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News Test Lab: How Hard Can You Pull?

Discussion in 'Tech Tips and Gear' started by ratagonia, Oct 29, 2013.

  1. ratagonia

    ratagonia

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    Location:
    Mount Carmel, Utah
    Test Report: How Hard Can You Pull?

    Walking down a canyon, you come to a drop. There is a piece of webbing coming out of the sand. You’re tired, hungry, can smell the beer waiting for you in the truck. You don’t really feel like digging out that deadman and seeing what the webbing is tied to or looks like. So you give a really strong tug on the webbing… good enough. You rap off into the twilight and are soon drinking fine malt beverages.

    Is pulling hard on the webbing a valid test?

    The question can be broken into two parts:
    - How hard can you pull?
    - Is that hard enough to be an effective test?

    This Test Report is about “How hard can you pull?” which is measurable.

    The second question is harder to answer. It is a philosophical question, and we wish to provide data that informs a canyoneer’s musings on the subject.

    Objectives
    The objective was to measure how much force an average-ish canyoneer could apply to a piece of webbing attached to a secure anchorage.

    Prediction
    Hank and Tom both predicted we would be able to pull with 1.5 to 2.0 times body weight.

    Test Procedure
    We tied a piece of webbing to the base of a totally solid post in my carport. A force gauge with peak capture was installed close to the post, then more webbing attached to the other side of the force gauge. Webbing was assorted 1” tubular webbing recycled from Zion canyons. For the two-person pull, we set up a 2:1 using a pulley and some rope, so we would not exceed the 440 lb maximum force of the force gauge.

    Testers were Hank Moon (160 lbs, male) and Tom Jones (175 lbs, male). Tom pulled on the webbing using his hands with Atlas Thermofit gloves, while Hank pulled on the webbing by clipping it into his harness. The footing was concrete slab.

    Upward Pull Test: in this test, we pulled close to straight up, though it was more like 30-40 degrees off-vertical. (We actually used the post in the carport, rather than the fencepost shown in the pictures.)

    pulltest01.

    Along Pull Test: in this test we pulled horizontally. We pulled from 10 feet away from the anchor (between 9.5 feet and 10.5 feet).

    pulltest02.

    Style of Pulling: Hank and Tom had different styles of pulling on the anchor – each had two different ways of pulling:

    Hank Static: pull as hard as you can without bouncing.
    Hank Bounce: pull, then let off to maybe 50 lbs, and then give it a good tug with a bounce.
    Tom Static-bounce: pull hard, then give an extra effort to pull as hard as you can.
    Tom Bouncy-bounce: pull, then let off to slack, and give it a fast hard yank as hard as you can.

    For the two-person test, we clipped a biner to the webbing, and each had our own piece of webbing to pull on, standing side by side. We called 1-2-3-pull and did similar to the Static-bounce described above, both at the same time.
    pulltest03.

    For each data point, the maximum of 4 or 5 tugs was recorded. Each of us produced 3, 4 or 5 data points for each test.

    Test Results
    Upward Pull Tests
    Hank – Static:218, 440, 440, 430
    Hank – Bounce: 212, 107, 144
    Tom-Static-Bounce:218, 218, 208, 195

    Along Pull Tests
    Hank – Static:149, 154, 149, 150
    Hank – Bounce: 177, 248, 193, 256
    Tom – Static-bounce:138, 170, 168, 196, 200
    Tom Bouncy-bounce: 140, 83, 142, 137, 188

    Two-person Static-bounce Along Test: 413, 485, 508

    Conclusions

    Hank:1.Bouncy testing generally preferable for horizontal loading
    2.A two-person test is generally preferable (total mass at least 2 x mass of heaviest person)
    3.Focus and technique is required to generate the highest load, the best test.

    Tom:
    1-3. What Hank Said.
    4. Pull tests produce inconsistent results, even when carefully administered. I like the 2-person test as it gives more consistent, and more severe test loads.

    Placing the Results in Context

    This kind of pull test is no substitute for acting smartly: backing the anchor up for all but the last person, rappelling softly, having the lightest person rap last, etc. -- all the things that constitute "best practice." Of course, part of "best practice" is to dig the thing up and rebuild from scratch, every time, despite being cold, hungry and ready to finish the day.
    Nick Smith, hank moon, Ram and 3 others like this.
  2. Kuenn

    Kuenn

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    So, Hank managed a 440 static upward pull? He's obviously not had back surgery...yet! :)

    This is good stuff - very nice report/data.
    hank moon likes this.
  3. Mountaineer

    Mountaineer Is that an X slot?

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    Excellent report. Very helpful! So about ~~body weight for the "along" pull. Higher with the bounce. Interesting.

    In the real world, sometimes it is hard to pull on the dead man without teetering over the lip/edge. Yikes. So in practice, you pull hard (the best you can), backup with meat, then send the first people down while observing.

    I wonder what the gauge would read back at the anchor point, with the rope going over a 90 degree friction, and one or two people bouncing below.
  4. peakbaggers

    peakbaggers "Beaten paths are for beaten men."

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    To help bring this test to a useful conclusion, how about comparing this data with typical forces generated on a few standard rappel scenarios? I know there are many variables, but some comparison might help us determine the sufficiency or insufficiency of our "testing." Is there perhaps a thread that has already covered rappel forces? Seems like I've seen that before.
  5. cirrus2000

    cirrus2000

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    Good, interesting stuff, Tom!
    I agree! I would love to see one of these taken along into a canyon, and try a few real world rappels. Having been a meat anchor a number of times, I am sure the rappeler's weight is substantially reduced most of the time - but by how much?
  6. ratagonia

    ratagonia

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    Have and will, however, the geometry of rappels varies so much...

    Was thinking of it as a training tool for teaching soft rappelling, too.

    Tom
    hank moon likes this.
  7. Ram

    Ram

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    I love the teamwork part of canyoneering, but do love to compete in one area. The soft rap. The decision of the meat anchor is final! ;) Go lightly into the night. Biggest key? "Create a bend" in the rope. Weight the rope more fully ONLY after you are out of sight of your meat and the rope has turned a corner/lip.

    Thanks Tom and Hank for the tests.

    Oh and make sure the back up is your sling and/or rope attached to the rap rope and not the deadman sling. Seems obvious? Have come upon the later a few times. RED ALERT on deadman anchors. I have set one, been the next one back a few months later with virtual certainty that no one was there in between. Sign of (muted and gone footprints) minor water flow over the somewhat coarse sand. We dug up the deadman and the webbing was cut through in two places. Water moving over the top of the sand, moves it. Sand below moves too, against the rock. Add the coarser sand and the abrasion level out of your sight CAN be significant. I love my sandtrap, i love my sandtrap!
  8. SARguru

    SARguru

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    Location:
    Edmonton Alberta
    This is great backyard testing. Related testing was done by Kirk Mauthner in the 90's when he still owned Rigging for Rescue, and looked at gripping strength. The idea was to see how much rescuers could hold in the context of belaying, back when people believed a mjnter hitch was appropriate for a 2 person rescue load. The results where quite surprising whereas some were not able to hold very much. Where this relates to Tom and Hanks is that some people may need to use Hanks harness method as their gripping ability wont permit them to get anywhere near actually testing the anchor. Its been years since i read the report which i thought i had puchased but dont see it on my book shelf.

    Nic
    hank moon likes this.
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