Two years on from the grounding of the container ship Rena off the Tauranga coast and salvors are still working to remove the wreck with the next phase of cutting the sunken section about to commence.

In the early hours of October 5, 2011 the Rena ship grounded on Astrolabe Reef about 25km off the coast of Tauranga causing one of the country's biggest environmental disasters.

From this, October 5 2011…

…to this, after Resolve Salvage & Fire completed reducing the bow section in July.

Now two years on Resolve salvors have reduced the bow section stuck fast to the reef, to below the water line, and they have made significant inroads on clearing the debris field resulting from when the ship broke in two in January 2012.

Salvors are about to begin cutting the ship's accommodation block, the house, from the aft end of the wreck now lying in 50metres of water.

To do this a specialised RMG 500 barge has arrived from Singapore where it was dry docked after its last job of clearing wrecks from the from the Sri Lankan civil war. The tow to New Zealand by the tug Resolve Gladiator took about 30 days.

Any wreck in any place other than Astrolabe Reef would be gone by now, says Resolve Salvage master Frankie Leckey.

'This crane is going to be preparing to lift off the house sections and each section is going to weigh about 250 to 300 tonnes,” says Frankie.

'The divers on the other barge are preparing everything, all the chains and lifting and cutting gear, so this crane can come out and pick up a piece. Once it picks a piece up it's going to set it on another one of our barges, then the people will start cutting it up and take it away to the scrap yard.”

The four storey accommodation block will be removed by chain cutting. A large chain will be pulled back and forth, slicing through the four storey house and bridge structure in two cuts.

The crane barge will be doing the chain cutting and hauling the removed sections to the surface, where they will be placed on another even bigger barge, expected to arrive October 15/16.

Each link in the chain weighs about 100kg and is made of 76mm thick steel. The anchors that will hold the barge in place while the yet to be assembled chain pullers pull the chain to and fro, will weigh 15 tonnes each. The wire strops that will guide where the chain cuts can be barely lifted, will be man-handled into place underwater by divers working at the air breathing limit.

'It worked out well for us,” says Resolve's programme co-ordinator Dave Maruszak.

'The depth we can go to is 50 metres and that is right at the accommodation block, starboard side where it is listing 55 degrees.”

The divers are breathing surface supplied air and do their stops on the way back to the surface.

Any deeper and they would have to go to mixed gas and saturation diving, which is a whole other level of complexity and expense. Under that regime the divers would after a day's diving, live in compression chambers on deck for the duration of the operation.

In recent weeks the divers have taken advantage of calm conditions provided by recent westerlies to prepare the ship's house for cutting by pre-cutting tunnels and guide channels so the chain will cut where they want it to.

The heavy lift vessel was brought in because two big lifts is quicker than cutting the house into smaller pieces, especially looking back at Resolve's experience last season where in 400 days on the reef they worked less than half that.

The crane barge RMG 500 arriving under tow from Singapore last week. Picture: Resolve.

He says the Rena is the longest job Resolve has done, due to the weather. Resolve came onto the job when it won the contract to reduce the bow section. They found the debris field and the owners and insurers hired them to clear that, and they now have the job of taking away the house.

'Normally if this was in a sheltered area we would be done,” says Frankie.

'For us when we started we were using the helicopters, and the weather didn't really bother us. But then when we get into doing the diving the bigger problem for us is the weather hitting the reef.

'So when the divers are inside, their life line is coming from the barge when they have to penetrate inside the house. If any of our lines break, the diver can be killed. So it's really, really difficult and dangerous.”

Resolve hopes to have removed the house sections by Christmas, but Frankie says that's also what they said last year about the bow section.

Once the sections are on the other barge it will take about two months to cut them up. It's not yet known where the 90m by 30m barge will be moored while that takes place.

The Rena salvage operation is proceeding one job at a time because there isn't the room on site.

'If we had other barges doing other things, they are likely to collide with each other, so we can only do one thing at a time,” says Frankie.

This week, two shore cranes will assist with the re-rigging, and unfolding of the RMG 500's A-frame.

Also on shore four big anchors will be assembled that will hold the barge during the cutting. The anchors weigh about 15 tones, are 21 metres long and have a holding power of about 1000 tonnes.

'So they are pretty big anchors,” says Frankie.

'We will prepare all this stuff in port ahead of when they need it out there. We have to be ahead of those guys out there. if we're not it slows them down, and they talk about us.”

The Rena's owners and insurers project spokesman Hugo Shanahan says the owners and insurers have s short message to the community in recognising the second anniversary.

'Two years on from the grounding, we would like to say thank-you for the huge amount of time and energy volunteered by the community in response to the grounding. For everything that has been done by many individuals and groups right across the community – we will forever be very grateful. '

Click here to read SunLive coverage for the first year after the grounding.

Salvage master Frankie Leckey briefing media on the next stage of Rena salvage

The A frame on the crane barge will be swung forward over coming days.