Dyneema Sling Extension How to best tie

May I please have tested facts, data, on how best to attach a dyneema sling to harness Tie-in-points (leg and waist loops) between:
a) Girth hitch to tie in points (girth reduce strength, no redundancy)
b) basket through tie in points with no knot in the basket sling (no redundancy)
c) basket through tie in points with overhand knot in the basket sling (knot reduce strength, it is redundant)
Please avoid just opinions as I’m looking for a guide style analytic constructive discussion based on facts 

Why are you attaching a Dyneema sling to harness? May help us give some better insight. If you are using it as a way to anchor yourself, don't. jUsT UsE a ClOve HiTcH

Noah R wrote: Why are you attaching a Dyneema sling to harness? May help us give some better insight. If you are using it as a way to anchor yourself, don't. jUsT UsE a ClOve HiTcH

I’m guessing to extend a rap. 

The two most common methods are a basket hitch to an overhand knot, or a girth hitch to overhand/overhand on a bight. Advantages and disadvantages to both as far as usability, but strictly in terms of strength, a dyneema sling is rated to 22kN and a knot reduces that by somewhere in the neighborhood of 30%. If you’re using a tether properly (ie not introducing slack) you won’t ever be able to generate enough force to break the sling in any of those tethering configurations. Now if you start introducing slack into the tether and taking falls directly onto it, there’s potential to generate enough force to break the sling. 

Yeah forget ever using dyneema as a PAS. Nylon is more dynamic and holds knots better.

Chris C. wrote:

I’m guessing to extend a rap. 

I hope you are right!

In a different context, this write-up and video from DMM has some data on the relative breaking strength of the basket hitch and girth hitch (lark's foot).  

Albi Eds wrote: Yeah forget ever using dyneema as a PAS. Nylon is more dynamic and holds knots better.

The only knot-holding concern I've ever heard re. Dyneema is the inability to tie Dyneema webbing (which you can't buy off a spool anyway, so moot point) into a loop. The sort of "tie an overhand in the middle" knots relevant to tethers are not subject to coming undone regardless of how slippery the material is.

On the other side, a Dyneema sling would be incrementally more prone to burning through if a moving rope e.g. rap line, were to run across it. So yea, use a nylon sling.

Gunkiemike wrote:

The only knot-holding concern I've ever heard re. Dyneema is the inability to tie Dyneema webbing (which you can't buy off a spool anyway, so moot point) into a loop. The sort of "tie an overhand in the middle" knots relevant to tethers are not subject to coming undone regardless of how slippery the material is.

On the other side, a Dyneema sling would be incrementally more prone to burning through if a moving rope e.g. rap line, were to run across it. So yea, use a nylon sling.

My understanding is that tying a knot in dyneema and then shock loading it like on a factor 2 fall can create enough force to cause the dyneema to burn through the knot and snap the material. My mentor always says "treat dyneema as if it is a steel cable" It's strong af but because it's more static material it should be treated that way. Also untying an overhand on a dyneema sling suuuuuucks!

Of course there is an exception with some materials that are blend like the Mammut Magic Slings which combine the best of both worlds, it's a nylon sheath with a twisted dyneema core and retains strength with knots tied in it. So perfect for a PAS, Quad and general tree slinging.

Sebastien Jacob wrote: May I please have tested facts, data, on how best to attach a dyneema sling to harness Tie-in-points (leg and waist loops) between:
a) Girth hitch to tie in points (girth reduce strength, no redundancy)
b) basket through tie in points with no knot in the basket sling (no redundancy)
c) basket through tie in points with overhand knot in the basket sling (knot reduce strength, it is redundant)
Please avoid just opinions as I’m looking for a guide style analytic constructive discussion based on facts 

You should hire a guide to get "guide style analytic constructive discussion." Otherwise, you're going to get MP-style discussion.

Just girth hitch it.
Never has failed for anyone who doesn't leave it on their harness for extended periods of time.

Next question

Chris C. wrote:

I’m guessing to extend a rap. 

I always tie in to anchor using the rope. Extended sling question here with is for extended belay device rappelling (single, tandem, counterweight, all rescue scenarios considered. 

To all, I’ve been climbing / guiding for 25 years so spare me your novice opinions and please stay constructive . 
We all know dyneema is static and the question here is technically a debate between sacrificing strenght  (with a girth or a knot after the basket), which provides redundancy but sucks to untie - could fatigue the dyneema (read longevity of dyneema repeatedly knotted in for a basket) vs the absence of redundancy with not having a knot      In the basket or by simply using girth hitch. 

Here’s an entire BD post on this. Short version. Girth hitch to your tie in loops. Avoid knots in any sling if at all possible.

​BD Personal Anchors explained​​​

I use a 120cm dyneema sling to extend my rap. girth hitch through master points, tie a bight about halfway to clip your ATC to, then use a locker on the free end and clip that back to your belay loop, use locker to anchor at rap stations, and always thread your ATC and weight before taking the locker off the anchor.

Sebastien Jacob wrote:

To all, I’ve been climbing / guiding for 25 years so spare me your novice opinions and please stay constructive . 

Um, have you forgotten where you are posting?

Marc801 C wrote: Um, have you forgotten where you are posting?

Take it easy Marc, he may be a ST refugee

Sebastien Jacob wrote:

I always tie in to anchor using the rope. Extended sling question here with is for extended belay device rappelling (single, tandem, counterweight, all rescue scenarios considered. 

To all, I’ve been climbing / guiding for 25 years so spare me your novice opinions and please stay constructive . 
We all know dyneema is static and the question here is technically a debate between sacrificing strenght  (with a girth or a knot after the basket), which provides redundancy but sucks to untie - could fatigue the dyneema (read longevity of dyneema repeatedly knotted in for a basket) vs the absence of redundancy with not having a knot      In the basket or by simply using girth hitch. 

You've been guiding for 25 years and don't know if a knot in your Dyneema rap sling is OK?

A knot will reduce the strength of a sling, but not enough for it to be a concern for body-weight rappeling. Replace your sling every couple of/few years and you're good. Next question.

Sebastien Jacob wrote: May I please have tested facts, data, on how best to attach a dyneema sling to harness Tie-in-points (leg and waist loops) between:
a) Girth hitch to tie in points (girth reduce strength, no redundancy)
b) basket through tie in points with no knot in the basket sling (no redundancy)
c) basket through tie in points with overhand knot in the basket sling (knot reduce strength, it is redundant)
Please avoid just opinions as I’m looking for a guide style analytic constructive discussion based on facts 

Single rope (no redundancy)

Single belay carabiner (no redundancy)

Single belay device (no redundancy)

Single belay loop (no redundancy)

Why do you need redundancy for gear rated far beyond the strength for the purpose for which it will be used, when all the items mentioned above are rated for dynamic forces?

Start there for a guide style analytic constructive discussion based on facts.

My go to method which I learned in a field session with a guide who posts here occasionally:

Basket hitch on the belay loop with a single length runner.

Pros: Strong, fast, and simple. Nothing to tie or untie. Easy to inspect for you and you partner, and spacing is just right for autoblock on the belay loop.

Cons: Not redundant, but I really don't expect a 22kn sling to fail. Name one climber ever who has had their rappel extension cut in half.

For multiple rappels this setup is about as clean as it gets, and is redundant as an added bonus.

John Clark wrote: I use a 120cm dyneema sling to extend my rap. girth hitch through master points, tie a bight about halfway to clip your ATC to, then use a locker on the free end and clip that back to your belay loop, use locker to anchor at rap stations, and always thread your ATC and weight before taking the locker off the anchor.

4/10 troll.

lol, let me make this account TODAY so i can demand people do research on my behalf because im too lazy to do it on my own...yet 'IvE BeEN CLiMbinG and GuiDIng 4 OVer 25 YEERZ!!! DOnt TEll mE Basic STuffS!'

well done though.