Slings - Static or Dynamic?

JohN Dee

Well as some of you know, for lowering, I use the sling and biner idea. I'm about to update my slings to a higher rating, but i'm not to sure which would work better...

Static or Dynamic?

I've been thinking probably static, because the shock loads that are created would be directly sent straight through onto my lowering line which is dynamic, but i'm not absolutely sure if that is the case?

Well anyways, I posted my opinion here, hopefully you guys post yours and I can be definate with my purchase.

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Sean Freeman

The rigging line we use is static esterlon 1/2" so the slings are static too.

Eric Frei

Hmmm, is that a first, dynamic rigging line, tell me more.

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JohN Dee

Lol Eric I feel like a knob now... Our lowering line is indeed static... I was always under the impression that is was dynamic until your post.... Which brings my attention to something else... With your climbing bridge.. Split tail as some call it, do you reckon static or dynamic would work better?

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We are what we repeatedly do... Excellence then, is not an act, but HABIT...

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Tree Machine

The short length has a lot to do with it, split tail or sling.

I don't think a dynamic sling (or dynamic split tail) would stretch much, given that the length is so short. For instance, a 1 meter long eye-eye sling with a 5% elongation at 100 Kg would stretch 5 cm (~2"). This is on paper. In the actual act, once the sling chokers down, the portion of the sling actually wrapping around the limb would stay (more or less) situated in a static sense, and the portion from the limb to the rigging line would take the 'stretch', making the overall stretch even less. I think this is so minimal as to offer next to nothing in the practical sense of shock absorbtion.

Now, of course, these numbers are anecdotal (not shown in a scientifically objective way whatsoever), but from a purely practical standpoint you would have to ask, what benefit would there be for the sling to stretch (which it does to a small degree anyway)?

I would worry about sewn slings stretching and distorting the stitching.

Research and science can measure, with a dynamometer, the forces exerted on the dynamometer, and those force totals are extrapolated to mean this is the force being placed on the, in our case here, the sling. But, that part of the sling around the limb and through the caribiner is subject to the force of friction as well, and that friction is affected by the diameter of the limb as well as the overall surface contact and the texture of the bark and maybe other factors like if the limb were wet.

From the standpoint of physics, the stretch characteristics of the overall sling can not accurately be measured. Without precise, accurate measurement, objective data can not be scientifically expressed. If it can not be scientifically expressed, anything we have to say is anecdotal.

Not that this is bad or anything, it just is what it is.

Any discussion, therefore, is conjecture. Information in this sense, then becomes empirical.

Some things don't need accurate measurement, just accurate interpretation of what's going on. So much of Arboriculture is just this.

Eric Frei

I think I have found a scientific document on this very topic written by a guy with a PHD

Only thing is it needs translating into something ordinary people understand.

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This site does a good job of explaining in plain English how the stretch factor works and how it is measured when the manufacturer gives it to you, yes there a standard way of doing it so all figures are from the same hymn book.

MountainZ.co.nz - All about mountains. Mountaneering, rock climbing, ice climbing, skiing, snow boarding.

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Most rope manufacturers will provided % stretch usually.

In this link New England Ropes - Climbing Products you can click on the ropes and get some figures.

In this link you can also do the same but these are dynamic ropes and stretch factors will be given.

New England Ropes - Climbing Products

Other figures around the net show that dynamic ropes will stretch as much as 50% before breaking, where as our static ropes only 15% ... but that's to breaking point which we dont do. This can be seen around page 13 of the attached document.

MountainZ.co.nz - All about mountains. Mountaneering, rock climbing, ice climbing, skiing, snow boarding.

Attached Files

friction_in_rope_rescue_Attaway.pdf (463.2 KB, 139 views)

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Tree Machine

Thanks, Ekka.

Wow, that pdf article is the best I've ever read. True, it takes some deciphering, but at the same time it's a technical article that doesn't require that you understand really any of the mathematics, just the concepts that the mathematics describe.

I've had two semesters of college physics, but truly I can't use or understand the equations, but friction IS physics. It follows universal laws of behavior and can be calculated. On planet earth, in outer space and throughout the universe, friction is friction. It's predictable and doesn't change. What does change is the friction coefficient, or how frictiony something is on something else.

The author does a fabulous job, though, as he drills the well deep into the heart of the the science but does an even MORE fabulous job of keeping the article on track in that we're talking about ropes, slings and friction devices. It's quite understandable if you weed out the stuff thats not understandable.

This is the stuff that we as riggers and climbers and search and rescue and aerial technicians do. I would encourage everyone to follow through and read the article, more or less ignore the math and formulas and pick out the nuggets of knowledge that apply, which is quite a bit of practical, understandable stuff. Just don't be intimidated by the equations.

Hey, here's a good supplier of all things slings and rigging. My personal, most-used rigging sling for solo, aerial rigging is the 4-foot, rated eye-eye sling, which when the two eyes are binered and clipped to your hip is only half that overall length so it doesn't get hung up in your feet.

George Hayduke

Sewn webbing slings have a long and successful performance history. They have been used in lots of applications and are solid workhorses. Worrying about thread or stitching stretching...huh? You gotta be kiddin' ???

Reminds me of The Worry Song by Monty Python

"I get so worried about
The baggage retrieval system they have at Heathrow"

I've taken short pieces of retired climbing lines and tied them into loops using double fisherman's knots and used them for rigging chokers. After doing some simple math to calculate the strength and considering that when I rig with them they work like draft horses. The only time I ever broke one was when I used them for ground dragging chunks and they came across a driveway or rock.

Tree Machine

What I'm saying is short of breakage, that would be the only worry, not that I'm worried about it on an emotional level, I climb on the same stuff as you, usually my own tied slings out of 1" tubular webbing with a Beer knot, or a Water knot, but usually the former. But actually worrying about the stitching? No need for concern. I'm sorry I wrote it like thatSure, as have we all. A seasoned rigger is going to have a collection of different slings, different materials, different length, different styles and different ratings for the various rigging tasks that come up.

Slings are the foundation of lifting or rigging down things that have mass.


Slings are static, by design, as stretch lends an element of unpredictability. When you have stretch, it's because you have elasticity. If you have elasticity you have the potential for bounce. Bounce is usually not good when dealing with heavy loads. But then again, that's a generalization.

Eric Frei

I have a swag of slings however my favourite ones are 9/16 double braid ... just the weight is real nice to flick through forks etc, nice to handle ... love em.

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rbtree

Bump this old thread.

Just some note about the various lines that can be used in tree work.

Full static lines are made from near zero stretch fibers; dyneema, spectra, vectran, kevlar.....some are jacketed double braids where the cover is polyester. These lines' stretch at break point is very low, and should not be used for any rigging where a shock load is possible. Pulling, lifting, speedlining applications are what they're best for.

Then, both our normal rigging, access and life lines are semi-static, as their stretch under body weight (climb lines) or 10% of tensile (lower lines) is 1-4%. So, there is enough give to keep shock loading down a bit. But that amount of stretch is far less than a dynamic rock climb line, and the reason why we should never risk a fall onto a slacked line, as the Kn forces will quickly reach injury causing levels.