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Herreshoff/Vaitses Meadowlark
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Discussion Starter · #1 ·
I have a 37' Herreshoff Meadowlark that needs new standing rigging, and I'm looking for advice on what to do, and for feedback on decisions made. I'm going to have a number of questions, and rather than tossing them all into a single post, I thought I'd ask them one at a time.

My boat is a ketch, with fairly short (28'6" main) masts in tabernacles. I can raise and lower them single-handed and likely will at least once per season.

Question 0, of course, is whether to replace with steel or synthetic. I've decided on synthetic for a number of reasons.

Question 1, then, is which synthetic?

I'm leaning towards Colligo Dux because they seem to have the most experience with synthetic rigging, and their explanations of why they've stayed with the older formula Dyneema seem solid.

I may or may not use Colligo's hardware, it's quite pricey, but that's an issue for future questions.

Right now, the question is what size to use.

If this was a production boat I could look up what size to use, but it's not. The best I can figure is to size based on the existing steel rigging.

The existing shrouds, forestays, and triatic stay are 3/16", the running backstays are 1/8".

I see no reason to retain the complexity of having two different sizes. 3/16" is 4.8mm. Colligo recommends sizing based on equivalent stretch, rather than strength, and lists Dux size 6 as equivalent to 5mm. But if you go into their online shop, they sell Dux in 5mm and 7mm.

So I'm thinking on using 7mm Dux, which should be far stronger and less stretchy than the steel wire I'm replacing.

Thoughts?

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Herreshoff/Vaitses Meadowlark
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Discussion Starter · #3 ·
Sometimes rigging is made in different sizes on purpose, so that IT breaks before something else does. Using an exaggerated example, in a pitchpole situation it might be better to lose the mast by having the backstays break than to have the backstays be so strong that they rip out the chainplates and carry away the stern quarters of the boat.
If that were a design consideration, I'd rather have a designed break-away point in the termination fittings than to have the line break at some arbitrary point.

My guess is that the backstays are 1/8" rather than 3/16" solely because the backstays have to be stowed away, and the thinner wire is easier to handle. Even 7mm Dyneema is easier to handle than wire, so I don't see the need.

The previous owner told me he never bothered to set the backstays. And for the lake sailing he did, he probably didn't need them.
 

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Herreshoff/Vaitses Meadowlark
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Discussion Starter · #6 ·
Rigging is engineered for the loads that they need to deal with and the amount of stretch that they are expected to be able to tolerate and pass onto the other components of the rig.
So I should try to match the stretch of the existing rig, and not make it significantly stiffer.

Colligo's charts give 6mm SK75 as equivalent stretch, but they don't sell 6mm, only 5mm or 7mm.

Other vendors don't sell SK75 at all, they've replaced it with SK78. But I can find 6mm SK78.

SK78 is supposed to have reduced creep, but does it have the same stretch?
 

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Herreshoff/Vaitses Meadowlark
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Discussion Starter · #8 ·
Franta says 30' is the max for lashings, not sure why. He doesn't say.
I have to figure it's a matter of how much force you need to apply to to get the proper tension, and I have to think that's more a matter of how long is the shroud then how long is the boat.

Curlew is 37' overall, but she's a ketch with fairly short masts.
 

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Discussion Starter · #11 ·
If the assumption is that the original rigging was sized properly, then you would want reverse engineer to use a Dyneema line with similar stretch characteristics to the stainless steel that it replaced.
Do you know where I can find stretch data for 1×19 SS, SK75, and SK78?
 

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Herreshoff/Vaitses Meadowlark
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Discussion Starter · #12 ·
So, according to this: Stainless Steel Wire Rope Technical Information

Elastic stretch can be calculated by the following formula:

Elastic Stretch = (W x L) / (E x A)

W = Applied Load ( kN )
L = Cable length ( mm )
E = Strand Modulus ( kN/mm²)
A = Area of Cable = (D2 x pi) / 4 (where D= Dia of cable mm)
Typical values for E are:

1x19 = 107.5 kN/mm²
7x7 = 57.3 kN/mm²
7x19 = 47.5 kN/mm²
Dyform = 133.7 kN/mm²
So, next to find the Strand Modulus for SK75 and SK78.
 
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