How do I get the shanty?

You can find two crewpeople under the tree in the grand hall. Only they're not very friendly.

Maybe there's another way to approach them.

Climb on the tree via the dome on the observation deck and eavesdrop.

Looks like you can pretend to be an officer pretending to be a lowly recruit.

These two are really overly suspicious for no good reason.

Show them the dongle to finally win them over.

Talk to them about the sleepy captain to finally get the sea shanty.