Round brass thimble strength?

[benz]

Are the round brass thimbles sold by sailmaker's suppliers sufficiently strong to use in the eye of an HM running backstay? I know they're meant for rope and all, but HM rope is different than poly, and I wonder whether the pressure put on the sides by a tensioned HM line would be enough to crush the thimble or deform it. Anyone done tests?
Ben

[benz]

Really? nobody knows?

[Brion Toss]

Hi all,
I really thought the answer was obvious: no. Round thimbles are rarely seen outside of reinforced, load-sharing places, like sail clews. They are easy to tie to (think: sheets), and easy to fabricate around. But they are also easier to deform, as their constant radius leads to compression of the side walls in mid-ring. Compare this with a teardrop thimble, narrower for a given radius at the load, and the shape is kinder to the line attached, as the legs are pushed apart so. You'll find rings in heavy-duty situations, where there shape has some advantage, but they must have stoutness to compensate for geometry.
I use round thimbles for lifelines and lazyjacks, primarily. Might not hold up too well under heavy runner loads. Ring Hitch, anyone?
Fair leads,
Brion Toss

[benz]

Thanks. The obvious is not always clear to me; that's why I like this forum.
Ben

[Brion Toss]

Thanks for the kind words, but in reviewing my previous entry, I note the effects of writing it late at night, at the end of a long day. There was a time when round thimbles were the only type available, even for heavy loads; the ones in sails are a surviving example, in a special context, as are other surviving round thimble or ring applications. And of course no thimble -- and no block-and-tackle -- is the best way to do runners, I think. Just one block on deck, with a good lead to take a continuous, single-part HM runner to the empty weather primary winch. Much more power, instant overhaul and take-up, no blocks banging you in the head, neat cheaper. And no thimbles of any shape needed.
Fair leads,
Brion Toss

[benz]

I am considering runners such as you describe, but have to work out a few issues of proper lead. And I'd have to buy another winch handle--something I've not missed since it went by the board a year ago or so. Do you fear possibly over-tightening the runner with a winch?
Ben

[Brion Toss]

Hi again,
Think about what the runners are meant to do: oppose the pull of the forestay, just as the backstay opposes the pull of the jibstay. If the working load of the forestay is something like 15 to 20% of break in a breeze, some of that load gets taken up by the mast's own stiffness, but most of it is left to the runners. It is possible to flatten the luff of the forestays'l too much, but it ain't easy, and it [/i]is[/i] easy to check the effect by eye. That leaves the most likely failure point to be the deck block and its padeye, so be sure of your scantlings.
Now compare your 40:1 or so winch power with the 4:1 of a typical runner setup. Basically, you can only hope to snub against the pull of the forestay, and that only if you take up in time; you cannot hope actually to flatten that luff. Plus of course, as mentioned before, those blocks are a literal and figurative headache.
Fair leads,
Brion Toss