Why use dyneema for anchors instead of nylon?

So I'm an AMGA Single Pitch Rock aspirant and in my teaining, one of our biggest points about building anchors is that nylons is the best option over dyneema due to its higher stretching capacity. In fact, my instructor insists that the only thing I should use dyneema for is draws. Anyway, in the little ice climbing I've done and onserved, I've come under the strong impression that ice climbers much prefer ro build belay anchors out of dyneema. Why?

It doesn't absorb water and then freeze.

Dylan Pike wrote:It doesn't absorb water and then freeze.

Dyneema doesn't absorb as much water as nylon and so is less prone to freezing.

Dyneema is absolutely fine for anchors as long as one is sensible about how one attaches oneself to the anchor. Attaching with dynamic rope is going to provide as much protection to the anchor (and a falling climber's body parts) as possible; in that case whether the anchor itself is made of dyneema is irrelevant.

The one situation that is not optimal is clipping a dyneema anchor with a dyneema tether. Even this is no big deal as long as the climber stays below the anchor and keeps any slack out of the tether.

If the climber is belaying a leader, the climber's attachment to the anchor should be via dynamic rope to provide some energy-absorbtion in the case of a factor-2 fall.

Yer definitely gunna die if you build that TR anchor with dyneema. TR anchors need tons of elasticity for those huge loads encountered.

Sorry, just have yet to have a good experience a single pitch "guide." From them either teaching false information, to making an anchor that looked like it could have been in top rope tough guys
, to them being worried about how fast we were moving off of our route next to them when we'd done two routes in the time it took them to rotate through one client on TR.

Maybe I'm being to critical here, but beyond any question of material properties, I find fault with the instructor's insistence of "always nylon." IMO, there are very few hard and fast rules like that in climbing and having an understanding of why you made your anchor a certain way is way more important than specifically which material your slings are made of.

Peak loads on the climber and gear are a function of many things. For this question, focus only on the length and elastic modulus of the components that make up the system.

In a system where the length of dynamic rope out is large, relative to the anchor sling, the material used for the anchor sling is insignificant. For an extreme example, consider a fall, where there is 60m of rope between the belayer and the climber. The peak force will primarily be a function of the rope's properties, not the anchor sling.

In a system where the the length of dynamic rope is small, relative to the anchor sling, the material used to for the anchor sling becomes more significant. For an extreme example, consider a fall, where there is 0m of rope between the belayer and the climber. The peak impact force will be lower with a nylon anchor sling than with a dyneema sling, but high enough in either case to potentially cause injury to the climber or to cause gear to pull out.

Factor 2 falls directly onto the anchor with little to no rope out, should be avoided, regardless of sling material used to build the anchor. In general, you should never climb above a webbing anchor, when tied directly in directly to the sling (no dynamic rope in system).

In summary, nylon slings are only significantly safer than dyneema slings in rare, avoidable cases of falls above the anchor with no dynamic rope in the system.

A fat nylon sling is great for a tether though. For abrasion resistance and that extra dynamic stretch. Pretty much all the other slings I use are dyneema. For the anchor i just use the rope

Matt.Zia wrote:Maybe I'm being to critical here, but beyond any question of material properties, I find fault with the instructor's insistence of "always nylon." IMO, there are very few hard and fast rules like that in climbing and having an understanding of why you made your anchor a certain way is way more important than specifically which material your slings are made of.

It also discredits the AMGA as a source of reliable information. But we don't know exactly what the instructor said or how he may have qualified his comment. We only have what the OP heard.

By the way, although nylon tethers will absorb more energy than dyneema ones, and don't break in factor-2 fall tests the way dyneema can, no one should confuse a nylon tether with a similar length of dynamic rope. For example, years ago one of the European alpine clubs tested a nylon runner and came up with a UIAA impact force of 18 kN. The UIAA has set 12 kN as the maximum allowable impact load for ropes in near factor-2 fall situations, and this based on old tests on humans in rocket sleds, where the harnessing distributed the load more evenly than a climbing harness. Industrial standards for fall-protection harnesses set the bar at 8 kN in the US and Canada, and tests using a humanoid manikin indicate that falling in a sit harness with the body parallel to the ground and facing up at impact will break the spine at 4 kN. (Fortunately climbers don't fall in this orientation much.)

If a climber believes that, for some reason, an anchor that is as resilient as possible is called for, then the best strategy is to build the entire anchor with the climbing rope.

Thank you RGold and GunkieMikie!

Indeed, please do NOT take a lone single-pitch instructor's opinion as "the AMGA way," nor as authoritative. There are plenty of AMGA-recommended books and videos to give you an idea of the range of appropriate tools and techniques, Mikeybarro!

As long as the rope is in the system, you've got a dynamic component and your worries about static materials are mostly mitigated.

Keep in mind, too, while Dyneema/Spectra doesn't technically absorb water, the fact that it's a woven material means there's always some water that inherently hangs out within the fabric itself if you expose it to running water---so eventually even Dyneema gets stiff/frozen/bitchy on wet/cold days!

Check out the excellent SPI book by FalconGuides and you'll be stoked on The Mountain Guide Manual coming out in May, also by Falcon. I haven't seen it yet, but Topher's book (Advanced Trad Climbing, I think is the title) published by the Mountaineers is probably awesome, too.

Good job pursuing your SPI, dude!

Do keep in mind guys that this instructor is no schmuck. He has over thirty years climbing experience, is a huge developer of the New River Gorge, and has several first big wall ascents in Argentina. That being said, when he criticized my use of dyneema to construct an anchor on bolts, he simply said, "There is a good option, and there is a best option. Dyneema will get the job done but I want to see you use the best option and that's nylon. And I want you to know why that's the best option... (reasoning for why)." So don't be too shocked by or too critical of the AMGA instruction.

If he really wanted you to use the best option, it would have been the rope itself...

Well in a single pitch environment using the rope to build an anchor doesn't make a whole lot of sense.

With the caveat that your instructor did include the bit about "good ways and better ways" I feel more comfortable with his assertion. One other consideration is that guiding in the single pitch environment generally doesn't include long approaches and often includes natural top rope anchors with slung trees, rocks, etc. For those reasons, nylon does make more sense as it's cheaper and you don't need to worry about weight/bulk, and nylon is better for tying knots than dyneema. But I'd still feel 100% comfortable using a dyneema sling in an institutional top-rope anchor.

Mikeybarro wrote:So I'm an AMGA Single Pitch Rock aspirant

In a single-pitch environment where the anchor loads come nowhere near testing the limits of the anchor material, there is no reality-based argument for nylon over dyneema in terms of strength and resilience.

There are, however, far more pressing concerns having to do with unanticipated abrasion of the anchor material, either because the top rope load swings through an arc or because some or all of the anchor passes over an edge. In the case of loading over an edge, static materials may be preferable to something stretchier that elongates and shortens under periodic loading and may contribute to sawing.

If any kind of abrasion seems possible, even when padding is used, I'd want to stay away from any of the ordinary thin slings used for multipitch and alpine climbing. If they are used, I'd be doubling and tripling them up for redundancy. It's not as if there is any imperative to go light.

The best material for top-rope anchors is beefy 9mm static rope. If any kind of rope or anchor sling motions are possible, it is best, if possible, to set up a gear anchor just over the lip on the cliff face and then have the main anchor back this up snugly, but without taking any load unless the gear anchor actually fails. The point of the gear anchor is to keep all rope motions and periodic loading away from the anchor strands.

RangerJ wrote: Related question - When did the aspirant term get attached to the SPI?

Rich, you've been using twins too much...in what world is 9mm "beefy"? Lol. I've heard people call for 11 mm static for such situations, but really some thoughtful padding can make such considerations redundant.

Maybe so Ted. I used "beefy" to contrast with other sling materials such as one-inch webbing.

In order for a Rock Guide wannabe to be an Aspirant they must take the class then take the Aspirant Exam then they go work in the field and take the Rock Guide Exam. This is why we are confused as to how one becomes an SPI Aspirant. You're just some dude who took a class and may-or-may-not know enough to pass the test.

Mikeybarro wrote: It means you have taken the class but have not taken and passed an exam, and so are not yet a certified SPI.