A fluttering leech....

[[2574]]

There's nothing worse than a fluttering leech, either headsail or mainsail, nor is there any pleasure in a hooked leech caused by a taught leech line. We have new sails this season and a pleasure they are indeed - but when the wind pipes up over 20kts an infernal fluttering leech develops and the only solution, seemingly, is the confounded leech line.....but is there a better way? What causes a leech to flutter? Is it equally balanced air pressure both sides of the sail causing a pressure fight on the trailing edge? Is it vortexes spinning off from a poorly trimmed sail draught? I'd welcome any tips/experience/guidance that the collective can offer such that I can sail forever afterward with an unhooked trailing edge and no throbbing of the dreaded flutter.....

 

[Daydream believer]

One assumes that on the jib you have it set so that the sheet applies the correct sheet angle & the correct leech tension.
Also you increase halyard tension as the wind pipes up. This applies tension to the leech in a small way & pulls the cloth forward.
Other wise- Badly made sail. Send it back. I had a Kemp genoa like that. Very poor & I had to have quite an argument when I sent it back. They were quite snotty.
A simple solution-- you could have a hollow cut in the leech, that would solve it.
Or you could have vertical battens put in if the leech has a slight roach.
The mainsail should NOT have a hook in the leech if you have to tension the leech so much that it hooks. That is almost certainly a fault. Speak to the sailmaker

PSlate edit
that being said, I recall Hood selling me a sail that did deliberately have a hook leech in the genoa. It had a bulge in the sail just before it & was meant to adjust the air flow as it left the sail. I saw no benefit & eventually had Cranfields cut the sail to remove the hook, which improved the set somewhat.
I did not buy another Hood sail so do not know if they continued with the idea.. That was back in the 70s

 

[neil_s]

Yep - have that problem. mainsail is in it's third year, and is fine until a reef is needed - then the flutter starts - but the leach line is now hidden in the reef!

 

[Daydream believer]

Yep - have that problem. mainsail is in it's third year, and is fine until a reef is needed - then the flutter starts - but the leach line is now hidden in the reef!

My sail has leech line cleats above each reef point. However, my sail does not flutter, so I have never had to adjust it.

If you have a flutter problem, I suggest that you get the sail maker to open the sail just above the reef to expose the line & sew in a cleat at that point so that you can tension it there.

 

[[2574]]

Yep - have that problem. mainsail is in it's third year, and is fine until a reef is needed - then the flutter starts - but the leach line is now hidden in the reef!

Ouch, that’s frustrating! Ear defenders needed!

 

[Amlov]

One of the problems we have had in the past is that the sacrificial strip has been put on a little tight, which causes more flutter on one tack than another. The leech line can also be sewn on a bit tight as well. So if your flutter is worse on one tack than another it might be a simple adjustment is needed.

 

[Daydream believer]

One of the problems we have had in the past is that the sacrificial strip has been put on a little tight, which causes more flutter on one tack than another. The leech line can also be sewn on a bit tight as well. So if your flutter is worse on one tack than another it might be a simple adjustment is needed.

It is one of the problems of buying cheap sails. The cloth stretches but the sacrificial strip may stretch differently. It then either pulls the sail cloth or cracks. causing it to fray.

 

[TLouth7]

I have seen sails with no seam or extra material along the leach. The logic I believe is that flutter is caused (or exacerbated?) by the extra mass at the leach, and so avoiding that prevents the issue in the first place.

It is a fault of my current genoa that it needs the leach line tension adjusting frequently. Perhaps this is a control that should be run back to the cockpit?

 

[Chiara’s slave]

Ours meeds frequent tinkering too at the moment. But our jib is very past it. It’s inability to set is due to use, and the passage of time, not any lack of skill on the sailmakers part.

 

[Daydream believer]

Ours meeds frequent tinkering too at the moment. But our jib is very past it. It’s inability to set is due to use, and the passage of time, not any lack of skill on the sailmakers part.

The OP has a new sail so should expect it to perform correctly- for a while at least.
There is little joy in sailing with a knackered jib, so one needs to bite the bullet & get it recut, or replaced altogether. As I said above, a fluttering leech can often be improved by getting the sailmaker to cut a hollow in the leech & that should not be too expensive, if it does not mean a new UV strip- which it should not normally. Hs can also adjust the horizontal seams near the trailing edge , but more difficult on older sails & more expensive.

 

[Chiara’s slave]

The OP has a new sail so should expect it to perform correctly- for a while at least.
There is little joy in sailing with a knackered jib, so one needs to bite the bullet & get it recut, or replaced altogether. As I said above, a fluttering leech can often be improved by getting the sailmaker to cut a hollow in the leech & that should not be too expensive, if it does not mean a new UV strip- which it should not normally. Hs can also adjust the horizontal seams near the trailing edge , but more difficult on older sails & more expensive.

I agree with your assessment. And we are actively looking to have a new jib made. And considering the possibility of a 3Di one. Thats unfortunately quite a big bullet to bite down on. A recut would be a waste of money, it is stretched out.

 

[benjenbav]

Fluttering leech is going to be inefficient as well as unattractive.

OP doesn’t like the hooked appearance of tightening a leech line but I wonder if it doesn’t work like a winglet in keeping the fast and slow moving air streams separate until away from the sail/wing and thereby increasing the efficiency of the sail/wing?

 

[Chiara’s slave]

No, sadly it doesn’t. You want the air to depart your leech fast and clean, over the back of your mainsail.

 

[benjenbav]

No, sadly it doesn’t. You want the air to depart your leech fast and clean, over the back of your mainsail.

But the fast airstream is over the back of the sail. Not a benefit to keep the slow air from joining it for longer?

 

[Chiara’s slave]

No, I’m 100% certain its not. The air isn't slow there. Go sit in the slot, and try it.

 

[Daydream believer]

No, I’m 100% certain its not. The air isn't slow there. Go sit in the slot, and try it.

No.--Air slows down in the slot.

 

[Chiara’s slave]

Ok! It’s pretty damn fast in mine, round the back of the main you’d think that was a good thing?
In any case, deliberately hooking the leech of your jib will not speed you up.

 

[Daydream believer]

Ok! It’s pretty damn fast in mine, round the back of the main you’d think that was a good thing?
In any case, deliberately hooking the leech of your jib will not speed you up.

. The air flow between jib & main up wind is slowed & whilst you think it is faster, I am afraid that you are mistaken.

 

[Chiara’s slave]

Even that being so, a hooked leech is a criminal matter. It changes the angle of the departing airflow, potentially backwinding the main. We can see this happening even with our full battens.

 

[Pye_End]

Anyone tried flutter reducing tape?

Eg. PSP Dacron Wave Leech Tape - Float Your Boat