Can boats sail faster than the wind propelling them?
Hoist up the John B's sail, see how the main sail sets, call for the Captain ashore and let me go home!
Asked by: David Powell-Evans, Wimbledon
Yes, although it sounds implausible.
With the wind blowing from behind and sails perpendicular to the wind, a boat accelerates. The wind speed on the sail is the difference between the vessel’s forward speed and that of the wind. Once the boat reaches the same speed as the wind it’s impossible to go any faster. But with the wind blowing from the front, the boat turns its sails into the wind by about 45°. The sails divert the wind slightly as it blows across them, which slows the wind and exerts a sideways force on the sail. The keel (the large fin that extends down beneath the hull) cancels out the sideways force. But, if the sail is angled correctly, some of that force also drives the boat forward. The vessel continues to accelerate until that force is matched by the drag of the water. So, with clever streamlined hull designs a boat can sail faster than the wind.