Theories on how a South Korean passenger ferry suddenly sank

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Theories on how a South Korean passenger ferry suddenly sank

By Josh Levs, CNN

April 17, 2014 -- Updated 1135 GMT (1935 HKT)

(CNN) -- As divers searched frigid waters off South Korea in low visibility, hoping to save hundreds of passengers, a dominant theory began to emerge about how the ferry sank.

It most likely struck something in the water, said Peter Boynton, a retired U.S. Coast Guard captain.

"The speed with which this ferry began to list and then roll over on its side suggests significant damage, most likely causing major flooding that would cause a vessel of this size -- almost 500 feet long -- to quickly roll onto its side. That's very likely the result of significant damage," he said.

Some passengers reported hearing a loud bang before the ship began sinking. That could be from cargo shifting or "some other internal damage," Boynton told CNN's "New Day." "But it does sound, from initial reports, it was more likely that something was struck."

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Terrain

 

Approximate location

When the ship left Seoul, it traveled through fog, which may have put it off course, said Mary Schiavo, former inspector general for the Department of Transportation.

"So if they hit something, that would have meant they were out of the channel, which is quite easy to do," Schiavo said.

'We are not dead yet' passengers texted

But the South Korean Oceans and Fisheries Ministry said Thursday that the ferry did not deviate significantly from its intended route.

The agency approved the ferry's intended route, and "there was no huge difference between their plan and the actual track chart," spokesman Nam Jae Heon said.

Schiavo said other possibilities include engine failure or an explosion, particularly in the engine room.

"But that probably alone wouldn't account for the sinking this quickly. It probably was something else that happened," she said.

Making matters worse, the ferry carried dozens of vehicles. Once an auto deck is breached, "it's typically open to very significant flooding," Boynton said. That could explain "why the ferry in just a matter of hours began to roll onto its side so quickly."

Coast guard and navy ships, as well as fishing boats, rushed into the area.

The challenge ahead

For rescue divers, a combination of factors makes saving people especially difficult: very cold waters, strong currents and low visibility, made worse by nightfall. "The underwater challenges are very, very significant and pose, I would think, tremendous risk for the people who I'm sure are doing their best to help," Boynton said.

For the passengers, the most immediate danger is the cold.

"Pretty much everyone we saw was wearing a life jacket," journalist Andrew Salmon reported on CNN International. "So the concern is hypothermia. If you're not picked up within two hours, you're in significant danger -- your body core goes cold."

Can they survive in air pockets?

Some of the rescued passengers report that when the ship began to sink, they were told to jump into the water immediately -- and not to take time to get into life boats. Sometimes after a breach, as the water begins gushing in, "there's a sucking, there's a motion, that just makes it impossible to fight," Schiavo said.

"So the order to abandon ship might have indicated that. ... It's almost like a suction that occurs when the water starts coming on, and you can't fight it."

But other passengers said they were told to stay on the ship. Sometimes, "conflicting commands" are given, Schiavo said. "There can be a lot of confusion in an event like this."

READ: Rescuers search dark, cold sea for survivors of shipwreck off South Korea

READ: Survivors tell of panic on board as ferry tilts, then capsizes

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South Korea Ferry: How Can a Huge Ship Sink?

By Tanya Lewis, Staff Writer   |   April 17, 2014 06:04pm ET

The sinking South Korean ferry had hundreds of high school students onboard for a school trip. 
Credit: Screenshot, CBS News

View full size image

The sudden sinking of a ferry carrying 475 passengers off South Korea's southern coast brings up the question: How can a large, modern passenger ship just sink?

A number of things can cause such a vessel to go down, from running aground on the ocean floor, to cargo shifting and capsizing the ship. Once the damage is done, ship officials must act quickly to evacuate passengers to avert a disaster, maritime experts say.

Millions of passengers take to the sea each year aboard ferries andcruise ships, and most of the time, the vessels return them safely to port. But from the sinking of the South Korean ferry to the Italian cruise liner Costa Concordia to the Titanic, disasters do occur. And when they do, the results can be tragic. [Disasters at Sea: 6 Deadliest Shipwrecks]

Causes of sinking

What caused the Sewol, the ill-fated ferry sailing from Incheon, in northwestern South Korea, to the island of Jeju to tilt steeply to one side and fill with water Tuesday morning (April 15) is not yet known. But many survivors said they heard a loud crash as the ship started tilting sharply. 

"We obviously don't  know a whole lot yet," said Rick Comeau, a vice president at the Maritime Simulation Institute in Newport, R.I. "However, it certainly sounds from the outset like the ship struck something."

Large ferries and cruise ships are compartmentalized, both front-to-back and side-to-side — "like an ice cube tray," Comeau told Live Science. If one compartment gets punctured, water should only flood that area.

In the case of the Titanic, which scraped an iceberg and sank in 1912, the ship's compartments were connected to each other at the top, so water entered the front bulkheads and flowed from one to the next, Comeau said.

Similarly, when the Costa Concordia ran aground off the coast of an Italian island in 2012, the watertight doors between compartments were open, allowing water to inundate the vessel.

Investigators are looking into the possibility that the Korean vessel was off course when the incident occurred, and may have hit something.

"We don't know specifically what happened with the Korean ferry, but it sounds like whatever it hit was long enough that it flooded multiple compartments," Comeau said.

If a ship has been punctured, creating a small hole, the crew will normally slow or stop the ship so that it doesn't push water into the opening, Comeau said. Another option is "counter flooding" the vessel by adding water to the other side. But if the ship is overflooded, it will sink. The ship's architect creates a book of guidelines for how much flooding the ship can withstand before it will sink, according to Comeau.

Another possibility is that large swells or a hasty maneuver could have caused the ship's cargo to shift to one side, changing the vessel's center of gravity and making it tilt over, according to Michael Bruno, a dean of engineering at Stevens Institute of Technology in Hoboken, N.J.

"Violent movement from waves could cause dislodging of cargo," Bruno told Live Science. Alternatively, "a sudden movement of the vessel itself [such as a fast turn, at high speed] can cause the vessel to roll," he said.

To err is human

All too often, it's not mechanical error but human error that is responsible for a maritime disaster, experts say.

"Some events are recoverable, some are not," Comeau said. But once something goes wrong, the ship's officers need to recognize when to declare an emergency, send out a mayday signal and get people on lifeboats, he said.

With the South Korean ferry, the captain was not the normal captain, but a relief, or backup, captain, according to Comeau. Many of the survivors said they were told not to move, a CNN affiliate reported, which may have delayed evacuation efforts.

"You can't out-engineer human error," Comeau said, but regular emergency training and refresher courses are essential, he added.

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