Smit and Mammoet complete wreck removal
Boskalis subsidiary Smit Salvage along with Mammoet Salvage have completed the complex wreck removal of a sunken car carrier that was presenting environmental and navigation risks to Europe’s largest port.
To engage seriously in marine salvage and wreck removal, participants must have a global capability. Operations literally on contractors’ doorsteps are perhaps rare but that opportunity arose for the two Dutch companies following collision between the car carrier Baltic Ace and container feeder Corvus J in December 2012.
Corvus J struck the side of the Baltic Ace which capsized and sank within 15 minutes, sadly with the loss of 11 of the ship’s 24 man crew. After assisting in the search for the missing crew, Corvus J was able to continue its voyage.
Baltic Ace had sailed from Zeebrugge bound for Finland while the container ship was on passage from Scotland when the collision occurred near the Noord Hinder Junction, a major shipping intersection around 40nm from Rotterdam. The sunken vessel lay on its side in a water depth of 35m and around 10m to 12m from the surface. Being in a busy shipping lane the wreck was clearly a danger to navigation, Dutch and Belgian maritime authorities subsequently monitoring the wreck closely.
The wreck also posed an environmental threat with 540,000 litres of pollutants on board including heavy fuel oil and lubricants. Petrol, oil and batteries within the cargo of more than 1,400 cars also posed an environmental threat.
Responsibility for removal of pollutants and the wreck itself fell on Rijkswaterstaat (RWS), part of the Dutch Ministry of Infrastructure and the Environment and a tender for its removal was issued at the end of 2013. Applicants had to submit three documents: the execution plan, a risk assessment and an environmental plan. The quality of the tender as well as the price was taken into account by RWS.
A joint tender including removal of the wreck, its cargo, heavy fuel oil and lubricants submitted by Boskalis and Mammoet was accepted in March 2014. The contract stipulated completion by the end of 2015 and with weather conditions only allowing working between April and September Boskalis and Mammoet planned the operation to be carried out over two seasons, pollutants being removed in 2014 and actual wreck removal in 2015.
Every such operation delivers experiences and ideas which are stored away for subsequent occasions and this operation drew on previous experiences. The sinking of the tanker Kyung Shin in Korea in 2010 and grounding of the Costa Concordia in Italy in 2012 resulted in Smit using ‘hot-tapping’ technology to remove pollutants, a solution adopted with Baltic Ace.
Pieter van Muren, Operations Manager with Smit Salvage explains: “…it is crucial to get the correct temperatures for optimum pumping of the various fuel oil grades. The oil is heated with inserts in the bunker tank. Steam is run through these inserts, which are cylinders of 2 meters long and 30cm in diameter. The steam plant was installed on a barge and provided constant heating to create the flow of oil in the tank. We initially thought the oil would be pumpable in a couple of days but actually it only took 36 hours. By early June, 460 m3 of fuel oil had been removed from the tanks and was safely discharged. The tanks were also flushed three times with so-called super-heated water to remove all sticky remains.”
It was determined early on that the vessel could not be lifted intact and the initial plan was to cut it into six sections of 1,500 to 2,000 tons each, the total weight including cargo being 12,000 to 13,000 tons. Again two previous wreck removals, the Russian submarine Kursk and the Tricolor another car carrier which sank in the English Channel provided the method of cutting up the Baltic Ace using a cutting wire.
It took around 30 hours to cut a section 25m wide by 25m high, followed by lifting the sections by sheerlegs crane onto a barge for transport ashore. The plan had to be modified however after holes were cut in the hull to insert lifting saddles or bollards creating strong points for the lift. It was discovered that the ship was deteriorating rapidly with frames breaking and coming loose so it was back to the drawing board and a new plan devised to cut the ship into more sections.
Pieter van Muren again explains: “Given a car carrier’s square shape, all the strength is in the lower deck up to around the 4thor 5th deck. The new plan involved eight sections instead. We would lift the keel up to deck 4 and then use the wreck grab for the upper decks and smaller parts on the seabed. For the cutting spread, the Baltic Ace was slightly different to the Tricolor when a jack-up barge was used. This time, we wanted to use barges with a heave compensation system. The pre-tensioned saw-wire (80 metres-120 metres), which has steel ‘bushes’ - with sharp bits of hard metal on the outside - along it, is pulled up and down by wire winches between the barges. Mammoet has developed an in-house horizontal drilling system and after drilling they pulled the wire underneath the wreck. In a constant hauling and heaving motion, it took 30 hours for each cut.”
By the end of September 2015 eight sections and around 5,000 tons of smaller parts had been loaded onto barges and transferred to Rotterdam presenting local residents with the surreal sight of this sliced up ship with its expensive cargo of new cars still largely in place, crushed beyond recognition from the whole experience. Final cleaning of the seabed by grab crane and divers completed the complex operation a task completed well before the deadline.
By Peter Barker
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