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testing deadman anchors - was- Re: Homepage photo

Discussion in 'Archives - Yahoo Canyons Group' started by Paul Martzen, Aug 26, 2005.

  1. Paul Martzen

    Paul Martzen Guest

    I will not argue against bolts, but Bucky's buried pack anchor seems completely reasonable to me. He could even test it with heavier people rapping first with human body backup anchors. What more can you ask for; other than Stevee's suggestion to haul up alternate deadman anchors from below to save the pack. I suspect that some of you have rapped off of far worse anchors at times. I certainly have. But from a safety stand point, I suspect such an anchor is very secure and safer than bolts.

    Some have speculated that the margin of safety for this anchor is slim as compared to a bolt because bolts are rated for many thousands of pounds while the deadman is not rated and may only hold a few hundred. I believe there are two errors in this thinking. The first is thinking that a deadman is weaker than a bolt or other anchor. When we really test this, I suspect we will find it takes very little burial depth to make a deadman stronger than any bolt.

    The second error is thinking that the deadman needs to be anywhere near as strong as a bolt. It does not. It merely needs to hold body weight or even less. At least if the pull is up, out of a pothole, over a rim and then back down. Where the anchor slings run over the rock seperating the pothole from the rap, there is considerable friction which absorbs a high percentage of the load. Depending on how much friction, the deadman only has to hold some portion of the rappellers weight. Would not surprise me if a pack filled with 50 pounds of sand and just sitting on the surface could support a 150 lb person rappelling.

    There is a final and in my mind nice advantage of a deadman over a bolt which is based on the type of failure they are each prone to. A bolt has to have a huge working strength, because any deterioration is not visible and its failure will be sudden and catostrophic. Also because of the locations we place bolts, there is no way to back them up usually other than with additional bolts. When we place bolts to facilitate a clean pull, as we should, the bolt holds the entire weight of the rappell for the entire distance. It also tends to be above any human back up options, meaning that failure of the bolt will cause a shock load on the backup anchors, (if they are below the bolt).

    The deadman or pack is not going to fail suddenly like a bolt, because it has to be pulled out of the ground, drug up out of the pothole and over the edge. This is going to happen relatively slowly and the movement will be visible and therefor correctable.

    You test such an anchor in practice initially by having people pull on it, but mainly by having the first and heaviest person rappell on the anchor while human backups are ready to give tension only if necessary. If as they send the first heaviest person down, they see that the pack is lifting up off of the ground or lifting the ground if it is buried, they can put their body weight onto the rope to supplement the pack till the first person is down. Then they can add more sand to the pack and rebury it deeper. Then they can test it on the next person to see if the pack will hold the entire weight. The people backups should be just slightly slack so that the deadman takes the entire weight unless it starts slipping.

    Being able to test an anchor in such a clear and simple way is a wonderful thing. --------

    Now that I have lectured, i have finally found the original story, but can't find the picture. Where is it? Sounds like Bucky did everything right to me. He went into the unkown, found an unexpected problem and dealt with it in a creative and effective way.

    Paul M.

  2. beadysee

    beadysee Guest

    --- In Yahoo Canyons Group, Paul Martzen <paul_martzen@y...> wrote: >Would not surprise me if a pack filled with 50 pounds of sand and just sitting on the surface could support a 150 lb person rappelling.

    Might be more surprised if it didn't...

    Ha ha!

    I concur with some of your stuff, and not other. I've seen deadman anchors blow up pretty quickly. And, doesn't matter the speed of disintigration if you're mid rappel...only need to take long enough to dump you.

    Seems like Bucker had a good anchor. Proof is in the puddin'.

    Margin? Who knows.

    Fun stuff.

    -Brian in SLC
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