Skysails[1] sells them commercially. I cannot find how many ships operate those other than two "prototypes"[2] [1] https://www.skysails-group.com/ https://www.

Skysails[1] sells them commercially. I cannot find how many ships operate those other than two "prototypes"[2] [1] https://www.skysails-group.com/ https://www.skysails-group.com/ [2] https://de.wikipedia.org/wiki/SkySails#Treibstoffeinsparung https://de.wikipedia.org/wiki/SkySails#Treibstoffeinsparung