Righting the Costa Concordia: how to flip a half-sunk ship

‘You take the front, I’ll take the back.’ EPA/Massimo Percossi

The huge Costa Concordia cruiseship is due to be righted in preparation for finally being towed away from the Italian island of Giglio. But why has lifting and removing the wreck taken so long, given that the accident occurred back in January 2012?

The first thing to remember is that structurally intact floating ships are designed to move with relative ease. But they are very heavy and large. Concordia is nearly 300m long and weighs in at over 114,000 tonnes - and that’s without taking into account the fact she’s full of sea water. To put it into perspective, the ship is as long as the Eiffel Tower is high, but more than ten times heavier.

Working with such a massive structure as this on flat, stable ground would be difficult. On an uneven seabed in 20m of water with waves and currents it becomes almost unachievable. Adding to the complications is the huge gash on one side of the vessel, making it impossible to float Concordia again on its own, but also weakening the whole structure.

Consider the reasons behind the major operations that have taken place around this vessel for nearly two years. The initial priority was to save lives. The next was to protect the environment - booms were deployed around the ship to prevent oil escaping, and the fuel on board was pumped out in the first few weeks.

Then there is the issue of gathering evidence for legal proceedings, though in this case recovering the ship is unlikely to reveal any new evidence of any use now that five crew have been convicted (though the captain has yet to come to trial). For a ship with light damage the final priority is to recover and repair the asset, and the sooner this is done the less expensive the repair. But Concordia is beyond repair, both physically and emotionally - few would want to sail on a cruise liner rebuilt marked by such tragic circumstances.

The focus now is to remove what is an eyesore and environmental threat for the island of Giglio as well as a constant reminder for those who lost loved ones in this disaster. It is important but only if it can be done safely. A rushed attempt to recover the vessel is at best likely to break up the ship, making the final recovery process slower and more dangerous. At worst it could lead to further loss of life; imagine ten Eiffel Towers crashing down around you.

The first priority has been to stabilise the ship and support it so that it doesn’t slide into deeper water. Water depth has a major impact on the engineering around the ship, and even an additional 10m could have made the current plans unfeasible.

The salvage team has had to weld huge steel sponsons - like supersized inflatable swimming armbands - onto the ship’s hull to add buoyancy. The sponsons on the raised side of the ship will first be flooded with seawater to help drag the ship from the angle at which it is lying back onto its keel, using gravity to help a system of cables pull the Concordia upright. Where the bow has been weakened by the hole in the hull, bracing has been added to prevent it shearing off - like a neck brace on a patient. Lastly, as pulling the ship upright to rest on rocky and sloping seabed would be very unstable, a level “mattress” of concrete and steel has been built underneath to provide a level surface on to which to roll the ship.

More than 30,000 tonnes of material (a quarter of the ship’s weight) has been used in the salvage operation, and the cost so far has been £500 million - more than Concordia cost to build. An operation of this scale takes significant time and we might equally comment on how it has been managed so quickly and efficiently, rather than how long it has taken. In the next few days, at the first sign of good weather and calm seas, the operation to right Costa will begin and take about 12 hours. Once it starts to roll a point of no return comes and the engineers will have to rely on the accuracy of their calculations.

As the vessel begins to right herself, material from inside the ship will spill into the sea and localised debris and pollution is likely. This will be minimised by floating booms around the vessel, but some environmental impact is inevitable. Less, of course, than leaving Concordia where she is. The first task once the vessel is upright and safely secured will be to try to locate the last two missing bodies from the wreck. This will be followed by several months of shoring up and making safe over the winter.

If all goes well Concordia will be towed away with the aid of the now air-filled sponsons in Spring 2014 as the weather improves. Her final fate - far less glamorous than the cruise packages she once offered - is to be broken up for scrap.