View Full Version : Jib Flutter
I have a Catalina 320. Generally when the wind is up over 15 knts I get a pronounced "flutter" from the leech of my 130% genoa while close hauled. My jib halyard seems tight enough. And the genoa block cars seem to be set so the jib sheet angle to the tack is about right. Have others experienced this problem? Any suggestions on the cause & how to deal with it? --Ron
Barry
08-22-2002, 02:59 am
Most Genoas have an adjustable leech line. There should be a small diameter line on the trailing edge of the sail that fits in a plastic jam cleat. Pull the string and add more tension especially when you're headed up wind. That will stop the flutter. Barry
Ed S.
08-22-2002, 03:49 am
My understanding is that you tighten the leechline in light air reaching or to help make a baggy shape when running downwind, and loosen to flatten the sail in heavier air. Tightening the leechline will stop the luffing, but will also change the draft position in the sail. I think the fluttering just means you are reaching or exceeding the boats ability to point upwind with this sail. Tried switching to a 100% jib?
Perhaps moving the block forward a bit might tighten up the leech while flattening the sail. I agree with Ed that tightening the leech line would create a baggy sail that is not desirable under the conditions you described.
all sails experience some stretch over time so their shape changes with use. In heavy winds you will want a flatter sail shape to depower the sail a little and this sheet position puts less tension on the leech side of the sail. The best remedy is to sew a leech line into the leech which is easy to do and allows you to tension the leech to stop the flutter. It is easily added to an old sail and should not be very expensive. I have leech lines in my main and my genoa and jibs and would not order a sail without them! dave
Doesn't moving the block forward actually allow more draft in the sail? I thought moving the block back flattened the sail. Am I confused? (Wouldn't be the first time).
Moving the block forward puts more tension on the leech and less on the foot, moving it back puts more tension on the foot and less on the leech. Moving the block forward allows more draft in the sail as you noted. A 45 degree angle of the sheet to the clew of the sail will equally tension the foot and the leech and give you the flattest sail shape. But to solve your flutter problem you want to tension the leech. If the leech is fluttering you want more tension on the leech. As previously noted the easiest solution is a leechline.
My understanding of where to position the jib block is in line with what "Dave of Mystic" described. I may be confused as to which Dave asked the question and/or answered it...
I was a little wrong in my last response. I spoke of a 45 degree angle of the sheet to the clew as equally tensioning the foot and leech. this is in the ballpark but actually to flatten the sail the most a sheet position in line with the "LP" of the sail would do this. This is the line through the clew of the sail and perpendicular to the luff of the sail. Maybe a sailmaker out there can add some expert advice. dave
If you have a fluttering jib leach: 1. Sail close hauled, get your tell-tales streaming on both sides of the jib. 2. Head up. If the higher tell-tales break before the lower tell-tales, you have your block too far back. 3. Tack, move the unloaded block forward. 4. Repeat 1-3 until all tell-tales break together. I'll bet your fluttering leach is long gone. If not, now you can try some other solution since you attempted the easy, cheap one first.