It should have been plain sailing for a South Korean ferry carrying hundreds of children and their teachers on an outing to the sub-tropical island of Jeju, an annual trip for Danwon High School. The Sewol had 476 passengers and crew on board, including 339 children and teachers. It had an experienced captain, was navigating well-known waters and had passed its annual inspections since it was bought second hand in 2012 by Chonghaejin Marine Co. Ltd. But prosecutors believe the vessel capsized after turning at too high a speed. Sixty-four people are known to have died and 238 are missing, presumed dead, mostly children. In an arrest document…