Two pieces in solid rock hold plenty of kilonewtons, why would anyone place more?

Seriously, I have read several comments lately on this site that lead me to believe many people feel that two good pieces make a satisfactory trad anchor. Has this become an accepted practice? I always like at least three. If you feel two is OK, what is your logic? I have always thought that three was considered the minimum.

Two's enough if they're solid. One would hold most falls. But you never know, so most of us seek redundency.

At least three pieces of removable pro (for a downward pull), two good bolts, or one solid tree/boulder. It's not that hard, people.

Jay

I use enough pieces to make the anchor solid and safe. Sometimes, that's three. Sometimes four. I've built one that had six. Others have had two.

When I am hanging off it. I prefer to see three because it makes me feel a little better.

At least three pieces of removable pro (for a downward pull), two good bolts, or one solid tree/boulder. It's not that hard, people.

Jay

what is your life is worth?

[IMG]http://img360.imageshack.us/img360/3974/screenhunter001.jpg[/IMG]

Two modern bolts, yes.

Two well-placed directionally secure (or secured) medium-large to large stoppers, ok.

Majid if reference to your picture... of course you need so many pieces if you place them under blocks that could move with a decent fall. Of course if a block shifts it doesn't matter how many pieces are under it so that picture looks like a three piece anchor to me, and the one on the left looks suspect.

My vote falls between sometimes two and always three (yes technically that makes me a sometimes two person). I feel like "sometimes" means more often than I would place them. I usually find at least two solid pieces and usually a third that I have confidence in. If I can find two perfect placements and I need to conserve gear in a size for the next pitch, or I can't find a good third placement I am happy with two. I will also go with two if there is a good stance acts as my primary piece and I am not worried about shock loading the anchor at the start of the next pitch.

For me my rule is three pieces unless the situation dictates otherwise, but I don't go into a climb with a "two sometimes" mentality.

Majid if reference to your picture... of course you need so many pieces if you place them under blocks that could move with a decent fall. Of course if a block shifts it doesn't matter how many pieces are under it so that picture looks like a three piece anchor to me, and the one on the left looks suspect.

Agreed. Especially considering that most of Majid's posts make him sound like the only safe climber in the universe, that is a piss poor anchor to post a picture of. It really doesn't matter how many pieces are on the right side or if they're good or not, if you fall on that and the (very loose and unstable looking) block topples over on you, it wouldn't really matter if the other pieces held or not.

I sort of count a good stance as a piece, but I still put in at least 3 pieces of removable pro if possible.
As a current weekend warrior, it's really not my goal to anaylze every possible failure mode of everything and figure out some sort of personal best practices, as some poeple seem to advocate. While you don't want to shut off your brain and do things just b/c you've been told to, my general goal is to keep current with generally accepted best practices, and do those. I think that means at least 3 pieces of removable pro.
(Finally, I'd MUCH rather have 2 pieces of bomber pro than 3 or more pieces of junk)

Did you read the thread? No-one is pulling numbers out of their ass. Almost all the replies advocate thinking things through.

You're creating a reality in your head again.

STFU n00b

The OP is refering to magic two why ? because climbers are using the two protections most of the time therfore, using two protection is almost standard practice in building a trad anchor.

sure other people like yourself (ms angry ) will build anchors based one , three....or whatever number of protections but majority of people only use TWO.

At least three pieces of removable pro (for a downward pull), two good bolts, or one solid tree/boulder. It's not that hard, people.

Jay

Even with one solid tree, I'm still going to want two connections off it.

...and we got off no problem.

interesting thread - some of the replies make me feel like a pussy, but i'm cool with that...

i go for 3+,
<snip>
i'm new to this ...

cracklover's one piece would scare the shit out of me, but i can see the sense in this if the placement is solid and the rock is good - though there's no chance in hell i'll be following suit any time soon.

steve

Cracklover: I do understand and agree with your example. My point, and I don't know if I'll succeed in convincing anyone, is to try to slightly undermine the "it's all situational" mind set that many people are espousing. I interpret that as thinking that every anchor is some unique thing (in way it it, but in a trival sense) and the climber is supposed to figure out how to set up an anchor from basic principles. That seems like a mistake to me.
It seems to me that standard recreational climbing depends on very few variables, and safety is maximized when the same basic methods are employed nearly always, with exceptions being few. I don't mean you can't have more than tool in your box, but you should have a limited number of tools, know how to use them, and not try to repeatedly invent new tools at the top of every pitch.

STFU n00b
read the posts and you'll see most use 3 and on occasion use 2

GO:

With respect to your one-piece "anchor," I guess I follow your logic: your partner, a woman, was probably much lighter than you (with your "fat ass"), and so this one piece was only there to keep you from accidentally falling off the ledge. It was NOT, in other words, intended to used as a typical multi-pitch anchor.

At least I hope not: it looks like a bomber piece for a downward pull, but worthless if the leader fall was capable of lifting your "fat ass" several feet off the ledge.

Am I reading that right?

I use enough pieces to make the anchor solid and safe. Sometimes, that's three. Sometimes four. I've built one that had six. Others have had two.

I was taught that, IF POSSIBLE, always place a minimum of three pieces of gear. I was wondering if that basic tenant is changing. I do like three!

Haven’t you seen Vertical Limit? Even three is not enough.

STFU n00b

The OP is refering to magic two why ? because climbers are using the two protections most of the time therfore, using two protection is almost standard practice in building a trad anchor.

sure other people like yourself (ms angry ) will build anchors based one , three....or whatever number of protections but majority of people only use TWO.

and not by some imaginary numbers out of your as* like how some of the climbers are using these days.

TIME FOR PULLING NUMBERS OUT OF MY ASS........

So everything is climbing is based upon matching the ultimate strength of your rope. Ropes are assumed to have a breaking strength of 30kN.
Tie a knot in it and you are down to 20 kN.

Try more like 9.3 kN for a "typical" climbing rope....

Well how about 22 kN? That's a nice round imaginary number that often gets batted around. Where does that come from?

Ropes are assumed to have a breaking strength of 30kN.
.

USNavy,

You will notice I said ASSUMED to have a breaking strength of 30 kN.

This assumption is accepted for all strength calculation of systems, anchors and general rigging.
For simplicity, this "Magic Number" is the same for low stretch and high stretch ropes.

The very abilities we find desirable in climbing ropes make testing predictions incredibly complex. A new rope out of the bag will be virtually unbreakable as it will just continue to stretch more and more.

I have personally witnessed a VERY old rope, with multiple core shots lift a 10000 load (after stretching to about 140% of its length.

The only way in a testing environment is to subject the rope to continued cyclic loading, in which repeated stresses are applied to the point where the elastic properties of the rope are reduced, and the long fibers are fatigued.

This is the method in which I have discovered all the testing thus far, if you find others, I would like to read them.

Again, my background is rigging, not testing methods, so hopefully I haven't botched up too much, but you can certainly understand where I am coming from.

It is somewhat accepted that all ropes will have a ASSUMED strength of 30 kN.
Simple physics would explain why bolts would approach this number, harnesses would be rated to half of that, and why I would have answered the OP in the fashion I did. In fact if you analyze most practiced methods, you will see that all systems we have been taught to use meet this 30kN(-30% for knots) strength.

USNavy,

You will notice I said ASSUMED to have a breaking strength of 30 kN.

This assumption is accepted for all strength calculation of systems, anchors and general rigging.
For simplicity, this "Magic Number" is the same for low stretch and high stretch ropes.

The very abilities we find desirable in climbing ropes make testing predictions incredibly complex. A new rope out of the bag will be virtually unbreakable as it will just continue to stretch more and more.

I have personally witnessed a VERY old rope, with multiple core shots lift a 10000 load (after stretching to about 140% of its length.

The only way in a testing environment is to subject the rope to continued cyclic loading, in which repeated stresses are applied to the point where the elastic properties of the rope are reduced, and the long fibers are fatigued.

This is the method in which I have discovered all the testing thus far, if you find others, I would like to read them.

Yes I know what you’re saying. You’re implying that the breaking strength of a rope under dynamic conditions is 30 kN. I am saying the static breaking strength is much less. That’s all. Was that old rope that held 10,000 lbs. an unmodified dynamic climbing rope 11 mm or less in diameter? Was the load being held by a single strand?

He just did. Did you follow the link? BD tested 4 rope samples with in a static pull test, and they found that they all failed at around 2200–2300 lbf, about 10 kN. How do you reconcile that test with your claim that ropes have an "assumed" strength of 3 times that figure.

Jay

What I am trying to say, is static breaking strengths are an inaccurate method for measuring high stretch ropes.
For example this is what I would expect to see in a test of breaking strength (although as mentioned, I am a rigger, not a tester)

Phase 1 - rope stretches and machine maxes at 5000 lbs.
Phase 2, machinery reset for further pull, DURING WHICH the load is reduced to 1500 lbs as the rope stretches
Phase 3 - rope stretches to machine maximum at 5000 lbs
Phasse 4 - Machine reset and load again reduces to 2600 lbs as rope stretches
Phase 5 - machine stretches, rope fails at 2700 lbs.

(Again these numbers are totally made up, but this is my understanding of how ropes are broken, and explains why static testing does not represent rope strength during use. Ropes are designed to reduce forces, and by that nature, testing ropes eliminates any represeantation of actual use.

...For trad gear I would pretty much always use at least 3 peaces. There are however occasions, ie where there are large tree’s, boulders or bolts to use, where the anchors are clearly so good that two or even one is OK, on the other hand there have been times when I have used 6 or seven peaces of gear to build an anchor.

What I am trying to say, is static breaking strengths are an inaccurate method for measuring high stretch ropes.
For example this is what I would expect to see in a test of breaking strength (although as mentioned, I am a rigger, not a tester)

Phase 1 - rope stretches and machine maxes at 5000 lbs.
Phase 2, machinery reset for further pull, DURING WHICH the load is reduced to 1500 lbs as the rope stretches
Phase 3 - rope stretches to machine maximum at 5000 lbs
Phasse 4 - Machine reset and load again reduces to 2600 lbs as rope stretches
Phase 5 - machine stretches, rope fails at 2700 lbs.

(Again these numbers are totally made up, but this is my understanding of how ropes are broken, and explains why static testing does not represent rope strength during use. Ropes are designed to reduce forces, and by that nature, testing ropes eliminates any represeantation of actual use.

Dynamic ropes are tested for a maximum impact force which is far below 30kN. As long as they can stretch far enough to dissipate the energy of the fall they will have a tension that is not much above that impact force.

Now that we're not really addressing the question could somebody who always uses three pieces make a justification why two is not adequate if they're bomber?

There's still a small chance that all the pieces will fail so why not place 4 or 27. If you have a 12 piece anchor and 11 of the pieces fail then you'll be on one. So by that trend of thinking we can't possibly be safe...ever. We're all gonna die!

There's still a small chance that all the pieces will fail so why not place 4 or 27. If you have a 12 piece anchor and 11 of the pieces fail then you'll be on one. So by that trend of thinking we can't possibly be safe...ever. We're all gonna die!

Because 3 is a magic number. 4 or 27 are not. Therefore, 3 is better.

pendereki - really liked your answer.

altelis - nice choice of music.

There's still a small chance that all the pieces will fail so why not place 4 or 27.

Because 3 is the fewest pieces of removable protection that, by visual inspection, appear individually infallible under the highest load believed possible, for which the probability of total anchor failure is infinitesimal.

Mods, lock 'er up.

Jay

I told you 3 was a magic number.

We're all gonna die!

Seemingly overlooked in this discussion is actually getting the climb done.I lead 95% of the pitches I climb.What use is a terrific three piece cam anchor that sucks up your red,yellow and blue C4 if there is a hand crack looming above?Belay anchors can't always,or even frequently look like Majid's truckstops,because some of us want to climb above that point,and get some gear in.

So,in reality,you may belay from four iffy stoppers equalised however you prefer,despite the existance of a great cam crack,because the person leading the next pitch is going to need the goods.

I'll take a solid Jesus piece over a nine piece POS like Majid posted every time.

That is false. The tension is proportional to the relative elongation of the rope. Hooke's Law.

Jay

Sorry Jay, I usually agree with things you say, but hooke's law only applies to the linear elastic region, and with dynamic ropes, once you are about at the maximum impact force you leave this region...

I chose sometimes 2 pieces, not because as majidiot wants everyone to believe, 2 piece anchors are the norm (they most certainly are NOT the norm), but because that was all that was available to me. I have also rapped off of a single nut on occasion, but my typical anchor consists of either 3 or 4 pieces (more if necessary).

As has been said it is all situation dependent.

Let me restate that as long as you don't exceed the energy of the test by much you won't get a tension in the rope much higher than the rated impact force.

Not even close. Not even the most extreme duty 11 mm dynamic rope will hold that. A brand new 10.5 mm dynamic rope will hold about 9 - 10 kN with a figure eight. The used 10.5 mm rope I tested held about 6.1 kN with a munter hitch.

Check this link out: http://www.blackdiamondequipment.com/...p_archive.php#120308

You will notice that the obviously new ropes tested on that page broke around 2200 lbs. Although I am not sure what diameter that rope is, it would be a safe to bet they are 10.5 mm or close.

[img]http://img255.imageshack.us/img255/8503/img2056eg5.jpg[/img]

Because 3 is the fewest pieces of removable protection that, by visual inspection, appear individually infallible under the highest load believed possible, for which the probability of total anchor failure is infinitesimal.

The maximum impact force figure for a rope is the maximum force measure in the first drop of the UIAA test. The requirement is that it be less than 12kN for single ropes. The force quickly goes up in the subsequent drops in the test; I've read up to 15kN by the 4th drop. I accidentally started this whole thing when I was thinking of the rope like a screamer which it isn't at all.

I just took a quick look at the literature and it seems that ropes are highly non linear and that the force-extension curve has significant upward concavity. The springiness increases as it stretches.

The following statement that I made on page 3 is incorrect as well:

It's not the energy but the fall factor that is important.

My main point is that there is no reason to think that ropes will hold a 30kN load. The UIAA tests must have a peak force number for the ropes when they snap but that is under highly unusual circumstances. Otherwise even in the extreme case of the 4th drop of the UIAA test the maximum tension in the rope is limited to around 15kN.

How much less probable is it than a removeable two piece anchor in which each piece is bomber by visual inspection?

How much more probable is three than four? I sucked at calculus and statistics but wouldn't it increase logarithmically for each piece placed (many things being equal, which might as well be ignored).

In which case if the probability of anchor failure for a two piece anchor is 50%, a three piece anchor is 5%, and a four piece anchor is only 2.5% then it makes sense to have more than two pieces but less so to have four pieces.

On the other hand if the probability for failure of a two piece anchor is 10%, a three piece anchor is 5%, and a four piece anchor is 2.5%, then it seems that a three piece anchor is not significantly better than a two piece anchor.

Under two mild assumptions, if p is the probability of one piece pulling, n is the number of pieces in the anchor, and P is the probability of all the pieces pulling, then P = p^n. Each piece added to the anchor, therefore, decreases the probability of total anchor failure by a factor of p.


None of those numbers is consistent with the equation for P above. Plug in some realistic numbers, see what you come up with, and if you still disagree that 3 is the "magic" number, post up.

Jay

is there a relatively and equally simple formula for approximating P when p is different for the different pieces in the anchor? or does that fuck the simple-factor up nice and good?

is there a relatively and equally simple formula for approximating P when p is different for the different pieces in the anchor? or does that fuck the simple-factor up nice and good?

So if we just peg the probability of one piece pulling at say 50% for simplification then the probability for total failure of:

2 piece anchor: 25%
3 piece anchor: 12.5%
4 piece anchor: 6.25%
5 piece anchor: 3.12%
6 piece anchor: .02%

If we go with a more likely probability of individual gear failure like say 10% then the difference is even smaller:

2 piece anchor: 1%
3 piece anchor: .1%
4 piece anchor: .01%
5 piece anchor: .001%
6 piece anchor: .0001%

If the gear has a 1% chance of pulling then it seems that a two piece anchor is highly likely to not fail (1 time out of 10,000).

Already I'm injecting my own risk tolerance into things by accepting at maximum a 6.25% probability of total failure.

I told you 3 was a magic number.

Huh? The rope does not have an absolute maximum impact force. The maximum impact force for a particular rope is a function of the fall factor and the weight of the climber.

Jay