As the search for survivors of the sunken South Korean ferry winds down, officials must turn their attention to the monumental task of salvaging the ship. It’s a delicate operation that experts tell NBC News could take several months — if not longer — to complete.
“This is going to be a big project,” said Kerry Walsh, marine casualty project manager for Seattle’s Global Diving & Salvage, which worked in the recovery of the Princess of the Stars passenger ferry when it capsized off the Philippines in 2008.
“Part of what’s going on right now on the backburner is [officials] are scrambling to come up with the plan,” Walsh said. “The challenge will be figuring out the engineering involved and coordinating that plan … which will involve a lot of people who need to work together.”
The Sewol ferry, at 480 feet long and 6,835 tons, toppled upside down after it capsized one week ago following a sharp turn at a high rate of speed, according to investigators.
The ferry carried mostly high school students on a trip to the southern tourist island of Jeju. There are 152 people still missing — 174 people were rescued as it began to sink, but no survivors have been found since. Families of the victims have reportedly given permission for the vessel to be hoisted from the seabed if no one is found alive by Thursday.
The job for professional salvagers will be a logistical puzzle.
“These things are never easy, and [officials] need to assess what combination of techniques would work best,” said Bob Umbdenstock, of salvage company Resolve Marine Group, which worked on the Deepwater Horizon oil spill in the Gulf of Mexico in 2010.
Initially, pumps would need to be attached to the Sewol and used to siphon out fuel, which would lessen the environmental impact when the ship is righted, Walsh said.
Any extensive damage to the hull would also need to be repaired to stop more water from getting in. When that’s completed, several industrial-sized cranes would be connected to the ship in just the right spots for turning it over.
“The most challenging would be the rigging of [the cranes to the ship], and raising it so the ship rolls right-side-up,” Walsh said.
The ship can be flipped to a point where the main deck is out of the water, he added, and then the water still inside the ship can be pumped out. But because the ship must be maneuvered while it’s completely submerged, anchors would be needed to keep it from shifting with the current, Walsh said.
The weather and visibility will also be factors.
“Even on a calm day, you have the water flowing like a river,” Walsh added.
Once the Sewol is upright, the search for bodies trapped inside would resume and the vessel could be towed ashore.
While the recovery has its own unique problems, how it stacks up to other salvage operations remains to be seen.
It took almost two years for the luxury liner the Costa Concordia to be righted after it sunk off the Italian coast in 2012, killing 32 people. The ship was only partially submerged and rested underwater on one side. That actually made it a more complicated recovery because engineers had to build an underwater metal platform to help hoist the ship, experts said.
The Princess of the Stars, at 23,824 tons, also took two years before it was finally towed to shallow waters. The process was delayed, in part, because of the discovery of a dangerous pesticide on board that needed to be disposed of first. More than 800 people died when the ship sank during a typhoon in 2008. Many of the victims were never found.
The far-smaller fishing vessel, the 830-ton Ehime Maru, sank in 2001 after the USS Greeneville submarine accidentally collided with it near Hawaii. Nine of the 35 passengers aboard the Japanese trawler died, and the U.S. Navy used a rig to raise the ship in a four-month process.
The operation was difficult because the ship had sunk 2,000 feet — far too deep for divers to help.
In the Sewol’s case, the ship is stuck in a channel only about 122 to 142 feet deep, officials said. There is room to maneuver, and the expertise of those involved will make a difference, Umbdenstock said.
“Luckily, the Korean marine industry is pretty well-developed,” he added.