Modern, mechanical sails have been tried, too. The Japanese Nippon Kokan built ships like this in the 1980's: http://collections.rmg.co.uk/collections/objects/

Modern, mechanical sails have been tried, too. The Japanese Nippon Kokan built ships like this in the 1980's: http://collections.rmg.co.uk/collections/objects/66022.html http://collections.rmg.co.uk/collections/objects/66022.html Apparently the savings in fuel consumption were ~10%, so not really worth the hassle. Viking Grace's new tube may actually be more effective if the 20% of fuel savings can be trusted, besides being simpler to operate and less intrusive.