'SWL/WLL'.....am starting to think this isn't a proper approach to rigging-lines (v. "where's the bounce?" :) )

eyehearttrees

Active Member
I'm hoping to discuss/learn a bit more on this topic before I begin contacting a couple manufacturers with pointed-questions, I'm new to real rigging but I've got a pretty solid understanding on the basics of dynamic-forces and I am just hitting a wall with the state of arboricultural rigging-ropes....My biggest gripes (or, perhaps, misunderstandings) are:

1 - The concept of a "SWL/WLL" for rigging, the way that it's commonly done, is just a silly way to approach understanding what your line can & cannot be expected to control. It is a metric wherein a line's STATIC tensile-strength is the baseline, and then, based on, it seems, the rigger's intuitions&experiences, a SWL/WLL is chosen -- this seems to be the default approach of rigging today. A line's elasticity seems to be an after-thought, when in reality it's just-as-critical as the static-tensile-ABS metric, in fact in some cases *more* important, for example: If someone snaps their Tenex/Yalex sling, the thought is generally "get a larger diameter", with almost nobody saying "uhh, these HMPE slings have low stretch, so for the same reason we wouldn't use Amsteel/dyneema here *despite* it's static-ABS, the upgrade from 3/4" tenex/yalex shouldn't be to 7/8" of the same, but rather to 3/4" of Polydyne with its 3% stretch" That latter sentiment is how things *should* be, based on how I understand force-vectors when you're slowing/controlling a descending log with a line that has stretch, yet static-MBS is the major metric used?

2 - With ^that in-consideration, I am just astounded that when I look at any of the current retailers'-magazines to find that *climb* lines are more-static than *rigging* lines, hell many rigging-lines' low-stretch gets highlighted as a feature!! I'm intending to ask Nice Guy Dave "What routine-rigging-circumstances would make one want their line to be more on the static side?", am very curious what the answer will be.....mech.advantage, lifting, hauling, winching, sure you will want static lines & pulleys, but for controlling the downward-descent of a cut log, which is the OVERWHELMING majority of usage of these ropes, super-static properties simply mean the line is less-suited for dynamic work which is inherently what dismantling requires whether you've got the best groundie and are super in-control and only using positive-angle rigging, or whether you're barely letting the line run before having the log snubbed in the air, in either case it is dynamic. The major companies like Samson and Yale have *increased* stretch with their newer offerings, Sterling's Atlas is making waves (being 4.5% stretch, a significant outlier, most bull line is 2-something-%), to me this indicates that things are moving the right way BUT I can't figure out how it's taken so long for them to get there?


Nobody wants to *feel* slop/bounce in their line, we want static *feel*, we'd use dyneema if dynamic-loading weren't a consideration, but whether it's the possibility of your climb-line needing to catch your body falling, or a bull line controlling logs' downward descents, there's gotta be an appropriate-% of stretch, an amount that'll be enough to safely cushion shocks but otherwise 'act static'. Rec/mountain climbers have climb ropes nearing 10% stretch, I'm not advocating for that, but we know that amsteel is unsafe to use dynamically and, with these extremes considered, and with Yale/Samson/Sterling moving to making more-elastic/dynamic bull lines, it's hard to think that it's a smart move to consider ANY bull-lines that are under ~2.5% stretch and in fact that 3% Polydyne & 4.5% Atlas may be the best out there - heck, seeing the relatively-higher elasticity in climb-lines finally helped me understand why the used-climb-line-as-rigging-rope concept seems to work so well for most....one may initially think "oh that line's only 6k ABS", but that's a static ABS, if the line has appropriate stretch for the application it'll perform better than a 10k ABS tensile-strength line that's got inadequate stretch.

Thanks for any thoughts on the matter, and for further consideration/explanation of the distinction I'm trying to make here is an outstanding (and short :) ) video by Yale illustrating what I mean:
^starts with them showing their ultrex (what most would know as single-carrier tenex), a 20k *static* line, holding >20k just fine, then they show a 6.5' drop of 220lbs (an easy force-load for people to picture) on the same line and it shatters it.....that was simply a 1,421lbs load at its peak, I'm pretty confident that most people would've done the math on this, concluded "1,421lbs is WAY under the 20k+ tensile, I'm below my 1:10SWL, this is gonna work!" only to find it does not....this is where static-ABS takes a back-seat to elasticity! I think the "static or dynamic?" paradigm isn't helping either, surely people are capable of simply talking %'s and don't need the placeholders of 'static'/'dynamic' to try to make 'categories' when the reality is it's a spectrum! Also, it's worth mentioning that there's not some uniform-stretch-% on a line, the stretch varies as the rope is stretched for instance the HMPE slings like yalex/tenex stretch a ton very early in their loading but are then super-static after, that's why the elasticity-spectrum graphs from Yale and Teuflbrg (and others I'm sure) are so useful, it's that area-under-curve that is your net shock-absorption-capacity of the rope, NOT static-load capacities and not even just "elongation at 10%ABS", but the actual graph....looking at Polydyne's it has me thinking that it's probably the optimal rope for 95% of rigging applications, maybe 2nd to Atlas but I'm uncertain because the company's younger age (2 decades) may make some have misgivings, so I'm sure you can imagine how confused I am that 1-something-% bull lines are even available (outside of a "winch-line" context, not pictured side-by-side with standard bull lines & gear that'd be used for dynamic rigging which, again, is almost all the rigging that's done in arboriculture!
 
Last edited:

*useless info*

Well-Known Member
The tensile of the line is usually a test value, better companies tending to be conservative and understate as a moral code of being understated and legal protection margin; some of which is probably insurance mandated.
.
Seems the ratios of SWL safety margin differ and somewhat self assigned, even different in different disciplines.
It is all a judgement consideratation at some point.
Elasticity can absorb more shock, with less transfer to connecting points.
>>static can offer more clearance and not fight elasticity in pre-tightening.
.
Everything is relative, so as; if jump up to higher SWL ratio in same material x construction ; delivers more shock to supports. Same as if 2:1 pulley on load for more strength/pre-tightening cuts load per leg in half (inline model) so less elastic dampening in whole. Rope as a wearable resource becomes an economy decision sometimes.
 

evo

Well-Known Member
Once your down that rabbit hole don’t forget to research abs vs mbs vrs MBS. Min breaking vrs max breaking.
Most ropes (rigging) are rebranded to the Arborist industry. There might be a tweak here or there regarding a weave or dye or coating. Follow the money and you will find that many rigging lines are the exact same as marine lines.
Sure there are some which are arb specific but most of these are climbing/rope access lines
 

Birdyman88

Well-Known Member
The 1421 lb is really "FT-LB", which is energy, not force and cannot be directly compared to SWL force. 220 lb x 6.5 ft drop = 1,430 lb - they probably made it 1,421 because the weight wasn't exactly 220 lb. So, we really don't know WHAT the actual peak force was!

Make no mistake, there is no way that 220 lb dropped from 6.5 ft generated the EXACT same peak force on completely different ropes of the same test length.

Now, go run Yale's own dynamic loading calculations using those numbers and the exact length of rope in their test and you'll get very different peak forces for each rope. They will be much higher on the less elastic ropes.

You're on the right track. Kust my 2 cents.
 
Last edited:

JeffGu

Well-Known Member
...most of these are climbing/rope access lines...
Even those are often developed for other at height industries, and sold as "arborist ropes" in our marketing circles. This isn't really a bad thing... if a rope is great for window washers and arborists, then it's a great rope for both purposes, and it is what it is. The marketing hogwash about "developed just for the arboriculture industry" is pure bullshit, and we all know it. When you find the exact same rope marketed as "developed just for the tower maintanence industry" on another website, the game's up.

I did some graphic design work for a guy many years ago, who ran a small advertising company. He once told me that honesty is a commodity and is subject to interpretation, even when the result is anything but the truth. I'm surprised the guy hasn't run for president.
 

evo

Well-Known Member
Even those are often developed for other at height industries, and sold as "arborist ropes" in our marketing circles. This isn't really a bad thing... if a rope is great for window washers and arborists, then it's a great rope for both purposes, and it is what it is. The marketing hogwash about "developed just for the arboriculture industry" is pure bullshit, and we all know it. When you find the exact same rope marketed as "developed just for the tower maintanence industry" on another website, the game's up.

I did some graphic design work for a guy many years ago, who ran a small advertising company. He once told me that honesty is a commodity and is subject to interpretation, even when the result is anything but the truth. I'm surprised the guy hasn't run for president.
I’m not griping, but it does lead me to question how fucken awesome it would be for a purpose built arborist rope. Think of the wrench, hitch hiker, runner, Akimbo, bungee knee ascender, uni or any of that crap.. imagine a dozen different true Arborist ropes?
 

JeffGu

Well-Known Member
Yeah, I'm not really complaining about the ropes so much as their goofy marketing propaganda... I realize that if you make a really, really good arborist rope for arborists, it might just be the perfect rope for a window washer, too. And, yeah... I'd market that shit to whoever wanted it. But I think I'd say "developed for arborists, window washers and peeping toms..." or whatever.
 

theatertech87

Well-Known Member
Just a couple of things to add to your thinking...

We in the arb industry live in a much more elastic world than other rope disciplines. Our trees bend and flex, unlike structural steel or rock faces, so where other industries need rope stretch, we can get away with dynamicaly loading our elastic anchors (relatively speaking) using static ropes.

A couple other locations where highly static lines can be desirable are...
-ziplines, where stretch causes unwanted drop.
-Any instance where you're not negatively rigging, high rigging point and tip tying is a great example; wherein you have substantially less dynamic load
- any time you are lifting a load (grcs, ropejack crane etc) where again there is limited dynamic load and type stretch becomes an inconvenience rather than a benefit.

If you want to go digging there are a couple threads that get into the math of how rope stretch over time the load slows dissipates (or nor) enough energy to not break the rope
 

KevinS

Well-Known Member
Your rigging is speced at 5:1. If it’s a 1/2” 8,000 lbs mbs so you shouldn’t go bigger than 1,600 lbs. When you reduce your load like that and you rig right it should be ok.

If you tip tie and swing it usually avoids the drop shock. If you drop rig a load just go less.

If you have a good rigger they’ll let it run and slow it to a stop to avoid shock. A crappie groundie will lock it off and slam it causing a full load and a crappie climber will take a full load every time and push the limits.

Know your limit and play within it. This goes for you, your gear and your tree.
 

KevinS

Well-Known Member
I was just rereading the original post and there’s a section where it talks about ‘Wanting using static line to catch yourself in a fall’

This is a misconception. Imagine 0 stretch like steel cable, tie off to that and drop into that too hard it’s like para cord if you look into the original parachute jumpers in the military they’d jump and if anything caught them like a tree, etc there bodies were the only thing that could give and there organs came out your orphvasises. Things like this is how and why stretch got introduced into systems. Even now if you’re in a bucket, etc de-acceleration lanyards are the top recommendation to break your fall

Low stretch is used to remove bounce from climbing systems to make higher efficiency of physical effort has nothing to do with being caught.


As far as rigging goes any sort of negative rigging should stretch IMO or you’re just looking to get rattled more at the top.

This leaves me wondering and of course I’m not a rope engineer. But they know to tell us to rig at a SWL of 5:1. 5:1 is the safety factor and I don’t assume they pulled that number out of thin air and when formulating such factors what would lead us to believe that they have over looked stretch. I think imo they looked at a lot kept there work in house and released the bottom number we need to know.

Just some thoughts
 

KevinS

Well-Known Member
I’m not griping, but it does lead me to question how fucken awesome it would be for a purpose built arborist rope. Think of the wrench, hitch hiker, runner, Akimbo, bungee knee ascender, uni or any of that crap.. imagine a dozen different true Arborist ropes?
For the time and effort and how different would it actually be vs $$$ makes it less likely. Also if we made one and a guy did towers in the off season and guys liked his rope what’s stopping them from getting a few rolls now it’s not strictly an arb rope anymore
 

evo

Well-Known Member
For the time and effort and how different would it actually be vs $$$ makes it less likely. Also if we made one and a guy did towers in the off season and guys liked his rope what’s stopping them from getting a few rolls now it’s not strictly an arb rope anymore
It doesn’t have to be exclusive to the arb industry, just made for and by Arborists.. thick cover, low bounce, 12mm etc
 

KevinS

Well-Known Member
It doesn’t have to be exclusive to the arb industry, just made for and by Arborists.. thick cover, low bounce, 12mm etc
Have to watch thick cover doesn’t milk too much and it can make feeling cores harder
 

evo

Well-Known Member
Have to watch thick cover doesn’t milk too much and it can make feeling cores harder
In my imagination if Yale 11.7 / Samson 16 strand had a baby and the best traits were carried down I’d buy spools of it even if it were ugly
 
I'm hoping to discuss/learn a bit more on this topic ...
//

Thanks for any thoughts on the matter, and for further consideration/explanation of the distinction I'm trying to make here is an outstanding (and short :) ) video by Yale illustrating what I mean:
^starts with them showing their ultrex (what most would know as single-carrier tenex), a 20k *static* line, holding >20k just fine, then they show a 6.5' drop of 220lbs (an easy force-load for people to picture) on the same line and it shatters it.....that was simply a 1,421lbs load at its peak, I'm pretty confident that most people would've done the math on this, concluded "1,421lbs is WAY under the 20k+ tensile, I'm below my 1:10SWL, this is gonna work!" only to find it does not....this is where static-ABS takes a back-seat to elasticity! ...
Not so fast. There's something *smelly* about these figures. Firstly, note that the tensile test is done to an eye-spliced rope; the drop test to a knotted one. Secondly, peak impact force is an attribute determined per rope but the "1,421" is given as though it's something absolute.

Playing around (as best an undereducated person might go) with a force calculator here
http://hyperphysics.phy-astr.gsu.edu/hbase/flobi.html
I put in 100kg for load and 2m for drop distance and with gravitational acceleration and a guesstimate that the rope DOES stretch 0.03m to impact the force is right there at 10_000#, which might not be all so far from the effective strength of the fig.8-knotted rope!?

In any case, the calculator's needed inputs suggest a more variable-determinant scenario than the simple drop-force constant Yale uses. (Their concluding example of a reaLife accident is more mixing of apples & oranges, IMO.)

*kN*
 

Crimsonking

Well-Known Member
In my imagination if Yale 11.7 / Samson 16 strand had a baby and the best traits were carried down I’d buy spools of it even if it were ugly
My dream rope is 11.7 htp. Tight, durable jacket, better diameter for grip, and insanely static.
 

Daniel

Well-Known Member
Our trees bend and flex, unlike structural steel or rock faces, so where other industries need rope stretch, we can get away with dynamicaly loading our elastic anchors (relatively speaking) using static ropes.

- any time you are lifting a load (grcs, ropejack crane etc) where again there is limited dynamic load and type stretch becomes an inconvenience rather than a benefit.
While I agree with the latter statement, especially when taking the slack out of long runs by hand, the former is complete nonsense and is likely a contributing factor to Pete Donzelli's death.. Suggesting that its good to Dynamically load static ropes on trees, just because trees have more give than a rock is the about the worst rigging advice one could give. @rico and JEFFGU show their ignorance on the subject by giving your post a thumbs up. This subject was completely discussed when the original rigging software came out and was well demonstrated in the yale rigging video over 10 years ago.
 

*useless info*

Well-Known Member
i think knot tests for our type of loads carried should have some kind of preceding Half Hitch or Marl. 3 (or more) 180arcs minimum on load.
This would include round sling choke, but decidedly not eye2eye.
>>unless the single Turn type choke of eye2eye upgraded to HH/Marl preceding
>>to give the 3arc grab on load as host mount for hitch.
.
Load carried with hitch meeting host/load at correct right angle only occurs when hitch point as pivot is inline with Center of Gravity(CoG). Other wise will softly (if hitch close to CoG) or hard slam (if hitch far from CoG) but in either case carry where the hitch is pulled lenghtwise along/parallel to load. The way that Ashley says never to pull Timber Hitch w/o HH preceding for Killick etc..
.
If this is done the Running Bowline etc. peculiarities, efficiency/strength aren't the main loaded geometry, and with the same preceding HH etc. form more equivalent strengths i would think.
 

rico

Well-Known Member
While I agree with the latter statement, especially when taking the slack out of long runs by hand, the former is complete nonsense and is likely a contributing factor to Pete Donzelli's death.. Suggesting that its good to Dynamically load static ropes on trees, just because trees have more give than a rock is the about the worst rigging advice one could give. @rico and JEFFGU show their ignorance on the subject by giving your post a thumbs up. This subject was completely discussed when the original rigging software came out and was well demonstrated in the yale rigging video over 10 years ago.
Yea what kind of "ignorant" fool would give the following statement a thumbs up?-

"Just a couple of things to add to your thinking...

We in the arb industry live in a much more elastic world than other rope disciplines. Our trees bend and flex, unlike structural steel or rock faces, so where other industries need rope stretch, we can get away with dynamicaly loading our elastic anchors (relatively speaking) using static ropes.

A couple other locations where highly static lines can be desirable are...
-ziplines, where stretch causes unwanted drop.
-Any instance where you're not negatively rigging, high rigging point and tip tying is a great example; wherein you have substantially less dynamic load
- any time you are lifting a load (grcs, ropejack crane etc) where again there is limited dynamic load and type stretch becomes an inconvenience rather than a benefit.

If you want to go digging there are a couple threads that get into the math of how rope stretch over time the load slows dissipates (or nor) enough energy to not break the rope"



I myself have been using fairly static lines (relatively speaking) in many of the above scenarios for decades, and low and behold, I'm still alive and not a single insurance claim, or smashed swing-set in sight..

In fact we used a static bull line (relatively speaking) while getting a large oak off of a house yesterday, and the static nature of the rope helped us TO NOT do any more damage while getting the tree off the home....
 
Last edited:

New threads New posts

Kask Stihl NORTHEASTERN Arborists Wesspur TreeStuff.com Kask Teufelberger Westminster X-Rigging Teufelberger Tracked Lifts Climbing Innovations
Top Bottom