Ddrt ropes being use for SRT

[Pacafist]

Now I’m not trying to debate whether or not one type of rope versus the other is better or worse. Most of the arguments I’ve seen come up on this issue seems as though it comes down to personal preference.

However, a thought occurred to me. To preface, this may be more of a question for a material engineer, but I was thinking about why manufacturers may not advertise lines like the Yale 11.7 for Srt if they do work so well for some people (after the break in period of course).

The first thing to come to mind is that there may be a safety aspect. So there’s a break in period to get all of the stretch out of a 24 strand Yale 11.7, if you’re using that on ddrt, you’re using the rope on a 2:1 system, therefore, in theory, it would take the rope twice as long (if there is even enough force to push it to its limit) to stretch to its max limit than if you’re using the rope on a 1:1 system.
If you’re using this on an srt system you’re working on it 1:1 so you’re taking a rope that’s designed to be used on a 2:1 system and putting twice as much strain on the line.

The questions are;
a) with this all in mind, is the integrity of the rope deteriorating quicker being used as an Srt line when it Is designed and sold exclusively for the purpose of ddrt?
B) if you take all of the elasticity out of a ddrt line, will the cover and the core still be sharing the proper amounts force when loaded?
C) there are lines specifically designed for both srt and ddrt, and the changes in the designs of the rope are pretty distinct, it’s not like they’re making one small change to the line and then marketing it as a new hybrid line, so what makes those better?
D) is it safe to climb on a ddrt line at 1:1 ratio after one has taken as much elasticity out of it as possible? Does it change the properties of the rope? Should you retire it twice as soon as you normally would retire that specific rope when used as ddrt?
E) does none of it matter cuz we’re tree climbers and do everything to ropes that we shouldn’t be doing anyway

 

[rope-a-dope]

I was not aware that ropes are made to be used in exclusively one way...
Every rope i have is used both ways, so i have no "control" by which to compare what I observe in my gear inspections.
The same amount of friction/force is applied to the rope in order to hold the same climber in both climbing styles. In MRS that friction just happens at 2 locations that the rope moves thru, instead of 1 main location at the climbers harness.
If anything i would expect MRS to cause more wear/less life because of the 2:1 ratio. To come down 50', 100' of rope must travel thru your device and your anchor.

 

[DSMc]

You are talking work positioning climbing systems, not fall arrest. Modern ropes of both types are strong and a climbers weight while work positioning is not going to challenge their capacity, be it an MRS or SRS system.

 

[Pacafist]

You are talking work positioning climbing systems, not fall arrest. Modern ropes of both types are strong and a climbers weight while work positioning is not going to challenge their capacity, be it an MRS or SRS system.

I didn’t mention the climbers weight at any point in time, although yes that would be a factor to consider further down the line. And yes I am speaking along the lines of work positioning. I’m trying to get at the fact that when one is using a 24 strand line for srt, they are essentially wearing the core down to as little stretch as possible; and if anyone had insights as to how this may effect the integrity of the rope

 

[Pacafist]

I was not aware that ropes are made to be used in exclusively one way...
Every rope i have is used both ways, so i have no "control" by which to compare what I observe in my gear inspections.
The same amount of friction/force is applied to the rope in order to hold the same climber in both climbing styles. In MRS that friction just happens at 2 locations that the rope moves thru, instead of 1 main location at the climbers harness.
If anything i would expect MRS to cause more wear/less life because of the 2:1 ratio. To come down 50', 100' of rope must travel thru your device and your anchor.

Well I wouldn’t say they’re exclusively designed for only one type of use, yea ropes are strong but you wouldn’t use your climbing line for a rigging line I would hope. Ropes are designed to have certain purposes, and those purposes may overlap into other things, but that’s what I’m trying to address.

Also, due to the laws of physics, unless I’m understanding what you’re saying about the force factors, I have to disagree:
An anchor at the base of a tree going up through the an anchor in a tree and coming down to a climber of 200KN will have 200kN of force on the climbing side of line and 200kn of force on the anchored side of the line, placing 400kn of force at the anchor point in the tree.
If a 200kn climber is attached to a line that goes up to an isolated anchor, and then comes right back down to hisself, his force is distributed evenly between the two lines at 100kn. The anchor having 200kn at this point.

Yea there will be more wear and tear on a system that is moving across bark constantly and shifting through more line constantly, but the amount of force on the line is half of what it would be if you were climbing fixed line.

 

[RBJtree]

I didn’t mention the climbers weight at any point in time, although yes that would be a factor to consider further down the line. And yes I am speaking along the lines of work positioning. I’m trying to get at the fact that when one is using a 24 strand line for srt, they are essentially wearing the core down to as little stretch as possible; and if anyone had insights as to how this may effect the integrity of the rope

This is the elongation data for Yale 11.7 from Yale's website. It states the green part of the graph is 263 ft/lbs, which I guess is the ft/lb equivalent to the 650 lb suggested working load (10% abs) as you can see by the graph, we are no where near the total possible stretch of this rope, Ddrt or srt. My understanding is, it is fine to use "Ddrt rope" for srt, it just tends to be more stretchy then most srt climbers desire. Using "srt rope" for ddrt could pose a risk durring a fall arrest situation because it would not stretch enough to cushion the quick stop at the end of the fall. But strenght is more than adequate in any ofthe ropes we use for either method.

 

[evo]

This comes from a decade or two ago. Double braid lines were just becoming popular within the industry, then enter SRT and toothed mechanical ascenders.
The standard use to be 12 strand and 16 strand ropes, which can be used srt but shouldn’t be used with mechanical toothed ascenders as any sort of significant fall can cause the ascenders to part the line. These tools were designed to be used with kernmantle lines. Part of the safety feature is that the toothed cam shreds the cover bunching up the cover to decelerate the fall.
Double braids fall into a in between category.

Now with the modern rope walking techniques and tools which do not rely on toothed ascenders pretty much any rope can be used. Not that one would want to for very long.

 

[Pacafist]

RBJtree and evo, thank you very much for the info. I didn’t realize that graph was available for public information but it solves my question for sure in terms of the technical data is concerned. Awesome find and deduction.
And thank you evo for the history behind the developments of the ropes; it helps to explain the other aspects of my thoughts regarding the reason a rope was developed.

 

[RBJtree]

I've been studying rope elongation and effects of shock loading lately in hopes of being able to calculate accurately how much a rope will stretch when rigging down a big log over valuables. Yale is the only company I have found that publishes these kind of graphs.

 

[Pacafist]

I've been studying rope elongation and effects of shock loading lately in hopes of being able to calculate accurately how much a rope will stretch when rigging down a big log over valuables. Yale is the only company I have found that publishes these kind of graphs.

Have you come up with anything good?

 

[RBJtree]

http://www.yalecordage.com/featured-industries/arborculture/dynamic-energy-arborist-rope
This article explains how to do some of the calculations. The ISA and others have log weight charts published. Using Yale's charts and math, I should be able to calculate stretch at any certain load, but I haven't actually tried it yet. A factor that I am not sure about is if used ropes loose significant stretch.

 

[ATH]

.... a climber of 200KN will have 200kN of force on the climbing side of line and 200kn of force on the anchored side of the line, placing 400kn of force at the anchor point in the tree.
.....

There is no such thing as a "climber of 200KN".....for 2 reasons:
1) Kilonewtons measure force, not mass (or weight)
2) If it was a measure of mass (but it is not - kinda like saying "if orange were pink"...they both have red, but that doesn't make them the same) that 200KN person wouldn't be climbing trees...

 

[RBJtree]

There is no such thing as a "climber of 200KN".....for 2 reasons:
1) Kilonewtons measure force, not mass (or weight)
2) If it was a measure of mass (but it is not - kinda like saying "if orange were pink"...they both have red, but that doesn't make them the same) that 200KN person wouldn't be climbing trees...

Although kn is not a measure of weight, it is commonly accepted that 1 kn is equal to 224.81 pounds. So the 200 kn climber would weigh 44961.6985 lbs.

 

[ATH]

Lbs of force...not weight. Force is mass x acceleration - so it has to be in motion.
There is a difference and it matters.

I am not trying to pick nits, just trying to help a misunderstanding.

 

[John@TreeXP]

At the end of the day, I still like to single up and double down. I think the descent on a stationary line is more abrasive than a belay on a doubled rope, if you have enough rope. Sometimes though, its just more efficient to SRS up and down.

 

[Pacafist]

Lbs of force...not weight. Force is mass x acceleration - so it has to be in motion.
There is a difference and it matters.

I am not trying to pick nits, just trying to help a misunderstanding.

Weight is a measurement of force, it’s the mass of an object in conjunction with the pull of the earth’s gravitational field. F=ma, that’s why there is no exact translation between N and lbs. they’re different units all together.
And the numbers were just an example, Newton’s would’ve been more appropriate.

 

[rope-a-dope]

Well I wouldn’t say they’re exclusively designed for only one type of use, yea ropes are strong but you wouldn’t use your climbing line for a rigging line I would hope. Ropes are designed to have certain purposes, and those purposes may overlap into other things, but that’s what I’m trying to address.

Also, due to the laws of physics, unless I’m understanding what you’re saying about the force factors, I have to disagree:
An anchor at the base of a tree going up through the an anchor in a tree and coming down to a climber of 200KN will have 200kN of force on the climbing side of line and 200kn of force on the anchored side of the line, placing 400kn of force at the anchor point in the tree.
If a 200kn climber is attached to a line that goes up to an isolated anchor, and then comes right back down to hisself, his force is distributed evenly between the two lines at 100kn. The anchor having 200kn at this point.

Yea there will be more wear and tear on a system that is moving across bark constantly and shifting through more line constantly, but the amount of force on the line is half of what it would be if you were climbing fixed line.

Your points about a base anchor seeing greater force than an isolated MRS are totally valid. And i might be confused about the original nature of your question, but i always thought that the force/load applied exclusively to the rope and carried through its fibers would be the same between SRS and MRS. The tree branch union is subject to a change in force/load, that I am sure of. But if the climber is the same weight and pulling with the same force on the rope, does the rope itself do more work?
Im thinking of those mechanical advantage diagrams of block and tackle pulley systems that show how pulleys multiply forces. The increased work capacity is in the movement of the ANCHOR but the pull applied to the ROPE inside the system is always the constant.
Im not getting anywhere on this. The more I think the less i understand.
Does anyone get what im after? Is there a difference in the force transmitted thru the rope depending on how its routed?

 

[DSMc]

... This is all taken from a "standstill". Forces change if movement is applied...

More than most climbers are aware of. The force of a bounce from a climber has the potential to be captured, by friction, in the branch TIP. Old sailors understood this, it is a form of what is called sweating the line.

 

[rope-a-dope]

Well, not really.
What im asking about is the internal tension of the rope.
Ignoring the crotch, and how much tension is there in the rope at that magic spot where two legs of rope suddenly become the same thing?
I take one side of my rope off my MRS system and tie it to the tree. The branch my rope is over "feels" like im pulling on it harder. Does my rope "feel" like its getting pulled apart at the branch with 2x the force of my body weight?
Now i send up a runninbowline to the same branch and sit on the same single leg of rope. Is there now less tension inside the rope? There is less force on the branch, but im pulling the rope apart just as hard, the end still is immobile.
Another situation....a loop runner is pulled apart @ 24 kN. Take the same exact webbing and stitch it into an eye2eye (assuming the stitching = strength of webbing) , bend it around a round, immobile anchor and pull apart one side. Does it take 12 kN?

 

[ATH]

This is not accurate. W=mg. Force = mass x acceleration, where acceleration is on a celestial body, such as earth, acceleration is gravity. Your mass remains constant from planet to planet, your weight changes. Weight is a force. You can solve for your mass using w=mg, where weight is your weight on earth, g is earths gravity, and m=w/g.

Force does not have to be in motion. Motion is kinetic energy. Ke=1/2mv^2. Where v= speed ( or velocity) and m=mass.

When you step on a scale on earth, you are seeing your weight expressed as a force. My 245lbs of weight is a force.

Yes, yes - that is even more technically correct. I was just trying to address the statement of "...a climber of 200KN..." as simplistically as possible. Thanks for expanding/clarifying/correcting!!!