Unless I'm not finding it, they didn't give special rules for if a huge ship hangs off the table. You will eventually have to turn, and based on the diagrams, the amount of drift from the tail end looks like it would force a corner off the table. And because there aren't rules listed for if they hang off, I would assume the ship "flees the battlefield" and is instantly destroyed, just like any other. So, you have to be super careful as you turn.
Fair enough. Starting the huge ship just a couple degrees off of parallel to the edge should allow it to gain plenty of wiggle room for its fish-tailing butt to safely move by the time you feel like making a u-turn.