The present invention relates to a mooring element latching assembly for releasably latching a mooring element of an offshore vessel mooring and riser inboarding system. In particular, but not exclusively, the present invention relates to a latching assembly for latching a mooring element of an offshore vessel mooring and riser inboarding system to a gimbal arrangement of the system. The present invention also relates to an offshore vessel mooring and riser inboarding system comprising a mooring element and such a latching assembly.

In the oil and gas exploration and production industry, there have been movements towards the use of Floating Production Storage and Offloading Vessels (FPSOs) and Floating Storage and Offloading Vessels (FSOs) for the exploitation of offshore oil and gas fields. An FPSO is moored in an offshore location and is typically coupled to a number of producing wells, for the temporary storage of produced well fluids, which are periodically exported to shore by tankers. FPSOs typically include facilities for separating recovered well fluids into different constituents (oil, gas and water), so as to stabilise the crude oil for onward transport by tanker. FSOs are similarly moored and allow for the storage of recovered well fluids, and may either be disconnected from their moorings for travel to an offloading location, or the recovered fluids may similarly be exported by tanker

A number of different systems have been developed for mooring vessels such as FPSOs and FSOs. These systems have been found to suffer from a number of disadvantages, including: that the ability of the vessel to weathervane is overly restricted; that they are difficult to install and hook up in the field; that they have an uncertain ability to allow the vessel to disconnect rapidly, reliably and safely from fluid risers; and that they provide a relatively restricted sea state capability.

A more recently developed system, disclosed in international patent application no.PCT/GB2005/003766 (published as WO-2006/037964) was designed to address the problems associated with such prior systems. This was achieved by providing a system including a connector assembly, for connecting a vessel to a mooring element in the form of a buoyant canister, in which relative rotation between the vessel and the mooring element about three mutually perpendicular axes of rotation is permitted. The connector assembly includes a support structure provided on the vessel, an outer gimbal member rotatably coupled to the support structure, and an inner gimbal member located within and rotatably coupled to the outer gimbal member. The connector assembly also includes a rotatable coupling allowing for rotation relative to the mooring element. By permitting such movement between the vessel and the mooring element, the system of WO-2006/037964 facilitates movement of the vessel under external loading during use, and reduces forces transmitted to/borne by the vessel and the mooring and riser system components. Accordingly, it has been found that the connector assembly in the system of WO-2006/037964 is not required to support the relatively large loads found in prior systems. In addition, the system of WO-2006/037964 permits all likely ranges of movement of the vessel relative to the mooring element without excessive wear or damage to components either of the system or to the vessel itself.

In certain situations, such as may occur in storm conditions when anticipated loading on the vessel would approach or exceed design maxima, or to facilitate maintenance repairs and modifications to the FPSO, it may be necessary to release the vessel from the canister. To this end, the system of WO-2006/037964 incorporates a locking mechanism which can be activated to selectively engage the canister. Whilst the system of WO-2006/037964 securely supports the mooring canister and provides an ability to release the canister relatively quickly in an emergency situation, it is generally desired to improve upon the locking mechanism disclosed in WO- 2006/037964.

According to a first aspect of the present invention, there is provided a mooring element latching assembly for releasably latching a mooring element of an offshore vessel mooring and riser inboarding system to a gimbal arrangement of the system, the assembly comprising: a primary latch mechanism comprising a plurality of primary latch members which are movable between release positions out of engagement with the mooring element and latching positions in which the latch members engage and support the mooring element; wherein each latch member has a load face adapted to abut and support the mooring element; and wherein at least a portion of the load face of each latch member is inclined such that, in use, the mooring element exerts a force on the latch members which acts to urge the members towards their release positions in the absence of a latching force acting on the primary latch members.

By providing a mooring element latching assembly having primary latch members including such inclined load faces, the mooring system can be arranged to failsafe release the mooring element, so that emergency disconnect can be achieved without specifically requiring application of an independent retraction force on the latch members. Accordingly, the latching assembly of the present invention provides a redundant capacity for the mooring element to be released in the event of failure of critical components (such as hydraulic and/or electro-mechanical control units associated with the latch members, including any required back-ups), however unlikely.

The latching force may be a force exerted on the primary latch members to move and hold them in their latching positions; may be exerted on the primary latch members by a secondary locking element or the like which locks the latch members in their latching positions; or may be a combination of the two.

Reference is made herein to the fact that at least a portion of the load face of each latch member is inclined. It will be understood that the load faces are so inclined in that the surfaces are disposed at a (non-parallel) angle from the horizontal. As will be described in more detail below, the gimbal arrangement of the mooring system facilitates movement of a vessel moored to the mooring element, and typically comprises inner and outer gimbal members. The primary latch mechanism may be provided on or in the gimbal arrangement, particularly the inner gimbal member, and thus may be moveable relative to the vessel (and indeed the sea or ocean in which the vessel is deployed) with the gimbal arrangement. Thus it will be understood that the primary latch member load faces/load face portions are inclined from the horizontal in a rest state of the mooring system and indeed in the absence of external loading on the vessel. The inclined load faces/load face portions may be inclined from an inner or leading end of the latch members (nearest the mooring element, in use) towards an outer or trailing end.

The assembly may comprise a temporary latch mechanism, which may comprise a plurality of temporary latch members which are movable between release positions out of engagement with the mooring element and latching positions in which the latch members engage and support the mooring element. The temporary latch members may be arranged to temporarily engage and support the mooring element until such time as the primary latch members have been moved to their latching positions. This may be achieved by selectively controlling actuation of the primary and temporary latch members, and/or by appropriate positioning of the primary latch members relative to the temporary latch members and relative to respective surfaces of the mooring element to be engaged and supported by the primary and temporary latch members. Each of the temporary latch members may have a load face adapted to abut and support the canister, and at least a portion of the load face may be disposed parallel to the horizontal.

The primary latch members may be arranged relative to the temporary latch members such that, on movement of the primary latch members to their latching positions, the primary latch members move the canister out of abutment with the temporary latch members. The primary latch members may be arranged to move the mooring element out of abutment with the load faces of the temporary latch members, and may be arranged to lift the canister off the temporary latch member load faces. In this fashion, loading may be transferred from the temporary latch members to the primary latch members automatically, on actuation of the primary latch members to their latching positions. The primary latch member load faces may be adapted to cooperate with a surface or surfaces on the mooring element having a corresponding incline, such that on movement of the primary latch members to their latching positions, the latch members carry the mooring element up the load faces of the latch members to thereby lift the mooring element off the temporary latch member load faces. This may be achieved by appropriate positioning of the primary load members relative to the temporary load members. For example, a distance between a leading end of the primary latch member load face and the temporary latch member load face may be smaller than a distance between abutment surfaces for the primary and temporary latch members on the mooring element.

The incline of the primary latch member load faces may be no more than about 25° and may be no more than about 20°. The incline of the primary latch member load faces may be no less than about 5° and may be no less than about 10 . The incline may be about 15°. Providing the primary latch member load faces with a relatively small incline may result in a majority of the loading on the primary latch members being vertically directed (at least in a rest state of the mooring system), with only a relatively small horizontal component. Accordingly, a majority of a latching force imparted on the primary latch members, when in their latching positions, may be used to support vertical loads imparted on the latch members by the mooring element, the remainder of the latching force serving for resisting movement of the latch members back to their release positions. However, the incline may be sufficient for the mooring element to exert a force on the primary latch members which is large enough to urge the latch members back towards their release positions in the absence of a latching force imparted on the members.

The primary latch mechanism may be fluid operated, and may be hydraulically operated, and the primary latch members may be urged from their release positions to their latching positions under applied fluid pressure. The primary latch mechanism may comprise a pressure control arrangement for supplying fluid under pressure to the primary latch members. The pressure control arrangement may comprise an actuator associated with the or each primary latch member, and there may be a plurality of actuators associated with each latch member, to provide redundancy. Accordingly, it will be understood that, in the unlikely event of failure of all actuators of the pressure control arrangement, the primary latch members can be returned to their release positions through the load exerted on the primary latch members by the mooring element. The actuator may comprise a cylinder which is coupled to a primary latch member by a piston which serves for moving the latch member, or any other suitable actuator.

The primary latch mechanism may comprise a locking arrangement for locking each primary latch member in its latching position. The locking arrangement may comprise at least one locking pin associated with each latch member, which may be moveable between release and locking positions. The locking pins may be biased by a spring or some other mechanical or electro-mechanical actuator, so as to failsafe lock, and the locking pins may be urged to their release positions under applied fluid pressure (or vice-versa).

The temporary latch mechanism may be fluid operated, and may be hydraulically operated, and the temporary latch members may be urged from their release positions to their latching positions under applied fluid pressure. The temporary latch mechanism may comprise a pressure control arrangement for supplying fluid under pressure to the temporary latch members, and may comprise one or more actuator associated with the or each latch member. The temporary latch members may be spring biased, and a spring may be provided between each latch member and its respective actuator. This may permit of movement of the latch member against the biasing force of the spring, which may facilitate engagement of the mooring element. For example, in use the mooring element may be brought up into the gimbal arrangement and may come into contact with the temporary latch members (which are in their latching positions). Further movement of the mooring element may cause the latch members to be deflected outwardly (relative to/away from the mooring element) by a deflection surface on the mooring element and, following passage of the mooring element past the latch members, the latch members may be urged back out (under the biasing action of the springs) to their latching positions to engage and support the mooring element. The temporary latch members may each comprise a deflection surface which may be declined and disposed at a (non-parallel) angle from the horizontal. The deflection surfaces may be declined from an inner or leading end of the latch members (nearest the mooring element, in use) towards an outer or trailing end. Providing the temporary latch members with such a deflection surface may facilitate passage of the mooring element.

The primary latching members may be arcuate and may fit together to define a substantially complete or a complete annular latch ring, when in their latching positions. In this fashion, the primary latching members may be adapted to abut and support the mooring element around a majority of a circumference, or an entire circumference, of the mooring element. This may provide a good distribution of the loading of the mooring element on the primary latch mechanism, and may provide a secure engagement with the mooring element in heavy sea-state conditions, when the gimbal arrangement is required to accommodate significant movements of the vessel relative to the mooring element.

The primary latch mechanism may be adapted to be provided on or in an inner gimbal member of the gimbal arrangement to which the mooring element is to be coupled.

According to a second aspect of the present invention, there is provided an offshore vessel mooring and riser inboarding system comprising: a gimbal arrangement; a mooring element adapted to be coupled to the gimbal arrangement; and a mooring element latching assembly according to the first aspect of the invention, for releasably latching the mooring element to the gimbal arrangement.

Further features of the mooring element latching assembly of the mooring system are defined above in relation to the first aspect of the invention.

The system may comprise a rotatable coupling for facilitating rotation of the gimbal arrangement relative to the mooring element. This may allow the vessel to weathervane about the mooring element. The rotatable coupling may take the form of a swivel, and may comprise a bearing arrangement. At least part of the bearing arrangement may be mounted on or provided in the mooring element. The bearing arrangement may comprise a first race component mounted on or provided integrally with the mooring element, a second race component coupled to the first race component and which the primary latch members engage when in their latching positions. One or more bearing elements may be provided between the first and second race components and which facilitate relative rotation between the race components. The first race component may be an inner race and the second race component an outer race, or vice-versa. The second race may comprise an inclined abutment surface or surfaces which the primary latch member load faces abut when in their latching positions. The abutment surface or surfaces may be of corresponding shape or profile to the primary load members, and may be of a corresponding incline to that of the primary latch member load faces. On movement of the primary latch members to their latching positions, the latch member load faces and the abutment surfaces of the bearing arrangement may cooperate such that the latch members carry the mooring element up their load faces, to thereby lift the mooring element off the temporary latch member load faces.

The mooring element may be buoyant and may take the form of an elongate mooring canister.

According to a third aspect of the present invention, there is provided a vessel incorporating the offshore vessel mooring and riser inboarding system of the second aspect of the invention.

Further features of the mooring element latching assembly of the mooring system are defined above in relation to the first aspect of the invention, and further features of the mooring system are defined in relation to the second aspect of the invention.

The latching assembly may have a utility with other types of mooring systems. In a further aspect of the invention, a mooring element latching assembly for releasably latching a mooring element of an offshore vessel mooring and riser inboarding system may be provided in which the assembly comprises: a primary latch mechanism comprising a plurality of primary latch members which are movable between release positions out of engagement with the mooring element and latching positions in which the latch members engage and support the mooring element; wherein each latch member has a load face adapted to abut and support the mooring element; and wherein at least a portion of the load face of each latch member is inclined such that, in use, the mooring element exerts a force on the latch members which acts to urge the members towards their release positions in the absence of a latching force acting on the primary latch members.

Further features of the latching assembly of the mooring system are defined above in relation to the first aspect of the invention. An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of an offshore vessel mooring and riser inboarding system, incorporating a mooring element latching assembly for releasably latching a mooring element of system, in accordance with an embodiment of the present invention;

Figure 2 is an enlarged, partially cut-away view of the mooring system of Figure 1, in which parts of the mooring system including the mooring element have been removed, for ease of illustration, and which better illustrates the latching assembly;

Figure 3 is a plan view of the mooring system shown in Figure 1 prior to connection of the mooring element to a gimbal arrangement of the system;

Figure 4 is a sectional view of the mooring system shown in Figure 1, similar to the view of Figure 3 and taken in the direction of the arrows A-A of Figure 2;

Figure 5 is an enlarged view of a top of the mooring element of the system shown in Figure 1 ;

Figure 6 is a further enlarged view of a swivel of the system which is shown in Figure

5;

Figure 7 is a view of primary latch members of a primary latching mechanism of the latching assembly shown in Figure 2, the primary latch members shown in release positions;

Figure 8 is a view of the primary latch members of Figure 7, shown in latching positions;

Figures 9 and 10 are enlarged plan and side views of one of the primary latch members shown in Figure 7; Figure 11 is a view of an edge surface of the primary latch member shown in Figure 10;

Figure 12 is an enlarged perspective view of a temporary latch member of a temporary latch mechanism of the latching assembly shown in Figure 2, which has been partially sectioned for ease of illustration, and which shows the latch member in a latching position;

Figures 13 and 14 are partially sectioned side views of the temporary latch member of Figure 12, shown in the latching and in a release position, respectively;

Figures 15 and 16 are front and side views, respectively, of a locking arrangement for the primary latch members of Figure 2, shown in a release position; and

Figure 17 is a view of the locking arrangement of Figures 15 and 16, shown in a locking position.

Turning firstly to Figure 1, there is shown a perspective view of an offshore vessel mooring and riser inboarding system indicated generally by reference numeral 10, and of part of a vessel 12 incorporating the system 10. The mooring system 10 incorporates a mooring element latching assembly according to an embodiment of the present invention, and which is indicated generally by reference numeral 14. The latching assembly 14 serves for releasably latching a mooring element 16 of the system 10 to a gimbal arrangement 18 of the system 10, and is shown in more detail in Figure 2 which is an enlarged, partially cut-away view of the mooring system with certain parts removed, for ease of illustration. The vessel 12 takes the form of an FPSO, and only a bow 20 of the FPSO is shown in the drawing. It will be understood however that the vessel may be of any other suitable alternative type and may, for example, be an FSO, an offtake tanker or a buffer tanker. The FPSO 12 will typically be for engagement in an extended well test (EWT) procedure, or a life-of- field production procedure.

The offshore vessel mooring and riser inboarding system 10 generally comprises a support structure in the form of a cantilever connector assembly 22, a frame 24 of the connector assembly 22 being shown in Figure 1. The connector assembly 22 is generally of a type shown and described in WO-2006/037964, the disclosure of which is incorporated herein by way of reference. The connector assembly 22 is mounted on the FPSO 12 in the region of the vessel bow 20. The system 10 also comprises the mooring element 16, which takes the form of a buoyant tubular mooring canister, and which is located in an offshore environment such as a sea or ocean 26. The mooring canister 16 is moored using a number of catenary mooring chains 28, which restrict rotation of the mooring canister 16 about its own axis. It will be understood that the catenary mooring chains may include any combination of chains and ropes.

The system 10 also comprises a second mooring element indicated generally by reference numeral 30, and which comprises one or more fluid path connector (one shown and given the reference numeral 32), which is connected via two or more jumpers (three shown and given the reference numerals 34a, 34b and 34c) to a multi- path swivel 36. It will be understood that any suitable number of jumpers may be provided according to particular circumstances. Also, in certain situations, the jumpers may be connected directly to flanges or the like on the top of the canister 16. Additionally, and for example in an EWT, the mooring system may be provided without the multi-path swivel and in-line swivels in an arrangement similar to a CHIKSAN ™ marine loading arm, coupling to a jumper back on the FPSO 12.

A rotatable coupling in the form of a swivel is also provided, which will be shown and described below. The jumpers 34a, 34b and 34c provide for connection to two or more respective risers (three shown and given the reference numerals 38a, 38b and 38c), which are coupled to and pass up through the centre of the mooring canister 16. Typically, the risers 38a to 38c will be arranged in a buoyant wave arrangement known in the art, to absorb movement of the risers and to prevent damage to the risers at a touch down point on the seabed. The risers 38a to 38c are fluid flow risers for the flow of production fluids (oil and gas) from a number of subsea wellheads, production facilities or the like (not shown) to storage tanks (also not shown) on the FPSO 12. However, in certain circumstances, such as in a well stimulation or treatment activity where it is desired to inject fluid into a formation, fluid may be supplied from the FPSO 12 downhole. Thus fluid may be transferred from the FPSO 12 down through the risers 38a to 38c. Electrical control lines or other lines or cables may be piggybacked on or in the risers 38a to 38c.

Turning now to Figure 3, there is shown a plan view of the mooring system shown in Figure 1, with the fluid path connector 32 and canister 16 removed, for ease of illustration. Reference is also made to Figure 4, which is a sectional view similar to Figure 3, taken in the direction of the arrows A-A of Figure 2. As best shown in Figures 3 and 4, the mooring system 10 also includes an outer gimbal member in the form of a gimbal or gimbal ring 40 which is rotatably coupled to the cantilever connector assembly 22 via trunnions 42. An inner gimbal member in the form of a gimbal or gimbal ring 44 is also provided, and is mounted within the outer gimbal 40 and rotatably coupled to the outer gimbal via trunnions 46 (Figure 4). The fluid path connector 32 is releasably mounted on the inner gimbal 44. The swivel referred to above is shown in Figure 5, which is a view of a top 47 of the canister 16, and is indicated generally by reference numeral 48. The swivel 48 is also shown in the further enlarged view of Figure 6. When the canister 16 is connected to the FPSO 12 as shown in Figure 1, the swivel 48 is connected to the inner gimbal 44, and provides for rotation between the inner gimbal 44 and the canister 16. A flared fairing 50 is provided and is coupled to the inner gimbal 44, and serves for guiding the canister 16 into engagement within the inner gimbal, as will be described below.

As will be understood by persons skilled in the art and from reading WO- 2006/037964, the mooring canister 16 is located in the ocean 26 and moored, for example, to a seabed (not shown), using the catenary mooring chains 28 and suitable anchors (also not shown). The arrangement of the mooring chains 28 and anchors restrict rotation of the mooring canister 16 about its axis under external loading. The FPSO 12 is moored to the mooring canister 16 through the frame 24 of the cantilever connector assembly 22, and the arrangement of the outer gimbal 40, inner gimbal 44 and the swivel 48. In this fashion, the FPSO 12 may move with three degrees of freedom relative to the mooring canister 16. Such movement may occur under external loading including wind, wave, tidal and/or current loading and allows for pitch, roll and yaw of the FPSO 12 relative to the mooring canister 16, as well as weathervaning. This may involve movement of the outer gimbal 40 relative to the support frame 24; the inner gimbal 44 relative to the outer gimbal 40; and/or rotation of the FPSO 12 about the canister 16 (achieved by relative rotation between the inner gimbal 44 and the canister 16 through the swivel 48). Heave and surge of the FPSO 12 are accommodated by movement of the mooring system 10 restrained by the catenary mooring chains 28.

The latching assembly 14, and its method of operation, will now be described in more detail.

The latching assembly 14 generally comprises a primary latch mechanism which is best shown in Figure 2 and which is indicated generally by reference numeral 52. The primary latch mechanism 52 comprises a plurality of primary latch members, and in the illustrated embodiment comprises four such primary latch members 54, which are shown in more detail in the enlarged view of Figure 7. The latch members 54 are moveable between release positions out of engagement with the canister 16 (shown in Figure 7), and latching positions in which the latch members 54 engage and support the canister 16, as shown in Figure 1. The primary latch members 54 are shown in their latching positions in Figure 2, and in Figure 8, which is a view similar to Figure 7.

Each primary latch member 54 has a load face 56, which is best shown in the enlarged plan and side views of Figures 9 and 10, and in the view of Figure 11 , which is a view of an edge surface of the primary latch member 54 shown in Figure 10. At least a portion of the load face 56 of each latch member 54 is inclined such that, in use, the mooring canister 16 exerts a force on the latch members 54 which acts to urge the members towards their release positions in the absence of a latching force acting on the latch members 54. In the illustrated embodiment, the entire load face 56 is inclined, typically at an angle of around 15 degrees.

The primary latch members 54 are arcuate and, in their latching positions, together define a substantially annular ring (Figure 8), which abuts and supports the mooring canister 16 around a majority of a circumference of the canister. The primary latch members 54 are fluid operated, and the primary latch mechanism 52 comprises a pressure control arrangement for actuating the latch members. In the illustrated embodiment, the pressure control arrangement comprises two actuators for each latch member 54, which take the form of hydraulic cylinders 60 (shown in phantom outline in Figures 7 and 8, and one shown in Figure T). The cylinders 60 carry pistons 61 (Figure 8) which are coupled to the primary latch members 54 and supply of hydraulic fluid into the cylinders 60 thereby urges the latch members 54 from their release positions (Figure 7) to their latching positions (Figure 8).

The primary latch members 54 and the cylinders 60 are provided integrally within the inner gimbal ring 44, as best shown in Figure 2. The primary latch members 54 are shaped to engage the swivel 48 on the mooring canister 16, which is best shown in the enlarged view of Figure 6. The swivel 48 includes a first race component in the form of an inner race 62 formed on the canister 16, and a second race component in the form of an outer race 64. The outer race 64 is made up of two semi-circular race sections which are coupled together at either end using nut and bolt arrangements, as shown in the broken outline highlighted section 66 on Figure 5. Upper, inner and lower bearings 68, 70 and 72 are provided between the inner and outer races 62 and 64 and may be of any suitable type such as roller bearings. These bearings 68, 70 and 72 allow for rotation of the outer race 64 within and relative to the inner race 62.

The outer race 64 defines an annular channel 74 which is shaped to receive the primary latch members 54 when they are moved to their latching positions. The channel 74 defines an abutment surface 76 which is inclined at a corresponding angle to that of the primary latch member load faces 56, such that they come into close abutment on movement of the primary latch members 54 to their latching positions.

The inner race 62 is provided as an annular collar which is secured to the main body of the mooring canister 16, and includes an upper annular lip 78 which defines a radially extending abutment surface 80. The lip 78 also defines an upper ramp 82 which is declined from the horizontal. The lip 78 is shaped to cooperate with a temporary latch mechanism of the latching assembly 14, which is shown in Figures 2 and 3 and which is indicated generally by reference numeral 84. The temporary latch mechanism 84 comprises a plurality of temporary latch members and, in the illustrated embodiment, comprises four temporary latch members which are indicated generally by reference numeral 86. One of the temporary latch members 86 is shown in more detail in the enlarged perspective view of Figure 12, which has been partially sectioned, for ease of illustration. The temporary latch member 86 is also shown in the two side views of Figures 13 and 14, which have again been partially sectioned.

The temporary latch members 86 take the form of pins which are mounted in housings 88 that are provided on the inner gimbal ring 44. As with the primary latch members 54, the temporary latch pins 86 are moveable between release positions (Figure 14) and latching positions (Figures 12 and 13). The temporary latch pins 86 are fluid operated by actuators in the form of cylinders 90 having pistons 92. The pistons 92 extend along a passage 94 within which the pins 86 are mounted, for exerting forces on the pins 86 to move them from their release positions to their latching positions. A spring 96 is provided between an end of each piston 92 and the latch pins 86, to bias the pins towards their latching positions. As will be described in more detail below, this permits inward deflection of the pins 86 away from their latching positions, when the mooring canister 16 comes into contact with the pins. Each pin 86 also includes an abutment surface 98 which is declined from the horizontal, to facilitate passage of the mooring canister 16. The abutment surface 98 is shaped to cooperate with the ramp 82 on the annular lip 78 of the inner race 62 shown in Figure 6.

In use, and during connection of the mooring canister 16, the canister is raised up through the inner gimbal 44. The primary latch members 54 are initially in their retracted, release positions. The temporary latch pins 86 are, however, in their extended latching positions shown in Figures 2, 12 and 13. In this position, the pins 86 protrude into a central aperture 100 defined by the inner gimbal 44 (Figure 3). As the mooring canister 16 is drawn up through the aperture 100, the ramp 82 on the lip 78 comes into contact with the abutment surfaces 98 of the temporary latch pins 86. Further movement of the canister 16 then urges the pins 86 radially outwardly (relative to the canister) against the biasing force of the springs 96, by cooperation between the ramp 82 and the abutment surfaces 98. When the canister 16 has been raised a sufficient distance, the lip 78 passes the temporary latch pins 86, which are then urged back to their latching positions by the springs 96. The canister 16 can then be seated upon the temporary latch pins 86, the abutment surfaces 80 on the underside of the lip 78 seating on upper load faces 102 of the temporary latch pins 86. It will be understood that, prior to being raised, the mooring canister 16 is in an equilibrium state where the inherent buoyancy of the canister balances the loading of the risers 38a to 38c and of the mooring chains 28. When the canister 16 is raised, the additional loading is borne by the temporary latch pins 86.

With the canister 16 securely seated on the temporary latch pins 86, the primary latch members 54 are actuated by the pistons 61, and move radially inwardly to their latching positions. The spacing between the primary latch members 54 and the temporary latch pins 86; and between the abutment surface 76 of the outer race 64 and the abutment surface 80 on the underside of the lip 78, is carefully selected such that the canister 16 will be raised during this movement of the primary latch members 54 to their latching positions. Specifically, the vertical distance between the abutment surface 80 and a junction 104 between the abutment surface 76 of the outer race 64 and a root of the channel 74 is greater than a vertical distance between a tip 106 (Figure 11) of the primary latch members 54 and the upper load faces 102 of the temporary latch pins 86. In this fashion, as the load faces 56 of the primary latch members 54 come into contact with the abutment surface 76 of the outer race 64, the abutment surface 76 travels up the load faces 56, thereby raising the canister 16. This lifts the canister 16 off the load faces 102 of the temporary latch pins 86, so that the load is now fully borne by the primary latch members 54. The temporary latch pins 86 may then be actuated to return to their release positions by reverse stroking the pistons 92, or the temporary latch pins 86 may be left in their latching positions to provide a backup latch.

In use, the FPSO 12 is moored to the canister 16 as follows.

The FPSO 12 is brought into the vicinity of the canister 16, previously moored in the ocean 26 and to which the risers 38a to 38c have been coupled. The top 47 of the canister 16 is then pulled into the gimbal arrangement 18. This can be by deploying a winch line (not shown) through the central aperture 100 of the inner gimbal 44, which is then connected to the top 47 of the canister 16, and the canister is winched up into the gimbal arrangement 18. Alternative methods of pulling in the canister 16 may be employed. The gimbal arrangement may be rotated to better accommodate the canister during pull-in, and the fairing 50 guides the canister 16 up into the inner gimbal 44. Initially and as described above, the primary latch members 54 are in their release positions, and the temporary latch pins 86 in their latching positions. The canister 16 is pulled further up into the inner gimbal 44 until the temporary latch pins 86 have latched-out beneath the lip 78. The canister 16 is then seated on the temporary latch pins 86, and the primary latch members 54 actuated as described above. The canister 16 is then securely seated on the primary latch members 54.

The fluid path connector 32 (previously stowed in a safe location to restrict green water loading) is then raised and deployed onto the inner gimbal 44. The fluid path connector 32 includes a number of guide prongs 108, each of which mates with a corresponding bucket 1 10 provided on a turntable 112 (Figure 2). The turntable 112 is mounted on the inner gimbal 44, and can be rotated by a motor 114 to facilitate alignment with the prongs 108. When the fluid path connector prongs 108 have been stabbed into the buckets 1 10, the turntable 112 is rotated by motor 114 to align the connector 32 with the canister 16. The connector 32 is then mated with the top 47 of the canister 16 using retractable, hydraulically operated arms 136 (Figure 1). The jumpers 34a to 34c are then fluidly coupled to the respective risers 38a to 38c, and fluid transfer may begin.

The canister 16 can be released as follows. Firstly, the fluid path connector 32 is released from the canister 16 and safely stowed. If actuated, the temporary latch pins 86 are also reverse stroked, and the canister can then be lowered back through the inner gimbal 44. The primary latch members 54 are then actuated back to their release positions by reverse stroking the pistons 61. This allows the canister 16 to fall away from the gimbals and latching system.

A redundant capability to actuate the primary latch members 54 is provided by each latch member having two operating cylinders 60. Additionally, a number of fluid pumps may be provided for operating each cylinder 60, to provide further redundant capacity. However, in the event of a hydraulic failure preventing return stroking of the pistons 61 of the cylinder 60 (and thus retraction of the primary latch members 54), the horizontal component of the loading exerted by the canister 16 upon the primary latch members 54 will be sufficient to urge the latch members back towards their release positions. This provides for an emergency disconnect of the canister 16 in the event of hydraulic failure, facilitated by the inclined load faces 56 on the primary latch members 54. A further, optional feature of the present invention is shown and described in Figures 15, 16 and 17. Specifically, Figure 15 shows a front view of a locking arrangement for the primary latch members 54, the locking arrangement indicated generally by reference numeral 116. Each of the primary latch members 54 would be provided with a similar such locking arrangement 116. The locking arrangement 116 comprises two locking pins 118 which are moveable between release positions (Figures 15 and 16) and locking positions (Figure 17), to selectively lock the primary latch members 54 in their latching positions. Each locking pin 1 18 is biased by a respective spring 120 towards its locking position. The primary latch members 54 are located between upper and lower support plates 122 and 124, each of which includes a pair of apertures 126 and 128, respectively. The locking arrangement 116 includes a cylinder 130 having a piston 132 which acts against a carriage 134 coupled to each locking pin 118, and which serves for moving and (optionally) holding the locking pins 118 in their release positions.

As best shown in Figure 16, when in their release positions, the primary latch members 54 reside entirely within a space between the upper and lower support places 122 and 124, blocking the apertures 126 and 128. Following movement to their latching positions (Figure 17), the pins 118 are moved to their locking positions to lock the primary latch members 54 in their latching positions. This is achieved either by bleeding-off fluid from the cylinder 130, such that the springs 120 urge the pins 1 18 upwardly; or automatically through movement of the primary latch members 54 clearing the apertures 126, 128 so that the locking pins 118 snap up under the biasing force of the springs 120. When it is desired to release the canister 16 and thus return the primary latch members to their release positions, the piston 132 is actuated to move the carriage 134 down to the position of Figure 15, thereby retracting the locking pins 1 18. Mechanical, electro-mechanical or other means may be provided for returning the pins 118 to their release positions in the event of a hydraulic failure.

Various modifications may be made to the foregoing without departing from the spirit and scope of the present invention. For example, the primary latch mechanism and/or the temporary latch mechanism may be electro-mechanically, mechanically or electrically operated (or a combination thereof and/or fluidly operated) and thus may include suitable alternative actuators for moving the primary/temporary latch members between their release and latching positions. The locking arrangement for the primary latch members may be similarly alternatively operated.

The latching assembly may be arranged to urge the temporary latch members back to their release positions following release of the mooring element from the temporary latch members. For example, the mooring element may urge the temporary latch members back to their release positions when it is raised by the primary latch members. This may be achieved by providing a lip or the like with an inclined ramp or surface which comes into contact with the temporary latch members, optionally with their declined lower surfaces, to urge the latch members back to their release positions.

The fluid path connectors can be separate for each riser and umbilical and can be deployed without the use of the guide prongs, buckets and turntable.

The primary and/or temporary latch members may be of other suitable shapes.

A spider or other suitable spacer may be (temporarily) located within the inner gimbal during pull-in of the mooring element, to act as a guide both for the winch line and for the canister, and so as to centralise the canister within the gimbal.