Hey Captains,
If you are on the border of the map, your ship will quickly become quite slow and non-agile. We have all ran into the border and tried to turn around, one thing you will notice with the slowing of your ship is you can end up showing a lot of broadside going really slow. This is definitely noticeable when you are in a BB and you are sitting there going "hurry, hurry" lol. Remember, if a ship is going head on to the border and makes no attempt to maneuver off of it, they will become very slow and an easy target to hit.
This is also a good point, you could have just not been paying attention to where you were headed and meet the border. I know I have done this before and the border slowing really does hurt when you are in a running gun battle.