Luiz,
My feelings about "rigid" sails vs. "flexable" sails are this. Sail technolory has come a long way from the cross cut dacron days. The computer generated load maps of sails, has resulted in triradial cuts, 3DL,and tape drive sail constructions. All in an attempt to more acurately oriant the cloth fibers along the lines of stress, or loads on the sails. Materals have also gone from polyesters to Pentex, Kevlar, and more recently Carbon Fiber. All of this technology has resulted from the need to build sails that maintain their designed shape longer.
We build dacron sails only for durability and cost. Most of our customers are racers, and want the best performance for their money. We try to build the lowest stretch, lightest, most durabil sails for their budget. Sails that are "rigid"
and hold their shape over a wide wind range, are, in my mind the objective. We come up with the best design that we can for all conditions,and try to select a material that will maintain that shape. Most beach cats have numerous adjustments to alter the shape for differant winds. If we build sails from stretchy materal, the overall shape will be flatter to begin with, to account for the stretch, resulting from increased wind loads. There is more guess work involved.They tend to be too flat in light winds, or too full for high winds If the proper cloth is selected, the sails should maintain their designed shape for the life of the cloth. I don't know of many top racers, that are buying several sails, to meet the various wind conditions.
In fact most regattas restrict changing sails.
I hope this helps.
Dave