Thats pretty much how its done.  <div>A panelled sail is cut and joined according to a template to give a required basic shape.  Afterwards, the required aerofoil is adjusted in by tweaking the bits of string around the corners and those controlling the boom and mast shape.  This works for single sheet sails as well.</div><div>Rigid wings are something else again, but all of them need to work both sides, unless the boat is only going one way.</div>