"The effect of sailing is produced by a judicious
arrangement of the sails to the direction of the wind."-William Falconer

When playing around with a sailboat in a bathtub it may seem as though the fastest
direction for a sail boat to travel would be downwind, but this isn't the case at all.

As a boat increases accelerates downwind, the force of the wind on the
 sails decreases and the resistance force created by the ships motion through
the water increases.

At wind speed, the sails feel no force from wind and the resistance force is at
its highest. This is why it is impossible for a sailboat traveling downwind to travel
at or faster than wind speed.

However, when travelling perpendicular to the wind, boats have achieved speeds greater than double the wind speed.

How is this possible?