We've all seen articles about massive container ships of the future using kites to supplement their engines, but I suspect a really solarpunk future would look a bit further afield, or perhaps further back in time for their ship designs.
I think in any future with humans and continents, people are going to be trying to cross the ocean. There might be less shipping in a world without our abundance of cheap energy, or more of a focus on reducing consumption and producing necessities locally, but people will still trade goods and travel. So what might the ships look like? Return to tallships? Solar panels and electric motors? I love reexamining traditional technologies to see how they can fit with modern engineering and design principles, safety features, and electronics, but I don't know much about ships, and especially not much about modern sailing.
So what do you think will be bringing back holds full of old world fashions harvested from the Chilaen desert?
For intercontinental container ships win, in almost all cases. Efficiency scales with size (power requirements scale with cross section, n^2, while capacity scales with volume, n^3). This is part of what creates the problem with modern society, they are SO good at their role that it is cheaper to ship all around the world, than to make locally.
What we can do is remove the fuel requirements. Solar and Wind turbines can create significant amounts of power, on a ship that size. Further, classic sails can be used for direct drive, when conditions are right.
It is also one of the best case situations for hydrogen. Hydrogen storage difficulty scales with the inverse of size. Small is hard, big is easy (comparably). Hydrogen can also be made from water and excess electricity. Conveniently, container ships tend to have access to unlimited water.
An electric container ship could run off renewables, with hydrogen providing a supplemental power source. When there is excess power (e.g. at dock, waiting to use a congested area, or just running at a relaxed pace) it can be turned into hydrogen onboard. If high speeds are required, it can be supplemented by coast based hydrogen generation (either on-shore, or floating).
This is a really cool idea - I hadn't considered that there might be a way to do container ships somewhat renewably
Recently the "Canopee" has been launched.
It's a cargo ship with automatic sails that is transporting the Ariane 6 rocket across the Atlantic.
https://archive.ph/GQGPk
There is also this company who was doing shipping on old yatchs but the are now building a modern sail cargo boat
https://www.towt.eu/en/towt-home/