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zibircut
Jul 21, 2008, 3:38 PM
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How big a rock would you trust for an anchor on top of a cliff?
Was on top of this cliff. Rock is very compact, with no cracks and very little foliage. But there were a bunch of boulders on top. Some about three feet by three feet by three feet. Seemed pretty solid at that time, and I did girth hitch them, for top roping purpose alone. about two of them.
Would you have trusted your anchors to these boulders?
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sonso45
Jul 21, 2008, 3:41 PM
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Depends on the situation but generally, I would not trust them alone. Although, I have slung boulders when nothing else was available and I was desperate.
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markc
Jul 21, 2008, 4:09 PM
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This is the sort of question that's really hard to answer generally. I've anchored to boulders without a second thought on numerous occasions. I've also passed up a rock that was way too small for my liking, only to find people using it as a single-point anchor. (I lifted one end of that rock by myself earlier in the day.)
Much like using trees, I look for something that is really well-anchored and of a very large size. If you'd need major machinery to move it, I'd certainly use it for a limb. Even with bomb-proof natural anchors, I like using at least two independent limbs. For slightly smaller boulders or trees, you can always equalize a group of them to form one limb.
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carbonrx8
Jul 21, 2008, 4:12 PM
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zibircut wrote: How big a rock would you trust for an anchor on top of a cliff? Was on top of this cliff. Rock is very compact, ... Some about three feet by three feet by three feet. Would you have trusted your anchors to these boulders?
The answer is most certainly "IT DEPENDS", but consider that as sandstone (not as dense as, say granite or other typical rocks) has a typical density of about 150 lbs per cubic foot, your rock likely weighed in at a least a good two tons (4000lbs.)
Now, if said boulder was perched on the edge and wobbled when you sat on it, it might not be a good anchor. But set back from the edge and solid when you hop on it, it was likely bomber.
(This post was edited by carbonrx8 on Jul 21, 2008, 4:15 PM)
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stymingersfink
Jul 21, 2008, 4:14 PM
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zibircut wrote: How big a rock would you trust for an anchor on top of a cliff? Was on top of this cliff. Rock is very compact, with no cracks and very little foliage. But there were a bunch of boulders on top. Some about three feet by three feet by three feet. Seemed pretty solid at that time, and I did girth hitch them, for top roping purpose alone. about two of them. Would you have trusted your anchors to these boulders?
Though this does not translate directly to they question at hand, it will offer you a guideline to keep in mind.
The real question then becomes how good are you at estimating how much those rocks/boulders weigh, and just how stable they are in their present location.
IMHO, If there's doubt in your mind as to the suitability of their use as anchor points, you'd be a fool to use them.
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stymingersfink
Jul 21, 2008, 4:23 PM
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stymingersfink wrote: zibircut wrote: How big a rock would you trust for an anchor on top of a cliff? Was on top of this cliff. Rock is very compact, with no cracks and very little foliage. But there were a bunch of boulders on top. Some about three feet by three feet by three feet. Seemed pretty solid at that time, and I did girth hitch them, for top roping purpose alone. about two of them. Would you have trusted your anchors to these boulders? The standard in the type of industrial work I do states than any anchor point should be expected to support 5,000lbs for every person attached to it. This offers a safety factor of nearly 5, as the load limiters in use are designed to keep impact forces generated from an accidental fall under 1200lbs. Though this does not translate directly to they question at hand, it will offer you a guideline to keep in mind. The real question then becomes how good are you at estimating how much those rocks/boulders weigh, and just how stable they are in their present location. IMHO, If there's doubt in your mind as to the suitability of their use as anchor points, you'd be a fool to use them.
Oh yeah... just for reference:
27 cubic feet in a cubic yard
1 cube foot of soil = 75-100 lbs
1 cube foot of broken or crushed granite = 95-100 lbs
1 cube foot of solid granite = 130-166 lbs
with this in mind, a 3x3x3 boulder, under even the best conditions, is a little small for one person to consider an anchor point of sufficient safety, let alone something sufficient for two people.
Would I rap off something like that if i had no other options? Probably. Would I use it to anchor the team? Doubtful.
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majid_sabet
Jul 21, 2008, 4:37 PM
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stymingersfink wrote: zibircut wrote: How big a rock would you trust for an anchor on top of a cliff? Was on top of this cliff. Rock is very compact, with no cracks and very little foliage. But there were a bunch of boulders on top. Some about three feet by three feet by three feet. Seemed pretty solid at that time, and I did girth hitch them, for top roping purpose alone. about two of them. Would you have trusted your anchors to these boulders? states than any anchor point should be expected to support 5,000lbs for every person attached to it. This offers a safety factor of nearly 5, as the load limiters in use are designed to keep impact forces generated from an accidental fall under 1200lbs. Though this does not translate directly to they question at hand, it will offer you a guideline to keep in mind. The real question then becomes how good are you at estimating how much those rocks/boulders weigh, and just how stable they are in their present location. IMHO, If there's doubt in your mind as to the suitability of their use as anchor points, you'd be a fool to use them.
you got any documentation or references on this ?
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zibircut
Jul 21, 2008, 4:39 PM
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That was granite and at 27 cubic feet, that would be about 3500 pounds. Guess atleast, that gives me a sense of comfort. Would require about 16 KN to move that boulder over. Good to know that now.
Ofcourse, there are other factors that made me sling it.
- it was flat at the base. we tried to move it, and it wouldn't budge.
- It bulged at the top.
- Essentially, it's shape, distance from the edge of the cliff (20 feet), size/volume, unavailability of any other anchor points tipped our decision at that time.
- Additional boulder to back up the anchor.
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crackmeup
Jul 21, 2008, 5:24 PM
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I'm guessing that if you are using a boulder as an anchor, most likely the force won't be upwards. You want to think about what would stop it from moving against a force in the direction you expect it to be pulled from. It would take 16 kn to lift it, but it could take much less to push it over the edge.
For example, a car weighs a few thousand lbs. Would you use a car as an anchor? What about a big truck? What if the truck was pointed against the cliff on a flat surface, no parking brake and in neutral gear?
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Tree_wrangler
Jul 21, 2008, 5:37 PM
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In reply to: Would you use a car as an anchor?
Of course. Have done it many times. Just need to make sure that you're actually anchoring to the frame, and in such a way that there are no pinchpoints on your tie-in. With a truck, there is usually a tie-in point waiting for you.
In reply to: What if the truck was pointed against the cliff on a flat surface, no parking brake and in neutral gear?
No way.
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stymingersfink
Jul 21, 2008, 5:46 PM
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majid_sabet wrote: stymingersfink wrote: zibircut wrote: How big a rock would you trust for an anchor on top of a cliff? Was on top of this cliff. Rock is very compact, with no cracks and very little foliage. But there were a bunch of boulders on top. Some about three feet by three feet by three feet. Seemed pretty solid at that time, and I did girth hitch them, for top roping purpose alone. about two of them. Would you have trusted your anchors to these boulders? states than any anchor point should be expected to support 5,000lbs for every person attached to it. This offers a safety factor of nearly 5, as the load limiters in use are designed to keep impact forces generated from an accidental fall under 1200lbs. Though this does not translate directly to they question at hand, it will offer you a guideline to keep in mind. The real question then becomes how good are you at estimating how much those rocks/boulders weigh, and just how stable they are in their present location. IMHO, If there's doubt in your mind as to the suitability of their use as anchor points, you'd be a fool to use them. you got any documentation or references on this ?
the statement about the load limiters we use is inferred by the training and equipment documentation that I have received.
the statement about safety factors is my own, arrived at by the reasoning center in my brain.
Do you have one of those? Does it work?
If you want specific references, do your own damn work. Search OSHA regulations/guidelines. I ain't gonna do it for ya.
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Arrogant_Bastard
Jul 21, 2008, 11:26 PM
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zibircut wrote: That was granite and at 27 cubic feet, that would be about 3500 pounds. Guess atleast, that gives me a sense of comfort. Would require about 16 KN to move that boulder over. Good to know that now.
I went climbing the other day and forgot to bring my Jr. Detective Rock Density Analyzer Kit with me. I ended up having to bail and leave gear.
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jt512
Jul 21, 2008, 11:57 PM
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Arrogant_Bastard wrote: zibircut wrote: That was granite and at 27 cubic feet, that would be about 3500 pounds. Guess atleast, that gives me a sense of comfort. Would require about 16 KN to move that boulder over. Good to know that now. I went climbing the other day and forgot to bring my Jr. Detective Rock Density Analyzer Kit with me.
Good thing, too, because, if you had, you'd never have gotten on any of those routes Saturday.
Jay
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