Just before Ryan went into the light, he said something rather ominous about not being able to give the money back. Return through the portal to the real world --
-- to discover that he rigged the boat to ... I don't know. Accelerate like crazy until it blows up? Something like that.
Whatever is going on, Rosa clearly needs to get off this boat fast before it comes to a terminal stop. (Actually, though, this isn't a time-limited puzzle. You can take your time figuring out what to do.)
Leave the wheelhouse and jump overboard, using the "gap" on the lower deck. Geromino! [sic]