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What is the formula for calculating rope breaking strength?
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tpcollins


Aug 3, 2014, 4:38 AM
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What is the formula for calculating rope breaking strength?
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I thought I remember a formula to determine safe drop load for a rope as follows:

200# x 2' fall = 400#, plus original 200# load = 600# total

10% of 5000# rope rating = 500#

So a 200# weight falling 2' would exceed the 5000# rope rating - correct? Thanks.


sbaclimber


Aug 3, 2014, 11:48 AM
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tpcollins wrote:
So a 200# weight falling 2' would exceed the 5000# rope rating - correct? Thanks.
If you are talking a dynamic rope.....no.


dynosore


Aug 4, 2014, 12:23 PM
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tpcollins wrote:
I thought I remember a formula to determine safe drop load for a rope as follows:

200# x 2' fall = 400#, plus original 200# load = 600# total

10% of 5000# rope rating = 500#

So a 200# weight falling 2' would exceed the 5000# rope rating - correct? Thanks.

Unimpressed

No to all the above. Think. If a 2' fall would break a climbing rope, we'd all be dead.


Partner cracklover


Aug 6, 2014, 6:28 AM
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tpcollins wrote:
I thought I remember a formula to determine safe drop load for a rope as follows:

200# x 2' fall = 400#, plus original 200# load = 600# total

10% of 5000# rope rating = 500#

So a 200# weight falling 2' would exceed the 5000# rope rating - correct? Thanks.

Just so you know, climbers' ropes do not have working loads. They're not rated that way because they're not used in a way that demands it.

Climbers' ropes are designed not to hold <fill-in-the-blank> lbs, but to stretch to absorb* the force of a long fall. Apples and oranges.

On the other hand, climbers ropes do follow a formula that can be used to determine the approximate force put on the top piece of gear (the one holding the fall) and on the climber. Other ropes - ones with a rated breaking strength - may not have this.

With that said, maybe you can clarify your question to one we could answer?

Cheers,

GO

*By "absorb" I mean - to convert the kinetic energy of a falling body into heat in the rope fibers.


tpcollins


Aug 6, 2014, 3:25 PM
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Re: [cracklover] What is the formula for calculating rope breaking strength? [In reply to]
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Thanks cracklover - I have a Petzl Aspir harness, with carabiners attaching a 30" Metolous Dyneema Daisy Chain to a Prussic loop AND a Ropeman 1 (I'm a bit paranoid) that connects to a Bluwater 7/16" Assuatline as my lifeline. Everything is rated 23kN-27kN and I could fall 18" to a maximum of 24".

I'm about 185 pounds and want to make sure nothing will fail.


dr_feelgood


Aug 6, 2014, 7:26 PM
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tpcollins wrote:
Thanks cracklover - I have a Petzl Aspir harness, with carabiners attaching a 30" Metolous Dyneema Daisy Chain to a Prussic loop AND a Ropeman 1 (I'm a bit paranoid) that connects to a Bluwater 7/16" Assuatline as my lifeline. Everything is rated 23kN-27kN and I could fall 18" to a maximum of 24".

I'm about 185 pounds and want to make sure nothing will fail.


Yer gunna die!

Just sayin'


tpcollins


Aug 7, 2014, 5:26 AM
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Thanks, this forum has been very helpful.


kennoyce


Aug 7, 2014, 8:08 AM
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dr_feelgood wrote:
tpcollins wrote:
Thanks cracklover - I have a Petzl Aspir harness, with carabiners attaching a 30" Metolous Dyneema Daisy Chain to a Prussic loop AND a Ropeman 1 (I'm a bit paranoid) that connects to a Bluwater 7/16" Assuatline as my lifeline. Everything is rated 23kN-27kN and I could fall 18" to a maximum of 24".

I'm about 185 pounds and want to make sure nothing will fail.


Yer gunna die!

Just sayin'

Normally, this response is kind of a joke, but in this case I think it is correct. You are connected to a static line with a static daisy chain (body weight only at that) and could be falling 18 to 24 inches on that setup? This is seriously a recipe for disaster.

At a minimum, get a dynamic rope and ditch the static line, and switch out the daisy chain for a sling or a pas if you need the adjustability.


lena_chita
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Aug 7, 2014, 10:01 AM
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Re: [tpcollins] What is the formula for calculating rope breaking strength? [In reply to]
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Have you read this latest response to your previous thread on the subject?

While I agree with Kennoyce about undesirability of falling on static line, you can adjust your setup so you are not falling anything more than couple inches. And your rope and daisy will hold (though daisy chain is not optimal, and you have the rope, so why use daisy in addition to rope?)

Also, it seems like there are hunting-specific safety classes that cover this topic, and they will probably serve your purpose much better than this forum. Look them up in your area.


kennoyce


Aug 7, 2014, 10:57 AM
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Re: [lena_chita] What is the formula for calculating rope breaking strength? [In reply to]
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lena_chita wrote:
Have you read this latest response to your previous thread on the subject?

While I agree with Kennoyce about undesirability of falling on static line, you can adjust your setup so you are not falling anything more than couple inches. And your rope and daisy will hold (though daisy chain is not optimal, and you have the rope, so why use daisy in addition to rope?)

Also, it seems like there are hunting-specific safety classes that cover this topic, and they will probably serve your purpose much better than this forum. Look them up in your area.

Thanks, I didn't realize this was the same guy. yeah, as long as you're not free falling onto this setup it will be fine. With the OP I was thinking he was TR-soloing or something like that where he was dragging a prussic and a ropeman up below him on a static rope using the daisy to attach his harness to the prussic and ropeman.

For a tree stand he's probably okay.


amarius


Aug 7, 2014, 11:17 AM
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Perhaps safety harnesses and tethers used in sailing would be of more use?
Marine Tethers


tpcollins


Aug 7, 2014, 11:58 AM
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The lack of a little "bounce" for the 18"-24" drop has me seriously looking at this Beal Dynamic lanyard since the 75cm/30" is exactly what I want. I assume the 150 daN or 3272# rating is sufficient? My original concern was that I read online that the "safety" breaking strength factor for a rope was listed at 10% - therefore I thought someone here could help me understand this.

http://bealplanet.com/sport/anglais/longes-dynaclip.php


(This post was edited by tpcollins on Aug 7, 2014, 11:59 AM)


marc801


Aug 7, 2014, 12:11 PM
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tpcollins wrote:
The lack of a little "bounce" for the 18"-24" drop has me seriously looking at this Beal Dynamic lanyard since the 75cm/30" is exactly what I want. I assume the 150 daN or 3272# rating is sufficient? My original concern was that I read online that the "safety" breaking strength factor for a rope was listed at 10% - therefore I thought someone here could help me understand this.

http://bealplanet.com/sport/anglais/longes-dynaclip.php
First, the rating on that item is a "resistance" of 1500 daN, which they also refer to as "breaking load". Secondly you're still incorrectly equating force figures of dynamic devices to breaking strength. They're related but not the same. You're also looking at dynamic and static ropes/devices as identical - they're not. You'll be fine with the Beal lanyard.


socalclimber


Aug 7, 2014, 6:27 PM
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As a general rule ropes don't break, they cut. You might want to look into Gym ropes. They are "semi" dynamic. In other words, not quite static, not quite dynamic.


jacques


Aug 21, 2014, 10:11 AM
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tpcollins wrote:
Thanks cracklover - I have a Petzl Aspir harness, with carabiners attaching a 30" Metolous Dyneema Daisy Chain to a Prussic loop AND a Ropeman 1 (I'm a bit paranoid) that connects to a Bluwater 7/16" Assuatline as my lifeline. Everything is rated 23kN-27kN and I could fall 18" to a maximum of 24".

I'm about 185 pounds and want to make sure nothing will fail.

The astm test is wrote on the rope. It is 12 KN maximum. Most of the rope today is 10 KN, that means a weight of a 1000KN or 2 200 poundsin a fall for a climber of 80 kilogram (176 pounds) so you are in the range and you can take a fall factor two with your rope without danger of falling. ordinarly, the static limit of an astm rope is 2400 kg, or 4 800 pounds. The rope will cut before they broke, except if your rope is older than five years or badly used.

too much think between the rope and you is also a mistake. I use an ascendedr directly on a locking carabiner to my harnest and a shunt with a sling to my harnest to have redundancy. clear, easy to check too.


majid_sabet


Aug 21, 2014, 1:44 PM
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just use the simple safety factor of 10:1

if you consider yourself as 1 KN (100kg climber falling at gravity rate of 9.8m/s)then your rope must be rated to 10KN or higher


tpcollins


Aug 21, 2014, 7:20 PM
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Thanks Majid, I knew I had read that 10% thingy somewhere.


marc801


Aug 22, 2014, 9:26 AM
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Oh dear god... Majid and Jaques giving rope physics advice to a non-climber hunter.
What has RC become?


JimTitt


Aug 22, 2014, 10:33 AM
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marc801 wrote:
Oh dear god... Majid and Jaques giving rope physics advice to a non-climber hunter.
What has RC become?

IŽll admit their replies made my eyebrows twitch, then I decided to go and do something worthwhile rather than replying.


tpcollins


Aug 22, 2014, 11:58 AM
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I didn't know so many rock climbers were actually liberals but I do appreciate the help. Smile


dr_feelgood


Aug 22, 2014, 1:39 PM
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tpcollins wrote:
I didn't know so many rock climbers were actually liberals but I do appreciate the help. Smile

T0-


sbaclimber


Aug 22, 2014, 2:06 PM
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marc801 wrote:
Oh dear god... Majid and Jaques giving rope physics advice to a non-climber hunter.
What has RC become?
What RC was destined to become. Sometimes you just can't avoid fate...Tongue


Partner rgold


Aug 24, 2014, 10:53 PM
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tpcollins wrote:
I have a Petzl Aspir harness, with carabiners attaching a 30" Metolous Dyneema Daisy Chain to a Prussic loop AND a Ropeman 1 (I'm a bit paranoid) that connects to a Bluwater 7/16" Assuatline as my lifeline. Everything is rated 23kN-27kN and I could fall 18" to a maximum of 24".

I'm about 185 pounds and want to make sure nothing will fail.

TP, I'm not trying to bust your balls (I'll leave that to the harness), but could you perhaps explain why you aren't using one of the products specifically made for hunters in tree stands? The set-up you are using is kludged together from components meant for other uses, and other than the harness, none of them is meant to arrest falls of any size.

A number of people have explained that the issue isn't braking strength per se, it is peak load. You could use a steel cable and have no breaking strength worries, but a two-foot fall would almost certainly produce internal injuries and might also break your back if you fall backwards. The rig you have absolutely has to be tightened up so that the most you can fall is an inch or two, otherwise you might be sorry you didn't just fall out of the tree and die.

If you can't have a system that limits all possible falls to inches, then you must have a system with shock-absorbing capability. Climbers use dynamic climbing ropes from this, that stretch to absorb fall energy without producing peak loads the body can't sustain. My guess is the hunting rigs are probably like industrial fall arresters, which include something that purposely rips stitches under load in order to absorb fall energy.

By the way, if you are going to fall two feet or so, you could end up hanging in space from your harness. If you are unconscious for a while, you may be subject to suspension trauma (aka harness hang syndrome), which is a very dangerous condition. Even if conscious, it would be very wise to practice how you will get back from hanging into the stand.

You mentioned getting electrical advice from electricians. Well I'm your electrician, my friend, and my advice is not to try to wire your own damn house. In other words, sell all that stuff for whatever you can recoup and buy something specifically designed for tree stand fall protection.


rocknice2


Aug 25, 2014, 6:48 AM
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tpcollins wrote:
Thanks, this forum has been very helpful.

This forum has been extremely helpful. You just haven't taken any of the advice given to you.

Get a dynamic or semi-static rope not a full static.
Buy a GriGri.
You already have a prussic and a Ropeman, just choose one to work with.
This setup will be shock absorbing and will allow you to descend and ascend a rope easily.

Dynamic rope will allow for the most shock absorption.
Semi-static will still allow for short falls but will be easier to climb up on.
Full static will bust you up if you take any fall greater than a few inches.


tpcollins


Aug 25, 2014, 7:10 AM
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Actually I have taken advice here and have changed my lanyard to the Beal Dynaclip which is made of dynamic rope. I saw a video online comparing various tests on daisy chains (that I first bought) showing them breaking on a short impact. The Beal stretched like a rubber band and didn't break - that's what I'll be using. And this lanyard will be kept snug all the time to the attachment line so if I do fall, I won't fall far.

I do have a Tree Spider treestand harness which is one of the best available. However, if I fall with the rear attached tether, I would be hanging forward thereby putting pressure on the femoral artery as well as being faced away from the tree.

I've tested both setups from a rafter in my garage and the Petzl harness does not put any pressure on the femoral artery like the Tree Spider does, plus with the lanyard tied into the front, I feel I have a better chance of getting back facing towards the tree for self rescue. Plus my lifeline is situated inline with my climbing sticks to aid in self rescue. If I became unconscious and then fell out of the stand, I believe my survival chances increase with the Petzl.

Thanks again for the help.

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