“Open Water” is based on a true story, and it’s a tense, if threadbare, tale of survival. But the finished film is bound to be overshadowed by the tale of how it was made. Actors Blanchard Ryan and Daniel Travis wore sharkproof chain mail under their wet suits, but that didn’t cover their hands. Or their heads. They also weren’t covered by insurance. “We just signed waivers saying that we wouldn’t sue each other,” Kentis says. “There was no way anyone would insure this movie. No way.” Both actors give terrific performances in what was going to be, one way or the other, the role of a lifetime. But the gold star for bravery goes to Ryan, who was bitten on the hand by a barracuda on her first day. “And she still stuck with it!” Kentis says. “She’s absolutely fearless.” Or absolutely nuts.