 perpendicular to each other which are rigidly secured to the member 14 but are connected to the

pipes

12 and 13 by means of swivel joints 23 and 22 respectively, similar to

joints

18, 19. Associated outrigger stays and 25' and axles 24 and 24' connect the pipe bends 15 and 16 to the spherical member 14. The connecting member 4 thus allows the rigid pipe lengths 5 to pivot relative to each other about any one or more of the three orthogonal axes at the center of the spherical member 14. The stay 25 extends from the pipe between the

joints

18 and 22 to the axle 24 on the pivot axis of the joint 22, and the stay 25' from the pipe between the

joints

19 and 23 to the axle 24 on the pivot axis of the joint 23; they resist any tendency of the joint as a whole to splay apart along the axis of the pipe lengths 5.

Referring to FIG. 4, a universal joint 4, lies above the lowermost pipe length 5. The lower end of this pipe length is connected to a right angle pipe bend 26 by means of a horizontal axis swivel joint 27. The pipe bend 26 is connected to the sea bed manifold 8 by means of a swivel joint 28.

The sea bed manifold 8 is supported in blocks 29 which are secured to the anchor 11. The link 9 is connected by means of a swivel joint 30 to a right angle pipe bend 31 which is in turn connected to the manifold 8 by means of a swivel joint 32. The swivel joints 27, 28, 30 and 32 are all similar to each other and to the

joints

18, 19, 22 and 23.

Pipe lengths 5 can be made up of pipes 33 formed into a continuous pipe length by butt-welding them together. Reinforcing external plate flanges 34 are provided at the butt welded junctions to help prevent dam age due to the surrounding water pressure.

FIGS. 5 and 6 show a second form of universal joint. Coaxial pipe lengths 5 lie on a ZZ axis. Swivel joints 35, allow the lengths to pivot relative to each other about that axis. A first pipe U-bend 36 leads to a swivel joint 37 of which the pivot axis is on a YY' axis. An axle 38 is also on that axis, and an outrigger stay 39 fixedly attached to the U-bend 36 pivotally retains it.

A pipe bend 40 leads to a swivel joint 41 of which the pivot axis lies on a XX axis. The axes XX, YY, ZZ are mutually orthogonal and intersect in a single point. A pipe U-bend 42 leads to the second joint 35. Attached to this bend is an outrigger stay 44, retaining an axle 45 lying on the XX axis. The

axles

38, 45 are attached to the bend 40; their action, and that of the stays to which they are pivotally retained, is to prevent strain falling on the

joints

37 or 41 by reason of the universal joint as a whole tending to splay or spread along the ZZ axis.

The swivel joints are of any suitable type, but preferably those which will be described in detail later.

The universal joint just described and it and the joint described with reference to FIGS. 2 and 3 are technically interchangeable in any of the marine loading/unloading stations described in this specification.

Referring to FIGS. 7 and 8 a second embodiment of marine loading/unloading system comprises a submarine pipeline 50 leading to a sea bed slewing anchor 51 and connected to a flexible conduit 52 at the anchor. The conduit 52 rises generally obliquely from the anchor to a variable buoyancy capture device 53 which is shown secured and connected to a tanker 54. The tanker 54 is moored directly to the anchor 51 by means of mooring lines 55. The submarine pipeline 50 may be connected to an undersea wellhead or, in the case of an offshore system, it can be connected to a shore installation.

The connection between the submarine pipeline 50 and the artculated pipeline 52 is effected (F IGS. 9-12) by using a pivoted double-bend 56 made up of two pipe bends and whose centre portion 57 is arranged concentrically with a vertical slewing axis of the anchor 51. The center portion 57 incorporates a swivel joint 58 allowing relative rotation of the two pipe bends making up the double-bend 56. The pipe 59 connecting the double bend 14 to the articulated pipeline 52 is secured to an outer slew ring 61 of the anchor 51 by means of a clamping collar 60. The outer slew ring runs on a fixed double conical P.T.F.E. bearing 62. The inner slew ring 63 is fixed to a support drum 64 of the anchor 51. This support drum is secured to an anchor block 65 fixed in the seabed. The pipe 59 can thus rotate on its swivel 58, relative to the submarine pipeline 50 when any moment is exerted on the pipe 59 about the anchor 51.

The end of the pipe 59 remote from the anchor 4 is connected to the articulated pipeline 52 via a rightangled bend and a swivel 66. The articulated pipeline is made up of a series of rigid pipe lengths 67, each, for example, between 100 and 150 feet long, connected together by means of swivels 68 and universal joints 69 which may be of either of the types described earlier.

Referring to FIGS. 13 to 16 at each swivel 68 and universal joint 69 a buoy 70 is secured to the pipeline 52 to maintain the articulated pipeline submerged but rising to a final height of about 75 feet below the surface of the sea where it is connected to the capture device 53. The pipeline 52 is thus kept at a depth such as to provide navigable areas over it and also reduction in the effect of rough sea conditions on the pipeline 52.

The variable buoyancy capture device 53 is connected to the articulated pipeline 52 by means ofa universal joint 71 incorporating

swivels

72, 73 and 74.

The capture device 53 comprises a vertical riser pipe 75 which can be raised or lowered out of the water. Attached to the vertical riser pipe are upper and

lower buoys

77 and 76, respectively.

The upper buoy 77 is a totally enclosed volume of polyurethane foam, some feet in diameter and 6 to 8 feet deep. A Yokohama fender system 78 is provided around the skirt of the lower buoy 76. The lower buoy 76 consists of a hollow shell construction forming a pressure chamber which can be flooded to allow the buoy to sink. When the system is not being used by a tanker the lower buoy 76 is flooded and the upper buoy 77 carries the total load by floating on the sea surface. The mass distribution of the device 53 is such that the

buoy system

76, 77 has inherent stability in the inoperative condition. The arrangement of the metacentric height and center of gravity of the device 53 when the buoy 76 is filled with water is such that the device has an inherent dynamic stability of equilibrium. Thus the riser pipe 75 tends to a substantially vertical position. Means provided for evacuating the water from the buoy 76 may be controlled from the tanker via one or more pipes and/or cables extending up the pipe 75 and may be in the form of a pumping device or a blowing device for filling the buoy with compressed air. At the top of the capture unit 53 is a wheel fender yoke 79 mounted to a tee-head 80 via a roller bearing swivel 81. The tee-head is itself mounted to the pipe 75 by means of a swivel 82. The whole arrangement can rotate around the seabed anchor 51. Orientation of the various parts of the arrangement will be determined by the direction of deep water and surface currents.

As a part of the system the tanker may be provided with equipment including a boom structure (not shown) mounted over the main longitudinal tanker deck piping 83. A pipe swivel 84 mounted above and horizontally to, the deck piping connects the latter to a pipe 85 located below the boom structure. The whole of this assembly is capable of being moved from the longitudinally stowed position through to project from the ships side.

When the boom structure is in position, a secondary member 86 of the structure is extended, lowered over the side of the tanker and secured to the trimming edge. At the top of this secondary structure a locking device (not shown) is provided onto which the fender yoke 79 at the top of the capture device is located. The front of the secondary member 86 is open to allow entry of the top part of the capture device.

Referring to FIG. 17, the pipe 85 from the tanker is connected to the tee-head 80 via a bolted flange connection 87. Inside the tee-head is located a shut-off valve 88 biased by means of a spring 89 to keep valve face 90 closed against a seat 91. The valve is operated by a ship-side push rod 92 which opens the valve in opposition to the closure spring 89. The valve 88 thus serves to isolate the tee-head until the latter is secured to the tanker piping which is itself provided with an isolating valve 93 movable with the push rod 92. To actuate the valves 88, 93 a hydraulic power unit 94 in series with a screw drive device 95 is provided.

Referring to FIG. 18, the tanker is moored to the seabed anchor 51 by means of two mooring lines 96 which are preferably made of polypropylene. When not in use these two lines 96 are held vertical and taut at the sea surface by marker buoys 97 connected to a common anti-chaffing gear generally indicated at 98 which is connected in turn to a mooring line buoy 99 and one or more submerged sea drogues 100 which hold the lines taut in tidal currents.

The system is so arranged that the mooring lines absorb as strain energy, sea forces acting on the tanker. This strain energy causes extension of the mooring lines, but this extension does not exceed the possible extension of the submerged articulated piping system. Consequently no mooring loads will be applied to this piping system.

When a tanker 54 approaches the loading/unloading station, a mooring messenger line (not shown) attached to the drogue 100, is picked up by conventional retrieval methods. The mooring lines are then secured to the tanker bow and in this position the mooring line buoy will be pulled below the sea surface. The method used to retrieve the capture unit 53 can be conventional, i.e., a launch or with development, a messenger line retrieved and connected to tanker winches, could be used.

The tanker boom is rotated to the ships side and secured. When the capture device 53 is brought to a position adjacent the boom the fender yoke 79 is grappled by the tankers crane and held. The lower buoy 76 is supplied with compressed air or is pumped out so that the complete capture device 53 is raised in the water. Compressed air and/or pumps continues or continue to force water from the lower buoy, until the fender yoke is higher than the tanker boom structure. Pneumatic or hydraulic power may be provided from the tanker via one or more cables and/or pipes extending up the pipe 75 or from a pneumatic or hydraulic accumulator system mounted on the buoy. The ships crane takes up load on the capture device and provides stability during this operation.

Claims

1. In a marine loading/unloading system having a seabed anchor providing connection between a seabed pipeline and a flexible conduit, the latter comprising a plurality of substantially rigid wall pipe lengths arranged between the seabed anchor and a sea surface position wherein at least one pair of adjacent said pipe lengths are connected by universal joint means for allowing swivelling about any one or more of three orthogonal axes intersecting in a single point at the center of said universal joint means.

2. A marine loading-unloading system for ships comprising a seabed pipeline, a seabed anchor, a flexible conduit, a fluid connection between said seabed pipeline and said flexible conduit at said seabed anchor, a plurality of substantially rigid wall pipe lengths joined to form said flexible conduit, at least one pair of adjacent said pipe lengths of said flexible conduit interconnected by universal joint means for permitting mutual rotation of the pair about any one or more of three orthogonal axes intersecting in a single point at the center of said universal joint means, means for mooring a ship to said seabed anchor, and flotation means causing said flexible conduit to rise from the seabed anchor to a surface position.

3. A marine loading/unloading system according to claim 2 wherein the said flexible conduit rises generally vertically from the anchor to a buoy forming said flotation means, mooring lines extending from the buoy to the anchor holding the buoy captive above the anchor, the length of the mooring lines being less than that of the conduit.

4. A marine loAding/unloading system according to claim 2 wherein the seabed anchor is a slewing anchor with a slewing portion, said flexible conduit rises generally obliquely from the slewing portion of the anchor to a permanently buoyant said flotation means a mooring line for a ship rises generally obliquely and is attached to the slewing portion of the anchor, a buoy for the mooring line on the surface of the water.

5. A marine loading/unloading system according to claim 4 wherein the said flotation means is a capture buoy including a riser, an upper buoyancy chamber on the riser, a lower buoyancy chamber on the riser, means for varying the buoyancy of the lower buoyancy chamber whereby the level of the buoy in the water may be adjusted, the upper buoyancy chamber being at all times a buoyancy sufficient to maintain the capture buoy at the surface of the water.

6. A marine loading/unloading system according to claim 5 wherein the flexible conduit includes a portion having a plurality of pipe lengths, adjacent lengths being linked to each other by horizontal-axis pipe swivel joints, buoys maintaining said plurality of pipe lengths generally horizontal at a predetermined distance below the surface of the water, a first said universal joint means being in the conduit between said portion and said capture buoy and a second said universal joint means being between said portion and said seabed anchor.

7. A marine loading/unloading system according to claim 1 wherein pipe swivel bearings in the at least one universal joint have at least one pair of conical bearing surfaces with a solid, stationary low friction bearing material between the surfaces of the pair.

8. A marine loading/unloading system according to claim 6 wherein pipe swivel bearings in the pipe swivel joint means and in the at least one of said universal joint means have at least one pair of conical bearing surfaces with a solid, stationary low friction bearing material between the surface of the pair.

9. A marine loading/unloading system comprising a seabed pipeline, a seabed anchor, a permanently buoyant buoy at the sea surface, a conduit rising from said seabed anchor to said permanently buoyant buoy, mooring means for ships departing from said seabed anchor, said conduit being made up of rigid pipe lengths, said rigid pipe lengths pivotally connected by means for providing that said conduit as a whole sustains no bending mement in any direction between said seabed anchor and said permanently buoyant buoy.

10. A marine loading/unloading system according to claim 9 wherein the permanently buoyant buoy is a loading/unloading buoy, a riser of the buoy projecting upwardly from the sea surface, and means of variable buoyancy on the buoy for adjusting the height of said projection.