# Leech line importance



## bobmcgov (Jul 19, 2007)

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.


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## JohnRPollard (Mar 26, 2007)

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).


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## FrankLanger (Dec 27, 2005)

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!
Frank.


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## tdw (Oct 2, 2006)

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.


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## Plumper (Nov 21, 2007)

10 It is tenportant!

Gaz


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## 6string (Oct 19, 2006)

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.

Jeff


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## Sailormon6 (May 9, 2002)

6string said:


> 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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## jaschrumpf (Jun 22, 2002)

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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## hellosailor (Apr 11, 2006)

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<G>) 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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## bobmcgov (Jul 19, 2007)

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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## AndrewScullion (Jan 31, 2008)

If you do not adjust the vang, outhaul, halyard etc regularly as you change points of sail or wind strength to keep the basic shape of the sails at an optimum, then the leach line will make no difference.

The leech line is for fine tuning at the very edge of the sail. In light airs you need to be able to slacken it off to get rid of that hook which will stall the delicate air flow. This leaves the sail fluttering in heavier winds so it gets tightened up where the hooking is forced out by the weight of the wind.

Hope this helps
Andrew


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## sailingdog (Mar 19, 2006)

Bob-

A leech line is not a replacement or alternative to a boom vang and mainsheet being used properly to control the sail shape on a mainsail or the proper positioning of the fairlead blocks on a headsail. It is used to finetune the shape of the leech for the wind strengths you're encountering.


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## Sailormon6 (May 9, 2002)

As the wind moves over the convex and concave surfaces of the mainsail, the sum of all the forces are pushing and pulling the sailcloth to leeward. The mast, boom and rigging hold the sail in place, so that it resists that force, but the leech of the mainsail, often with a big roach, is relatively unsupported. In strong winds, those forces can cause the leech of the sail to fall off to leeward, but, when it moves into the stream of wind that is flowing off the leeward side of the sail, it flips back. That's when the sail starts to flutter at the leech. It alternately moves back and forth between those opposing forces.

The leech line adds support to the leech, to prevent it from falling off to leeward in strong winds. But, as the windstrength decreases, the tension on the leech line is too great, and it causes the leech to cup, which creates turbulence as the wind flows off the sail. Thus, in order to finely adjust the shape of the leech so that it permits the wind to flow smoothly off the leech of the sail, the leech lines need to be adjusted in accordance with the speed of the wind that is moving across the surfaces of the sail. Generally that means you'll increase leech line tension when sailing to windward in stronger winds, and decrease tension as the windspeed decreases, and as the boat bears off the wind.

The general idea is to shape the leech of the sail so that it allows the wind to flow smoothly off it. If it curls slightly, the efficiency of the sail is reduced.


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## bobmcgov (Jul 19, 2007)

sailingdog said:


> Bob-
> 
> A leech line is not a replacement or alternative to a boom vang and mainsheet being used properly to control the sail shape on a mainsail or the proper positioning of the fairlead blocks on a headsail. It is used to finetune the shape of the leech for the wind strengths you're encountering.


Oh yeah -- I'd guessed the 1/16th inch cord was no substitute for a 4:1 block and tackle. But is it most useful downwind? Close hauled, it seems the leech tension is mostly a product of mainsheet and vang. The reason I ask is I've never seen one led forward as John Pollard suggests, tho that would seem a necessity for adjustment downwind. Most cleat right on the leech.


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## Plumper (Nov 21, 2007)

I skippered a large yacht (100 tonnes) and the leach line came down the luff to the tack so it could be worked at the mast and it had a 2:1 purchase on it. The leech lines in the headsails were all adjusted at the tack and the genoa also had a 2:1 purchase on it. This was because you couldn't reach the clews of any of the sails from deck.


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## JohnRPollard (Mar 26, 2007)

bobmcgov said:


> Oh yeah -- I'd guessed the 1/16th inch cord was no substitute for a 4:1 block and tackle. But is it most useful downwind? Close hauled, it seems the leech tension is mostly a product of mainsheet and vang. The reason I ask is I've never seen one led forward as John Pollard suggests, tho that would seem a necessity for adjustment downwind. Most cleat right on the leech.


Bob,

I think the leechline is equally useful upwind and downwind. The annoying fluttering that sometimes develops along the leech principally occurs on upwind legs, which is when I find myself most often adjusting it (usually increasing the tension to stop the fluttering, but sometimes easing the line if there is too much tension causing the leech to hook in).

The reason for the "overhead" leechline I previously described is that when sailing off-the-wind, we usually ease the tension on the leechline. But most of us forget to do that until after we've eased the boom out on our new down-wind course. It's nice to not have to pull the boom in to adjust the leechline. On our sail I can go forward to the tack and yank the leechline, it will pop out of the intermediate jam cleat and then I can set the tension on the cleat along the foor of the sail by the tack.

Normally I'd have the sail here and I'd illustrate with some photos, but after 18 seasons it's at the Doyle loft being measured for a replacement.


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## christyleigh (Dec 17, 2001)

JohnRPollard said:


> 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.


I've got to set up something like that because now unlike my last couple boats I just can't sail that close to the wind. So most of the time the leach is just outboard enough that even with a nice big beefy 1 x 3 stanchion rail to lean on to makes me think as I'm stretching to adjust them - I really shouldn't be doing this


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## bobmcgov (Jul 19, 2007)

CL: In my life, thinking "I really shouldn't be doing this" is nearly always followed by proof that I really shouldn't be doing that. Then it's off to get the Band-Aids. Almost never fails.

John: Pshaw. Eighteen seasons. Barely eligible to vote. The main on our new San Juan is original 1973. Doyle would send it back with regrets. Leach flutter? You could take the trailing edge of this sail and use it for Kleenex. Since our winds are so high, I'm looking for ways to prolong life of our new sails. Sounds like leach lines might matter. Thanks, all, for the education!


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## JohnRPollard (Mar 26, 2007)

bobmcgov said:


> John: Pshaw. Eighteen seasons. Barely eligible to vote. The main on our new San Juan is original 1973.


Bob,

And here I thought _I_ was being a thrifty yankee. You've got me beat by a factor of two!! Hmmm, maybe I can make it last....


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