I can't tell if they're ignoring the DM, or just think it's a railroad to get the plot moving.

I think Nat has realised this part is railroaded but wanted to make sure. Cory is sure it's because it's a trap and they should do something else.

I don't think it's really railroading. They the players want to get to the grand line, to kick Poseidon's keister, this is the most accessible route according to the source books. And I don't believe they're ignoring DM, she's just not there, more seriously, they're listening to Gordon, not ignoring him. They are fairly aware that they're about to hit some tough skill checks to avoid crashing, if GM's description of steering being hard is anything to go by. Well, Nat's aware, at least.