If you are going to have a quest system, NPC enemies, puzzles and adventure based play you should have a peaceful quest or merchant only mode or server or vice/versa.
I have been struggling for days to complete a single merchant mission only to be annoyed by aggressive players who seek only to ruin my day, steal my crates and sink my ship in a childish display of dominance. Some players have limited game time and this is frustrating. I repeatedly take a friendly posture, use lights, chat, etc. and am repeatedly disrespected.
Rewarding aggressive player behavior by awarding experience for stolen items seems unfair as well. Shouldn't experience be gained from voyage completion? Ships supplies should be off limits to discourage petty aggression. There are barrels on every island, and floating randomly in the water. Making ships supplies available to petty looting only encourages aggression against peaceful players.
There is no need for questing or experience if the game is going to be PVP only. Just make it a $20 boat battle game. Why bother Questing? Love the sailing and treasure hunting, but forced PVP is NOT fun. I enjoy hunting for treasure, merchant quests, solving riddles and killing skeletons. I DO NOT enjoy be FORCED to fight other players all the time. There is a deep sea of fun game in there waiting to come out, but it seems the shallows is where its wallowing at the moment.