http://www.cnn.com/2014/04/16/world/asia/south-korea-ship-sinking-cause/index.html?hpt=hp_t1
Theories on how a South Korean passenger ferry suddenly 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."
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. ... 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."