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Tech Tip: Question Pulley for long raps?

Discussion in 'Tech Tips and Gear' started by NateFlet, Sep 25, 2018.

  1. NateFlet

    NateFlet

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    How would one rig a pulley onto an anchor for easier rope retrieval on long raps? I suspect just switching out the quick-link for the pulley, adding a biner block, and using a quick-link to close the pulley would work. Are there possibly any concerns with rapping off a straight pulley?
  2. ratagonia

    ratagonia

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    Assuming you are using a pulley designed for life-safety applications, there is no problem. I have done this a few times on the last rap in Heaps, using a Petzl Oscillante. Since then I have recognized it as unnecessary. For LONG rappels (>300') might maybe be a good idea, but generally the problem with a pulling a long rappel is rarely the friction at that point - more often friction elsewhere in the system, or crossings of the rope (which can usually be managed, if one makes the effort to manage such things).

    https://www.petzl.com/US/en/Sport/Pulleys/OSCILLANTE

    Tom
    Last edited: Sep 25, 2018
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  3. Brian in SLC

    Brian in SLC Brian in SLC

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    There used to be a pulley at the top of the Sentinel Buttress at Moore's Wall in North Carolina. Was for a long-ish double rope rappel and made pulling a full sized climbing rope down a snap. Custom stainless rig and looked really expensive. Dimly recall there was a back up frame in case the pulley axle failed as well...but I'll have to look for a photo of it.

    Anyhow, was kinda slick. Not sure its still there. I think folks rappel twice now.
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  4. gajslk

    gajslk

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    If you're using one of those little plastic pulleys that you put on a carabiner, a biner block would be a bad idea unless your blocking biner is huge. As in big enough to not go through the pulley biner in any possible way. Even after crushing the pulley. A double rope rappel would be a much better idea in that situation.
  5. NateFlet

    NateFlet

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    I would be using a rated aluminum pulley. Of course I would be sure the biner block would not be able to slip through the pulley. Using a plastic pulley on large drops would be a death wish


    Sent from my iPhone using Tapatalk
  6. Kuenn

    Kuenn

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    Have used a pulley on >300 raps, not really for DRT pull downs as for SRT pull-and-bag. (Biner off the chinstrap gets exhausting on a 600 footer.) It does offer a friction-less advantage that is worth it on the long ones, IMO.

    I'm not a fan of the nylon sheave, I use a Petzl Fixe for these applications. Although this little guy looks interesting too....if you got a sack of money.

    Petzl P75SL Rollclip Z Screw-Lock Pulley
    upload_2018-9-26_16-42-6.
  7. NateFlet

    NateFlet

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    Interesting, I figured I should stay away from carabiner pulleys as they have a much smaller wheel, making for a sharper angle, thus a harder pull? Not sure if a micro pulley sized wheel would make much of a difference though.
  8. Kuenn

    Kuenn

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    My knowledge here:

    A rope bends up to 180 degrees around a pulley sheave (any angle greater than that, you need to go back to pulley school). With all things being relative, if the sheave diameter is 1" or 6" the mechanical advantage is the same, i.e. force required does not change based on sheave size. The "friction factor" at the pulley is the results of the bending and unbending of the rope around the pulley axle. Hence, friction has more to do with rope stiffness than the radius size of the sheave (within reason, more on this below). Also, anything less than 180 angle reduces friction.

    Practical example: A soft braid 11mm rope pulls much easier than static 11mm rope... and I've pulled a lot of 11mm static rope through a pulley! (Progress capture makes a huge difference in pull effort, but that's a different discussion.)

    As Tom stated, "generally the problem with pulling a long rappel is rarely the friction at that point". Having pulled and bagged literally miles of rope through a pulley I have found Tom's statement to be absolutely true. Have used 1 - 2.5 inch sheave pulleys and have not noticed a difference with those diameters. (And frankly, any sheave larger than that makes me wonder if you're also packing a dutch oven in your gear stash.) Rock, bushes, mud, water, rope path, are the friction biggies.
    Last edited: Sep 27, 2018
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  9. NateFlet

    NateFlet

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    Ahh I feel quite stupid. I meant to speak of the diameter of the pulley wheel, not the angle, as that remains constant :facepalm:. But even so, the diameter of the wheel would not make a difference now that I've learned.

    With what I've heard, is it worth leaving a pulley at the top of a rap? It sounds like good rope management seems to be the only way to make a rope retrieval easier?
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  10. Kuenn

    Kuenn

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    No need to feel that way. It is a good question for continuous process improvement for those off-standard long rappels. The diameter of the pulley wheel (sheave) will change the friction factor, even for stiff rope, it's just that I've not noticed a difference with the pulleys I pack along. If I inferred otherwise it was a bad explanation on my part.
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