The only times I have trouble with sailing is when the waters are too narrow or tacking into the wind would take me too close to certain biomes.

Between some of these comments and some of what I've seen on vids, I'm left wondering just how many players actually know how to tack?

PS: also it's worth carrying a hoe and pickaxe when coasting and looking for passages to somewhere; often I find that only a few rocks need to be broken up or a bit of riverbed lowered. Karve is much better for that type of sailing than Longship.