Shipping is already tremendously automated. The remnants are most difficult, and the environment is difficult and has some particularly bad failure modes.

There are numerous tasks shipboard which aren't readily automated, and once you have one person aboard, you tend to need more (cooks, maintenance, multiple shifts, mechanics, etc.).

The reduction in employment in shipping since the 1950s, particularly relative to cargo handled, is already immense, much of that from containerisation though.

Yeah, good point, ships are pretty automated. But ships really do need crews for constant maintenance and supervision. You can put the helm on autopilot but that's about all it can do.

Now, let's talk about this again when someone makes a decent R2 unit.