Is that 10% best case or average case? Also, what's the capex on the the sails, and what's the additional opex (training, maintenance)? Not trying to pooh-pooh

Is that 10% best case or average case? Also, what's the capex on the the sails, and what's the additional opex (training, maintenance)? Not trying to pooh-pooh the idea, but as said, I've seen articles like this regularly for decades, and it hasn't become the norm, so I'd figure there's a reason for that.