Several hundred salvage workers will endeavour to right the Costa Concordia wreck on Monday, more than 20 months after the luxury cruise liner crashed into a reef and partially sank. It is a vital but uncertain step in the costliest-ever maritime salvage operation.

Thirty-two passengers and crew members were killed after the 290-metre, 11-storey cruise ship struck a reef off the Italian island of Giglio in January 2012. Francesco Schettino, the ship’s captain, is on trial for abandoning the ship and manslaughter. Four other crew members and a company official have been sentenced to prison.

In January, Franco Gabriele, the head of Italy's civil protection agency, said the cost of the operation could reach $530 million, up from the $400 originally estimated. More recent estimates put the budget at $825 million.

Based on sea and weather conditions in Monday's dawn forecast, authorities on Sunday gave the final go-ahead for the ambitious operation in the waters off Tuscany, an engineering feat that has never before been tried in such conditions.

What has been done so far?

In April 2012, Florida-based Titan Salvage and Italian firm Micoperi were awarded the contract to remove the ship from Italy’s Giglio Island. Work got underway the following month.

The first task was to anchor and stabilize the wreck in order to keep it from slipping further into the sea, making it less dangerous to work on. Workers attached the Costa Concordia to the coastline using four “submarine anchor blocks.”

Other work included building a “false bottom,” or underwater platform, on the seabed below the wreck, which it will sit on once it has been righted. Fifteen steel containers called “caissons” were also installed on the side of the ship that is above water to right the ship.

To cushion the more delicate bow of the ship, crews have cradled it in protective material, a measure likened to putting a protective neck brace around an accident victim before being moved.

Canada will also have its role in the salvage operation. Waterloo-based 2G Robotics is set to deploy its underwater laser scanner next week to provide a detailed picture of the submerged section of the ship. 

What is parbuckling?

In the language of maritime salvage, parbuckling means to use leverage to right a sunken ship that’s resting on its side or is upside down.

It’s usually conducted to help recover smaller marine vessels, but there have been a few exceptions. After the attack on Pearl Harbour in 1941, parbuckling was used on two U.S. naval ships that had been partially sunk. In the case of USS Oklahoma, it was successful. But when crews tried to right USS Utah, the ship slid along the seabed near shore and the salvage operation was abandoned. Its ruins still lie along the Hawaiian coast.

Although parbuckling is a tested way to set capsized vessels upright, the operation has never been applied to a huge cruise liner. In the case of the Costa Concordia, righting the ship will take place gradually over a number of hours. Hydraulic pumps will pull cables attached to steel containers that have been fastened to the ship, and onto the underwater platform on the seabed below. Tanks filled with water on the exposed side of the ship will also help rotate it upward.

What are the risks?

One of the challenges is to rotate the vessel without dragging it lower onto the seabed on which it lies.

The Costa Concordia wreck

An aerial view of Costa Concordia as it lies on its side next to Giglio Island. Salvage crews will endeavour to right the luxury liner next week, a vital but uncertain step in the costliest-ever maritime salvage operation. (Alessandro Bianchi/Reuters)

The platform built onto the seabed below could help reduce that risk, but there’s still a danger the ship could over-rotate off the platform and plunge into the sea. Cables have been connected to the ship’s starboard turrets to help balance it as it rotates.

Another problem, according to the Concordia wreck removal website, is that the force of parbuckling could deform the ship’s hull. And there is a chance the cruise liner could split apart or fall back on its side near an Italian island.

The ship’s unknown condition after it has been soaking in the water for 20 months could also pose as a risk, according to Frank Van Hoorn, senior naval architect of Argonautics, a California-based marine consulting company.

“There could be some deep deterioration going on internally that nobody knows,” he told CBC News.

The wreck’s angle – 66 degrees – also makes the operation more difficult, Van Hoorn added.

What happens next?

If things go well, 15 more steel containers will eventually be installed on the right side of the deck, to match those that have already been attached to the left side. Those tanks will be used to help refloat the cruise ship so that it can be brought into an Italian port and cut up for scrap.

Bodies of two of the 32 victims, an Italian passenger and a Filipino crew member, were never found. Once the ship is set upright and stabilized, its interior will be searched again in hopes of finding their remains.

But if the attempt to right the wreck goes awry, the salvage team doesn’t have a "Plan B."

Franco Gabrielli, head of Italy's Civil Protection agency, said this week that the possibility of the Mediterranean cruise liner falling apart is a "remote event." But, he added, "If the ship doesn't turn" back upright, "there is no other way" to try it again.

In that case, Van Hoorn predicts a grim ending for the luxury liner.

“There’s always a Plan B, which is to scrap it on the site and take it apart into small bits and pieces,” he said.

With files from The Associated Press