Earlier in the year six ships were accidentally released to the test server which weren't fully complete, the ship of the line being one of them. Because the Ship of the line was already released as an enemy ship, many players bought it. However, there were five other ships that most people didn't buy.
Note: The screenshots you are about to see are not confirmed ships that will be released. This is all speculation but it's very likely these ships will enter the game sometime in the future.
Here are the modified(barely) player versions of some enemy ships which may or may not be released in the future.
Phantom:
Ghost War Sloop:
El Patron's Ship: (Notice the player blue/red markings on this ship. This is what distinguishes our player ships from the enemies, at least for now)
Player Version of the Black Pearl:
There hard to see but you'll notice on the back of the ship there are the player ship markings.
Ship of the Line:
Again I note that these pictures are actually models currently from the phase files, however these have NOT been confirmed by POTCO as ships to be released in the future. Until the next update, enjoy these to keep you thinking.
P.S. Every ship has three classes. There have not been any indications in the phase files which point to any different classes of any of these ships.
EDIT: I apologize for a mistake I made. El Patron's ship type does NOT have any player markings on it, although at first glance you may think it looks like an average player ship.