Most material have directional strength, much like Dacron/woven family. By using radialcut to better orient the cloth, in small panels, along the best loadpath for the sail, a lighter material can be used to?achieve the same strength found in the simpler crosscut design. If the same crosscut material is used for a radialcut, with no weight improvement, it will be stronger/last longer under the same wear conditions.
Radial is more work and has more waste which make up for the extra cost.
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David
David Godin