As far as my knowledge goes about the shipping industry: ships are already 90% automated (since they simply go straight forward for days/weeks). There is not much to do for a captain/officer whilst in the middle of an ocean.

AFAIK most of the humans on board of a vessel are there to perform maintenance (most of which can be done during transit).

Yes, we can automate the last 10% to make the ship sail itself, but we'd still need humans on board to perform maintenance.