Eccentric visionaries make the world go ’round. Then there are the foolhardy dreamers whose terrible misjudgments forecast tragedy by increments. Mistake after mistake, aggravated by desperation, they collapse into the widening abyss of their own lost ambition. It’s a nightmare, but it also makes a hell of a story.

Such is the saga of Donald Crowhurst, the tragic subject of this 2006 British documentary opening today at the Angelika Film Center. If the name sounds familiar, you probably remember the 1968 Sunday Times Golden Globe Race, in which the amateur yachtsman competed with eight other men in an effort to sail around the world single-handedly without ever stopping. Much of the film’s drama comes from the slow buildup of expectation that painfully leaks away into the disaster that is foreshadowed from the start. This is made exponentially worse because, at numerous points, it could all have been averted.

Crowhurst, a cheerful if hard-luck inventor whose business was failing, seized on the race as a chance to win a 5,000 pound prize while drawing publicity for the navigation devices he sold and prove to himself that he was capable of something most thought impossible. What happened instead, after he embarked on October 31 from Teignmouth Harbor in a 40-foot trimaran he christened the Teignmouth Electron, has since become the source of literature (Robert Stone’s “Outerbridge Reach”) and opera (Rinde Eckert’s “Richard Ravenshead”). “Deep Water” slowly unravels the mystery of how Crowhurst, who was expected to be only the second of the original nine sailors to complete the race, vanished into the Sargasso Sea, leaving behind a journal of disoriented ramblings. But most of his reported journey, detailed in a deceptive log and trumpeted on Fleet Street by an opportunistic press agent, never happened.

Directed by Louise Osmond and Jerry Rothwell, the film is predictably by-the-numbers, the kind of documentary whose parade of talking heads, unctuous voice-overs, weathered news clippings, liver-spotted BBC footage, and Steve-Zissou-on-acid visual embellishments will sooner or later land in heavy rotation on the Discovery Channel. The filmmakers must sense the surging waves that imperiled their subject, because they grip tight to heavy-handed imagery, exploiting the tortured jottings discovered in the abandoned Electron as a framing device. “MERCY” flashes on the screen as the story begins, looming large in Crowhurst’s handwriting, the sea swirls vertiginously, and there is no recourse to Dramamine. Glub.

The basic elements are strong enough that it’s a shame Ms. Osmond and Mr. Rothwell oversell it. Against an array of skilled and schooled competitors, Crowhurst reached far outside his comfort zone to test himself. As he had no money for the project, he inked a deal with the devil to voyage to the deep blue sea. His agreement with a wealthy sponsor included a clause that forbade him to give up the race, lest he repay the cost of the boat. Trapped by his pride and disabled by his lack of preparation and sailing acumen, Crowhurst was screwed. His trimaran, unlike more then-conventional designs, was untested against deep-sea conditions, and plans to customize it with technological innovations were cast aside in the rush to beat the deadline for launching the boat. So Crowhurst hatched a scheme that went haywire, never choosing the sensible option of simply coming home to his family (even if his foolishness would have put them all out on the street).

Luckily for history, Crowhurst and the other sailors took along tape recorders and movie cameras to document their journeys, and these grainy 16 mm glimpses, matched to the solitary confessions of their journals, constitute the film’s soul. The filmmakers parallel Crowhurst’s gradual descent into madness with the story of Bernard Moitessier, a Frenchman whose wife describes him here as “a poet and philosopher.” He lives up to her billing. Writing beautifully about the transcendental peace he feels, he gives up the competition on the final leg only to venture further around the world, so enraptured is he by the spiritual insights the ocean has given him. Anyone doing this for money or fame, he muses, is doomed. And he was right.