Predicted heavy winds could trigger container ship breakup
by Richard Gladwell on 8 Oct 2011
Strong onshore winds are expected on Tuesday and Wednesday on the Bay of Plenty coast where the container ship Rena lies stuck on Astrolabe Reef.
The Rena is expected to take heavier seas, after the wind changes on Tuesday Bay of Plenty Times
At today's media conference several speakers alluded stronger winds being expected on Monday, but did not elaborate, instead pushing the line that oil recovery could start late Sunday (NZT) and could be completed before winds increase.
The latest prognosis from www.predictwind.com!Predictwind shows winds increasing in strength to 20-25kts on Monday from a NNE direction.
At this stage the winds are predicted to increase further on Tuesday, initially from a more northerly direction before swinging back through the east on Wednesday.
Of equal concern is the sea state which will see the area hit by waves predicted to increase from the current two-three feet from an offshore direction to over eight feet from a variety of onshore directions.
The Rena ran aground on the Astolabe Reef, off Tauranga Harbour, on the east coast of New Zealand, on Wednesday morning. So far over 20 tonnes of oil has leaked from her into pristine waters which form some of New Zealand's best cruising grounds, as well as having serious implications for fish, birds, whales and dolphins and other wildlife.
A massive clean up operation is in the process of being established in anticipation of a major oil leak from the ship, which has been likened to have the potential ecological impact of several times that of the Queensland disaster of 2009 when only 230 tonne s of oil were spilled.
Salvage experts told today's media conference that the Rena, a 236 metre fully laden container ship with 25 Philippine crew, had her bow locked on the reef, while her stern sections were free floating. She has 1700 tonnes of heavy fuel oil aboard.
They also revealed that her double bottom, while intact at the stern was badly crushed at the bow.
Experts have been surveying the stricken ship, which is Liberian registered and 20 years old, and reported that while there had been some flexing of the ship, there was no deformation of the hull plates at the hinge point - where the floating aft section met the wedged forward section of her hull.
That situation while encouraging, must be read against the background that the seas she is currently experiencing are from bow-on, while when the wind changes and increases in strength the seas will increase substantially and hit the floating aft section first, putting substantially more strain on the vessel.
The increased wind and sea state is caused by a intense low pressure system which will move down the east coast of New Zealand on Tuesday and Wednesday bringing a change in the flat water conditions that have existed since the container ship grounded on Wednesday.
The change in the wind and sea state will substantially increase the chance of the Rena breaking her back. It will also delay any container lifting activity, and will probably impact the offloading of her 1700tonnes of heavy fuel oil.
Today the salvage experts announced a three stage plan to remove the Rena from the Astralobe Reef. The first stage was the removal of the fuel oil, the second was removal of sufficient containers to lighten the ship, and the third was to pull her off the reef.
While it may be possible to remove the fuel oil before the winds increase in strength, it was emphasised that the 11 degree list of the ship would make it very difficult to lift containers off. Additionally because the ship is so laden with containers it is hard to find a space to lower necessary fuel pumping gear on board.
At this point, the intention is to place various vessels around the Rena and use these variously to take oil aboard and also containers which are intended to be lifted by helicopter. However those activities were predicated on the current sea state, and were described as 'complex'. The increased sea state would probably make any work impossible until winds dropped on Thursday - assuming the ship survives intact until then.
The plan is to have a vessel tethered astern to take the offloaded oil, and to transfer this to a larger oil ship. It is not known if the www.lander.co.nz!Lancer inflatable barges capable of taking 100tonnes of oil each would be deployed. maritime New Zealand owns two of the 100tonne barges, which can be used in a heavy sea state for oil collection and transfer.
Salvage experts had opted to tow the collection vessel to the storage vessel for offloading rather than have a longer and slower trip to Tauranga for offloading.
If additional inflatable barges are required there are many around the world, lancer Technical Director Ronald Winstone told Sail-World earlier today. 'We supplied 62 x 100tonne (100,000 litre) barges to the US Coastguard', he said. '100tonnes is the largest barge that is recommended as it becomes better to have 2 x 100 tonne barges than 1 x 200 tonne. By having two, one is filling as one is offloading. '
'The barges are ideally suited for offloading in the conditions being experienced at the moment.
'The first option is to put the barges alongside the ship and allow the ship to use it's pumps to offload. The ship is unlikely to have hoses to transfer the oil from their internal pipes into the barge, but hoses can be helicoptered on board the ship. The ship has already said that it's pumps have moved the oil from some tanks to other safer tanks.
'If the ship is unable to connect its plumbing to hoses, then it is possible to drop a pump onto its deck.
'To set up a pump on board is relatively easy, especially where the ship is in a relatively safe position.
'The barges can be moored alongside, or tethered off 25 metres or more. The hose can be fed out over the water, in the same way that is done when the barge is operating with a skimmer.
'The important point of the Inflatable Barge is that it is very compact when deflated and can be transported to the site very easily. Once at the site it can be operational in 1 hour. It can be towed empty at 10kts and full at 4 - 5 knots,' Winstone added.
The next update is expected Sunday afternoon at 1530hrs.
Rena Saturday press conference from Sun Live on Vimeo.
Rena run aground from Sun Live on Vimeo.
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