N Jones, Swabbing the decks, New Scientist, 27 November 2021, p 45

In the marine world, attention is growing regarding the reduction of emissions with examples of the use of LNG, methanol and ammonia replacing both marine diesel fuel and bunker fuel. Other features include reducing speed by half and improving the hull shape, plus possibly the re-introduction of the 1925 Flettner wind towers, and the more recent Cousteau’s Turbosail, Econowind’s Ventifoils, and the Airseas Seawing Kite.