I think this idea is old but, when a pirate attack a ship, the pirate take all, the gold and the resources in the ship... Maybe the game can implement, in NPC Trade fleets and again PvP too:
PLUNDER!

You plundered X gold coins!

Your fame increased by X!

Your ship X is loaded with the cargo plundered whit:

30 Tools!
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Maybe you can add the gold bars in the Treasure Fleet... The ships of course need to be more strong. And add more hostility again the nation of the Treasure Fleet.