The fuel cost for moving one container over the Atlantic on a big container ship is about 30$. A container takes 30 tons. So 12 containers could move that cargo for a fuel cost of 360$, the scale is unbeatable; both economically and environmentally.
Things like this can only ever be a type of artistic thing rather than used for real shipping.
On top of that the sails will degrade with time and the ship will need to be repaired and there is allot more crew and manpower needed per unit of cargo.
Everything has environmental cost in CO2 emissions, and the amount of useful work you get from a large container ship per amount CO2 emissions is insane. The only thing that can get you those kinds of numbers is scale.
I'm convinced that this sail boat generates an order of magnitude less of that (I can't find any estimate of it)
Whatever the initial CO2 cost of the construction of this boat is, I'm sure that it's a net benefits if it's used long enough
[0]: https://www.ecsa.eu/sites/default/files/publications/2020%20...
https://backend.orbit.dtu.dk/ws/portalfiles/portal/158911010...
6000km from France to NY
3g * 6000km * 350tones / 1000 / 1000 = 6.3 metric tones of CO2.
I don't know how much disel the sail ship might use, but 6.4 tones of C02 is equivalent of 1974L of disel.
According to their own website https://graindesail-logistics.com/en/ they aim for 1.8 g off CO2 per km per ton.
1.8 is lower than 3g. If those aims are reached I guess they are "more green" than I thought. But the gain is quite small, if you truck that cargo for 160km all the CO2 savings are gone. A modern truck emits 45g of CO2 per km.
There are market niches for many things that target things that are impractical for various reasons. There is nothing wrong with that.