We did the Santander route on the economy ferry and no problems as announcements were very limited especially at night and there were very few families on board. Engines I find sleep inducing once the ship is in steady speed mode, but should they stop I would wake instantly.Never done the overnight Caen to Portsmouth. We did the overnight Portsmouth to Santander and no issues sleeping as it seemed a lot quieter engine wise. Perhaps it was because we were a distance away from the engines which were a quiet murmur.