MOKPO, South Korea (AP) — Strong currents, rain and bad visibility hampered an increasingly anxious search Thursday for 287 passengers, many thought to be high school students, still missing more than a day after their ferry flipped onto its side and sank in cold waters off the southern coast of South Korea. There were 475 people aboard, including 325 students on a school trip to a tourist island, and some of the frantic, angry parents gathered at Danwon High School in Ansan, which is near Seoul. At the school, some desperate relatives lashed out in frustration, screaming threats at the news media. Coast guard spokesman Kim Jae-in said that in the next two days, three vessels with cranes onboard would arrive to help with the rescue and salvage the ship. The water temperature in the area was about 12 degrees Celsius (54 Fahrenheit), cold enough to cause signs of hypothermia after about 90 minutes of exposure, according to an emergency official who spoke on condition of anonymity because department rules did not allow talking to the media. Kim said coast guard officials were questioning the captain, but declined to provide details or speculate on the cause of sinking. Kim denied earlier reports by Yonhap news agency that the ferry had turned too swiftly when it was supposed to make a slow turn. Coast guard officers, experts on marine science and other specialists planned to gather Thursday in Mokpo to start discussions on how the ship sank.