Leech line importance - SailNet Community
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post #1 of 19 Old 01-29-2008 Thread Starter
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Leech line importance

The archives turned up little, except to indicate leech lines are useful to reduce flutter. But there seems to be one on this genoa we got, and Mack Sails (whose web site I really like) attaches great importance to them, soooo....

On a scale of one (least important) to ten, how essential are leech lines to sail trim and boat performance? Are they worth the cost/trouble when you are ordering or making your sails? Are they most important in headsails, or in mains?

TIA.

Buccaneer18, Grainnia
SJ21, Diarmuid
Albin Ballad 30, Fionn
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post #2 of 19 Old 01-29-2008
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Bob,

Leechlines help to stabilize the trailing edge of the sails, which improves their efficiency by reducing drag/turbulence at the trailing edge. Maybe more importantly, they stop the annoying fluttering. They need to be adjustable because varying degrees of tension will be needed depending on the wind strength and point of sail.

We don't have any leechlines on the sails of our sailing dinghies. But our cruising boat has them on her headsails and mainsail. I don't notice the lack of them in the dinghies, but wouldn't want to go without them on the mothership. I'm not sure where the size threshold is that they become desirable. My best guess is that your boats are probably somewhere in that borderline range, though.

If you can afford the modest extra expense, I would recommend including them on a new headsail or mainsail. Also, if you go that route, I recommend having the leech line for the mainsail turn the corner at the clew and come forward along the foot to where you can adjust it up near the tack. This will allow you to adjust it when the mainsail is eased all the way out when sailing off the wind. You can also have an intermediate jam cleat attached on the leech just above the clew so it can be quickly adjusted from the cockpit when sailing upwind (I think this arrangement is called an "overhead leechline" but I could be mistaken).

Last edited by JohnRPollard; 02-01-2008 at 02:49 PM. Reason: changed "hanging leechline" to "overhead leechline", which I believe is the correct term
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post #3 of 19 Old 01-29-2008
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A leech line is not an expensive addition, either on a new sail, or to be added later by a sail loft. But in my opinion it is vital to good sail trim and to sail longevity, as well as to the sailor's sanity--the flutter of either the mainsail or the headsail can be very annoying in a breeze, and it will contribute to the sail wearing out faster. As well, you will get better performance by being able to adjust it. Well worth doing!
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post #4 of 19 Old 01-29-2008
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To my mind they are a must have on a keel boat at least. Ignoring the performance aspect the noise of a big genoa without a leach line or with an incorrectly adjusted leach line is a pita.

Andrew B

“Life is a trick, and you get one chance to learn it.”
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post #5 of 19 Old 01-29-2008
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10 It is tenportant!

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post #6 of 19 Old 01-29-2008
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I come at this discussion from the perspective of performance and racing. I sail a 20' scow with only a main sail. 220 Sq ft. Our leach cord is used off the wind to cup the sail after releasing the outhaul some. This creates a bigger bag to catch the wind. When reaching, you adjust according to how far off the wind. Put more on the further off the wind you go.

The only time used going to weather would be in exceptionally light winds. You put a small amount on to increase the camber in the sail, giving it a greater draft, thus creating more lift.

If you are using it to take out the flutter, your sail is in need of a little trimming at the loft. I have seen this when battens are not proper length. You could also check on whether your leach tension is proper, is the main sheet trimmed in enough. Try putting the vang on and see if that takes out the flutter. Primarily the sail is stretched out and needs a little nip and tuck.

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post #7 of 19 Old 01-30-2008
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Quote:
Originally Posted by 6string View Post
If you are using it to take out the flutter, your sail is in need of a little trimming at the loft.
I have to disagree. I had a blazing fast set of sails that needed a touch of leech line to prevent flutter, even when they were new. I only say this because I'd hate to see people think their sails are out of shape simply because they need a little tension on the leech line to keep them from fluttering. The principle purpose of leech lines on a sail isn't to change the shape of the sail. They're used to support the leech.
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post #8 of 19 Old 01-30-2008
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I come at this as a sailor who ripped a mainsail due to leech flutter (and age of the sail, no doubt). It was my first time on a larger boat (28') as a skipper, and in all the times I'd sailed with other skippers on boats that size (5 or 6 times) I'd never seen one used.

We were sailing out of the South River near Annapolis, MD in a rented boat, and while the winds were up a bit they weren't too bad -- maybe 12-15 kts. As we got closer to the Bay I noticed that the leech was fluttering quite a bit, but didn't know what to do about it. When we got out on the bay it was blowing pretty briskly (St. Thomas reported 22 kts max gusts when I checked it later), there were 3-4' swells and two of my three crew were sick. However, none of the other sails I spotted were reefed either, though at least one was under headsail only.

Winds were from the north, so we decided to make our offing past the St. Thomas light and tack for the Severn River, and as soon as the sail came around it split right up the seam where the fluttering had been happening. Much excitement ensued getting the main down, but one of my sick crew was magnificent, going forward to pull down the main as we came into the wind -- the other healthy crew member declined to go up in those swells.

Anyway, we got the main down and headed back in under the jib. I called the marina where we rented the boat, and they were amazed it had split and offered to put on another main for us if we wanted them to. With two sick crew we decided to call it a day. But ever since, I've kept a good eye on leech flutter and made sure to adjust the line in a timely manner.
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post #9 of 19 Old 01-30-2008
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The cost of repairing a torn leech, or a WORN leech, from all that fluttering is going to be way more than the cost of a leech line. Do ask the loft what options they have, because some lines can be adjusted with one hand--and they hold. Others are constantly pulling out and needing to be reset, a PITA.

Whatever fitting and cordage they use, make sure to tell them (nicely) that if it doesn't hold, you're going to rip it out and come garotte someone with it.

Does it manke you sail any faster? Dunno, but it stops that damned annoying fluttering, which CAN'T be much good for speed, since it is breaking up flow.
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post #10 of 19 Old 01-31-2008 Thread Starter
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So is a leech (leach, letch, leche, spelling optional) line a sail-based alternative to a vang/mainsheet, and therefore most useful on downwind points of sail when it's otherwise hard to sufficiently tension the leech? Or does it rather alter the harmonic of the fabric edge, which may not respond even to hard vanging and downward sheeting cuz it's stretched out?

It's clear that kind of vibration could hammer the fibers and resins on a sail; laminates must be really prone to leech fatigue, no? Are the gains worthwhile on smaller, high aspect sails like blade jibs and the tall narrow main of the San Juan 21? (23' luff; 8.5' foot)

Heh. Sometimes I think sailors are kittens and just enjoy having another string to pull. & then realize how bloody incomplete my youthful sailing education was. Never saw a leech line back then. Never saw a traveler. Never saw a jib car, even on quite large boats. No one jibed, not on purpose -- it was considered terrible form. One comes about, thru the wind properly, dontcherknow, or one doesn't sail at'tall. These my teachers talked about sailing a lot, they smoked pipes and waved them about convincingly, they even raced one another about the lakes in a genteel, old-money sort of way.

But I'm starting to suspect they weren't very good sailors. I've learned more from you lot in six months than in eight years before the mast in New York. Sheesh. Where the hell were you in ... say ... 1980?

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