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#1154810 - 05/22/17 01:20 PM ATC Guide mode in crevasse haul system?
Buckshot Offline
member

Registered: 03/31/11
Posts: 132
TRs: 2 Photos: 4
Loc: Grant County, WA
Is there a problem with using an ATC in guide mode at the anchors instead of a pulley and prussik to build the hauling system in a z-pulley?
Is it too much friction?
Won't the ATC in guide mode also capture progress as well as a pulley/prussik?
It seems simpler but no one seems to teach it so I am interested in why.
Forgive me if this is already covered someplace else.

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#1154812 - 05/22/17 02:48 PM Re: ATC Guide mode in crevasse haul system? [Re: Buckshot]
mthorman Offline
member

Registered: 03/24/13
Posts: 192
TRs: 12 Photos: 208
Loc: Spokane, WA
It works just fine. Yes the ATC will capture the progress. When I took a 1 day crevasse course with RMI a few years ago they showed this way and we practiced both this and a carabiner with prussik. The only negative I can think of is if you needed to rappel down to get to the patient for some reason and you just used your ATC up top.

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#1154816 - 05/22/17 06:59 PM Re: ATC Guide mode in crevasse haul system? [Re: Buckshot]
dave schultz Online   content
enthusiast

Registered: 06/20/12
Posts: 351
TRs: 24 Photos: 225
Loc: Newport, RI
I disagree with Marlin.

The mechanics of it will, in fact, work, but the forces are generally not considered acceptable. It will be hard to nearly impossible to haul up a victim going through an ATC (or similar) in guide mode without generating excessive forces on the anchor (by needing to add mechanical advantage).

The only way I have been taught, read, and teach is the progress capture pulley or a prussik.

Your concern of needing to rappel should also be a non-issue because you can always rappel with a munter.

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#1154818 - 05/22/17 07:57 PM Re: ATC Guide mode in crevasse haul system? [Re: Buckshot]
montypiton Offline
old hand

Registered: 07/04/06
Posts: 770
TRs: 4 Photos: 0
Loc: central Washington
it does in fact work, but it's damned inefficient. If you're looking to save weight/complexity, bite the bullet and buy a microtraxion - a progress-capture pulley that also works as an ascender if you happen to be the one in the hole. I wouldn't normally buy/recommend a hundred-dollar pulley, but Petzl microtraxion is one that might even be worth paying retail. Mine lives on my harness, and sees more use than I ever expected before I started carrying it.
-Haireball

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#1154878 - 05/28/17 07:16 AM Re: ATC Guide mode in crevasse haul system? [Re: montypiton]
hanman Offline
enthusiast

Registered: 12/11/02
Posts: 394
TRs: 27 Photos: 269
Loc: Arlington
CT Roll N Lock is pretty light and quite functional. I got one recently and use it for many rope access tasks. ATC would be terrible for this use, super inefficient as previously stated.


CT Roll N Lock


Edited by hanman (05/28/17 07:18 AM)

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#1154879 - 05/28/17 08:38 AM Re: ATC Guide mode in crevasse haul system? [Re: Buckshot]
mthorman Offline
member

Registered: 03/24/13
Posts: 192
TRs: 12 Photos: 208
Loc: Spokane, WA
I agree with the fact that an ATC will have a lot of friction and be inefficient in comparison to a pulley. However when compared to a single carabiner I think it would be a similar amount of inefficiency (although an experimental test with a dynamometer would be interesting to me to compare).

I have done a bunch of testing using a variety of carabiners in a 3:1 system instead of pulley and measuring their efficiency. The pulley I tested came in around 93% efficiency as compared to a true theoretically 3:1 system. The carabiners all ranged from 65% to 72% depending on how fat the carabiner was. The fatter carabiners such as a Petzl Attache were the best. My theory is that an ATC with a fat carabiner would be somewhere in the 60-70% range as similar to the carabiners. Plenty happy to abandon my theory if actual tests prove otherwise.

Anyway the best solution as Haireball stated is to just use a Petzl microtraxion. It serves the function of a pulley with a progress capture very well and it lives on my harness when I am in glaciated terrain.

Hanman I have never seen the CT Roll N Lock but it looks light and nice. Is the locking mechanism more toothed like a Microtraxion or Tblock or is it more of a general rope grab pinch mechanism. BTW your link doesn't seem to work on my computer.

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#1154886 - 05/28/17 05:58 PM Re: ATC Guide mode in crevasse haul system? [Re: mthorman]
hanman Offline
enthusiast

Registered: 12/11/02
Posts: 394
TRs: 27 Photos: 269
Loc: Arlington
The Roll N Lock has horizontal ribs, kind of like a micro/rescuescender but perhaps a bit sharper. They say it can engage webbing as well for an adjustable PAS which I though was somewhat interesting. Really light device.

Here's another link to try... Link



MH


Edited by hanman (05/28/17 06:01 PM)

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#1154888 - 05/28/17 08:26 PM Re: ATC Guide mode in crevasse haul system? [Re: hanman]
mthorman Offline
member

Registered: 03/24/13
Posts: 192
TRs: 12 Photos: 208
Loc: Spokane, WA
Originally Posted By: hanman


Here's another link to try... Link


MH


Link works fine this time. I like the looks of that. Interesting that it fits webbing too.

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#1155095 - 06/07/17 12:46 PM Re: ATC Guide mode in crevasse haul system? [Re: dave schultz]
hands Offline
stranger

Registered: 07/23/09
Posts: 5
TRs: 0 Photos: 0
Loc: Los Angeles, Portland/Hood Riv...
I'm with you on the inefficiency due to increased friction, but a little confused on how that translates into increased force on the anchor. Is there something else about the system in not grasping? Just curious.

-matt

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#1155108 - 06/08/17 09:44 AM Re: ATC Guide mode in crevasse haul system? [Re: Buckshot]
Bronco Offline
Deskjockey

Registered: 02/16/01
Posts: 3531
TRs: 14 Photos: 111
Loc: Port Gardner, WA
My feeble minded understanding is that if you have to pull harder due to the increased friction, you're introducing more force on the anchor.

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