Asked by: George Jeffries, St Albans
This seems like defiance of the laws of physics, but it just needs the right shape and size of sail to trap enough of the air-mass blowing in the wind. The resulting transfer of momentum can propel yachts to impressive speeds, especially if friction is minimised – some sleek catamarans can achieve 80km/h using 35km/h winds.
Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.