Review and observations on the TMC feasibility study
In response to the Full Wreck Removal Feasibility Appraisal Report dated the18th June 2014 prepared by TMC (Marine consultants) Ltd. on behalf of the owners and underwriters of the MV RENA, the Regional Council engaged Global Salvage Consultancy (GSC), to review the TMC report and prepare a report on the findings of their review.
The GSC Report Review and observations on the TMC feasibility study of the MV Rena wreck site has been released to assist in informing the public on the feasibility of a full wreck removal at Otaiti/ Astrolabe Reef.
The container vessel MV RENA grounded on the Astrolabe Reef in the Bay of Plenty, New Zealand on 5th October 2011. Despite the efforts of salvors, who managed to remove most of the fuel oil and containers, the vessel eventually broke in two and sank. Since 2012 contractors have been engaged in the partial removal of the wreck and its associated debris.
The TMC Report only considered traditional wreck removal methods, focusing primarily on two methodologies, namely the use of sheerlegs or jack-ups. However, GSC has considered a further option whereby a converted tanker is used as a dedicated salvage platform, which improves overall workability, safety and reduces costs. There is another option that is available which proposes that the remaining parts of the wreck are covered in an environmentally responsible way by using sourced rock material. This is a technically viable option but GSC understands that it may not be culturally appropriate.
MV RENA wreck movement April 2013 versus April 2014
(Image Credit: www.renaproject.co.nz)
The report reviews the condition of the wreck in the context of the feasibility of technically removing it and related health and safety issues, in particular regarding the aft section of the wreck. The review on the stability of the aft section reveals that removing it is an extremely delicate and risky operation due to the instability and limited structural integrity of this section. Consequently, diver intervention should be reduced to a minimum.
Risk assessments were conducted to compare the realistically feasible managed (As Low As Reasonably Practicable) risk levels of each of these four scenarios using an identified generic risk top- 17 analysis. These ALARP risk assessments consider both commercial and safety driven scenario performance.
GSC is aware that the RENA wreck site is a sacred place for multiple Maori tribal groups. This means that not only the current presence of the wreck itself, but also that each wreck handling scenario poses a threat to cultural sensitivities. If lives are lost in the short- or long-term this may directly impact the spiritual wellbeing of people. These community risks have been assessed along with operational, environmental, logistical and contractual and liability key threats by the top-17 analysis.
With respect to the review of the two methodologies explained in the TMC Report, GSC is of the opinion that both options are proven salvage techniques but they are unsuitable given the weather and sea conditions at the Astrolabe Reef. The given methodologies, in their present form should not be considered viable options, and certainly not for the aft section.
Since risk levels for the wreck removal scenarios in the TMC Report are unrealistically high, GSC has considered the alternative option of converting a tanker into a salvage platform which would provide enhanced workability, reduced operational safety exposures and a lower daily cost.
GSC is however of the view that a limited operation, which is well planned and executed with the appropriate equipment spread and tooling would certainly allow for the removal of major parts of the fore section, major parts of the midsection and a large area of the debris field. It is worth emphasising that if the wreck, equipment, cargo and associated debris field are left on the seabed as requested in the consent application, it is highly likely that this will attract recreational divers and souvenir hunters, which in turn might cause a long-term risk of injuries and even fatalities. GSC considers that this risk can be mitigated by removing as much of the debris as possible, as well as the fore section and major parts of the midsection.
It is self-evident that the presence of the wreck and debris field presents new barriers to the natural progression of waves and as such will alter the behaviour of the wave and current systems around and over the reef and therefore, affect the erosion of the reef in some areas.
GSC is of the view that in the shallow waters, the larger parts of the fore end will, due to the hydrodynamic action caused by wave run-up, backwash, tide and current, increase local erosion of the bedrock resulting in increased embedment. However, depending upon their structural stability, such action will eventually act to weaken these larger wreck parts to the extent that portions of it will collapse, detach and fall away from it. Lighter objects, under the same influence, will either be driven into deeper pockets within the reef or swept off it to deeper sections of the Reef.
In deeper water the heavy debris associated, for example, with the remains of Cargo Holds 4 and 5 will in due course eventually collapse further and break up under the influence of the cyclic loading induced by the shoaling of long crested swells. GSC is of the opinion that this debris will, due to the undertow generated, migrate down the natural erosion debris field in Northerly and Easterly directions.
Regardless of whether a decision will be made for a full, part or no wreck removal, the TMC Report does not address the stability aspects and consequences of the aft section of the wreck itself and the implications on the wreck removal options.
In general, the TMC Report gives a rather limited view on the feasibility of traditional scenarios for a full wreck removal operation based on its existing assets and methodologies, which results in GSCs opinion, in a higher than expected estimate of the total project cost.
In summary, GSC is of the view that the TMC Report is missing some critical aspects, which are required to compile a full appraisal of the feasibility for a full removal of the wreck. However, GSC in general is in concurrence with the conclusions of the TMC Report that a full removal operation will be faced with operational challenges and compounded total costs, making it overall disproportionate. A limited operation, however, focusing on the remains of the bow and mid-section, as well as clearing the debris field, appears to be both reasonable and feasible.
Source: MV Rena Resource Consent / Image Credit: Wikipedia
To read the report please click on the image below:
