A documentary by Aaron Lieber. Rating unavailable

Bethany Hamilton: Unstoppable is meant to be a biopic about a feisty girl who overcomes adversity. But it's more successful when viewed as a surfer doc in the tradition of Riding Giants or Step Into Liquid.

The story of the famous 13-year-old wunderkind who lost her arm to a tiger shark in 2003 celebrates the sport that drew her back to the waves in spectacular style.

A veteran surf-film maker, and a rider himself, director Aaron Lieber follows the now grown-up Hamilton to monster waves in Hawaii, Tahiti, California, and Fiji, capturing the star holding her own in world championships. It's inspiring stuff, even for those who think a duck dive is a term reserved for waterfowl. The sight of the one-armed surf star zipping through rad barrels and carving up wave faces is earnestly awe-inspiring. This despite the fact the film itself has the high sheen of a freshly waxed surfboard.

The unassuming heroine has the right stuff to inspire girl power. With her sun-bleached golden hair and determined jaw, she shows a kind of uncomplicated grit you don't see celebrated in the selfie era. It's clearly in her blood: as home movies show, even at 13 and lying in a hospital bed recovering from the horrific injury she calmly insisted she would get back surfing again: "It's pretty much my dream."

Oddly, that's the sum total of insights into Hamilton's psychology that we get in Unstoppable.

Even the many quick-cut interviewees here—relatives, surfing competitors, her husband—rarely come off as more than talking heads. Lieber tries to allude to tension in Hamilton's life—her struggles with fame (hello, Oprah and The Amazing Race), and her attempts to nurse a newborn while competing internationally—but every obstacle is presented with the same blithe, impenetrable determination.

Lieber traces Hamilton's life from before the attack, when her parents worked two or three jobs each to support their kids' idyllic Kauai-surfer upbringing, to her rehabilitation and return as a top-tier athlete. No one believes her new imbalance will allow her to stand on a surfboard again, let alone compete internationally.

Even a scene where Hamilton later refuses an ESPY Award for athlete with a disability—she regularly trounces able-bodied competitors—is explored with zero depth.

Soon she's back on the waves again, setting her jaw, a tiny human mastering a spectacular blue beast. Hamilton is a fearless risk-taker.

The film about her? Not so much.