Flapping Leech? (Video)

Tim Good

Tim Good

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The leech on my Yankee and Staysail flap when going up wind. Here are the facts:

1. They are both new sails by SouthWest.
2. I have tried moving the cars fore and aft with no real improvement.
3. I have tried tightening the leech line with only a little improvement.
4. I have a a heavyweight Genoa and Staysail by Hood which don't flap.

Am I doing something wrong? Are they just cut as "off wind" cruising sails or is it something else?
 
You should not need excessive leach tension in a new sail. You might try varying the halyard tension which seems to be the only obvious thing you have not tried, but I suspect it's the cut and you should take them back to SouthWest, or get them to come to you.
 
A video here is worth a thousand words. There's a serious problem with the cut on those sails. A jib should be fairly round in the front third with the back two thirds being fairly flat to provide a nice clean laminar exit.

I would recommend returning to sailmaker without delay.
 
dom said:
A video here is worth a thousand words. There's a serious problem with the cut on those sails. A jib should be fairly round in the front third with the back two thirds being fairly flat to provide a nice clean laminar exit.

I would recommend returning to sailmaker without delay.
Click to expand...

Can't resist it.
You don't like the cut of his Jib.
 
It is difficult to see from that film whether increased luff tension would pull the draft of the sail forward and improve matters or not because you can't see how far forward the draft actually is, but its worth experimenting with halyard tension to get the draft well forward if possible. The amount of flapping is about what I get on my genoa if the leach line comes undone, and although I still get some flapping going hard upwind in 20 knots apparent wind its nothing like that on my now several years old tri radial laminate genoa if the leach line tension is OK, so if a bit more halyard tension does not cure it the sailmakers need to sort it out with a re-cut.
 
KREW2 said:
Can't resist it.
You don't like the cut of his Jib.
Click to expand...

Very sharp! :D

Agree with Norman and others' halyard advice in principle, but the amount of halyard tension at those wind strengths should not be huge. But to be honest I'm pretty sure that halyard tension is not the problem here as a smidge more will remove the little creases along the luff and I can't imagine that will come near to settling the leech.

Edit looking at the vid again reinforces my opinion that the jib shape is not right at all as the draft is simply too far back. I am also a little concerned about the way the reinforcing patch has been stitched into the clew area of the main.

I'd def get the sailmaker's input without further delay.
 
dom said:
A video here is worth a thousand words. There's a serious problem with the cut on those sails. A jib should be fairly round in the front third with the back two thirds being fairly flat to provide a nice clean laminar exit.

I would recommend returning to sailmaker without delay.
Click to expand...

If they are new sails - agreed.
 
Ok so.... these sails came with the boat when I bought it. New and unused but South West Sails went under in 1999.

Can anyone recommend any especially knowledgeable sail makers that could cast their verdict?
 
Pm me if you like and I'll recommend a Solent based outfit which is a bit racy but very very good. But as a wildcard, there's a girl on here who goes by the name of Wilkinson Sails and her advice is usually spot on. I'd certainly be interested to see what she has to say.
 
The leach of a genoa is cut with a curve in it to prevent motorboating by increasing tension. Impossible to see if yours have that curve.

But you are tensioning the leach line with a slack sheet arent you? If what you are doing is setting everything up, then after finding a flapping leach you are tugging on the loaded leach line, you will struggle to get it tight enough.
 
Solo sails not so far from you could fix them.
They're top notch from the sails and mods I've seen.
Essentially the fix is to tighten the leech.
Winding on the leech line should remove most of the flutter and moving cars forward will also help but the tendency would be to introduce a pronounced hook.
Not sure from the angle of the video how much hollow was cut into the leech and the simple physical fix could just be to re-cut the leech with more hollow.
 
The problem you have is called (leach) flutter. It is a major concern of aeroplane wings etc (very destructive) not just sails where it is mostly harmless. It is a function of the mass of the leach itself. A leach cord is the more common fix which increases the tension of the leach. It can fix the flutter but too much tension causes a hook in the leach which is detrimental to smooth flow.
Other fixes can be small battens fitted in the leach equally spaced up the leach. Not much good for a furling jib.
If as said a hollow is cut in the leach rather than a straight line the tension of the sail itself can put tension on the leach.
I have one jib made for a larger dinghy where the leach is hot knife cut but with no hem of any sort so there is very little mass at the leach so no tendency to flutter. An idea that never took off.
However I have one jib which tends to flutter and is very annoying and so far resisting a fix. I have to drop the jib to increase the leach cord tension. So it often seems easier to put up with the flutter. good luck olewill
 
northcave said:
Ok so.... these sails came with the boat when I bought it. New and unused but South West Sails went under in 1999.

Can anyone recommend any especially knowledgeable sail makers that could cast their verdict?
Click to expand...

Peter Sanders (of Sanders Sails, Lymington). If you email him a link to that video, I expect he'll confirm immediately not just what's wrong with it, but also the best path to getting it sorted. I've talked to many sailmakers last year before ordering a new Genoa, and while they all more or less knew what they were talking about, Peter stood out for not only having encyclopedic knowledge of sails, but also for being able to explain clearly and precisely the technical details of fabrics, cuts and features and the reasons behinds his recommendations.
 
Yngmar said:
Peter Sanders (of Sanders Sails, Lymington). If you email him a link to that video, I expect he'll confirm immediately not just what's wrong with it, but also the best path to getting it sorted. I've talked to many sailmakers last year before ordering a new Genoa, and while they all more or less knew what they were talking about, Peter stood out for not only having encyclopedic knowledge of sails, but also for being able to explain clearly and precisely the technical details of fabrics, cuts and features and the reasons behinds his recommendations.
Click to expand...

+1 to that. Enormously helpful and capable and reasonably priced.
 
William_H said:
The problem you have is called (leach) flutter. It is a major concern of aeroplane wings etc (very destructive) not just sails where it is mostly harmless. It is a function of the mass of the leach itself. A leach cord is the more common fix which increases the tension of the leach. It can fix the flutter but too much tension causes a hook in the leach which is detrimental to smooth flow.
Other fixes can be small battens fitted in the leach equally spaced up the leach. Not much good for a furling jib.
If as said a hollow is cut in the leach rather than a straight line the tension of the sail itself can put tension on the leach.
I have one jib made for a larger dinghy where the leach is hot knife cut but with no hem of any sort so there is very little mass at the leach so no tendency to flutter. An idea that never took off.
However I have one jib which tends to flutter and is very annoying and so far resisting a fix. I have to drop the jib to increase the leach cord tension. So it often seems easier to put up with the flutter. good luck olewill
Click to expand...

Interesting post. I had a fluttering leach bad with the previous genoa whether arty fatty owner had specified a uv strip on the wrong side and insisted it be cured by putting a uv strip on the other side. So that sail had ywo uv strips and a leach line that was next to useless.
 
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