What's Wrong?

[oldno7]

A new thread to help understand anchoring and it's intricacies.


The first pic is provided by mzamp

discuss

[skiclimb3287]

If I am not mistaken, on a wrap 2 pull 1, the water knot should be against the front of the tree so that more friction is working in your favor to help reduce the stress on the knot.

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[SRG]

If I am not mistaken, on a wrap 2 pull 1, the water knot should be against the front of the tree so that more friction is working in your favor to help reduce the stress on the knot.

Yes, this is one of the major advantages of the wrap 2 pull 1 rigging. In the first pic the water knot would have less force applied to it if it were positioned on the front of the tree. Even less force if it were a wrap 3 pull 2.

In the picture, the quicklink is attached to the webbing at an overhand on a bight. I think this knot would become the weak spot in the rigging and negate the strengthening effects of isolating the water knot mid-tree.

[ratagonia]

Yes, this is one of the major advantages of the wrap 2 pull 1 rigging. In the first pic the water knot would have less force applied to it if it were positioned on the front of the tree. Even less force if it were a wrap 3 pull 2.

In the picture, the quicklink is attached to the webbing at an overhand on a bight. I think this knot would become the weak spot in the rigging and negate the strengthening effects of isolating the water knot mid-tree.

While your point may be technically true, it is an insignificant difference, for two closely related reasons:

A. The diff between the two locations of the back-knot is perhaps 7000 lbs for one and 6500 lbs for the other. Even with two hefty canyoneers rapping at the same time, you would be hard pressed to produce anywhere near this kind of load, unless one of em had an SUV in his pocket.

B. The weakest point in this rigging is the overhand knot next to the rapide. This knot is likely to be around 6500 lbs, maybe a little less.

May I suggest that understanding the significance of choices in your rigging is an important skill, in addition to knowing what the "textbook" best practice is.

[ratagonia]

A new thread to help understand anchoring and it's intricacies.


The first pic is provided by mzamp

discuss

This anchor does not need a piece of webbing or rapid link. The rope can be placed around the dead tree, and it will pull just fine. Leaving webbing and a rapid link is litter, and unnecessary in this case.

(unless, actually, it is not).

[SRG]

May I suggest that understanding the significance of choices in your rigging is an important skill, in addition to knowing what the "textbook" best practice is.

I understand that in this case the main reason for choosing this style rigging was likely to hold the anchor at a specific point on the tree, not due to the bomber nature of the wrap-3-pull-2, but still I thought I'd point it out cause this is a "What's wrong?' thread, where someone posts a picture of rigging and then someone else posts what they see wrong with it.... I saw what looks like an improperly rigged wrap-2-pull-1.

[nonot]

Not sure what you're poking at oldno, maybe the bight next to the rap ring is too close to the tree, resulting in much larger forces than necessary due to the triangular angle increasing the load, but I've rappelled on worse.

[Bootboy]

I'd hit it

[oldno7]

My input and it's just that.

A textbook rigging of a wrap 2 pull 1, does indeed place the water knot at the front of the tree or whatever you are anchoring to.

The difference may be semantics, but it is never wrong to get the best performance out of an anchor set up.

I do have a "bit" more concern on the small overhand knot that the rapide is tied into.

My math gives a single strand of webbing around 4200lb breaking strength. Putting this overhand in, reduces that by roughly 30%.

Knots in rope or webbing will generally be the weak/breaking point of a system, we cannot avoid them but we should use them wisely.

At one point in my canyoneering career, I would argue the overhand knot in the end of a wrap2 pull 1, had a "slight" chance of adding redundancy, depending on whichever side of your webbing might fail, a very small chance, but once again, it cannot be wrong to rig your anchors for optimum strength. If one is to add the overhand, I might suggest that the longer you leave the bight, the more an anchor will remain equally loaded with lateral movement by a rappeller.
The beauty of not adding an overhand is that the rapide can float from side to side if a rappeller is moving laterally while abseiling.

This type of discussion by canyoneers usually benefits all. I would say when the majority are satisfied with solving a problem/or lack of, on an anchor picture, someone post another to discuss.

No input should be belittled, all input is encouraged.

[oldno7]

The good I see in this set up is, a wrap 2 pull 1 was initially used for 2 reasons:

1-to keep the webbing up and out of the watercourse
2- to facilitate an easy pull

[unimog]

From my training, the water knot is on front for two reasons: 1- so it sees less tension; 2- it is more visible and easier for each rapeller to inspect.

[oldno7]

From my training, the water knot is on front for two reasons: 1- so it sees less tension; 2- it is more visible and easier for each rapeller to inspect.

Valid points

[oldno7]

Not sure what you're poking at oldno, maybe the bight next to the rap ring is too close to the tree, resulting in much larger forces than necessary due to the triangular angle increasing the load, but I've rappelled on worse.

Not really "poking" at anything, just trying to stir up discussion on a topic that needs attention as born out by a recent death and a recent 60' fall.

Please feel free to add a picture for discussion.

[canyoncaver]

That knot in the front is good to about 4,000 lbs tops. Unless you guys use some other kind of webbing that I'm not familiar with.

4,000 lb. webbing X 2 = 8,000 divided in half for overhand knot = 4,000.

The knot is also unnecessary. It does not provide any redundancy. Leaving the knot out does not increase strength, it only reduces unnecessary complexity. 4,000 lbs is plenty of strength for a rappel anchor.

[Scott P]

The knot is also unnecessary.

That's what I was thinking.

What is the purpose of the knot where the rapid link is?

[SRG]

Canyoncaver,
I'm confused by these two statements as they seem to be saying opposite things...

4,000 lb. webbing X 2 = 8,000 divided in half for overhand knot = 4,000.

and

Leaving the knot out does not increase strength, it only reduces unnecessary complexity.

It seems from your first explanation that leaving the knot out would indeed increase the breaking strength from 4,000 to 8,000lbs. Could you please explain?

[canyoncaver]

Oh sorry, yes I should explain.

When you knot webbing, it decreases its strength by about 50%. Two knots also decrease the strength by 50%, not 100%. Three knots also decrease the strength by 50%, not 150%. This is because when pulled to failure, the webbing will break at one of the knots somewhere near 4,000 lbs of force. It doesn't matter which knot.

In the example above, there is already a water knot in the webbing, so removing the overhand does not restore any strength.

Hope this helps. If not, let me know.

[oldno7]

Oh sorry, yes I should explain.

When you knot webbing, it decreases its strength by about 50%. Two knots also decrease the strength by 50%, not 100%. Three knots also decrease the strength by 50%, not 150%. This is because when pulled to failure, the webbing will break at one of the knots somewhere near 4,000 lbs of force. It doesn't matter which knot.

In the example above, there is already a water knot in the webbing, so removing the overhand does not restore any strength.

Hope this helps. If not, let me know.

Generally I would agree but in the instance of a wrap 2 pull 1, stress on the water knot is reduced. Thus if there is to be a breaking point from direct load(doubtful), the week point is the overhand knot--not the water knot.

On the redundancy issue--go and tie a wrap 2 pull 1, there will have to be one strand overlapping the other. Depending on whether there is a failure of the under strand or the loaded strand, an overhand knot MIGHT be redundant. Try it....

[canyoncaver]

On the redundancy issue--go and tie a wrap 2 pull 1, there will have to be one strand overlapping the other. Depending on whether there is a failure of the under strand or the loaded strand, an overhand knot MIGHT be redundant. Try it....

Yeah, I hear ya. I just don't consider that redundant enough to really be called redundant. At least not by my high standards...

[bjp]

it is never wrong to get the best performance out of an anchor set up.

Well, I think it's pretty clearly true that it is never wrong to get the best performance out of an anchor setup when all else is truly equal. But all else isn't equal -- people have limited attention, memory, and time. In this case, I think the evaluation of the inline water knot should be "it will not break" rather than "it would be stronger if it were in the front". When evaluating the options of "spend a bit of extra time to scoot the knot around to the front" and "screw it, just rappel on it as-is" using EARNEST criteria, both anchors are far Stronger than they need to be -- there is no change in the safety afforded by Strength between the two options. But, there is a change in Time -- the first option takes some additional time/attention and that is a limited commodity. I would argue that any extra effort spent ensuring that the joining water knot is in the front of this anchor makes the group marginally less safe.

Of course, if someone is setting up the anchor and it takes the same amount of time to put the knot in front as in back, then everyone should learn to put the knot in front because all things are equal, and that is the stronger anchor.

So, from the perspective of "how should this anchor have been rigged by a perfect canyoneer", I think you're totally right. But, from the perspective of "I constructed/found this anchor; now what should I do?", the knot should stay at the back.

This:

While your point may be technically true, it is an insignificant difference
...
May I suggest that understanding the significance of choices in your rigging is an important skill, in addition to knowing what the "textbook" best practice is.