Owners of the Rena are coming under fire after a series of independent reports into the cost and removal of the vessel from Astrolabe Reef describe the process as grossly exaggerated.

International marine and engineering consultancy firm London Offshore Consultants says compared to the total further cost of between US$425m and US$546m, in addition to the UAS$300m already spent, it would cost between US$422m and US$540m and about five years to remove the wreck.

The Rena broke in two in January 2012. Photo: File.

The Costamare, which owned the Rena through its subsidiary Daina Shipping Company, figures were to be regarded with "a degree of caution" due to uncertainties over the condition of the wreck, the weather and rates for contractor's work, the report states.

The consultancy firm was commissioned to peer review documents Costamere submitted in support of its application to leave the ship's wreck on the reef.

The former containership struck the reef on October 5, 2011, subsequently breaking up and spilling fuel oil and cargo into the Bay of Plenty.

Much of it washed ashore on local beaches in what became the region's largest environmental disaster.

The report states if an offer of full wreck removal is put out to international tender "then solutions would be offered that may prove to be far less costly".

LOC shipping services group director Nick Haslam in the report states removal falls into three components; bow section, debris field and stern section.

For the bow section it is proposed the removal of seven bow pieces will take 176 days equating to US$79m.

About 50 tonnes of debris has been removed from the debris field with an estimated 3900 tonnes remaining. It could be recovered in 80 days, with a further 30 days required for 'sweeping” the area with a magnet – costing US$29.5m.

The stern section would require 29 separate lifts resulting in a timeline of about 513 days – costing between US$314m and US$432m.

It is understood Government ministers were given the LOC reports before the Government announced it would push for only part of the wreck - above 30 metres - to be removed.

Cost and workers' safety were cited as reasons for leaving the rest of the wreck on the Astrolabe Reef, but LOC says all options have not been canvassed, and an offshore crane could be used to remove the full wreck.

The Government had also been told in the reports that in similar situations internationally, governments tended to demand wrecks be removed, with the minimal threat to environmental or navigational safety having "no impact" on the relevant authorities' decision to impose total wreck removal notices.

Spokesperson for the ship's owners and insurers - Daina Shipping and The Swedish Club – Hugo Shanahan says it is not appropriate to comment on individual matters raised by the Crown desktop reports ahead of a hearing.

The hearing will see various expert opinions and evidence heard and tested by an independent statutory authority.

Hugo says the analysis, methodology and science behind the resource consent application proposal is robust and of a high-quality – based on more than two years' knowledge and experience of dealing with the wreck and its local environment.

'The owner and insurer continue to fund a significant, multidisciplinary engineering and environmental management response to the casualty.”

Earlier this year the Waitangi Tribunal clarified three deeds of settlement were signed in October 2012: the Claims Deed, the Indemnity Deed, and the Wreck Removal Deed.

The settlement included $27.6m for Crown's claims against the owners for clean-up costs and other public bodies, including Maritime New Zealand and the Bay of Plenty District Health Board.

An additional $10.4m would be paid 'for public purposes” to the Crown if the remainder of the wreck can be left on the reef.

The clean-up was estimated to cost about $47m, leaving a shortfall of about $20m based on the negotiated settlement.

The payment from Daina was said to be contingent on the shipping company making "substantial cost savings" by leaving the wreck on the reef after a successful resource consent application.

The Rena owner's resource consent application will be heard in the Environment Court. The application for that hearing is expected to be lodged in mid-October.