# static or dynamic??



## Ob1 (Jan 5, 2007)

Starting to do some pruning, and wondering about using my "dynamic" rock climbing rope: Are 'dynamic' or 'static' ropes generally preferred for tree work? Why? 
Thank yee gennelman.


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## rbtree (Jan 6, 2007)

Tree ropes are semi static. They stretch 1-2% under body weight, and maybe 20% at break. so don't fall on them, it will not be pretty.


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## Ob1 (Jan 6, 2007)

Thanks for the warning!


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## Blinky (Jan 10, 2007)

rbtree said:


> ... so don't fall on them, it will not be pretty.



True words. I've fallen on dynamic rock ropes lots of times, as long as i didn't bang into something it was always a soft stop. Fell on my tree rope (Poison Ivy) a few weeks ago and the sudden decel made my whole body hurt for a day and a half... like I'd been in a car wreck.

Hard to limb walk on rock rope though, the stretchyness makes it less predictable when you lean on it.


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## treeseer (Jan 10, 2007)

I like using dynamic rock ropes, because I like the bounce when bodythrusting, but the bounce can be quivery while limbwalking, true. It's highly style-dependent; most climbers do not like as much movement/response as I do, I suspect. with the use of lanyards and redirects and second lines I do not worry about falling on either kind.

If you do a lot of pruning you may want to change to a tree rope. try them out first if you can, so you know it fits your climbing style. Blinky you won't be dropping anymore willya? I worry about your parts getting bruised.


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## Blinky (Jan 11, 2007)

treeseer said:


> ... Blinky you won't be dropping anymore willya? I worry about your parts getting bruised.



Me toooo!


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## TheTreeSpyder (Jan 14, 2007)

By the ratings our ropes are as RB says; then we double them over to saddle.

This raises the SWL; thereby reducing (further) it's reciprocal; elasticity.

This is true even in rigging. A pulley on support, holding a 300# load; places 600# on said support. A 2:1 places only 450# in same scenario; a 3:1 only 400#. So, in a static hang; as the item becomes easier to lift/hold it also has payoffs of placing less load on support; higher SWL, able to hold more etc.

But; if the load is moving/ is not static; whereby we are partially relying on the dynamic capacites of the rigs, support load effects invert(maybe not immediately, but with real dynamic movement). For as the SWL of the rigs goes up, the elasticity goes down. Elasticity is a function of the materials, construction, length and percentage of the tensile strength used. Higher tensile strength used; less SWL and more elasticity. So, with a 2'+ drop the higher power rigs will place more loading on the support; unless a lot of line is in system, as measured on both sides of the final pulley (final leg of support on load and return as control side).

This is why SRT bowlined to support has more bounce than same line and support in DdRT; then even more if SRT is anchored to ground.


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## Ob1 (Jan 27, 2007)

*?*

Blinky and Treeseer, I appreciate your perspectives. I'm excited to get climbing in a couple weeks and see what all these terms feel like in practice.

TreeSypder, I'd love to know what you're talking about. It sounds like great information, unfortunately, as a rookie I don't what what SWL, SRT, DdRT, or rigs are.:help: Would you do me the favor of defining these for me, or directing me to a source that would? 
Thanks for your help.


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## Blinky (Jan 27, 2007)

Ob1 said:


> Blinky and Treeseer, I appreciate your perspectives. I'm excited to get climbing in a couple weeks and see what all these terms feel like in practice.
> 
> TreeSypder, I'd love to know what you're talking about. It sounds like great information, unfortunately, as a rookie I don't what what SWL, SRT, DdRT, or rigs are.:help: Would you do me the favor of defining these for me, or directing me to a source that would?
> Thanks for your help.



While tree climbers aren't as bad as the Army, I'm finding plenty of acronyms to figure out as I get into it.

SWL - Safe Working Load - I think it's about 1/10 of the breaking strength of the system or component. Formally called Working Load Limit which is defined as the tensile strength divided by the design factor. You should never exceed SWL in normal work circumstances.

DRT - Double Rope Technique - The time tested way for a climber to move safely around in a tree. You need to understand DRT before you start climbing, get 'The Tree Climber's Companion' by Jeff Jepson. In a nut shell, you get the rope doubled down from a high crotch and tie one end to your harness; then, using a bridge (extra tail on the tied end or a 'split tail') you tie into the other (longer) side of the rope with a friction knot. You then are part of a closed loop extending between you and that high crotch. Sliding the friction knot up or down the rope changes the size of the loop so you can go up or down easily and securly. You can both climb and manuever on DRT.

Treeseer will tell you to use a rope, a snap and a tautline hitch to start with... and there's merit in that because it's simple and clean. I think a split tail with a Blakes hitch is a more versatile without making things too complicated.
Note that locking biners for rock climbing are not good for treework because the rope can unlock them. Spring for a 'posi-lock' type of biner ( http://www.wtsherrill.com )

SRT - Single Rope Technique - Use of a single strand of rope, generally for tree ascent and descent. I've not used it yet but ascent is about twice as efficient with SRT.

Rigging is how you go about lowering pieces of the tree if you have to. It's all about understanding SWL, dynamic loading, mechanical advantage systems, knots and procedure... advanced stuff. Learn to climb and manuever and you'll start getting into rigging as you go. Make no assumptions about rigging, getting it wrong can be catastrophic. Listen to Spyder, he's got a firm grip on rigging.

I'll say it again... get 'The Tree Climber's Companion' by Jeff Jepson. If you're a rock monkey it will be a quick read.

If anybody sees errors in this, please chime in... I'm not exactly an old hand at this.


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## TheTreeSpyder (Jan 27, 2007)

Thanks for helping to clarify!

i think SWL isn't really arbitrarily set; can be 10:1 (700# of force on a 7000 test line), 20:1; etc. This makes it harder buying gear sometimes; trying to figure out an advertiser's SWL ratio; multiply the rating by it; then doing same with other advertised item that has a different SWL ratio; to be able to compare the 2! 

Otherwise it is just a guideline as you set stuff up. We may say the more the SWL and/or the higher tensile the better. In our metal devices this is probably true; unless trying to leave one weakpoint of chain to blow out first; like a mechanical fuse(non-tree work). In more dynamic devices of rope etc. (and metal etc. at angle to be spring); we have another thing to consider that this thread is about. Part of the 'formulae' for whatever elasticity in a system is the inverse of the present SWL. For as the loading goes up; the SWL goes down; but elasticity comes up; thus the SWL and elasticity are reciprocals.

Static is non-moving/ dead weight; dynamic is when something is moving. Dynamics in a line can help absorb this part of the force; to not build line tensions as high as in a static line from a dynamic event.

Elasticity; can be used for storing force or dampening force. Dampening can help dampen the impacts of moving/dynamic force; to be softer on your bod and TIP(Tie In Point); or other support in rigging. If pulling a tree over you might fight the elasticity; but then if you keep pulling as the tree starts coming you might work in concert with the elastic recoil. If TreeSeer can bounce right witht he elasticity in footlock it can help; but if timing of this dance isn't right; he just fights it.

So, there are 2 components of rope; we shouldn't just pay attention to the static 'macho'/pure strength to task side. We should also consider, the softer/ more feminine side of not letting go, that has forgiveness; the elasticity-and what is needed per task. A static line will hold you, but jerk you. An elastic line will give more of it's elastic capability, the more there is in the system per loading of each leg. One point is that when we double our ropes over a branch, each leg has less load in DRT/DdRT than SRT; so we get less elasticity from it!

In rigging more line through a pulley and to ground can give more elastic length/ therefore buffering. But frictional/non-pulley redirect; gives less elastic line buffering of dynamic forces. This is especially true when the rigging point is below the load. The CG(Center of Gravity) moves freely from it's height above the pulley, to below it; giving great loading. The height of the 1st hitching off the pulley is not the operative of total force as commonly thought; in fact rasing it farther from pulley(but still short of the CG) gives extra elastic buffering length to system.

Atattched are some numbers output by the Sherrill/ArborMaster Rigging Calculator; showing how length of line, height of CG and SWL effect elasticic dampening/buffering in rigging.


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## moray (Jan 28, 2007)

*Reciprocals?*



TheTreeSpyder said:


> Thanks for helping to clarify!
> 
> i think SWL isn't really arbitrarily set; can be 10:1 (700# of force on a 7000 test line), 20:1; etc.
> 
> Part of the 'formulae' for whatever elasticity in a system is the inverse of the present SWL. *For as the loading goes up; the SWL goes down; but elasticity comes up*; thus the SWL and elasticity are reciprocals.



Can you explain this further? I understood the SWL to be an arbitrarily set fraction of the rope's tensile rating. The rule would be: do anything you want to the rope, but be sure no part of it experiences tension beyond the SWL.

You can have two brands of rope with very similar tensile ratings but one can stretch several times as far as the other under the same load. Rock climbers love the stretchy nylon ropes, arborists like the much stiffer dacron ropes, but both may have the same tensile rating. And as you rightly point out, the stretch in a rope, for a given load, is proportional to the length under tension. If SWL is a fixed number, but stretch varies with type of rope and with rope length, how can one be reciprocally related to the other?


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## TheTreeSpyder (Jan 28, 2007)

If you look at manufactures ratings of elasticity in ropes; it is usually/ most accurately stated as at 10% of tensile rating gives elasticity X; at 20% elasticity is greater than X.

So the more loaded a line, the greater the elasticity! But the more loaded, the greater the % of the tensile strength used; so the lower the SWL. At a 10:1 SWL there is less elasticity than at 5:1 SWL. That is why in the last category of the spreadsheet; where the load weight is the altered variable; when the load weight is cut in half; the line tension doesn't drop by half. This is another aspect of the 4x for 1/2 tension thumbrule. To drop line tension from dynamic loading in half; we must either have 4x as much line in system(as shown in the spreadsheet where length of line from hitch to brake is variable) or drop the load weight to 1/4(in these ranges)! If we just double the line length or cut the load weight in half; we drop the line tension to ~70% in these dynamic examples; not 50%.

This vital elasticity is the softer/ feminine/ forgiving side of rope; usually we git caught up in just the macho/ pure strength consideration of the tensile strength. But, this softer side of the rope is the first to fade; and running high into the elasticity also has the downside of decreasing the useable CtF(Cycles to Failure). So, there is no free ride; just tradeoffs; as all ways, in all things(power/speed tradeoffs from same source force etc.).


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## pbtree (Jan 30, 2007)

Click on Spydie's link in his signature - there is lots of good info there...


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## moray (Jan 31, 2007)

TS, this is very interesting thread, as it deals with some of the deeper properties of ropes. The better we understand them, the safer we will be.

Your spreadsheets reveal aspects of rope behavior under dynamic loading that I am sure most of us weren't aware of (I know I wasn't). Most interesting is the fact that the maximum load produced by a dropped weight is not proportional to the weight, but to the square root of the weight. The rope can be considered a kind of spring, at least for loads below the elastic limit of the rope. The elastic limit would be reached at roughly 1/4 the breaking strength of the rope.

Treating the rope as a spring, and assuming the fall distance is much greater than the stretch distance, it is straightforward to derive a number of other relationships:
(1) Maximum force on the rope is proportional to the square root of the energy absorbed.
(2) Maximum force on the rope is proportional to the square root of the weight of the dropped load.
(3) Maximum force on the rope is proportional to the square root of the distance the load falls.
(4) Maximum force on the rope is proportional to the square root of the stiffness of the rope.
(5) Maximum stretch of the rope is proportional to the square root of all the things above.

Here's a link I found that has a nice discussion of this stuff:

http://www.bstorage.com/speleo/Pubs/rlenergy/Default.htm




TheTreeSpyder said:


> If you look at manufactures ratings of elasticity in ropes; it is usually/ most accurately stated as at 10% of tensile rating gives elasticity X; at 20% elasticity is greater than X.



Elasticity is a slippery word, but I have never seen it used, as you seem to be using it, to mean "amount of stretch." The rope manufacturer's tables actually show "elastic elongation," which is the percentage elongation of the rope from a load equal to a given percentage of that rope's breaking strength. It applies to all ropes of that type, regardless of diameter. If you know the elastic elongation, the load, and the rope's breaking strength, you can calculate the amount of stretch.



TheTreeSpyder said:


> So the more loaded a line, the greater the elasticity! But the more loaded, the greater the % of the tensile strength used; so the lower the SWL. At a 10:1 SWL there is less elasticity than at 5:1 SWL.



Safe working load (SWL) is another quantity you mention, but here again you seem to be using it in a way I have never seen before. I think the manufacturers always set this number to be less than the elastic limit of the rope, but other than that it is more or less arbitrary. It is a fixed number, not a variable. It does not go up or down because you have loaded the rope. And except for the elastic limit constraint, it has nothing to do with "elasticity."


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## Blinky (Feb 2, 2007)

Long as we're on the subject of ropes, this is just an interesting side note...

I took a 3' section of long retired Mammut Dynaflex (over 25 years old; dynamic rock rope; held several screamers while in service) and removed the sheath to make a dog collar. The core was two woven strands of nylon. Each of those strands became a chew/pull toy for the dog, an extremely hyper Border Collie puppy who utterly disfigured them. A few months later I hitched each end of one of them and weighted it in my harness... fully expecting to break it. No dice, I couldn't break it or slip the knots even by bouncing on it.

1/2 of a 25 year old rope, ragged and slobbered on by a dog for a few months and it still holds body weight without strain...

Moral:
Kernmantle sheaths make great dog collars and climbing ropes are incredibly durable. From what I understand, even a 25 year old rope will retain most of it's static tensile strength. Aging does seriously affect breaking strength under dynamic loads... like, it will break the first time you drop a weight on it. (ref. Wilderness Search and Rescue - Setnicka)

Though it was worth mentioning.


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## moray (Feb 2, 2007)

*aging dog leash*

Cool post! Nothing like a real test of some kind to see how tough these ropes really are.

As to aging, I could speculate from my chemistry background that the most significant source of aging of a rope stored in the dark (away from UV light) would be ozone and other reactive compounds in the air. Store a rope in a closed box, and even that disappears. What's left? Possibly minimal (probably unmeasurable) degradation from cosmic rays. Probably UV at mid-latitudes is orders of magnitude worse than all the other factors combined, and even it is very slow to harm polyester. I personally wouldn't hesitate to use a 25-yr old rope that was stored in the dark.

A story: the local professional arborist, a real old-timer, is still climbing on his original 3-strand, 1/2 inch polyester rope. He has been using that rope as a full-time arborist FOR 33 YEARS!!!!

Finally, at my very loud urging, he has bought and started using a couple of modern ropes. I am trying to get him on the Internet so he can join ArboristSite.


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## TheTreeSpyder (Feb 3, 2007)

We are still on same coast hear. Elasticity is a property of rope etc. Elastic elongation is using this property(?) for the immediately recoverable part of elongation; that can also be used for force storage. We can also have parts of formula recovering from stretch a half hour later and some never recover; but still slow a fall. Impact of fall will be acceleration of fall divided by deceleration of deformations, both permanent and elastically. Both the input increase and the output increase; just manipulate the distance part of force over time.

But, any deformation is giving up distance, so all slows/ dissipates force (along with frictions between fibers giving up heat); but only the immediately recoverable elastic part can give you bounce, slop or be used to store force to use as either side of equal opposite is changed; whether adding more force or relieving load, to point where elastic contraction can take over and keep moving past or with more force than your efforts, from the force storage. 

Or something like that, heck i'm not a genius in a lab, just another idiot willing to hang life by a thread! But, these are the models i formulate by.

In SWL some speak of not just arbitrary ratio set different by each manufacturer as a percentage/ ratio of tensile strength; but also the SWL of a system's ratio of capacity to expected loading. One might say in dragging 4:1 is okay ratio, lifting 10:1 or life support 20:1. Maybe i'm just lysdexic; but as the safety ratio goes lower, the elasticity comes up; reciprocally (somewhat). Some years ago of these boreds; i started pointing out that just being macho and screaming for more tensile; that 100:1 SWL or more was the key to safety; ignored the female/forgiving/ softer side of safety; what elasticity does for us, and also how we fight it. Whether it fights us in inline tension purchase with pulleys, or non-inline/perpendicular purchase of sweating in etc. Also, how a 2:1 gives more capacity, so is safer statically and loads support less than 1:1, but on dynamic instance/impact can be less safe; because once again we are just looking at macho/ pure strength of line, not the softer forgiveness. Dynamics on 2:1 get less elastic response from line, so pull on support harder.

This elasticity i term as the feminine side of the balance is also the 1st to fade i think. So for life support this could be a consideration. Also, nylon absorbs more water from air than other synthetics, and along with it contaminates from the air? Strong bases (battery acid fumes) and strong acids (feline urine) degrade rope greatly. Some markers do to; the inert ingredients can legally change according to market price. Strength loss from markers don't show on standard straight pulls as well as as the marked region turns over the edge of cliff etc.


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