I've hinted at this in previous posts and no one took the bait. If cordelettes are being constructed with 7mm nylon and clipped with a single strand at a leg of the anchor, then your not getting the doubling effect that some have suggested. You would if you were finishing off the end with a two-stranded loop which requires some extra doubling when you tie the knot. This uses up alot more material shrinking the working length.

I guess each leg of the anchor provides a portion of the anchor's overall strength, so in that way I might be comforted in knowing that the overal strength of the "system" is say 6500 lbs (in a 3 leg anchor), but the weak point of any given leg is going to be about 10kN which is the approximate tensile strength of 7mm nylon.

Of course 10kN is nothing to sneeze at and that is only one leg.

My point is that saying its ok to use 7mm because your getting double strength seems incorrect if you just clip in with a single loop knot which is how most images of cordelettes show it.

I think your setup doesn't really matter nor does the thought of producing more strength.

The holding strength of the pro will fail before the cord. Then the friction on the biner will fail the cord by burning through it - failing a cordalette from impact force isn't even a consideration (nor is the knot in which the cord is joined -- but that's my opinion).

What I think does matter is the manner in which energy is disbursed between the placements, which has been discussed fairly well I thought & published in the new anchor books; and the introduction of a dynamic belay in the system as well as deformation.

However, what matters even more to me is not subjecting the anchor to a fall to begin with.

As I understand, you don't just clip into one loop. You make your 2 or 3 point anchor, bring all the loop ends to one biner and tie a knot at the masterpoint. This way, as long as at least one loop and its anchor holds, you are still safe. So in essence you are tied with 2 or three separate loops all knotted together at the masterpoint.

And it seems that a loop is not exactly double strength, not only due to the knot, but also the point of contact at the end of the loop with the load/biner, where it is a single horizontal span of cord reversing directions(the loop end). I don't know the physics of it, but you are technically still on one length of cord.

For those not clear on the "single strand" application of the cordolette, it involves taking out the knot of the cordolette and using it as a "rabbit runner". Bights are tied into either end and clipped into the outer pieces. This method gives you more length when equalizing pieces that are farther apart. However, as JmH said, if equalizing only two pieces, one must tie a double-bight knot at the master point to achieve redundance. As far as reduced strength from using a single strand, I'd agree that as long as you're using an appropriate diameter for cord (7mm or 5.5 kevlar), strength should not be an issue relative to the rest of the system. Sterling 7mil cord has a single strand rating of 3000lbs. or so. For those with reservations, or a robust girth, I've seen dynamic 7mm cordolette on the spools as well.

JmH,

Based on your recent slew of threads about intro climbing areas, double-biner strengths, cord strengths, etc I think you're over thinking this stuff when you could focus on basics. People should ask questions and understand their systems, but I'm under the impression that you will benefit way more from focusing on solid pro-placements, rope management, some basic self rescue, etc (foundation type stuff). I would recommend spending time on those things, instead of things that have pretty much withstood the test of time. For instance: worrying too much about if 10kN is sufficient (you'd likely die from something else in that fall, anyhow), I think you'll benefit more and enjoy the experience!

Anyhow, nothing negative intended here, just think it's a tendency for some folks to first focus on the less-basic areas, when that could easily come later. Excuse me if I've misunderstood.

Cheers,
Avery

brenta amazing job describing it! you pretty much got everything as close to acurate as need be, I think friction plays a pretty big role too, can't quite remeber if mentioned any of that. I am a Metallurgical engineer and that was pretty much everything we went over for steel cables in my statics class. These same theories can also be aplied to rope also with a few different considerations. It seems like JmH keeps posting on here about this. If you really want to keep on believing that one strand is the same as a loop then reduce your wieght and make rabit cordeletes with one cord and use small figure eight loops for the carabiners, etc. In your mind you will be getting the same strength. I might also recomend picking up a physics course then picking up a course on ropes and cables (probably a civil engineering statics course) and decide for yourself.
But again your protection or the rock itself (breaking away from nuts on the rotten limestone I mostly climb) will fail before the rope fails even if you only use one stand, not much protection is rated above 12kN.
Good post too Avery Nelson! good coments about focusing on aditional areas!

Nice explanation! I guess what I was thinking was that at the point of contact between the cord and biner is that the tension in the rope has to get transfered to the biner additively(to equal the full load) which causes the (more extreme?) compression of the cord along the few millimeters in contact with the biner(or pulley).

Assuming there is no knot, would that be the weak point of the system?

At that point is the tension along the parallel direction of cord preserved in addition to a perpindicular compression force arising for transfering force to the biner? Or is the tension purely turned into a compression force? Does it make sense what I am asking?

Not sure exactly what you meant but Yep, that was all the discusion of what it is going around and how tight the radious is in JmH's previous forums to this topic. That is also why carabiner manufactures often tell you the rope bearing radius diameter, to be friendlier to the rope. Really shape radiouses such as directly hooking your cordelet to like nut wires will actually break "cut" the rope on falls. The breaking begins actually at the outer edge away ( because actually there is added tension there the "compression"(it isn't really a compression as they would still be under tension just significantly less than the outside) isn't particularily harmfull but the rope still has to hold the same wieght and since the fibers under the 'compresoin' aren't holding there share of the load which means that the ones under tension are holding more than they would normally be subjected to) from the wire and as it breaks the system gets weaker and keeps breaking moving towards the wire, I saw a film from a high speed camera once. I hope this helps explain it, I am sure brenta could do a better job as he seems quite knowledgable and able to explain his knowledge, I am not very good at explaining what I know.
But seriouslly guys don't get hung up on all the physics it is good to understand what you are doing but don't just focus on this focus on other climbing techniques, anchor building, self rescue,... stuff to make a better climber and keep you from getting into situations where this would become a problem. Like Avery Nelson
mentioned. Happy climbing!

Ah, that is interesting about the cutting beginning on the opposite side if reference to slinging a wire directly.

I just find trying to understand the physics interesting. I once tried to derive the fall factor equation, but could never succesfully get it. I think I just wasn't understanding something, I came close though!

If anything, studying the actual physics reinforces my trust in the gear, since the forces rarely reach what the gear can actually tolerate.

Thanks for the info!

Andrew, your explanation is quite clear. Was the movie you saw of a steel cable or a climbing rope?

Joseph, the formula that gives impact force as a function of the fall factor (as you find it on the Beal site) is derived starting from the energy balance equation ks^2/2l = mg(fl+s), where l is the length of the rope (before stretching) that catches the fall, s is the maximum stretch of the rope, f is the fall factor (fl is the height of the fall), m is the mass of the climber, g is the gravitational acceleration, and k is the rope modulus, that is, the force that would double the length of a piece of rope; s^2 is s squared.

Divide both sides by l to get k(s/l)^2/2 = mg(f+s/l) and solve this second degree equation for s/l. Finally, the peak force is given by Hooke's Law: F = k(s/l).

Oh... gotta use energy equations... duh...
I think I tried it using Newton's equations only. I came up with something that is close to the fall factor, but not quite that.

Thanks for the info!

brenta the video was of a kevlar rope/cable often used to replace steel cables in winches. It was unsheathed so you could see what was going on, and the kevlar unsheathed cable is a slightly different weave than climbing rope as it is designed to hold it's shape with out a sheathing. If I remember right steel cables are not near as prone to this as ropes which (my asumtion) is partly why cables are used on small pro like nuts (however it also makes placement much easier). Webbing doesn't experiance this as much either because it is thinner... why it works good for cams and larger hex nuts (where there is enough room on the protection to use webbing).

Thanks!

JmH, the loop that runs through the carabiner is double strength because the strand on each side takes half of the load. I understand your intuitive sense that because the loop going through the biner only touches it at one point it would be the single strand strength, but it just ain't so. I can't quite figure how to explain it, so you shouldn't take my word for it, but you can test it. Tie one loop of cord and one rabbit runner of the same cord and clip each to a biner and one between them and then with 2 much stronger cords tie one end of the assembly to a tree and the other to a solid part of your car and go! The rabbit runner will break every time. (The loop strength is not really double because those strength ratings are derived from testing with the ends wrapped around a 4" drum so you would need biners with a 2" rope bearing radius to get double strength, and, of course, no knots.)

Actually you could test this with sewing thread without the use of the tree and car, and you could repeat the test hundreds of times for a dollar or two.