Reality Check
 

In the midst of planning replacement standing rigging, I’ve learned why it’s important to size turnbuckles at about 4/3 the breaking strength of the wire.
My heavy 33’ cruiser’s original cutter rig is somewhat over-sized.
Best I can learn, without doing a test (on the hard) the RM is somewhere from 20,000 lbs.(Selden’s online calculator) to the high 20’s (Apprentice, pg 136.) So to assume 25,000 lbs, and using the calculations in the Apprentice, I’d need breaking strengths of 7908 for the uppers and 5711 each for the 4 lowers. Well within the limits for 5/16” wire, but I’ll stay with it anyway.
Turnbuckles that are proportionately stronger than 5/16" wire would have 5/8” screws. But since the wires are so robust, I’m thinking I can do with 1/2” screws, like the original Navtecs have.
I emailed Hayn to ask about breaking strength of their 1/2” T/Bs. Their answer, twice, was only that it “exceeds” the #11,125 breaking strength of 5/16” wire (I though it was around #10,600, but that aside for now). I’d go with a brand with better info available, except for the high praise for Hayn from Brion T.
So: First, is it reasonable to use T/B’s of less than 4/3 the strength of wire that’s oversized to begin with?
And second, am I unreasonable to expect a more specific answer from Hayn’s sales engineer in Connecticut?
And another one--are T/Bs with T-toggles better/worse than those with eye-toggles? (I'll use swageless fittings.)
Thanks again for looking at this. I’m new at this stuff.

pre-tension
 

when you have a fat wire, it takes more force to put the correct amount of pre-tension on it. If you take an 8th-inch piece of wire, you can pull it pretty tight between your hands. Take a piece of half-inch wire, and you can't pull it hard enough by yourself to get the catenary out. So regardless of strain on your rig when sailing, getting a proper tune with undersized turnbuckles will already make them work harder. I expect those Hayn's can probably take it, but I'd be inclined to stick to the size specified for the wire in use.

If you're replacing all your shrouds, this might be a good time to consider going synthetic. It's easier than you'd think, and Colligo (no relation to me) is a one-stop-shop for all the kit you'll need.
Ben
zartmancruising.com

I would second a serious look at synthetics. Saving a huge % of the weight of the rigging while increasing the strength is always a good thing.

Thanks for the replies. I'd much rather have gone with synthetics, but for the cost. Per Colligo's online catalog, the 11mm uncovered dynex dux, stretch equivalent to 5/16" wire, is $9.35, almost 2x the cost of Loos 1x19 wire. Covered dux, which I'd definitely want, is substantially more than that. Hardware costs are roughly equivalent. So it would end up costing me about twice as much.
Too bad, too, as the weight advantage is significant.
JV

I have haven't used Dux in a while. Take a look at Alpha Ripes HSR.

Whoa
 

Hi again,
Way back before things wandered off into cost comparisons, we were looking at load vs wire sizes. To get a 25,000ft.lb. RM at 30 degrees, you would have a 25ft or so waterline.Is that the case? To get about 8,000lb required strength for the uppers, assuming a safety factor of 2.7 or so, the half-beam to the chainplates would have to be over 5ft. Is this so? If it is, staying with wire that size is not in the interest of the boat, nor of your wallet. If you arrived at different numbers, perhaps you could describe how.
Many wire size numbers these days are for the rated strength of 316, hence the discrepancy you saw. 5/16" is still way too big.
I don't know why Hayn wouldn't give you a break number for their 1/2" turnbuckles. Navtec shows 14,700 for theirs, which I am sure is conservative. Also sure that Hayn's are at least as strong.
As for configuration, shouldn't be any useful difference in strength. But Hayn's bends are noticeably fairer than others'
Fair leads,
Brion Toss

Brion,
Thanks for weighing in, and addressing the original question. You're right about the numbers.
The DWL is 27.5' and 1/2 beam is 5.335.
I interpolated a RM of 25000, probably high but it's a heavy (#13500, 33') boat.
The formula on pg 136 gives me (pardon the detail):
(25000x1.5) / 5.335 = 7029.
That x 2.5 SF x .45 for the uppers = 7907
That x 2.5 x .325 for the lowers = 5711
I had been reluctant to second-guess the designers, given my own limited knowledge, so I arbitrarily stuck with 5/16" wire and 1/2" T/Bs. And I want to be confident offshore with it; I sail out of Penobscot Bay, Me.
Loos' website table says I could go to 1/4" uppers (302/4) or 9/32 uppers (316), smaller for the lowers. That seems tiny, though I can't support that intuition with facts. It's obviously a huge advantage in cost and weight. It might even make covered Dux affordable.
Do you think I'm being too arbitrary in my original plan? Or too conservative in over-estimating my RM to begin with? I'd sure like to feel OK about looking at cheaper, lighter options.
PS: The chainplates are thru the side decks, so somewhat closer to the mast than 1/2 beam.
John

Aha
 

Hi again,
The measurement you need is to the chainplates, not the side of the boat; the chainplates set the length of the lever arm that produces rig loading. Run things again, measuring, for convenience, to the upper shroud chainplates, which are typically athwart the mast. You'll get higher numbers. The question is, how high? I am going to bet that 9/32" uppers and jibstay will be right, with maybe 1/4" lowers and backstay.
Fair leads,
Brion Toss

Thanks. I'm going to go up and measure to the chainplates in the next day or so and re-calculate. Occurs to me, though, that I'll still have to go with TBs that have 1/2" pins, since I replaced the chainplates already. Unless there's a way to bush them.