Common understanding seems to be that pulling tension to cunningham moves the sail's draft forward. It also opens the leech, flattens the main and removes the wrinkles along the luff but they are not relevant in my question. Why does pulling cunningham make the sail cloth behave like this. Intuitively one could think the opposite, that the instead of moving the sail's draft forward pulling cunningham should move draft aft away from increased tension. Can anyone explain or maybe provide a link to an applicable sail shape theory.