In 2015 cargo ships transported 70 trillion ton-kilometers. The largest vessel here displaces 45 tons, so how many sailing vessels and sailors able to work for such low wages do you need to make a dent?
i expect that if some of these ships show a decent profit, they will eventually be able to build a new ship on their own.
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.
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.
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.
[1] https://www.freightwaves.com/news/carrier-capacity-cuts-send...
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.
seriously look at these things
I can buy this ship for ~4M USD https://www.oceanmarine.com/detail.cfm?5280%2DDWT%2DRORO%2CG...
Then transport 5,000 tons from Newark to London in ten days with <10,000 USD of bunker fuel.
Bunker fuel is very very cheap. I don't see how you can compete on either the fixed or variable costs with conventional shipping in the current regulatory regime.
An added issue with a flotilla approach is the decreased ability to handle sea state, which impacts the costs for insurance/LOC for shippers, as well as the useful coverage with respect to routes and seasonality.