Author Topic: Dyneema shock/safety cords  (Read 3609 times)

Offline Topimo

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Re: Dyneema shock/safety cords
« Reply #50 on: June 15, 2018, 12:18:13 pm »
This leads onto another point: what do people think is the best way of protecting a traverse such as this without using a descender, which is sub-optimal in a number of ways (takes ages, uses a lot of excess rope, clumsy)? If bolting a new traverse (no P bolts to clip into) which is very exposed (ie few useful foot and handholds), I generally use my jammer on my short cowstail as a positioning tool backed up by my long cowstail (screwgate) clipped to a knot above the jammer (to avoid the situation I outlined above). If there are truly no real holds, I would use a skyhook for positioning, but then this has to go on a cowstail or other attachment point. this is where carrying an extra attachment point comes in handy. Obviously you can clip the previous bolt and just reach out sideways from there, but then you would end up using a shit load of bolts on a traverse line, especially if you have short arms like me.

A non-toothed jammer like a Shunt/Microcender?
Fig-8 descender as it's smoother?
C-rigged simple?
A running clove hitch?

Offline nobrotson

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Re: Dyneema shock/safety cords
« Reply #51 on: June 15, 2018, 01:19:26 pm »
the fig8 and clove hitch could put twists in the rope, so not ideal. Locking off a fig8 is a bit of a faff as well so I would probably not use that. I used to try the clove hitch and found it faffy and inconvenient as well. shunt is quite a nice looking bit of kit that I don't have and have never used, though I am not sure how much I would use it in caving outside of this purpose (quite a good backup option I guess). C rig could work quite well, never considered that. I think its quite good to use progression knots so that the derigger has a bit more protection as well, and it means you don't have to faff adjusting the rope lengths too much as you may do if using a descender.
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Online Mark Wright

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Re: Dyneema shock/safety cords
« Reply #52 on: June 15, 2018, 02:41:45 pm »
I use a Shunt for vertical and horizontal aid climbing unless there is somebody there to offer me a belay through, e.g. a GriGri.

The only issue with a Shunt is if you grab it or grab the rope above it if you did take a fall. Your natural reaction in a fall is to grab whatever is in front of you. I know, I've done it.

Its unlikely you would have much of a use for it outside of this application though.

A cheeper alternative is to simply use some type of Prussik knot.

I've also used a half loaded Stop which saves carrying anything else and this has worked OK for me on a number of occasions and still gives you the auto-lock facility.

Mark

Offline nobrotson

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Re: Dyneema shock/safety cords
« Reply #53 on: June 15, 2018, 03:43:38 pm »
I use a Shunt for vertical and horizontal aid climbing unless there is somebody there to offer me a belay through, e.g. a GriGri.

The only issue with a Shunt is if you grab it or grab the rope above it if you did take a fall. Your natural reaction in a fall is to grab whatever is in front of you. I know, I've done it.

Its unlikely you would have much of a use for it outside of this application though.

A cheeper alternative is to simply use some type of Prussik knot.

I've also used a half loaded Stop which saves carrying anything else and this has worked OK for me on a number of occasions and still gives you the auto-lock facility.

Mark

Never considered the idea of getting a belay but the concept appeals to me especially considering the nature of one of the leads we hope to pursue in Austria this year. Should have been obvious.

If you were to use a prussik knot is there a particular material that you would recommend using for the prussik knot, bearing in mind that you said accessory cord shouldn't take falls (which I agree with). I have used a 60cm 8mm dyneema sling as a prussik loop before which seemed to work quite well but would the dyneema react well to being fallen onto?
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Online Mark Wright

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Re: Dyneema shock/safety cords
« Reply #54 on: June 15, 2018, 04:02:39 pm »
Having a belay is probably the safest option and could be done through either a fully or half loaded Stop depending on the rope diameter and stiffness.

I would probably use something like 5mm or 6mm accessory cord for the Prussik knot. You don't have to worry about the energy absorbency as this comes through the Prussik knot slipping should there be a fall.

Mark

Offline nobrotson

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Re: Dyneema shock/safety cords
« Reply #55 on: June 15, 2018, 04:23:28 pm »

I would probably use something like 5mm or 6mm accessory cord for the Prussik knot. You don't have to worry about the energy absorbency as this comes through the Prussik knot slipping should there be a fall.

Mark

cheers, I thought as much but had never considered the material before so thought I would ask.
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Online Mark Wright

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Re: Dyneema shock/safety cords
« Reply #56 on: June 15, 2018, 07:37:15 pm »
Tree surgeons and rope rescue teams use them all the time, especially in the US.

Heres a link to one of the rope rescue equipment manufacturers with information on prusik cord.

https://www.cmcpro.com/equipment/prusik-cord-load-release-hitch-cord/#learn_more


This one shows prusik knots used in a rescue system (top right of the block of photographs on the second to last page)

https://www.cmcpro.com

The relatively low breaking strengths might be a bit misleading. When they are tied in a loop they are twice as strong and because of the number of times they are wrapped around the main rope you don't really need to worry about any loss in strength because of the knot or the lark's foot loop as the dynamic fall slippage would only ever allow a minimum of loading.

I used prusik knots over 20 years ago on the Humber Bridge. We had them wrapped around the metal handrails to stop a potentially very high FF5 fall factor. They were replaced regularly. 

Mark

Online Mark Wright

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Re: Dyneema shock/safety cords
« Reply #57 on: June 15, 2018, 07:45:38 pm »
I've just noticed Starless River sell a complete SRT kit aimed at beginners and it has an 8mm accessory cord security lanyard and foot loop combination.

Mark

Offline Wardy

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Re: Dyneema shock/safety cords
« Reply #58 on: June 15, 2018, 08:33:11 pm »
At SpanSet we sell a variation on a lifting sling that is tested / used for choking round vertical scaffold tubes as an anchor point for fall protection.
Effectively it is a prusik used on a metal tube so locks up well, but can be slid into position.
Again whilst it is not the strongest use of the sling (to counteract this we use an over spec sling) it offers a really high level of safety as it can be placed high reducing the fall potential - Showing that whilst equipment choice is important, understanding how to get the most from the equipment you have is possibly even more important.
Which is why training for beginners is vital and discussions like this on a forum are great.
Wardy

Offline GT

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Re: Dyneema shock/safety cords
« Reply #59 on: July 21, 2018, 10:28:33 am »
Now that things have calmed down with work I wanted to re-visit this. After the original post, and my reply and subsequent questions, rather than answering with just my personal opinion I wanted to reply with a little more substance.

So I set about running a few drop tests with a load cell and a variety of different cords between a jammer and test mass. I've had some interesting results so far, which I'll happily share in due course, however wanted to complete a broader set of test including the Petzl advocated taped lanyard (Spelengyca), 8mm semi-static (which is actually rated as an accessory cord) and the original posts question on dyneema shock cord.

I've ordered and received some of this stuff (https://www.roostersailing.com/pd/Rooster-Dyneema-Shock-Cord_106711.htm) but  the thickest I've found is 6mm with a mean breaking load of 240kg; so basically not strong enough!

So back at the original post; what shock cord did you envisage using? Could you get me a link to the cord you were thinking of using? I should get some time to re-visit and finish the testing next week and get something written up...

Online Mark Wright

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Re: Dyneema shock/safety cords
« Reply #60 on: July 21, 2018, 12:07:45 pm »
I think the thread title has probably confused people.

I doubt the OP envisaged the use of the term 'shock cord' to mean an 'elastic cord' as GT is suggesting.

Mark 

Offline FionaH

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Re: Dyneema shock/safety cords
« Reply #61 on: July 21, 2018, 03:41:32 pm »
I can't speak for OP but I can tell you they are away on expedition at present so it might be more than a week before you get a response, GT.

Offline Chocolate fireguard

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Re: Dyneema shock/safety cords
« Reply #62 on: July 21, 2018, 07:09:23 pm »

I used prusik knots over 20 years ago on the Humber Bridge. We had them wrapped around the metal handrails to stop a potentially very high FF5 fall factor. They were replaced regularly. 

Mark

Nobody likes to show ignorance and I've been waiting weeks for somebody else to ask, but they all obviously understand.
How do you get a FF5?
The only way I can think of is to have part of the arresting rope replaced by steel cable, which can't be right.

Offline pwhole

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Re: Dyneema shock/safety cords
« Reply #63 on: July 21, 2018, 07:36:33 pm »
I'm guessing that if connected to a diagonal cable without the choke of a prussick and a fall were to occur, you'd slide all the way down the cable to the next junction and then your lanyard-arrest distance would kick in, so there's essentially two 'separate' fall factors to be added together?

Offline Chocolate fireguard

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Re: Dyneema shock/safety cords
« Reply #64 on: July 21, 2018, 08:44:36 pm »
I think I see.
So the cable and handrail were parallel and without the prusik on the handrail it would have been possible to slide down the cable for a (vertical) distance equal to 4 times the lanyard length?

Online Mark Wright

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Re: Dyneema shock/safety cords
« Reply #65 on: July 21, 2018, 08:49:29 pm »
I think I see.
So the cable and handrail were parallel and without the prusik on the handrail it would have been possible to slide down the cable for a (vertical) distance equal to 4 times the lanyard length?

That's exactly it.

Via Ferrata lanyards are designed for such FF's.

Mark

Offline GT

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Re: Dyneema shock/safety cords
« Reply #66 on: July 22, 2018, 11:30:09 am »
We'll be doing some drop tests on that soon as well!!

Offline rhyst

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Re: Dyneema shock/safety cords
« Reply #67 on: July 30, 2018, 08:25:37 pm »
In the original question I was referring to this sort of dyneema cord: https://starlessriver.com/shop/ropes_and_cords/pure_dyneema_5mm_per_metre

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Offline GT

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Re: Dyneema shock/safety cords
« Reply #68 on: July 30, 2018, 08:33:11 pm »
Cheers Rhys, so thats not really shock cord at all :)

Will drop some when the weather improves!!

Offline GT

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Re: Dyneema shock/safety cords
« Reply #69 on: January 03, 2019, 10:26:37 am »
Finally got around to writing up the results on some various options for lanyards between hand jammers and harness. The link is below but the rub of it is don't fall onto your jammers!

Dynema and sling type lanyards don't stretch so yield high impacts. 5mm accessory cord snapped (as did the dynema bungee cord)...

http://www.train4underground.co.uk/2018/12/30/drop-tests-on-srt-foot-loop-lanyard/

Offline marysboy

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Re: Dyneema shock/safety cords
« Reply #70 on: January 03, 2019, 11:05:22 am »
very interesting, thank you for doing that.