over. >> reporter: even this ship can sink frighteningly fast. in 1991, the oceania cruise ship was sinking for a day. but abc news was there for the final few moments. if survivors are in the water, a sinking ship can suck them under the water, forcing them to get back to the surface. off south korea, the sewol was reportedly in a rocky area. if it struck a rock and breached the hull water could start pouring in from one compartment to another tipping the vessel, then its stern sinking. soon, only the top of the bow visibility. the ferry upside down in the water. it's the water's incredible rushing force that makes escape nearly impossible. if they jumped, 25 feet from the upper deck into the chilly waters. >> you wouldn't want to jump unless you knew it was sinking or you had a place to go in the water, like a life raft. many made the leap, others may have. david kerley, abc news, washington.