There's a gap in the side of the boat that's supposed to be blocked by ice & invisible clipping but there's a gap you can drop through to get in.
Inside is a door that, from your perspective, is on the floor. You can enter it by doing a crawling dive into it from the side. This puts you in the engine room but there's a door in your way that won't open & you can barely see because you're trapped in the dark space between the 2 doors.
In one instance, I got past the 2nd door but I don't know what I did because I didn't realize it was special at the time so I forgot. I just assumed I'd found an opening in the darkness but examination with the camera badge showed me that there was no opening.
I'm not sure what I phased through. The door, a wall, the ceiling, or what?
Edit: I made a mistake in the title. I meant to say Rock the Boat.