what are the consequences to poor judgment in the navy?

Answer 1

anything from Captain's mast to Courts martial. punishments can be anything from extra duty and loss of rank and /or pay to Brig time and a Bad Conduct Discharge.

and of course, really stupid people can get their shipmates KILLED.

Answer 2

That's really broad. Poor judgment can lead to nothing at all, or people dying. You need to be more specific.

In general, sailors showing poor judgment in day to day operations will be counseled, receive poor marks on their fitrep (like an annual report card) and be subject to disciplinary action.