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

[Matthew Sebring]

As a partial response (based only on my limited understanding on the subject - and this is removed from the obvious such as weight and windage). In order to get the slack and stretch out of a wire you need to tension it to a specific point which usually ends up being a percentage of it's ultimate strength. To get that same performance out of a larger wire you need to tension it somewhere in the same percentage range. However, since the breaking strength of that wire is so much larger the corresponding tension you need is much higher delivering much greater loads to the boat and rig.
Take an overly simplified and extreme example: Let's say we've got a columbia 22 with some 3/16th wires. We've decided we're going to take this boat around the world and simply don't believe the 3/16 wires are strength enough so we beef it all up with 1/2" Now you can easily visualize that tension needed simply to take the slack out of the shouds and the sag out of the stays would be enough to damn near punch that tiny deck supported mast right through the cabin top.

[cmm]

Thank you for the input - I didn't know that 1x19 wire had to be pre-streched (like pre-stretched nylon rope) before or during initial use.

However, one can imagine that a Valiant 40 could handle the tightening of its lowers, whether they are 5/16" or 3/8" in diameter. So are there any other structural issues that may come into play?

Regards
Martin

[Brion Toss]

Weight, windage, and cost are far from trivial issues; any one of them might make for a compelling reason to go with smaller wire size. And the loads needed to tune oversize wire, as pointed out above, are not trivial either. But I don't get the feeling that we are talking about the same thing when we say "structural difference." If I understand you correctly, you think that objections to 3/8" lowers are minor compared to some imagined benefit(s). It is at times like these that I become aware of how evangelistic I can be on this subject. Really, I know I take it all too seriously. But what we are talking about here is a series of relationships in an astonishing, elegant machine. Nothing in a well-designed rig is arbitrary. It isn't a matter of having the wire break before something else, it is a matter of everything being in harmony. And there is no benefit in having it out of harmony. Yes, bigger wire is stronger, but what does that get you, if the loads don't require it, except more frequent reefing (more weight, more windage), more compression on the mast, more tension on the hull, an unsatisfactory tune, and thus worse performance, and more expense? Once you have met the loads, with whatever the appropriate safety factor is included, going bigger is not better.
I recommend going heavier where it is needed. If you want to hoist large heavy objects over people's heads, a safety factor of at least 10 to 1 makes sense, but safety is heavy, and a sailing vessel can only afford so much before the weight results in danger.
Think of this question as a window into your rig. Look at the whole thing, and discover the elegance that is available to you there.
Fair leads,
Brion Toss

[cmm]

I wish there were more evangelistic operators in the yachting industry - I'd love my engine installer to become evangelistic about using stainless fasteners in my bilge.
Thanks, I fully take your point, Brion, and re-reading your earlier post "the lowers should be sharing less than half the total load", I interpret that to mean a pair of fore and aft lowers working together share less than 50% of the total load on one side of the boat, and so each lower carries less than 25% of the load (and therefore need not be as strong as the 3/8" upper shroud).

Although it hasn't been said in the thread, I presume Matt's Valiant has Upper and Intermediate shrouds, and that the "total load" referred to by Brion is the sum of the Upper, Intermediate and Lower loads.

Martin