For Redford (at age 77) the most grueling aspect of the shoot was not the stunts, most of which he insisted on performing himself, but the dismal daily routine of being perpetually waterlogged throughout the production.
This is the only movie in the 100-plus year history of international filmmaking that has only one actor and one writer/director but eleven executive producers as well as six other producers of varied titles.
The director adhered to what he termed his "bungee cord rule". A general shooting principle whereby the camera could not be above, below or farther from Redford than a cord could be stretched. Furthermore, in an effort to create a claustrophobic 'first mate intimacy' between audience and subject, DP Frank G. DeMarco filmed extensively within arm's reach of Redford using a 32mm lens on his Alexa camera.
Robert Redford was very frustrated that the studio did not promote the film for awards, both for J.C. Chandor in writing and directing and himself for acting (a feeling echoed by numerous film critics who liked the film and were surprised it was given a small release with little publicity) and has cited this experience as a reason he has moved towards taking fewer acting jobs and preparing strongly for retirement from acting altogether.
The trivia item below may give away important plot points.
Director/writer J.C. Chandor says that the intention of the final shot was that the audience would feel one of two things: either it's a real hand in the water or it's the hand of God. Chandor personally feels that the sailor died at the end of the film, since it's what the man would've wanted by that point of the story.