By Josh Levs
As divers searched frigid waters off South Korea in low visibility Wednesday, 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."
Earlier, when the ship left Seoul, it traveled through fog. By the time of the accident, conditions were clear. But it's possible that the ferry went off course in the fog, 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. ... What people don't see when they look at the glassy expanse is underneath, there are intricate and detailed channels maintained. If it got out of the channel, it could have hit something.
"It's also very common to have engine failures, explosions, those kinds of things on the ship, particularly in the engine room. And it would have sounded like some kind of a boom or an impact sound. But that probably alone wouldn't account for the sinking this quickly. It probably was something else that happened."
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.
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."
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 reports suggest that other passengers 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."
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