SS vs Synthetic rigging

Discussion in 'Multihulls' started by fhrussell, Apr 3, 2016.

  1. waynemarlow
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    waynemarlow Senior Member

  2. BobBill
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    BobBill Senior Member

    Excellent. Thanks.
     
  3. Tom.151
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    Tom.151 Senior Member

    Good info and leads me to a related question I haven't heard addressed anywhere yet, maybe you can help here...

    As you pointed out (thank you), the creep rate is based on both load and time -- so maybe we should figure out approx what that means for a non-RTW boat, with it's fully loaded 24/7 schedule.

    Is the expected creep for a particular sailor's usage substantially different or not???

    First maybe adjust creep for the time NOT sailing. It would seem that for most recreational sailing (those of us not sailing 24/7) that the issue of creep might actually be significantly reduced or even be negligible for boats sailed with the rig fully loaded for 10 hours a week (as an example), which would be approx 5 percent of the time (per month). ((I wish I got to sail even half of that :) ).
    So if the OP's sailing routine was for example 10 hrs loaded up sailing per week then his creep would be reduced by 95% (per month). So in this case creep would diminish to 5% of 0.1% = .005% per month. In other words it would take 20 months to get the same physical amount of creep as expected (the one tenth of 1%) as was expected.

    That reduction alone might make the whole question of creep moot.

    The second question in my mind is What can we (and the OP) anticipate would be the actual loading in the shrouds during that time the boat is NOT sailing and how much less than the loaded up figure?
    This of course will vary wildly, depending on the rig design and it's intended use. For boats like my rotating wing-masted trimaran, the stays are nearly slack (when not sailing) by the very nature of the rig -- so I'd discount the creep during non-sailing time altogether. For highly tuned racing boats it's completely the other end of the spectrum and AFAIK many full on race rigs are set up so that the rig is loaded enough to pre-stretch the rig so as the sailing loads don't UN-tune the rig. But really that's for those who know about that stuff.

    Cheers,
     
  4. Stumble
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    Stumble Senior Member

    Tom,

    Creep numbers are generally given for X load (as a % of MBL) applied 100% of the time. Like a mooring line under permanent load (deep water commercial anchorages), or the pretension for standing rigging. Then induced loads from actually sailing are pretty much ignored, at least on a typical boat, if you are doing a nonstop round the world race you need to take them into account.

    Typically standing rigging comes out to have about double the strength of the wire it replaces in order to keep creep low enough (.1"/year) to be manageable. Smaller line gains a reduction in windage and weight, but can dramatically increase creep, so you need to be very careful about this.

    As an upside my pretension actually went down on the dyneema shrouds compared to 1x19 wire. There was actually less constructional stretch in the rope than the wire. Which was a nice unexpected positive.


    The reason that creep while sailing is generally ignored is that people just don't sail that much. Creep numbers assume the load is applied 8,760 hours/year. Unless you are sailing a reasonable percentage of those hours it just gets lost as a rounding error.
     
  5. fhrussell
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    fhrussell Boatbuilder

    Great information! Thank you Tom, BobBill, Wayne, and Stumble.
    Tom, given that Twiggy has slightly greater specs (displacement, sail area, etc..) than my boat, is the 1/4" all you are using all around? I was thinking more along the lines of 7mm-9mm for sidestays and headstay.

    Even if I don't come to using your remaining Amsteel, you are always welcome to go for a sail once I am done with the latest refurb. It's slow going, but hope to be complete before summer 2017 if not by September 2016.
     
  6. Stumble
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    Stumble Senior Member

    I would really recommend contacting John Franta at Colligio Marine to have him design your rigging. Even if you don't choose to buy the components from him, I think he will do the design itself for a reasonable charge.
     
  7. Tom.151
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    Tom.151 Senior Member

    Frank,
    For the Twiggy (trimaran) I was using a 9200# rated 1/4' "Amsteel Blue Plus" made by Samson (sold by Defender)

    I did not use any Amsteel for the headstay as it had a roller furler for the headsails and, at the time, I was unsure of the best way to control/prevent/minimize wear from the R/F (because, for that particular furler, the wear would be hidden from sight). Nowadays, I'd just use a double braid cover over the SK75 for wear protection and be done with it ;)

    Didn't work out the loading for the headstay, so have no comment on sizing the headstay. If I were doing it now I'd just use the as-designed headstay wire size to ascertain the target breaking strength and work backwards from that to choose the proper size synthetic.

    For sizing the shrouds I used the loaded displacement and the BOA to get the max righting moment at capsize (RM = Displ x 0.5xBOA) and from that the load in the shroud ( Load = RM / BOA) which came out to 1750# which is less than the target of 20% of the rated breaking strength of the 1/4" 9200#.

    Cheers,
     
  8. Packeteer
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    Packeteer Junior Member

    fwiw, I use Amsteel 3/16 for hanging my hammock. it's awesome gear, but yes a lot of stretch the first time
     
  9. fhrussell
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    fhrussell Boatbuilder

    I spoke with John Franta today and had a nice conversation about east coast multihulls, west coast multihulls, Madness and Jzerro proas, Jim Brown, and John's report of seeing Buddy Ebsen's PolyCon recently in Catalina in pristine condition.
    I'm gathering some info to send to him so he can design the appropriate rig. His knowledge of old CSK's was helpful in that he is familiar with the old school, monohull-thought rigging of these older multis and my desire to simplify. He owns an older tri that raced the TransPac in the early '70's. The kind of conversation I know any one of you would appreciate! :)
     
  10. bruceb
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    bruceb Senior Member

    practical experience

    I have a 33'tri that I was rebuilding and I have converted to mostly synthetic rigging, recently launched. First, I own a roll swedge machine and I have wire on hand so cost was not part of my decision process.
    From bare mast, near as I can determine, a "Colligo" system would be about 1/3 more than wire if you had to buy all the components the first time and replacing just the wire or line somewhat less for the synthetic, assuming reusable wire ends. I don't think you can justify synthetic on just cost.
    However, I am really happy with my choice of a synthetic system as it seems to do everything else better. As measured on my rig, I saved 60 Lbs aloft between replacing wire stays and using dyneema halyards, and they are all stronger than what they replaced. That is a LOT of weight on a 40' mast.
    I have re-tightened the rig several times in the first month, now it seems very stable with no more noticeable set/creep. Mine was all pro spliced and pre stretched by a Colligo certified rigger. I do most of my own halyards and smaller splices. I think the Colligo rigging parts give me peace of mind but they are pricey, on a smaller boat other solutions would probably work quite well. I have "X" stays under my tramps I made with 1/2" amsteel and big stainless eyes and they seem to be working well also.
    If you trailer, synthetic is so much easier to deal with I can't imagine using anything else.
    B
     

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  11. OzFred
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    OzFred Senior Member

    Seeing those numbers makes me happy to be using the metric system. Much easier to see the comparative sizes as:

    6.4mm … 6.0mm … 11.1mm

    Back on topic now…:p
     
  12. bruceb
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    bruceb Senior Member

    Metric?

    The metric system sounds like a foreign conspiracy;)
    2,4,6,8 we ain't goina metricate- and you wont either as long as the USA sets the size of plywood for the world:D
    B
    (Metric IS a lot easier to use, and my stays are 9mm lowers and 11mm uppers using heat set and pre-stretched dynex :) )
     
  13. waikikin
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    waikikin Senior Member

    I thought your measurements were based on the British imperial system excepting for short change on a gallon...
    That could well be a foreign conspiracy given the history..
    Jeff.
     
  14. rogerf
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    rogerf Junior Member

    1 person likes this.

  15. bruceb
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    bruceb Senior Member

    knots

    Great link Roger, I had seen some of those but that is very complete. Much of my boat is "tied" together and I am still learning some of the latest/best dyneema knots.
    B
     
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