"I knew Bethany's story, of course, but I thought 'what an incredible role', explains Robb. " I was so fascinated by all of the challenges. What would it be like to have your arm taken and what would go through your head and how would your faith be challenged? "
To play the role, Robb had to learn how to surf well enough to play a champion. The young actress admits she never got to that level, but, tutored by Hamilton, she did pick up the basics.
"Bethany taught me a ton and really helped me figuring out where the 'channel' is and how to look for waves and what to do and just about knowledge of the sea and being comfortable in it for sure," Robb says.
The filmmakers use special effects to digitally 'remove' Robb's arm. However no tricks were necessary for the surfing scenes because Hamilton herself does the breathtaking wave riding.
Now 21, she says she hopes audiences find inspiration in the depiction of the sport she loves.
"Not a lot of people know that much about surfing, so I hope they're educated on it," Hamilton says. "And most of all if people are going through a hard time, they could be encouraged and find inspiration to push through those hard times and see that, in my family's case, so much good has come out of it."
Hamilton credits her Christian faith with helping her find that positive message. Director and co-writer Sean McNamara says he felt that had to be part of the film.
"Soul Surfer is about a girl who is a surfer, but that is not what the real story is about," McNamara notes. "The story is about what happens with her family and, with the tragedy that she has, how she can get back on the board. Part of her character is that she is a Christian. That is just part of who she is, so we didn't want to hide from that. It was just part of who she was so it came out in the script."
"How can this be God's plan for me? I don't understand."
"I don't know why terrible things happen to us sometimes, but I have to believe that something good is going to come out of this."
Soul Surfer marks the acting debut of country music star Carrie Underwood, who plays the church youth leader who is Bethany's spiritual guide.
"This story is about having faith when the chips are down and when something terrible has happened that you don't know how to deal with," explains Underwood. "I feel like we can all learn something from Bethany's story and when the little things in our lives don't go so well we can take a lesson from her and realize how small that really is."
Bethany Hamilton won her first amateur surfing championship just two years after she lost her arm. In 2007 she realized her dream of becoming a professional surfer. She also established the "Friends of Bethany," a non-profit foundation dedicated to supporting shark attack victims and amputees around the world.
