hrtsailor is correct only in that the force increases as the square of the velocity. The absolute figures quoted are for a flat plate, perpindicular to the applied wind velocity.

Sails are foils (well, really just camber lines) and the forces are much different. They vary more with the angle of attack in a given wind velocity - but the force is still proportional to the square of the velocity.

100 mph wind has 100 times the force of 10 mph wind.