All things above deck

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Postby Bigears » Tue May 15, 2012 6:04 pm

lets revisit spreader lengths. At the Greensboro MYC Regatta, it seemed that the spreaders on a couple of the top boats are shorter than mine. My spreaders are currently 4.25 inches long measured out from the mast on each side. I believe that particular length came from the old Optimizing Book, but am not sure. No where in the current build instructions, in Scott's excellent build addendum, or in this Forum can I find a definitive spreader length(s). Is there a particular length currently preferred by sailors near the top of the pecking order?
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Re: spreaders

Postby Bigjake » Wed May 16, 2012 11:44 pm

Spreaders' length determine two things:

a. The angle made by the shroud when it "enters" the mast. For clarification, if there are no spreaders, then this angle might be 5 to 10 deg. but the spreaders increase it. The longer the spreader the bigger the angle. You want this angle to be as big as possible.

b. The angle between the shroud and deck. You want it to be as close to 90 deg as possible.

Having said that, you don't want the spreaders to be so long that they will be suscepticle to failure by the compression loads they carry. Bear in mind that the resistance of the spreader to failure (and thus its ability to support certain loads) is determined by a combination of length, diameter and material.

Any length addressing the above constrains should work. Also important is to mount the spreader in and angle so that it will bisect the angle made by the shroud passing over its tip.

Blue ..22
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Re: spreaders

Postby s vernon » Mon May 21, 2012 1:14 pm

The main thing we are told to try to do is to keep the mast straight sideways. 4.25 inch long spreaders do a pretty good job of keeping the mast straight sideways. Then it comes down to uppers and lowers tension versus wind strength. Most of us want to make the spreaders removable so we make them straight and we do not worry about precisely bisecting the angle on the upper stay.

The info in Optimizing is pretty much still valid and wonderful. Too many people get overwhelmed by the amount and quality of info. General advice - Try to take it in small chunks, maybe ignore (for now) anything that looks too scientific, and make marks in the margins. If you take a lot of time to search through the book there are many very good pages.

Optimizing Chapter 11 (Page 173) is outstanding and it talks about sideways mast bend.and everything else that you might want to know about sail shape controls. I cannot find a discussion of spreader length. I guess they figured people will just go with close to the standard length and make them be straight then adjust the backstay and stay tension like it says in chapter 11.

You might want to look at the Model Yachting articie online. More info and more and bigger pictures. http://www.ec12.info/MY/MY168.htm

Thanks for the compliment. I think If I could sail as gud as I write, I would still be in mid-pack or lower. I am planning to do better on the water next year. :-)
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s vernon
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