These are actually two ideas
Remove the borders of the map and implement some sort of procedural open sea, like Avalanche did with the desert in the Mad Max game.
You can still navigate via compass and stars and you find more lucrative ship wrecks. This could later be expanded with ghost pirate ships roaming the area, that are equally challenging like an average skilled player crew. The open sea may have slightly tougher sea conditions, but not a full storm.
You only have a limited amount of time like 30 or 60 minutes or so in that area, because if you stay too long your ship and crew gets cursed and die. There's a small chance that the crew will spawn randomly on the main map as ghost ship until the ship is sunk, giving the victor a nice reward. Returning from that zone with treasures to the main map without getting cursed gives a bonus rewards as well when cashing in the loot.
As a ghost ship in the main area you have the objective to board at least one ship and free yourself from the curse by playing a special chanty which is only available when you are a cursed crew, the ship will slowly sink while you play that song. This will give you a small amount of reputation in a random faction and makes you spawn at a random island with your original ship and a cursed treasure chest, which contains a good amount of gold.
If the crew that is being boarded decides to not interfere and let the cursed do their thing they spawn at a random island as well with their original ship and also a cursed treasure chest, but sinking the cursed crew still gives a higher reward.
