Container ships and cruise liners move the world's goods and tourists, but shipping produces around three percent of global greenhouse gas emissions, much of it from heavy fuel oil and soot. DW Documentary tracks the people trying to change that by looking backward and forward at once. Austrian captain Andreas Lackner and two friends run the Tres Hombres, an engine-free clipper that has carried up to 40 tons of cargo since 2010, from Caribbean cocoa and rum to 20,000 bottles of organic wine shipped from La Rochelle to Copenhagen. Ralf Oltmanns, a former teenage sailor turned advertising entrepreneur, has modernized the Flettner rotor, a spinning cylindrical sail invented decades ago, which he says can cut fuel use by 5 to 25 percent depending on wind and size. Shipping executive Anna Braren fitted her company's first vessel with the rotor in 2021. Interviews and on-deck footage follow both projects as they test whether old wind technology and new engineering can make global shipping meaningfully cleaner.