Standing Rig tension

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NYSail

NYSail

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Jan 6, 2006
3,178
Beneteau 423 Mt. Sinai, NY
Hello all, I am tuning the standing rig on my 1986 P36-2. On my last boat, I would tune the rig without a tension guage and never had a problem. With my new boat I want to be a bit more scientific about tuning. With the initial static tuning, what tension should we put on the rig in terms of a percent of breaking strength. I have a furling jib, upper, intermediates and lower shrouds. I have a Loos Pt-3 guage that indicates the absolute breaking strength of the wire. Last year I tuned the rig as I always did and she sailed well, however I want to be able to set the rig to an exact symetrical point statically and then make adjustments when out. Where do I go from here. Thanks all Greg
 
RichH

RichH

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Feb 14, 2005
4,773
Tayana 37 cutter; I20/M20 SCOWS Worton Creek, MD
12% is normal initial tension

.... dont just apply 12% and go to the next shroud but 'work up' to 12% in increments of say 5% then a final few % on each shroud. ARe you setting any 'prebend' in the mast? 3/4" mast bow per spreader set? .... this to avoid mast pumping? If so set rig to 12%, then adjust/tighten forward lower shrouds to set a visible mast forward bow while relaxing the aft lowers, then apply a 'few more' % to the backstay. If you truely have 'intermediates' then set them and the forestay (staysail stay) after all the others (and during the mast bowing) Then obviously go sailing at a heel and see if those tensions keep the mast straight and in column when at a normal maximum heel. Dont forget to lubricate your rigging screws with lanolin, etc, (Lanocote) to prevent 'galling' and seizing. :)
 
M

MoonSailer

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Jun 7, 2007
875
Pearson- 323- Mobile,Al
Just Enough??

I have my rigged tuned just tight enough to eliminate leeward shrouds sagging under normal use. I have a Loos gauge and it enables me to be sure the tension is even. Fiberglass isn't a particularly ridgid material and it is probably possible to bend many boats by applying too much tension. Once I adjusted my shrouds unter sail. We had strong winds and 6' waves and the leeward shroud was going slack when we hit a wave. I tightend things up until this stopped. Back at the dock I noted the tension and adjusted everyone. Remember longer wires need more tension than shorter shrouds. ie uppers versus lowers. If the upper is the same tension as the lower the upper mast can move and cause metal fatique
 
RichH

RichH

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Feb 14, 2005
4,773
Tayana 37 cutter; I20/M20 SCOWS Worton Creek, MD
Yup .... ultimate tensile strength.

12% of the ultimate tensile strength of the wire. Interestingly its not the 'looseness' of the wire that causes fatigue; but, rather repeating load cycles, especially when stainless is loaded above 30% of its Ultimate strength. Usually when cyclically loaded stainess is quite stable versus fatigue when loaded to much less than 30% of its ultimate strength ... of course there are other shape/design factors that can contribute to fatigue but the general rule of thumb is not to load more than 30%. When loaded above 30% stainless for engineering purposes is rated typically for only a million or so 'load cycles' before fatigue failure is complete. Why I bring this up is that racers typically tension their backstays to 30% or more (which loads the other shrouds in reaction) during races .... so if you do tension this high be sure to 'keep a good eye' on your rigging and inspect regularly for the tell-tale signs of fatigue.
 
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MoonSailer

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Jun 7, 2007
875
Pearson- 323- Mobile,Al
Fastique of the metal in the mast

I was referring to the aluminum mast fatiquing and breaking at the spreaders. I've seen several mast that broke just above the spreaders.
 
RichH

RichH

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Feb 14, 2005
4,773
Tayana 37 cutter; I20/M20 SCOWS Worton Creek, MD
Fracture above the spreaders ....

Probably due to improper shroud tension that allowed the top of the mast to flex while the lower shrouds are too tight .... PLUS improperly designed spreader attachments where the fatigue crack propogates from the spreader attachment holes (called a 'stress riser'). Add normal mast compression loads and you have fatigue thats amplified/enhanced by 'buckling' failure. Such failure is a good reason to drop the mast every few years, remove ALL the fittings and assay (with dye penetrant solution, etc.) for cracks eminating/radiating from all the screw holes, etc.
 
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Smitty

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Sep 16, 2005
108
Cal 28-2 Milford, CT
Brion Toss has an excellent video

called "Tuning your Rig". In it he explains the theory and the practical sides of rig tuning and walks you through several real life tuning jobs. I have it, and I learned a lot from it. It's very worthwhile. It's available from his web site (and maybe other places as well). -Smitty
 
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