OK, I know it uses the wind and you angle the sail in such a way that move your boat/ship forward. That's all I know. I've always wonder how ships go around before the motor ship existed. I'm sure they look for existing wind/current route but how do you get to point B from A and get back to A with a sail? Surely they don't wait until the wind actually blows the other way or take an extra 1000mi to get back to A? Or do they? Perhaps that's why the Argonaut has so many rowers ?