Rena disaster: High-tech gadgets go where no diver can

A remote underwater vehicle is lowered to find containers and debris from the Rena in the Bay of Plenty. Photo / Alan Gibson

From submersible probes to smartphones, the ongoing job of cleaning up the Rena's mess has been a triumph for gadgetry.

This month saw the first deployment of a remote underwater vehicle (ROV) used by environmental recovery specialists Braemar Howells, contracted to recover containers and debris.

Operations manager Neil Lloyd said the ROV had been part of the company's contingency plan since the grounding last October and acted as its "eyes and hands" on the ocean bed.

The seabed around Rena has been described by salvors as a container "graveyard".

ROVs were used in areas where sonar technology had mapped out potential debris from the ship but was too deep for divers to reach.

Capable of diving to depths of more than 900m, it undertakes visual inspections of large areas of sea floor.

If any containers were found, the ROV could use its manipulating arm to attach a magnetic transponder, while the team watching its camera could assess whether the container was damaged or intact.

"In some cases we can use the ROV to get the container number and determine what the cargo is, its priority for recovery, its potential impact should it release or break, or whether it's either inert or is something that's a danger to the environment."

Both Braemar Howells and salvors Svitzer have been using transponders which, in the early days of the salvage, were attached to the more precarious containers.

There were two types of these "pinger" transponders - one model could send back signals for 30 days, the other could last for 18 months.

"The 18-month pingers generally go on objects more significant, such as debris that's a lot deeper than the team can work at or small items that may take time to recover."

The pingers also let the clean-up team know when a container moved.

Another type of beacon was capable of being dropped from an aircraft next to a container, which it would drift alongside, while other electronic sea probes were being used.

Sonar devices had played an important part in sounding out containers during the response and one type towed behind vessels - the SeaKing side scan sonar towfish - appeared to have been mistaken for prey by hungry sharks.

One of the most crucial gadgets in the company's arsenal was the high-tech photoionisation detector, or PID, used to detect hazardous chemicals.

The communication equipment used ranged from satellite phones to the stock-standard smartphone - "probably the one thing that has come to the forefront of this operation that we haven't used so much in the past", said Mr Lloyd.

While there was still debris washing up on coastlines, particularly on inaccessible beaches, Braemar Howell's main focus was now on recovering thousands of troublesome plastic beads.

At the lower end of the tech scale, six specially modified leaf vacuums sucked up and spat out sand on beaches - leaving the beads in the machine.

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* Vacuum machines operated by environmental recovery specialists Braemar Howells have been used specifically to suck up thousands of plastic beads and other items spilt from the Rena.

* Sonar towfish devices, which have been targeted by sharks during the salvage, are pulled behind vessels to sound out containers in the sea.

* Transponder beacons called "Pingers" were fixed to the more precariously placed containers in the early days of the salvage.