Here's the tricky thing about "north of Gran Granada"--typically, it's WAY north of Gran Granada. I've found that if it shows the shoreline, I can typically find it by going along the coastline and trying to dock the ship in between the smaller settelments and pirate's coves. I wish I could draw out the map for you, I'd show ya where I typically find it... hmm... trying to remember now.... ok, I believe it's just south of New London settlement... basically if you look at Gran Granada on the map and then go to the shoreline that you can access by boat directly north of it, you'll be able to find it easier.
Good luck!