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Hybrid robot vehicle undertakes record-breaking dive

There is an underwater vehicle flavour to Jeremy Cresswell’s look at what’s fresh on the hydrographic front, notably a new type of hybrid robot vehicle for deepsea survey and a semi-submersible vehicle designed to replace small survey monohulls.

The robotic vehicle Nereus, developed at the US’s famous Wood’s Hole Oceanographic Institute (WHOI) is capable of operating both as a tethered remotely operated vehicle (ROV) and as an autonomous underwater vehicles (AUV).

It looks like a cross between an ROV and a catamaran and has just been on a voyage to the bottom of Challenger Deep in the Mariana Trench in the western Pacific Ocean. The dive to 10 902m took place on 31st May and makes Nereus the world’s deepest-diving vehicle and the first to explore the Mariana Trench since 1998.

According to Wood’s Hole, the hybrid ROV/AUV format makes this machine ideal for exploring and surveying the ocean’s last frontiers.

“With a robot like Nereus we can now explore virtually anywhere in the ocean,” said Andy Bowen, the project manager and principal developer of Nereus at WHOI, following the historic dive.

“The trenches are virtually unexplored, and I am absolutely certain Nereus will enable new discoveries. I believe it marks the start of a new era in ocean exploration.”

To reach the trench, Nereus dove nearly twice as deep as research submarines are capable of and had to withstand pressures 1000 times that at Earth’s surface-crushing forces similar to those on the surface of Venus.

Only two other vehicles have succeeded in reaching the trench: the US Navy-built bathyscaphe Trieste, which carried Jacques Piccard and Don Walsh there in 1960, and the Japanese-built robot Kaiko, which made three unmanned expeditions to the trench between 1995 and 1998. Neither of these is presently available to the scientific community. Trieste was retired in 1966, and Kaiko was lost at sea in 2003.

Building on previous experience developing tethered robots and AUVs at WHOI and elsewhere, the engineering team fused the two approaches together to develop the hybrid.

Both ROVs and AUVs are now mature technologies, with AUVs especially increasingly utilised for hydrographic and seismic survey operations.

The tethering system for Nereus presented one of the greatest challenges as conventional steel-reinforced umbilicals would be too heavy and, according to WHOI, break under its own weight.

To solve this challenge, the Nereus team adapted fiber-optic technology developed by the US Navy’s Space and Naval Warfare Systems Center Pacific (SSC Pacific) to carry real-time video and other data between the Nereus and the surface crew.

Similar in diameter to a human hair and with a breaking strength of only 4kg, the tether is composed of glass fibre core with a very thin protective jacket of plastic.

Nereus carries some 40km of this cable in two canisters the size of large coffee cans that spool out the fibre as needed. By using this very slender tether instead of a large cable, the team was able to decrease the size, weight, complexity, and cost of the vehicle.

NCS Survey has chosen GAPS, IXSEA’s Global Acoustic Positioning System, for the acoustic positioning of a number of subsea structures for a North Sea renewables project due to start this month.

Staying in the US, C&C Technologies of Lafayette was at the time of writing, preparing to perform sea trial its unmanned semi-submersible (USS) in the Gulf of Mexico.

The vehicle was designed and built over the last three years as a substitute for the standard hydrographic survey launch. Powered by a 30bhp diesel engine, C&C says the vehicle will be ideal for large nautical charting surveys and mine defence work.

The USS is designed to operate just below the water’s surface with a mast extending above the waterline. Payload sensors include a keel-mounted side scan sonar, multibeam echosounder, and CTD (conductivity, temperature, and depth). The mast includes a video camera, C-Nav DGPS, and wireless antenna for high-speed telemetry of data.

According to the company’s CEO Thomas Chance, like an AUV, the vehicle will be able to operate autonomously in a wide range of sea conditions, yet with the exposed mast, data can be reliably positioned with DGPS and relayed back in real time.

C&C Technologies operates worldwide and provides a broad range of offshore survey services, C-Nav global DGPS services, and claims to be the world leader in deepwater AUV operations. However, it was not C&C Technologies vehicles that Scottish firm NCS Survey ordered. Instead the firm went for a pair of Gavia AUVs – one 500m-rated system and one 1000m rated system. These systems are specifically aimed at the shallow water market and are understood to be the first Gavia AUVs to enter the oil and gas market as a service provided by a survey contractor – but general survey, not seismic.

As a response to NCS Survey’s decision to select Hafmynd, the Icelandic manufacturer of these vehicles has created a new line named the Gavia Offshore Surveyor.

Delivery is expected in late September this year but NCS Survey have already secured a contract, which started in May and will use the demonstration system from Hafmynd for this project.

The Offshore Surveyor has numerous improvements and upgrades from the standard Gavia vehicles that enhance the operation and usability for commercial applications. Both NCS Survey systems will have a payload of a multi-beam echo sounder (MBES), sidescan sonar, digital camera, doppler velocity log (DVL), Kearfott T24 IMU, DGPS and sound velocity meter. In addition, each system will be fitted with a Seebyte SeeTrack module to allow the tracking of linear features such as pipelines and trenches.

The sounder is a Geoswathe Plus 500kHz machine capable of a survey swathe width of up to 190m. There are various SSS options for the vehicle but NCS Survey have opted for the unit that has been proved with the Seebyte module, a Marine Sonic Technology 900/1800kHz system.

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