I think the main problem is going to be, quite frankly boredom. I was sailing around early today and was wondering.. so now what? This game has to fill in the gaps with content (I know its alpha just making a point) or make the game something similar to Stronghold Kingdoms, where you log on for maybe 20mins to 1 hour a day to update stuff ect. Sailing around from port A to port B for 20 minutes is boring, now you can either fill the sea with AI pirates and the occasional player, which may interest you some of the time, but there has to be an additional supplement of content to keep the user actively engaged. My opinion would be that you don't just sail 1 ship on its own, instead you can do many things from sailing all 30 minutes from port A to B, or you can return to a hub center such as each nations main port, where you can craft, construct plantations, manage small businesses ect whilst your ship/ships are sailing. It's the same as EVE online, but with that system you can literally mine ore from an asteroid, then select your destination and go AFK until you arrive, and have an alarm system which tells you that you have arrived at your destination, or if you have been intercepted by an enemy ship.