Of the nine seafaring souls who, in 1968, left Britain to compete in a nonstop solo sail around the world, Donald Crowhurst was surely the least experienced, the least prepared. A mild-mannered electronics engineer who lived with his wife and children in the English countryside, Crowhurst appears in Louise Osmond and Jerry Rothwell's fascinating documentary, Deep Water, as a man out of his depth, so to speak.

Crowhurst built a swift trimaran equipped with the latest gadgets. It boasted a self-righting mechanism, in case his three-hulled vessel flipped into stormy waters of the southern capes. But in the newsreel footage that Osmond and Rothwell use so effectively, the 36-year-old amateur, readying his ship in a port town months before the race, looks lost, baffled, out of sorts.

How can this man seriously think he can endure weeks upon weeks alone on the ocean? Waves the size of office towers, relentless winds - he can barely maneuver his dinghy past the mooring. (Note: I've been waiting years to use that phrase in a review - "maneuver his dinghy past the mooring.")

Like Into the Wild, Sean Penn's mesmerizing, melancholy adaptation of Jon Krakauer's book about a young American who wanders into the Alaskan outback (it opens Sept. 28), Deep Water is a story about survival in the elements, about man putting himself into extreme, and extremely stupid, situations.

Osmond and Rothwell interview Crowhurst's wife and son, and the publicity agent who helped hype the big event. The widow of Bernard Moitessier, a Crowhurst competitor (and a far more able-bodied seaman), talks about her husband's single-minded obsession, his deep need to sail. And Moitessier himself, through journal entries, reveals much about the mind of a man in a state of absolute solitude - a tiny dot in a tiny boat bobbing in endless seas beneath endless sky.

What happens with Crowhurst - who kept his own journals, and filmed himself aboard his vessel, the Teignmouth Electron - is what Deep Water is about. It is about his eight fellow sailors, of course, and about the different ways human beings respond to stress, to isolation, to challenge.

At the risk of giving too much away, I'll say this: The story of Donald Crowhurst is not one of remarkable courage or remarkable endurance.

But it is remarkable.

Deep Water ***1/2 (out of four stars)

Directed by Louise Osmond and Jerry Rothwell. With Donald Crowhurst, Clare Crowhurst, Simon Crowhurst, Robin Knox-Johnston and Francoise Moitessier de Cazalet. Distributed by IFC Films.

Running time: 1 hour, 33 mins.

Parent's guide: PG (adult themes)

Playing at: Ritz EastEndText

Contact movie critic Steven Rea at 215-854-5629 or srea@phillynews.com. Read his blog, "On Movies Online," at http://go.philly.com/onmovies.