Let's say you made a boat that could hold 4 standard cargo containers. Sail powered, solar electric + batteries. Fully autonomous. Then have autonomous loading and unloading of containers as well. Build a fleet of boats.
The beauty of it would be zero waiting. Boats are always ready to take the next container, and loading takes only 5 minutes, then it leaves right away. Even if it were slower than standard container ships, it's always moving.
Let's say a typical call is about 5000 moves. So that would mean about 625 of your small vessels. It won't take 5 minutes to load the containers, because the discharge containers need to be unlashed and the load units need to be lashed (which you can't do during operations). It'll be more like 30 minutes to discharge, load and get the next boat alongside (in the best case). You could shift the boat along the quay for lashing (or shift the crane, but that takes the same amount of time)and get the next boat working. Even then the productivity will be at least half of what a typical terminal can do. The overhead per boat is simply to high.
That's not even taking into account the seaworthiness of these small vessels or the logistics of getting all these boats in and out of port without congestion.
If the ships only carry 4 TEU (or 4 FEU), then lashing is likely not needed if they use Twistloc's welded to a boat deck that is designed for the dynamic loads. With only four containers, I wouldn't even dock/undock the ships; keep them continuously moving, and pick and place the containers dynamically as the boats move through canal lock style controlled conditions. There are Twistloc designs that are purpose-built to automatically work with the container cranes with no manual intervention.
The idea is impractical because the fast turnaround is not going to offset the overhead of a separate boat per 4 containers. People usually don't think of container ships, but they're bean-counter-efficient designs, and the boat overhead costs per container are absurdly low.
We're at multi-year highs now nearly touching $2590 USD per FEU Asia-West Coast on the spot market, maybe around $4-5K if you're doing a one-off by your lonesome through a freight forwarder [1]. But the opex cost per TEU per day for the larger container ships is around the $10 USD zone [2].
Using super slow steaming numbers, which would be comparable to sailing vessels' time, we're likely looking at 15-20 days for that Pacific voyage. Say 20 days to be generous to the case of the autonomous boats, so the opex cost for that voyage works out to about $400 USD per FEU. Amortized capex works out to maybe another $500 USD per FEU in normal economic conditions, plus overhead for maintenance (the ocean is a real PITA), plus some profit off the top?
Whatever that capex really is, building and financing those autonomous 4-container boats have to squeeze into about that budget, plus whatever of the opex they can skim over for not having to pay for bunker fuel (which is absurdly cheap, yay externalities) and crew (a fraction of the opex) [3]. I'd probably look into vanadium redox or iron batteries, since I'd want to amortize out way longer than say a Panamax does. Everything that touches the phrase "marine-grade" gets magic 10X cost pixie dust sprinkled on it giving the bean-counters who buy the stuff micro-strokes every day (bean-counters on the other side of the sale get hookers and blow, there's gonna be a Nobel for the person who figures out how to replace 304 grade stainless with something as cheap as pig iron and just as workable), so I find it hard to see how the numbers pencil out wrapping lots of ship around so few containers, until the global economy radically changes to a form we don't recognize today.
One last thing: sails at scale are freaking hard to recycle. These days with sails mostly relegated to recreational markets, there is sufficient demand for the bags and other stuff they make out of used sails. I think the Dacron-based remnants that is in tatters can be sent into PET recycling streams, but the more exotic stuff is going to be more challenging like windmill blades. Commercial quantities of beaten sails would be an interesting problem to solve.
>If the ships only carry 4 TEU (or 4 FEU), then lashing is likely not needed if they use Twistloc's welded to a boat deck that is designed for the dynamic loads. With only four containers, I wouldn't even dock/undock the ships; keep them continuously moving, and pick and place the containers dynamically as the boats move through canal lock style controlled conditions. There are Twistloc designs that are purpose-built to automatically work with the container cranes with no manual intervention.
on a ocean going vessel you wouldn't need to lash them, no. On a ship this small I would most certainly do. We can probably devise a hypothetical solution for this as well, though.
I tried to illustrate (badly) how hyper-efficient modern container operations are. People don't really realize how much work has been put in optimizing all this stuff.
Leaving aside a lot of potential issues, I'm not sure how you envision how a boat this size is meant to scale to the size where it replaces modern container freight operations (many of which will be substantially automated themselves.)
Let's say you made a boat that could hold 4 standard cargo containers. Sail powered, solar electric + batteries. Fully autonomous. Then have autonomous loading and unloading of containers as well. Build a fleet of boats.
The beauty of it would be zero waiting. Boats are always ready to take the next container, and loading takes only 5 minutes, then it leaves right away. Even if it were slower than standard container ships, it's always moving.