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Go Back   SailNet Community > General Interest > General Discussion (sailing related)
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  #1  
Old 11-30-2007
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cunningham ?

I was watching great video that Giu made about the use of a cunningham. My boat, a Pearson Vanguard doesn't have a cunningham as Gui has but it does have a Jackline. The jackline extends 9" up along the luff of the main. After watching the video I t looks like it was intended to do the same thing as the cunningham is does. The main difference I see is that it attaches much further up along the luff. Is this beacuse the main on my boat has such a low aspect ratio? The luff is 32'-6" and the foot is 14'-9".

Assuming that the jackline will work as a cunningham how much "bag" should I create in the lower part of the main in light airs? how do you tell when you have moved the draft too far forward? Learning to trim the main is something that I have neglected in my lifetime of sailing.

thanks
Mike
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Old 11-30-2007
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I really am curious to learn that there is yet another use of the term jackline, beyond what I use to clip my tethers to when sailing offshore.
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Old 11-30-2007
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Mike,

Assuming that what you describe is a cringle for another sort of line that can act as a cuninhgam, and not a reef cringle, that will function the same way to you, but less effective because it is higher in the sail.

The cuningham is good because it pulls down on the lower side of the sail, but is also easier and faster to pull on a line with a purchase than it is to pull the halyard.

Tension in light winds, release as much tension as you can, before you find the horizontal wrinkles, for low winds, so the draft moves aft. (see ion the video)

The only way to find out if you tensioned too much, is, by experimenting and by tensioning until you have long vertical wrinkles along the mast lenght.

But because your sail is being pulled higher, the lower part will have a tendency to create a "belly" bellow that cringle. Avoid that. With a cuningham you sacrifice a litle sail down by the tack cringle in exchange of better foil shape

If you look carefully in the video, it answers both your questions...

Last edited by Giulietta; 11-30-2007 at 09:50 PM.
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Old 11-30-2007
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Assuming your main is in reasonably good shape and not blown out from age or overuse, the general advice would be:

For light air (or moderate air but lumpy seas) the maximum draft should be about halfway between luff and leech. This "closes" the leech, gives you more power (but less speed), and you point better.

For heavier air, (or moderate to heavy air and flat seas), tighten the luff/conningham to put the max draft about 35-40% aft from the luff. This "opens" the leech, is faster, but you don't point as high. The open leech also eases the tendency of too much weather helm in a blow. At the same time, you should tighten the outhaul to flatten the sail overall.

How to tell? That's what those horizontal stripes you sometimes see on the main are for. Look upwards (or take a photo and bring it to your sailmaker) and you can see where the deepest part of the curve is, longitudinally speaking.

Lots of books and maybe some online diagrams will explain it a lot better than I can.
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Old 11-30-2007
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AFAIK, jacklines are the lines that run fore-aft that tethers attach to.
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True Blue,

The two types of jacklines are not really that different . The one on the deck keep you attached to the deck. the one on the mast keeps the luff slides attached to the luff on the lower part of the sail. The jackline is attached to the luff about 9' above the clew. It runs though the luff slides on the lower part of the main.

I would imagine that I could also control the draft by combining the topping lift, with the down haul and the jackline. By cleating off the jackline and easing off of the down haul a little bit it would be possible to move the draft with the topping lift. right??

Nolatom,

the main is new UK sail with only one season.

Giu,

thanks for the tips and for taking the time to make the videos. I have some pictures of of the sail but I don't have enough posts to post them.
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don't believe that line that attaches the lowest slugs to the luff is called a jackline.
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Old 11-30-2007
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SD,

yes, it's called a Jack line. It's an old term. A quick search on google turned up this picture. It's shown on a hank on sail but it's the same on the main and used when reefing.

http://www.blumhorst.com/potterpages...0010/h0002.htm

Mike
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here's a better discription and photos.
http://www.cruisingdirect.com/Jackline.htm
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Old 11-30-2007
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