Salvors face one of the most dangerous and expensive underwater operations ever undertaken in New Zealand as they try to recover hundreds of containers from the sinking Rena, says a salvage expert.
New Zealand Diving and Salvage general manager Howard Saunders says a technique known as saturation diving is likely to be used after the ship's stern began its descent yesterday, three months after grounding on the Astrolabe reef.
The stern, which has about 400 containers in its hold, is in a precarious position on the reef and was last night about 75 per cent submerged. As it sank it left behind tonnes of timber, debris and containers that littered Matakana Island and Waihi Beach.
Maritime New Zealand said an observation flight this morning found neither section of the ship had changed significantly overnight. A small amount of debris remains around the wreck, as well as a light oil sheen.
Oil off the ship is expected to first reach Motiti Island, before stretching as far Matakana Island and Maketu. Fortunately only "tens of tonnes" are expected to spill.
Environment Minister Nick Smith said the Rena was "in its death throes" and the Government's priority was now minimising the environmental damage as it sank and broke up.
Mr Saunders said that by law the Rena would have to be removed after it sank the 80 to 90 metres to the seabed.
That would require one of the biggest and most dangerous salvage operations undertaken in New Zealand.
He said the salvors would probably be working in depths of greater than 30m, so they would have to use a saturation diving spread - rarely seen in New Zealand - with pressurised chambers and diving bells that enable divers to live and work safely at depth for days and even weeks.
One is in operation off the Taranaki coast at a natural gas rig.
"You can live down there with food ... sometimes they call them habitats and people live on the bottom, but most modern operations are not that long."
He said the underwater salvage job would be among the biggest projects in New Zealand's maritime history and possibly among the most expensive.
Some saturation dive teams charged US$150,000 dollars (nearly $190,000) a day.
"I think the Wahine took more than 12 months [to salvage] but that was done fairly slowly and the water depth was nowhere near as deep as it is here," he said.
Mr Saunders said removing containers from the Rena above water had been dangerous enough.
"Under the sea it's going to be even worse," he said. "If they are subject to any current or it's not stable on the bottom and it's moving around the whole operation becomes a bit of a nightmare."
Paul van't Hof, of Svitzer Salvage, would not be drawn yesterday on the future of the salvage operation.
"That's something we can only decide after doing our inspections, at the moment we would be guessing and we have to change our plans," he said.
Maritime New Zealand's national on-scene commander Alex Van Wijngaarden said oil spill response teams had placed booms in sensitive areas, and the oiled wildlife centre in Tauranga and volunteer programme had been reactivated.
Six penguins affected by oil from the Rena were reportedly being treated at the centre yesterday.
A spokeswoman for container recovery company Braemar Howells, Claudine Sharp, said it had identified 49 containers yesterday, of which about 25 had beached at either Matakana Island or Waihi Beach.
She said the company had 13 vessels between Waihi Beach and Motiti Island to try to catch the drifting containers and attach them to a specialised barge.
Yesterday more than 60 people were helping with the clean-up at Waihi Beach. At least 30 more worked from Papamoa to Kaituna Cut, and another 20 helped remove timber, paper, plastic and milk powder that continues to wash ashore from the Rena's cargo.
Transport Minister Gerry Brownlee yesterday praised the clean-up efforts of volunteers at Waihi Beach, saying they had "tolerantly put up with all the inconvenience that comes from these types of events".
Asked what the Government's position was on the wreck, he said it "will have to be removed".
Once the weather had settled, "a closer inspection will be able to give the technical experts a greater understanding of how the ship is likely to respond".By James Ihaka Email James