Crews on those ships are spending nearly all their time maintaining them.

Many flag and port states already allow One Man Bridge Operation (OMBO) in many circumstances. This means there's basically on person on the bridge, and maybe one other person down in the engine room keeping an eye on a floating city block moving through the water at 15 knots

The 5 wage slaves on current ocean giants aren't even a rounding error on any calculation.

This idea that putting $500m+ of assets in the water, but thinking that even one person on the boat is too many has got to be one of the silliest things in modern capitalism (obviously the crown goes to orbital AI data centers).

The same bosses will pay multiple security guards, in addition to staff, to guard <$10m in goods at a Walmart. But when 50x the goods are in the ocean, suddenly the staff is the limiter?

Never going to happen in your lifetime.

Salt water, is nasty, it gets everywhere, the environment on boats is damp. Ships are complicated and require constant effort to keep running.

Any sort of "automation" you build in is subject to those same environmental conditions, and wont last long.