EoW May 2009

technical article

Deep-Sea ROV Cable By Jarrett S Shinoski Research & Development, CommScope Claremont, NC; Dave Weaver and Tom Tolman Oceaneering International Inc, Hanover, MD

Abstract The Deep-Sea ROV cable has changed the world of deep-sea exploration forever. With this technology, explorers and historians have been able to investigate the interiors of such shipwrecks as the Titanic and the Bismarck. This unique cable has been used as a communications link between the operator and two specially designed ROVs (Remote Operated Vehicle) referred to as the Deep-Sea ROV and the Hybrid AUV (Autonomous Underwater Vehicle)/ROV. This cable is 900microns in diameter and carries a single fibre for sending information to and from the fibre optic telemetry system. Mike Cameron of Dark Matter LLC originally developed this technology in 1999. Mike Cameron and his brother James Cameron used this ROV technology in documentary films before Oceaneering International purchased the technology in January 2005. Oceaneering has plans of bringing this technology into the mainstream by utilising both of the ROV’s unique capabilities, for potential uses such as the inspection of undersea equipment, port security monitoring, and search and rescue missions. The Oceaneering ROVs are revolutionary and have created a paradigm shift in ROV design. The two ROVs are self-contained units that house their own batteries for power and spool out their own cable for communications. A typical ROV sends power and commands through a large tether, which restrains the path of the vehicle and how far the vehicle can penetrate into a wreck. In addition, the tether is commonly spooled out from the command centre via a very large reel. Since the fibre optic tether is expendable, the Oceaneering ROVs have the unique capability of running into one opening and out through another with no restrictions on entry and exit points and no restrictions on depth of penetration into a cavity. The Deep-Sea ROV cable gives these ROVs a competitive edge.

1 Introduction The Deep-Sea ROV cable was evaluated by both the manufacturer and the end user for two different but similar applications. This specialised cable was already being used for the Deep-Sea ROV, but needed to be optimised to perform well in a newer application. This new application was a Hybrid AUV/ ROV with both autonomous and normal ROV capabilities. Many cabling trials, laboratory tests and field tests were conducted in order to hone in on the proper cable design. Oceaneering had requested a new cable design containing only one fibre and with a diameter close to 900microns. This invention was a 3 rd generation Deep-Sea ROV cable. 2.1.1 First generation cable The first generation cable was a 2-fibre cable consisting of two multimode fibres with an overall diameter of approximately 1.4mm. One fibre was for information sent to the ROV (to control the ROV) and the other was information sent back from the ROV (live video feedback). This cable contained many ends of strength elements for increased tensile strength. Later on, the Oceaneering team replaced the fibre optic systems so that they could send information bi-directionally via a single fibre rather than two separate ones. 2.1.2 Second generation cable Still maintaining the same diameter for mechanical compatibility, this second generation cable contained only a single fibre. The cable was still 1.4mm in diameter but added an additional jacket of protection. In between the two jacket layers was a layer of strength elements for added tensile strength and abrasion resistance. 2 Cable design 2.1 Customer request

The cable spools out by way of a proprietary mechanical payoff system built into the ROV itself, eliminating the need for a fibre optic slip ring. The Deep-Sea ROV contains approximately 600metres while the Hybrid AUV/ROV contains 2,000metres of this very fine 900micron cable. This cable contains one optical fibre, speciality strength members, and oil. The optical fibre is a typical single mode fibre 255microns in diameter, utilised for controls and feedback. The strength members aid in both tension control and cable durability. The oil gives the cable its incompressible properties at depths of up to 6,100metres (20,000 feet). The outer jacket is a special polymer blend used to achieve the correct buoyancy of the cable in the water column. The ROVs are so small, and contain so much cable, that an improperly weighted cable would wreak havoc on an ROV’s buoyancy controls. This cable was qualified using both standard testing practices and distinctively new test methods. Mechanical and environmental performance was tested and the cable was subjected to the most severe requirements of three different standards. The three standards were the ANSI/ICEA S-87-640-2006, the GR-20-CORE, and the EN 187105. To get a better idea of the performance of this cable, it was tested to failure under the general guidelines of the specifications. In addition, several custom tests were developed in order to predict the reliability of the cable. A specialised hydrostatic pressure test bench was employed by Oceaneering in order to simulate the pressure on the cable at extreme ocean depths. A buoyancy requirement was also created by Oceaneering in order to achieve the proper buoyancy. A specialised test for hockling (the marine term for kinking) was created by CommScope in order to benchmark the hockle performance of each cable. From these test results we could assure Oceaneering the best possible cable for their special application.

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EuroWire – May 2009