I have been playing for a few days now and in my opinion you have a simple flaw in the way you are handling death. If a ship is sunk all the players from the sunken vessel can continually re-spawn right back at that spot where they just sunk allowing them effectively harass the winning team or worse, destroy all their opponents progress by throwing there treasure in the water or sinking their ship. I am not sure I understand why you would have this set up to work like this. Simple fix would be to have players re-spawn with their ship once it is sunk or at a minimum increase the re-spawn timer. I have yet to be in a battle that did not end with both ships sinking. Shouldn't the primary goal be to keep your ship afloat?
Additionally, when i spend and hour or two hunting treasure I expect to see some reward/progression in return. When every battle ends in a loss for both teams it makes it pretty difficult to see how that is going to happen. Unless you are one of those players who is not hunting treasure and seeking only to engage in combat with other players and have no interest in progression. Which is ultimately what leads to all the harassment.
I get the overall concept, but there needs to be a winner and a loser in the battles. Both teams losing every time doesn't make much sense.