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North_by_Northwest

The "Body As Anchor" Belay Poll

The "Body As Anchor" Belay Poll  

120 members have voted

  1. 1. The "Body As Anchor" Belay Poll

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kinda like the theory of climbing low angle slabs, you keep as much weight over your feet as possible, as opposed to leaning on your hands. fruit.gif

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Weight of Climber, ie tension in rope: 170 lbs, or 756 Newtons

Height of Belayers waiste while standing 3 feet, or 0.9144 meters

Height of belayers waiste while sitting: 10 inches, or 0.254 meters

Distance of belayer from edge: 5 feet, or 1.524 meters

 

Here we go laugh.gif:

 

SITTING

theta=arctan(0.254/1.524)=9.46 degrees

Force towards cliff

756cos(9.46)=745.72 Newtons, or 167.64 lbs

Force to feet

756sin(9.46)=124.25 Newtons, or 27.93 lbs

 

STANDING

theta=arctan(0.9144 /1.524)=30.96 degrees

Force towards cliff

756cos(30.96)=648.29 Newtons, or 145.74 lbs

Force to feet

756sin(30.96)=388.91 Newtons, or 87.43 lbs

 

So when standing there is 3.13 times more force applied straight down to your feet, which is good because you can't travel through rock and you get 3.13 times better traction. There is also 1.15 times less force pulling you straight towards the edge.

Interesting data Bill, but it seems a variable that is missing is the coefficient of static friction. Butt (and perhaps legs) and feet versus just feet?

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Interesting data Bill, but it seems a variable that is missing is the coefficient of static friction. Butt (and perhaps legs) and feet versus just feet?

 

 

The coeficients of static friction doesn't matter. When you compare the two in a ratio, that variable cancels out anyways, because the coeficient of friction is the same for both cases. Sitting down, most of the weight goes to your feet anyways. If you legs are on the ground, your feet arn't. Your butt is on the ground moon.gif, but most of the force is still on your feet, but yeah, the butt moon.gif does add a little friction, depends on surface area moon.gif, weight and material. For some of you maybe, the surface area may help out quite a bit. wink.gif

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The most important term in the equation, BALANCE, is missing. The reason the sitting belay is more stable is balance. Three points are in contact: your two feet and your butt. When the there is no load most of your weight is on your butt. When the rope goes tight the load transfers to the feet, which hopefully you have positioned on against a couple of solid rocks, so you'll never have to explore the coefficient of static friction between your soles and the the rock. We are WAY over analyzing this, aren't we?

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If you are standing and belaying from the hip, and the pull is a bit outward as opposed to downward, (as is likely on easier terain) you are going to topple over, especially if you didn't anticipate the direction of pull well. This situation will be the same if the terrain is generally steep but you are on a ledge a short ways back from the edge, again some outward pull. If you prefer to stand on the edge of the cliff with no anchor, so that you can have a nice clean downward pull, ..I don't know why a person would. If the terrain is quite easy and you have difficulty keeping up with their rate of travel with your belay, and they ever fell, you'd get pulled right off your standing stance.

Take care with losing the rope, sliding off the hips, with the standing hip action. If you are sitting with your feet braced widely against even small edges, you are in business, even if you didn't anticipate the direction of pull well. One can also use a hand to brace with. The rope won't slide off your hips. One can also belay dynamically when seated quite well to prevent getting pulled off a stance. I don't really believe in a good dynamic belay with an unanchored standing hip belay. Maybe the shoulder belay if the terrain is steep. Just some thoughts from my experiences, having done a fair bit impromptu belays, hip, shoulder, rock, snow.

 

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