Costa Concordia: Salvaging a shipwreck

After wrecking at sea a year and a half ago, the Italian luxury liner awaits one of the most expensive and daunting salvage operations ever

The following script is from "Costa Concordia" which aired on Dec. 16, 2012, and was rebroadcast on Sept. 1, 2013. Lesley Stahl is the correspondent. Rich Bonin and Sabina Castelfranco, producers.

Ever since the wreck of the Costa Concordia a year and a half ago, the huge Italian luxury liner has been sitting, semi-submerged, off the coast of Tuscany, looking like a big, beached whale.

It's the largest passenger ship ever capsized, easily surpassing the Titanic. And, as we first reported last year, removing the ship has turned out to be the most complicated, the most expensive, the most daunting and the riskiest salvage operation ever.

The Costa Concordia is a rusting carcass, sitting precariously on two underwater mountain peaks. The swimming pools and jacuzzis where passengers sunbathed and sipped cocktails, now empty and askew. A clock remains frozen in time, marking the hour and minute when the ship lost power.

And below, ghostly vestiges of the ship's contents litter the ocean floor in what the Italian authorities have designated an official crime scene. Thirty people died; two are still missing.

Nick Sloane: Welcome on board.

Lesley Stahl: Thank you.

Nick Sloane from South Africa is the senior salvage master. He took us out to the wreck site.

Lesley Stahl: How big is that ship?

Nick Sloane: She's huge and what you see at the moment is only 35 percent of her. So 65 percent underneath is like an iceberg underneath there.

Now the plan is to roll the 60,000-ton ship in one piece onto an underwater platform, raise it and then float it away so it can be cut up for scrap.

Lesley Stahl: So, you're planning to rotate a ship that weighs 60,000 tons.

Nick Sloane: Yeah.

Lesley Stahl: So, let me see. You're going to-- this is the ship. You have to do it like--

Nick Sloane: We'll roll it upright--

Lesley Stahl: --the whole thing together at once, creaking.

Nick Sloane: All the way along the three football fields long.

Lesley Stahl: Three football fields long?

Nick Sloane: Yeah. And we're going to rotate it all at the same time.

It sounds like an experiment in defying the laws of physics. The actual work is being shared by Nick Sloane's Titan Salvage, an American wreck removal company, and Micoperi, an Italian engineering firm. Sergio Girotto is the company's project director - in charge of re-floating a 60,000-ton ship filled with seawater.

Lesley Stahl: So, you have to create much more buoyancy than even the original weight of the ship, because of all the water?

Sergio Girotto: Absolutely. Absolutely.

A team of engineers came up with something ingenious: to in effect, weld a new ship onto the shipwreck. It starts here with the construction of towering steel boxes called "sponsons".