Eh, if you're using a Raft, you should be sticking somewhat close to a shore anyway. Encountering a Serpent while on a raft is basically a guaranteed death unless you have a good enough Bow to take it out in a few shots.

The Karve is faster, and offers storage plus some durability, but yeah, ramming it in to rocks will destroy it quickly.

The Longship is pretty fast even when just paddling against the wind.. but if you have the wind at your back, makes great pace and you can outrun everything except maybe Deathsquitos if you get too close to the Plains. It also offers enough durability that running it across some rocks isn't as devastating as with the other ships. It also offers much more storage.

That being said, never leave home without the materials for a Work Bench in your inventory, especially when sailing. That way, if you have to repair your ship mid-voyage you can just shore it somewhere safely (Meadows, preferably), drop a Work Bench, repair the ship, destroy the Work Bench for your materials, and continue sailing.

Also, if you carry the stuff with you to make Portals for quick returns to home, be sure to also always drop a Work Bench on the shore near your boat to keep things from spawning near it. Not so much of an issue once you move out of rendering range, but better to be safe than sorry.