On the day Sean McNamara met Bethany Hamilton, her family handed the veteran Hollywood director the surfboard she was sitting on when a tiger shark bit off her left arm.

The Hamiltons had already shared their story with McNamara, but the surfboard was more intimate and visceral. The orange-slice-shaped bite in the tiny board was 17 inches wide.

The Kauai family continued to open themselves to McNamara, showing him homemade videos of their daughter playing the ukulele as a child, clowning around at the hospital after the attack and heading into the surf for the first time after the near-fatal attack, her stitches barely healed.

It was a powerful experience for McNamara.

"I had the feeling right then that the full story of what they went through had to be told," he said. "And that it would become a family film about courage."

Six years later, the director is about to share the Hamilton family’s emotional ride with movie audiences. "Soul Surfer," a tragedy-to-triumph biopic, will open in 2,300 theaters on Friday. The feature film from TriStar Pictures and FilmDistrict stars AnnaSophia Robb as Bethany, Academy Award-winning actress Helen Hunt as her mother, Cheri, and Golden Globe nominee Dennis Quaid as her father, Tom.

What happened to the young surfer would seem like a ready-made drama.

Hamilton was 13, a surfing prodigy who seemed destined to rule the waves as a professional, when she was attacked by a tiger shark while surfing near Tunnels Beach on Oct. 31, 2003. Experts estimated the shark was 14 feet long. Her entire left arm was gone and she lost more than half her blood.

Within a month, though, Hamilton was surfing again and would ultimately return to competing at the highest level. She became an inspiration to people around the world.

A surfer himself, the 48-year-old McNamara was moved by Hamilton’s passion for the sport. But as a director with credits stretching back to the early 1980s, including the hit Disney series "That’s So Raven" and the Makaha-based "Beyond the Break," McNamara was just as moved to probe further into her story.

"Most people would never want to go in the water again," he said by phone from Los Angeles. "So from a story point of view, that intrigued me. But then as far as a movie is concerned, it has to be much deeper. You have to see a family crumbling or having conflict with each other and holding it together."

HAMILTON’S STORY has been told often by the media, as well as in the 2004 young-adult book "Soul Surfer: A True Story of Faith, Family, and Fighting to Get Back on the Board" and the 2007 documentary "Heart of a Soul Surfer." Throughout, Bethany’s message has included her Christian faith and McNamara knew — even as he sought to target a general audience — that her beliefs would have to be part of "Soul Surfer."

"That was my goal," he said. "I said I am going to make the faith-based audience feel this and at the same time make the mainstream audience love this."

The director wound up co-writing the script after several failed attempts by others, including one team of writers who wanted to give a drug addiction to the fictional version of Hamilton.

"They wanted Bethany into crack and I said, ‘No, no, we are going to do the real story,’" McNamara said. "But you do have to find the conflict within her story."

The finished film exceeded McNamara’s expectations as well as those of the Hamilton family, who had maintained a strong grip on the creative process because they feared Hollywood would slant the story. Bethany Hamilton, now 21, called the whole process "gnarly."

"You never know what will happen when Hollywood gets a hold of it," she said. "It was really challenging going back and forth and trying to rewrite stuff. They had their writers but still my family and I would come up with stuff here and there in different scenes that needed work."

CASTING ROBB was an idea that came from Hamilton and her mother. They had seen the tiny, blonde actress in "Charlie and the Chocolate Factory" and "Bridge to Terabithia." Then 16, Robb arrived in Hawaii a month prior to the start of filming in January 2010 so she could spend time on Kauai with Bethany.

"She trained to look like a surfer and she learned to surf," said Hamilton, who was on Oahu last month to promote the movie. "She put a lot of pressure on herself. I didn’t know how to help her prepare. She just grilled me with questions. She really did her research."

McNamara had never heard of Robb but said he now considers her one of the best actresses he’s ever worked with.

Her role was demanding, especially when the actress had to maneuver through breaking waves while pretending to have only one arm, the director said. Robb wore a prosthetic device on her shoulder and a green sleeve on her arm to allow special-effects technicians to erase her arm from the screen. McNamara shot the scenes twice — once with Robb and once without her so that the space where her arm appeared could be cut out and replaced with the empty background footage.

"We would do 15 versions of each shot and there were 700 shots in the movie that either digitally removed her arm or digitally removed her face because Bethany did the surfing," he said. "Hopefully most people won’t know it is an effects film, but the reality is, it is. But it is a subtle effects film."

Perhaps the most powerful scene in the movie is the one that everyone knows is coming: the shark attack.

McNamara gave a lot of thought to how he would frame the sequence of events and when the beast would rise from the water. He wanted to first set the surfer’s life in context. He wanted a portrait of a happy family painted in stark relief against a frightening moment of flashing teeth.

"I needed to show enough of her so you fell in love with her and fell in love with her family and got to know her with two arms so we understood what the loss was," McNamara said. "But it is not a shark movie. I don’t want to scare people."

Even so, when the director shot the scene of the young surfer being carried bleeding to shore, it was so graphic that her father, Tom Hamilton, had to leave the beach. "It was like living it," he said at the time.

And the filmmakers added intensity to the scene with a camera setting identical to the one used in the opening battle scene of "Saving Private Ryan," said David Brookwell, one of the film’s producers.

"All of the post-shark attack shots we used an adjusted setting in the camera called a ’45 degree shutter’ which gives it a staccato look and creates a subliminal feeling of urgency," Brookwell said in an email.

Hamilton still lives on Kauai, but she’s racked up more than a few frequent-flier miles.

She surfs professionally in about 10 events a year on the ASP Women’s Star tour, but lately she’s had to wedge her surfing career into speaking engagements and a promotional tour for "Soul Surfer." Last month, after two weeks pumping the film, she flew from California to Australia for a contest that earned her only $450. Then she was back in Hawaii for more publicity. In two weeks, she’ll be back in Australia for another contest.

When she first met McNamara, Hamilton told the director she didn’t want to make a movie that was "cheesy or corny." She wanted it to be inspirational.

"What my family and I went through is something that is going to encourage other people," she said. "Whether they are going to go through something, or have gone through something or are going through something, I just hope it can encourage them to push on. It’s exciting and it turned out really good. And the surfing is sick."

» "Soul Surfer" will screen at 7 tonight at the Hawaii International Film Festival’s 2011 Spring Showcase at the Regal Dole Cannery theaters. The film will open in theaters nationwide on Friday.