Thread: GIS sail tweaking

opps close footed .... leach tension is a separate byproduct of the booms springiness not how much tension you are putting on the system at a given moment

Good questions oz, and I currently don't have a couple of San Diego IPA's under my belt, but I'll give it a go anyway. I can only speak to my sail (occasional cuss words ommitted), and all my evidence is empirical. Going loose footed gave me more power in low to moderate wind in the chop I usually sail in. Going loose footed improved my pointing performance, particularly with my sail on the leeward side of the mast. Removing my full length battens also helped. With my old bendy boom, lashing the foot versus going loose footed made very little difference to my leech tension. With my bendy boom, lashing my foot did not decrease the amount of boom bend under downhaul and sheet pressure, but it did flatten and distort my sail, which is flat to begin with. My sail came with the upper leech flap out of the box. I first noticed it when lashed with full battens pointing in 15 knots with two people on board. Since then it has gotten worse, as I think the flap is stretching the sail material in bad ways.

I have a balance lug on my 16' boat. It is loose-footed. Draft in the lower half of the sail and thus power are controlled by the outhaul. If the sail had been laced to the boom or even on a track, the friction would have been too great to allow adjustment of the outhaul while sailing. The boom should not bend in gusts when the sail is loose-footed as that would shorten the boom's length from tack to clew and put more draft in the sail just when you don't want it. If the sail is attached along the boom, a bit of vertical bend would flatten the bottom of the sail just as a slightly bendy yard does to the top of the sail. I don't know what would happen to the leech. Nothing I suspect.
Peter

"If managing the presure during gusts is important the surely the main area's for that are mast flex (reduced luff tension) and sheeting out are the primary controls??
sorry haveing a hard time understanding where the advantages of loose footed are plus a couple of reds under the belt LOL[/QUOTE]"

The mast should not flex and the luff should have more tension in gusts so it will remain straight and not change the shape of the sail by mast bending with reduced luff tension. Instant response to gusts if beating is first to take advantage of the increased weather helm and come into the wind some more and point higher. If necessary, ease sheet. If not beating, ease sheet as you say. Maybe bear off a bit. A slightly flexible yard allows the sail to flatten and have less power in gusts, so that heeling is less. Yard bend and luff tension are adjusted with the downhaul. Now to down a red myself. Cheers, Peter.

I tried various combinations of lashed foot with less tension in the lashings, lashing some but not all foot grommets, etc. I tried adjusting outhaul tension with tightly lashed (as glug said - this is irrelevant), loosely lashed, partially lashed and totally loose foot. By far, my favorite is the loose foot. I think I gain about 6 inches to a foot of driving sail area close to the boom by not lashing - as a tightly lashed foot on my sail has no lifting shape until it transitions into the curvature of the body of the sail. My sail being flat, that takes a bit.

Now the sail on Gruff is another matter! I love that cut, with the transition from the separate vertical foot panel orientation to the cross cut body. It looks like the sail designer thought a good bit about how to create a low lifting area, while maintaining a tightly lashed foot, and allowing for boom flex without overly flattening the sail. Back to one of my favorite pictures!

I sewed the batten pocket on my sail, but I could not get out on the water last weekend, so I have to wait to test it. Very simple procedure. The supplies (enough for two pockets) cost $24 from Sailrite. I used the sewing machine I bought my daughter a few years ago for sewing lessons, nothing fancy, just your basic Janome home sewing machine. This machine has a tricot stitch setting that sailrite recommended, but they say any zigzag would work. The hardest part was keeping the stitches straight when sewing the assembled pocket to the sail, as the weight of the sail messed a bit with the foot feeding smoothly, but it's on there, and not coming off very easily!

It was good to lay out the sail on a flat surface to get a look at the cut again. My sail has a distinct baggy area in the upper leech by the peak. Not sure if it's always been this way, or if it stretched that way from use. I'm guessing this is where the leech flutter comes from. My leech in this area is curved the opposite of having leech roach. I'm sure there is a nautical term for a leech of this shape. It curves in, not out, or straight. If the batten doesn't fix things, I have a spool of thread, needles and a machine ...

I've been thinking that it's funny that we have boats with very prescribed designs and components, but when we get to the sail, it's the opposite. Each loft cuts their sails differently, and I suppose, keeps secret how they make their sails "better" than the other guy. It would be cool if you could have a prescribed perfected cut for a specific boat design, and give it to the loft to make the sail exactly to those parameters.

Originally Posted by warm beer

My leech in this area is curved the opposite of having leech roach. I'm sure there is a nautical term for a leech of this shape. It curves in, not out, or straight.

Hollow.

If the batten doesn't fix things, I have a spool of thread, needles and a machine ...

And an order with Sailrite under your belt. I smell... HOME MADE SAIL! You know you want to; I'm ready to root you on every step of the way!

Originally Posted by davlafont

Hollow.

And an order with Sailrite under your belt. I smell... HOME MADE SAIL! You know you want to; I'm ready to root you on every step of the way!

It did occur to me! Do you sew the panels from the inside out so you don't have too much to roll up under the sewing machine arm?

Belay that question - I'm thinking it doesn't matter as long as you only have one panel worth of material added at a time?

Originally Posted by warm beer

It did occur to me! Do you sew the panels from the inside out so you don't have too much to roll up under the sewing machine arm?

Belay that question - I'm thinking it doesn't matter as long as you only have one panel worth of material added at a time?

Correct. But, even if you have to work with whole sail--like when adding the reinforcement patches for the reef tacks and clews--you should still be able to roll half the sail tight enough to fit through the arm. I actually rolled both ends up like a scroll for space purposes and found that it also helped manhandle the beast.

That would be a fun project. I watched all their "how-to" videos for the fully battened main. I can't see where they generate depth to the sail. Is there any broadseaming?

Undoubtably broadseamed. Using double stick tape is essential but once the two edges are lined up it feeds through the machine like a straight line. It's only when you're done when you see that it won't lay flat.

They might also incorporate some rounding along the head and/or foot to help create draft.


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Originally Posted by davlafont

Undoubtably broadseamed. Using double stick tape is essential but once the two edges are lined up it feeds through the machine like a straight line. It's only when you're done when you see that it won't lay flat.

They might also incorporate some rounding along the head and/or foot to help create draft.


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Nice! I've been reading up on Dacron sailcloth and sail layout - warp, fill, thread count, panel orientation, that sort of stuff. Standard dacron sailcloth has more fill fibers than warp. The fill fibers are 90 degrees to the length of the cloth (warp fibers are parallel). Typical sails with Dacron use a crosscut layout to take advantage of the higher number fill fibers, as the greater the fiber count the greater resistance to stretching under load. With a lug rig, the article I read suggests that the greatest stress is from the throat to the clew, so the panels can be aligned 90 degrees to the leech, to resist leech stretch or a bit closer to 90 degrees from throat to clew.

I'm thinking that for Simon's radial sail, with panels radiating from the clew, the sailmaker used reverse count cloth, that has a higher number of warp fibers than fill, or maybe even one of the newer Dacron's that use a different less stretchy fiber for the warp, that is kept as straight as possible in the weave (no back, forth crimping), such as Challenge Warp-Drive. By making the radial sail this way, you could orient warp strengthened cloth along the leech from clew to peak, from clew to throat, and from clew to tack - all key directions of potential stretch. That just leaves the luff, but the luff can be reinforced with rope or tape to prevent stretching from tack to throat?

Originally Posted by warm beer

Nice! I've been reading up on Dacron sailcloth and sail layout - warp, fill, thread count, panel orientation, that sort of stuff. Standard dacron sailcloth has more fill fibers than warp. The fill fibers are 90 degrees to the length of the cloth (warp fibers are parallel). Typical sails with Dacron use a crosscut layout to take advantage of the higher number fill fibers, as the greater the fiber count the greater resistance to stretching under load. With a lug rig, the article I read suggests that the greatest stress is from the throat to the clew, so the panels can be aligned 90 degrees to the leech, to resist leech stretch or a bit closer to 90 degrees from throat to clew.

Oh yeah, you're gonna wanna stitch yer own...

I'll venture to very edge of my own (limited) knowledge here by adding: warp and weft (fill) count can vary and still be "balanced" or "bi-directional" by using fibers of different size and/or strength in the two axes. For our purposes as amateur sailmakers (and small boat sailors) the balanced cloth makes sense. For our purposes, there's no difference in strength based on orientation (vert vs. cross). What cross cut panels do is give you more seams to work with--through broadseaming--in the area where you want to develop draft.

I haven't read that the clew-throat stress is the highest, although it makes perfect sense to me. I have read that it's good practice to have a "tack seam" running from the leech perpendicular to the tack. That might have more to do with potential for broadseaming in that important area. Beyond that, conventional practice is to line up either the warp or the weft parallel to the leech.

I'm thinking that for Simon's radial sail, with panels radiating from the clew, the sailmaker used reverse count cloth, that has a higher number of warp fibers than fill, or maybe even one of the newer Dacron's that use a different less stretchy fiber for the warp, that is kept as straight as possible in the weave (no back, forth crimping), such as Challenge Warp-Drive. By making the radial sail this way, you could orient warp strengthened cloth along the leech from clew to peak, from clew to throat, and from clew to tack - all key directions of potential stretch. That just leaves the luff, but the luff can be reinforced with rope or tape to prevent stretching from tack to throat?

Now we're talking secret sauce speculation. The Doyle Ploch radial raises way more questions than it answers. The matter of bias at the luff has been questioned on Woodenboat Forum, in particular the fact that each panel along the luff is at a different bias angle and that over time they may stretch at different rates. Does that matter? Yet another question... All I know is that it looks awesome. Todd Bradshaw (who posed that bias question) has presented his own thoughts on a tri-radial lug, one which radiates from tack, clew and peak. See post #11:
Balanced lug sail questions

Thanks for the thread reference. A good read! Processing ....