Patent Description:
The present invention relates generally to disconnectable mooring systems for floating vessels, and more particularly to disconnectable spread mooring systems and riser tower systems for vessels moored on location to load fluids, such as hydrocarbons, from subsea pipelines and risers.

This invention relates to disconnectable mooring systems to moor floating vessels to load or unload one or more products from the moored vessels. Typically, the floating vessels are tankers, and particularly floating storage offloading ("FSO") vessels, and floating production, storage and offloading ("FPSO") vessels.

Various types of mooring systems to secure a floating vessel on location in a body of water are known in the art. A representative disconnectable turret mooring system, illustrated in <FIG>, includes two basic parts-a geostationary buoy that is detachably connectable to a turret assembly of a floating vessel. The floating vessel carries the turret assembly which is rotatably disposed within the vessel hull and which opens to the sea near the elevation of the keel of the vessel. The geostationary buoy is moored to the seafloor by a number of anchor legs. The turret assembly includes a hydraulically-actuated mechanical connector designed and arranged to disconnectably mate with a connector element or hub located on the geostationary buoy.

The disconnectable turret mooring arrangement provides a fluid flow path between a subsea well, pipeline or component and the floating vessel when the vessel is moored to the geostationary buoy. A fluid transfer system ("FTS") includes a flexible conductor or riser, as shown in <FIG>, spanning the distance between the seafloor and the geostationary buoy. Other piping and a fluid swivel on the vessel is used to complete the connection between the riser and the system on the vessel. In this turret mooring system, the floating vessel is allowed to freely weathervane about the geostationary turret in response to wind, waves and currents. When the geostationary buoy is completely separated from the floating vessel, the buoy is designed and arranged to sink to a neutrally buoyant position, typically about <NUM> meters below sea level, and the vessel can leave the location.

Typically, the floating vessel moors to the geostationary buoy by first recovering the submerged buoy upwards to the structural connector of the turret assembly using a retrieval line with a winch system. The structural connector is then locked into engagement with the connector hub which moors the floating vessel to the seafloor.

A representative disconnectable tower yoke mooring system with jumpers for a shallow water application is illustrated in <FIG>. The tower yoke mooring system includes a jacket structure fixed to the seafloor. One or more decks are mounted on the jacket structure in addition to a turntable. A yoke has one end releasably connected to a yoke head pivotably attached to the turntable and a second end connecting with a mooring support structure mounted on the floating vessel. The yoke and yoke head each have a mating connector portion arranged and designed to connect the yoke to the yoke head. When the connector portions are engaged and locked, the yoke is securely attached to the yoke head, allowing a rigid interconnection between the floating vessel and tower structure. When the yoke is connected to the yoke head, the floating vessel is allowed to weathervane about the jacket structure. Riser piping extends from the seafloor to the jacket deck and connects to fluid jumpers or hoses which span between the jacket deck and the floating vessel. Electrical jumpers may also span between the jacket deck and the vessel. In the event of predicted abnormally high sea states, the yoke may be disconnected from the yoke head and secured to the floating vessel and the vessel removed prior to the abnormally high sea state event. Assignee's <CIT> discloses a disconnectable tower yoke mooring system.

A representative spread mooring system, shown in <FIG>, includes a plurality of anchor legs extending from the bow and stern of the floating vessel to the seafloor. The anchor legs are typically chain or wire, or a combination of chain and wire. An anchor is typically attached to the seafloor-end of the anchor leg and the vessel-end of the anchor leg is arranged and designed to be connected to a chain stopper assembly on the vessel. The spread mooring system is commonly utilized in an area with directional environments. In the conventional spread mooring system, the anchor legs must be retrieved onto the floating vessel or released to the seafloor in order for the vessel to move off location.

Another disconnectable mooring system is disclosed in <CIT>, which discloses a vessel (<NUM>) that includes at least two anchor lines (<NUM>,<NUM>) having a first end connected to winches (<NUM>,<NUM>), respectively, that are located near the bow (<NUM>) and near the stern (<NUM>) of the vessel (<NUM>). A second end of the anchor lines (<NUM>,<NUM>) are connected to counterweights (<NUM>,<NUM>), respectively, which are connected to the seabed by means of chains or cables (<NUM>, <NUM>), respectively. The stiffness of the mooring system can be adjusted by changing the weight of the counterweights (<NUM>,<NUM>) or by changing the length of the anchor lines (<NUM>,<NUM>) by paying out or pulling in the anchor lines (<NUM>,<NUM>) via the winches (<NUM>,<NUM>).

Hurricane or typhoon or cyclone waves can present significant risks and challenges to spread mooring systems, particularly in shallow water. Retrieval of the anchor legs requires substantial time and effort, in addition to substantial time and effort in placing the anchor legs when moving back on location after the inclement weather has passed.

It is desirable to have a mooring system that can be disconnected and reconnected efficiently. It is further desirable to have a mooring system that can be disconnectable in high sea states.

Disconnectable spread mooring systems for a vessel having a bow and a stern floating at a water surface and methods for disconnecting vessels therefrom are provided. The disconnectable spread mooring assembly includes a forward chain table assembly releasably connected to the vessel at the bow and an aft chain table assembly releasably connected to the vessel at the stern. Each of the forward and aft chain table assemblies include one or more buoyancy compartments and the forward and aft chain table assemblies are arranged and designed to float at or near the water surface when disconnected from the vessel. The assembly also includes a plurality of bow mooring legs having first ends attached to the forward chain table assembly and having second ends capable of being anchored at spaced locations on a seafloor. The assembly also include a plurality of stern mooring legs having first ends attached to the aft chain table assembly and having second ends capable of being anchored at spaced locations on the seafloor. The assembly also includes a first connector assembly connecting the forward chain table assembly to the vessel at the bow and a second connector assembly connecting the aft chain table assembly to the vessel at the stern. The first and second connector assemblies are arranged and designed to unlock and release the forward and aft chain table assemblies from the vessel. The assembly also includes a first tie-back hawser or chain, or combination of hawser and chain, connected to the forward chain table assembly and a second tie-back hawser or chain, or combination of hawser and chain, connected to the aft chain table assembly. The assembly also includes one or more fixed jacket structures fixed to the seafloor. The first and second tie-back hawsers or chains, or combinations of hawser and chain, are arranged and designed to connect to the one or more fixed jacket structures when the forward and aft chain table assemblies float at or near the water surface.

A method for disconnecting a vessel having a bow and a stern floating at a water surface from a disconnectable spread mooring assembly at a moored location, the disconnectable spread mooring assembly including a plurality of bow mooring legs anchored at spaced locations on a seafloor and connected to a forward chain table assembly connected to the vessel at the bow, and a plurality of stern mooring legs anchored at spaced locations on the seafloor and connected to an aft chain table assembly connected to the vessel at the stern, where each of the forward and aft chain table assemblies includes one or more buoyancy compartments and the forward and aft chain table assemblies are arranged and designed to float at or near the water surface when disconnected from the vessel, the method comprising the steps of: unlocking a first connector assembly securing the forward chain table assembly to the vessel. The method also includes releasing the forward chain table assembly from the first connector assembly. The method also includes unlocking a second connector assembly securing the aft chain table assembly to the vessel. The method also includes releasing the aft chain table assembly from the second connector assembly. The method also includes attaching a first tie-back hawser or chain, or combination of hawser and chain to the forward chain table assembly. The method also includes attaching a second tie-back hawser or chain, or combination of hawser and chain to the aft chain table assembly. The method also includes connecting the first and second tie-back hawsers or chains, or combinations of hawser and chain to one or more fixed jacket structures fixed to the seafloor, where the forward and aft chain table assemblies float at or near the water surface. The method also includes moving the vessel to another location with the forward and aft chain table assemblies and pluralities of bow and stern mooring legs remaining at the moored location.

The invention is better understood by reading the detailed description of embodiments which follows and by examining the accompanying drawings, in which:.

The preferred embodiments of the present invention will now be discussed with reference to the drawings. The preferred embodiments are a disconnectable spread mooring and riser tower system for a floating vessel V for abnormally high sea areas, such as hurricane/typhoon/cyclone wave applications, particularly in shallow water. <FIG> and <FIG> show a preferred embodiment of the disconnectable spread mooring and riser tower system, referred to generally as <NUM>, mooring a vessel V. The disconnectable spread mooring and riser tower system <NUM> includes a disconnectable spread mooring system <NUM> and a riser tower system <NUM>.

The disconnectable spread mooring system <NUM> comprises a plurality of mooring or anchor legs <NUM> extending from the bow of the vessel V to the seafloor F and a plurality of mooring or anchor legs <NUM> extending from the stern of the vessel V to the seafloor F. The anchor legs <NUM>, <NUM> may include lengths of chain or wire or combinations of chain and wire, and include an anchor.

<FIG> shows a quantity of eight bow anchor legs <NUM> and eight stern anchor legs <NUM>, however, different numbers of anchor legs may be used. As shown in <FIG>, four of the bow anchor legs <NUM> are placed forward of the vessel V to the starboard side (right side looking forward) and four of the bow anchor legs <NUM> are placed forward of the vessel V to the port side (left side looking forward). Similarly, four of the stern anchor legs <NUM> are placed rearward of the vessel V to the starboard side and four of the stern anchor legs <NUM> are placed rearward of the vessel V to the port side. Preferably, the lengths of anchor legs <NUM>, <NUM> are initially placed using tug boats or work boats. It is to be understood that the placement, orientation, quantity and length of the anchor legs <NUM>, <NUM> are dependent on numerous factors which are not limiting of the scope of the claimed invention.

Referring to <FIG>, one end of each of the bow anchor legs <NUM> is connected to a forward disconnectable chain table assembly <NUM> and one end of each of the stern anchor legs <NUM> is connected to an aft disconnectable chain table assembly <NUM>. The disconnectable chain table assemblies <NUM>, <NUM> are similar to one another and may be identical. The disconnectable chain table assemblies <NUM>, <NUM> include one or more buoyancy compartments that can be arranged and designed to float at or near the water surface when disconnected from the vessel, as described below with reference to the forward and aft chain table assemblies <NUM>", <NUM>".

Referring to <FIG>, the riser tower system <NUM> comprises a jacket structure <NUM>, or a tower, affixed to the seafloor F, typically via piling. The riser tower system <NUM> includes a plurality of decks <NUM> mounted on the jacket structure <NUM> at various elevations above the water level L, typically mean water level. It is to be understood by those of skill in the art that the decks <NUM> are arranged and designed to support various equipment, for example, a manifold, piping, hoses, J-boxes and jumper pull-in equipment. One or more risers <NUM> connect with subsea piping, a subsea well or other subsea component and are attached to the jacket structure <NUM>. The risers <NUM> may be connected to a manifold or other equipment on the decks <NUM>.

In the embodiment shown in <FIG> and <FIG>, a jumper support structure <NUM> is installed on the deck of the vessel V adjacent one side (port or starboard). In <FIG>, the jumper support structure <NUM> is located along a mid-section of the vessel V. It is to be understood that the location of the jumper support structure <NUM> may be located elsewhere on the vessel V. For example, it can be located at the bow area (or stern area) of the vessel V as shown in the alternative arrangement of <FIG>.

As shown in <FIG>, the jumper support structure <NUM> preferably includes one or more decks arranged and designed to support piping, J-boxes, and jumper pull-in equipment. During normal operation with the vessel V moored near the riser tower system <NUM> via the connected chain table assemblies <NUM>, <NUM> and anchor legs <NUM>, <NUM>, one or more flexible jumper hoses and/or umbilicals <NUM> are utilized between at least one riser tower deck <NUM> and the vessel jumper support structure <NUM> with connectors to transfer fluids, air, power and control signals, etc..

<FIG> illustrates the portion of the disconnectable spread mooring system <NUM> at the bow of the vessel V in a preferred embodiment. It is to be understood that the following description is also applicable to the portion of the disconnectable spread mooring system <NUM> at the stern. Each disconnectable chain table assembly <NUM>, <NUM> includes a chain table structure <NUM> preferably having a chain stopper <NUM> to which one end of the anchor legs <NUM>, <NUM> is attached. The chain table structure <NUM> may be a generally box-shape or cylindrical shape with plates, stiffeners or frame with bracing. <FIG> is a plan view of a chain table structure <NUM> with a plurality of chain stoppers <NUM> and connected anchor legs <NUM> and an upper connector hub <NUM>. In certain chain table assembly embodiments, at least a portion of the cross-sectional area of the bottom of the chain table assembly <NUM>, <NUM> includes a plate member or mudmat <NUM> (<FIG>). As noted above, the chain table assembly <NUM>, <NUM> additionally have one or more buoyancy compartments as discussed below in conjunction with other embodiments of the invention.

With reference to <FIG> and <FIG>, the floating vessel V preferably includes a forward chain table support structure <NUM> extending forward of the vessel hull and an aft chain table support structure <NUM> extending rearward of the vessel hull. As shown in <FIG>, each chain table support structure <NUM>, <NUM> includes a connector assembly <NUM>, preferably hydraulically-powered, arranged and designed to engage the connector device or hub <NUM> of the disconnectable chain table assemblies <NUM>, <NUM>. Such connector assemblies <NUM> are well known in the art. Preferably, the connector hub <NUM> is located at or near the upper end of the disconnectable chain table assembly <NUM>, <NUM>.

A representative connector assembly <NUM> is shown latched or engaged in <FIG>. The representative connector assembly <NUM> shown is a hydraulically-actuated collet connector assembly. The connector assembly <NUM> is positioned inside of the chain table support structure <NUM>. The hydraulic connector assembly <NUM> has a stationary housing <NUM> mounted within the chain table support structure <NUM>. The stationary housing <NUM> is preferably a substantially cylindrical housing having a bore <NUM> therethrough. The stationary housing <NUM> includes an outwardly facing shoulder <NUM> and an extension or projection <NUM>. One or more spaced apart fingers or collet segments <NUM> can be disposed about the housing <NUM> between the shoulder <NUM> and the projection <NUM>. The outwardly facing shoulder <NUM> can be adjacent to and in contact with the fingers <NUM>.

The hydraulic connector assembly <NUM> may include a movable sleeve <NUM> disposed about the housing <NUM>. The movable sleeve <NUM> can have an inwardly directed flange 60f at one end and a band 60b at an opposite end. The band 60b can be adjacent to and configured to contact the one or more fingers <NUM>. Linear movement of the sleeve <NUM> in a first direction (downward) allows the fingers <NUM> to rotate or pivot to a closed or locked position as shown in <FIG> and linear movement of the sleeve <NUM> in an opposite, second direction (upward) allows the fingers <NUM> to rotate or pivot about the outer surface of the housing <NUM> to an open or unlocked position.

One or more actuators <NUM> may be used to move the sleeve <NUM> about the outer surface of the housing <NUM>, allowing the fingers <NUM> to rotate or pivot open and close. The one or more actuators <NUM> can be positioned between and connected to the inwardly directed flange 60f of the movable sleeve <NUM> and the outwardly facing shoulder <NUM> of the stationary housing <NUM>. The actuator(s) <NUM> can be hydraulic or pneumatic and are preferably hydraulic cylinders. When more than one actuator <NUM> is used, the actuators <NUM> are controlled by a singular control to provide simultaneous operation and movement of the sleeve <NUM>. The actuators <NUM> can be actuated from the vessel V by accumulators and telemetry-controlled valves. Accumulators and telemetry-controlled valves are well known to those skilled in the art.

Still referring to <FIG>, a mating hub <NUM> of the hydraulic connector assembly <NUM> is mounted to the chain table assembly <NUM>. Preferably, the mating hub <NUM> is an annular member having a bore <NUM> extending therethough. The mating hub <NUM> may include a recessed section or receptacle <NUM> sized and shaped to receive the projection <NUM> on the assembly housing <NUM>. The mating hub <NUM> may also include a notched or profiled outer surface <NUM>. The profiled outer surface <NUM> is configured to engage and hold a similarly contoured profile disposed on the fingers <NUM> such that when the fingers <NUM> rotate or pivot to their locked or closed position, the shaped profiles located on the fingers <NUM> and the profiled outer surface <NUM> of the mating hub <NUM> matingly engage one other, as depicted in <FIG>.

<FIG> shows the hydraulic connector assembly <NUM> engaged with the mating hub <NUM>. The actuators <NUM> have moved the moveable sleeve <NUM> in the downward direction, with the band 60b pushing the fingers <NUM> to rotate or pivot inwardly (toward the outer surface of the housing <NUM>), such that the fingers <NUM> engage the recessed profile <NUM> of the mating hub <NUM>. In this closed position, the fingers <NUM> are generally parallel to the bore <NUM> of the housing <NUM> and overlap the profiled outer surface on the mating hub <NUM>, forming a lock and key engagement therebetween. Also in this closed position, the projection <NUM> on the housing <NUM> can be located within the receptacle <NUM> of the mating hub <NUM>. With the fingers <NUM> forcibly inserted in the mating hub recess <NUM>, the chain table assembly <NUM>, <NUM> is securely connected to the chain table support structure <NUM>, <NUM>. Preferably, secondary mechanical locks (not shown) in line with the actuators <NUM> keep the connector locked without the need of hydraulic pressure. Secondary mechanical locks may be interference sleeve locks such as the Bear-Loc™ locking device, manufactured by Wellman Dynamics Machining and Assembly Inc. of York, Pa.

Preferably, each chain table support structure <NUM>, <NUM> includes a pull-in or winch assembly <NUM> (<FIG>), such as a traction winch assembly, for lowering and retrieving the disconnectable chain table assembly <NUM>, <NUM>, as will be described below. It is to be understood that the pull-in assembly is intended to include any combination of winches, hydraulic cylinder, chain jack, strand jack or other pulling mechanism well known to those of skill in the art.

In the preferred embodiment, an alignment pin assembly <NUM> is provided to maintain the proper alignment of the disconnectable chain table assemblies <NUM>, <NUM> with the vessel V, as shown in <FIG>. The alignment pin assembly <NUM> prevents rotation of the disconnectable chain table assemblies <NUM>, <NUM> relative to the floating vessel V when the disconnectable chain table assemblies <NUM>, <NUM> are connected to the connector assembly <NUM>. It is to be understood that the alignment pin assembly <NUM> can take many forms well known in the art. For example, the alignment pin assembly <NUM> could be a pin extending downwardly from the chain table support structure <NUM>, <NUM> which is arranged and designed to be received in a receiver at the upper end of the disconnectable chain table assembly <NUM>, <NUM>.

As stated above, the present invention provides a mooring system that can be disconnected efficiently and in high sea states. This is accomplished, in part, in certain embodiments of the present invention by disconnecting and lowering the forward and aft disconnectable chain table assemblies <NUM> and <NUM> away from the vessel V. <FIG> illustrates a sequence of steps (not in accordance with claim <NUM> or claim <NUM>) in disconnecting and lowering the forward disconnectable chain table assembly <NUM> to the seafloor F. It is to be understood that the same sequence of steps applies to disconnecting and lowering the aft disconnectable chain table assembly <NUM>.

A retrieval rope <NUM> has one end connected to the forward disconnectable chain table assembly <NUM>, and a second end connected to the winch line <NUM> of the winch assembly <NUM>. Preferably, a tag line with a surface buoy <NUM> is also attached to the retrieval line <NUM>. The connector assembly <NUM> is activated to its unlocked position and the load of the forward disconnectable chain table assembly <NUM> with the connected bow mooring legs <NUM> is transferred to the winch assembly <NUM>. The winch assembly <NUM> then lowers the disconnected chain table assembly <NUM>. The winch line <NUM> is disconnected from the retrieval rope <NUM> and returned to the vessel. The mudmat <NUM> at the bottom of the disconnectable chain table assembly <NUM> (not in accordance with claim <NUM> or claim <NUM>) rests on the seafloor F and creates a suction with the seafloor F providing stability. Preferably, the chain stoppers <NUM> and connector hub <NUM> are located above the mudline as shown in <FIG>.

The sequence of steps involved in moving the moored vessel V off location from the spread mooring and riser tower system arrangement <NUM>, as shown in <FIG>, will now be described. Initially and before mooring leg disconnection, all the jumper hoses and cables <NUM> spanning between the riser tower decks <NUM> and the jumper support structure <NUM> of the vessel V (see <FIG> and <FIG>) are disconnected and pulled onto the vessel V or onto the riser tower <NUM> as shown in <FIG>.

Preferably, the aft disconnectable chain table assembly <NUM> with stern mooring legs <NUM> is disconnected first during the mooring leg disconnection. Upon lowering the aft disconnectable chain table assembly <NUM> , the vessel V swings away from the riser tower <NUM> a safe distance, preferably via its thruster at the stern, as shown in <FIG>. The forward disconnectable chain table assembly <NUM> with bow mooring legs <NUM> is then disconnected from the vessel V as described above. After all the disconnections, the vessel V can sail away to a safe harbor leaving behind the disconnectable spread mooring system <NUM> and the riser tower system <NUM>. It is to be understood that alternatively the forward disconnectable chain table assembly <NUM> with bow mooring legs <NUM> may be disconnected first, in which case the vessel V would then swing away from the riser tower <NUM> a safe distance, preferably via a thruster at the bow, and lastly the aft disconnectable chain table assembly <NUM> with stern mooring legs would be disconnected.

The present invention also provides for efficiently reconnecting the disconnectable spread mooring system <NUM> upon the vessel V returning to the location. <FIG> shows a sequence of steps in retrieving the forward disconnectable chain table assembly <NUM> and reconnecting it to the vessel V. It is to be understood that the same sequence of steps applies to retrieving and reconnecting the aft disconnectable chain table assembly <NUM>.

The surface buoy and tag line <NUM> are used to locate the forward disconnectable chain table assembly <NUM> and the winch line <NUM> is connected to the retrieval rope <NUM>, which is connected to the forward disconnectable chain table assembly <NUM>. Preferably, the tag line with the surface buoy <NUM> is retrieved to the vessel V. The winch assembly <NUM> draws in the winch line <NUM> and raises the disconnectable chain table assembly <NUM> along with the connected ends of the bow anchor legs <NUM>. With the connector assembly <NUM> in its unlocked position, the alignment pin <NUM> stabs into the receiver and the connector hub <NUM> is received in the connector assembly <NUM>. The connector assembly <NUM> is then locked to retain the connector hub <NUM> and the forward disconnectable chain table assembly <NUM> is reconnected to the vessel V.

After reconnecting the forward and aft disconnectable chain table assemblies <NUM> and <NUM> to the vessel V, the flexible jumper hoses and/or umbilicals <NUM> between the riser tower <NUM> and the vessel V can be connected to resume normal operations.

<FIG> illustrate an alternative configuration of the disconnectable spread mooring and riser tower system <NUM>' with the riser tower system <NUM> at the bow of the vessel V. The jumper support structure <NUM> is located at the bow of the vessel V, preferably adjacent to or on the forward chain table support structure <NUM>, as opposed to being located along the mid-section of the vessel V as in <FIG>.

Referring to <FIG>, the bow anchor legs <NUM> are placed forward of the vessel V to the starboard and port sides of the vessel V, preferably using tug boats or work boats, with the riser tower system <NUM> directly in front of the bow. Similarly, the stern anchor legs <NUM> are placed rearward of the vessel V to the starboard and port sides of the vessel V. With the bow and stern anchor legs in place, the jumper hoses and cables <NUM> can span between the riser tower decks <NUM> and the jumper support structure <NUM> of the vessel V.

The sequence of steps involved in moving the vessel V off location in this alternative configuration is very similar to the sequence described above with respect to <FIG>. Initially, all the jumper hoses and cables <NUM> spanning between the riser tower decks <NUM> and the jumper support structure <NUM> of the vessel V are disconnected and pulled onto the vessel V or onto the riser tower <NUM>. Preferably, the forward disconnectable chain table assembly <NUM> with bow mooring legs <NUM> near the riser tower <NUM> is disconnected first in the manner described above. The aft disconnectable chain table assembly <NUM> with stern mooring legs <NUM> is then disconnected as described above. If the stern of the vessel V is initially placed near the riser tower <NUM>, the aft chain table assembly <NUM> with stern mooring legs <NUM> will be disconnected first. The vessel V may then use its own power to move away from the riser tower system <NUM> and then can sail away to a safe harbor.

It is to be understood that reconnecting the disconnectable spread mooring system <NUM> upon the vessel V returning to the location may be accomplished as described above with respect to <FIG>.

<FIG> discloses an alternative orientation for the disconnectable chain table assembly <NUM> shown in <FIG>. In <FIG>, the disconnectable chain table assembly <NUM> is connected to a chain table support structure <NUM>' at an angle with respect to vertical. The hydraulic connector assembly <NUM> is also oriented at an angle with respect to vertical and the winch assembly <NUM> is preferably positioned such that the winch wire <NUM> is in coaxial alignment with the connector assembly <NUM>. The alignment pin assembly <NUM> is similarly angled. The remaining components may be the same as discussed with respect to <FIG>.

One purpose for the angled connection of <FIG> is to aid in the reconnection operation of the disconnectable chain table assembly <NUM> with the connector assembly <NUM>. As shown in <FIG>, the bow mooring legs <NUM> all generally extend forward of the bow of the vessel V. As the disconnectable chain table assembly <NUM> is retrieved and pulled into the connector assembly <NUM>, a large moment is produced and the chain table assembly <NUM> with connector hub <NUM> is not vertical, but angled. By placing the connection at an appropriate angle with respect to vertical, the moment does not have to be overcome on making the connection with the connector assembly <NUM>. It is to be understood that this may also be applicable to the aft disconnectable chain table assembly <NUM> and the connection at the stern of the vessel V.

<FIG> illustrates another embodiment in which a forward disconnectable chain table assembly <NUM>', the connector assembly <NUM> and a forward chain table support structure <NUM>" are below the water line L. Preferably, the winch assembly <NUM> is mounted on the bow of the vessel V and a guide member or members <NUM> provide guidance of the winch line <NUM> from the winch assembly <NUM> to the chain table support structure <NUM>". It is understood that the chain table assemblies may be mounted partially or fully submerged as shown in <FIG> and released and retrieved as described below with reference to <FIG>. It is also to be understood that this is also applicable to the aft disconnectable chain table assembly <NUM> and the connection at the stern of the vessel V.

<FIG>, <FIG> and <FIG> disclose other embodiments having forward and aft chain table assemblies with buoyancy compartments, referred to as <NUM>" and <NUM>" respectively. In <FIG>, the buoyant forward chain table assembly <NUM>" connects to a forward connector assembly <NUM> above the water line L, similar to the arrangement in <FIG>. A tie-back hawser <NUM> has one end connected to the buoyant forward chain table assembly <NUM>" with the other end secured to the vessel V. It is to be understood that the buoyant forward chain table assembly <NUM>", upon disconnection from the connector assembly <NUM>, is lowered into the water with the winch assembly <NUM> and allowed to float at or near the water line L. The winch wire <NUM> is then disconnected and the tie-back hawser <NUM> continues to connect the floating chain table assembly <NUM>" to the vessel V. The buoyant aft disconnectable chain table assembly <NUM>" is similarly lowered and allowed to float at or near the water line L with a hawser <NUM> connected to it.

In a mooring and tower arrangement as shown in <FIG> and with the forward and aft buoyant disconnectable chain table assemblies <NUM>" and <NUM>" lowered and floating at or near the water line L, the free end of the hawser <NUM> connected to each chain table assembly <NUM>", <NUM>" may be connected to a fixed structure, as for example the fixed jacket structure <NUM> of the riser tower system <NUM>, for the period of time the vessel V is off location, as shown in <FIG>. It is to be understood that the hawser <NUM> could alternatively be a chain or a combination of hawser and chain.

Alternatively, and in addition to other mooring and tower arrangements, the buoyant disconnected chain table assemblies <NUM>", <NUM>" may be connected to a buoy secured to the seabed with a mooring line by conventional offshore operations.

In <FIG>, the forward chain table assembly with buoyancy compartment <NUM>" connects to a submerged forward connector assembly <NUM> mounted to a submerged forward chain table support structure <NUM>", similar to the arrangement shown in <FIG>. In <FIG>, the submerged forward disconnectable chain table assembly with buoyancy compartment <NUM>" is released from the hydraulic connector assembly <NUM> and allowed to submerge further into the water until it reaches neutral buoyancy. A tie-back hawser <NUM> has one end connected to the chain table assembly <NUM>" and has a second end on the vessel V. The submerged aft disconnectable chain table assembly <NUM>" is similarly released and allowed to submerge further into the water until it reaches neutral buoyancy with a hawser <NUM> connected to it.

Referring to <FIG> (not in accordance with claim <NUM> or claim <NUM>), with the buoyant disconnectable chain table assembles <NUM>", <NUM>" floating in the water, both tie-back hawsers <NUM> can be pulled-in on the vessel V with winch assemblies (not shown) and connected to each other by a conventional offshore hardware/rope link assembly <NUM>", preferably with a quick release hook or shark jaws. A retrieval rope <NUM>" (<FIG> (not in accordance with claim <NUM> or claim <NUM>)) has one end connected to the tie-back hawser/hardware/rope <NUM>", and a second end connected to the winch line of the winch assembly. Preferably, a tag line with a surface buoy/light <NUM>" is also attached to the retrieval line <NUM>". The connected hawsers <NUM> and retrieval line <NUM>" and tag line with buoy/light <NUM>" are lowered into the water by the winch assembly and released, as shown in <FIG>.

The reconnection procedures follow the reverse of the disconnection procedures. The tag line with surface buoy/light <NUM>" (not in accordance with claim <NUM> or claim <NUM>) is retrieved and the hawsers <NUM> are disconnected from one another. Referring to <FIG>, the winch wire <NUM> of the winch assembly <NUM> is passed through the connector assembly <NUM> of the chain table support structure <NUM>" and the mating hub <NUM> of the chain table assembly <NUM>". The winch assembly <NUM> is used to draw in the chain table assembly <NUM>" to the chain table support structure <NUM>". When pulled in, the hydraulic connector assembly <NUM> is actuated to engage with the mating hub <NUM>.

A guided subsea connector <NUM>, preferably with a turndown shaft or a wheel, can also be utilized to connect the tie-back hawsers <NUM> together in the water or on the seabed by a winch line of a winch assembly on the vessel as shown in <FIG>. The hawser <NUM> from the chain table assembly <NUM>" with one side of the connector fixed at a pre-determined position is connected with the second hawser on the vessel, see <FIG>, and dropped into the water. The second hawser, preinstalled and connected with the winch wire on the vessel, will pass through the connector <NUM> fixed on the second chain table assembly, see <FIG>, to be pulled-in for making a connection. The connector <NUM> can also be fixed at the end of the second hawser <NUM> and the winch wire will pass through for making a connection as shown in <FIG>.

Alternatively, mudmats <NUM> with a large stabbing <NUM> on each are preinstalled on the seabed F (not in accordance with claim <NUM> or claim <NUM>) near bow and stern areas. Referring to <FIG> (not in accordance with claim <NUM> or claim <NUM>), a receptacle <NUM> in the center of each chain table assembly <NUM>", <NUM>" is used to set the chain table assembly on the stabbing <NUM>. After disconnection from the connector assembly <NUM>, each chain table assembly with buoyant compartment <NUM>", <NUM>" is pulled by the disconnected vessel close to the preinstalled mudmat <NUM> and then fully flooded to set down onto the stabbing <NUM> on the mudmat <NUM> in a guided manner. A remotely operated vehicle ("ROV") may be used to guide the chain table assembly <NUM>", <NUM>" onto the stabbing <NUM>. The chain table assembly may be secured on the stabbing <NUM> with a devise. Upon reconnection, after removing the securing devises if any, air will be pumped into the buoyant compartments of the assembly <NUM>", <NUM>", preferably via an ROV, to bring it back to the connection height for reconnection. When the chain table assembly <NUM>", <NUM>", reaches its natural floating position, it can be pulled to the connector assembly <NUM> by winch assemblies <NUM>.

<FIG> and <FIG> (not in accordance with claim <NUM> or claim <NUM>) disclose another embodiment having forward and aft chain table assemblies with buoyancy compartments, referred to as <NUM>" and <NUM>" respectively, submerged and connected with a pre-installed tie-back chain <NUM> underneath the vessel V. It is to be understood that the buoyant forward chain table assembly <NUM>", upon disconnection from the connector assembly <NUM>, submerges lower in the water and floats submerged at neutral buoyancy. The buoyant aft disconnectable chain table assembly <NUM>" is similarly disconnected and allowed to float in the water at neutral buoyancy with the preinstalled tie-back chain <NUM> connected to both chain table assemblies <NUM>" and <NUM>" after disconnection as shown in <FIG>.

Claim 1:
A disconnectable spread mooring assembly for a vessel (V) floating at a water surface (L), the vessel (V) having a bow and a stern, the disconnectable spread mooring assembly comprising:
a forward chain table assembly (<NUM>") releasably connected to the vessel (V) at the bow;
an aft chain table assembly (<NUM>") releasably connected to the vessel (V) at the stern, wherein each of the forward and aft chain table assemblies (<NUM>", <NUM>") comprises one or more buoyancy compartments and the forward and aft chain table assemblies (<NUM>", <NUM>") are arranged and designed to float at or near the water surface (L) when disconnected from the vessel (V);
a plurality of bow mooring legs (<NUM>) having first ends attached to the forward chain table assembly (<NUM>") and having second ends capable of being anchored at spaced locations on a seafloor (F);
a plurality of stern mooring legs (<NUM>) having first ends attached to the aft chain table assembly (<NUM>") and having second ends capable of being anchored at spaced locations on the seafloor (F);
a first connector assembly (<NUM>) connecting the forward chain table assembly (<NUM>") to the vessel (V) at the bow;
a second connector assembly (<NUM>) connecting the aft chain table assembly to the vessel at the stern,
wherein the first and second connector assemblies (<NUM>) are arranged and designed to unlock and release the forward and aft chain table assemblies (<NUM>", <NUM>") from the vessel (V);
a first tie-back hawser or chain, or combination of hawser and chain, (<NUM>) connected to the forward chain table assembly (<NUM>");
a second tie-back hawser or chain, or combination of hawser and chain, (<NUM>) connected to the aft chain table assembly (<NUM>"); and
one or more fixed jacket structures (<NUM>) fixed to the seafloor (F),
wherein the first and second tie-back hawsers or chains, or combinations of hawser and chain, (<NUM>) are arranged and designed to connect to the one or more fixed jacket structures (<NUM>) when the forward and aft chain table assemblies (<NUM>", <NUM>") float at or near the water surface (L).