I had a thought, that it would be pretty #solarpunk to do international shipping with solar powered sailboats. So I looked it up and found that robo-sailboats are a thing already, though in their infancy:
I'm struck by how this sort of thing could be within reach of hobbyists. The ideal POC would be a single-container cargo ship that could use solar power to do GPS, telemetry, and sail management. And go transatlantic or transpacific to prove it.
@russss Larger ships are still great, but I think there's room "at the bottom" for swarms of smaller vessels. One of the challenges to do this now with traditional boats is:
* Paying people to person the boats
* Paying to fuel all these inefficient little boats
* Little boats can get sunk
If the boats are solar/sail powered, autonomous, and cheap, then these problems don't look so intractable anymore.