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Why not use dynamic rope for one-sticking?

raisins

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I think you're on the right track. The biggest difference between static and dynamic rope in a fall is the amount of time that it takes to resolve the momentum and end the collision. Dynamic ropes buy you more time to resolve the forces by extending their length.

A dynamic rope that extends the collision time in a fall will reduce forces on the body compared to a static rope. How much reduction is the big question and there are so many variables that lab testing with some high tech dummies/equipment would be needed before we could come to any data driven conclusions.

The equation used to express the collision is derived from newtonian physics (f=ma). It's the impulse-momentum equation if you're interested in researching more on it.
Thanks, it seems to trade seconds for distance and abstracts away from the work concept towards momentum. I believe that the work equation is interchangeable with kinetic energy (m*a*d = 1/2 m*v*v....if we neglect energy at start).

The useful bit (F*change in time OR seconds) expands to mass * m/(s*s) *s, I believe.

So, the more seconds (rope stretch) to decelerate from free fall to zero (hanging on rope) then the less the deceleration has to be at any single instant in time. Even if you only increase the rope stretch time from 0.1 seconds to 0.2 seconds, you've still cut the force of deceleration in half. I think this happens so quickly in real life that it steps around our common sense (we don't see collisions and their aftermath closely enough to notice this and incorporate into our daily understanding).

Sound about right?

If I get time, I'll work a toy problem both ways and see if the answers compare.
 

BTaylor

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Every time I read one of these threads every half year or so I wonder why I one stick. Makes me think long and hard about 2TCing, or at least one sticking with only one aider step and advancing the tether more than once per stick placement. Less slack should equal less risk.
Exactly why I am switching to the JRB cinch climb method, no slack means no fall. Might swing around a bit if you lose footing or something but no fall is appealing, esp since I am not a youngling anymore.
 

dubbeltap69

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As a rock climber I've learned the difference between taking a fall on a static rope vs. a dynamic rope. The height of the fall doesn't matter on a dynamic rope as it stretches, that is not the case for a static rope. I hope to never experience a fall while using a static rope as my back is already jacked up, which is why I use a dynamic rope. Most of the gear we saddle hunters use, carabiners especially, are NOT rated for use with a static rope. Just my $0.02.....
 
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_Dario

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I have to respectfully disagree that the height of the fall doesn’t matter. It is one half of the fall factor equation. It matters A LOT
 
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Fl Canopy Stalker

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As a rock climber I've learned the difference between taking a fall on a static rope vs. a dynamic rope. The height of the fall doesn't matter on a dynamic rope as it stretches, that is not the case for a static rope. I hope to never experience a fall while using a static rope as my back is already jacked up, which is why I use a dynamic rope. Most of the gear we saddle hunters use, carabiners especially, are NOT rated for use with a static rope. Just my $0.02.....
I wouldn’t say carabiners aren’t rated. The break strength of carabiners are all formulated using static pulls. However going hand in hand with what you said, it’s this reason that makes me use tatical d carabiners. As the elongated d shape is the strongest shape of carabiner. Pear or modified d being the happy median and the oval carabiner shape is the weakest.
 

dubbeltap69

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I wouldn’t say carabiners aren’t rated. The break strength of carabiners are all formulated using static pulls. However going hand in hand with what you said, it’s this reason that makes me use tatical d carabiners. As the elongated d shape is the strongest shape of carabiner. Pear or modified d being the happy median and the oval carabiner shape is the weakest.
Yes, you are correct also. I should have stated, "Aluminum carabiners which almost everyone uses, are not rated for falls using a static rope."
 

_Dario

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You are correct. How about "It doesn't matter as much when using a dynamic rope."
well that’s what this thread is about and my whole argument is that it really doesn’t matter at all if you are using a dynamic rope or static rope. We’re talking about a 4 or 5 foot fall with virtually the same amount of rope. You are not afforded the luxury of 30 feet of dynamic rope clipped to your harness. On top of that we are talking about landing into fall restraint devices and not even fall arrest devices. It’s just a bad idea. You can go through simulations, dummies, cutting edge sensor placement. Or you can wear a linesman belt and the whole thing is moot.
 

Fl Canopy Stalker

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Yes, you are correct also. I should have stated, "Aluminum carabiners which almost everyone uses, are not rated for falls using a static rope."
It’s also one of the reasons I stay away from Kong ducks and Ropeman 1’s nowadays.
 

raisins

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I wouldn’t say carabiners aren’t rated. The break strength of carabiners are all formulated using static pulls. However going hand in hand with what you said, it’s this reason that makes me use tatical d carabiners. As the elongated d shape is the strongest shape of carabiner. Pear or modified d being the happy median and the oval carabiner shape is the weakest.
links to a few for reference?
 

raisins

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Every time I read one of these threads every half year or so I wonder why I one stick. Makes me think long and hard about 2TCing, or at least one sticking with only one aider step and advancing the tether more than once per stick placement. Less slack should equal less risk.
12 treehopper polymer steps with attachment daisy chains and carry sacks is 4.5 lbs total

i might switch to aluminum pioneer steps this year and get the total weight down to around 3.5 lbs

easy to climb with a tether and lineman's both in play (advancing both each step) and the further fall if 2 feet (between step length)
 

raisins

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It’s also one of the reasons I stay away from Kong ducks and Ropeman 1’s nowadays.
Off topic, but do you have a reference for the fall used to determine dynamic elongation of climbing ropes?

With dynamic elongations of 28 percent like this one


you're getting well over a foot of stretch on a fall with 6 feet of rope if the 28 percent is achieved.

interesting graphs of force vs elongation
 

Fl Canopy Stalker

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There are also links on petzl
links to a few for reference?
The tree stuff article is a long long article but when you get to shape, it has to do with how much of the load transfer is put on the solid aluminum side of the carabiner vs how much load transfer is placed on the gate. The gate is always the wink point in a carabiner. An oval places even amounts of force on each side therefore it’s the weakest. The pear or modified shape places a little more on the solid side away from the gate. It also has a wider opening on one end so it’s great for loads requiring wider points of attachment. The D shaped carabiner places the most load onto the solid side of the carabiner so it is the stronger at shape. However a d isn’t really compatible with ascenders or descenders (even if it fits through them, it’s no longer keeping the load to the stronger side) and it usually has the smallest gate opening. The small gate openings do not bother me because my prusik nor my bridge are bigger than the .71” opening and I usually do not use ascenders. Even if I did though the d in that configuration would still be stronger than the ascender so it’s still not my weak point.
 

Fl Canopy Stalker

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Off topic, but do you have a reference for the fall used to determine dynamic elongation of climbing ropes?

With dynamic elongations of 28 percent like this one


you're getting well over a foot of stretch on a fall with 6 feet of rope if the 28 percent is achieved.

interesting graphs of force vs elongation
I’d have to research the internet some to find you links for reference. Here is a great article on dynamic ropes. Testing, markings, elongations all explained:
 

Fl Canopy Stalker

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Th
Off topic, but do you have a reference for the fall used to determine dynamic elongation of climbing ropes?

With dynamic elongations of 28 percent like this one


you're getting well over a foot of stretch on a fall with 6 feet of rope if the 28 percent is achieved.

interesting graphs of force vs elongation
The problem with the 1’ on 6’ is that the biggest contributor to the stretch absorption is where your connection point is. So even though you’ll get some extra stretch from the eye and portion of the rope wrapped around the tree, the largest portion of force absorption is going to be between your prusik and where the tail of rope you hang on exits the eye. That portion is going to do the bulk of the stretch and force absorption. The rest of the rope wrapped on the tree is more secondary and won’t help as much because of its friction around the tree. This is similar to how a connection point on a platform strap only sees a small portion of the overall weight placed on the platform. So you might get a foot of stretch but the first 4” are handling a bulk of the load and while one sticking your fall factor could easily be 1.5 or even 2 : 1. So a 1.5’ fall on 1.5’ of rope would hurt but 2.5’ fall on that 1.5’ would hurt even more. This is my biggest issue with one sticking. I have tried to create contraptions and used different connection concepts, I can’t find a way to eliminate the slack from the system. Using a linesman rope is difficult on aiders, which could cause someone who doesn’t practice it to fall as well but it’s the only way to minimize slack while one sticking. It’s doable but hard.
 

hauscaliber

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Thanks, it seems to trade seconds for distance and abstracts away from the work concept towards momentum. I believe that the work equation is interchangeable with kinetic energy (m*a*d = 1/2 m*v*v....if we neglect energy at start).

The useful bit (F*change in time OR seconds) expands to mass * m/(s*s) *s, I believe.

So, the more seconds (rope stretch) to decelerate from free fall to zero (hanging on rope) then the less the deceleration has to be at any single instant in time. Even if you only increase the rope stretch time from 0.1 seconds to 0.2 seconds, you've still cut the force of deceleration in half. I think this happens so quickly in real life that it steps around our common sense (we don't see collisions and their aftermath closely enough to notice this and incorporate into our daily understanding).

Sound about right?

If I get time, I'll work a toy problem both ways and see if the answers compare.
Yes, increasing collision times during split seconds can have a dramatic reduction of forces on the body. That's one of the reasons how air bags are effective during vehicle crashes (along with enlarging surface area to reduce stress on the body).
 

_Dario

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I think it’s really not that hard (LB plus 3 step aider) once you practice and understand to put your weight back into your LB rather then climb like a traditional ladder.

What I do think is hard and dangerous is advancing your tether while still in the aider
 
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