Sailing is very effective. The raft is slow, the Karve in low winds is slow unless the wind is abeam and paddling is faster than or equivalent to tacking at wind speeds slower than 4. The long boat is always faster tacking than paddling at any wind speed.

The fair winds section of the boat is 270 degrees so 3/4ths of the time you'll have fair winds when you don't you tack which is keeping the wind on the bow in the fair winds section and then turning 90 degrees to catch the wind on the other side in a zig zag pattern which as I mentioned is faster than paddling most of the time.

Sailing is faster than sprinting an equivalent distance and much faster after you run out of stamina from sprinting and the boat has a cargo hold so it is the fastest way to transport ore or smelted metals.

Late game you get a forsaken power that always gives you fair winds when it active and its active for 5 minutes with a cool down of 20 minutes. If you have 4 players in your boat you can alternate and always have fair winds.

Once you can build portals you only ever have to sail to a new island one time (the first time) unless you want to move ore or smelted ingots. (Which will be changing with the difficulty sliders in the up coming patch.)