Actress Emma Caulfield was originally cast in the movie as Lauren, the strongest swimmer of the group. But upon arrival at the shooting location, it quickly became apparent that Caulfield was terrified of being in the water and was replaced.
The original script for the film was simply called Adrift, and was based on a short story by author Koji Suzuki, best known for writing the novel Ring which then became the film Ringu (1998), a Japanese horror classic. The script had already been written before the release, and success, of Open Water (2003). It initially had no connection to it. When the script was finally picked up for production, it was retitled Open Water 2: Adrift in certain countries (including the United States) to capitalize on its success.
The song in the opening (seeing the characters driving to the port) is called "Godspeed" while the yacht also has the name "GODSPEED" on it.
Promotional posters claim the film is based on actual events. This is false. The actual script is an adaptation of Koji Suzuki's short story Adrift, a piece of fiction. The marketing tactic comes from the success of Open Water (2003), which was actually based on a true story.
The character and motivations of "Dan" are based on childhood struggles of director Hans Horn and the fact that he was generally seen taking alone time in public swimming pools. This is the basis of the pivotal scenes in the movie where Dan is seen wading merely feet from his comrades, as Horn was known to frequently do.