Patent Description:
The invention is particularly concerned with enabling vessels of opportunity to be used for ROV deployment and not only specialised ROV support vessels (ROVSVs). In the context of the invention, a vessel of opportunity is a vessel that is not intrinsically designed, equipped and crewed to operate UUVs such as ROVs. A vessel of opportunity is instead designed primarily for other purposes, such as carrying supplies for offshore installations, items of equipment for installation subsea, or other cargo.

ROVs are commonplace for performing tasks underwater in depths or locations where the use of divers is not feasible or safe, especially in the subsea oil and gas industry. ROVs can be described either as free-flying ROVs or as tether-controlled ROVs, as taught by <CIT>. Small observation-class or inspection-class ROVs may be used for underwater monitoring or inspection tasks. Larger work-class ROVs may be used for underwater work or subsea intervention tasks.

IMCA R <NUM> Guidelines for Installing ROV Systems on Vessels or Platforms published by the International Marine Contractors Association describes the main methods for launching an ROV from a surface vessel into the sea. Those guidelines explain that over-the-side deployment may be employed on a vessel of opportunity or by an ROV handling system installed permanently on an ROVSV. The alternative of deploying the ROV through a moonpool can cope with higher sea states but inevitably requires permanent installation and a specialised vessel.

When overboarding an ROV over the side of a vessel, a dedicated A-frame may carry a tether management system (TMS) to which the ROV is initially docked to form a TMS/ROV assembly. The TMS stores a tether that effects power and data connections with the ROV. An umbilical effects power and data connections between the vessel and the TMS and hence, via the tether, with the ROV.

<CIT> discloses an A-frame system for a free-flying ROV. <CIT> exemplifies a TMS. <CIT> discloses a typical tethered ROV with a TMS.

Typically, an A-frame lifts and luffs a TMS/ROV assembly outboard, suspended from an umbilical. The umbilical is paid out from a winch beside the A-frame and runs over a sheave on the A-frame until the TMS/ROV assembly reaches the required depth in the water. The ROV then undocks from the TMS underwater, whereupon the TMS deploys the stored tether and remains underwater while the ROV performs its subsea mission. By using an intermediate TMS, the ROV is decoupled from motion of the vessel and is able to operate across a larger radius.

It will be apparent that the umbilical is used as a lifting cable and so must be able to withstand tension arising from the suspended weight of the TMS/ROV assembly. The thickness of the weight-bearing umbilical therefore limits the depth to which the TMS/ROV assembly can be delivered, for a given size and capacity of winch. This problem is of course exacerbated if the umbilical has to support the weight of a heavier work-class ROV. There is also a need for dedicated structures and equipment on the deck of the vessel, which militates against the use of a vessel of opportunity.

Rapid deployment platforms are known for use with small ROVs, namely observation-class or inspection-class ROVs. Such platforms comprise an umbilical winch on a mobile A-frame structure that carries a cage for the ROV. An example is offered by Seatronics Limited of Aberdeen, UK for its Predator ROV system (trade marks acknowledged). Again, the umbilical must bear the weight of the ROV and its cage, restricting use of the system to inspection tasks in shallow water such as in quays, harbours or ports.

Other efforts have been made to enable ROV deployment without requiring a surface vessel or platform to be fitted with specialised deployment equipment. For example, <CIT> describes the use of a deployment module to carry a TMS/ROV assembly. The deployment module can be lifted inboard and outboard by a crane of a vessel or platform. The deployment module is fitted with a winch that carries a weight-bearing umbilical, capable of supporting the weight of the TMS/ROV assembly.

In <CIT>, the crane of the surface vessel or platform lifts the deployment module from an inboard position on the deck of the vessel or platform to an outboard position over the sea. A power and signal cable connects the deployment module to the vessel or platform.

With the deployment module held by the crane above the surface of the sea, the TMS/ROV assembly is disengaged from the deployment module and, while suspended by the umbilical, lowered by the winch to the seabed. The weight of the TMS/ROV assembly is therefore transferred initially from the deployment module to the umbilical and then from the umbilical to the seabed.

The deployment module is then lifted back onto the deck of the vessel or platform with the umbilical, now slack, extending over the side of the vessel and down to the TMS/ROV assembly. The ROV can then undock from the TMS, swimming away from the TMS on a tether to perform a subsea mission.

On completing the subsea mission, the ROV docks again with the TMS on the seabed and the deployment module is lifted by the crane again to the outboard position over the sea. The winch on the deployment module then winds in the umbilical, lifting the TMS/ROV assembly from the seabed and eventually out of the water and back into engagement with the deployment module. The weight of the TMS/ROV assembly is therefore transferred initially from the seabed to the umbilical and then from the umbilical to the deployment module. Finally, the deployment module is lifted back onto the deck of the vessel or platform, carrying the TMS/ROV assembly with it.

The solution proposed in <CIT> is complex and yet is not capable of delivering the TMS/ROV assembly to a mid-water depth above the seabed, if required. Also, in essence, the umbilical winch is merely moved from the deck of the vessel or platform to the deployment module. The problems of a lengthy weight-bearing umbilical remain.

<CIT> discloses a system based on shipping containers for adapting a vessel to support UUV operations. The system includes a crane and therefore reduces reliance on equipment available on the vessel, but is complex and cumbersome as a result. <CIT> proposes a similar approach.

In more distant prior art, <CIT> proposes arrangements for launching underwater moving bodies from land.

Against this background, the invention provides a method of deploying a UUV from a surface vessel or platform to perform a mission underwater according to claim <NUM>.

The UUV is fully submerged in the water before being undocked from the TMS. The TMS may also be submerged in the water before the UUV is undocked from the TMS. In that case, the TMS is then lifted and held clear of the water while the undocked UUV performs the mission.

Conveniently, a crane may be used to lift the UUV and the TMS outboard from the vessel or platform and to suspend the TMS over the water. Efficiently, that crane may be a crane forming part of the equipment fitted to the vessel or platform.

During the mission, the suspended TMS may be moved up and down relative to the vessel or platform in compensation for heave of the vessel or platform. The suspended TMS may also be stabilised with elongate links such as tag lines that extend from the vessel or platform to the TMS.

The umbilical may be deployed in response to outboard movement of the TMS from the vessel or platform, for example by being pulled from a storage location by virtue of the outboard movement of the TMS.

The method of the invention may further comprise the preliminary step of positioning a mobile UUV support unit on a deck of the vessel or platform. Then, the UUV and the TMS may be moved from the UUV support unit outboard of the vessel or platform. The umbilical may also be deployed from storage on the UUV support unit.

Communication with the UUV may be effected via the UUV support unit. For example, the UUV may be controlled from the UUV support unit, potentially using control personnel located onboard the UUV support unit.

The method of the invention may further comprise the subsequent step of returning the UUV to the TMS after the mission, while retracting the tether, and then docking the UUV with the TMS. For this purpose, the TMS may be lowered into the water before docking the UUV with the TMS underwater.

In summary, the invention provides techniques for deploying a subsea vehicle such as an ROV, or a package that requires a control umbilical, from the deck of a vessel and into the sea. Correspondingly, the invention also provides techniques for returning the vehicle or package from the sea and back to the deck of the vessel.

In embodiments to be described, a control umbilical or tether for the vehicle or package is fitted to a drum located in a frame of a TMS. The frame includes a control system for managing pay-in and pay-out of the tether, a latch that secures the vehicle or package mechanically to the frame for lifting as an assembly, and a lifting point that is suitable for lifting the complete frame and vehicle assembly into and out of the water. A short surface umbilical or cable links the tether on the drum to a surface control system that controls the vehicle.

To launch the vehicle, a crane of the vessel lifts the vehicle latched to the frame from the deck and locates the frame and the vehicle over the sea as a single package. The crane then lowers the frame and the vehicle into the water to a depth of a few metres. The now neutrally-buoyant vehicle unlatches from the frame, the tether is paid out and the vehicle is free to operate to perform a subsea mission. The frame is then lifted clear of the water and stabilised using the crane lift line and fore and aft guide wires. Recovery of the vehicle is a reverse of the process.

The invention has several advantages. For example, no dedicated ROV launch and recovery system (LARS) needs to be fitted to the vessel. The crane of the vessel provides all of the lifting capability that is required, including heave compensation if available.

The system can be rapidly mobilised to a vessel, without requiring welding or fabrication. Conversely, the system can be removed easily from the vessel or moved aside when no longer required, freeing up valuable deck space for other requirements.

Thus, it is provided for rapid mobilisation of a task-optimised vehicle or package onboard a vessel to deliver a desired service. There is no requirement for deck-mounted LARS or supporting structures that are expensive and time-consuming to mobilise.

It is also enabled a modular system to be adopted, in which a deployed vehicle or package can be specific to a particular subsea task. When required, the crane can lift and deploy a different vehicle or package optimised for a different task, potentially choosing from a selection of vehicles or packages provided on a deck of the vessel.

Embodiments of the disclosure which are not claimed provide a system for quick deployment of an ROV from a vessel of opportunity. The system comprises a mobile support, such as an ROV van, comprising a garage location for an assembly of a TMS and an ROV. The TMS/ROV assembly is connected to the mobile support by a short umbilical, which is preferably less than <NUM> long. The umbilical may be spooled inside a storage compartment or on a winch of the mobile support when not in use.

The TMS comprises lifting provisions whereby the TMS/ROV assembly can be lifted by any vessel crane. The ROV can be uncoupled from the TMS mechanically while remaining connected to the TMS via a tether or other communications link.

The TMS may be held above the water when the ROV is diving. Tag lines may extend between the suspended TMS and the vessel, at least when the ROV is diving.

Embodiments of the disclosure also implement a method to deploy an ROV quickly from a vessel of opportunity. The method comprises: fastening a mobile support on a deck of the vessel; using a crane of the vessel to lift an assembly of a TMS and an ROV from the mobile support, with the TMS/ROV assembly connected by an umbilical to the mobile support; lowering the TMS/ROV assembly until at least the ROV is in water; decoupling the ROV from the TMS; paying out an ROV tether from the TMS; and operating the ROV while the TMS remains suspended above the water.

Keeping the TMS above water close to the surface allows the umbilical to be simple, short and easy to manage. Also, only one winch needs to be used in the system, namely the winch of the TMS, compared to at least two winches in the closest prior art.

Whilst the invention facilitates ROV deployment from a vessel of opportunity, the invention could be used to provide additional ROV-operating capacity for any vessel, including a specialist ROVSV.

Thus, in accordance with the invention, an ROV docked to a TMS is lifted outboard into water beside a vessel while deploying an umbilical that effects communication with the ROV via a tether of the TMS. After undocking the ROV to swim away from the TMS while deploying the tether, the TMS is suspended over the water while the ROV performs a subsea mission. A mobile or transportable ROV support unit can be positioned on a deck of a vessel of opportunity to facilitate deployment of the ROV, the TMS and the umbilical and to control the ROV during the mission.

The schematic drawings, which are not to scale, show a vessel of opportunity <NUM> floating on the surface <NUM> of a body of water <NUM> such as the sea.

To operate a UUV exemplified here by an ROV <NUM>, the vessel <NUM> is adapted in accordance with the invention by placing a transportable, self-contained ROV support unit <NUM> onto an open working deck <NUM> atop the hull <NUM> of the vessel <NUM>. The ROV support unit <NUM> can be lifted aboard the vessel <NUM>, for example using a crane <NUM> mounted on the working deck <NUM> of the vessel <NUM> or dockside, or may be driven onto or towed aboard the vessel <NUM>.

In this example, the ROV support unit <NUM> is a mobile unit fitted with at least one pair of wheels <NUM> that enable the ROV support unit <NUM> to be positioned or repositioned at any convenient location on the working deck <NUM>. The ROV support unit <NUM> may therefore be a vehicle, which may be a towable vehicle such as a trailer or a self-propelled vehicle such as a truck.

Once positioned on the working deck <NUM>, the ROV support unit <NUM> may be tied down or anchored with suitable fastenings, such as chains or chocks, to ensure stability when the vessel <NUM> is at sea. Also, whilst the ROV support unit <NUM> could, in principle, provide its own electrical power from an on-board generator or from internal batteries, the ROV support unit <NUM> may conveniently be powered via a cable connection from an external source such as the electrical power system of the vessel <NUM>. Such fastenings and power connections have been omitted from the drawings for simplicity.

The ROV support unit <NUM> hosts and supports a TMS/ROV assembly <NUM> that comprises a TMS <NUM> connected to the ROV <NUM>. When not in use on a subsea mission, the ROV <NUM> is latched to the underside of the TMS <NUM> and hence is coupled mechanically and substantially rigidly to the TMS <NUM>. Thus, the crane <NUM> can lift the TMS/ROV assembly <NUM> as a unitary load from the ROV support unit <NUM> into the water <NUM> before a mission and from the water <NUM> back to the ROV support unit <NUM> after the mission. The ROV support unit <NUM> therefore does not have, or need, its own crane or other lifting device.

When the ROV <NUM> is latched to the TMS <NUM> and the TMS/ROV assembly <NUM> is suspended in air on a wire <NUM> of the crane <NUM>, the weight load of the ROV <NUM> is borne via the TMS <NUM>. For this purpose, the TMS <NUM> is surmounted by a lifting formation on its upper side, such as a padeye <NUM>, for engagement by a lifting tackle or a hook <NUM> suspended from the wire <NUM> of the crane <NUM>.

When in the water <NUM>, the ROV <NUM> can be unlatched and hence uncoupled mechanically from the TMS <NUM> to swim away from the TMS <NUM> to perform the mission. As is conventional, the ROV <NUM> is propelled to swim by on-board thrusters. After the mission, the ROV <NUM> swims back to or is pulled back to the TMS <NUM> to be latched and hence re-coupled mechanically to the TMS <NUM>. Thus, the ROV <NUM> is surmounted on its upper side by a docking formation <NUM> that is engageable with a complementary remotely-operable latch formation <NUM> on the underside of the TMS <NUM>.

While the ROV <NUM> is unlatched from the TMS <NUM> to swim underwater <NUM>, the ROV <NUM> remains connected to the TMS <NUM> by a deployable, reelable tether <NUM>. The tether <NUM> provides power and two-way data connections between the TMS <NUM> and the ROV <NUM>, as required for the ROV <NUM> to perform the mission.

As is conventional, the TMS <NUM> comprises a reversible reel or winch <NUM> for deploying and retracting the tether <NUM> as appropriate. The length of the tether <NUM> deployed between the TMS <NUM> and the ROV <NUM> determines the maximum operational radius of the ROV <NUM> around and with respect to the TMS <NUM> for a given vertical separation between the ROV <NUM> and the TMS <NUM>.

The ROV support unit <NUM> comprises an ROV control system <NUM>, a garage <NUM> for the TMS/ROV assembly <NUM> and a storage location <NUM> for an umbilical <NUM>. The umbilical <NUM> provides power and two-way data connections between the ROV control system <NUM> and the ROV <NUM> via the TMS <NUM> and the tether <NUM>. The umbilical <NUM> is conveniently in a coiled configuration when it is stowed in the storage location <NUM>, for example in a vertical-axis carousel, as shown, or on a reel.

The ROV control system <NUM> is exemplified here by an ROV van that accommodates ROV-operating personnel <NUM> such as pilots and/or other mission specialists. Displays <NUM> and control interfaces <NUM> provide for control inputs and for visual feedback between those personnel <NUM> and the ROV <NUM>.

The plan view of <FIG> shows that the ROV control system <NUM> of the ROV support unit <NUM> is connected for data exchange with the control system <NUM> of the crane <NUM>. This enables coordination between operation of the TMS/ROV assembly <NUM> and operation of the crane <NUM>. In particular, the ROV control system <NUM> can control the crane <NUM> to lift the TMS/ROV assembly <NUM> into and out of the water <NUM> and to hold the TMS <NUM> steady by activating an optional heave compensation system of the crane <NUM>.

In <FIG>, the crane <NUM> is shown with its jib <NUM> slewed inboard to lift the TMS/ROV assembly <NUM> from the open-topped garage <NUM> of the ROV support unit <NUM>. <FIG> shows the jib <NUM> then slewed outboard to lower the TMS/ROV assembly <NUM> into the water <NUM>.

As the TMS/ROV assembly <NUM> is lifted away from the garage <NUM> and toward the water <NUM>, the umbilical <NUM> is deployed by being pulled progressively out of the storage location <NUM> of the ROV support unit <NUM> as shown in <FIG>. Deployment of the umbilical <NUM> is effected automatically, simply by pulling the umbilical <NUM> through the open top of the storage location <NUM>. <FIG> shows that the deployed portion of the umbilical <NUM> lies on, and extends across, the working deck <NUM> and then hangs overboard between the working deck <NUM> and the suspended TMS/ROV assembly <NUM>.

<FIG> also shows the TMS/ROV assembly <NUM> lowered into the water <NUM> to a depth of a few metres, advantageously beneath the potentially turbulent splash zone near the surface <NUM>. The ROV <NUM> has substantially neutral buoyancy whereas the TMS <NUM> suitably has slightly negative buoyancy to maintain some tension in the wire <NUM> of the crane <NUM>.

The ROV <NUM> is then undocked from the TMS <NUM>, as shown in <FIG>, to be free to swim to the depth required by the mission as shown in <FIG> also shows that the wire <NUM> of the crane <NUM> is retracted to lift the TMS <NUM> clear of the water <NUM> while the ROV <NUM> performs the mission. The tether <NUM> is paid out by the reel <NUM> of the TMS <NUM> accordingly. The tether <NUM> then extends through the surface <NUM> of the water <NUM> between the TMS <NUM> and the ROV <NUM>.

<FIG> show the TMS <NUM> suspended on the wire <NUM> of the crane <NUM> above the surface <NUM> and, optionally, stabilised against swinging on or twisting about the wire <NUM> by a pair of tag lines <NUM> that act in tension between the TMS <NUM> and the hull <NUM> of the vessel <NUM>. As can be appreciated in the plan view of <FIG>, the tag lines <NUM> converge toward each other in the outboard direction toward the TMS <NUM> when viewed from above.

<FIG> also shows that the TMS <NUM> can optionally be moved up and down by a heave-compensation system that, cyclically, pays out and retracts the wire. This avoids heave, roll or pitch of the vessel <NUM> transmitting unwanted vertical forces to the ROV <NUM> via the tether <NUM>. The heave-compensation system may conveniently be implemented in the control system <NUM> of the crane <NUM>, shown in <FIG>.

At the end of the mission, the TMS <NUM> is lowered back into the water <NUM> to a depth beneath the splash zone as shown in <FIG>. The ROV <NUM> swims back to the TMS <NUM> as the TMS <NUM> retracts the tether <NUM> onto the reel <NUM>. Alternatively, or additionally, retraction of the tether <NUM> onto the reel <NUM> of the TMS <NUM> can pull the ROV <NUM> toward the TMS <NUM>.

Once the ROV <NUM> is docked again with the TMS <NUM>, the TMS/ROV assembly <NUM> is lifted out of the water <NUM> as shown in <FIG> before the jib <NUM> of the crane <NUM> is slewed back inboard to lower the TMS/ROV assembly <NUM> into the garage <NUM> of the ROV support unit <NUM>. The umbilical <NUM> is re-stowed in the storage location <NUM> of the ROV support unit <NUM>, ready for future re-deployment as shown in <FIG>.

After use, the ROV support unit <NUM> can be lifted or driven off the vessel <NUM> to allow the vessel <NUM> to resume its primary duties. The ROV support unit <NUM> can then be used again on another vessel of opportunity. Alternatively, the ROV support unit <NUM> can be moved to a holding location elsewhere on the vessel <NUM> to be ready to support future ROV missions when required.

Many variations are possible within the inventive concept. For example, the ROV support unit could include a crane or hoist that is capable of lifting the TMS/ROV assembly into and out of the water. In that case, the vessel need not be fitted with a separate crane. Alternatively, a separate crane of the vessel need not be tied up when operating the ROV.

The ROV control system on board the ROV support unit could be a relay for conveying control data and visual feedback between the ROV and a separate master control unit, which could be located elsewhere on the vessel or indeed at another offshore or onshore location.

Elongate links other than tag lines, such as rods or other structures acting in tension or compression between the TMS and the vessel, could be used to stabilise the TMS when lifted clear of the water.

Claim 1:
A method of deploying an unmanned underwater vehicle (UUV) (<NUM>) from a surface vessel (<NUM>) or platform to perform a mission underwater, the method comprising:
moving the UUV (<NUM>), docked to a tether management system (TMS) (<NUM>), outboard from the vessel (<NUM>) or platform and into water (<NUM>) beside the vessel (<NUM>) or platform;
deploying an umbilical (<NUM>) that extends outboard from the vessel (<NUM>) or platform to the TMS (<NUM>) to effect communication with the UUV (<NUM>) via a tether (<NUM>) of the TMS (<NUM>);
fully submerging the UUV (<NUM>) in the water (<NUM>) and then undocking the submerged UUV (<NUM>) from the TMS (<NUM>);
swimming the UUV (<NUM>) away from the TMS (<NUM>) while deploying the tether (<NUM>), wherein swimming the UUV (<NUM>) comprises propelling the UUV (<NUM>) using one or more of the thrusters of the UUV (<NUM>); and
while suspending the TMS (<NUM>) over the water (<NUM>) beside the vessel (<NUM>) or platform, using the UUV (<NUM>) to perform the mission while communicating with the UUV (<NUM>) via the tether (<NUM>) and the umbilical (<NUM>).