NO153092B - SINGLE POINT DEFENSION AND FLUID MANAGEMENT SYSTEM - Google Patents

Description

The present invention relates to a single point mooring

and fluid handling system for the transfer of a fluid from an underwater pipeline to a line connected to or connectable to a floating vessel moored at the system, which system comprises a plinth placed in use on the seabed,

a riser connected to the base by means of a universal joint, which riser is fully submerged in use, a fluid swivel placed on top of the riser, a hose guide tongue, and a spacer buoy mounted on top of the fluid swivel via a universal joint.

The purpose of the present invention is to provide a system of the above-mentioned type which entails improvements and/or simplifications compared to previously known systems.

This is achieved according to the invention in that the riser has positive buoyancy, that the hose guide tongue is attached to the fluid swivel so that it acts as a weight arm to facilitate rotation of the fluid swivel, and that a chain beam is mounted on top of the spacer buoy in a way that allows the chain beam to move in two orthogonal planes.

The use of a riser with positive buoyancy provides better hydrodynamic properties than was possible in previously known constructions that use riser columns that do not have positive buoyancy, but which are provided with one or more buoyancy chambers that provide all the buoyancy required by the system as a whole . In particular, the construction according to the invention provides greater stability and thus better behavior in difficult sea conditions.

The use of a construction that has positive buoyancy so to speak

its entire length also means that there will be a better stress distribution when the construction is exposed to particularly difficult sea conditions.

The use of a hose guide tongue attached to the fluid swivel so as to act as a weight arm to facilitate rotation of the fluid swivel provides the obvious advantage that the design as a whole permits relative rotation between the hose through which the oil is transferred and the stem of the riser column. Furthermore, the hose guide tongue enables the fluid swivel to rotate independently of the spacer buoy mounted on top of the riser. Compared to what is known from NO-PS 143 616, these characteristic features dictate that the connection between the riser and a vessel to which oil is transferred,

is much more resilient. The consequence of this is that the problems associated with maintaining a safe mooring in deep water and under difficult weather conditions are reduced. The same advantages arise from the use of a chain beam mounted on top of the spacer buoy in such a way that the chain beam can move in two orthogonal planes. The overall construction is also relatively simple, compared e.g. with the complicated arrangements exemplified by US-PS 3,641,602. The use of a relatively

a

simple construction of great stability also gives the advantage that the riser-pipe structure can be placed as a whole and furthermore that it can be released from the manifold on the seabed. Furthermore, the construction makes it possible to use a system consisting of an oil storage vessel and ferry tanker.

Further advantageous features of the invention will be apparent from the independent claims.

The floating storage vessel will mainly be moored to a place on the seabed at or near the wells using means that allow the vessel to take up a position in accordance with the prevailing weather conditions. The mooring can consist of several anchor chains or other systems that provide a connection with the bottom. It is preferred to use a submerged anchoring arrangement, preferably in the form of a buoyancy chamber connected to a gravity plinth and/or piled plinth in shallow water, or a buoyancy chamber connected to one or more buoyancy-provided riser columns which in turn are connected to a gravity plinth for large water depth. For both the shallow and deep water systems, "mooring chains" are attached to the top buoyancy chamber called a "distance buoy" and are fed into the ship at a point at its keel. The "mooring chain" may be a mooring line consisting entirely of chain, or it may be a combination of chain and wire. The importance of the chain lies in its weight and tension-changing ability due to changes in the length and shape of its chain line. A method for mooring a vessel at sea using such a device is also provided. Dynamic positioning can be used if necessary by the storage vessel to ease disproportionate loads in the mooring and to keep the vessel in the most appropriate position when wind, waves and current create difficult sea conditions. Three references are preferably available to hold the storage vessel, e.g. a ship, in position relative to the mooring.

For applications in shallow and deep water, the vessel's yaw movements are taken into account in the hose couplings in the storage vessel (e.g. a ship) to avoid twisting of the hose (not

This can be done in the case of a single riser or a single underwater hose using a rotatable seal or as described below. When several hoses are used, a rotating plate built into the ship above the waterline can be used. The risers or submerged hoses are connected with

suitable connection ports on the underside of the rotating plate. Flexible, helically coiled tubing is attached to the connection ports on the top of the rotating plate. These flexible hoses form an orderly helical arc. There will be enough flexibility in the curvature and bending of the hoses to allow the ship to turn out of position relative to the rotating plate 90° both to starboard and port without the need to use rotatable seals for the hoses. When mooring in shallow water, oil will pass into the base and to the fluid swivel mounted immediately above it, from where it will continue in one or more hoses to the storage vessel. When mooring in deep water (mostly over 55 m), oil will pass from a collector pipe on the seabed through a flexible pipe to the riser above the shelf. The oil will then be fed through the riser or a pipe that is attached to the riser and runs along its entire length. At the top of the riser, the oil will continue through the fluid swivel and out to one or more flexible hoses leading to the storage vessel.

In the preferred system for shallow water there is one joint connection, while in the system for deep water there are preferably two or more joint connections. The fluid swivel is arranged above the plinth in the shallow water system and at the top of the riser in the deep water system. In both cases, the fluid swivel is preferably placed at a depth that is not greater than that divers can reach it without using anything other than air as breathing gas. Before connection to the storage vessel, the mooring chain can hang vertically from the top of the chain beam on the distance buoy, its end being attached to a hanging line and a marker buoy on the surface. The underwater hose(s) attached to the fluid swivel is advantageously hung from a chain line and held with its end at approx. 20 m deep below the SWL using a line and a marker buoy.

Both the shallow and deep water systems can be provided with an additional section so that they will break the surface. In this case, the further section is preferably flanged to the spacer buoy, and the mooring shackle is attached to the top of the further section. With such a surface-breaking section, it is advantageous to use a mooring cable instead of a chain beam and a chain. The reason for incorporating this duality is so that an oil operator can only use transport vessels in the initial and final production phases of the field's development and can use a storage vessel when the size of the oil production makes this necessary.

In shallow water, the preferred arrangement for mooring the floating storage vessel makes use of a chain tube built into the vessel which directs the chain to a winch mounted on the rear deck. The chain tube advantageously has a bell-shaped mouth to distribute the mooring load and can be located between the bow and the vessel's center of rotation. The vessel will thus be able to rotate or adjust according to the weather around the mooring chain pipe when the weather conditions change.

In deep water, a preferred arrangement for mooring the floating storage vessel utilizes a spindle cylinder built into the vessel, which cylinder contains the mooring equipment, underwater hose handling equipment, and diving equipment. The spindle cylinder in the ship is placed in a suitable place, mainly somewhere between the bow and 1/3 aft, preferably just forward of the center of rotation. The vessel will thus be able to rotate or align itself according to the weather around the chain tube in the spindle cylinder when the weather conditions change.

The collecting pipe on the seabed is attached to the oil line at the riser above the bottom link connecting the riser and the plinth. The hose guide for the hose leading from the fluid swivel is balanced and/or supported. Before connecting to the tanker, the mooring chain hangs vertically from the chain boom at the top of the distance buoy, and its end is attached to a line and marker buoy. The underwater hose attached to the swivel hangs in a chain line with its end approx. 20 m water depth using a line and a marking buoy. The spacer buoy in both the shallow and deep water systems is specially dimensioned and shaped for optimal resistance and restoring forces and is usually submerged. A section can be added to this so that it will break the surface. In this case, the added section is preferably flanged with the spacer buoy, and the mooring shackle can be attached to the top of the additional section. When using the surface-breaking section, a mooring line can preferably be used instead of a chain. The reason for incorporating this duality is to give an oil operator the opportunity to use only tankers in the initial and final production phases of field development and to use a storage vessel when the size of the oil production dictates such a vessel.

The floating storage vessel can moor with its own help to the submerged mooring as soon as it has been determined that the underwater hose has not wrapped itself around the vertically hanging mooring chain due to current action.

In the shallow water system, the storage vessel will approach the mooring between the marking buoy for the hose and the marking buoy for the mooring chain. The mooring chain buoy and its line will then be hoisted aboard one side of the ship and the hold. The mooring chain is attached to a continuous wireline that passes around the hull in a cleat and into and through the mooring chain tube. When the chain reaches the top of the tension chain it will be passed over a play and the excess chain will be stored in a chain box. The buoy and the line marking the underwater hose will then be hauled aboard the other side of the storage vessel just ahead of the hose-disc system which is preferably mounted on the ship's bulkhead. A precursor extending the length of the disc system from an on-board oil sump and through the hose control is attached to the hose which is currently attached to a puller on the redoubt. The hose is lowered and led through the hose guide, over the disc and along the track to the collecting pipe where its end is connected with a coupling. Depending on how many fluids are carried from/to the mooring's fluid swivel, a multiple hose system using hose sheave systems on both sides of the ship can be used. In the deep water system, the storage vessel will approach the mooring between the mark buoy for the hose and the mark buoy for the mooring chain. The mooring chain buoy and its line are hauled aboard to one side and stowed. The mooring chain is attached to a continuous wireline which is routed around the hull in a knot and into and through the mooring tube.

When the chain reaches the top of the mooring pipe, it is secured while the end is passed over a play. Surplus chain is stored in a chain box. The buoy and connecting line marking the underwater hose are then hoisted aboard on the other side of the ship. The hose or hose bundle is attached to a continuous wireline which is routed around the hull in a knot and into and through the hose pipe. When the connecting end(s) of the hose(s) have reached the connection point, the connection is made.

In both the shallow-water and deep-water systems, the length of the mooring chain in the water would depend on the weather conditions and the vessel's draft. In the shallow water system, the length of hose in the water is adjustable, while in the deep water system the length of hose in the water remains fixed.

The means for transferring oil from the storage vessel to a transport tanker preferably comprise 1) manual or automatically controlled tension release mooring winch with line, a mechanical clamping device and 2) one or two oil hoses. The mooring line is preferably provided with "color marking" so that the length of line that has been issued at any time can be seen by the visible color. The line is attached to the cargo tanker by means of a winch and/or stopper. 01jeovering hoses run over appropriately raised A-frames and hang in chain lines between the top of the A-frames and the bow of the cargo tanker. Other arrangements can be used if desired. The oil lines from the A frames can have a fixed length in system "a" or varying length in system "b".. Other arrangements can be used such as a simple boom mounted on a rotating table.

In system "a", the oil line transports crude oil from the pump room to the base of the A-frame(s) where there is a flexible link, e.g. a kiksan joint. The oil pipe continues up the A-frame where there is another flexible link, e.g. a kiksan joint, approximately midway on the A-frame. The flexible oil hose follows the curved surface above the top of the A-frame and forms a catenary between this and the bow (and intake coupling) of the transport tanker. The shape of the oil hose chain line and adjustment for "chain line in water" or "chain line in air" can be adjusted by lowering or raising the top of the A-frame to a suitable level.

The A frame in system "a" and system "b" is identical in all respects. It is a construction with each leg hinged approximately halfway along its length so that one part of the A-frame can be folded back on top of the other part using hydraulic cylinders mounted at each leg to gently lower one part onto the other. In the extended position, the A-frame can be raised or lowered, either hydraulically or by a hoist system that includes a rigid leg. At the top of the A-frame there is a curved device with a suitable radius for bending the hose and an extension to allow lateral movement of the hose.

In system "b", the oil line transports the crude oil from the pump room to a collection pipe on deck just in front of the superstructure. Flexible pipelines (oil hoses) are preferably fed from the collecting pipe in static troughs to washers (cross heads) which are designed so that they can move in fixed tracks forward and aft in a given length of the floating storage vessel, under the influence of self-tightening devices, e.g. e.g. self-tightening winches. The two or more flexible pipelines and associated equipment can be arranged on the floating storage vessel so as to increase the oil delivery quantity from it or to use a hose to transfer oil to the transport tanker and to transfer polluted ballast water from the transport tanker to the floating storage vessel where the ballast water is treated.

The storage vessel can be provided with a stand pipe arrangement connected to the collector pipe from the flexible hose as an alternative to the disc mounted on guides which are preferably fixed or fixable with a constant tension device and which in use connects the collector pipe with flexible hose to the transport tanker.

Where a disk is used, this is preferably constructed bg positioned so that the oil hose can be guided around the disk and fed out from the storage vessel, preferably under constant tension, during which the disk and its guide device move in or on a track.

Preferably, the guide device for the disc is in the form of a slide. The disc is advantageously provided with a hose control device to control the movement of the hose around the disc.

For a better understanding of the invention and to show how it can be implemented, reference should be made to the design examples shown in the drawing.

Fig. 1 and 2 respectively show a schematic elevation of a floating oil storage vessel according to the invention and a perspective sketch of a section of the vessel;

fig. 3 shows a deep water mooring system and parts of an oil transfer arrangement;

fig. 4 illustrates a surface breaking modification of the mooring shown in fig. 3;

fig. 5 illustrates a shallow water underwater hose handling system from the mooring to the storage vessel;

fig. 6 illustrates a surface breaking modification of the system shown in fig. 5;

fig. 7 illustrates in greater detail parts of the mooring system in fig. 3; and

fig. 8 shows on an enlarged scale a section of the system illustrated in fig. 5 and 6.

In fig. 1 and 2 an oil unloading vessel is shown which is preferably between 210,000 and 255,000 tonnes and which is provided with a collecting pipe 1 which forms the outlet for oil from the vessel's tanks via the pump room. In system "a", an oil line H is attached to the manifold 1 and passed through or around a number of structures before being attached to the flexible oil hose which is passed over the top of the A-frame.

In system "b", an oil line H is attached to the header 1 and a flexible hose runs in a "static" trough to a guided disc (crosshead) and then into an "active" trough to and over the A-frame aligned aft. The collecting pipe is arranged at such a height that the extension pipe in system "a" or the hose in system "b" does not need an unnecessary bend.

In system "b", the trough 3 is deep enough to accommodate any hose diameter used. The hose H is led out of the trough 3 and around a disc 5 which is mounted on a guide carriage 7. A hose guide tongue 5 is arranged to guide the hose out of the static trough 3 and onto the disc 5, or vice versa. The hose guide tongue can take the form of a concave shell with spindle bearings on which the hose can slide, which bearings are secured to a foot that slides in the bottom of the static trough 3. A similar hose guide tongue 4' is arranged on the other side of the disc 5

and serves to lead the oil hose into a second hose trough designated as active trough 12.

The hose pulley can be mounted on the guide carriage by means of a ball bearing arrangement 8. The diameter of the hose pulley 5 is mainly determined by the smallest bending radius which can be tolerated by the oil hose-^ The tangential edge of the circumference of the pulley is placed as close as possible to the hose troughs 3 and 12 to minimize deformation and wear of the snake. When the disc is not in use, it can be mechanically attached to the vessel.

The guide sled 7 comprises a frame mounted on wheels which are steered

of two rails overlapping the tops of the wheels. Hose guide tongues 4 and 4' are attached to the guide slide 7. Furthermore, brake shoes 6 are attached to the guide slide and serve, firstly, to prevent the hose from jumping out of the disc 5, and secondly, to act as an emergency braking system in the event of malfunction, e.g. loss of tension in the constant tension anchorage to be described below, or breakage of the oil hose.

A self-tightening winch 10 is arranged on the vessel and is connected via a wire 10' to the guide sled 7 when the oil delivery apparatus is in use. The winch 10 ensures that the sheave 5 is held with a largely constant tension when oil is delivered through the hose H and further provides driving force for movement of the sheave 5 along the rail passage 50 when the oil delivery via the hose H has ended and the hose is hauled back from the transport tanker. An auxiliary winch can be arranged to assist with movement of the disk 5 in the opposite direction, if necessary.

A shaft 9 passes through the disk 5 and the guide slide 7 and serves to reduce the stress on the ball bearing 8 when pressure is exerted against the disk 5.

The brake shoes 6 can be operated by any suitable mechanism. In one embodiment, a hydraulic line 11' which is fed from a further winch 11 is used to add the brake shoes 6. The hydraulic line is not self-tightening, and the winch 11 is operated so that it cannot pull tight. Thereby, the risk of breaking the hydraulic line is prevented, which would otherwise be possible if it were exposed to tension that exceeds its strength.

The active hose trough 12 comprises concave spindle bearings at the bottom of the trough and cylindrical roller bearings along the side walls of the trough. These are arranged to reduce the friction between the hose and the trough 12, but are not necessary in the static hose trough 3 because there is no relative movement between the hose H

and the 3 surfaces of the trough. The trough 12 extends along the vessel from the location of the disc 5 and its track to the part of the vessel from which the flexible oil hose is fed out. The end of the trough 12 remote from the disk 5 is provided with either an extended hose outlet 17 at deck level (see fig. 1) or with an A-frame on which the hose passes over the apex (see fig. 3). Such an A-frame follows the routing of the hose and allows a displacement of more than 34° to port and starboard of the floating storage vessel in relation to a transport tanker to which oil is transferred. The A-frame is designed so that half of it can be folded back on

its lower part by means of a hinge that can be locked or unlocked, by means of a hoist system with a rigid leg and the use of

two hydraulic cylinders that allow the top section to be gently lowered onto the base section. In the folded position, the equipment can be considered stowed, and maintenance can be carried out on the top section. The top of the A-frame has a radius of curvature that is adapted to the bending radius of the hose, and this part is extended

so that the hose can move laterally within certain limits from the center without obstruction or wedging of the hose. This allows gearing of the transport tanker. The length of the extended and locked A-frame depends on the one available

space at the stern of the ship and how much overhang the folded A-frame can be allowed to have beyond the stern of the ship. A horizontal puller 13 (see fig. 1) above the hose and the trough is arranged in front of the bottom part of the A-frame in system "b" and serves to hold the oil hose in place in the trough 12. The mooring system

must not necessarily be placed in the position shown

on the drawing. The mooring equipment includes a tension release and/or manually controlled device for a mooring line, e.g. a winch and a damping roller. In cases where the hose is brought over to the transport tanker using the mooring line as a guide, a number of blocks can be arranged, which blocks are fitted with a clamp and ride along the mooring line in use. The clamps serve ten 1 to attach the oil hose via the blocks to the mooring line. The blocks and clamps can be stored in any suitable position when not in use, and this is indicated for convenience at 15 in fig. 1.

In the design example shown in fig. 1, the hose is passed through one or more pairs of vertical hose pullers 16 which may be located near the extended hose outlet 17. These pullers 16

can take the form of vertical rolling cylinders as spring pressure against the hose. It is assumed that the bollards will be approximately 1.8 m high. The bollards should be made of a material capable of

to hold the hose sufficiently without damaging it. Instead of rolling cylinder pullers, concave spindles can be arranged to

give a tighter grip on the hose and thereby prevent vertical movement.

In fig. The mooring line is indicated generally at 19, and a single block and clamp 20 is shown. The blocks are lightweight constructions attached so that they can move freely on the mooring line. The clamps can be attached to the respective blocks by means of a rod with limited movement at the block. The clamps can be of an easily adaptable and adjustable type for retaining the oil hose. The material on the inside of the clamp should be such that it provides sufficient grip on the hose without

give rise.:to wear.

Before the oil hose H runs over to it. floating storage vessel, it passes in system "b" over one or more rollers 18 which serve to prevent the hose from hitting the ship's rail and which prevent wear and undue stress on the hose when significant movements occur in bad weather. Similar rollers may be located at the apex of the A-frame.

In the embodiment of an oil storage vessel shown in fig.

3, the hose H is freely suspended from the top of the A-frame over to the transport tanker. The chain line can be adjusted so that it is completely in the air or runs through the sea.

An alternative arrangement (not shown) is that the oil transfer hose H is completely submerged between the oil storage vessel and the transport tanker. Other hose handling arrangements can also be used where this is desirable - e.g. using cranes.

The floating storage vessel also includes precursor equipment 21. and means to allow the lines to move freely on the surface behind the storage vessel or to hang the lines up behind the storage vessel, e.g. using a telescopic boom. The precursor can also be shot over. A cage may be provided to protect the precursor's throwing position.

A preferred mooring system for shallow water for use in the invention is shown in Fig. 5. The mooring system comprises a base 30' placed on the seabed, to which base a fluid swivel 39' is attached. This is connected to a universal joint which in turn is connected to a distance buoy 41', ■ and on top of this there is a chain boom 42'. An oil line placed on the seabed is connected (directly or via a collecting pipe) with the shelf 30'. The shape of the distance buoy may deviate from the largely cylindrical shape shown in fig.

5. A hose guide tongue, as shown in fig. 3 and 7, can be attached to the fluid swivel in a balanced and/or supported state. The tongue ensures that the hose clears of the mooring socket and that sufficient torque arm is available to rotate the fluid swivel as required. 01jeslangen (e) 44'

is located in the hose guide tongue and serves to transfer oil to the storage tanks in the storage vessel.

In contrast to the deep-water system where the underwater oil line passes up through a hose pipe in the ship and the length of hose in the water is fixed, the shallow-water system gives the opportunity to

raise the underwater hose 44' up along the side 60 of the ship through a "stinger" 51 to a vertically placed disk 52 which slides in rails 53 along the side of the ship 60 (see fig. 8). The position of the disc regulates the amount of hose in the water and thus allows adjustment within certain limits of the hose chain line in relation to the length of mooring chain from the storage vessel to the mooring. Rollers 54 are arranged to smooth the path of the hose against the disc

52. On the ship, the hose runs over the disc 52 and along rollers

55 to the amidships header where its coupling end connects with a quick release coupling.

One or more hoses can be handled in this way on one or both sides of the storage vessel. The distance buoy of the mooring is placed sufficiently deep that it is not significantly affected by wave action and so that it provides optimal effect of the mooring chain.

In fig. 3a shows a preferred design example

a deep water mooring system for use with the invention. The mooring system comprises a plinth 30 placed on the seabed, and a riser pipe 32 is attached to the plinth by means of a universal joint 31. An oil pipeline 33 placed on the seabed is connected via a collecting pipe 34 and a flexible bottom hose 35 to an oil line 36 which is arranged on the outside or the inside of the riser 32. At the top of the riser a platform 37 is arranged around a coupling 38, and on top of this a fluid swivel 39 is arranged which is connected to

a universal joint 40. A spacer buoy 41 is attached to the universal joint 40. and a mooring chain 42 extends from a chain beam, which can rotate about two axes on top of the spacer buoy, to the oil storage vessel. The shape of distance

the buoy may deviate from the largely cylindrical construction shown in fig. 3a. A hose guide tongue 43 is attached to the fluid swivel 39 and forms a channel through which the oil hose(s) 44 are guided. The hose guide tongue is supported or balanced so that it serves as a rocker arm for rotation of the fluid swivel. The hose serves to carry oil from the oil line 36 to the storage tanks in the storage vessel. The distance buoy is placed sufficiently deep so as not to be exposed to strong wave action.

In the design example shown in fig. 4, the distance buoy is modified to change its characteristics and it is here extended up to the surface by means of a cylindrical member 45. This is connected above the waterline by means of a mooring 46 to the bow of the oil storage vessel or transport tanker. This modification can be used for both shallow-water and deep-water mooring.

The storage capacity of the floating storage vessel can be as large as necessary, and the aim is generally to allow a constant supply of oil from the oil wells to the floating storage vessel at the same time as the oil is delivered in batches from the floating storage vessel to the transport tankers. The transport tankers can be thought to have a capacity of between 80,000 and 100,000 tonnes, but smaller vessels, e.g. with a capacity of 60,000 tonnes, can be just as useful in certain cases.

The floating storage vessel may have a main propulsion machinery of approximately 26,000 - 28,000 hp. The vessel may be equipped with "dynamic assistance" propulsion to ease mooring forces built up by the vessel's movement or yaw movements and to keep the vessel in an optimal equilibrium position in relation to the acting forces.

Dynamic assistance differs from dynamic positioning by

that its function is not to keep the ship in a fixed place in relation to the seabed. Dynamic assistance will use which one

any or several of a large number of selected points and directions given certain environmental criteria, mooring parameters,

and the vessel's draft and size.

In addition to acting as the main oil storage vessel, the floating storage vessel can also be used for oil production facilities in cases where underwater well completion is used. Facilities for cleaning the oil before transport to a refinery may be included in the floating storage vessel. Use of the storage vessel as described could possibly allow oil production without the use of a production platform with self-supporting or floating construction.

The proposed method for supplying oil from the floating storage vessel to a transport tanker shall be described in the following with reference to fig. 3a, b. First, the transport tanker will steer on a safe course until it is approx. 60 m from the storage vessel. The transport tanker has already picked up the floating or discarded precursor from lot 21. Alternatively, the precursor can be transferred at this stage by means of a telescoping boom mounted under one of the A-frames (see Fig. 3b). The mooring line and the file chain 19 attached to the forerunner are towed from the floating storage vessel over to the transport tanker. At this stage, in system "b", the disk 5 and the guide slide 7 together with the oil hose H will be in the forward position towards the midship as shown in fig. 3a. In system "b" 45 m or so of hose will be attached to the storage vessel. When the mooring line is attached, the transport tanker will stay in position approximately 45 - 75 m behind the floating storage vessel, depending on the weather conditions, the transport tanker's load and hose length, for safety reasons. As soon as a suitable distance between the floating storage vessel and the transport tanker is achieved, the transport tanker, if its propeller steering is fine enough, will reverse and give a certain tension in the mooring line so that jerk stresses are avoided. A precursor attached to the mooring line and attached to the delivery end of the oil hose H is then slowly pulled over to the transport tanker carrying the oil hose H. During this process, in the case of system "a", the hose is carefully lowered from its stowed position into the water and limped to the transport tanker.

With system "b", the disc 5 moves from the midship area on

the floating storage vessel in the direction aft towards the stern of the storage vessel. As the oil hose is fed out from the trough 12 and guided by suspension in the mooring line, clamps 20 are fixed around its circumference at regular intervals, which clamps are carried along by their blocks which can move freely along the mooring line. When the oil hose has arrived on board the transport tanker, a quick-release coupling is inserted into a corresponding coupling on the transport tanker to thus complete the oil flow line. Where an A-frame is used, the hose is led from the trough 12 over the A-frame which has a built-in continuation of the trough 12 and a suitable radius of curvature above its apex. The oil hose is hauled aboard the transport tanker, and a quick-release coupling is fitted into a corresponding coupling. The disc 5 is then tightened using the winch 10 so that the oil hose is kept in constant tension. Under these conditions, the connection between the floating storage vessel and the transport tanker is resilient and can allow an additional 45 m of separation movement between the vessels. Lateral drifting of a vessel in relation to the others can be tolerated from the side of the hose as long as the bow of the transport tanker does not move laterally more than 30 m to port or starboard of the storage vessel's longitudinal axis. Oil is pumped through the oil hose from the tanks in the floating storage vessel to the tanks in the transport tanker. When the transfer is finished, the above operations are carried out in reverse order so that the oil hose is pulled back from the transport tanker and its length, which can be 300 m, is handled by moving the disc 5 along its track in a direction away from the transport tanker.

For faster transfer of oil, the floating storage vessel is equipped with a double delivery system as shown in the drawing. The drain hose can advantageously be up to 50 or 60 cm in diameter, which allows a high oil transfer rate. Easier handling and the transport tanker's maneuverability may, however, require 30 cm cables.

Delivery of oil from the line 33 on the seabed to the oil storage vessel can take place continuously. Thus, problems associated with rapid pressure changes in the oil lines are eliminated.

A method of installing the mooring arrangement shown in fig. 3 shall be described in the following example.

After the base and riser have been brought into place, the device consisting of the fluid swivel with flanged or Graylock-type coupling, hose guide tongue, universal joint and distance buoy is connected to the riser separately or together in the following way, using either an anchored barge, a vessel with dynamic positioning or a dynamically assisted storage tank to be subsequently moored to the mooring. An extendable bridge crane is used which has a reach from the vessel of 7.5 - 9 m and which is large enough to lift and move the device individually or in parts. This crane is used to swing the parts or the device into a vertical position in a controlled manner using winches and a "tipping sled" which is mounted on guide rails and whose position is regulated by means of a winch. (This slide can be the slides 7 shown in Fig. 1 and 2). In the vertical position, the top of the distance buoy is held in a frame to avoid oscillations. Steering wires from two self-supporting winches or other heave-compensating devices are routed from their respective disc positions on the bridge crane frame through carabiner-type fixtures that are attached to the spacer buoy. Two divers take these wires down to the diving platform at the top of the riser and fasten them in predetermined positions opposite each other. The wires are tightened using self-tightening winches or other tensioning devices.

Two gates that can be opened by means of valves on the spacer buoy have at this point been opened, one at the bottom of the buoy and the other near or at the top. On the buoy structure itself, there is a specially constructed buoyancy section that is not displayed by the buoy space which is in connection with the two ports. This particular buoy section serves to keep the device vertical when in the water, but it does not keep the device afloat, i.e. it does not provide any positive buoyancy for the spacer buoy or the complete device.

When the device is lowered into the water, which takes place slowly to allow the water to flow in and drive air out from the main body of the buoy, it is controlled by two tension wires which are attached to the diving platform 37 at the top of the riser. The divers, who have contact with the surface, control the final immersion of the device and its joining with the riser. The flange type or Graylock type coupling is attached.

The line that was used to lower the device is slackened. The upper port on the spacer buoy is closed, and a predetermined quantity of water is forced out through the lower port by pumping air into the spacer buoy using an air line from the surface. The lifting/lowering wire is separated from the buoy, and the two guide wires are released from the carabiner guides on the buoy. The bottom gate then closes properly. The chain is lowered and attached to the distance buoy. The oil hose is lowered and attached to the swivel. The guide wires are used to lower both the chain and the hose. The guide wires are released from the diving platform. The type of vessel on the

the surface used when attaching the device determines the final method for attaching lines and marker buoys or chain and hose attachment to the mooring and hose positions in the storage vessel.

After the facility is brought into position, it will usually be maintained by a team of air divers from the floating storage vessel mooring to the shallow or deep water mooring.

When a major overhaul or replacement of parts that cannot be done underwater or the mooring is to be dismantled is necessary, the device can be lifted to the surface and hoisted aboard either with the help of an anchored barge, a dynamically positioned auxiliary vessel or the dynamically assisted storage vessel that has been the mooring to the mooring. If an anchored barge or a dynamically positioned auxiliary vessel is used, the mooring chain and oil hose are released from the storage vessel and attached to wires with marker buoys. The mooring chain hangs straight down along the side of the mooring, and the oil hose hangs in a chain line. In cases where the dynamically assisted storage vessel is to lift the device, it is not necessary to first release the mooring chain and the oil hose from the vessel.

Two divers release the control cables attached to the diving platform. They guide the wires through the carabiner fixtures that are part of the distance buoy. The oil hose and chain are released at this point and lifted to the surface. The lifting line is attached to the top of the buoy and hung slack. The oil line on the riser is closed or will have been closed before lifting the hose, chain or device begins. The main body of the spacer buoy is filled using a water inlet valve and an air valve at the bottom, respectively. the top or near the top of the buoy. There is enough buoyancy in the specially designed buoyancy section at the top of the buoy to keep it in a vertical position. When the main body is filled with water, the two large gates are opened, one at the top and one at the bottom. The Graylock-type or flange-type coupling under the fluid swivel is loosened, and the slack in the lifting line is tightened. The device is lifted to the surface, after which water will automatically drain from the distance buoy when the device is lifted clear of the water. At the top of the lifting movement, the buoy is fed into a holding frame to avoid oscillations. The guide wires are released from the carabiner fi/S^tures on the buoy, and they are also released from the diving platform at the top of the riser. A marker buoy is set out to mark the position of the riser. The bridge crane that holds the device is retracted until the device is in such a position that it can be attached to the "tipping sled" which is in a semi-vertical position. When the device is attached, the tipping slide is lowered to a horizontal position. The lifting line is released from the device. The tipping sled is then guided inwards on its rails to a place where maintenance on the device or replacement of parts can be carried out. The lifting tackle on the bridge crane can be used to move large parts of the installation.

When necessary, e.g. in case of emergency, the underwater hose will be automatically released or passed out through the bottom of the ship by means of a continuous wire hanging from a chain line, and identified by means of a surface buoy released from the side of the ship. The mooring line attached to the winch is released and passed through the hawser pipe and marked using the surface buoy attached to the chain by means of a line. The chain hangs in a vertical position.

In an exemplary embodiment of the invention, the spacer is constructed so that it can be modified to form the construction shown in fig. 4. This comprises a two-part construction, the upper part of which can be changed to provide an extension to the surface as shown in fig. 4. This extension can be used as follows. The transport tanker will approach the surface extension of the device which has a floating hawse and a forerunner. The underwater hose hanging in a chain line with the connecting end at 20 m water depth is provided with a buoy, and its precursor is attached to the precursor of the floating line. The forerunner will be caught from the ship's bow and brought aboard, after which it is hauled in so that the hawser comes with it and can be secured with the help of a winch or puller. The precursor for the oil hose is brought on deck, and the oil hose will follow this. The coupling end of the oil hose is attached to the quick-release coupling. After the wrapping of the tanker is completed, the procedure is carried out in reverse order and the lines are dropped into the water.

The connection between the storage vessel and the transport tanker is, as explained above, springy and allows significant damping of the mooring forces between the vessels. This is important, especially in emergency situations such as the loss of the mooring line between the vessels. Under such conditions, the crew will have time to carry out an orderly unwinding and/or disconnection of the oil hose H.

To help the "dynamic assistance operation" and to contribute to the directional control of the storage vessel, ailerons can be used whose angles in relation to the wind can be changed. One or more rudders can be arranged on the ship's stern to help control the storage vessel's yaw movement and increase the longitudinal stability of the vessel in relation to the environmental conditions. The possibility that the ailerons can contribute with a forward force vector in the same way as a sail is foreseen and can help to reduce the forces to which the mooring and the mooring chain are exposed. The Coanda effect can also be used to improve the efficiency and power of the ailerons. Where more than one aileron is used, their angle of attack may be equal or different to provide optimum efficiency of the required power. The rudders can be adjusted manually or automatically. They can be made of canvas or metal, depending on what turns out to be best in relation to the built-in Coanda effect and total efficiency and cost.

The air rudders are preferably placed where, from the outside, the given shape of the ship will make the best use of the laminar flow of air above and around the ship. Turbulent air will be avoided as much as possible.

The Coandaé effect can be exploited in three ways. The first exploitation involves shielding the front section of each rudder. The screens on either side of the rudder can be fixed, rotatable and/or retractable. The operating mechanism for extending or retracting the screens can be manual or automatic, mechanically, hydraulically or electrically operated.

The second utilization of the effect directs air with. high velocity along the surface of the airfoil by incorporating air nozzles suitably oriented and located, the number of which will permit coverage of the entire surface of either one or both sides of the airfoil. The design of the surroundings around the opening of each air nozzle has a critical shape that allows the most efficient distribution of the air into the laminar flow of air at high speed along the rudder. The high velocity airflows will come from a long tube-like chamber arranged in connection with the vertical axis around which the rudder rotates, i.e. its mast. The air in the tube-like chamber will be kept to a minimum

of pressure to be determined, which pressure can be maintained either naturally or by means of a fan via an air duct.

The third utilization of the effect can be achieved by means of the shape of the surface of the airfoil itself.

The control of the device (the relative device) of the ailerons can be done by means of mechanical, hydraulic or electrical means. Pressure transducers can be used to measure forces that can be analyzed mathematically to optimize the desired force effect.

In preferred embodiments, the mooring between the storage vessel and the transport tanker will consist of: (a) a file chain;

(b) a synthetic fiber rope; and

(c) wire.

A wire winch will be located at the stern of the storage vessel. Above this there will be a winding drum for the fiber rope. Aft of the wire winch, which may be a yielding winch, there will be a concave roller with thick ends over which the mooring line will pass. The roller is held at a given height above and aft of the wire winch by means of two arms which revolve around an axis. The arms are held in position using springs or hydraulically controlled jacks. The concave roller, the arms and the operating mechanism are called the damper. The damper is designed and adjusted so that it absorbs part of the cyclic shock loads in the mooring line. This prevents extraordinary movements of the transport tanker and avoids accentuated movements of it. The fiber rope is not attached to a puller or winch, and for this reason its life is extended.

Claims (5)

1. A single point mooring and fluid handling system for transferring a fluid from an underwater pipeline (3 3) to a conduit (44) connected to or connectable to a floating vessel moored at the system, which system comprises (a) a pedestal (30) which in use is placed on the seabed, (b) a riser (32) which is connected to the base by means of a universal joint (31), which riser is completely submerged in use, (c) a fluid swivel (39) placed on top of the riser (3'2)_, (d) a hose guide tongue (43), and (e). a distance buoy C41) mounted on top of the fluid swivel (39) via a universal joint (40), characterized by (1) that the riser (32) has positive buoyancy, (2) that the hose guide tongue (43) is attached to the fluid swivel (39) so that it acts as a weight arm to facilitate rotation of the fluid swivel (39), and (3) that a chain beam is mounted on top of the spacer buoy (41) in a manner that allows the chain beam to move in two orthogonal planes. 2. System according to claim 1, characterized in that the distance buoy (41) has a largely cylindrical shape. 3. System according to a preceding claim, characterized in that a pipeline (36) is placed on the side of the riser (32). 4. System according to a preceding claim, characterized in that a mooring chain (42) or rope is connected to the top of the distance buoy (41). 5. System according to a preceding claim, characterized in that the base (30) is a gravity base.