The Titanic sinks again.

i thought big ships like these would get tugged into a harbor//shallow water

He's being held hostage by his pet rock, so tugging it away is probably no option on the short term. This probably also is the reason why it didn't sink fully yet, I can't imagine it'd be so steep near that rock that an entire cruise ship could sink.

 Spoiler

Edit: Nevermind, interpetated your message in the wrong way.
They do tug big cargo ships into harbours, no idea if they do that with cruise ships too though.