I like the idea.
The problem I see is that it requires some work on the part of the NPC AI:
- They need to "own" craft and know how to use them (beware: robbers and Njerps would be able to steal yours!).
- They need to know how to fight while on a craft (drop paddle to use a bow, pick it up to move again, move towards/away from the target, possibly using a shield for protection, and NOT jump into the water to try to close the distance swimming...