cmedsailor
regular
Reged: 10/09/2007
Posts: 112
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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
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sailorman
regular
Reged: 21/05/2003
Posts: 9913
Loc: East Coast
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the broken line is in fact called a " Leach Line" this is there to solve your problem
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cmedsailor
regular
Reged: 10/09/2007
Posts: 112
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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.
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moody1
regular
Reged: 10/12/2005
Posts: 145
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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.
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Thistle
regular
Reged: 02/10/2004
Posts: 661
Loc: Forth estuary
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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.
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William_H
regular
Reged: 28/07/2003
Posts: 3335
Loc: West Australia
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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
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cmedsailor
regular
Reged: 10/09/2007
Posts: 112
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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
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moody1
regular
Reged: 10/12/2005
Posts: 145
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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
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.
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racylady112
regular
Reged: 20/01/2005
Posts: 1968
Loc: Dorset
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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.
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Before I can trade up I need to sell see here
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cmedsailor
regular
Reged: 10/09/2007
Posts: 112
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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.
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