Originally Posted by Jeff_H
Triradial makes little sense on a sail as small as a SJ-21 working jib especially when working with woven polyester fabrics. While tri-radial cutting makes a lot theoretical sense, the reality is that much harder to get the fiber orientation, stitch tension and broad seaming sufficiently accurate that a small triradial sail ends up with a better flying shape than a simple broad seamed cross cut sail. I personally spent the money to go to the tri-radial route on a small high aspect ratio jib, and ultimately went back to a broad seamed jib to replace it for performance reasons.
Beyond that, tri-radial sails produce a lot more fabric waste, require a lot more skill to build well, and are far more labor intensive to build. Now then if you want a real improvement in performance I would consider adding a full length head batten and slighlt over length lower battens, then building the sail with nuetral or even positive roach.
Jeff: Ya, tri-radial did seem overkill for anything less than laminated racing sails. But the simple miter cut -- in which the bottom panels are oriented vertically and seamed to a cross-cut upper section along the LP -- is only about one extra seam over a pure cross-cut. Suspect that's a pretty fussy seam, tho! One of these:
Cristamd: I'm using Sailcut
, a free open-source program. Fun and easy to play with. Although unless you are using a computer-driven fabric cutter, you are left printing out long coordinate lists and plotting panels by hand. Which I really don't mind doing.