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post #9 of Old 06-22-2013
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Re: Genoa Cut Flat for reefing????

Originally Posted by smurphny View Post
Is there some rule of thumb or formula for calculating headstay sag? I just finished up a storm jib and really just estimated the amount of sag that would occur to my inner forestay but I agree that it's a m/m that often is ignored. Most of the headsails I've seen have little to no luff curvature sewn in to account for deflection. Calculating the direction of that deflection and in what wind direction and speed and the resultant curvature is also a difficult thing to figure.
I don't know of any way to calculate headstay sag. On my boat the sailmaker put a piece of tape perpendicular to the luff on my jib half way up. We then raised the jib with a light line at its head and while sailing stretched the line tight to the tack. Pictures were taken from the tack with various backstay tensions. We could then use the pictures on a monitor to reasonably measure the range of headstay sag. This was a parameter in his computer design software. My AP jibs are designed for a wide range of sag options and I use that range to allow the same sail to function across a very wide range of windspeeds.

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