Flutter in my leech

[almeyer]

I've noticed the last couple of times out sailing that I've got fluttering in the leech of my sail. The rig is a standing lug on a Penobscot 14. Last Sunday I finally decided to do something about it, and thought that if I brought the halyard attachment point further back on the yard, that would give more tension to the leech. I didn't think about moving the yard parrel back as well, but it seemed to help some. The wind was up a little last Sunday, so I was sailing with a reef tucked in. Then last night I set the sail up again to rinse off the salt residue, and immediately noticed a large crease going from tack to peak. I undid the yard parrel, thinking to move it back later, and it helped reduced the crease a little, but only got rid of the crease when I reduced the tension on the tack downhaul. I thought a lot of tension on the luff was a good thing, so I'm wondering if I'm taking the right approach, or if I've somehow distorted the sail. Any suggestions would be appreciated. Here's some photos of how I've got it set up:

the yard parrel, a simple toggle and eyesplice
http://im1.shutterfly.com/media/47b7cf26b3127ccec2db1ef0fd3b00000010O00ActHLVi5bt2 IPbz4E/cC/f%3D0/ps%3D50/r%3D0/rx%3D480/ry%3D320/

the tack downhaul
http://im1.shutterfly.com/media/47b7cf26b3127ccec2db156a3c0c00000010O00ActHLVi5bt2 IPbz4E/cC/f%3D0/ps%3D50/r%3D0/rx%3D480/ry%3D320/

and here's the whole rig
http://im1.shutterfly.com/media/47b7cf26b3127ccec2db07c53caa00000010O00ActHLVi5bt2 IPbz4E/cC/f%3D0/ps%3D50/r%3D0/rx%3D480/ry%3D320

Thanks in advance for any help.
Al

[Todd Bradshaw]

A crease formed by a line of tension between the tack and peak is not always a bad thing. Once you're out sailing and the mainsheet load enters the sailshape equation the sail may smooth out and be fine. A lot of gaff rig sailors set their sails with a similar crease on purpose and rely on sheet tension to even everything out. Only one way to find out for sure...go sailing and see what happens. I don't believe you're in any serious danger of damaging the sail though, whether the crease goes away when sailing or not. If not, it's probably time to move the halyard attachment point back to where it was.

You can also spread the sail out and check the cut of the leech. With that last panel straight and flat on the floor, the typical leech will have about 1" of hollow cut into it for every six feet of leech length (12' leech has 2" of hollow. etc.) The deepest spot in the hollow shaped leech should be pretty close to mid-leech. Not all sailmakers use this formula. Some hollow very little and a few none at all. With age, these leeches are usually more prone to flapping. The cure for a flapping leech (assuming that messing with the rig won't fix it) on a vertically cut sail is generally to re-cut the leech with a slightly deeper hollow.

[almeyer]

Thanks, Todd. I'll move the yard parrel back to match up with the new halyard location, take it out, and see what happens. It would sure be nice if fiddling with the rig takes care of the problem. I'm not interested in real high performance, which is a good thing since this is not a high performance boat, but it's fun to tinker around and understand some of what's going on. The sail is only about 4 yrs old, but sailing season down here runs from late February or early March through about Thanksgiving, and I try to be out almost every weekend. I'll also see how much hollow I've got. Thanks again.
Al

[lagspiller]

Hmmm....
I'm probably begging for trouble, but I'm not sure I agree with the advice. The Oselver has a similar rig, a spree with a snotter on the spree, a cunningham and an outhall on the boom, probably more similar than a gaff sail would be. When racing that rig it is extremely important to get out all the wrinkles and creases. All three adjustments on the sail are continually re-adjusted through the race to balance the forces and keep the wind flow laminar, avoid fluttering.... The direction of sail, windforce and other factors all must be accounted for by the tension on all three adjustments or you not only get creases and flutter, wrong opening and twist but also the depth and power of the sail doesn't match the conditions.

A deep wrinkle along the mast tells me that the cunningham is much too tight for the conditions. If you play with your adjustments while under weigh, you should be able to make the sail wrinkle in any direction starting from the corner where the boom meets the mast. Find the sweet spot in between wrinkling vertically and wrinkling horisontally. Adjust then to get the right depth for the power of the wind (simple rule: more wind - flatter sail), and make sure the deepest part is where you want it for the particular sailing conditions.

Another adjustment that is popular in the Oselver is a line from the peak to the end of the boom. That can be adjusted to lift the boom slightly and let more air out at the leech... that seems to be very helpful in ending flapping in the leech - which steals a lot of boat speed.
Your rig may have a lot more adjustment possibilities than you think. In the Oselver, these kinds of tiny adjustments... sometimes only a small centimeter more or less tight in one direction... mean being first or last over the finishline.

There isn't a single, given correct tention along the mast (or tack). That must be adjusted all the time. IOW - tightest possible is probably not a good idea. To my eye the deepest part of the sail (what we call the bus - don't know the english word) seen in the lower picture is too far back to be most effective and the boom outhall is too tight.

[Todd Bradshaw]

This is not a spritsail, it's a standing lugsail. The tensions involved are quite different. For example, easing the downhaul does little on a standing lug other than reduce the luff tension, raising the throat corner and lowering the peak and clew corners as the entire sail rotates in profile. When you ease the downhaul on your spritsail (you probably don't actually have a cunningham unless there happens to be a second ring about 12" above the tack ring) it eases the luff tension, but does not drop the peak corner in the process. Since a lugsail's luff is not connected to the mast, the only thing keeping that edge straight and preventing it from flapping is luff tension, so lugs always have to have a lot of luff tension.

They are both four-sided sails, but the rigging and rig tensions on the lug are very different from those on a spritsail.

[lagspiller]

Ok. I'll have to go with that. But the mention of using sheet tension to flatten out creases does seem to indicate to me that it would be a heavy weather setting. Reducing tension at the other end of the sail in lighter winds seems the logical approach.

[Todd Bradshaw]

"...using sheet tension to flatten out creases does seem to indicate to me that it would be a heavy weather setting"

It's standard procedure on some types of rigs. Though obviously there are limits to how much tension you want to have to apply to pull the crease out and at some point you may want to readjust things instead.

There are also times when a perfectly smooth sail may not be the highest performing one. A good example would be conditions where you might want to flatten the sail's shape as much as possible and shift the draft as far forward as possible. Trying to point high or sail in very light air or heavy air are examples. This is done with either downhaul or cunningham tension (as well as outhaul tension in some cases) by increasing luff tension until the luff round is used up and not contributing much draft. Instead, it forms a vertical crease right behind the mast. Sailing an upwind leg with a crease behind the mast may look unusual, but there is a pretty good chance that the sail will be faster and point higher because the rest of it is flatter and a better shape for the task at hand. The outhaul can do the same type of thing - gathering foot round into a crease along the boom to reduce draft in the bottom part of the sail.

Even on a simple spritsail, you can adjust draft and its placement to some extent by adjusting luff tension. You can also adjust upper sail draft by adjusting snotter tension. Less snotter tension allows the head to sag a bit between the throat and peak and increases draft in the top third of the sail. Increasing snotter tension pulls sag out of the head edge and flattens the upper part of the sail. Most of us don't readjust the shape of our sails every time we turn from upwind to downwind or from downwind to upwind while out for an afternoon of recreational sailing, but if you're looking for maximum performance, it's likely to make a difference and at times you may even be sailing with creases that you put in on purpose.

[lagspiller]

Never seen anyone sail with creases, but I understand the idea. The oselvers are in final training for the nationals right now - might be interesting to try practicing a new technique. Even if it doesn't work, it will make the guys in the other boats flip. Good psyco-terror... :D

[almeyer]

I rely on sheet tension probably more than I should. Since the sheet is always held in the hand, I've got instant feedback on how much air is filling the sail. If the sheet tension falls off, I take that as a sign that I'm probably pointing too high, or need to adjust the sheet. I try to read the telltale on my leech and the pennant at the peak and adjust the sail accordingly, but admittedly I'm still on the learning curve.
My sail is loose footed, tack and clew lashed to the boom. For a winter project I thought about making a new boom about 3" longer, and rigging an outhaul at the clew. Then I could adjust the round (correct term?) along the foot depending on whether the wind is light or heavy. Do you think this would be a worthwhile effort? As it stands now, the only thing I normally adjust is whether to reef or not.
Al

[Todd Bradshaw]

The major effect of outhaul tension on a loose-footed sail is the ability to adjust draft in the bottom third or so of the sail by tightening or easing the outhaul. It might be worth doing a little experimentation some afternoon with various amounts of tension (even though you'll likely need to stop and re-tie it). If it seems to be affecting performance favorably, it might be worth the time to install a system that you can adjust quickly out on the water. Keep in mind that these changes in performance tend to come in small amounts (don't expect the boat to suddenly jump out of the hole and plane across the water just because you adjusted the outhaul) but they can make a difference. Increasing your speed by 1/2 of a knot on most monohulls is a pretty big achievement, yet without a meter or GPS you might not even notice it unless sailing against a similar boat. The same with an increase of 2 or 3 degrees of pointing angle. Every little bit of extra efficiency helps though, and once the novelty of basic sailing wears off the quest to sail as efficiently as possible is something that can keep you busy and interested for a lifetime.

[almeyer]

Thanks for the advice, Todd. I went out and played with it today. My initial setting was too far back; that crease was so horrendus that I didn't think any amount of sheet tension would get rid of it. So I moved it a little forward -I must sound like Goldilocks - this one is too far forward, this one too far back...but I found a setting that I like and got rid of the flutter. It's only about an inch back of the original location, and I sailed today with full sail rather than a reef, but it seems to have worked.
Thanks again.
Al