weight limit?

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18 years 8 months ago - 18 years 8 months ago #122898 by Bradley Ford
weight limit? was created by Bradley Ford
What is the weight limit for safely descending on a friction hitch with a dynamic climbing system? I know there are variables such as type of hitch, type of rope, and friction from the tie in point, but I'm hoping to find some reasonably determined guideline.

Thank you,

Bradley Ford

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18 years 8 months ago - 18 years 8 months ago #122899 by nickfromwi
Replied by nickfromwi on topic weight limit?
Wow, good question!

First off, there are so many types of hitches a person could choose. And if you find one that slips at low loads, many of these you can just add a wrap or two to give a little more friction.

There are reports of prusiks and klemheists not slipping until the 1000lb range. This is not to say, "A prussik can hold a thousand pounds." Under the right (or should I say wrong) circumstances, they can slip at significantly lower loads.

Maybe we should set up a test.

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18 years 8 months ago - 18 years 8 months ago #122940 by Bradley Ford
Replied by Bradley Ford on topic weight limit?
Nick,

Were the tests you reference done on a static or dynamic climbing system? And were they determing the weight limit for safely descending (controlled slipping with the option of stopping) or for causing the hitch to fail?

I have safely descended (knock on wood :D ) with a dynamic climbing system on 1/2'' XTC using a 5-3 Blake's; my climbing weight is ~175 lbs., so I can offer that the limit is at least 175 lbs.

Bradley Ford

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18 years 8 months ago - 18 years 8 months ago #122941 by Tear
Replied by Tear on topic weight limit?
My climbing weight is about 195, on the same system, and I've never worried. When I was taking my facilitator course, I also descended with Tim Kovar's, who's a lot bigger than I,weight on my rope, and was fine.

Joshua

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18 years 8 months ago - 18 years 8 months ago #122947 by nickfromwi
Replied by nickfromwi on topic weight limit?
Here is one test. Not super scientific, but it get's the point accross.

http://www.xmission.com/~tmoyer/testing/pull_tests_11_98.html

There is a lot of pulling going on there. The prussik info is down towards the bottom.

I've seen prussik hold many hundred pounds, and I've seen others slip at way less than a hundred. It's just a matter of trying it out low and slow. Get used to your materials. And take it easy when you try new things!

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18 years 8 months ago - 18 years 8 months ago #122959 by Bradley Ford
Replied by Bradley Ford on topic Does ANSI Z133 cover this?
Does anyone know if the ANSI Z133 safety standard covers safe descending weight limits for hitches with dynamic climbing systems?

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18 years 8 months ago - 18 years 8 months ago #122960 by nickfromwi
Replied by nickfromwi on topic Weight limit.
No it does not.

What is the application here? What are you planning?

I am going to go out on a limb here and say that every person that can put on a saddle will be able to find a suitable friction hitch.

You're under two hundred pounds, so I know you're thinking something fishy. Tell us!

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18 years 8 months ago - 18 years 8 months ago #122962 by Bradley Ford
Replied by Bradley Ford on topic Hidden agenda--ulterior motive? Certainly ...
... I want to understand more about tree climbing systems. Part of the education I need relates to this guideline.

I want to know the capabilities and limitations of the climbing systems I use. If I descend using SRT and a Petzl I'D, I know from Petzl's specifications for the I'D that the maximum "normal working load" is 150 kg. I'd like to know the corresponding weight limit for safely descending on a friction hitch using a dynamic climbing system.

Since the limit is above normal use, here's a hypothetical question that stresses the need to know this limit: (Referencing Joshua's post earlier in this thread) Could Joshua have safely "rescued" Tim if they each weighed 350 lbs.?

Brad

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18 years 8 months ago - 18 years 8 months ago #122963 by nickfromwi
Replied by nickfromwi on topic weight limit?
I guess this wouldn't be too tough to test. Climb up, set up in a dynamic double rope system, then clip a buddy to one of your d-rings!

However, you wouldn't be testing it if there was the possibility of failure. It might be a good idea to have other friends there to put one or both of you on a super loose "just in case" belay.

What climbing hitch would you use for this?

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18 years 8 months ago - 18 years 8 months ago #122964 by icabod
Replied by icabod on topic Misunderstanding
Bradley,

I think your question shows an unclear understanding of how a friction hitch works. You do not descend on a friction hitch as you do on a descent control device such as an 8, rack, tube, or other device such as the I'D. Descent on a DdRT system, using a friction hitch, is controled by friction between the control hand of the person descending and the friction between the rope and the TIP. The friction hitch acts to prevent downward motion by providing enough friction inside the hitch when loaded to arrest motion of the running line. During descent you are forced to release the load on the hitch to make any downward motion.

This said, in a rescue situation (which is not what TEAR was describing) the incapicated individual should be lowered to the ground on his own rope and descent control system. The chances of an individual being able to control the weight of two humans on the same DdRT system using only the friction provided by his hand and the rope/cambium friction to control descent are poor. The addition of a descent control device, I would recomend a rack system whose friction can be adjusted per need, in place of the friction hitch would make it a safer, but still dangerous, opperation.

Cam "Icabod" Taylor

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18 years 7 months ago - 18 years 7 months ago #122967 by Tear
Replied by Tear on topic Sorry for the misunderstanding
A little misunderstanding: Tim was definitely on his own rope and knot for our practice rescues. The specific instance I was thinking of was one exercise when he was "unconcious," and I had to have some of his weight on me in order to support his neck and back. The majority of his weight was still on his own rope, but some was on mine, since I was holding him.
Josh

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18 years 7 months ago - 18 years 7 months ago #122969 by Bradley Ford
Replied by Bradley Ford on topic What's your answer?
Some of you teach DRT and verticle rescue. Do you present any guideline or information relative to this weight limit?

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18 years 7 months ago - 18 years 7 months ago #123048 by Bradley Ford
Replied by Bradley Ford on topic weight limit?

Originally posted by Bradley Ford
(Referencing Joshua's 2003-10-27 and 2003-10-29 posts in this thread) Could Joshua have safely "rescued" Tim if they each weighed 350 lbs.?

Brad

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18 years 7 months ago - 18 years 7 months ago #123053 by Tear
Replied by Tear on topic weight limit?
Following TCI's guides of having a rescued individual's weight primarily on their own rope, I would say yes. Because obviously, we got into the tree somehow, so our knots have been holding each of our individual 350 lb. weights. There shouldn't be any real difference between the stress on the rope while climbing and being rescued/rescuing. Does that make sense to anyone besides me?

JOsh

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18 years 7 months ago - 18 years 7 months ago #123056 by Bradley Ford
Replied by Bradley Ford on topic weight limit?
Makes sense to me.

Suggests that I pose my original question again:

What is the weight limit for safely descending on a friction hitch with a dynamic climbing system?

Nick's idea of testing this myself may have to suffice as a single point of information, although I would be surprised if I were the first to perform such a test. Suggestions about performing this test welcome; I don't like the idea of using myself (or anyone) as weight for this test, since to find a limit I must produce at least one rapid, uncontrolled descent.

Brad

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