A description of the new documentary “Raw Faith” — which premiered at the Maine International Film Festival in July and screens at the Nickelodeon in Portland at 7 p.m. Thursday — sounds like the sort of nice, well-meaning inspirational story that secretly makes peoples’ eyes glaze over: The true-life tale of a Maine family’s dream of building a ship in order to take people with special needs on sea cruises.

Instead, Gregory Roscoe’s compelling film recalls nothing so much as a Maine version of a Werner Herzog movie, where a man becomes obsessed with an eccentric dream that brings him too close to the inherent dangers of nature, and risks losing literally everything to his quest.

Specifically, the decade-long journey of Maine electrical engineer-turned self-taught shipbuilder George McKay recalls Herzog’s film “Fitzcarraldo,” in which a man with a seemingly impossible dream attempts to haul an enormous steamship over a rainforest mountain. In “Raw Faith,” McKay sells his home and enlists his family in a quixotic plan to build a massive, fully functional replica of a three-masted galleon in order to take physically challenged people and their families on ocean voyages.

Working for years on a roadside in Addison alongside his three sons, his wife and his daughter (who’s afflicted with Marfan’s Syndrome), McKay, touting the knowledge gathered from “a couple dozen books,” did indeed create the Raw Faith — a 118-foot-long, 300-ton behemoth.

Which is impressive, even if the Raw Faith would never win any beauty contests. Or inspire any confidence whatsoever in anyone who saw it.

Lovingly (and awkwardly) hammered together from castoff lumber and slathered with tar and George’s steadfast dreams, the ship, looking like something castaways cobbled together to escape a desert isle, was finally launched in 2003. Like almost everything involved in the ship’s career, the launching provokes in the viewer a mix of admiration, elation and intense anxiety that the all-around ramshackle enterprise will come crashing down on the heads of the McKay family.

That ambivalence permeates the film, with harbormasters, Coast Guard officials and gradually even the members of George McKay’s family expressing their respect for what the man has accomplished alongside a growing unease with his single-minded and often unfathomable fixation on making the Raw Faith what he dreamed it would be.

Over 10 years, we see the idealistic McKay change, hardening in his approach to his family, bristling at the quite reasonable concerns and regulations of maritime officials, and introducing talk of God’s will and Satan’s obstacles to his mission’s narrative.

Eventually driving away even the one son who sailed with him for years as his only crew, he rails against what he considers his family’s abandonment with a sad, suppressed rage that’s both affecting — and alienating. To Fitzcarraldo, add elements of King Lear, Noah and Ahab.

This level of emotional complexity is very impressive, as McKay’s decade-long odyssey reaches what seems its inevitable conclusion: What began as an unapologetic celebration of one man’s eccentric dream becomes instead the gripping tale of what happens when monomaniacal passion clashes with the needs of others — and the unforgiving sea.

Dennis Perkins is a Portland freelance writer.