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A Sand Trap Is A Marginal Anchor

Discussion in 'Tech Tips and Gear' started by Canyonero, Apr 27, 2017.

  1. Canyonero

    Canyonero

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    When ghosting canyons, it is critical to remember two things:

    # 1 A sand trap is not just an anchor, it is a process. You must follow the process to ensure safety.

    # 2 Even if you follow the process, your margin of safety may not be very wide.

    We had an example of these key principles this week entering Upper Neon Canyon. Cliffed out, limited sand, a less than ideal placement. Alternatives involved a great deal of backtracking, leaving sling, or a fiddlestick placement that would probably get a rope stuck. Here's what it looked like:

    IMG_4657.JPG IMG_4656.JPG
    Let me describe what you're looking at here. 60 foot drop, first 30 kind of roll down, then 10 vertical, then last 20 feet overhanging. Rope going down is the rap line. Rope going up is to the meat back-up in a decent but not awesome stance.

    The process involved sending the first guy down with an ultra-soft set rappel. No problem, sandtrap held. Throw a little extra sand in just for kicks. Next guy goes down. No problem. Throw a little more sand in. Third guy takes 2 packs, probably 250 lbs total (last rappeller is 185.) No problem. Throw a little more sand in. Finally, I rappel. Again, no problem with the soft set/full friction rappel. 10 feet off the deck, I decide...let's see what this thing can really hold. I slide quickly down 5 feet, then lock it off hard. Down comes the sand trap as I step down onto the ground.

    How much more force do you generate by doing that? Another 100 lbs? 200 more lbs? I don't know, but that was the margin of error on that anchor. With good technique, it would certainly hold 250 lbs, but I don't think it would have held 500.

    Now that I'm Monday morning quarterbacking it, the right thing to do would have been to send the first guy down and farm sand BACK UP to the sand trap in potshots and really fill that sucker up. And probably do it tostada style instead since there wasn't much of a lip there anyway (the little bush doesn't count much.)

    At any rate, my point is that the process matters and even when the trap passes the testers, you still might not have much margin. And make sure that when the placement is really marginal that the lightest, smoothest rappeller goes last, without a pack, just for a little extra margin.

    And yes, we ghosted the canyon. It turns out the drop at the Golden Cathedral is a really great sandtrap placement (much, much better than this one.)
    Deagol, Yellow Dart, danf and 4 others like this.
  2. hank moon

    hank moon lovely ligatures

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    Hey, GREAT thread title and thanks for sharing this experience. I'm not super experienced with Sand Traps, so have a few questions/comments:

    - What is a "soft set rappel" ? Haven't heard that term before.

    - Did your rappel process involve sequencing (heaviest to lightest)?

    The force generated on the anchor depends on a variety of factors such as rope stretch, edge friction, your weight, rate of speed, etc. Suffice to say that the tension created in the rope above you was greater than 2X your bodyweight, probably a lot more. I'm sure @ratagonia or @Brian in SLC could make a quick guesstimate. Hard to say how much of that force was transmitted to the anchor, but obviously a lot more than your bodyweight (the rope/rock friction in that setup looks to be significant).

    What rope were you using? Looks like Canyonero!

    I generally start by overfilling, then maybe removing sand depending on anchor behavior with the initial (heaviest) rappellers. BTW the backup rope in the photos appears to be under tension. Not sure of context of the photos, but the backup rope should not be under tension during testing.

    With a SandTrap, shouldn't the lightest, smoothest rappeler generally go last, regardless of security of placement?
    Last edited: Apr 27, 2017
  3. Canyonero

    Canyonero

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    Soft set would be the opposite of when you lean back really hard and jump over the edge.

    Everyone was about the same size unfortunately.

    I'd be curious to hear their take on that amount of force.

    It was Canyonero rope.

    Back-up rope might have looked tight in the picture, but it definitely was not under tension during testing.

    Sure, lightest last is always a good idea. But that's true when you're rappelling off a four foot oak too. With an average or better placement, it's not terribly relevant. When it's going to hold 1000+ lbs, it doesn't matter all that much who goes last. And proper technique definitely matters more than weight.
    hank moon likes this.
  4. Bootboy

    Bootboy Atwood Gear

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    We use the term "soft set" when using marginal anchors. Set means to weight the anchor. To softly set usually means going over the edge smoothly on your hip to avoid fully weighting the rope before you go over the lip and once weighted, to rappel smoothly making an effort to maximize friction on the rock and minimize force on the rope, to avoid any shock load to the anchor.

    To add sand to an anchor that didn't move really doesn't accomplish much. If it held for the first, and usually heaviest person, all you're doing is incrementally making the pull harder.
    hank moon likes this.
  5. ratagonia

    ratagonia

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    I think we have used the term Soft Rappelling or Soft Start. Some measurements of forces in rappelling (though not really a study) indicate it is pretty easy to generate 2X body weight, but hard to generate 3X or more.

    Nice thing about the SandTrap is that it has a big sweet spot. The Sweet Spot being the difference between the least sand that can hold the rappel and the most sand that still allows retrieval. This particular spot looks like it has zero retrieval issues; therefore, no compelling reason not to put a ton of sand in and/or on it. We engineer-types like being precise; but the SandTrap is a good device to be over-the-top with. LOAD IT UP. (Well, not so much that TWO people can't pull it.)

    Has anyone here stuck a SandTrap because it had too much sand in it? I know the closest I have come is when it took three of us full body weight to retrieve one, ONCE.

    Tom
  6. Canyonero

    Canyonero

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    No, it usually sticks because it catches on something, not due to too much sand. In this case though, there wasn't much sand and I wasn't smart enough to farm it uphill.
    ratagonia likes this.
  7. Steve Woodford

    Steve Woodford

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    In this situation, I see a lot of sand still all around and, as you say, you could have meat anchored someone down to fill potshots up to you. A Sandtrap Sandwich (double tostada) works great in flat(or almost flat) situations, especially with very long raps. We always carry 2 Sandtraps when ghosting canyons.
  8. Rapterman

    Rapterman

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    Hi Steve
    Can you show what a Sandtrap Sandwich would look like?????
    :)
  9. Steve Woodford

    Steve Woodford

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    The You tube vid that I posted....
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  10. Kuenn

    Kuenn

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    @Steve Woodford thanks for the video explanation, very nice! Still not sure I have the (politely termed) "wherewithal" to do that @ 300'. Not that it can't be safe, you proved that. This anchoring method not being an exact science and having a host of variables, i.e. it requires as much innate aptitude as it does mental prowess... and its close companion the water-trap, IMO.

    Like bridge building, its not that we can't build one safe. It's how light can we build it and still make it safe.
    andrew vaughan and ratagonia like this.
  11. Steve Woodford

    Steve Woodford

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    Glad you recognize the limitations inherent in these retrievable anchors. That attitude is what contributes to safer canyoneering or any sport activity for that matter. The advantage of the Sandwich is the ease of retrieval compared to that much sand on a single Sandtrap, which is actually impossible to pull down without major effort by a few people...
  12. Deagol

    Deagol too many hobbies

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    another point: it would be good to not undercut the healthy patch of crypto by stealing sand from it's base. Better to get unconsolidated sand from elsewhere if possible.

    I like the sandtrap, but don't have a ton of rappels on it under my belt. I defiantly send the pack down first and do the minimum-force rappelling techniques described here.... and get down as quick as possible.
    Steve Woodford likes this.
  13. Steve Woodford

    Steve Woodford

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    Yes, Crypto-biotic soil is a pet peeve of mine! I have seen too many canyoneers walk over it instead of taking the longer route or walking from rock to rock. Whenever I took clients out, the first thing I explain to them is the story and importance of Crypto to the environment and that even one footstep can destroy a 100 years of development. Good point. And I see more sand just over the lip too....In some canyons, it is always smart to leave someone up top so the lead can ascertain if there is enough sand further down canyon at next rap. This leaves the option of farming more sand down....
    ratagonia and Deagol like this.
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