How do sailing ships work?
Bigpathome, there’s definitely a pressure difference across a sail, just as with an aircraft wing! Air flows faster round the outside due to the convex shape of the sail, and slows due to the concave inner surface of the sail. Faster air is at lower pressure than slower air (along a streamline, Bernoulli’s Principle – overly simplified, but it works) and the pressure imbalance ‘sucks’ the sail downwind. One of the differences though is the angle of attack – an aircraft wing is moving with high velocity relative to the air, so the flow is more or less parallel to the wing. A sail will have an AoA of 45 degrees or greater (I’d love to find a boat that could sail at 15 degrees to the wind! Funnily enough high performance dinghies, which will get upwind very fast, actually point lower, but the additional speed they have more than compensates for the extra distance travelled) Another key issue is the centreboard or keel – this is a foil that is below the boat and counteracts leeway (the boa
