The sail on that ship is 100' high, and looking at the aspect is around 15' wide, or 1500sqft. That type of sail I think only harneses half of that area, so half of 1500' or 750' best case.
I can say with complete confidence that if all the energy from two of my boats were towing one of those ships, even in a hurricane, it's going to increase fuel efficiency by approximately 0.0%
EDIT: I just did a random sample of wind speed [1] of points on the globe on international shipping routes [2] and it looks like they are generally around 10-15km/h. Thats barely enough to get my boat up to speed. There is a reason sailboats take very particular routes and don't just go from point A to B
[1] https://earthjustice.org/sites/default/files/world-cargo-shi...
[2] https://earth.nullschool.net/#current/wind/surface/level/ort...