“The Discoverers” isn’t quite good enough to be the ample, quirky comedy that actor Griffin Dunne (“Dallas Buyers Club”) deserves, given his complex yet thoroughly entertaining turn in the film as an aging washout in matters of family and work.

Writer-director Justin Schwarz’s central contrivance — Dunne’s character, a marginal college professor named Lewis, reluctantly takes his kids on a half-baked re-creation of Lewis and Clark’s 19th-century expedition in order to connect with his widower father (Stuart Margolin) — never quite gels.

But the script’s strengths are really in several little detours, where Dunne’s familiar persona as a well-meaning but grasping, comically exasperated traveler through life’s mysteries gets to shine.

On his way to an academic conference in Oregon (where Lewis hopes to build enthusiasm for an unpublished, 6,000-page history tome) with his blasé teen children Zoe (Madeleine Martin) and Jack (Devon Graye), the long-suffering hero’s plans are waylaid by a family crisis. Rather than giving a lecture to salvage a doomed writing project, Lewis tries to save what’s left of his relationship with his father by joining a historical re-enactment of the 1804-06 Corps of Discovery.

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Schwarz can’t make enough out of that goofy notion — visually or narratively — to get a comic steam going. But there are sidebar pleasures to be found in such moments as Lewis’ awkward bonding with Zoe over her first menstrual period, or the way he clumsily tries to make his disheveled apartment presentable to unexpected guests.

A threadbare character clinging to self-respect is always going to be a richer — and funnier — nucleus for a movie than a grand joke. That’s the lesson here.

Tom Keogh: tomwkeogh@yahoo.com