I remember reading once that the polynesians used to navigate with just a stick thrown in the water. They'd look at how the waves bounced of the stick and canceled out or something like that, and they knew where they were. I was studying waves in physics class in HS at the time, so somehow the principles of constructive and destructive interference were applicable.
I'd be interested in learning how the ancient Vikings navigated the stormy North Sea, I've read that they used a stone that refracted the sun's rays a certain way, but I don't know if that's just myth or loosly based on reality.
Sailing on a great wooden ship would be cool.