According to [0], a typical container ship generate 12.5 g of CO2 per ton per km, which means that one trip from France to NY with 350T of cargo would release about 35T of CO2 in the atmosphere.

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...