Thread: Prusik loops

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    Default Prusik loops

    Just curious, do most people leave their prusik loops tied or re tie them each use?

    Thanks

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    Prussik loops, after they are tied, should be tightened with a 9:1 MA to tighten and set the knot so that it does not have any movement in the loop when you use it. It is close to impossible to untie one after it has been tensioned like this. All of which to say is: we leave ours pre-tied.

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    Thanks for the info!

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    We keep our 8mm prusiks tied after they have been made..I really dont think u need to to tighten it with a 9:1. Once you establish a rope program it should contain a Rope Log and Inspection program. This should be done by a rope tech as he/she is most fimilar with rope cordage and webbing. And once you you use it for a rope brake or other use it will tighten. But yes u can do a 9:1 as well but Ive never heard of doing that..

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    The reason for pre-tensioning the prussik loop is because some cord that has a slippery finish can result in some scary slippage when shock loaded. The last thing you want to see is the tail from your double fisherman dissappear. That can pucker up the old sphincter. It is also worth while to test your cord on the brand of rope you will be using. Prussiks work very well but are very much dependant on the proper compatability between the cord and the host rope. Any time you switch brands, it is advisable to test the compatabilty again.
    Sometimes, in order to make an operation idiot proof, you must remove the idiot!

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    You might try Sterling's bound loop prusiks. They have some pros: quick, easy, and strong. Cons: $$.

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    keep them tied.
    9:1 MA...what? How much weight on the end of the 9:1?
    Just tie it real tight and dress it well. If you place the weight of one person onto that should be good enough. Also check your equipment before and after using making sure that the tied knots are still tied.
    Last edited by MEDIC0372; 07-31-2006 at 05:28 PM.

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    MA= Mechanical Advantage

    One person pulling on a 9:1 system. Hook prussik around a static object and pull the prussik with a carabiner on the end of a 9:1 MA.

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    Quote Originally Posted by MEDIC0372
    Just tie it real tight and dress it well.
    Not so. To be truly functional, the tails of the double overhand bend (colloqially known as double fisherman's) should be short as possible so that they don't interfere with function. For this to be safe, when prusiks (especially for tandem prusik belay) can come under considerable shock loads, it IS necessary to pretension the knots while holding the tails with a pliers to prevent them from slipping into the knot (which you will see them do as you add tension).

    And, when tying pre-assembled rigging that's meant to be used over and over in the same form, it is best to keep the knots tied. The internal tensions within the knot, which are what weakens rope when tied, will relax over time and find a new equalibrium in the tied configuration. Untying a tight knot will then introduce new tensions in the fibers until they can relax again.

    - Robert
    aVERT - a Vertical Emergency Response Training
    To Avert Disaster in the Vertical Environment

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    Riversong...if you are going to quote me please complete the quote. I did say, If you place the weight of one person onto the loop that should be good enough. Also check your equipment before and after using making sure that the tied knots are still tied.

    Your statement that the tails of the double overhand bend (colloqially known as double fisherman's) should be "short as possible" so that they don't interfere with function is WRONG. The tails should in fact be about 1 inch long. And, in my 25 plus years I have never needed to use pliers to hold the tails in place.

    Just tie it real tight with one inch tails and dress it well place the weight of one person onto the loop to pretension the knot and that should be good enough. Also, as stated, check your equipment before and after each use to make sure that the tied knot is still tied the way you want it.

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    Quote Originally Posted by MEDIC0372
    If you place the weight of one person onto the loop that should be good enough.
    If the prusik is used for a tandem prusik belay, which could capture a suddenly dropped rescue load of 600 lbs with shock loading multiplying that by several times, then pre-tensioning the knot with one body weight is certainly insufficient.

    The tails should in fact be about 1 inch long. And, in my 25 plus years I have never needed to use pliers to hold the tails in place.
    1" or less will do. But the reason you've never needed to hold the tails with pliers is that you've never pre-tensioned your double overhand bends sufficiently to guarantee that they won't suck their tails under an extreme shock load - always plan for worst case scenario.

    Check out what happens when you pre-tension with a 9:1 MA pulled by one person with two hands (up to 900 lbs tension). What you'll see is that the tails get drawn back into the knots, rendering them insecure. And this is the same thing that will happen if a prusik is required to suddenly catch a rescue load.

    If you don't pre-tension for maximum expected loading, then your prusiks are NOT safe.

    - Robert
    aVERT - a Vertical Emergency Response Training
    To Avert Disaster in the Vertical Environment

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    I have dropped tested them at 600 lbs . I have seen them slip, melt but never did I see the tails and/or the knot itself slip.

    I am NOT telling you that you cant do what you want to do but DO NOT STATE that my way "is certainly insufficient"...thats just not nice.

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    Quote Originally Posted by MEDIC0372
    DO NOT STATE that my way "is certainly insufficient"...thats just not nice.
    "Not nice"? Stating that you're method of pre-tensioning with one body weight is insufficient for a loop knot meant to hold a rescue load in shock loading is simply common sense.

    Quote Originally Posted by MEDIC0372
    Your statement that the tails of the double overhand bend should be "short as possible" so that they don't interfere with function is WRONG.
    However, stating that minimizing the tails to optimize the function of a prusik is WRONG (your emphasis) is "nice"?

    This isn't about "nice". This is about what works, what's safe, and what's sensible.

    - Robert
    aVERT - a Vertical Emergency Response Training
    To Avert Disaster in the Vertical Environment

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