Why not use dynamic rope for one-sticking?

[raisins]

I’m not conflating anything. I understand the differences here. And my setup does not transfer the load to my body over 1-2 square inches. More like 1-2 square feet. My entire booty, up around my hips, and potentially part of my thighs and crotch. Your setup may be different. But certainly in that orientation the greatest concern is the effect on the spine, so I’d think surface area is not a great indicator regardless.

no one falls and hits the ground perfectly spreading the force over their bodies and i don't know where anyone would get 1 to 2 square inches

no careful testing has been done and no one has ran the math in this specific scenario (fall factor of 1 on a static line with a tree saddle and what that does to the body) in the correct way (a way that would pass peer review) so we are all spit balling somewhat and so it comes down to force of personality and who can sound more authoritative and who wants to be right the most

i don't know if it matters in the end, but the only thing i'm willing to state nearly definitively is that a dynamic rope cannot be worse than a static rope in these scenarios....either equal or somewhat better

appealing to "a 6 foot fall is still going to snap your back" isn't convincing to me, what about a 6 inch fall on dynamic vs. static? is that the difference between ouch that hurt and physical therapy for 2 months? no one knows and so arguing it is somewhat pointless.....and the 6 inch fall/slip is more common than a 1.5 factor fall

we then get into something akin to the sunk cost fallacy....

 

[Exhumis]

It would be interesting to see some practical testing. Not just for dynamic v. static, but for falls in general that saddle hunters might encounter. Someone said something along the lines of "best case scenario, you'll be eating from a straw either way". I think that's a bit strong when talking about 4-6 ft falls. The How not to Highline guy made a good point in one of his videos. A lot of the data supporting that line of thinking is from lab tests using steel blocks and steel anchor points, cables, etc. Basically immovable objects. We on the other hand are bags of water, and the rest of our rigging and gear introduces even more movement and flexibility into the rig.

Be interesting to see some real-world tests is all I'm saying.

Here you go. Maths:

Forces at work in a real fall - Petzl USA

www.petzl.com

Fall factor and impact force - theory - Petzl USA

www.petzl.com

 

[raisins]

Here you go. Maths:

Forces at work in a real fall - Petzl USA

www.petzl.com

Fall factor and impact force - theory - Petzl USA

www.petzl.com

thanks for the links that explain fall factor well

still doesn't address a question like 'if you take a 6 inch slip and fall in a saddle with X length of rope involved (i believe that bridge and tether length should be considered including the amount of rope wrapped around the tree), then how hard is it on you with a static rope vs a dynamic rope?"

i'm still of the opinion that 4 inches of give is WAY better than 0 inches of give (maybe watching climbers bounce on their ropes is making us think that only that type of damping is worthwhile)

based upon, to quote again,

work = mass x acceleration x distance

with the 4 inches of give being the distance and work stays the same in either scenario then you cut deceleration force by 4....in reality a distance of 0 inches in the distance doesn't make sense because the acceleration would tend towards (in this case negative) infinity as the distance tends towards zero....but just stating that points out something interesting (edit: rearrange work equation to work/distance = mass x acceleration to see how changing distance cuts acceleration/deceleration, since mass doesn't change)

edit: the rope does the work to decelerate (negative acceleration) your body's mass and it does so over some distance, it is better to do it over a longer distance because then if work stays the same (same mass, same potential energy) then the deceleration has to increase inversely as distance increases

i'm beating this dead horse because i feel people are using common sense when it doesn't apply, you instead have to trust the math and physics because we did not develop our common sense of everyday life watching things drop on a rope with a force meter attached

as an example, amsteel rope can be many times stronger than a nylon rope but the nylon rope survives a drop test that instantly snaps the amsteel...the reason is that the instantaneous force (force = mass x acceleration) is much more on the amsteel because it does not spread it over any distance (while work stays the same)....the same goes for the human body

 

[Exhumis]

Here’s a good site I linked awhile back:

Rope Rescue Fall Factors

Fall factors and rescue physics

roperescuetraining.com

.
Here’s a calculator I found

Fall Factor Calculator

how to fall

ferforge.tripod.com

IIRC from school a grown man can withstand like 12kn of force. Based on the calculations if I took an 8’ fall on static line I’d have a bad day

 

[Spartan]

We just need to put a crash test dummy into a saddle and drop them with the different ropes at different heights. I believe those dummies have several accelerometers inside them at critical points to provide real world data on the forces observed at those points. Basically tells you if the person would have been fine, or injured at certain points, or just plain killed.

I can provide the saddle and ropes if someone else has a high-end crash test dummy laying around

 

[raisins]

Here’s a good site I linked awhile back:

Rope Rescue Fall Factors

Fall factors and rescue physics

roperescuetraining.com

.
Here’s a calculator I found

Fall Factor Calculator

how to fall

ferforge.tripod.com

IIRC from school a grown man can withstand like 12kn of force. Based on the calculations if I took an 8’ fall on static line I’d have a bad day

12 kilonewtons is an instantaneous force

a newton*meter or kilonewton*meter is a unit of work

if you double the distance over which the rope slows your body (applies a deceleration force), then you half the instantaneous force you experience

so a static rope only giving 0.1 inches is much worse than a dynamic rope that gives only 1 inch

that's where i think our intuition is failing....folks are stating "it's only 1 inch of give"....I'm stating "1 inch of give is 10 times better than 0.1 inches of give in regards to the instantaneous force experienced by your body"

 

[raisins]

We just need to put a crash test dummy into a saddle and drop them with the different ropes at different heights. I believe those dummies have several accelerometers inside them at critical points to provide real world data on the forces observed at those points. Basically tells you if the person would have been fine, or injured at certain points, or just plain killed.

I can provide the saddle and ropes if someone else has a high-end crash test dummy laying around

iphones have accelerometers in them and there are ways to access the data

if you can download the right app, then you can put a sandbag with legs in a saddle and then strap a phone to it and drop

however, a sand bag dummy is too dynamic and a mannequin too static

we need to use something that mimics a human and embed the phone at the place your anatomically most interested (lower back or hips?)

 

[_Dario]

We can’t forget we are talking about using fall restraint devices vs arrest. I feel like that should be talked about first before we even get to ropes. There are some super knowledgeable folks on here about this and I’m not one of them. I just know the only way I’m ganna one stick is with a linesman. It takes about 3 extra seconds and actually makes the climb easier after you’ve practiced with it like 5 times.

 

[raisins]

A lot of good feedback and info. I do still find it a bit odd, though, that this group of people that tend to be incredibly nit picky about safety (not a bad thing, and often myself included), wouldn't mostly use the rope option that will reduce fall forces even if just by a hair, maybe just 0.1%. It reminds me of the quick-link vs. carabiner justification for the girth hitch. The potential to damage the biner from the bend or even reduce it's capability is so incredibly small. It's a similar 0.1% increase in safety going with a QL and people drive it home for that exact reason. Because if there is an option that is slightly safer, then you should use it. And I do use a QL for that exact reason. Just interesting that that same mentality doesn't get applied to the ropes as well.

Someone mentioned in this thread that dynamic ropes are more expensive. I looked at them quite a bit yesterday and today and found that to not be the case. There are several name brand dry dynamic ropes 8-9mm that are only about $1 per foot, compared to the $1.40-$2.00 per foot of the usual suspect static equivalents that we commonly use.

But I did notice one huge difference when trying to buy dynamic vs. static: No camo options. Most are quite bright, especially at 9mm for some reason, which is what I use. Actually hard to even find just a bare black, but there are some very limited options there. I do wonder if that may influence it a bit.

it's much harder to find dynamic rope by the foot

there's a few places but the selection is limited (they only offer a few by the foot)

i guess it is because a rock climber using dynamic rope has no use for 10 feet of it

so, it is more expensive in that to get the exact rope you want you might have to buy 100 feet or whatever length

the might quote a by the foot price, but they won't sell you a random number of feet...you have to buy it as packaged

 

[raisins]

.

As @kyler1945 said if you fall with your tether at your knees it doesn't matter what tether you are using. It will most likely end or seriously change your life. That's not a non answer, it's just pointing out worrying about your tether in that instance is pointless.

that's only being asserted with no testing of dynamic vs static and no complete math/physics treatment

life changing injuries are not all the same

 

[Fl Canopy Stalker]

I’m gonna skip all 3 pages of this and highlight 3 major reasons people use static rope instead of dynamic. If someone has pointed these out, I apologize but again I didn’t filter through all 3 pages of responses.
1) dynamic rope stretches. It’s nice to tether to the tree sit down and stay at the actual height you placed your hitch instead of ending up 8” lower because the spongy rope stretches. A “misconception is that the rope will suddenly be out of spec for a belay device….. It can be used with a belay device in spec which means you can safely rappel on it however static rope handles rappelling much better than dynamic for a couple reasons. One is the heat generated while rappelling by either mechanical or a friction hitch. Second is while rappelling, your rope is under constant load so static rope is the better choice due to lack of stretch.
2) and this is a big one: static rope has a much stronger and more abrasion resistant cover. Part of allowing a rope to stretch for shock absorption is making the cover a looser softer knit. Unfortunately dynamic ropes don’t handle rubbing, swinging, and sliding across tree bark nearly as well as static ropes with tighter cover knit and thicker cover ratios. Rope is an expense. Having to buy new dynamic rope for tethers or rappel length every season (or even half season depending on how much you hunt) gets costly. Static lines tend to make it longer.
3) and this is an opinion but if you read responses from other threads, I think you’ll gradually draw the same opinions….. There is a shroud of misconception involving ropes for hunting. One is color. Many static and tatical ropes are available in very natural and neutral colors such as black, tan, olive and brown. People feel better having neutral natural camo ish colors. (think camo patterns, military coloring of saddles ect) companies, including myself capitalize on this. It’s why Samson predator and deep woods, are more popular than say velocity, vortex, or blue moon. They are all 11mm 24 strand ropes but Predator is way more popular for us saddle hunters! Dynamic ropes rated for single rope (not twin or 1.5 which aren’t strong enough to be used alone) are usually bright and colorful so that climbers can easily identify it and so rescuers can see it against the side of the mountain. So it’s not as appealing for a saddle hunter who fancies himself some form of Tree Ninja. Another misconception is that since our tethers are only 6 to 8’ they won’t reduce force. It’s true that having 20 or 60 feet of rope will definitely soften a fall, way more than a couple of feet of rope however, in a fall any reduction of speed and force can be the difference in the outcome. I will say this though. Using a short dynamic rope while one sticking will not make falling safe. Just as using a screamer will not make falling safe. Sorry guys tell me about what Becky from REI said all you want, but until one of you has proven the opposite with drop tests, documented forces and real case studies, falling in a saddle with a high fall factor is not safe. Introducing slack is not safe.

 

[Fl Canopy Stalker]

Ra

thanks for the links that explain fall factor well

still doesn't address a question like 'if you take a 6 inch slip and fall in a saddle with X length of rope involved (i believe that bridge and tether length should be considered including the amount of rope wrapped around the tree), then how hard is it on you with a static rope vs a dynamic rope?"

i'm still of the opinion that 4 inches of give is WAY better than 0 inches of give (maybe watching climbers bounce on their ropes is making us think that only that type of damping is worthwhile)

based upon, to quote again,

work = mass x acceleration x distance

with the 4 inches of give being the distance and work stays the same in either scenario....in reality a distance of 0 inches in the distance doesn't make sense because the acceleration would tend towards (in this case negative) infinity as the distance tends towards zero....but just stating that points out something interesting

edit: the rope does the work to decelerate (negative acceleration) your body's mass and it does so over some distance, it is better to do it over a longer distance because then if work stays the same (same mass, same potential energy) then the deceleration has to increase inversely as distance increases

i'm beating this dead horse because i feel people are using common sense when it doesn't apply, you instead have to trust the math and physics because we did not develop our common sense of everyday life watching things drop on a rope with a force meter attached

as an example, amsteel rope can be many times stronger than a nylon rope but the nylon rope survives a drop test that instantly snaps the amsteel...the reason is that the instantaneous force (force = mass x acceleration) is much more on the amsteel because it does not spread it over any distance (while work stays the same)....the same goes for the human body

Raisins you are right on my man… Bridge does factor into rope length in a fall. If you have a 30” dynamic bridge and an 8’ dynamic tether. Let’s say you are hooked in half way, you get the benefit of 4’ (not just the 10” from your prusik to the eye but also the stretch of the eye and rope around the tree) Plus the 30” of your bridge. That should theoretically reduce your fall farce over a static rope and amsteel bridge somewhere between 70 and 140 lbs but still won’t make falling safe with a 1 to 1 or 1.2 to 1 fall factor from one sticking.

 

[raisins]

Ra

Raisins you are right on my man… Bridge does factor into rope length in a fall. If you have a 30” dynamic bridge and an 8’ dynamic tether. Let’s say you are hooked in half way, you get the benefit of 4’ (not just the 10” from your prusik to the eye but also the stretch of the eye and rope around the tree) Plus the 30” of your bridge. That should theoretically reduce your fall farce over a static rope and amsteel bridge somewhere between 70 and 140 lbs but still won’t make falling safe with a 1 to 1 or 1.2 to 1 fall factor from one sticking.

still not safe, but might be the difference between walking with a limp or being in a wheelchair

 

[raisins]

Ra

Raisins you are right on my man… Bridge does factor into rope length in a fall. If you have a 30” dynamic bridge and an 8’ dynamic tether. Let’s say you are hooked in half way, you get the benefit of 4’ (not just the 10” from your prusik to the eye but also the stretch of the eye and rope around the tree) Plus the 30” of your bridge. That should theoretically reduce your fall farce over a static rope and amsteel bridge somewhere between 70 and 140 lbs but still won’t make falling safe with a 1 to 1 or 1.2 to 1 fall factor from one sticking.

what do you think about incorporating something like a screamer into the bridge of a saddle? seems like it would accomplish something similar and be more out the way and not complicate and lengthen your tether setup

 

[GCTerpfan]

that's only being asserted with no testing of dynamic vs static and no complete math/physics treatment

life changing injuries are not all the same

I haven't read all of the responses since my initial post but, I wasn't really commenting on the difference between static and dynamic rope. I actually use a dynamic tether. I was speaking to the OP stating he climbed until his tether was at his knees. Falling 4 feet with a fall factor near 2 is going to most likely result in injuries (possibly serious). This has been tested, and proven for decades and standards and regulations have both been established based on that data.

Debating if I a dynamic rope "might" make a slight difference when other very easy things, like keeping slack out of your tether "will" make a big difference is pointless IMO.

 

[raisins]

I haven't read all of the responses since my initial post but, I wasn't really commenting on the difference between static and dynamic rope. I actually use a dynamic tether. I was speaking to the OP stating he climbed until his tether was at his knees. Falling 4 feet with a fall factor near 2 is going to most likely result in injuries (possibly serious). This has been tested, and proven for decades and standards and regulations have both been established based on that data.

Debating if I a dynamic rope "might" make a slight difference when other very easy things, like keeping slack out of your tether "will" make a big difference is pointless IMO.

that's the part that is being asserted, that the difference is slight and not enough to worry about

that hasn't been tested in this scenario, at least i haven't seen it

you're right that we were discussing a greater than fall factor 1 event, which is also considered bad with dynamic rope....but how much worse is it with static? maybe a lot worse because you'd have to add a snapped rope and falling however many feet to the ground whereas a dynamic rope might be more likely to not break

when we move to smaller fall factors, then the discussion becomes more interesting, when we are moving away from 'bazooka vs 50 cal' comparisons

 

[GCTerpfan]

that's the part that is being asserted, that the difference is slight and not enough to worry about

that hasn't been tested in this scenario, at least i haven't seen it

you're right that we were discussing a greater than fall factor 1 event, which is also considered bad with dynamic rope....but how much worse is it with static? maybe a lot worse because you'd have to add a snapped rope and falling however many feet to the ground whereas a dynamic rope might be more likely to not break

when we move to smaller fall factors, then the discussion becomes more interesting, when we are moving away from 'bazooka vs 50 cal' comparisons

Well I think we can agree that the difference between falling 4' on static versus dynamic is less than the difference between falling 4' or falling 6" on either rope.

 

[cedar paul]

Static line gives you the most bang for the buck when ascending srt meaning you are not losing advance due to stretching.

 

[Fl Canopy Stalker]

what do you think about incorporating something like a screamer into the bridge of a saddle? seems like it would accomplish something similar and be more out the way and not complicate and lengthen your tether setup

That’s a no for me. The weaker stitching in a screamer is made to tear way in a fall to decelerate the fall momentum. They are not strong enough for constant loading because even a tiny dynamic event could cause them to tear away. Screamers do absolutely nothing in our application. I know I know someone will tell me how screamers are used in full body harnesses. What they won’t mention is that those screamers are usually accompanied by a short dynamic (bungee) with climbing rated webbing covering it. The bungee stretches to help absorb force while the screamers break away to slow the fall and if the fall is hard enough, the climbing rated tubular webbing that covers the bungee also stretches some as it stops you. Also you fell from under your connection point in a harness that is designed to keep you upright and distribute your weight across more surface area than just your waist. I’m another thread I gave DMM’s reply to why their screamer wasn’t made to use in our application. Yates wouldn’t even dignify my email about using theirs with a reply.

 

[hauscaliber]

12 kilonewtons is an instantaneous force

a newton*meter or kilonewton*meter is a unit of work

if you double the distance over which the rope slows your body (applies a deceleration force), then you half the instantaneous force you experience

so a static rope only giving 0.1 inches is much worse than a dynamic rope that gives only 1 inch

that's where i think our intuition is failing....folks are stating "it's only 1 inch of give"....I'm stating "1 inch of give is 10 times better than 0.1 inches of give in regards to the instantaneous force experienced by your body"

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.