I believe the current cap for nautical xp is level 65. I also noticed the level 70 badge, but when the Nautical cap was only 50, I had a spot for the level 60 badge too. I think this may just be KI planning ahead. :)
At the moment, the Nautical Level Bar disappears when your Nautical Level is the same as your Character Level (or above). Check the Character Sheet and note what the numerical value is for your Nautical Level. Then, get some Nautical Experience and check the Character Sheet again to see if the Nautical numerical value has changed. It is my understanding (at least at the lower levels) that, when your Nautical Level is at or above your Character Level, that you get less than the normal Nautical Experience.