These flexible areas then deform smoothly into a shape resembling a conventional cambered rigid airfoil. The amount of camber is controlled by a combination of out haul tension and the physical stiffness of the materials, just like a normal sail. The rigid leading edge is stiff enough to handle all bending loads, which eliminates the need for a traditional mast and shrouds. While the basic concept is simple, the exact shape that the deformed wing sail will take and its efficiency, is difficult to predict without building a prototype. Some excellent research has been done on flexible airfoils, both single and double sided, with a variety of leading edges.
Theories are important, but the real proof is how well a full size operating prototype performs.
I selected a wind surfer for the prototype, in order to reduce cost, weight and labor. Three years, and many hours later, the theory was put to test. The basic dimensions I selected were based on a standard 60-70 sq. The thickness of an airfoil is usually expressed as a percentage of the chord. I basically guessed at these values.