Read the caveats at the bottom of the article -- the ship owner who has to make the capital investment doesn't pay for the fuel, so there's a perverse disincentive to invest in this technology (assuming it works).
Maybe the SkySail could own the sail system and sell the "thrust" - basically charging a success fee for saved fuel. In a similar vein in how the airlines don't own the engines of their airplanes but rent them from manufacturer - https://aviation.stackexchange.com/questions/12528/jet-engin...
Of course this is an armchair thought experiment, but I am curious about your opinions.
Not really a disincentive, if the person paying the fuel could pay less it for it while using fleet X it would surely be a competitive advantage to the fleets owner. Perhaps the keyword in the quote is "untested", with a unwritten "why bother unless I have to / other owners do it".
Exactly. The key hurdle is getting the first ship fleet owner to invest in the technology. Once that's working, he'll have a competitive advantage offering renters lower fuel costs. He'll have some combination of higher booking rates or ability to charge higher prices, effectively splitting the gains