GB1564755A

GB1564755A - Marine riser mooring apparatus

Info

Publication number: GB1564755A
Application number: GB1159277A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-03-18
Filing date: 1977-03-18
Publication date: 1980-04-16

Description

(54) MARINE RISER MOORING APPARATUS (71) I, WILLIAM JEREMIAH RYAN, a citizen of the United States of America, of P.O. Box 367, Loreauville, State of Louisiana, United States of America, do hereby declare the invention, for which I pray that a patent may be granted to me and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a combined marine mooring and cargo transfer apparatus, for use for example between a supertanker offshore and a pipeline to shore based facilities.

The invention seeks particularly to provide a relatively stable floating pipeline which rises from the ocean floor to a position well above the hull of the ship, which is held in a relatively vertical position by the buoyant force of the water and has articulating ability to "weathervane". It will be able to conform to all of the movements of the ship while limiting its horizontal movements.

The present invention is also concerned with attaching the top of the floating riser to a mooring pedestal on the bow of the ship by means of a mooring winch which overcomes the buoyant force of the riser.

The attachment allows fluid to flow between the ship and the riser while performing the mooring function.

The invention also seeks to provide the elements of articulation such as flowthrough pins in universal joints, and heavy duty swivel joints which have the structural ability to accommodate the mooring forces as well as conduct fluid flow and to provide a method of cushioning the tension and compression of the mooring loads on the riser. Another problem which the present invention seeks to overcome is the provision of an anchor means which is capable of attachng itself to the bottom as well as removing itself back to a floating condition.

According to the invention there is provided a marine riser moorng apparatus by means of which fluids can be transferred between a submarine source and a marine vessel, comprising: a an elongated buoyant fluid conveying riser means for transmitting fluids between the source and the vessel, said riser means being connected at its lower end portion to the source and connectable in use at its upper end portion to the vessel; b anchor means attached to said lower end portion of said riser means; c articulation means connecting the lower end porton of said riser means to said source and permitting universal articulation of said riser with respect to the source;; d the upper end portion of the riser means having a substantially rigid riser head having connecting means which in use are rotatably and pivotally connectable to a structural pedestal rigidly fixed to said vessel, said pedestal provided with a fluid conveying aper ture therein and enabling universal articulation between the riser means and the pedestal, said riser head being sealably fitted to said riser means, said riser head having a fluid transmitting portion, said fluid transmitting portion of said riser head cooperating with said riser means and said pedestal to pro vide a fluid flow passage extending from said riser means through said riser head into said fluid conveyng aperture of said pedestal.

One of the major problems facing the superport operations today is that of attaching the mooring lines in rough sea conditions. The most popular techniques involve the attachment of mooring lines to a relatively active anchor buoy. This is accom plished by a boat which picks up the mooring lines. A man from the boat boards the buoy and makes the attachment. Or he must attach the mooring lines from the ship to floating mooring lines from the buoy. Seas that have wave heights of five feet or better make this attachment method dangerous or it might not be attempted at all. Delays because of weather limit productivity and are very expensive.

Also, the most popular systems involve floating hoses which connect the flow lines on the ocean bottom to the cargo piping on the ship. These hoses are also handled by boats that position them next to the ship, where they are lifted aboard by cranes on the ship. Obviously, this operation becomes hazardous in rough sea conditions. These hoses then must be hand connected to the ship's piping system.

This operation requires many men, boats and time.

Floating hoses are very expensive and must be changed frequently because of the high stress exerted on them by the action of the waves. Another problem of floating hoses is that they can become pinched between the ship and the buoy, should the ship drift into the buoy. Such pinching activity normally requires the changing of the hoses or may even cause spillage.

The single point mooring (SPM) system is considered by many to be the safest and most economical method of offshore superport operations. It is not new in the art since it has been in operation since 1959.

The SPM system is based on a floating buoy which is anchored to the ocean floor and serves as a mooring buoy. A flow line from shore facilities is located on the sea bottom being connected to a flexible hose in the area of the buoy anchor. It extends to the surface where it attaches to floating hoses which are connected to the ship's cargq lines. This arrangement allows the ship to weathervane around the anchor while the cargo is being transferred.

Several proposals for the offshore tanker cargo transfer are known. However, none of these proposals discloses a relatively solid but flexible riser which is capable of structurally mooring the vessel while performing the function of cargo transfer in one manipulation.

In contrast to prior art actually used in offshore superport operations, - the present invention utilizes a riser design which is basically rigid but is equipped with articulating elements which enable it to move in all directions to conform to the movements of the ship. The riser structure is designed to accommodate the mooring forces produced by the ship as well as form a method of internally conducting cargo between the ship and other facilities.

The basic, over-all object of the present invention is to provide a simplified method of mooring supertankers offshore, which combines the mooring process and the connection of cargo transfer piping into one simple operation and structure.

Another object of the present invention is to provide a relatively stable mooring and cargo transfer buoy that a ship can attach to, and release from, in rough sea condition.

Another object of the present invention is to increase safety by minimizing the necessity of personnel to handle equipment. The man that does handle equipment does so in a more stable environment.

No one is required to be in an area where heavy equipment is being moved.

Another object of the present invention is to minimize the possibility of cargo spillage by reducing the amount of moving parts. The elements that are required for complete articulation are located in areas that are not subjecetd to the danger of the ship running into them. These parts are also designed for severe use and long life. Flexible hoses, if used at all, are subjected to minimal movements. They are not located where they are subjected to severe wave action or where the ship can hit them.

Another object of the invention is to reduce maintenance by simple, heavy duty design. Should the ship run across the buoy, it will push it over and pass by.

Very expensive, short life, floating hoses are eliminated.

Another object of the present invention is to minimize the time required to moor the ship and to attach the cargo transfer lines. This simple technique of attaching the riser to the ship can be accomplished in a matter of minutes even in rough seas.

Whereas, the conventional method may take several hours or may even require waiting for the sea to subside, in order to moor at all.

The present invention can release the vessel from its cargo piping and mooring in a matter of seconds, where the conventional method may take hours.

Another object of the present invention is to minimize the necessary facilities and manpower requirements. Only one winch and operatior is required to moor the ship and connect the cargo transfer piping; whereas, the conventional methods require boats and crews to handle the mooring lines and floating hoses, and also a service derrick is required on the ship to lift the hoses aboard, and men are also required to be on deck to handle the hoses and make the connections.

Another object of the present invention is to reduce operational cost by reducing maintenance, manpower requirements, eliminating floating hoses, and minimal tug requirements.

A summary of the advantages of the present invention is as follows: 1. Simple construction.

2. Minimum maintenance.

3. High stability.

4. Minimium space required while not in operation.

5. High ecology value (spillage mini mized).

6. Low fouling characteristics.

7. Ease of attachment.

8. Mooring can be safely and easily accomplished in rough sea conditions.

9. No expensive floating hoses are required.

10. No boats are required to handle hoses.

11. Only one man is needed to handle the mooring rigging.

12. Operational safety is increased.

13. The time required to moor the ship and begin cargo transfer is a matter of minutes.

14. Ship standby time is minimized.

15. Disconnection of the cargo lines and release from the mooring buoy is accomplished by one man in seconds.

16. The cost of the present invention should be less than other systems now in use.

Some embodiments of the present invention, will be described by wav of example and with reference to the accompanying drawings, in which like elements are given like reference numerals and in which: Figure 1 is a side view of the preferred embodiment of the riser mooring apparatus of the present invention, showing it in its floating, non-use disposition; Figure 2 is a similar, side view of the preferred embodiment of Figure 1, while in its mooring disposition, Figures 3 and 4 are side views of two additional embodiments of the riser mooring apparatus of the present invention, showing them while in their mooring disposition, Figure 5 is a top, perspective view of the attachment structure used between the head of the riser and the bow of the ship to be moored, showing their disposition immediately prior to attachment.

Figures 6 and 7 are plan and side, partial views, respectively, showing the fluid flow into the connection in the head of the riser mooring system of the present invention; while Figure 8 is a cross-sectional, side view of the piping into the connection, taken along section lines 8-8 of Figure 6.

Figure 9 is a side, cross-sectional view of the mooring pedestal on the ship's bow with the riser head connected thereto, show ing the oil flow into connection therebetween.

Figure 1 is a generalized profile view of the preferred embodiment of the riser of the present invention in a free-floating state. "Hang line" 20 is a Nylon line fixed in the center of the riser head 10. It is used to attach the riser head 10 to a pedestal on the bow of a ship, as will be explained more fully below.

The riser stem 11 is stiffened by means of a truss 19.

The bottom of the flow line 13 is attached to a flexible hose 18 by means of a swivel connection 17. Additional swivels 17 are added to the hose 18 to prevent torque.

Anchor lines 16 are attached to swivel arms 15 which prevent fouling.

The general configuration of the riser stem lends to considerable stability in rough sea conditions. This is the result of the relatively long length of the flotation caisson 12 which has a minimum diameter.

A ballast bulkhead 14 is provided which will allow flooding in order to lower the centre of gravity and increase stability.

The long flotation caisson 12 will position the anchor lines below the bottom of the ship to prevent fouling.

Figure 2 is also a general profile, similar to Figure 1, but showing the riser attached to the pedestal on the bow of the ship 23.

This connection moors the ship and allows the cargo to flow between the ship 23 and the riser 10.

This arangement allows the ship to "weathervane" about its anchorage 16 and will work very well in deep water where the ship cannot damage the flexible hose 18 by pushing it into the ocean floor 31.

Figure 3 is a profile of a second embodiment of the riser attached to the ship 23, showing the action of the riser as the ship drifts into it. The inboard anchor lines 16 are in tension while the motion of the ship 23 will force the riser downward. A swivel bottom shoe 30 is provided in this embodiment to protect the flexible hose 18 from damage from the ocean floor 31.

In the embodiment of Figure 3, an upper truss (element 19 of Figures 1 & 2) is not used and the riser stem 11 is constructed of a tubular member which has a built-in curve. Material used in the riser stem 11 has spring qualities which allow bending from tension or compression but will return to its original shape. This will cushion the mooring loads.

Figure 4 is a profile of a third embodi ment of the riser system showing the ship 23 attached to the riser stem. In this embodiment, the riser is fixed to the ocean floor 31 by means of a bottom mat 32 which is equipped with shear fins 33 that penetrate the ocean floor 31 to resist movement. Anchors (not shown) or other means may also be added to resist the movement of the bottom mat.

The riser is connected to the bottom mat 32 by means of a heavy duty swivel 34 and flow-though hinge pin 35. This arrangement will allow complete articulation of the riser and eliminate the flexible hose with its high maintenance cost. Fluid is transferred through this connection.

The sump bulkead 37 is welded tight to the flow line 13 and the inside of the flotation caisson 12 forming a chamber for fluid to flow through the yoke jaws 38 and through the flow-through hinge pins 35 into the swivel connector 39.

The embodiment of Figure 4 also includes a shock absorber 36 attached to the riser stem 11 in order to assist in the cushioning of the mooring loads. If the riser stem 11 is equipped with a flowthrough hinge, then there will be no bending in the riser stem and the shock absorber 36 must assume all of the mooring forces as well as the cushioning activity.

Figure 5 is a top perspective view of the bow of the ship equipped with a combined mooring and cargo transfer pedestal 40. The riser head 10 is shown being pulled down by the mooring winch 21 where it will be positioned around the pedestal 40. Latching members 26 will engage themselves under a vertical retainer ring 41 provided on the pedestal to maintain the coupling in operative alignment (see also Figure 9).

Cylinders 28, or other suitable means are provided to push the latching members outboard to release the connection. This action will allow the bouyant force of the riser to lift the riser head 10 off of the pedestal 40. The hang line 20, which has been disconnected from the winch line 25, will follow through the pedestal hawse pipe 79 making the ship 23 completely free of the riser head.

The pedestal 40 is securely fastened into the bow of the ship in a structurally desirable manner to withstand the mooring forces. A cargo transfer line 42 is welded into the pedestal 40 to permit fluid flow through this connection. As a result, all supplemental or separate anchor lines or mooring chains are eliminated, and the mooring and fluid transfer functions are combined into a unitary, simplified structure.

Figure 6 is a plan view of the riser head assembly 10. Flow arrows indicate the path of the fluid between the pedestal 40 and the riser stem 11 by means of the hollow pins 50, and hollow yoke jaws 51. A swivel collar 52 is provided around the riser stem 11 to allow rotational movement in order to compensate for the movements of the ship about the axis of the stem 11.

The latching members 26 are also shown in an inboard position. Cylinders 28 are spring loaded to maintain the latching members 26 in the inboard position in order to engage under the retainer ring 41 to prevent the riser head 10 from lifting off of the ship's pedestal 40.

Pressure applied to the cylinders 28 will push the latching members 26 against the spring pressure outboard of the retainer ring 41 during the releasing procedure.

Oil seal 53 is provided to prevent leakage between the riser stem 11 and the swivel collar 52.

Figure 7 is a side view of the riser head assembly 10. The pedestal housing 54 can rotate around the axis of the flow-through hollow pins 50 to compensate for vertical and horizontal movements when it is attached to the ship's pedestal 40.

Figure 8 is a vertical, cross-sectional view at the centerline along section lines 8-8 of Figure 6, illustrating the structural arrangement between the riser stem 11 and the swivel collar 52. The rings 55 and 56 are welded to the riser stem 11 on both ends of the swivel collar 52 to prevent longitudinal movement. Since these rings are independent of the swivel collar 52, the riser head assembly 10 is free to rotate about the axis of the riser stem 11.

The stop ring 56 and the swivel collar 52 have machined surfaces of identical diameters in the region of the seal 58 between the seal stops 57 (Figures 7 and 8). These stops 57 will maintain the position of the adjustable seal tightener 59 and the seal 58.

The top and bottom plates 60 and the side plates 61 are welded to the swivel collar 52 in an oil-tight manner.

Figure 9 is a side, cross-sectional view at the centerline of the connection between the riser head assembly 10 and the ship's pedestal 40, with the pedestal structure being illustrated in phantom line and the arrows indicating fluid flow.

An expandable side seal 62 is provided to allow maximum clearance between the structures while assuring an oil-tight seal.

Another expandable seal 63 is provided to prevent leakage between the top of the pedestal 78 and the hinge stiffener plate 69.

A pressure line 64 is located in an appropriate position to expand the seals and provide an oil-tight condition.

The flow-through pins 50 are welded to the pedestal cap housing 54 in an oil-tight manner.

The inboard jaw plate 70 (Figures 6 and 9) is designed to accommodate all of the forces in the system. Doubler rings 65 in conjunction with jaw plate 70 are designed to supply adequate bearing surfaces for the flow-through pins 50.

SeaT66 is supplied to make an oil-tight connection between the flow-through pins 50 and the riser head assembly 10. A threaded pressure ring 67 will keep the seal 66 oil tight. It is not intended that the seal arrangement be limited to this configuration as it may be adequately handled in many other ways.

The top plate 68 is welded in a fluidtight manner to the flow-through pins 50 and the pedestal housing 54.

A hang line sleeve 80 is also welded in a fluid-tight manner in the center of top plate 68 and the hinge stiffener plate 69.

Ring 82 is designed to transmit the mooring forces between the top of the ship's pedestal 40 and the riser head assembly 10. It is welded oil-tight to the hinge stiffener plate 69 which maintains structural continuity to the flow-through pins 50.

The hinge stiffener plate 69 also forms an oil-tight barrier between the top plate 78 of the pedestal 40 and the riser head assembly 10 by means of the expandable seal 63.

Horizontal rings 71, 72, 73 and 74 associated with vertical stiffeners (not shown) are designed to transmit the mooring forces between the sides of the ship's pedestal 40 and the riser head assembly 10. Rings 72 are welded tight to the cylindrical housing 54 and form a pressure chamber for the expandable seal 62. Rings 74 form a housing for the latching members 26. They are designed to clear the vertical retainer ring 41 which is welded to the ship's pedestal 40.

Latching members 26 are designed with a beveled underside in order that they will be forced outboard as they are pulled down over. the retainer rings 41. Springs (not illustrated) will return these latching members 26 under the rings 41 (as shown). This will prevent the riser head assembly 10 from inadventently lifting off of the ship's pedestal 40.

Sloping rings 75 and 76 are provided to add strength as well as to assist in the centering operation when the hang line 20 is pulling the riser head 10 down over the ship's pedestal 40.

Since there is considerable shear and chafing action on the top area of the hang line 20, as the riser head assembly 10 is being pulled down around the ship's pedestal 40, a short section of chain, wire rope, or other flexible, mechanical resistant material may be used more effectively.

However, it is important that most of the length of the hang line 20 be of a stretch able material such as Nylon line.

The ship's pedestal 40 (shown in phantom line) is a tubular member of suitable strength to support the mooring forces.

It is also connected to the ship's cargo transfer piping in order that the fluid may be pumped through it.

An "L"-shaped hawse pipe 79 is welded oil-tight into the ship's pedestal 40 as shown. The ends of the hawser pipe 79 are bell shaped to reduce chafing of the winch line 25 and the hang line 20.

For a further understanding of the method and structure of mooring and re leasing the riser head 10 to the ship pedestal 40, reference may be made to United Kingdom Patent No. 1525501, in which the boat attacher and docking pedestal are generally analogous.

Complete articulation of the riser is accomplished in the following manner: The anchor lines are attached to swivel arms which allow complete rotation of the riser. The swivel connections on the flexible hose also allow complete rotation without creating torque in the hose.

If a shoe is used to protect the flexible hose from the bottom, its ability to swivel will allow complete rotation.

When the riser is connected to the ocean floor by the bottom mat as shown in Figure 4, rotation is accommodated by the swivel connection, while the angular movement is a function of the flow-through hinge pins.

The attaching head on the top of the riser also allows complete articulation of its attachment to the ship.

Vertical and horizontal movements are allowed by the flow-through pins in the attaching head. Transverse or rolling movements are accommodated by the ability of the attaching head assembly to rotate about the riser stem by means of the swivel collar.

Radial movements are allowed by the ability of the attaching head to rotate about the ship's mooring pedestal.

The buoy includes a relatively long flotation caisson structure having a relatively small diameter, such proportion insuring greater stability in rough sea conditions. Ballast is added to the bottom section of the flotation caisson, keeping buoyancy to a minimum. A flow line is located down the center of the buoyant caisson and extends above the bow of the ship it will service. The extension above the floatation caisson has a curve shape for operational purposes. A fitting is located on the top end of the flow line which is capable of securely attaching to a mooring pedestal located on the bow of the ship.

This arrangement allows fluid flow between the riser structure and the ship as well as forming a substantial mooring linkage between the ship and the anchor lines which are attached to the bottom of the buoy. A flexible hose connects the flow line of the buoy to the service flow line.

Although the device is primarily a rigid structure, it is equipped with elements which allow complete flexibility.

The apparatus also includes the use of a mooring winch on the ship. The line from the winch is conducted through a hawse pipe in the center of the mooring pedestal and is attached to a hang line, which extends down from the center of the attaching head of the riser structure.

The winch will pull the attaching head down around the mooring pedestal where it is automatically latched. A universal seal makes this connection oil tight. This simple operation moors the ship as well as connects the fluid lines. Cargo transfer can commence immediately. A quick release system allows the buoyant force of the riser structure to lift the attaching head off of the mooring pedestal. The hang line will follow through the mooring pedestal and the ship is completely free.

WHAT I CLAIM IS: 1. A marine riser mooring - apparatus by means of which fluids can be transferred between a submarine source and a marine vessel, comprising: a. an elongated buoyant fluid conveying riser means for transmitting fluids between the source and the vessel, said riser means being connected at its lower end portion to the source and connectable in use at its upper end portion to the vessel; b. anchor means attached to said lower end portion of said riser means; c. articulation means connecting the lower end portion of said riser means to said source and permitting univer sal articulation of said riser with respect to the source;; d. the upper end portion of the riser means having a substantially rigid riser head having connecting means which in use are rotatably and pivot ally connectable to a structural pede stal rigidly fixed to said vessel, said pedestal provided with a fluid convey ing aperture therein and enabling universal articulation between the riser means and the pedestal, said riser head being sealably fitted to said riser means, said riser head having a fluid transmitting portion, said fluid transmitting portion of said riser head cooperating with said riser means and said pedesetal to provide a fluid flow passage extending from said riser means through said riser head into said fluid conveying aperture of said pedestal.

2. Apparatus according to claim 1 wherein said riser head further comprises a fluid transmitting, bifurcated yoke, said yoke being sealably fitted to said riser means and a fluid transmitting pedestal cap, said cap being pivotally and sealably connected to said yoke at the bifurcations of said yoke, the fluid flow passage extending through the bifurcations in said yoke through said pedestal cap, said cap being sealably connectable in use to said pedestal to allow fluid to flow between said pedestal cap and the aperture of said pedestal.

3. Apparatus according to claim 1 or claim 2 wherein said head connection means allow the vessel to pivot about said riser means about both a pivot axis substantially perpendicular to and a hinge axis substantially parallel to the water surface.

4. Apparatus according to claim 3 wherein said apparatus also provides a mooring for the vessel and wherein said head connection means is fixed with respect to the vessel when in use, said two axes being fixedly located with respect to the vessel and said riser means having a constant length.

5. Apparatus according to any one of the preceding claims wherein the forces created by the relative movement of the vessel and the submarine source are transmitted between them only through said connection means.

6. Apparatus according to any one of the preceding claims, wherein a winch means is associated with said pedestal by means which said riser head and said pedestal can be operatively connected.

7. Apparatus according to claim 6 wherein a hang line is provided on said riser head and the pedestal is provided with a hawse pipe means for guiding said hang line through said pedestal; and the winch means is attachable to said hang line for pulling said hang line through said hawse pipe means to bring said riser head into operative connection with said pedestal.

8. Apparatus according to any one of the preceding claims and comprising latch means for securing said riser head to said pedestal.

9. Apparatus according to claim 8, wherein the latch means comprises reciprocating catch means on said riser head which clamp said riser head to a circular flange provided on the pedestal when said riser head operatively couples with said pedestal, said catch means being provided

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. capable of securely attaching to a mooring pedestal located on the bow of the ship. This arrangement allows fluid flow between the riser structure and the ship as well as forming a substantial mooring linkage between the ship and the anchor lines which are attached to the bottom of the buoy. A flexible hose connects the flow line of the buoy to the service flow line. Although the device is primarily a rigid structure, it is equipped with elements which allow complete flexibility. The apparatus also includes the use of a mooring winch on the ship. The line from the winch is conducted through a hawse pipe in the center of the mooring pedestal and is attached to a hang line, which extends down from the center of the attaching head of the riser structure. The winch will pull the attaching head down around the mooring pedestal where it is automatically latched. A universal seal makes this connection oil tight. This simple operation moors the ship as well as connects the fluid lines. Cargo transfer can commence immediately. A quick release system allows the buoyant force of the riser structure to lift the attaching head off of the mooring pedestal. The hang line will follow through the mooring pedestal and the ship is completely free. WHAT I CLAIM IS:

1. A marine riser mooring - apparatus by means of which fluids can be transferred between a submarine source and a marine vessel, comprising: a. an elongated buoyant fluid conveying riser means for transmitting fluids between the source and the vessel, said riser means being connected at its lower end portion to the source and connectable in use at its upper end portion to the vessel; b. anchor means attached to said lower end portion of said riser means; c. articulation means connecting the lower end portion of said riser means to said source and permitting univer sal articulation of said riser with respect to the source;; d. the upper end portion of the riser means having a substantially rigid riser head having connecting means which in use are rotatably and pivot ally connectable to a structural pede stal rigidly fixed to said vessel, said pedestal provided with a fluid convey ing aperture therein and enabling universal articulation between the riser means and the pedestal, said riser head being sealably fitted to said riser means, said riser head having a fluid transmitting portion, said fluid transmitting portion of said riser head cooperating with said riser means and said pedesetal to provide a fluid flow passage extending from said riser means through said riser head into said fluid conveying aperture of said pedestal.

with resilient means which allows said catch means to expand when said riser head is being fitted over said flange and to contract when said riser head is completely coupled with said pedestal and said catch means engages the underside of said flange.

10. Apparatus according to any one of the preceding claims wherein said riser head is provided with seal means for preventing leakage of fluid from said system when fluid is flowing through said riser means, said riser head and said pedestal.

11. Apparatus according to claim 10, wherein said seal means is a pressure activated seal.

12. Apparatus according to any one of the preceding claims, wherein said riser means is provided with truss means for stiffening said riser means.

13. Apparatus acording to any one of claims 1 to 11, wherein said riser means is provided with a shock absorber means for stiffening said riser means, said shock absorber means being attached to the upper and central portions of said riser means at respective end portions of said shock absorber means.

14. A marine riser mooring system substantially as hereinbefore described with reference to the accompanying drawings.

15. A method of mooring a marine vessel to a marine riser mooring apparatus according to any one of the preceding claims and substantially as hereinbefore described with reference to the accompanying drawings.