GB2463569A - A brake assembly for an offshore vessel mooring and riser inboarding system - Google Patents

Abstract

A brake assembly is for an offshore vessel mooring and riser inboarding system (12, Fig 1) comprises a support structure 18, an outer gimbal member 36 rotatably coupled to the support structure and an inner gimbal member 40 rotatably coupled to and mounted within the outer gimbal member. The brake assembly 10 is disclosed which comprises a first brake arrangement 44a and 44b for restricting motion of the inner gimbal member of the system relative to the outer gimbal member of the system and a second brake arrangement 46a and 46b for restricting motion of the outer gimbal member relative to the support structure of the system. The first and second brake arrangements are each selectively actuable between a release configuration in which the brake arrangement allows substantially unrestricted motion of the respective gimbal member, and a braking configuration in which the brake arrangement restricts motion of the respective gimbal member. Also disclosed are an offshore vessel mooring and riser inboarding system incorporating the brake assembly, and associated methods.

Description

BRAKE ASSEMBLY FOR OFFSHORE VESSEL MOORING AND RISER

INBOARDING SYSTEM

The present invention relates to a brake assembly for an offshore vessel mooring and riser inboarding system, to an offshore vessel mooring and riser inboarding system incorporating the brake assembly, and to associated methods. In particular, but not exclusively, the present invention relates to a brake assembly for an offshore vessel mooring and riser inboarding system comprising a support structure, an outer gimbal member rotatably coupled to the support structure and an inner gimbal member rotatably coupled to and mounted within the outer gimbal member.

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-2006/03 7964 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.

It is amongst the objects of embodiments of the present invention to further improve upon systems known prior to the development of that disclosed in WO-2006/03 7964, and also to improve upon the system of WO-2006/037964 itself.

According to a first aspect of the present invention, there is provided a brake assembly for an offshore vessel mooring and riser inboarding system of a type having a support structure, an outer gimbal member rotatably coupled to the support structure and an inner gimbal member rotatably coupled to and mounted within the outer gimbal member, the brake assembly comprising: a first brake arrangement for restricting motion of the inner gimbal member relative to the outer gimbal member; and a second brake arrangement for restricting motion of the outer gimbal member relative to the support structure; wherein the first and second brake arrangements are each selectively actuable between a release configuration in which the brake arrangement allows substantially unrestricted motion of the respective gimbal member and a braking configuration in which the brake arrangement restricts motion of the respective gimbal member.

According to a second aspect of the present invention, there is provided a brake assembly for an offshore vessel mooring and riser inboarding system, the brake assembly comprising: a first brake arrangement for restricting motion of an inner gimbal member of the system relative to an outer gimbal member of the system, the inner gimbal member rotatably coupled to and mounted within the outer gimbal member; and a second brake arrangement for restricting motion of the outer gimbal member relative to a support structure of the system to which the outer gimbal member is rotatably coupled; wherein the first and second brake arrangements are each selectively actuable between a release configuration in which the brake arrangement allows substantially unrestricted motion of the respective gimbal member and a braking configuration in which the brake arrangement restricts motion of the respective gimbal member.

The brake assembly of the present invention may have a particular utility with an offshore vessel mooring and riser inboarding systems of the type disclosed in International patent application no PCT/GB2005/003 766 (published as WO- 2006/037964), the disclosure of which is incorporated herein in its entirety. In providing a brake assembly for an offshore vessel mooring and riser inboarding system of this type, the present invention may offer an ability to brake and thus restrain the gimbal members of the system against movement. This may provide numerous advantages including mitigating the effects of external loading on the gimbal members which may be experienced during transit and when the gimbals are unconstrained by any connection to a mooring system (via a floating canister or in other manner). Such loading may be caused by factors including: motion of the vessel; wave slam effects; and/or buoyancy effects when immersed, particularly in heavy sea-state/adverse weather conditions. In addition, the ability to prevent uncontrolled rotation of the gimbal members after release of a first mooring element from the system may provide important advantages. This is because the system incorporating the brake assembly of the present invention will typically include a riser flow path connector which provides, for example, for fluid connection between a vessel carrying the system and fluid risers, via suitable jumper flowlines. The connector is typically supported by and releasably coupled to the inner gimbal member, and may be separated from the inner gimbal member either before or after the mooring element (canister) is released. The brake assembly may therefore be actuated as soon as practicable following release of the canister, so as to seek to prevent undesired movement of the gimbal members which may otherwise occur due to any out-of-balance loading which may exist by provision of the fluid path connector on top of the inner gimbal ring.

The first brake arrangement may comprise at least one brake unit, and may comprise a plurality of brake units. The first brake arrangement may comprise at least one pair of (optionally opposed) brake units. The or each brake unit may be adapted to be mounted on one of the outer gimbal member and the inner gimbal member and to interact with the other one of the outer gimbal member and the inner gimbal member, respectively, so as to restrict motion of the inner gimbal member relative to the outer gimbal member. Where the first brake arrangement comprises a pair of brake units, or a plurality of pairs of brake units, the units in the or each pair may be provided on opposite sides of the one of the outer gimbal member and the inner gimbal member, and may be spaced approximately 1800 apart around a perimeter or circumference of the respective gimbal member.

The or each brake unit may be arranged to interact with the other one of the outer gimbal member and the inner gimbal member by gripping the respective gimbal member, and may thus be arranged to selectively grip the other one of the outer gimbal member and the inner gimbal member, so as to restrict motion of the inner gimbal member relative to the outer gimbal member. The or each brake unit may be arranged to grip the other one of the outer gimbal member and the inner gimbal member when the brake arrangement is actuated to the braking configuration.

Alternatively, the or each brake unit may be arranged to interact with the other one of the outer gimbal member and the inner gimbal member by locking the other one of the outer gimbal member and the inner gimbal member, and may comprise at least one locking element adapted to engage the other one of the outer gimbal member and the inner gimbal member. The locking element may be a pin, rod, bar, dog, key or the like and may be biased (for example, spring biased) for engagement with the other one of the outer gimbal member and the inner gimbal member. The locking element may be adapted to engage in a detent, such as a recess or slot or channel, formed on or in the other one of the outer gimbal member and the inner gimbal member. A number of detents may be provided to thereby provide a number of detent positions.

Providing a biased locking element may allow for release of the inner gimbal member in the event of a potential overload, and thus may permit slippage (movement) between the inner gimbal member and the outer gimbal member. A biasing force exerted on the locking element may be selected to be at a level or within a range which allows the locking element to be urged out of engagement with the detent on or in the other one of the outer gimbal member and the inner gimbal member, which may occur if the brake assembly experiences an unexpected load whilst the brake arrangements are in the braking configuration and which may otherwise cause damage to one or more component of the brake assembly and/or the system. The biasing force may be selected to be at such a level or within such a range by providing a biasing spring or the like with an appropriate spring force. Alternatively, the locking element may be shearable/frangible, or a housing for the detent may be provided having mountings which are shearable/frangible.

In the braking configuration of the first brake arrangement, the or each brake unit may be arranged so as to interact with said other one of the outer gimbal member and the inner gimbal member so as to restrict motion of the inner gimbal member relative to the outer gimbal member, and in the release configuration may be arranged so as not to interact with said other one of the outer gimbal member and the inner gimbal member (or any interaction may be minimal so as to avoid presenting a substantial restriction to motion of the inner gimbal member relative to the outer gimbal member).

The or each brake unit may comprise a pair of brake callipers, or a plurality of pairs of brake callipers, each calliper carrying at least one brake pad. The/each pair of callipers may be adapted to grip said other one of the outer gimbal member and the inner gimbal member to restrict motion of the inner gimbal member relative to the outer gimbal member. Said pair of brake callipers may be arranged to grip said other one of the outer gimbal member and the inner gimbal member when the first brake arrangement is in the braking configuration, and to release said other one of the outer gimbal member and the inner gimbal member when the first brake arrangement is in the release configuration. The callipers in the/each pair may be moveable towards and away from one another to respectively grip and release said other one of the outer gimbal member and the inner gimbal member. The first brake arrangement may comprise a brake element which may be adapted to be mounted on said other one of the outer gimbal member and the inner gimbal member, and the brake element may interact with the brake unit. The brake element may be mounted on a main body of the other one of the outer gimbal member and the inner gimbal member, or may be mounted on a trunnion or the like by which the inner gimbal member is rotatably coupled to the outer gimbal member. Where the brake unit comprises at least one pair of callipers, the brake element may comprise or may take the form of at least part of a brake disc which may, in use, be gripped by said calliper pair. Use of callipers/brake discs may be advantageous in that a degree of slippage may be allowed should the brake assembly experience an unexpected load whilst the brake arrangement is in the braking configuration, and which may otherwise cause damage to one or more component of the brake assembly and/or the system.

The second brake arrangement may comprise at least one brake unit, and may comprise a plurality of brake units. The second brake arrangement may comprise at least one pair of (optionally opposed) brake units. The or each brake unit may be adapted to be mounted on one of the support structure and the outer gimbal member and to interact with the other one of the support structure and the outer gimbal member, respectively, so as to restrict motion of the outer gimbal member relative to the support structure. Where the second brake arrangement comprises a pair of brake units, or a plurality of pairs of brake units, the units in the or each pair maybe provided on opposite sides of the outer gimbal member, and may be spaced approximately 1800 apart around a perimeter of circumference of the gimbal member.

The or each brake unit may be arranged to interact with the other one of the support structure and the outer gimbal member by gripping the other one of the support structure and the outer gimbal member, and may thus be arranged to selectively grip the other one of the support structure and the outer gimbal member, so as to restrict motion of the outer gimbal member relative to the support structure. The or each brake unit may be arranged to grip the other one of the support structure and the outer gimbal member when the brake arrangement is actuated to the braking configuration.

Alternatively, the or each brake unit may be arranged to interact with the other one of the support structure and the outer gimbal member by locking the other one of the support structure and the outer gimbal member, and may comprise at least one locking element adapted to engage the other one of the support structure and the outer gimbal member. The locking element may be a pin, rod, bar, dog, key or the like and may be biased (for example, spring biased) for engagement with the other one of the support structure and the outer gimbal member. The locking element may be adapted to engage in a detent, such as a recess or slot or channel, formed on or in the other one of the support structure and the outer gimbal member. A number of detents may be provided to thereby provide a number of detent positions. A biasing force exerted on the locking element may be selected to be at a level or within a range which allows the locking element to be urged out of engagement with the detent on or in the other one of the support structure and the outer gimbal member, which may occur if the brake assembly experiences an unexpected load whilst the brake arrangements are in the braking configuration. The biasing force may be selected to be at such a level or within such a range by providing a biasing spring or the like with an appropriate spring force. Alternatively, the locking element may be shearable/frangible, or a housing for the detent may be provided having mountings which are shearable/frangible.

In the braking configuration of the second brake arrangement, the or each brake unit may be arranged so as to interact with said other one of the support structure and the outer gimbal member so as to restrict motion of the outer gimbal member relative to the support structure, and in the release configuration may be arranged so as not to interact with said other one of the support structure and the outer gimbal member (or any interaction may be minimal so as to avoid presenting a substantial restriction to motion of the outer gimbal member relative to the support structure).

The or each brake unit may comprise a pair of brake callipers, or a plurality of pairs of brake callipers, each calliper carrying at least one brake pad. The/each pair of callipers may be adapted to grip said other one of the support structure and the outer gimbal member to restrict motion of the outer gimbal member relative to the support structure. Said pair of brake callipers may be arranged to grip said other one of the support structure and the outer gimbal member when the second brake arrangement is in the braking configuration, and to release said other one of the support structure and the outer gimbal member when the second brake arrangement is in the release configuration. The callipers in the/each pair may be moveable towards and away from one another to respectively grip and release said other one of the support structure and the outer gimbal member. The second brake arrangement may comprise a brake element which may be adapted to be mounted on said other one of the support structure and the outer gimbal member, and the brake element may interact with the brake unit. The brake element may be mounted on a trunnion or the like by which the outer gimbal member is rotatably coupled to the support structure, or may be mounted on a main body of the outer gimbal member or a structural component of the support structure. Where the brake unit comprises at least one pair of callipers, the brake element may comprise or may take the form of at least part of a brake disc which may, in use, be gripped by said calliper pair.

The first and/or second brake arrangements may be fluid actuated and may be hydraulically actuated. The first and/or second brake arrangements may be arranged to have a failsafe configuration which may be the release configuration (so as to failsafe release and allow the respective relative movement between the inner gimbal member and the outer gimbal member or between the outer gimbal member and the support structure), or which may be the braking configuration (so as to failsafe brake and restrict the respective relative movement between the inner gimbal member and the outer gimbal member or between the outer gimbal member and the support structure). The failsafe may be enabled by an appropriate arrangements of hydraulic pressure and/or mechanical or electromechanical components arranged in an appropriate fashion, and which may comprise a piston(s), spring(s) and/or motor(s).

It will be understood that, in the release configuration of the first and second brake arrangements, the brake arrangements may allow substantially unrestricted motion in that the brake units may present no restriction to motion whatsoever, or that they may present a sufficiently small restriction to motion (for example, through minor surface contact between the brake arrangements and the respective gimbal member/support structure) in relation to a turning moment and/or forces carried by the gimbals as to effectively present no restriction.

It will also be understood that the first and second brake arrangements may restrict motion in that they completely lock the gimbals/support structure against any relative movement, or (preferably) that they exert a force on the gimbals/support structure which is large enough so as to lock the gimbals/support structure in normal use and when a mooring element of the system is not connected to the gimbals (such as when in transit) other than when a sufficiently large force is exerted, whereupon slippage (for example) may occur.

The brake assembly of the present invention may be capable of easy and rapid activation and de-activation since, although it is desirable to restrain the gimbal members against uncontrolled rotation when the vessel is unconnected to a mooring element of the system, it is preferred that there be no such restraint once the mooring element (or other relevant member of the mooring system) has been picked up and connected, as such restraint may then induce high bending moments with associated stresses in the affected structures. For the same reason, it may be preferred that the brake assembly of the present invention be capable of slipping under overload.

According to a third aspect of the present invention, there is provided an offshore vessel mooring and riser inboarding system comprising: a support structure adapted to be mounted on a vessel; an outer gimbal member rotatably coupled to the support structure; an inner gimbal member rotatably coupled to and mounted within the outer gimbal member; and a brake assembly according to either of the first or second aspects of the present invention.

Further features of the brake assembly of the system of the third aspect of the present invention are defined above in relation to the first and/or second aspects of the invention.

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

According to a fifth aspect of the present invention, there is provided a method of selectively braking inner and outer gimbal members of an offshore vessel mooring and riser inboarding system, the method comprising the steps of: selectively actuating a first brake arrangement of a braking assembly for the system from: a release configuration in which the brake arrangement allows substantially unrestricted motion of an inner gimbal member of the system relative to an outer gimbal member of the system within which the inner gimbal member is mounted and to which the inner gimbal member is rotatably coupled; to: a braking configuration in which the brake arrangement restricts motion of the inner gimbal inember relative to the outer gimbal member; and selectively actuating a second brake arrangement of the braking assembly from: a release configuration in which the brake arrangement allows substantially unrestricted motion of the outer gimbal member relative to a support structure of the system to which the outer gimbal member is rotatably coupled; to: a braking configuration in which the brake arrangement restricts motion of the outer gimbal member relative to the support structure.

Actuating the first brake arrangement to the braking configuration may cause the brake arrangement to interact with one of the outer gimbal member and the inner gimbal member so as to restrict motion of the inner gimbal member relative to the outer gimbal member. The brake arrangement may be arranged to interact with the respective gimbal member by gripping the gimbal member. Alternatively, the first brake arrangement may be arranged to interact with one of the outer gimbal member and the inner gimbal member by locking the one of the outer gimbal member and the inner gimbal member relative to the other one of the gimbal members. Said one of the gimbal members may be locked to said other gimbal member using an at least one locking element which engages the respective gimbal member. The locking element may be moved into engagement in a detent, such as a recess or slot or channel, formed on or in the one of the outer gimbal member and the inner gimbal member which is to be locked relative to the other. A number of detents may be provided to thereby provide a number of detent positions.

Actuating the second brake arrangement to the braking configuration may cause the brake arrangement to interact with one of the outer gimbal member and the support structure so as to restrict motion of the outer gimbal member relative to the support structure. The brake arrangement may be arranged to interact with the outer gimbal member/support structure by gripping the outer gimbal member, or the support structure, as appropriate. Alternatively, the second brake arrangement may be arranged to interact with one of the outer gimbal member and the support structure by locking the one of the outer gimbal member and the support structure relative to the other one of the outer gimbal member and the support structure. Said outer gimbal member/support structure may be locked to said other one of the outer gimbal member and the support structure using an at least one locking element which engages the outer gimbal member/support structure. The locking element may be moved into engagement in a detent, such as a recess or slot or channel, formed on or in the one of the outer gimbal member/support structure which is to be locked relative to the other.

A number of detents may be provided to thereby provide a number of detent positions.

The first and/or second brake arrangements may be fluid actuated and may be hydraulically actuated. The method may comprise the step of setting a failsafe slippage pressure for the brake arrangements, to thereby apply a failsafe maximum braking force, and the failsafe pressure may be selected to be at or below a level at which the slippage between the inner gimbal member and the outer gimbal member, and/or between the outer gimbal member and the support structure (as appropriate), may safely occur.

The method maybe a method of disconnecting a vessel from a mooring element of the offshore vessel mooring and riser inboarding system, which may include braking the inner and outer gimbal members as described above, and which may comprise the further step of disconnecting the mooring element from the inner gimbal member to thereby disconnect the vessel. Braking will typically occur following disconnection of the mooring element from the inner gimbal member, or at substantially the same time.

According to a sixth aspect of the present invention, there is provided a method of disconnecting a vessel from a mooring element of an offshore vessel mooring and riser inboarding system and preparing the vessel for transit through an offshore environment, the vessel being connected to the mooring element through an inner gimbal member of the system, the method comprising the steps of: selectively actuating a first brake arrangement of a braking assembly for the system from: a release configuration in which the brake arrangement allows substantially unrestricted motion of an inner gimbal member of the system relative to an outer gimbal member of the system within which the inner gimbal member is mounted and to which the inner gimbal member is rotatably coupled; to: a braking configuration in which the brake arrangement restricts motion of the inner gimbal member relative to the outer gimbal member; and selectively actuating a second brake arrangement of the braking assembly from: a release configuration in which the brake arrangement allows substantially unrestricted motion of the outer gimbal member relative to a support structure of the system to which the outer gimbal member is rotatably coupled; to: a braking configuration in which the brake arrangement restricts motion of the outer gimbal member relative to the support structure; and disconnecting the mooring element from the inner gimbal member to thereby disconnect the vessel.

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 a brake assembly for an offshore vessel mooring and riser inboarding system, the vessel mooring and riser inboarding system itself, and of part of a vessel incorporating the system, in accordance with an embodiment of the present invention; Figure 2 is an enlarged view of the brake assembly shown in Figure 1 with parts of the vessel mooring and riser inboarding system removed; Figure 3 is an enlarged plan view of the brake assembly of Figure 1 with parts of the vessel mooring and riser inboarding system removed; and Figure 4 is an enlarged view of a protective cage for part of a brake alTangement of the brake assembly of Figure 1.

Turning firstly to Figure 1, there is shown a perspective view of a brake assembly 10 for an offshore vessel mooring and riser inboarding system 12, and of part of a vessel 14 incorporating the system 12, in accordance with an embodiment of the present invention. The vessel 14 takes the form of an FPSO, and only a bow 16 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 offiake tanker or a buffer tanker. The FPSO 14 will typically be for engagement in a life-of-field production procedure or an extended well test (EWT) procedure. The brake assembly is also shown in the enlarged view of Figure 2, and in the enlarged plan view of Figure 3, in which part of the vessel mooring and riser inboarding system 12 has been removed.

The offshore vessel mooring and riser inboarding system 12 generally comprises a support structure in the form of a cantilever connector assembly 18, a frame 20 of the connector assembly 18 being shown in Figure 1. The connector assembly 1 8 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 18 is mounted on the FPSO 14 in the region of the vessel bow 16. The system 10 also comprises a first mooring portion in the form of a tubular mooring canister 22, which is located in an offshore environment such as a sea or ocean 24. The mooring canister 22 is moored using a number of catenary mooring chains 26, which restrict rotation of the mooring canister 22 about its own axis. It will be understood that the catenary mooring chains 26 may comprise any suitable combination of chains and/or ropes.

The system 12 also comprises a second mooring portion indicated generally by reference numeral 28, and which comprises a fluid path connector 30, which is connected via jumpers 32a, 32b and 32c to a multi-path swivel 34. The second mooring portion 28 also comprises a rotatable coupling in the form of a swivel (not shown) including a bearing arrangement provided between the canister 22 and part of the connector assembly 1 8, which will be described in more detail below. The jumpers 32a, 32b and 32c provide for connection to respective risers 33a, 33b and 33c which are coupled to and pass up through the centre of the mooring canister 22.

Typically, the risers 33a to 33c will be arranged in a buoyant wave arrangement known in the art, to absorb movement of the risers 33a to 33c and to prevent damage to the risers at a touch down point on the seabed. The risers 33a to 33c are fluid flow risers for the flow of production fluids (oil and gas) from a number of subsea weliheads, production facilities or the like (not shown) to storage tanks (also not shown) on the FPSO 14. 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 14 downhole. Thus fluid may be transferred from the FPSO 14 down through the risers 33a to 33c. Electrical control lines or other lines or cables may be piggy-backed on or in the risers 33a to 33c.

The system 12 also includes an outer gimbal member in the form of a gimbal or gimbal ring 36 which is rotatably coupled to the cantilever connector assembly 18 via trunnions 38 (Figures 2 and 3). An inner gimbal member in the form of a gimbal or gimbal ring 40 is also provided, and is mounted within the outer gimbal 36 and rotatably coupled to the outer gimbal via trunnions 42 (Figure 3). The fluid path connector 30 is releasably mounted on the inner gimbal 40. A flared fairing 41 is also connected to the inner gimbal 40, and acts to guide the canister 22 into engagement within the gimbal 40, as will be described below.

As will be understood by the persons skilled in the art and from reading WO- 2006/03 7964, the mooring canister 22 is located in the ocean 24 and moored, for example, to a seabed (not shown), using the catenary mooring chains 26 and suitable anchors (also not shown). The arrangement of the mooring chains 26 and anchors restrict rotation of the mooring canister 22 about its axis under external loading. The FPSO 14 is moored to the mooring canister 22 through the frame 20 of the cantilever connector assembly 18, and the arrangement of the outer gimbal 36, inner gimbal 40 and the swivel. In this fashion, the FPSO 14 may move with three degrees of freedom relative to the mooring canister 22. Such movement may occur under external loading including wind, wave, tidal and/or current loading and allows for pitch, roll, heave and surge of the FPSO 14 relative to the mooring canister 22.

The brake assembly 10 of the present invention has a particular utility with offshore vessel mooring and riser inboarding systems such as the system 12 described above, and which systems include a support structure such as the cantilever connector assembly 18, outer gimbal 36 and inner gimbal 40. In particular and as noted above, when the FPSO 14 has been moored to the canister 22, relative movement between the FPSO and the canister is permitted by the outer gimbal 36, inner gimbal 40 and the swivel. This may involve movement of the outer gimbal 36 relative to the support frame 20; the inner gimbal 40 relative to the outer gimbal 36; and/or rotation of the FPSO 14 about the canister 22 (achieved by relative rotation between the inner gimbal and the canister 22 through the swivel).

In the absence of a connection with the mooring canister 22, such as occurs during transit of the FPSO 14 to the site where the FPSO is to be moored and indeed away from the site, the outer and inner gimbals 36 and 40 would be unconstrained. It is desired to prevent movement of the gimbals 36, 40 due to motion of the FPSO 14, due to wave slam effects and due to buoyancy effects on the gimbals should they be submerged during transit. Additionally and as will be described in more detail below, an out of balance condition can potentially occur following release of the mooring canister 22, due to the mounting of the fluid path connector 30 on the inner gimbal 40.

The brake assembly 10 of the present invention provides for the ability to restrict motion of the gimbal 36, 40 to thereby mitigate these disadvantages.

The brake assembly 10 generally comprises a first brake arrangement for restricting motion of the inner gimbal 40 relative to the outer gimbal 36, and which includes two brake units 44a, 44b. The brake assembly 10 also includes a second brake arrangement for restricting motion of the outer gimbal 36 relative to the support structure 18, in particular relative to the frame 20, and which includes two brake units 46a, 46b. The first and second brake arrangements are each selectively actuable between a release configuration in which the brake arrangements allow substantially unrestricted motion of the respective gimbal 36, 40; and a braking configuration in which the brake arrangements restrict motion of the respective gimbal 36, 40. Thus, when actuated and in the braking configuration, the brake units 44a, 44b of the first brake arrangement act to restrict motion of the inner gimbal 40 relative to the outer gimbal 36; and the brake units 46a, 46b of the second brake arrangement act to restrict motion of the outer gimbal 36 relative to the frame 20.

The structure and method of operation of the brake assembly 10 will now be described in more detail. Turning firstly to the first brake units 44a and 44b, each brake unit comprises a pair of callipers 48a and 48b carrying respective sets of brake pads 50a and SOb. The first brake units 44a, 44b are each mounted within an inner perimeter of the outer gimbal 36, and are located within a space 51 provided between the outer and inner gimbals 36, 40. Brake elements in the form of arcuate brake disk segments 52a and 52b are mounted on the inner gimbal 40, and extend towards the respective brake units 44a, 44b. The brake units 44a and 44b are arranged such that the pair of callipers 48a, 48b of each unit straddle the corresponding brake disk segment 52a, 52b. As can be seen particularly in the plan view of Figure 3, the brake disk segments 52a, 52b and the respective callipers 48a, 48b are arranged on an axis which is perpendicular to an axis of the trunnions 42 of the inner gimbal 40. In this fashion, and when the first brake arrangement is in the release configuration, the inner gimbal 40 can freely rotate relative to the outer gimbal 36, during which movement the brake disk segments 52a and 52b cycle back and forth between the corresponding callipers 48a and 48b. It will be noted that the brake disk segments 52a, 52b have a length which is selected to provide for a maximum expected degree of movement of the inner gimbal 40 relative to the outer gimbal 36 (under external loading) between opposite extremes of motion.

The brake units 46a and 46b of the second brake arrangement are each mounted on the frame 20 of the support structure 18. The brake unit 46a includes two pairs of callipers 54a and 54a', each of which carry respective sets 56a and 56a' of brake pads.

The brake unit 46b is of similar construction and thus will not be described herein; it will be noted that corresponding components to those of the brake unit 46a share the same reference numerals with the letters a and a' replaced by b and b', as appropriate.

The trunnions 38 of the outer gimbal 40 extend through bearings (not shown) provided in housings 58 on forward ends of the frame 20. Brake elements in the form of brake disks 60a, 60b are carried on the trunnions 38 corresponding to the brake unit 46a and 46b, respectively. Accordingly and in a similar fashion to the brake segments 52a and 52b, the brake disks 60a and 60b are received within the corresponding sets of callipers 54a, 54a' and 54b, 54b'.

On actuation of the brake units 44a and 44b of the first brake arrangement, the brake pads 50a and 50b of the sets of callipers 48a and 48b are urged towards one another, to clamp the respective brake disk segments 52a and 52b. In this fashion, further rotation of the inner gimbal 40 relative to the outer gimbal 36 about the trunnions 42 is restricted. The sets of callipers 48a and 48b are hydraulically operated and thus the callipers 50a, SOb are urged toward one another to clamp the brake disk segments 52a, 52b under applied fluid pressure. A hydraulic control line 62 for actuating the brake units 44a, 44b extends from a control station (not shown) on the FPSO 14, down a leg 64 of the frame 20 to the brake unit 46a. From there, the control line 62 extends to the brake units 44a and 44b. Although not illustrated, the control line 62 also extends to the second brake unit 46b (although a separate line may be provided for the unit 46b).

A clamping force applied by the calliper sets 48a, 48b on the disk segments 52a, 52b is dependent upon the fluid pressure force applied to the callipers, and thus ultimately upon the applied fluid pressure. The pressure force may be chosen to provide a clamping force which can be overcome by the inner gimbal 40 under extreme operating conditions, to thereby permit movement of the gimbal even when the first brake arrangement has been actuated. This may be desired, for example, to prevent damage to the brake assembly 10 and/or components of the mooring system 12. In particular, with the first brake arrangement in the braking configuration, the inner gimbal member 40 may experience an unexpectedly large external loading, such as an unexpectedly large wave slam or buoyancy effect. In such circumstances, it may be desired to allow slippage between the disk segments 52a, 52b and the respective sets of callipers 48a, 48b, as the forces may otherwise be sufficiently large so as to cause damage.

The brake units 46a, 46b of the second brake arrangement operate in a similar fashion to the brake units 44a, 44b. However, the brake units 46a and 46b are provided with the two sets of callipers 54a, 54a' and 54b and 54b' respectively. This enables a larger clamping force to be exerted upon the brake disks 60a and 60b than on the brake disk segments 52a and 52b for a common applied fluid pressure. This is because at least some of the external forces acting on the inner gimbal 40 (for example, buoyancy effects and wave slam) will be transferred to the outer gimbal 36.

Accordingly, the brake units 46a and 46b will typically be exposed to greater loading than the inner gimbal 40.

Approach, connection and disconnection of the FPSO 14 to the mooring canister 22 typically occurs as follows.

Prior to connection with the mooring canister 22, and whilst the FPSO 14 is transiting to the offshore site 24, the first and second brake arrangements of the brake assembly are actuated, and thus in the braking configurations described above. In these configurations, motion of the inner gimbal 40 relative to the outer gimbal 36, and of the outer gimbal 36 relative to the frame 20, are restricted. Also during transit, the fluid path connector 30 is disconnected from the inner gimbal 40 and stored in a safe location. Figures 2 and 3 show the brake assembly 10 with the fluid path connector disconnected. Four primary latch members 65 (three shown in Figure 2) and four temporary latch members 66 are provided for releasably engaging the canister 22.

The temporary latch members 66 are hydraulically operated and engage a profile on the canister 22 to temporarily support the canister. The primary latch members 65 are similarly hydraulically operated and, when actuated, engage in a race of the bearing on the canister 22, lifting the canister off the temporary latch members 66, which can then be retracted.

To connect to the canister 22, the FPSO 14 is positioned such that a head (not shown) of the canister is approximately below the fairing 41. Winch lines (not shown) can then be connected to the head of the canister 22, and the canister winched up and secured within the swivel. The fluid path connector 30 is then deployed on to the inner gimbal 40 (Figure 1) and secured in position using retractable, hydraulically operated arms 67, guide prongs 68 on the connector 30 stabbing into buckets 69 on a turntable 71 mounted on the inner gimbal 40. The first and second brake arrangements are then actuated to the release configurations; this occurs at an optimum, desired stage during connection with the mooring canister 22. Actuation to the release configuration may occur: prior to winching-up of the canister 22; as the head of the canister enters the fairing 41; following entry of the head of the canister into the fairing; or following full connection of the canister. Factors affecting the decision as to when to actuate the first and second brake arrangements to the release configurations may include the prevailing seastate and/or other weather conditions.

Following movement to the release configurations, unrestricted movement of the FPSO 14 relative to the canister 22 is allowed and accounted for by the outer gimbal 36, inner gimbal 40 and swivel.

Release of the canister 22 is achieved in reverse fashion, the brake arrangements remaining in their release configurations until the stage of disconnection and release of the canister 22, or shortly after disconnection and release. Once again, factors affecting the decision as to when to actuate the first and second brake arrangements to their braking configurations may include the prevailing seastate and/or other weather conditions. With the brake arrangements in their braking configurations, the fluid 1 5 path connector 30 can then safely be released from the inner gimbal 40, by releasing the primary latch members 65 and the temporary latch members 66 (if actuated), and then stowed.

The first and/or second brake arrangements can be arranged to have a failsafe configuration, which can be the release configuration (so as to failsafe release and allow the respective relative movement between the inner gimbal member 40 and the outer gimbal member 36, or between the outer gimbal member 36 and the support structure 18), or which may be the braking configuration (so as to failsafe brake and restrict the respective relative movement between the inner gimbal member 40 and the outer gimbal member 36 or between the outer gimbal member 36 and the support structure 18). The failsafe may be enabled by an appropriate arrangement of hydraulic pressure and/or mechanical or electromechanical components, arranged in an appropriate fashion.

Turning finally to Figure 4, there is shown a protective cage 70 for the brake unit 46a.

The cage 70 is mounted on a base structure 72 connected to the frame 20, and on which the brake unit 46a is also mounted. The protective cage 70 protects the components of the brake unit 46a against damage through inadvertent contact with objects such as, for example, the mooring canister 22 or other more permanent structures, such as may occur during docking of the FPSO 14. It will be understood that a similar cage (not shown) is provided for the brake unit 46b. The brake units 44a and 44b may also be provided with suitable protective cages. However, the location of the brake units 44a and 44b within the space 51 ensures that the gimbals 36 and 40 themselves provide a degree of protection for the units.

Various modifications made to the foregoing without departing from the spirit and scope of the present invention.

For example, the or each brake unit of the first brake arrangement may be arranged to interact with the other one of the outer gimbal member and the inner gimbal member by locking the other one of the outer gimbal member and the inner gimbal member, and may comprise at least one locking element adapted to engage the other one of the outer gimbal member and the inner gimbal member.

The or each brake unit of the second brake arrangement may be arranged to interact with the other one of the support structure and the outer gimbal member by locking the other one of the support structure and the outer gimbal member, and may comprise at least one locking element adapted to engage the other one of the support structure and the outer gimbal member.

The locking element may be a pin, rod, bar, dog, key or the like and may be biased (for example, spring biased). The locking element may be adapted to engage in a detent, such as a recess or slot or channel. A number of detents may be provided to thereby provide a number of detent positions. Providing a biased locking element may allow for release in the event of a potential overload, and thus may permit slippage (movement) between the inner gimbal member and the outer gimbal member or the outer gimbal member and the support structure, as appropriate. A biasing force exerted on the locking element may be selected to be at a level or within a range which allows the locking element to be urged out of engagement with the detent, which may occur if the brake assembly experiences an unexpected load whilst the brake arrangements are in the braking configuration and which may otherwise cause damage to one or more component of the brake assembly and/or the system. The biasing force may be selected to be at such a level or within such a range by providing a biasing spring or the like with an appropriate spring force. Alternatively, the locking element may be shearable/frangible, or a housing for the detent may be provided having mountings which are shearable/frangible.

Whilst the first brake arrangement is shown and described as comprising brake units provided on the outer gimbal member and brake elements on the inner gimbal member, this arrangement may be reversed. Additionally or alternatively, the brake arrangement may comprise at least one brake unit on the outer gimbal member and at least one on the inner gimbal member, and thus at least one corresponding brake element on the inner gimbal member and at least one on the outer gimbal member.

Whilst the second brake arrangement is shown and described as comprising brake units provided on the support structure and brake elements on the outer gimbal member, this arrangement may be reversed. Additionally or alternatively, the brake arrangement may comprise at least one brake unit on the outer gimbal member and at least one on the support structure, and thus at least one corresponding brake element on the support structure and at least one on the outer gimbal member.

Whilst a brake assembly for an offshore vessel mooring and riser inboarding system of a type comprising a support structure, an outer gimbal member rotatably coupled to the support structure and an inner gimbal member rotatably coupled to and mounted within the outer gimbal member is described herein, it will be understood that the present invention may be applicable to other types of system that incorporate gimbals.

It will be understood that the risers are primarily fluid flow risers for the transfer of fluid to and or from a vessel moored using the mooring and riser inboarding system.

However, the system/brake assembly of the present invention has a utility with other types of riser including power/control risers (which may comprise a bundle of electrical and/or hydraulic power and/or control cables).

Claims (32)

1. CLAIMS1. A brake assembly for an offshore vessel mooring and riser inboarding system, the brake assembly comprising: a first brake arrangement for restricting motion of an inner gimbal member of the system relative to an outer gimbal member of the system, the inner gimbal member rotatably coupled to and mounted within the outer gimbal member; and a second brake arrangement for restricting motion of the outer gimbal member relative to a support structure of the system to which the outer gimbal member is rotatably coupled; wherein the first and second brake arrangements are each selectively actuable between a release configuration in which the brake arrangement allows substantially unrestricted motion of the respective gimbal member and a braking configuration in which the brake arrangement restricts motion of the respective gimbal member.
2. 2. An assembly as claimed in claim 1, wherein the first brake arrangement comprises at least one brake unit which is adapted to be mounted on one of the outer gimbal member and the inner gimbal member and to interact with the other one of the outer gimbal member and the inner gimbal member, respectively, so as to restrict motion of the inner gimbal member relative to the outer gimbal member.
3. 3. An assembly as claimed in claim 2, wherein the first brake arrangement comprises at least one pair of opposed brake units which are spaced around 1800 apart around a perimeter of the respective gimbal member.
4. 4. An assembly as claimed in either of claims 2 or 3, wherein the or each brake unit is arranged to interact with the other one of the outer gimbal member and the inner gimbal member by gripping the respective gimbal member.
5. 5. An assembly as claimed in either of claims 2 or 3, wherein the or each brake unit is arranged to interact with the other one of the outer gimbal member and the inner gimbal member by locking the other one of the outer gimbal member and the inner gimbal member against movement.
6. 6. An assembly as claimed in claim 5, wherein the or each brake unit comprises at least one locking element adapted to engage in a detent formed in the other one of the outer gimbal member and the inner gimbal member.
7. 7. An assembly as claimed in claim 6, wherein the at least one locking element is biased for engagement with the other one of the outer gimbal member and the inner gimbal member, to permit release of the inner gimbal member in the event of a potential overload.
8. 8. An assembly as claimed in claim 6, wherein the at least one locking element is frangible.
9. 9. An assembly as claimed in any one of claims 2 to 8, wherein the or each brake unit comprises at least one pair of brake callipers, the pair of callipers adapted to grip said other one of the outer gimbal member and the inner gimbal member.
10. 10. An assembly as claimed in any one of claims 2 to 9, wherein the first brake arrangement comprises a brake element which is adapted to be mounted on said other one of the outer gimbal member and the inner gimbal member, and wherein the brake element is arranged to interact with the brake unit.
11. 11. An assembly as claimed in claim 10, wherein the brake element is adapted to be mounted on a main body of the other one of the outer gimbal member and the inner gimbal member.
12. 12. An assembly as claimed in any preceding claim, wherein the second brake arrangement comprises at least one brake unit, which is adapted to be mounted on one of the support structure and the outer gimbal member and to interact with the other one of the support structure and the outer gimbal member, respectively, so as to restrict motion of the outer gimbal member relative to the support structure.
13. 13. An assembly as claimed in claim 12, wherein the second brake arrangement comprises at least one pair of opposed brake units which are spaced around 1800 apart around a perimeter of the gimbal member.
14. 14. An assembly as claimed in either of claims 12 or 13, wherein the or each brake unit is arranged to interact with the other one of the support structure and the outer gimbal member by gripping the other one of the support structure and the outer gimbal member.
15. 15. An assembly as claimed in any one of claims 12 to 14, wherein the or each brake unit is arranged to interact with the other one of the support structure and the outer gimbal member by locking the other one of the support structure and the outer gimbal member.
16. 16. An assembly as claimed in claim 15, wherein the or each brake unit comprises at least one locking element adapted to engage a detent fonned in the other one of the support structure and the outer gimbal member.
17. 17. An assembly as claimed in any one of claims 12 to 16, wherein the or each brake unit comprises at least one pair of brake callipers, the pair of callipers adapted to grip said other one of the support structure and the outer gimbal member to restrict motion of the outer gimbal member relative to the support structure.
18. 18. An assembly as claimed in any one of claims 12 to 17, wherein the second brake arrangement comprises a brake element which is adapted to be mounted on said other one of the support structure and the outer gimbal member, and wherein the brake element interacts with the brake unit.
19. 19. An assembly as claimed in claim 18, wherein the brake element is adapted to be mounted on a trunnion by which the outer gimbal member is rotatably coupled to the support structure.
20. 20. An assembly as claimed in any preceding claim, wherein the first and second brake arrangements are fluid actuated and arranged to have a failsafe release configuration so as to failsafe release and allow the respective relative movement between the inner gimbal member and the outer gimbal member, and the outer gimbal member and the support structure.
21. 21. An offshore vessel mooring and riser inboarding system comprising: a support structure adapted to be mounted on a vessel; an outer gimbal member rotatably coupled to the support structure; an inner gimbal member rotatably coupled to and mounted within the outer gimbal member; and a brake assembly; wherein the brake assembly comprises: * a first brake arrangement for restricting motion of the inner gimbal member relative to the outer gimbal member; and * a second brake arrangement for restricting motion of the outer gimbal member relative to the support structure; * wherein the first and second brake arrangements are each selectively actuable between a release configuration in which the brake arrangement allows substantially unrestricted motion of the respective gimbal member and a braking configuration in which the brake arrangement restricts motion of the respective gimbal member.
22. 22. A system as claimed in claim 21, wherein the brake assembly is a brake assembly as claimed in any one of claims 2 to 20.
23. 23. A vessel comprising an offshore vessel mooring and riser inboarding system as claimed in either of claims 21 or 22.
24. 24. A method of selectively braking inner and outer gimbal members of an offshore vessel mooring and riser inboarding system, the method comprising the steps of: selectively actuating a first brake arrangement of a braking assembly for the system from: a release configuration in which the brake arrangement allows substantially unrestricted motion of an inner gimbal member of the system relative to an outer gimbal member of the system within which the inner gimbal member is mounted and to which the inner gimbal member is rotatably coupled; to: a braking configuration in which the brake arrangement restricts motion of the inner gimbal member relative to the outer gimbal member; and selectively actuating a second brake arrangement of the braking assembly from: a release configuration in which the brake arrangement allows substantially unrestricted motion of the outer gimbal member relative to a support structure of the system to which the outer gimbal member is rotatably coupled; to: a braking configuration in which the brake arrangement restricts motion of the outer gimbal member relative to the support structure.
25. 25. A method as claimed in claim 24, wherein actuating the first brake arrangement to the braking configuration causes the brake arrangement to grip the respective gimbal member.
26. 26. A method as claimed in claim 24, wherein actuating the first brake arrangement to the braking configuration causes the brake arrangement to lock the respective gimbal member relative to the other one of the gimbal members.
27. 27. A method as claimed in any one of claims 24 to 26, wherein actuating the second brake arrangement to the braking configuration causes the brake arrangement to grip the one of the outer gimbal member and the support structure.
28. 28. A method as claimed in any one of claims 24 to 26, wherein actuating the second brake arrangement to the braking configuration causes the brake arrangement to lock the one of the outer gimbal member and the support structure relative to the other one of the outer gimbal member and the support structure.
29. 29. A method as claimed in any one of claims 24 to 28, wherein the first and second brake arrangements are fluid actuated and the method comprises the step of setting a failsafe slippage pressure for the brake arrangements, to thereby apply a failsafe maximum braking force.
30. 30. A method as claimed in claim 29, wherein the failsafe pressure is selected to be at or below a level at which slippage between the inner gimbal member and the outer gimbal member, and between the outer gimbal member and the support structure, can occur.
31. 31. A method as claimed in any one of claims 24 to 30, wherein the method is a method of disconnecting a vessel from a mooring element of the offshore vessel mooring and riser inboarding system, and which comprises the further step of disconnecting the mooring element from the inner gimbal member following braking of the inner and outer gimbal members.
32. 32. A method of disconnecting a vessel from a mooring element of an offshore vessel mooring and riser inboarding system and preparing the vessel for transit through an offshore environment, the vessel being connected to the mooring element through an inner gimbal member of the system, the method comprising the steps of: selectively actuating a first brake arrangement of a braking assembly for the system from: a release configuration in which the brake arrangement allows substantially unrestricted motion of an inner gimbal member of the system relative to an outer gimbal member of the system within which the inner gimbal member is mounted and to which the inner gimbal member is rotatably coupled; to: a braking configuration in which the brake arrangement restricts motion of the inner gimbal member relative to the outer gimbal member; and selectively actuating a second brake arrangement of the braking assembly from: a release configuration in which the brake arrangement allows substantially unrestricted motion of the outer gimbal member relative to a support structure of the system to which the outer gimbal member is rotatably coupled; to: a braking configuration in which the brake arrangement restricts motion of the outer gimbal member relative to the support structure; and disconnecting the mooring element from the inner gimbal member to thereby disconnect the vessel.