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-   -   luffing the leech ... (http://www.sailnet.com/forums/racing/18561-luffing-leech.html)

mikehoyt 07-26-2006 10:36 AM

luffing the leech ...
 
Our boat is a with fractional rigged 26 footer with swept back spreaders. We carry a 100%, 150% genoa and full batten main and spinnaker ...

The other day I was out sailing with my daughter in very light breeze (approx 5 knots). We were tacking upwind and she went below for a nap on a particularly long tack.

I looked at the trailing edge of the 150 and noticed that there was a hook indicating the leech was too tight for conditions. As it was a lzay day and we weren't racing I decided it was driving me crazy. So I eased the leech line and waited for it to play out.

On this day the wind was so light that we were not trying to point particularly high but were trying to keep the boat moving. The windex was just outside the feathers and normally we can point about 10 degrees higher but at the price of speed.

OK. So after I eased the leech the aft 1/3 of the sail started to luff even though the leading telltales were streaming on oth windward and leeward sides. It was an oscilating motion almost like a flag waving.

When I sheeted the genoa in a bit and trimmed to point a bit higher the oscillation ceased.

As it was a lazy day I spent some time thinking about this. The luffing was obviously not great but neither was the hook in the leech with which it had not ocurred. So what did this tell me about the sail? Perhaps I needed to move my cars from the genoa track outboard to the rail? (approx 5 inches).

Any thoughts?

The boat is a 1979 Hinterhoeller Niagara 26. The sail is a North 150% Radial Kevlar purchasd new in 2003.

Thanks

Mike

Full Tilt 2

Gary M 07-26-2006 10:48 AM

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

sailortjk1 07-26-2006 11:16 AM

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?

mikehoyt 07-26-2006 12:21 PM

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

mikehoyt 07-26-2006 12:22 PM

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 ...

Sailormon6 07-27-2006 10:25 AM

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.

tsailed 08-07-2006 03:11 PM

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.

hellosailor 08-07-2006 03:39 PM

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.

Sailormon6 08-08-2006 11:21 AM

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.

Teaksail 08-08-2006 06:13 PM

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.


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