how much force is put on the TIP branch as opposed to DRT say 200 lb climber
SRT Question
- Thread starter irish93stang
- Start date
If the other end of your rope is tied to the base of the tree then you are putting double your weight on the tip branch. 200lb climber goes to 400lbs. The nice thing about single rope is that if your tip branch breaks you usually have a ton of backups, depending on how you set your line. something you don't get with double rope.
ok thanks for the quick response
southsoundtree
Been here much more than a while
- Location
- Olympia, WA
Somewhat less than 400 pounds, but basically double. Some of the reactive force (the second 200 pounds, or somewhat less) is reduced due to the friction over the branch. A zero friction pulley point would result in a full 200 pounds.
Remember to keep your TIP as close to the union as possible, and bounce test if in question at all, or even if you don't question.
Remember to keep your TIP as close to the union as possible, and bounce test if in question at all, or even if you don't question.
- Location
- Basel, Switzerland
Jako,
I would disagree that the fact that you line runs over multiple branches can be seen as a back-up.
Depending on the distance between the limbs, in case of the failure of one of the limbs this might result in a major dynamic drop onto a cammed device, i.e. chest or hand ascender. The result of this can be damage to the cover and/ core of your line, damage and/ or failure of the device, severing of the line.
It won't take an astronomically high impact force to cause major damage to the climbing line... the exact degree of damage depends upon multiple factors- amongst other things – upon the combination of mechanical devices and climbing line.
The baseline is that you should be equally diligent when setting lines regardless of whether you intend to use a doubled line or a single line, you should also consider that in case of an emergency the TIP may need to bear the weight of two climbers...
Regards,
Mark.
I would disagree that the fact that you line runs over multiple branches can be seen as a back-up.
Depending on the distance between the limbs, in case of the failure of one of the limbs this might result in a major dynamic drop onto a cammed device, i.e. chest or hand ascender. The result of this can be damage to the cover and/ core of your line, damage and/ or failure of the device, severing of the line.
It won't take an astronomically high impact force to cause major damage to the climbing line... the exact degree of damage depends upon multiple factors- amongst other things – upon the combination of mechanical devices and climbing line.
The baseline is that you should be equally diligent when setting lines regardless of whether you intend to use a doubled line or a single line, you should also consider that in case of an emergency the TIP may need to bear the weight of two climbers...
Regards,
Mark.
what about the stresses from a double footlock ascent? just trying to get a grasp on the physics
- Location
- Hawaii
I've seen climbers use a shock absorber?? on the end of the line where they attach to the tree that is supposed to dampen the shock load. I think some have taken them off of old fall protection lanyards.
jp
jp
- Location
- Basel, Switzerland
Well, that would depend on where you place the shock absorber, wouldn't it? And upon which device gets hit first - this is not entirely easy to solve, can be done - but needs careful thinking through.
Again, there's an obvious remedial action you can take, which is to be careful when selecting anchor points and not be complacent because you're under the impression you're backed up by a limb three meters beyond your main TIP, for instance. This is not a backup.
Again, there's an obvious remedial action you can take, which is to be careful when selecting anchor points and not be complacent because you're under the impression you're backed up by a limb three meters beyond your main TIP, for instance. This is not a backup.
- Location
- south carolina
Mark, this is a good point and if I'm honest, I have had branches break on the fall side of this kind of SRT tie off. This resulted in quite a drop, it was a somewhat bungee drop, but not fun and I'm sure, not very safe. Again, these weren't branches that broke above my TIP but below, on the opposite side of the tree, where my rope was comming back down from the TIP. They broke creating slack and fall potential in my system. I'm just glad it happened pretty low and that I wasn't hovering over a large limb or something when it happened.
I don't tie off this way any more, unless there is a very good reason to do so. I don't attach myself to my ascender either for the reasons that you mentioned above. The way I ascend wouldn't be allowed in a comp., I don't think, but I think it is safer than being attached to the ascender.
I don't tie off this way any more, unless there is a very good reason to do so. I don't attach myself to my ascender either for the reasons that you mentioned above. The way I ascend wouldn't be allowed in a comp., I don't think, but I think it is safer than being attached to the ascender.
southsoundtree
Been here much more than a while
- Location
- Olympia, WA
[ QUOTE ]
what about the stresses from a double footlock ascent? just trying to get a grasp on the physics
[/ QUOTE ]
When you have a rope doubled over the branch for footlocking with you weight on both strands, it is entirely different than having the rope doubled over a branch with you weight on one side, and the other side tied off.
In the footlocking situation, or a doubled rope technique (ignoring friction in the latter case) your 200 pound body weight is basically split to 100 pounds of force on each side of the rope.
When SRTing with a rope choked around the stem at the top of the tree, you have 200 pounds on the rope.
Let's say that you are SRTing with the rope redirected over a branch (ignore friction for a minute) back to the ground level where have the rope anchored to a 200 pound friend's harness, you can climb with your 200 pounds of weight on the one side of the branch, and your friend's 200 pounds of weight on the other side of the branch, with the rope staying stationary.
You can see that the redirection branch has 400 pounds of load on it, right? 200 on each side combines to 400.
Now, go to the normal SRT scenario where you are tying onto the base of the tree. In order for the rope to stay stationary, there needs to be force equal to your weight to keep the rope stationary. Ignoring friction, the redirection branch still experiences 400 pounds of force.
Now consider friction. If you have 50 pounds of friction force of the rope over the crotch, the force to balance your 200 pounds would be 150 pounds, with a net force on the redirection crotch of 200+150= 350 pounds of force.
This is the same reason that rigging through a pulley (ignoring friction) results in the pulley anchor point experiencing double the load, and a pulley on a the end of a rope over a crotch double doubling the force, so the crotch supporting the rope experiences quadruple the force.
Does this compute?
what about the stresses from a double footlock ascent? just trying to get a grasp on the physics
[/ QUOTE ]
When you have a rope doubled over the branch for footlocking with you weight on both strands, it is entirely different than having the rope doubled over a branch with you weight on one side, and the other side tied off.
In the footlocking situation, or a doubled rope technique (ignoring friction in the latter case) your 200 pound body weight is basically split to 100 pounds of force on each side of the rope.
When SRTing with a rope choked around the stem at the top of the tree, you have 200 pounds on the rope.
Let's say that you are SRTing with the rope redirected over a branch (ignore friction for a minute) back to the ground level where have the rope anchored to a 200 pound friend's harness, you can climb with your 200 pounds of weight on the one side of the branch, and your friend's 200 pounds of weight on the other side of the branch, with the rope staying stationary.
You can see that the redirection branch has 400 pounds of load on it, right? 200 on each side combines to 400.
Now, go to the normal SRT scenario where you are tying onto the base of the tree. In order for the rope to stay stationary, there needs to be force equal to your weight to keep the rope stationary. Ignoring friction, the redirection branch still experiences 400 pounds of force.
Now consider friction. If you have 50 pounds of friction force of the rope over the crotch, the force to balance your 200 pounds would be 150 pounds, with a net force on the redirection crotch of 200+150= 350 pounds of force.
This is the same reason that rigging through a pulley (ignoring friction) results in the pulley anchor point experiencing double the load, and a pulley on a the end of a rope over a crotch double doubling the force, so the crotch supporting the rope experiences quadruple the force.
Does this compute?
- Location
- Retired in Minneapolis
During one of my SRT itterations I incorporated a Yates Screamer into the rig at my harness. Adding the screamer on MY end would reduce the impact load on ME.
After talking with Paolo/Laz we calculated the stretch in Tachyon and realized that there is plenty of shock loading capability in just the rope.
This discussion needs to go on. But, like some folks have pointed out, if you do take a fall you're likely going to get hurt or damaged. Don't count on Screamers or rope stretch when you setup your climb.
This thinking is like holding onto your seatbelt buckle and thinking that you're going to be able to clip it in the moment before there is an accident. NOT!
After talking with Paolo/Laz we calculated the stretch in Tachyon and realized that there is plenty of shock loading capability in just the rope.
This discussion needs to go on. But, like some folks have pointed out, if you do take a fall you're likely going to get hurt or damaged. Don't count on Screamers or rope stretch when you setup your climb.
This thinking is like holding onto your seatbelt buckle and thinking that you're going to be able to clip it in the moment before there is an accident. NOT!
The attached article highlights how dangerous it is to have even a small, 'back-up' branch break when you have your SRT line set up through the crown and tied off at the base.
The article shows how the mantle of a kernmantle construction 'static' rope as commonly used for SRT can be severed with a dynamic force of as little as 4kn. In tests they were able to generate this force with a 100kg weight falling only 500mm. Scary!
The more I read about SRT the more concerned I am. It is too easy to be pushed for time and accept a less than desirable TIP which could so easily turn nasty.
The article shows how the mantle of a kernmantle construction 'static' rope as commonly used for SRT can be severed with a dynamic force of as little as 4kn. In tests they were able to generate this force with a 100kg weight falling only 500mm. Scary!
The more I read about SRT the more concerned I am. It is too easy to be pushed for time and accept a less than desirable TIP which could so easily turn nasty.
- Location
- Perrysburg, Ohio, U.S.A.
"The more I read about SRT the more concerned I am. It is too easy to be pushed for time and accept a less than desirable TIP which could so easily turn nasty. "
I totally disagree. It is just as easy to be pushed for time with a doubled rope system. To blame the climbing method for a climber's lack of concern for their own safety is absolutely ridiculous.
There has been a nasty trend that myself and some other climbers in my area have been noticing, that too many climbers are putting the responsibility for their safety on the systems, and not on themselves. If I pick a bad TIP and fall to my death, whos fault is it? MINE!!! Not the Allgear rope I use, or the Hitchlimber I use, or the Oceans Dyneema I use, or the Ergovation I use. MY FAULT. If someone has a concern that a technique is unsafe, then dont use it. But my God, its your own responsibility to keep yourself safe, not the manufacturers!
Why are so many people on here looking for reasons to call SRT unsafe? And Im not trying to pick on you, browncow, I apologize if it seems that way. It is as safe as any other climbing method, if not more so, but so many people are trying to invalidate it as a viable work practice. I can pick apart doubled rope technique just as easily, or footlocking, but I wouldnt, because there is risk inherent in EVERY technique we use. To take jabs at one and not others is asinine.
I totally disagree. It is just as easy to be pushed for time with a doubled rope system. To blame the climbing method for a climber's lack of concern for their own safety is absolutely ridiculous.
There has been a nasty trend that myself and some other climbers in my area have been noticing, that too many climbers are putting the responsibility for their safety on the systems, and not on themselves. If I pick a bad TIP and fall to my death, whos fault is it? MINE!!! Not the Allgear rope I use, or the Hitchlimber I use, or the Oceans Dyneema I use, or the Ergovation I use. MY FAULT. If someone has a concern that a technique is unsafe, then dont use it. But my God, its your own responsibility to keep yourself safe, not the manufacturers!
Why are so many people on here looking for reasons to call SRT unsafe? And Im not trying to pick on you, browncow, I apologize if it seems that way. It is as safe as any other climbing method, if not more so, but so many people are trying to invalidate it as a viable work practice. I can pick apart doubled rope technique just as easily, or footlocking, but I wouldnt, because there is risk inherent in EVERY technique we use. To take jabs at one and not others is asinine.
[ QUOTE ]
[ QUOTE ]
what about the stresses from a double footlock ascent? just trying to get a grasp on the physics
[/ QUOTE ]...You can see that the redirection branch has 400 pounds of load on it, right? 200 on each side combines to 400.
[/ QUOTE ]
I would add to this that you definitely don't want to ignore the dynamic force involved in footlocking. Each upward thrust with the legs probably easily doubles the climber's effective weight, essentially a non-stop bounce test all the way to the top. That best-case 400 lbs. is now 800 lbs., maybe even more.
[ QUOTE ]
what about the stresses from a double footlock ascent? just trying to get a grasp on the physics
[/ QUOTE ]...You can see that the redirection branch has 400 pounds of load on it, right? 200 on each side combines to 400.
[/ QUOTE ]
I would add to this that you definitely don't want to ignore the dynamic force involved in footlocking. Each upward thrust with the legs probably easily doubles the climber's effective weight, essentially a non-stop bounce test all the way to the top. That best-case 400 lbs. is now 800 lbs., maybe even more.
[ QUOTE ]
I totally disagree. It is just as easy to be pushed for time with a doubled rope system. To blame the climbing method for a climber's lack of concern for their own safety is absolutely ridiculous.
There has been a nasty trend that myself and some other climbers in my area have been noticing, that too many climbers are putting the responsibility for their safety on the systems, and not on themselves.
[/ QUOTE ]
I agree, well said and it's not just climbers.
Dave
I totally disagree. It is just as easy to be pushed for time with a doubled rope system. To blame the climbing method for a climber's lack of concern for their own safety is absolutely ridiculous.
There has been a nasty trend that myself and some other climbers in my area have been noticing, that too many climbers are putting the responsibility for their safety on the systems, and not on themselves.
[/ QUOTE ]
I agree, well said and it's not just climbers.
Dave
- Location
- Perrysburg, Ohio, U.S.A.
[ QUOTE ]
[ QUOTE ]
[ QUOTE ]
what about the stresses from a double footlock ascent? just trying to get a grasp on the physics
[/ QUOTE ]...You can see that the redirection branch has 400 pounds of load on it, right? 200 on each side combines to 400.
[/ QUOTE ]
I would add to this that you definitely don't want to ignore the dynamic force involved in footlocking. Each upward thrust with the legs probably easily doubles the climber's effective weight, essentially a non-stop bounce test all the way to the top. That best-case 400 lbs. is now 800 lbs., maybe even more.
[/ QUOTE ]
Good point here. I think the bottom line that needs to be stressed here is that there are dynamic forces at work everywhere in tree climbing, and its up to the end use climber to understand the forces they are imparting on the tree and their gear.
[ QUOTE ]
[ QUOTE ]
what about the stresses from a double footlock ascent? just trying to get a grasp on the physics
[/ QUOTE ]...You can see that the redirection branch has 400 pounds of load on it, right? 200 on each side combines to 400.
[/ QUOTE ]
I would add to this that you definitely don't want to ignore the dynamic force involved in footlocking. Each upward thrust with the legs probably easily doubles the climber's effective weight, essentially a non-stop bounce test all the way to the top. That best-case 400 lbs. is now 800 lbs., maybe even more.
[/ QUOTE ]
Good point here. I think the bottom line that needs to be stressed here is that there are dynamic forces at work everywhere in tree climbing, and its up to the end use climber to understand the forces they are imparting on the tree and their gear.
- Location
- Basel, Switzerland
I can't quite relate to the way people seem to get really tripped up on how they access a tree.
For me whether you use SRT systems or FL a doubled line is entirely down to personal preference, physique, technical competence, style etc.
Or maybe you use both.
How much time per day do we spend in access. Five minutes? Tops! There's other issues I can get much more excited about.
Such as anchor points: Anchor points need to be sufficiently dimensioned! Nothing subjective or discretionary about that... an anchor point is either good or bad.
Access trees in whichever way you like, but choose good TIP's to do so.
For me whether you use SRT systems or FL a doubled line is entirely down to personal preference, physique, technical competence, style etc.
Or maybe you use both.
How much time per day do we spend in access. Five minutes? Tops! There's other issues I can get much more excited about.
Such as anchor points: Anchor points need to be sufficiently dimensioned! Nothing subjective or discretionary about that... an anchor point is either good or bad.
Access trees in whichever way you like, but choose good TIP's to do so.
[ QUOTE ]
... Each upward thrust with the legs probably easily doubles the climber's effective weight, essentially a non-stop bounce test all the way to the top. That best-case 400 lbs. is now 800 lbs., maybe even more.
[/ QUOTE ]
It is always good to test your assumptions. This one was pretty far off the mark. I just tested this with my load cell, which conveniently remembers the highest reading until its memory is cleared. Just hanging on my SRT line I measured 166 lbs. A very vigorous upward lunge only got me up to 224 lbs., or an increase of 35%. I am sure others could increase that figure, but I doubt very much that anyone, in ordinary SRT operations, would go much beyond that.
... Each upward thrust with the legs probably easily doubles the climber's effective weight, essentially a non-stop bounce test all the way to the top. That best-case 400 lbs. is now 800 lbs., maybe even more.
[/ QUOTE ]
It is always good to test your assumptions. This one was pretty far off the mark. I just tested this with my load cell, which conveniently remembers the highest reading until its memory is cleared. Just hanging on my SRT line I measured 166 lbs. A very vigorous upward lunge only got me up to 224 lbs., or an increase of 35%. I am sure others could increase that figure, but I doubt very much that anyone, in ordinary SRT operations, would go much beyond that.
it seems that the safest way to access a tree using SRT with ascenders as far as weight and only weight goes is to tie your rope off to your TIP as apposed to the base of the tree, eliminating any excessive force on your branch. I had no idea how little margin of error there was for dropping on ascenders without cutting into the rope, thanks for the heads up. Bottom line I definitley agree with shawn as far as the responsibility of the climber deciding his or her own safety...it's always been on us to make sure we get home safe at the end of the day.
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