Tension measurement for synthetic fibre rigging

Discussion in 'Sailboats' started by patrik111, Nov 23, 2009.

  1. patrik111
    Joined: Sep 2003
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    patrik111 Junior Member

    All,

    What is the general approach to achieving a controlled tension if synthetic fibre rigging is used?

    I would like something that would allow loading of the stays to get some forestay tension, but not too much.

    Kind regards
    Patrik
     
  2. Kay9
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    Kay9 1600T Master

  3. patrik111
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    patrik111 Junior Member

    Kay 9,

    Thanks, This was one of the documents being very helpful up till exactly the tension point. it is left as a cliffhanger in close to the end of the page.

    Furhter ideas?
     
  4. Kay9
    Joined: Oct 2006
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    Kay9 1600T Master

    Sorry. Ill have to admit its one area I know next to nothing about. I was hopeing that one site would be your answer.

    Have you tried calling Sampson to see what they say?

    http://www.samsonrope.com/

    K9
     
  5. patrik111
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    patrik111 Junior Member

    Might just need to resort to that, but I think I will see if I can make a crude measuring device, or at least draft for some peer review.

    //Patrik
     
  6. Kay9
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    Kay9 1600T Master

    I had at one time a device that kind of clamped on wire rigging. It was sold by Sampson as well. Now I dont know how or why it worked, but as you tensioned the stay a mechanical meter went up in pounds. Im betting that have something like this for synthetic as well.

    K9
     
  7. Paul B

    Paul B Previous Member

    If your synthetic rigging is PBO you can use the Harken Rigtune Pro to measure the static rig tension on each stay.

    Of course it is a Harken item, so the cost is about $350.00 US.
     
  8. patrik111
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    patrik111 Junior Member

    Mainsheet load

    As I will have a end boom sheeting with curved traveller track at similar distance to the mastbase as the forestay, I belive that a very significant contributor to the forestay tension is how hard I sheet the main, I would like some input on what I could expect that a normal man would pull on a rope. Would you expect around 30kg? More? Less?

    Input needed for jib design. Ordered yesterday.
     
  9. RHough
    Joined: Nov 2005
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    Location: BC Summers / Nayarit Winters

    RHough Retro Dude

    Harken has a formula for calculating mainsheet loads.

    About 50 lbs / 24kg is a reasonable load at the human end.

    Loading Formula
     
  10. Paul B

    Paul B Previous Member

    I think it depends on how much of their core muscles the trimmer is able to use.

    The action of pulling on the mainsheet is similar to a seated one armed cable row from the lower pulley, in most instances. Sometimes it is more similar to a curl action.

    If you are steering and doing the mainsheet yourself 50 pounds might be at the athletic end of sailors abilities.

    I know my mainsheet tail load is far less than that.
     
  11. RHough
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    RHough Retro Dude

    True enough! Big difference between driving and trimming compared to just trimming.

    My mainsheet system has to keep trimming loads below the load it takes to move the traveler. Not upsetting the windward sheeting traveler is a higher priority than actual mainsheet load. So a 4:1 <> 16:1 Gross/Fine system is needed ... even though the sheet loading does not require that much purchase.
     
  12. jfranta
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    jfranta Junior Member

    Hi Patrick, If you are using Dynex Dux we will soon have calibrations for a Loos gauge for various sizes. Stayed tuned to our website for this. I talked with the Harken guys in la Rochelle and they told me they are working on a digital gauge for synthetic line (greater than 5 mm) but don't know when it will be out. You can however use any gauge for relative loading side to side but no absolute numbers can be had.

    John Franta, Colligo Marine.
     
  13. patrik111
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    patrik111 Junior Member

  14. RHough
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    RHough Retro Dude

    So you've been selling rigging for how long?

    And you have NO way to measure the tension?

    Any rigger knows that all you need is a sharpie and a measuring tape.

    For each 5% of breaking load every rigger knows that 1x19 SS wire stretches 1mm over 2000mm, Dyform is .95mm over 2000mm and rod is .7mm over 2000mm.

    A two meter stick and a set of calipers is all you need to set the tension.

    Harken and Loos sell tension gauges at nose bleed prices to people that can't use a simple stick and calipers.

    If you had any engineering data for the rope you sell as rigging, you could publish the simple numbers so your DIY riggers could save the price of a tension gauge. What an amateur! Instead of having elongation for % MBL ... you have NOTHING?

    You are selling rigging that if the tension is wrong by 5% it goes into unrecoverable creep and you have NO way to measure the tension?

    Seems to me that ABSOLUTE numbers are MORE important for your Dynex Dux than for any creep free rigging like SS wire or rod or PBO and you expect people to what? Guess?

    Good job.


    NOT
     

  15. Gashmore
    Joined: Feb 2008
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    Gashmore Junior Member

    "For each 5% of breaking load every rigger knows that 1x19 SS wire stretches 1mm over 2000mm."

    Well, not exactly. From the Navtec specs 1x19 it would range from .93mm in 3/32" to .69mm in 3/4". While it can get you within 8 or 9% up to 1/4" but could be as much as a 20% high in larger diameters.
     
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