Here we have the first sign that something is up with Bakura.

Note the fact that he's walking around freely on the ship. In the original manga, he was part of Yugi's group, none of which had to sneak on board. However, in the anime, only people with star chips can get on board.

He cannot have been invited. For one thing, he quite blatantly does not wear one of the gloves. Bakura does not have a Duel Monsters track record, and has not been invited to duel.

So why is he able to walk around on the deck? Moreover, why does he have Ryou's calm expression? He even looks a little unhappy. Is this an oversight, or is Ryou just so used to waking up in strange places that he takes it in his stride? He clearly doesn't see a reason to hide. Apparently the guards find it okay once you're already on the ship.

But how did he get there to begin with? It clearly didn't involve murder or theft, as he has no star ships and the travel wasn't delayed. Moreover, he wasn't visible in the crowds before the ship set off, meaning he either showed up last-moment, or was already on-board.

Maybe he put someone to sleep to get past.