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-   -   Jib pattern: miter or crosscut? (http://www.sailnet.com/forums/gear-maintenance/40795-jib-pattern-miter-crosscut.html)

bobmcgov 02-21-2008 07:47 PM

Jib pattern: miter or crosscut?
 
Looks like I'll be stitching up a working jib for our SJ21. At 82 sqft, it shouldn't pose too much difficulty. The sail development software I have can accomodate all sorts of patterns, from crosscut to tri-radial. I've read for basic dacron headsails, the old-fashioned miter-cut jibs are really good, resisting stretch much better than pure crosscut sails.

Another advantage is smaller element size, which will allow easy template building. (I plan to loft the patterns on masonite rather than right on the fabric: will allow VERY precise layout, and repeatability if we need another jib.)

Wotcha think? Any opinions on cloth weight? We're very windy and gusty; looking at the 5.x oz high-modulus cloth. Overkill for a sail this small?

ETA: luff 20', leech 18.25', foot 9'.

sailingdog 02-21-2008 07:55 PM

What strength winds are you talking here??

bobmcgov 02-21-2008 07:58 PM

Quote:

Originally Posted by sailingdog (Post 269900)
What strength winds are you talking here??

Mean windspeed 14+. Daily winds over 30. It's on a CDI roller-reefing unit.

sailingdog 02-21-2008 09:33 PM

The cloth sounds about the right weight, given the size of the boat, and wind speeds of 14-30 knots. :) I'd go with a tri-radial or miter-cut jib rather than a crosscut.

Be aware that I don't do sail design or make sails myself... and that this post is JMHO.

cristamd 02-21-2008 09:50 PM

Bob,

What software are you using for the sail design and pattern printing?

Thanks,
~Matt

Jeff_H 02-21-2008 10:11 PM

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

bobmcgov 02-21-2008 10:26 PM

Quote:

Originally Posted by Jeff_H (Post 269972)
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

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:
http://macksails.com/images/genoa01b.jpg

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.:)


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