I replied to your question a few days ago. I tell you the same thing now, don't use POTC since it's an unfinished port and it won't work with Maelstrom properly. Instead, download New Horizons which is basically a same game with some improvements.

Hi, samdg. I had the same problem with the Open Sea mod activated. Kindly go to "new-horizons/PROGRAM/InternalSettings.h" and make sure OPEN_SEA_MOD is at 0. If you play on Iron Man difficulty, this will be automatically activated.

I apologize for the delay, but I did finally get a chance to check into this and I did eventually discover the problem.  I just uploaded an update for POTC today that should solve the problem.  Please update the POTC mod and you should be able to load a saved game and proximate islands on worldmap should load once you exit to sea.