Why is a sailboat faster than the wind pushing it? ?

Question

I was thinking that the current gives it some speed, but it would likely cause friction instead, I saw on tv today that fast sailboats will travel twice the speed of the wind pushing them, i just don't understand how this works. Feel free to explain using physics i understand much of it.

Answer 1

cause the sail creates low pressure zone that pushes the boat faster than  the wind

Answer 2

Sailing down wind, they can't sail faster than the wind, they are only pushed by the wind and as you indicated, friction and other factors will cause them to be slower than the wind.

Very performance oriented sailboats can sail faster than the wind when sailing up wind (close reach), or kind of sideways to the wind (beam reach)  At these angles of attack, the boat is not being pushed by the wind, but rather the sails act as foils much like an airplane wing.  Since the sail and foil it creates are curved, the wind passing on the inside of the arc has to travel less distance than the wind on the outside of the arc.   Since the same amount of air passes on each, side, the air on the outside must be more spread out or have the molecules farther apart.   This means it is compatively lower pressure than the the inside.  As basic physics tell us, air likes to move from high to low pressure, so the boat is basically pulled forward. The forces pulling it sideways are mostly cancelled out by the hull shape and centerboard or keel.