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  1. #1
    Senior Member traftonm's Avatar
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    Do prussic knots not work well?

    Tested my cuben fiber tarp last night. They were calling for rain so I set it up in the yard. We had a storm that had 50 mph winds. I did not get wet but the tarp seemed like it was going to blow away. Tuned out the Prussic Knots slipped on both ends. I changed back to the Whoopee set up I had. Its a little heaver 1/2 oz but I know I won't slip. Is thes just a falt of the PRUSSIC knot?
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  2. #2
    REV's Avatar
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    from what i know, one of the benefits of prussiks are the fact they will slip before the tarp tears. but, if youre wanting to you can tighten them, by adding more wraps of the knot, effectively giving it more grip.
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  3. #3
    olddog's Avatar
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    I was playing with a SLS of 1/8" amsteel and 1/8" prussiks. It was new material and the knots slipped easily until they had worked up and down the amsteel a few times. As the Rev states I also added another wrap to increase the friction. Seems I read somewhere that prussiks worked better with smaller diameter line on larger line.
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  4. #4
    Senior Member NewtonGT's Avatar
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    only time ive had problems with slipping was with grip clips. my prussik knots never slipped. but like rev said you can add more loops.
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  5. #5
    Senior Member zukiguy's Avatar
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    I tried prussic knots first on my zing-it ridgeline and couldn't seem to get them to hold much at all. I switched to a klemheist knot with about 5 wraps using some smaller diameter line I had laying around and they hold like a clamp. Maybe give that a try.

  6. #6
    BrianWillan's Avatar
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    Quote Originally Posted by zukiguy View Post
    I tried prussic knots first on my zing-it ridgeline and couldn't seem to get them to hold much at all. I switched to a klemheist knot with about 5 wraps using some smaller diameter line I had laying around and they hold like a clamp. Maybe give that a try.
    The reason your klemheist knot held was more due to it being a smaller diameter line first and foremost, the number of wraps second and finally the knot itself. Making the prussic with the same smaller diameter line even with 3 wraps will hold properly.

    The reason people use the same diameter line for both the guy line and the prussic for tarp purpose is that the prussic will slip beyond a given forces. If I recall correctly Opie tested this with 1.75 mm Lash-It and found a prussic slipped at 30 pounds of force. This is beneficial for tarps in that the guyline will slip before the tarp fabric rips. With all of these small light, high tech lines that are used, we have to realize that their break strength is quite high as well (450 pounds for 1.75mm Lash-It), so it is good to have a designed in weak point in the system to save the fabric of these increasingly lightweight and expensive tarps that are now in use.

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  7. #7
    gargoyle's Avatar
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    50mph winds...lucky you still got a tarp.
    An extra wrap does alot.
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  8. #8
    DaleW's Avatar
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    Prusik (not prussic, it was named after Dr. Karl Prusik) knots need to be smaller line than the main rope they slide on. I've found the coated lines like Dynaglide and Zing It to be a little cranky with some knots and Amsteel is slippery stuff too. I've had better luck with Prusik/line combos if I give the knot a good tug to set it. It works better when the coating has been used a little.

    I could see where using a Prusik on a tarp would loosen up as the wind load changed. I like the idea of rubber snubbers with cloth that doesn't stretch. They do that with boat moorings to keep from ripping hardware out.

  9. #9
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    i use 2mm cord on 3mm accessory cord (with 3 loops) and it holds rock solid. have not tested in high winds but I do make my tarp very taught along the ridgeline with them

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