Observatory Cable Laying SystemKeith ShepherdKeith TamburriReuben Mills

Canadian Scientific Submersible Facility9860 West Saanich Road

Sidney, BC Canada

Abstract

Cabled ocean observatories use cable ships or other surface vessels to lay long heavy armoured cable on theseafloor which typically forms the backbone of the observatory network. It is not practical, and would beextremely difficult to lay shorter cables connecting two instruments or instruments to the nodes. Other RemotelyOperated Vehicles (ROV's) have the technology to lay lighter weight or short cables where the users arefortunate to have either low power requirements, close proximity of instrument to node, and a benignenvironment for the cable to lay. There has been no solution to lay long extension cables that have armourpackages, or large conductors required for high power or remote applications. Heavier cables also have betterbehaviour on the seafloor, resisting spanning, rock damage and movement in currents.

NEPTUNE Canada, and other observatories have a requirement for numerous extension cables to be laid thatare up to 10 km in length and have a cable weight in water of several thousand pounds. These cables arerequired for connecting instruments that are placed some distance from the node and main cable.

The Canadian Scientific Submersible Facility (CSSF) has designed and built a Remotely Operated Cable LayingSystem (ROCLS) that works in conjunction with the ROPOS ROV. The ROPOS system was built with athrough frame lift capability of 4000 lb. to a depth of 2500 metres. Thus the cable laying system can have anoverall weight of 4000 lb. including cable. With this system the cable can be gently and precisely laid on theseafloor. With theROCLS attached to the ROV, we can visually watch cable touchdown, as well as using theobstacle avoidance sonar to identify obstacles. The ROV thrusters provide the force to manoeuvre aroundobstacles. The drum is hydraulically driven and can drive cable out, reel cable back in or provide back tension ifrequired.

Further capability is provided by a capacity to couple and decouple the ROV to the package while it is on theseafloor. This allows the vehicle to free swim and connect the cable ends to the instrument packages and to thenode. The vehicle can also perform other routine ROV services. It can then re-couple to the cable laying systemand continue laying cable, or recover the empty drum to the surface. Spare loaded cable drums can be carriedand easily swapped out offshore, saving time and effort particularly when the offshore spread is on hire.

This presentation describes the system design and operation, as well as the various cable types and weights thatcan be managed.

CSSF has developed a system that meets a unique requirement for ocean observatories that cannot be otherwiseeasily achieved. The system is simple, robust, has a large payload and can be deployed with the existing ROPOSoffshore spread. The ROPOS system, complete with the ROCLS, can be deployed from most scientific researchvessels currently used for offshore oceanography in and around North America.

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I. SYSTEM DESIGN

The CSSF team has been working with ocean observatory groups since the engineering concepts and challengesassociated with this new scientific infrastructure were first being discussed. While solutions to most challengescould be visualised, there was no obvious solution for the connection of the observatory nodes' and remotely locatedinstruments. Some instruments will be located many kilometres from the main backbone cable's path. Existingsurface based and subsea cable installation technology cannot lay the short 100 to 8000 meter long, small diametercables required in a controlled manner. These cables' touchdown must be constantly monitored while being laid, inorder to avoid major obstacles, spanning, bird nesting and hockling. A system for deploying these cables directlyonto the seabed has been designed and built by the CSSF team.

II. ROPOS BACKGROUND

In 2005 the Canadian Scientific Submersible Facility completed a comprehensive in-house upgrade of the ROPOSROV system. Included in the upgrade was a 4000 lb through frame lift capability and a heave compensated LaunchAnd Recovery System (LARS). These capabilities give the ROPOS ROV the ability to deploy and recover heavypackages to and from the seafloor in a controlled fashion. With these capabilities, the Remotely Operated CableLaying System (ROCLS) gives cabled observatory managers, engineers and scientists increased flexibility inplanning their deployments and installations. Additionally, the side launch configuration of the ROPOS LARSsystem allows an increased weather window for operations and frees up the stem A-frames for other offshoreoperations. ROPOS' Ultra Short Base Line (USBL) navigation package ensures un-interrupted meter-scale accuracyover the course of the entire lay, providing survey quality positioning of the cable and the deployed scientificinstruments to depths of 2700 metres.

III. SYSTEm DESCRIPTION

..................................................The.. ROCLS......system......is hecomprisedic mprs ofo

heth

.................made....up...of..the...outer....lift....frame,.....cable..

...drum...assembly...and..the...drum..drive.

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IV. DESIGN CONSTRAINTS:

During initial planning of this project, certain key design features were identified to ensure the successful operationof the system.

The system allows the laying of cable and connection of the cables with their respective nodes and instruments, allwithin the same dive. This saves having to recover and reconfigure the vehicle for different operations, thus savingship time and reducing costs. To enable this efficiency, the ROCLS system must allow the operators to easily coupleand decouple from the Drum Frame on the seafloor.

Protecting the vehicle's hydraulic and electrical systems during the operation is important. To accomplish this, theROCLS system is not mated or de-mated with the hydraulic or electrical circuits subsea.

Efficient use of ship time has been a constant driver in the ROCLS design and engineering processes. On a typicalcable installation cruise, the ROCLS system may be called on to deploy over a dozen extension cables withoutresupply. The ROCLS system drums can easily be removed and reinstalled, allowing multiple drums to be pre-spooled on shore, or re-spooled offshore while cables are being laid.

V. CABLE CAPACITY

The system has two methods of deployment that allow different capacities of cable to be carried. The difference isbased upon the vehicle's carrying capacity and the air vs. water weights of the cables. Normally the Drum Frame isattached to the vehicle during launch. Cables over a certain weight in air will have to be deployed separately fromthe vehicle. Typically this will be done with a deck winch fitted with wire and an acoustic release to release theDrum Frame once it has reached the sea floor. The vehicle then free swims down and latches in on the seafloor.Routine cable laying then can proceed.

ROCLS drum capacity was designed around 8000 meters of 14mm (.55") O.D. polyurethane jacketedelectrical/optical cable or 5750 meters of 18mm (.70") cable of similar internal construction with an Aramid strengthmember and second outer jacket.

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VI. CABLE INSTALLATION PROCESS

Launching the system is as easy as positioning the vehicle over the Drum Frame with the LARS, latching andsecuring the package to the vehicle and deploying the combined system in a fashion similar to normal operatingprocedures.

The cable lay process itself is best summarized in point form:

* Latch onto ROCLS drum frame with the appropriate drum loaded.* Lower the complete package over the side.* Lower the system to the appropriate location on the seafloor and land.* Unlatch the deployment package; vehicle becomes free swimming.* Remove one flying lead from the drum and make connection to the node or instrument.* Secure cable to node with Yale grip to ensure cable cannot pull directly on cable connector during

lay process.* Latch onto Drum Frame and lift off seafloor.* Move across seafloor laying cable, manoeuvring around obstacles identified with sonar and video

cameras.* Use the vehicle thrusters to deflect the cable touchdown point around obstacles.* Manage slack and cable tension by controlling payout or even winding cable back onto the drum.* Monitor cable dynamics with multiple process cameras including lowlight camera on stinger.* Upon completion of the lay, wind any remaining cable off in a controlled, retrievable fashion.* Place Drum Frame near the instrument and unlatch* Land Vehicle alongside Drum Frame on seafloor and remove bitter end of cable with media

converter can and connector.* Plug the connector into instrumentation package.* Fly back and latch into Drum Frame and recover system to load next cable for deployment.

VII. EXTRAORDINARY PROCEDURES

One major concern in handling heavy packages sub sea is the loss of vehicle hydraulic or electric power and theresulting implications to the package and the vehicle. During a lay process, the best solution to a loss of vehiclecontrol is to automatically release the package on the seafloor. However during transits to and from the seafloor anunwanted release of the deployment package could result in a high altitude drop. Additionally during the recoveryand deployment of the system, an unwanted release with the system suspended over the deck of the ship creates anunsafe situation for the system and crew. To address this concern we have designed the system so that the operatorcan configure hydraulic latch circuits such that they will automatically release the package or to lock the package inplace, to conform to mission-specific deployment and safety requirements.

VIII. CARGO WINCH

A separately deployed Drum Frame may land on the sea floor at an extreme angle or on its side, making a standarddocking procedure impossible. To manage this, the Toolskid has been fitted with a submersible winch allowing thevehicle to lift the Drum Frame off of the bottom and dock mid-water, or to simply move the Drum Frame to a betterlocation where the Vehicle can dock.

IX. CONCLUSION

The described cable laying system allows ROPOS to easily deploy observatory cables which would otherwise bechallenging to install. The docking Toolskid can also be used to deliver and recover other large and heavyinstruments quickly, easily and safely to the seafloor. A pair of simple latch receptacles can be designed into the topof other instrument packages, allowing ROPOS to lock in and lift the instrument for launch, deployment and

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recovery. Scientific instrumentation packages or cable wet plant components of up to 4000 lb in water can then beeasily deployed or moved to new locations with better than 5 metre absolute accuracy. Since the ROPOS system isdesigned for easy installation on a variety of offshore vessels, it can perform observatory work worldwide.

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