M/S Viking Grace, an LNG-fuelled cruise ferry, is the first passenger ship in the world which has been equipped with a Rotor Sail. The 57,565 GT M/S Viking Grace currently operates in the archipelago between Turku (Finland) and Stockholm (Sweden), and is one of the most environmentally-friendly cruise ferries in the global maritime industry. With the addition of Norsepower’s technology, the vessel will further reduce its emissions, fuel burn and fuel costs; reducing carbon emissions by circa 900 tonnes annually; equivalent to cutting 300 tonnes of LNG fuel per year. Viking Grace was retrofitted in April 2018 with one medium-sized Norsepower Rotor Sail unit that is 24m in height and 4m in diameter, making it the first-ever global LNG/wind electric propulsion hybrid ship.
https://www.norsepower.com/cruise-ferry
ps. The wife and I have used this ferry, which sails past the island we are living on It can be quite windy here