Dyneema and Nylon Drop Test

Symbioun

Symbioun

Location
Toronto ON
Interesting video done by the people at DMM. It's not really directed at the arboriculture community, but it started me questioning the use of dyneema slings in a dynamic rigging situation. It would be great to hear some feedback.

DMM

And you will need Quicktime to view this video.
 
There is a difference between having static/ nonstretch components in a dynamic rigging situation, and having a complete static system. Additionally, the tree will absorb some energy, to greater and lesser extents depending on the size/ shape of the tree at the rigging point.

I wouldn't use a dyneema sling to attach a block to a tree, then use a UHMWPE rope, and wrap and lock a POW, then drop a log onto it.

I would use an appropriately sized dyneema sling to attach a block to a tree, use a static-ish/ regular or polydyne-type rigging rope, wrap the POW, then drop a log onto it, letting it "run".

How much "give"/ stretch does a tenex or rope anchor sling have?
 
southsoundtree is exactly right. It's the totality of the system that needs some stretch to avoid excessive dynamic loads. You already have components of the system with essentially zero stretch (blocks, shackles, POW) and you don't seem to be worried about that. Same goes for the sling as long as it is a small part of the total. And as SST implies, if you let it run, no part of the system needs to have any stretch.
 
WOW! Thank you for posting this.
Very interesting. That'll give us climber's with dyneema or spectra bridges something to think about.

Sean, using polyester or a poly/nylon combo is the best thing riggers can use in catching wood. I only use my poly cover/Dyneema core rigging ropes on the GRCS for lifting purposes. For catching wood, the poly cover/nylon core rigging ropes come out.
 
Good point Norm. I didn't think about the people climbing on dyneema blend bridges.

SST: It's true you can just allow the wood to run and dissipate the energy using the POW and the elasticity of the rope. But wouldn't it make better sense for your system to have a greater amount of elasticity to disperse the energy throughout the whole system? Using a poly/nylon sling could add 10-12 feet of elasticity in the system that wouldn't be there if using a dyneema sling.
 
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WOW! Thank you for posting this.
Very interesting. That'll give us climber's with dyneema or spectra bridges something to think about.

Sean, using polyester or a poly/nylon combo is the best thing riggers can use in catching wood. I only use my poly cover/Dyneema core rigging ropes on the GRCS for lifting purposes. For catching wood, the poly cover/nylon core rigging ropes come out.

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I agree with what you are saying in the latter half. I don't know if I gave the impression to the contrary.

As to the beginning, what is the implication of having a dyneema/ spectra bridge? Is there not pretty much always some shock absorbing aspect to the system with a climbline, aside from climbing on a dyneema core (type) rope? I wouldn't want to drop onto any short tether with any fall factor, really. Whether nylon or spectra, the body of the climber would be absorbing most of the energy. No good.
 
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SST: It's true you can just allow the wood to run and dissipate the energy using the POW and the elasticity of the rope. But wouldn't it make better sense for your system to have a greater amount of elasticity to disperse the energy throughout the whole system? Using a poly/nylon sling could add 10-12 feet of elasticity in the system that wouldn't be there if using a dyneema sling.

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I'm not sure about the 10-12 feet of elasticity part. What do you mean by this? If you mean a 10-12 foot sling, the effective length would be less. It would only be 10-12' if it wasn't wrapped around anything. Friction with the tree reduces effective amount of stretch.

I think that it would make more sense to use a stretchier rope for reducing the impact force given the appropriate amount of distance to an obstacle is available.

Additionally, a person that is blocking down wood on short sections of traditional ropes can re-direct at the base of the tree through a block to a remote anchoring tree for the lowering device to add more effective length of rope into the system to increase the elasticity of the system.
 
Good discussion!

One bad thing about using HMWPE slings is the low temp rating they have. They can burn easily under the impact of heavy shock loads, even in a dynamic loading operation.

I have a 5/8 spectra sling but it's seen little use, so I can't say my knowledge is first hand. Ny guess is, it would take a lot of use before it lost enough tensile strength to be a problem, due to its ~55,000 lb rating.
 
Thank you. Does Vectran and Spectra fall into a similar category? Would a polyester cover on a HMWP sling give a modicum of stretch? Paul
 
Paul,

Have you heard about Dynasorb/ Polydyne? They are stretchy/ elastic rigging ropes. Sorta a bungie cord for rigging.

I haven't used them, but some others here surely have.

The cover will protect the core. I don't believe that any energy absorbing will occur.





I'm a rock climber as well as a tree climber. Rock climbers routinely look at 10 foot falls with no "running" at the friction device/ belay device (akin to the lowering device).

I've fallen as far as 35 feet before. This is not that much. No harm from the fall. There were static components in the fall arrest system (three carabiners (well actually carabiners do a stretch a little under load), amongst other gear) attached to a rock face that doesn't move, unlike a tree moving a slight bit. The important part is that the whole system is not static.




This is a video about rock climbing, not rigging moving parts of trees.

What this video is testing is essentially analogous to putting a dyneema sling around a very stout tree, and attaching it to a rigid dyneema harness, climb up above the tie-in point and drop to the end of the sling, or climb up so that the harness is even with the tie-in point and drop.

The test show what would happen if the climber were to attach themselves to a mid-wall anchor point ("belay anchor"/ "belay station") on a tiny ledge where they could stand without holding on, with a dyneema sling, have slack in the tie-in system, then slip off the ledge into free fall.

I attach myself by the dynamic lead climbing rope to the anchor in such situations for this reason, and others.
 
Hi all,
Mark Twain said, "If a cat jumps up on a hot stove, it'll never jump up on a hot stove again. Of course, it will never jump up on a cold one again, either." I like Sean's system approach of seeing component characteristics in the context of the job, rather than fixating on selected variables.
As a note from the sailing side of things, Nylon is indeed capable of absorbing energy, which is why it is almost universally used for mooring and anchor lines, but it is also fabulously vulnerable to chafe and UV, and will abrade/melt itself internally under heavy loads, notably where it passes over things like blocks and fairleads. And because it is elastic, more of its length will rub on these surfaces, exacerbating chafe and heat.
Regarding UV, recent tests on some roughly 10-year-old nylon in the Chesapeake showed strength reductions down to about 1/3 of original. The line was lightly used, and didn't tend to break at chafed spots, but where sunlight had the most effect.
Other than that, there is such a thing as too much elasticity; sure you just absorbed the shock load, but did you also just launch the object off on an interesting new vector? That's why I love to watch someone who is good at managing drops with a dynamic belay, using a moderately elastic line -- they take the energy to zero. Very Aiki.
As for the Spectra saddle bridge, the run is too short for elasticity to matter one way or another. It seems that what you want there is utter strength, as well as abrasion resistance.
Fair leads,
Brion Toss
 
Hey guys, great thread.

I believe this video was made as a response to a lot of debate and controversy going on in the rock climbing community with younger climbers using slings and daisy chains rather than their climbing lines to attach themselves to anchor points while doing multi-pitch climbing.
While there are many variations in danger levels (on the one end, using 2 nylon daisies with no slack on good quality bolt hangers is not really dangerous, and on the other end using dyneema slings with lots of slack on a trad anchor could be extremely dangerous) many folks have been unaware of this danger as dyneema slings became integrated into the average climber's toolkit. I appreciate that many folks such as DMM and Black Diamond have gone out and released warnings to this effect, and this video is the clearest and simplest explanation I've yet seen of the issue.
I especially appreciate that they didn't insult anyone's intelligence here; they clearly explained the materials, their properties and limitations, rather than resorting to 'do this don't do that' narratives. One thing I would have liked to see is another run of the test with a girth hitch on one end of the sling, as this is how most rock climbers attach slings to their harnesses.

NewMainer- pretty sure that's the new DMM Dragon cam, which has a VERY similar design to the camalot. I'm one who thinks that for what they are camalots are damn near perfect, but I bet if anyone can make a better one it's DMM.
 
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