Originally Posted by Jeff_H
What you are proposing makes no sense at all. It will be too flat in light air, and too big to roll effectively in heavy going.
I have been working a paper studying the trade off between sail shape and sail size. This is intended to look at using more smaller and more powerfully shaped headsails vs bigger flatter sails. A part of that research has looked at how far you can roll a sail even with a tapered foam luff before its shape greatly diminishes its effectiveness requiring an excessive reduction in sail area and drive.
Even with a foam luff, the best you can expect is to roll the sail 10-15% of its area before the sail is too full to offset its reduced area. After that the creeping of the fabric on the rolled sail, with the head sliding towards the foot and vice versa, automatically powers up the sail.
If your goal is to optimize the wind range of the sail, this is best achieved with a smaller fuller cut headsail. Used in conjunction with a backstay adjuster, and cut for a lot of headstay sag in lighter winds, you can produce jibs with a very wide range. That would be a better approach to research.
That's why I rarely use the large genoa. It is really only useful for light wind and tends to cause too much weather helm in anything >10 knots. The OP is probably best off with a 100% "working jib" as far as size goes, cut to a standard profile/depth. There is a great little freeware program, Sailcut CAD Sailcut CAD | Sailcut
, which I have used in building a couple of sails. It prints out nice drawings with detailed m/ms for the broadseaming.