Removal of the Rena is technically possible but the question is whether it is "dangerous or disproportionate" to do so, a salvage expert says.

Netherlands-based salvage expert Camiel de Jongh yesterday appeared for the Bay of Plenty Regional Council, as consent authority, during hearings into whether the Rena should be abandoned on the Astrolabe Reef (Otaiti).

The Rena's aft section was unstable on Astrolabe Reef and was likely to move in a future storm, while its bow section has moved to a place from where it could be more easily removed, Mr de Jongh said.

"Removal is technically possible, the question is whether it could be dangerous or disproportionate to do so.

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"The aft section is unstable and, combined with the working depth, would create a very dangerous working environment for a salvage operation.

"The [bow] sections have been demonstrated to be very mobile and may continue moving in coming years."

Mr de Jongh said the removal of the wreck pieces should depend on the extent and seriousness of the damage to the reef environment their movement may cause, an area outside his expertise.

Mr de Jongh also highlighted the possibility of a risk to navigation from further movement of the sections.

If this were to happen, Mr de Jongh advocated removal of the piece or relocation to deeper water.

"The question is whether, as a result of these risks, it is necessary to remove the bow pieces now, or whether the risks can be dealt with through a requirement to address the issue in future, in the event it becomes one."

The equipment that had been used during the salvage was not the best available for the job and this could be why the projected cost of removing the ship was so high, Mr de Jongh said.

"We have some professional doubts that the equipment used over the last couple of years is the best available in our industry.

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"We are of the opinion that there might be more suitable equipment on the market to deal with the bow pieces, so we harbour doubts from our side that the actual cost will be as high as submitted by [marine consultancy] TMC."

Mr de Jongh said he could not give an accurate estimate of how much removal was likely to cost, as this would need to go out to international tender.

"If you go out for tender now, there hasn't been any big wreck removal operation going on in the last year, so everybody will be very eager to put an offer on the table.

"At the same time, you're in a very remote area, so it will be expensive."

Lance Marshall, a senior naval architect and mechanical engineer, said depending on the depth and metal thickness of items, the total decay of the wreckage remains was estimated to take 70-220 years.