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andy_lemon
Nov 7, 2001, 7:08 PM
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Dr. Pete: Most of my climbing is done via top ropes. There are a few climbs, not many, that consist of nothing more than a couple of bolts and hangers at the top of the cliff. I would normally put a couple of draws on the bolts and run the rope through them. Well, I have come across a couple of climbs were the draws were not long enough to allow free movement of my rope. My rope would jam when weight was put on it. So, I run a 4ft sling through the two hangers and it will allow plenty of room for my rope to move freely, attaching a couple of beeners to the ends of the sling. This forms what is called the "American Triangle" so I've read. I have recently read in a Mountaineers book "From Gym to Crag" that the American Triangle is an unsafe method to use as a rappell anchor because it puts tremendous stress on the bolts/anchors, which I thought, gee, if it is unsafe to rappell off of then it must not be safe to top rope off of.
So in a case like I've described, what do I do? Use two individual slings? Is it safe enough to keep top roping off of?
Thanks
Andy
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rrrADAM
Nov 7, 2001, 7:14 PM
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It just weights the anchors in a direction other than straight down.
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benjo
Nov 7, 2001, 8:04 PM
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That is not true, it does a lot more than change the direction of the force. The greater the angle your slings form from the belay bolts, the more force is put on each individual anchor. It's just laws of physics which I don't understand, but have read a lot about. Here's an example.
x x x x
\ / \_ _/
\/ \ /
R R
Well, I tried. The anchor on the left puts less force on the bolts because the angle the slings make is more acute. The more obtuse the angle the slings make, the more it stresses the anchors.
If you have two bolts that are far apart and want to toprope from them, or rap off them, instead of using draws, use individual longer slings, one on each bolt. Make sure they are equalized.
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rrrADAM
Nov 7, 2001, 9:36 PM
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OK, benifit of my job here at a Nuke plant, I just talked with a Rigging Engineer, he's the expert on these kinds of forces.
It's actually better to have a large angle versus a short, or acute, angle. As the angle lessons the forces grow exponentially. Preferable for this is always two seperate slings of length to permit equal loading.
I have seen several of these and when I have webbing with me, I cut all off and replace with the prefered method explained above. At .12 cents a foot, it's cheap.
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wigglestick
Nov 7, 2001, 10:50 PM
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I don't mean to butt in on Petes turf here but I think I actually know the answer so please excuse me:
I think that the american triangle that is being referred to as unsafe is different what you people are talking about. You are talking about the angle that made between the two quickdraws. An american triangle is when say you have a biner on each of the 2 bolt hangers. And one solid loop of webbing running through each of those biners freely. Let me see if I can draw this
B--------B
.\......../
..\....../
...\..../
....\../
.....P
Where B is a biner on a bolt or other anchor
---- & / & are a single piece of webbing
..... is empty space
P is the point where you run your rope through
Now most of us would make something like this
B..........B
.\......../
..\....../
...\..../
....\../
.....P
Now there are different ways to do this and some are better than others but I won't get into this here.
No for all you engineers here who want to do some structural analysis of the top scenario you can see that each of the strands coming up from P is holding half of the load. (with me so far?) No in situation B this is ok because that means that half the load is held by each bolt. But in situation A since the webbing is running free through each biner at the bolts we know that the load on each side of the biner must be equal (oh I wish I had my statics textbook with me now) so the load on each bolt is approaching 2 times what it is in situation B (I think it is more like 1.75 times). To demonstrate this take 2 pushpins and put them in a horizontal line on a corkboard. Now take a rubber band and loop it around the two pushpins. No grab only the botton strand of the rubberband and pull down. The pushpins will probably pull out. Now do this same thing grabbing both strands of the rubber band. The pushpins don't come out as easy do they? I have no idea if this makes sense to anybody. Go read and engineering statics textbook.
I found a better illsutration of what not to do:
http://www.climbing.com/Pages/rockcraft/Ropework/rw_image_pages/RW-rapp-triang.html
Never again will I try to create a diagram in my post.
[ This Message was edited by: wigglestick on 2001-11-07 15:25 ]
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rrrADAM
Nov 8, 2001, 1:04 AM
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We all were refering to an 'American Triangle' or 'Triangle of Death', whatever anybody wants to call it, we know what it is.
Good diagram though.
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passthepitonspete
Nov 8, 2001, 4:39 AM
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The Dr. Piton Citation for Technical Expertise is hereby awarded with deep gratitude to the ever-so-bitchin' Wigglestick who usurped Dr. Piton's forum by correctly, accurately and (might I add) beautifully explaining the dangers of rigging your anchors using the
AmericanTriangle, thus sparing Dr. Piton the effort.
Dr. Piton liked the diagrams and link, but particularly loved the analogy with the rubber band and the pins. It was exceptionally creative, and allowed us to
visualize a somewhat abstract problem using a concrete, or at least rubber, example.
Dr. Piton would add to add a couple technical points of clarification.
To maximize the strength of the anchors, they must be equalized. They will not be equalized by simply clipping on two quick draws that come together at
one point on the bottom, although this will admittedly be better than theAmericanTriangle
There are two ways to equalize two anchors. One is with a cordalette, and although this is better than two quick draws, it will still not approach the perfect equalization that a "twisted long sling" will create.
Continuing with Wigglestick's analogy, go back to the two pushpins stuck in the cork.
(damn, I just love
that.....)...
Replace Wigglestick's regular length rubber band with a double length one, and do NOT construct an American Triangle!. Replace the pins with bolts with carabiners attached, and replace the rubber band with a double-length sewn sling. Grab the middle part of the sling as W-stick describes, and pull both sides down together into a "V". The longer the sling, the farther the "V" goes down, and hence the less the load on the anchors.
Now, here's the key:
Take the middle part of the double-length sling and put a twist into it to create an 8 - it is through this you will clip one locking carabiner and [preferably]
pulley OR two or more non-locking standard carabiners with the gates opposed.
There are only TWO ways to do this - the right way, and the wrong way. The wrong way will not create the 8, and will leave
you with a rig that will fail if EITHER of the two anchors fails!!.............
YIKES!!!
You have to rig it the right way, and then everything will just be
swell...... Make sure you get right.
It's right when you have used the sling to perfectly equalize the two anchors by clipping the carabiner into the right part of the "8".
It is essential to ensure that the angle created on top of the "V" is NEVER GREATER THAN 120 DEGREES because if it is, it will increase the loading on both anchors to more than if all the load were attached to only ONE anchor!!!!
This is fundamental.
You need to "get this".
That angle must always be less than 120 degrees. Just make sure you have a long enough sling. If you need to extend it, do not girth hitch any slings together. You have to maintain "slipperiness" so that there is as little friction as possible in the system to create "equalization".
"Slipperiness" is not to be confused with "Sassiness".
Instead, take two quick draws and clip one to each bolt. Use the carabiners on the ends of the quick draws to clip the double-length sling into and create
the "8", get it?
And yes, for anyone feeling even more anal than me, you can use girth hitches to lengthen the quick draws off of each bolt - just make sure there's a
carabiner on the end of the extension. Duh.
And that, my friends, is the better way.
[Aside: Why is the American Triangle so pejoratively regarded, while the European Death Knot seems to enjoy some sort of avant
garde status, despite its very frightening experience?.......
Answer: Because the European Death Knot is safe, and the American Triangle is not.]
*Edited for clarity -fiend*
[ This Message was edited by: fiend on 2001-11-17 10:10 ]
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rrrADAM
Nov 8, 2001, 4:47 AM
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I guess you failed to read the 4rth post down, eh Pete ???
Pete says...""
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rrrADAM
Nov 8, 2001, 8:40 AM
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And what you are describing is called a 'Sliding X'. This will perfectly equalize the anchors and allow for latteral movement while still equalizing. However, if one placement should fail the other will be shock loaded, this is not good, especially for traditional placements.
Better to use two long slings, individually, that are the correct length to equally support the load.
Better stick with the aid stuff, it seems as though you are not up to snuff in the other areas.
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wigglestick
Nov 8, 2001, 4:17 PM
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Thanks for the Compliments Doctor. But I will leave the diagram drawing to you from now on.
I would have to agree with rrradam about the sliding x though. It is good and all when you have 2 bombproof anchor such as 2 big old honking new bolts. But if your anchor was a little more suspect like 2 nuts (you would never want to rely on only 2 nuts) then the sliding x is not that good of an idea. If you had three anchors you could use a cordalette but when you have 2 anchors I would use a slightly longer sling than you would use for the sliding x and then tie an overhand knot in the middle which would eliminate the extensions in the anchor so that if one of the two anchors failed the other would not be shockloaded. But this is nitpicking. I would never build an anchor out of less that three pieces. But I have used this on an anchor of 2 old bolts and i had nothing else to back them up with.
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passthepitonspete
Nov 8, 2001, 7:25 PM
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Well done, lads!
You two guys definitely "get it".
.......... ..........
And you're right, Adam ...... those frickin' little smilie things are enough to drive you round the bend!
Well, at least my diatribe with all the smilies looks a bit better now.
The only real problem is that it's still a bit "wide", but everything else works, so I will reluctantly say, "that's enough."
It is not always easy for the perfectionistic Dr. Piton to say, "that's enough."
In fairness to Adam, I think I started my answer before he made his fourth post.
Yes, you guys are right. Only use the "sliding X" when both points are bomber. You should never rely on only two points unless they are both bomber. And not all bolts are bomber!
When in doubt, build all the redundancy into your system that you possibly can! On big walls I carry huge honkin' cordalettes and regularly build stations from five and six anchor points. If I had six points, I would build two "sliding x's" to reduce my number of points to four, then I would use the cordalette on the four. My cordalette is only long enough to connect four closely-spaced pieces.
If the pieces are more widely spaced, then I will have to throw a long sling onto the most remote piece(s) in order to get my cordalette to get 'em all.
What Wigglestick correctly describes is really a two-point cordalette, isn't it?
Thanks again, dude. Like I said, you get the award. Big time. Drawing those drawings is enough to drive you round the bend!
[ This Message was edited by: passthepitonspete on 2001-11-08 12:15 ]
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