If they want the largest vessel that DOES NOT burn fuel oil, they may as well just do what sailors did before steamships, follow the trade winds and currents to sail back to Europe during the winter.
They have just shown their historical ignorance of what seafaring life was like before steamships. One was dependent upon wind and tide when crossing the ocean, that is why it sometime took 2-3 months or more to cross the Atlantic from North, Central, or South America, depending upon the time of year.
Perhaps reading a few historical accounts of crossing the ocean, such as written about the voyage of the Mayflower, or the novels of C.S. Forester or Patrick O’Brian to get an idea of life in a sail/wind powered ship.
Kudos to Patrick O'Brian and his wonderful Aubrey-Maturin novels..
LOL...the heck with "reading". Let'em work their passages on a sailboat. It might be a sufficient revelation to wise some of them up.