Why not thinking outside the box? Rather than having mermaid to appear to return to the ship even if their ship sank, spawn a yellow inflatable raft. Once their ship sank, the inflatable raft spawns where its very location that their ship sank where players can hop on the raft floating back to the outpost at a real-time which is slower than any sloop. Once they arrive back at any outpost, they can do two things: buy a new ship and/or pay for a bounty reward system. If they rammed and sank their own ship by themselves, no bounty system appears.
The rafting would move a lot slower but still able to reach back to civilization and buy a new ship is far better than a respawn system that they are currently use.
If a player feels that they are being unfair targeted upon through a PVP that steals their treasure, they could use a bounty reward system where players could pay at a price to reward any crew in the online world that sinks a bounty crew of 4 at an outpost. With the current system where online players is being sighted, it is shown as white lettering but with the bounty system, red lettering or yellow or whatever color you choose be shown and identified as a bounty and upon their defeat, the different crew get the bounty rewards to be paid by the players.
It could be abused but the bounty system needs to be moderated and approved for online play. This would enhanced the gameplay and prevent a quick spawn and go back to the very same location for some revenge. That player that wishes a bounty must deposit the gold themselves and must decide whether it be worth it. Bounty system ends when a players or crew ends their playing session or changes their server. Once the player or the crew is bounty, had their ship sank, cannot use a bounty upon their very next spawn as a revenge.