The movie is based on the novel "Dead Calm" by Charles Williams. Orson Welles had filmed it under the name of "The Deep" (previous title: "Dead Reckoning"), based on his own script. The film starred Jeanne Moreau, Laurence Harvey, Michael Bryant, Welles' then-wife Oja Kodar, and Welles himself. The original story had more characters in it than the 1989 film version. Filming lasted from 1967 till 1969. A few scenes could not be filmed, due to the death of Laurence Harvey in 1973, and so Welles' version never reached the big screen.
Around 1997, there were rumors that Orson Welles material had been revised and seemed "as good as complete (compared to the shooting script)," and that his widow, Paola Mori, was trying to get it cut and distributed.
The tall ship used was 'Golden Plover' based in Airlie Beach, near Australia's Great Barrier Reef Whitsunday Islands where Dead Calm was filmed. A full size model ship was burned in the film and 'Golden Plover' lived to sail another day.
The trivia item below may give away important plot points.
The film originally ended with Rae bashing Hughie's head in with the spear gun and throwing him into the ocean on the inflatable mattress to float into the distance, before turning the boat around and saving John from his makeshift raft. The last shot of the movie was Rae hugging John and telling him she loved him and that she hadn't given up hope, giving her character closure from her hopeless outlook at the film's bleak opening. Audiences, however, weren't satisfied with Hughie's ambiguous fate (although the implication was that Rae had killed him with the blows to the head), and the ending was re-shot at the behest of studio heads, who were afraid audiences would spread bad word-of-mouth.