a quick fix...
I have seen a lot of complaints about ships getting where they shouldn't (i.e. in the middle of North America on their way to the Hudson Bay). IV are working on a solution. However, in the meantime, I have made an altered version of sailable.bmp, and packaged it into a mod. This version of sailable.bmp removes sailable regions that are completely inaccessible (in North America and in the Mediterranean), and closes up some other very small sailable regions around the world (the Caribbean, near Madagascar, the Sea of Japan, and in Indonesia). It also opens up some areas in the Caribbean (Cuba is sailable), widens out the Bering Strait a bit, widens out the area north of Iceland, and gets rid of a few artifacts. I think this should fix most of the major exploits that people are complaining about. Please, give it a try, and let me know.
You can grab it from the add-ons section of Ambrosia's website.