Problem with the leech of mainsail

[cmedsailor]

Hello,
The leech of my in mast furling mainsail when going upwind “vibrates” (sorry for the poor terminology). I have tried lots of actions to eliminate it but with no success. I tried tensioning more or less the foot of the sail with the outhaul as well as the luff tension with the halyard, I tried sheet in more or less and also rising up a little the boom. Nothing worked. I must mention however that this thin line running along the leech (don’t know the name) is broken and I realise that could probably help. Is it a matter of bad trimming or is my mainsail loose and is asking me for a change? Any ideas?
Thanks

 

[sailorman]

the broken line is in fact called a " Leach Line" this is there to solve your problem

 

[cmedsailor]

In fact it is not the leach line (thanks sailorman) that is broken but the block (is this the correct word?) holding it. If I pull it with my hand to increase the tension of it the leech looks slightly better but the problem is not eliminated completely.

 

[moody1]

IMHO and Hubbies - Leech lines are the devils work. A leech that is vibrating is showing that air is coming off it well, its the differential pressure that causes the flutter. The differential pressure is the reason sails work, as in aerofoils.
Tightening a leech line and stopping the flutter can hook the leech and decrease the performance of the sail. Compromise is to tighten just enough to decrease the vibration but not enough to hook the edge over.

 

[Thistle]

There's normally a small jam cleat to hold the leech line and it sounds as though that it what is broken; it should be a simple job for a sailmaker to replace.

Think, too, about other ways of tensioning the leech: you've tried sheeting in harder but applying more kicker may also help. And don't overlook the obvious - make sure that your topping lift is not still under tension and preventing the boom being pulled down.

 

[William_H]

It should be fairly simple to replace the little jamb cleat in situ. They can be bolted on with a 1/8 or 5/32 screw and nut or just lashed in place with whipping twine. olewill

 

[cmedsailor]

Guys I already have a spare cleat to replace it. The question is what to do with this flapping leech besides the leech line. The leech line decreases the problem but not eliminates it. So, I am trying to figure out whether it is a matter of trimming, or old sail, or probably simply the fact that all furling main sails (with no battens of course) behave like this. By the way do they?
Thanks

 

[moody1]

[ QUOTE ]
Guys I already have a spare cleat to replace it. The question is what to do with this flapping leech besides the leech line. The leech line decreases the problem but not eliminates it. So, I am trying to figure out whether it is a matter of trimming, or old sail, or probably simply the fact that all furling main sails (with no battens of course) behave like this. By the way do they?
Thanks

[/ QUOTE ]

The vibration is caused by the pressure difference one side of sail to the other. The main is cut with a curved leech and so will never be a tight straight edge. This allows it to flutter side to side. As it does the pressure difference is bled of and edge then flaps back, to end up getting pressure difference again - the cycle repeats. As the sail generates more lift and speed the fluttering increases.
A simple illustration of the effect is the sheet of paper held in front of mouth and you blow along it. The free end away from you then does the same as your leech - it flutters.
As mentioned before, it shows your sail is working well.

 

[KREW2]

Well thanks for that, and I hope what you say is true. My leach has always fluttered and I put it down to the sail being old, Having said that the boat sails well to wind, and I get a good turn of speed, even in light airs. You may have just saved me the cost of a new sail.

 

[cmedsailor]

moody1 I am exactly in the same position as racylady112 so ...thanks, that was a relief.
My boat also sails well to wind, amazingly good for a furling mainsail. Tested well while racing. So it's good to hear that my mainsail seems rather to be still OK.

 

[moody1]

Up to a point of course. The fluttering will lead to stretching and wear of the seams / stitching. This in turn can increase the bagginess of the leech and in so doing lessen the sails performance. But this is over a period of time and has to be strong vibration to occur.
Stretched sails are common anyway !

 

[sail045]

Hi try adjusting the tension on the kicker, and adjust the leech line a little at a time. There is a big difference between sloppy flapping on a beat,close hauled, and vibration of a well trimed sail, try adjusting the down haul line at the foot of the main,tensioning the luff of the sail. Adjusting the kicker tension increases /reduces the downward force of the boom, stretching the body of the sail causing the leech to flap/vibrate. Getting the above right produces a very pleasing "Vrooom" sound on a good beat, showing that the sail is working as well as possible . Hope that helps you

 

[sailorman]

[I must mention however that this thin line running along the leech (don’t know the name) is broken ]


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your words /forums/images/graemlins/blush.gif

 

[William_H]

Trailing edge flutter is a real problem. While the reasons it occurs are correct you don't have to put up with it. The leach line will increse the tension on the leach to minimise flutter. One trick the sailmaker does is to put a concave curve in the leach. Unlike most mainsails with roach which is a very convex curve.(but they have battens to control the leach) The flutter problem will become worse as the sail ages and the leach stretches.

If the leach cord will not stop the flutter then it is time to take it to the sailmaker for adjustment of the seams at the leach. You could try to flatten the sail with mainsheet tension /vang tension but basically the middle of the sail is taking the load before you tension the leach. good lcuk olewill