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Go Back   SailNet Community > Out There > Racing > luffing the leech ...
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Thread: luffing the leech ... Reply to Thread
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Topic Review (Newest First)
08-11-2006 01:16 AM
paulk Seems like you're asking about luffing in the aft 1/3 of your jib and everyone is telling you about getting rid of leech flutter. Perhaps the jiblead needed to be moved more forward in the light air. This might tend to tighten the angle of attack of the aft section of the sail, (giving it more "belly") and stop the luffing in that section. In really light stuff, I find that sometimes opening up the slot (moving the lead outboard, as you mused) keeps the airflow moving better and the boat moving faster, because you're not trying to "bend the wind" so much. I do whatever's fastest.
08-08-2006 07:13 PM
Teaksail
Cupped or Fluttering leech?

the leech of all sails will, at some time, flutter, and the only way to do away with the fluttering is to pull on the leech line which makes that edge cup. Even mainsails will have this problem except that the battens prevent to much cupping or fluttering.

Heres the reason...Stretch. The sail cloth at the leech takes more load and abuse (tacking agaist the rig) than anywhere else on the sail. The stretching of the sails makes the local leech longer than what was designed. This usually happens after some time but if it happens right away with a new sail then that sail is under built for the conditions it is being used. The more stretchy the material the sooner it will happen and larger the affected area will be.

The only remedy is to either live with it or have your sailmaker re-cut the leech and ask if they can add any strength to the leech by adding a leech ply or some other second layer.

With new sails be sure that the salesman or sailmaker does not under build your sail, AND, be sure that YOU do not use the sail outside of it's intended range.
08-08-2006 12:21 PM
Sailormon6
Quote:
Originally Posted by tsailed
I bought a new 135 from Ulmer year before last. The leach fluttered on the wind from the first time it was hoisted. To stop the flutter I had to put enough tension on it to put a nasty looking 1" hook in the trailing edge.
tsailed, years ago I bought a new North 155 that acted exactly like your Ulmer 135. When I put enough tension on the leech line to eliminate the flutter, it looked to me like it had an awfully deep cup, but I assumed North knew what they were doing, and won a lot of races and regattas with that sail for over 20 years. To this day, I honestly don't know exactly how much cupping is too much, but, if the sail is fast (and that one was blazing fast), I don't care. I just put enough tension on the leech line to stop the flutter, and don't worry about it.
08-07-2006 04:39 PM
hellosailor Mike, remember that anytime you are curious, some audio cassette tape and some sail repair tape (to stick it on with) will give you cheap telltales that you can stick anyplace you want, to observe the flow.
08-07-2006 04:11 PM
tsailed I bought a new 135 from Ulmer year before last. The leach fluttered on the wind from the first time it was hoisted. To stop the flutter I had to put enough tension on it to put a nasty looking 1" hook in the trailing edge. I took it back to the sail maker and they cut some hollow in the trailing edge. It had almost no impact. The sail maker handed me some BS about this being the latest way sails were cut so they were flatter and better up wind. "It's supposed to be like that, yea thats it, we meant it to be that way." The next sail I bought was from Quantum. In Ulmer's defence I must add that we have had great result racing the boat since I started using their sail, in spite of the nasty looking hook in the leach. We are competitive even in light air flying a 135 when most are flying a 155. I think it is because our tacs are quicker, and the 135 will fill in lighter breeze than a larger sail.
07-27-2006 11:25 AM
Sailormon6 Generally a fluttering leech means the airflow is disturbed or separated from the sail. The reason is probably because the sailcloth is too thin and flexible to hold its shape by itself. The leech lines put just enough tension on the leech to help it hold it's shape.

I have always believed that a fluttering leech is more detrimental than a cupped leech, so I put whatever tension on the leech lines is necessary to stop the fluttering.
07-26-2006 01:22 PM
mikehoyt Gary

Do you know where hull#1 is now? Our boat is hull #2 and was originally owned by Ken Dodds of Barrie I believe ...
07-26-2006 01:21 PM
mikehoyt Yeah it does sound simple. I managed to do that ...

But my real question is what this means about the air flow over the back 1/2 of the sail.

Also - to remove with the leech line creates more hook and I had understood hook to be not good.

HAd seen this before with more wind but only on last 1 foot of sail and more rapid flutter. This really looked like the ripples in a slowly flapping flag and was approx last 1/3 of sail.

Mike
07-26-2006 12:16 PM
sailortjk1 After easing the leech line it started to flutter, right?
Before easing it had too much hook, right?
What about finding a happy medium? Ease enough to take out the hook but not soo much that it flutters? Does that sound too simple?
07-26-2006 11:48 AM
Gary M Hi Mike, sounded like a Niagara, I used to own hull #1, had great fun with it. What you are seeing would not correctly be described as luffing it sounds like a light air version of the fluttering you get on the leech of a jib when you do not have enough tension. Perhaps the stiffness of the kevlar caused a larger section of the leech to move or oscilate.
I do not think it is a big deal, a small amount of tension would likely eliminate it.

I would not move out to the rail. In light air you generally put a little twist in the genoa by moving the car back one. However you may find that the wind up higher is a bit stronger and therefore more forward so then you would not twist it, perhaps even go the other way.
Gary
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