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sittingduck


Dec 1, 2009, 10:46 AM
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An alpine anchor to analyze
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From the other day on an alpine ice-climb, anchor rigged by me wearing big mittens.

- 2 screw-gate carabiners
- 2 fig 8's on a bight
- 2 clove-hitches

We used a 50m 1/1 rope and a 60m 1/2 rope, so it made sense rigging with the 60m rope.




altelis


Dec 1, 2009, 11:22 AM
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only thing i would change is putting a knot in the section of rope in b/w the two screws. without the knot, the gear pulls or the rope gets cut (however unlikely) the anchor is poop.

with a knot its redundant.

other than that, assuming the ice is good and there's more than a single thread in the ice, gtg.


sittingduck


Dec 1, 2009, 11:29 AM
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altelis wrote:
only thing i would change is putting a knot in the section of rope in b/w the two screws. without the knot, the gear pulls or the rope gets cut (however unlikely) the anchor is poop.

with a knot its redundant.

other than that, assuming the ice is good and there's more than a single thread in the ice, gtg.

The ropes coming down from the screws are connected to the powerpoint. One by a screw-gate carabiner and the other going into the fig-8 knot that makes the powerpoint. If the rope you mention gets cut the powerpoint will still be connected to both icescrews. Sorry that the picture is a bit obscured by my sloppy rigging.


altelis


Dec 1, 2009, 11:37 AM
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sittingduck wrote:
altelis wrote:
only thing i would change is putting a knot in the section of rope in b/w the two screws. without the knot, the gear pulls or the rope gets cut (however unlikely) the anchor is poop.

with a knot its redundant.

other than that, assuming the ice is good and there's more than a single thread in the ice, gtg.

The ropes coming down from the screws are connected to the powerpoint. One by a screw-gate carabiner and the other going into the fig-8 knot that makes the powerpoint. If the rope you mention gets cut the powerpoint will still be connected to both icescrews. Sorry that the picture is a bit obscured by my sloppy rigging.

No, I get that. I see that. But WHY make it that complicated with that much slack in the red rope's knots?

If it were me? I would only have incorporated ONE rope into the anchor. Just like you did with red rope. But put a knot in b/w the screws and clip myself with a clove in the rope going to me into that knot. Leave the second rope out of the anchor completely (including as a connection to the anchor). Gives more versatility.

LIke I said though- as long as you put that knot in I would climb on it even with the 2 ropes being included....


sittingduck


Dec 1, 2009, 12:01 PM
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If you put a knot in the rope between the ice-screws you do not get dynamic equalization.
The slack I think you have in mind, is there to allow dynamic equalization.
Incorporating both ropes in my self belay gives me a redundant powerpoint.
Maybe it looks complicated, fact is that I rig this in a minute wearing mittens. Knitting a pair of mittens is complicated rope management, rigging this anchor isn't.


altelis


Dec 1, 2009, 12:19 PM
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the slack i'm looking at is b/w the cloves and the knot in the red rope. this does NOT provide for dynamic equalization.

i guess that i'm just not sold on the importance of dynamic equalization (at least most of the time).

i know the anchor isn't going to take a while to construct, and its not over the top complicated. but what is complicated is how you expect it to function. you have, in essence two anchors. one you expect to dynamically equalize and a second as a backup in case a piece blows and the dynamically equalizes anchor fails.

why?

just throw that knot in and don't obsess about the dynamically equalizes bit.


majid_sabet


Dec 1, 2009, 12:23 PM
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sittingduck wrote:
If you put a knot in the rope between the ice-screws you do not get dynamic equalization.
The slack I think you have in mind, is there to allow dynamic equalization.
Incorporating both ropes in my self belay gives me a redundant powerpoint.
Maybe it looks complicated, fact is that I rig this in a minute wearing mittens. Knitting a pair of mittens is complicated rope management, rigging this anchor isn't.

you used a dynamic line to build that anchor and like or not, you have a semi dynamic anchor to start with which subject to 30% elongation is SOL fall factors. the several inches of slack that you got in between the two points will rip that ice screw out so put a fig 8 in the master point and do not worry about micro equalization.


sittingduck


Dec 1, 2009, 12:38 PM
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Sure the slack could have been tighter, I'll tune it in next time.
You are not sold on dynamic equalization, why do that make me obsessive about it?
You chose a method that likely will put all the force on one piece, while I use a method that likely will put 50% of the force on each piece.
I consider this an important factor for my anchor to withstand a FF2 fall, that is WHY I use it.


majid_sabet


Dec 1, 2009, 12:49 PM
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alright

let me ask you this

if I get puller and start pulling those ice screws out (one by one), How many KN do you think it requires to pull them out ?


sittingduck


Dec 1, 2009, 12:56 PM
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majid_sabet wrote:
alright

let me ask you this

if I get puller and start pulling those ice screws out (one by one), How many KN do you think it requires to pull them out ?

Try the search function or start your own thread about ice-screw properties.
Whatever you do, please stop spamming this thread.


rockforlife


Dec 1, 2009, 1:02 PM
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majid_sabet wrote:
alright

let me ask you this

if I get puller and start pulling those ice screws out (one by one), How many KN do you think it requires to pull them out ?

if they were put in right, in good ice... more than you think


altelis


Dec 1, 2009, 1:26 PM
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sorry, you aren't obsessed by it. like i said, its prob fine.

but my way won't put all the force on one piece, either- fairs fair.


hafilax


Dec 1, 2009, 1:39 PM
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I probably would have lowered the power point. Looks like the angle is close to 90*.

The question of equalization vs. shock loading may never get answered. It seems to be an even more convoluted question with ice screws as far as I can tell. I just did a quick search and came up with a paper I hadn't read before.
http://www.mra.org/..._IceScrews_Final.pdf
They did some drop tests at Ouray. Seems that screws can fail anywhere between 4 and 15kN in 'good' ice. Experience in placing screws is perhaps more important than for placing rock gear.

With FF2 drops they never got above 9kN which is probably due to the maximum impact force properties of the ropes. The data points over 9kN and up to 14kN were FF1+ and the highest were FF1.4+ in simulated lead falls.

Given that seemingly well placed screws can fail at surprisingly low loads means that answering the equalization vs. shock loading question could be of great value. It also shows that the pulley effect must also be taken into account when planning for the worst case scenario.


sittingduck


Dec 1, 2009, 1:48 PM
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altelis wrote:
sorry, you aren't obsessed by it. like i said, its prob fine.

but my way won't put all the force on one piece, either- fairs fair.

How much equalization do you get in the case of a pendulum?

You advised me to belay myself with only one of my ropes to the anchor. If I did that, the powerpoint would be a single strand fig 8 loop. In the case of a FF2 fall, this loop would be the only component connecting me and my partner to the mountain.

The ropes get pretty badly abused in the mountains, with crampons and ice axes, hence the 1/1 rope and the double loop at the powerpoint.


altelis


Dec 1, 2009, 1:59 PM
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when i tie anchors like this i use a double loop knot (usually an 8, though a bowline on a bight works too).

i also try and incorporate as much "stance" into alpine anchors as possible, which helps the most with a pendulum. though, for the second the fall will pull from the last piece of pro (a known place), and the pull for the leader will be from the first piece of pro (a piece one can take a good guess about). and a ff2? well, that will pull straight down.

again, i want to stress that i would prob climb on it, and have climbed on similar anchors before. i was just saying what i would have done differently in a similar situation. not saying yours is wrong, just saying i apparently have different priorities (apparently).


sungam


Dec 1, 2009, 2:34 PM
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hafilax wrote:
I probably would have lowered the power point. Looks like the angle is close to 90*.
That' my only real comment, though I would have clove-hitched the screws.


sittingduck


Dec 1, 2009, 2:51 PM
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hafilax wrote:
I probably would have lowered the power point. Looks like the angle is close to 90*.

That scared me to when looking at the picture. I think it is the point of view that makes it look that way. Imagine leaning towards and below the anchor, the angle would look more and more like 180*. I know I am aware of that angle when I rig my anchors. Thanks for noticing.

hafilax wrote:
The question of equalization vs. shock loading may never get answered. It seems to be an even more convoluted question with ice screws as far as I can tell. I just did a quick search and came up with a paper I hadn't read before.
http://www.mra.org/..._IceScrews_Final.pdf
They did some drop tests at Ouray. Seems that screws can fail anywhere between 4 and 15kN in 'good' ice. Experience in placing screws is perhaps more important than for placing rock gear.

With FF2 drops they never got above 9kN which is probably due to the maximum impact force properties of the ropes. The data points over 9kN and up to 14kN were FF1+ and the highest were FF1.4+ in simulated lead falls.

Given that seemingly well placed screws can fail at surprisingly low loads means that answering the equalization vs. shock loading question could be of great value. It also shows that the pulley effect must also be taken into account when planning for the worst case scenario.

Shockloading seems to be right up there with the microfractures, when it comes to adding enormous peak loads to the anchor. It will be great when someone bust that myth. Strange that it takes so long?

Interesting article. Ice quality and experience seems to be key, and anything else than ice-screws is worthless as protection on ice. For instance, using the axes as part of the anchor has little to no value. I still use snargs on slush and warthogs on top outs, even if I doubt they will hold a fall.

Appreciate your comments hafilax.


sittingduck


Dec 1, 2009, 2:56 PM
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sungam wrote:
hafilax wrote:
I probably would have lowered the power point. Looks like the angle is close to 90*.
That' my only real comment, though I would have clove-hitched the screws.

The screws are clove hitched. It says so in the first post: "two clove hitches".


sungam


Dec 1, 2009, 3:05 PM
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sittingduck wrote:
sungam wrote:
hafilax wrote:
I probably would have lowered the power point. Looks like the angle is close to 90*.
That' my only real comment, though I would have clove-hitched the screws.

The screws are clove hitched. It says so in the first post: "two clove hitches".
So they are. Cool beans, it seems.
Although, tbh, if I'm reading the situation right you are leading on twins or doubles, right?
I would have cloved one to each screw, then just sat back and belayed off myself. Though having said that, this will be my first season with an autoblocker so my tactics will probably be changing.


hafilax


Dec 1, 2009, 3:13 PM
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I wouldn't call shockloading a myth*. It's a question of knowing in what situations shock loading is dangerous. Rigging an anchor with dyneema and clipping to it with a dyneema sling would make shock loading a worry whereas using dynamic materials may reduce the effect. It's understanding the transition between the two regimes that needs to be explored.

Ice is another issue because with 2 screws there is a relatively high probability that one could fail at a modest load and maybe even both of them. The properties of ice in responding to a dynamic load are far more complicated than with rock and metal.

So what is the best strategy for creating an anchor system that is least likely to fail? I don't know the answer and it would be nice to have something more concrete than people's gut feeling as to how much equalization and shock loading play a role in that equation.

*nor microfractures for that matter since they are important outside of climbing


sittingduck


Dec 1, 2009, 3:14 PM
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altelis wrote:
when i tie anchors like this i use a double loop knot (usually an 8, though a bowline on a bight works too).

If you use a bunny ear fig 8 on your powerpoint, and one of your loops blows, your knot is compromised since the bunny ear fig 8 is not redundant. Meaning the other loop will blow to.

altelis wrote:
i also try and incorporate as much "stance" into alpine anchors as possible, which helps the most with a pendulum. though, for the second the fall will pull from the last piece of pro (a known place), and the pull for the leader will be from the first piece of pro (a piece one can take a good guess about). and a ff2? well, that will pull straight down.

again, i want to stress that i would prob climb on it, and have climbed on similar anchors before. i was just saying what i would have done differently in a similar situation. not saying yours is wrong, just saying i apparently have different priorities (apparently).

Could you post a picture or a drawing of a simular anchor? I'd be very interested!
We have different priorities, no problem.


sittingduck


Dec 1, 2009, 4:01 PM
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In reply to:
I wouldn't call shockloading a myth*. It's a question of knowing in what situations shock loading is dangerous. Rigging an anchor with dyneema and clipping to it with a dyneema sling would make shock loading a worry whereas using dynamic materials may reduce the effect. It's understanding the transition between the two regimes that needs to be explored.

The way shockloading has been hyped here at this forum is worthy of mythology imho.
The anchor has no static components, myth or not, there is not much more I can do to take the myth into consideration. Maximum equalization between two good placements is the method I chose to avoid shock loading. The question is, do I know what constitutes a good ice-screw placement?

Edited to add quote tags


(This post was edited by sittingduck on Dec 1, 2009, 4:07 PM)


sittingduck


Dec 1, 2009, 4:29 PM
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In reply to:
Although, tbh, if I'm reading the situation right you are leading on twins or doubles, right?
I would have cloved one to each screw, then just sat back and belayed off myself. Though having said that, this will be my first season with an autoblocker so my tactics will probably be changing.

Yes and no, it is a 1/1 rope and a 1/2 rope. Used as doubles.

What if you collected the ropes between you and the screws and tied a fig 8 on a bight on it? Then you could have one rope run through a carabiner in this powerpoint. If the leader where to fall on the anchor you would not have him hanging only from your belayloop and belay carabiner. One rope would go directly to the leader and one rope upward, through the powerpoint, and then to the leader.


hafilax


Dec 1, 2009, 4:39 PM
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sittingduck wrote:
In reply to:
I wouldn't call shockloading a myth*. It's a question of knowing in what situations shock loading is dangerous. Rigging an anchor with dyneema and clipping to it with a dyneema sling would make shock loading a worry whereas using dynamic materials may reduce the effect. It's understanding the transition between the two regimes that needs to be explored.

The way shockloading has been hyped here at this forum is worthy of mythology imho.
The anchor has no static components, myth or not, there is not much more I can do to take the myth into consideration. Maximum equalization between two good placements is the method I chose to avoid shock loading. The question is, do I know what constitutes a good ice-screw placement?

Edited to add quote tags
You miitigate shock loading by using your ropes in the anchor and limiting extension. You equalize the anchor in the hopes that by sharing the load between the screws you may not have to test whether or not shock loading is a myth.


sungam


Dec 2, 2009, 12:46 AM
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sittingduck wrote:
In reply to:
Although, tbh, if I'm reading the situation right you are leading on twins or doubles, right?
I would have cloved one to each screw, then just sat back and belayed off myself. Though having said that, this will be my first season with an autoblocker so my tactics will probably be changing.

Yes and no, it is a 1/1 rope and a 1/2 rope. Used as doubles.

What if you collected the ropes between you and the screws and tied a fig 8 on a bight on it? Then you could have one rope run through a carabiner in this powerpoint. If the leader where to fall on the anchor you would not have him hanging only from your belayloop and belay carabiner. One rope would go directly to the leader and one rope upward, through the powerpoint, and then to the leader.
That would magnify the forces exherted on the anchor by the pully effect.
Also, I generally get some kind of stanceness going on (even if it's just a very small chopped ledge) I can take some of the weight on me, using the anchor as little as possible. If need be I can escape the system fairly rapidly.

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