Ditto Kate Elliot re: Bishop Museum and privileging sources on Nainoa Thompson and Mau Pialug over Heyerdahl on Polynesian voyaging and navigation. (Pialug could apparently perform amazing - as in, westerners who hadn't seen him do them would claim they were flat-out impossible without compass and sextant - feats of navigation by memorizing star positions and gauging wind and water currents, as well as observing flotsam and seabirds.)

My mother used to work at Bishop Museum, so when I get a moment, I can ask her about further sources beyond the ones people have mentioned you should look at, and/or nuances to the scholarship that didn't make it to the page.