Why should uppers be thinner than lowers?

[mholmes]

We just purchased a valiant 40 (Syzygy #201) and we are redoing the whole gang with wire using norseman fittings. The original manual that came with the boat gives the diameters of the lowers (two lowers each side) as 3/8", and uppers as 5/16".

It seems strange to me that the uppers should be weaker than the lowers. Is there a good explanation for this? Are not the uppers under much greater tension? Is there any reason I should change it?

much thanks for a stellar forum,
Matt

[Brian Duff]

Umm, I think the upper should be as large as the lowers. (Load supposed to be 32.5% on each of the 2 lowers per side, 45% on the upper - in theory, see Brion Toss 'The Riggers Apprentice' or any yacht design book). We re-rig Valiant 40's with a forestay, backtsay, uppers and lowers of 3/8" 1b19 cable and the inner forestay and deck intermediates of 5/16" 1by19 cable. All the pins on the mast and chainplates are usually 5/8", except the inner forestay stuff is sometimes 1/2" , on those boats.

On that boat, or anyboat with bonded chainplates (yuck!) and or internal chainplates, be sure to remove and inspect the chainplates as part of the re-rigging. It doesn't matter if there are no evedince of leaks, check them anyway, why spend $6500 on rigging (just materials cost) if the chainplates might break ?
Be sure someone that knows what they are looking at inspects the chainplates. We just re rigged a V40 and the owner removed chainplates himself (to save $$), took them to a local metalshop to be polished/inspected. Well, we got back the 10 chainplates, of which 3 were OK to use ! All the others had cracks in them (I recall it was a 1979 boat). I know the starboard chainplates for the upper and fwd lower are hard to get out but do it.
Also, the tang bolts, compression tubes and tangs should be checked. These rigs have aluminium compression tubes that have often corroded away or been cut by the wire halyards they came with.

Nice boat really (it seems from working on them) , I hope to get some ocean sailing on one some day...

[Brion Toss]

Hi,

Way back in the last glacial epoch, when I was starting in rigging, I would often come across the oddity you describe. I knew that, with the rig configuration you describe, the lowers should be sharing less than half the total load, but I'd still find uppers smaller than lowers.
With the help of research, hard thinking, and a very seasoned, generous yacht designer (standing on the shoulders of giants), I concluded that what I was seeing was an artifact of pre-masthead-Bermudian rig practice. See, loads were distributed differently in gaffers and many early Bermudian rigs, with the higher loads lower on the mast. So uppers and jibstay, meant for light-air sails, were lighter wires. As rigs developed, even some otherwise very competent designers lagged behind in adjusting scantlings. But then, rig design has always been a weak spot for naval artichokes.
Regarding your fine boat, remember that it was designed by a fairly larval Bob Perry. He has since gone on to approach godhood in all design matters, and one part of that has been to make more sensibly-scantlinged and -configured rigs. Witness, for instance, his abandonment of aft-led intermediates since the days of the Valiant.
You could check with Bob, but I'd be strongly inclined to leave the uppers at 3/8", make the lowers 5/16", and throw away those aft-led intermediates, replacing them with HM runners, led to a winch.
Oh, and remember that there are otherwise-configured rigs where it still makes sense for uppers to be smaller than lowers. Bermudian included. Load distribution is an important item.
Fair leads,
Brion Toss

[mholmes]

Well that answers my main question--I will be going with 3/8 for the uppers as well. thanks.

I think I will take your advice about removing the intermediates and replacing them with amsteel running backstays as well. My only remaining question is how to make the top junction between amsteel and the tang. Is it as simple as an eye splice, with a thimble, and putting the cotter pin in the tang through that eye splice?

thanks!
matt

[Brion Toss]

Hi again
I prefer to put a heavy-duty thimble in, just as I would for wire. The radius of the clevis pin would be a bit minimal, and there would also be the possibility of chafe, unthimbled.
As for the shrouds, how about 5/16" for the lowers?
Fair leads,
Brion Toss

[cmm]

Originally Posted by Brion Toss

Hi again
I prefer to put a heavy-duty thimble in, just as I would for wire. The radius of the clevis pin would be a bit minimal, and there would also be the possibility of chafe, unthimbled.
As for the shrouds, how about 5/16" for the lowers?
Fair leads,
Brion Toss

I apologize for entering this thread from the side, but my eye caught Brion's recommendation to keep the lowers 5/16 instead of 3/8.

In this game it is very easy for novices like me to think, "the thicker the better".

The only counter advice to oversizing my rigging wires I have heard, came from a fellow yacht owner who feels it is better that wire is the weakest link - if it was not, something more threatening to yacht integrity may suffer damage (e.g. chainplate may rip out or a bulkhead may be damaged) in the event of an abnormal stress.

Brion, is your advice to Matt to reduce his lowers form 3/8 to 5/16, at all related to the same consideration - i.e. if the wire is too strong something else may break, or is there a different reason?

Re-framing it as a more general question, heavily oversized rigging wire will resist breakage more; but are there any negative, structural consequences (setting aside things like wire and terminal costs, windage and weight)?

Thanks
Martin