Amanda Crew actually learned how to sail a boat for the film. In some scenes, you can make out bruises on her legs which was the price she paid for her lessons.
Zac Efron underwent three weeks of intensive training in how to sail a boat. He proved to be so adept at it that no stunt double was required for him in most of the longshots of Charlie St. Cloud sailing.
The chief reason why Ray Liotta took on the film was his 10-year-old daughter, who was desperate to meet Zac Efron. A similar reason impelled Kim Basinger to take on the role of the mother, i.e., her daughter Ireland.
The town where the St. Clouds live is actually a composite of four different towns in the Vancouver area.
Chris Massoglia was originally chosen to play an 18 year old version of Sam to be more faithful to the final scene of the book, but for reasons unknown, he was replaced by Charlie Tahan in the final film.