Would you sign on for three months in shark-infested waters on a tippy raft under a captain who can't swim? The shrewdest joke in the sure-fire Kon-Tiki — a film about Thor Heyerdahl's 4,000-mile South Pacific expedition to prove that ocean-faring Incans could have settled Tahiti — is that practically every character Heyerdahl meets can't wait to join his suicide trip. Codirectors Joachim Rønning and Espen Sandberg have scared up the kroner to make a handsome Norwegian feature about Heyerdahl's 1947 journey — and, rather than risk a redubbing, they shot this English-language twin at the same time, with the same actors. As passive drift gives way to seasonal currents, Kon-Tiki works up a nice head of storytelling steam. Still, exciting as they are, we've sailed these sea lanes before. Anybody who owed as much to a loan shark as these filmmakers owe to Steven Spielberg would be dead by now. Tick 'em off as they go by: the shooting star against an inky sky, the claustrophobic shark cage, plus more bristling dorsal fins than your average stegosaurus. Without conspicuously meaning to, Kon-Tiki raises a question that remains ticklish among explorers and filmmakers both: Who, finally, gets the credit? At the climax, the hero galumphs proudly ashore in Polynesia — with the sailors who risked their lives staggering along behind. Does heroism always have to mean hogging the frame once within reach of the loving cup? As usual, posterity gets the last laugh: Most anthropologists today think Heyerdahl was wrong about the settlement of Polynesia. Won an Oscar, though.