Thursday, 12 January 2012

Wreck removal

With Rena now parked (badly) on Astrolabe Reef, how do you remove 11,000 tonnes of steel, engines and containers from 30 metres under the sea? Some very cool technology been developed just for this problem which, if the NZ Government plays hard ball, may be brought to bear on the problem.



The English Channel is of the world's highest collision risk areas, as ships transit to and from the major European and British ports. When the Norwegian-owned car carrier Tricolor sank off Ramsgate in 2002, after a collision with the container ship Kariba, the wreck had to be removed from the busy shipping channel. A third ship even ran over the submerged Tricolor despite navigation warnings, a standby ship and marker buoys.

Salvors Smit International developed an industrial-sized equivalent of the cheese cutter - essentially an abrasive wire (or chain) rigged to saw the large carcase of the hull into smaller, more manageable pieces. The technique was also used on the wreck of the Vinca Gorthon when she sank in the Baltic on top of a gas pipeline and to remove the explosives-laden bow of the Russian submarine Kursk when it sank off Murmansk.

Tricolor was cut into sections and lifted out - with many of the 2,871 Volvo, Saab and BMW cars still lashed down inside the vehicle decks - before being scrapped in Zeebrugge.


Tricolor cutting rig

If Rena's wreck is to be removed from Astrolabe Reef, barges could be set up either side and the cutting wire strung underneath the hull. The winches saw the wire though the hull reducing the single structure into bite-sized chunks. A sheer-legs derrick barge would then lift the sections on to flat -top barges for transport to port and eventual scrapping.


Tricolor's engineroom and propeller being lifted out of the sea


Tricolor hull section on a barge to Zeebrugge

An expensive proposition and one which Rena's P&I Club will be fighting hard to avoid. The Swedish Club carries the financial liability for wreck removal and will be looking for the lowest cost solution - maybe removal of the accommodation block and leaving the bow high and dry on Astrolabe Reef.



When salvage gets to this point, any remaining cargo is 'collateral damage'. Here's what a Volvo looks like after the cutting wire has been through it. So, an interesting challenge with the outcome dependent on the conditions Maritime NZ puts the wreck removal in what is a remote and non-navigable location. It can be done, but at what cost.

The Antipodean Mariner

3 comments:

  1. I think I've seen one if not two Government Ministers ion TV saying it had to go. I'd imagine that given the terrain she's lying on, that another storm like last weekend's might see her shift anyway. There's also talk that the bow is likely to break up too.

    A caller on talk back yesterday said " I don't believe it took as long as it did for the barge to get here from Singapore" and "Why didn't they pump oil off from one side while removing containers from the other" Almost another Tui ad in itself.

    If left there, the bow section would show up on other ships radar for a few years.

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  2. Looks like we have another car carrier in the North Sea sunken at a depth slightly less than the ship's beam. I wonder if they'll cut her up like that as well.

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