This illustration from the Costa press office shows some of the parbuckling job to come:
While it's never been attempted on such a scale, the principles are proven. Navy salvage teams used parbuckling to raise the USS Oklahoma in 1943:
Every marine salvage job is different. The Oklahoma project had to deal with suction from harbor mud, for example.
Concordia is a very large and structurally damaged ship in a tenuous position: it's resting on a few rocky ledges, with some sections entirely unsupported. This problem isn't obvious to the eye, but is plain enough to salvage engineers. Here's an image showing the underwater layout, from Italian authorities:
- First, install equipment on shore and underwater, such as anchor points and support platforms
- Next, attach huge pontoon floats to the port side (the side that's been above water all this time)
- Then haul it upright, so that it sits in flooded condition atop a temporary underwater platform customized for the reef profile
- Then attach a second set of pontoons to the starboard side (the side that's now underwater)
- Pump out the pontoons so that the ship's keel clears the platform, then tow the assembly to a dry dock for repairs
One of the foremost risks here is breaking the damaged ship in two (or three) pieces as the cables drag it upright. So the winches will take the strain very slowly.