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Old 02-13-2015
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increasing and consolidating standing rigging size

My boat has a mix of standing rigging, lower shrouds (two on each side) are 3/16" wire. The rest are 7/32". I have Sta-Lok fittings all around.

I am doing more and more ocean sailing and would like to go up a wire size (seems like a good idea and would probably ease my mind a bit when the going gets rough). Up one wire size would mean going to 7/32" on the lowers and 1/4" on everything else.

But I'm wondering if it would be wise (and OK) to go up to 1/4" all around. That would be going up *2 sizes* on the 4 lowers and up one size on the rest. This way all of my standing rigging would be the same diameter wire and it would simplify my spares quite a bit. (both wire and fittings).

However I understand that going up *too* much can overstress the boat fittings. is going up to 1/4" on the lowers too much in this case?
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Old 02-14-2015
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Re: increasing and consolidating standing rigging size

Very few boats were built with undersized standing rigging. When standing rigging fails, it is usually a matter of a failure at a terminal, where it passes over a spreader tip, or where there is a bad lead angle at the chain plate or tang. There are downsides to oversizing the rigging or changing to a single size. Lower shrouds are generally smaller than uppers so that the uppers and lowers stretch proportionately keeping the mast straight, or curved the right way. The added weight signicantly makes the boat feel less stabile because it is less stabile. I would therefore suggest replacing the rigging as the boat was designed and built.
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Old 02-14-2015
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Re: increasing and consolidating standing rigging size

In addition to what Jeff has said, I checked "yacht rigging safety factors" recently and learned that masts are generally designed with a safety factor of 5. To me, that means that they are designed to withstand five times the load they have to carry normally in operation. This is why boats that pitchpole in storms don't automatically lose their masts. (Some do, but the forces on a submerged mast and sail must be incredible. You might also WANT the mast to break before the leverage ripped it out of the mast step and gashed a hole in the hull in such a situation.) As Jeff mentioned, standing rigging is designed to create a balanced whole. Changing the stretch characteristics of the lower shrouds could lead to them pulling out your chainplates. Their causing the mast to bend differently from how it was designed could lead to stress fractures in the mast as well.
Taking your concern about the rig to an absurd degree, consider what would happen if you replaced your mast with a much stronger one made from a steel I-beam. A small 16' beam in my house weighs literally half a ton. Your 50' steel mast would never break, but it would totally screw up everything else about the boat:weighing it down, making it top-heavy, changing your pitching moment, slowing you down... definitely not worth it. While standardizing has its merits, sometimes things need to be customized in order to work properly.
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Old 02-14-2015
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Re: increasing and consolidating standing rigging size

Jeff is spot on with his recommendations.

Increasing the 'strength' of the wire will not increase 'reliability' of the standing rig, unless you also strengthen all the chainplates, the chainplate 'knees', the wire to mast connections, etc. because the rigging should be tensioned to a uniform % of the wire breaking strength - usually to 12-15% tension. This is to precisely control the 'elasticity' of the wire.

If you do choose to increase the wire diameter, you will also have to have the luff of all your jibs, genoas recut to match the new natural 'sag' of the new thicker forestay when sailing. Specifically, if your new forestay (& backstay) is operating at less 'stretch' than the original 'design', you can very easily wind up with a boat that will have significantly less ability to 'point', and will be prone to 'skidding off to leeward' when attempting to point and with much more heeling -- a very 'cranky' boat when 'beating'.

If your intentions are to cross oceans, then perhaps increasing wire size would be prudent, including ALL the other components of the standing rig structure.

Last edited by RichH; 02-14-2015 at 09:37 AM.
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Re: increasing and consolidating standing rigging size

Great information, I had no idea of the ramifications. Thank you all!

I don't see crossing oceans in my future but I do intend to take longer coastal trips and to cross to Bermuda in a few years.

So I will stick with the original wire sizes and be confident that it was properly designed.

One more question: the wire, chainplates and sta lok fittings are about 12 years old. It all looks good no surface rust, no cracks in the fittings or chainplates. no broken strands in any of the wires. Seems wise to replace the wire, but is there any concern reusing the sta lok fittings?
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Re: increasing and consolidating standing rigging size

The issue that breaks 98% of all rigging is crystallization of the microscopic metal grain structure or 'fatigue'. Fatigue is cumulative and additive, starting from 'day one'. If your intention is 'serious' sailing, have no precise history of the rigging, replace it with new.

For the 'average' sailor (actually sailing, and not afraid to let the boat heel over) the typical recommendations for a total rigging change-out every 10-12 years is a good one .... about the equivalent of sailing one complete circumnavigation (about 1 million load 'cycles' where the rig, chainplates, and all the 'connectors', etc. 'possibly' have exceeded 30% of ultimate tensile strength).

FWIW - this would be equivalent to a 'blue water' design built with a structural 'safety factor' = 3 .... with respect to the rigging. Your boat is a 'coastal design' probably with a structural safety factor = 2. So, if this boat (@SF=2) has been sailed an equivalent of 16,000 nMi there's a high possibility that all the rigging is nearing the end of its typical 'service life' - and a higher probability of rigging fatigue failure.

Follow Jeff's advice, change the rigging, etc. to 'new' if youre planning on 'serious' sailing.

;-)

Last edited by RichH; 02-14-2015 at 10:38 AM.
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Old 02-14-2015
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Re: increasing and consolidating standing rigging size

The only thing I would add would be to check that the rigging on your boat is indeed as designed. It is not unusual for a boat owner to re-engineer things in the distant past. You wouldn't want to replace components that were selected because they were on sale in 1989.
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Old 02-14-2015
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Re: increasing and consolidating standing rigging size

What are the typical stretch percentages in 1 x 19 wire?
If one wanted one to increase the strength factor of a given wire size would going to 302/304 be too much of an increase for the factors RichH suggests?
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Old 02-14-2015
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Re: increasing and consolidating standing rigging size

A riggers 'rule of thumb': 1 mm stretch per 2 meter length of wire is equivalent to 5% of the breaking load, irrespective of the diameter of the wire.
Ref.: p29 of: http://www.riggingandsails.com/pdf/selden-tuning.pdf

302/304 is more subject to chlorine/halide corrosion ... increases the 2-phase destruction: 1. accelerated crevice corrosion in the surface micro-cracks formed by 2. fatigue.
..... probably just like what happened to your OEM Tayana propshaft.

Im Ty37 #423 and I back-calculate a SF of 4! for the Ty37 rig ... BUT about 0.2 SF for the OEM Grand Deer toggles, etc. & have had 'surprise' failure w/ the toggle bolts when I first got this boat; and, about SF=2 if the chainplates arent routinely torqued. :-(

IMO - 316 or 316L is the best in 300 series stainless for 'ocean work'.


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Re: increasing and consolidating standing rigging size

Here are a couple of other considerations. What are pin sizes of your clevis pins? My guess is 3/8". 1/4" is usually 7/16" or 1/2". Doubt if your chain plates would take 1/2". My experience with 2 different 28.5 footers that I have owned is that 7/32" for headstay, backstay, and upper shrouds are very sturdy. 3/16" for lower shrouds is also what I had. (Sabre and C&C)

I experienced a 60 knot microburst with the Sabre at night with full sails up. The shrouds and stays did not break but the 1/2" through bolt for lower shroud tang pulled through the mast and took down the rig rather abruptly.
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