The Open Sea is the large open area connecting the many ports and making travel between them possible.
It is single rendition of the Caribbean area. It includes the Atlantic Ocean from the Gulf of Mexico up to Bermuda in the North East and Guyana in the South East.
Traveling the Open Sea goes reasonably fast. Traveling the length of the map will take less then an hour and a lot less in faster ships.
Just like Ports the Open Sea is persistent (as opposed to instanced) and players can see each other and even engage in activities together like forming groups and engaging NPC fleets or other Players.
The Open Sea is filled with traveling NPC fleets and the occasional Player.