curiosity kills the cat: rappelling off a thin cord

If you’re going to go with thin cord to save weight, doesn’t using a specialised device like the prihana defeat the purpose?

There are many hitches available, beyond the simple munter, that work well on thin rope, and you can always back it up with a prussic if you want even more friction.

You can always make due with only beaners for both belay and rappel, even with doubles.

Tom’s paper is usful when you realise that an aramid rap line will be permanently weakend by the knot used for rappel. This effect is likely to be cumulative on subsequent rappels.

For that reason alone I would only rap once on it, and toss it after.

They get discarded after one use.

I wanted to echo the various points made about abrasion and cutting over natural edges) as the main concern in all climbing lines used for raping in Mtn./ outdoor enviornments. The breaking strength and heat resistance are distant considerations when compared to actual accident causes. Of course, user error and lack of training are the #1 causes of rap accidents.

A dry treatment on a rope is as important as actual rope weight, a wet rope can double in weight and a saturated rope loses half it’s ability to perform.
I am very interested in this thread because I’m using a 9.1mm rope with a 7mm haul line.
As Ron points out loading a rope over an edge is a huge issue in strength.

This website inspired me to buy 10 foot lengths of several ropes and tech-cords and test their abrasion resistance.

My test rig differed somewhat from the link above. One end of the rope was attached to a secure anchor 10′ above the ground. To keep the rope under tension, I tied into the other end so that I was suspended 3′ above the ground. I then measured the time/sweat required to saw through the rope with a blunt rock.

The 5 mm maxim tech cord (polyester cover, technora core) was disturbingly easy to saw through; much easier than 8 mm perlon. The polyester cover provided marginal abrasion resistance, but the technora core cut like a hot knife through butter.

Last yar I was introduced to 8 mm Dyneema (I think) on a tree climbing trip to Borneo.

We were in remote areas and so went light. A typical 600 foot rope for tree climbing fills an expedition pack. A 600 foot 8 mm spectra maybe one-quarter.

Anyhow, we were using Pirahna’s for rapping, but I really prefer Grig-gris and I’Ds because of the no-hands feature with them.

This year in the big Doug-firs of WA I started using my Grig-gris and I’Ds on the 8 mm Spectra and they worked great (all of this for rapping — generally tree climbers have anchors above) — any comments on why this might not be a good idea? Is it just the heat build-up? The Pirhana seemd to get hotter than my Gri-gri and the I’d won’t let me rap fast enough to cook the rope it seems.

Anyway, using 8 mm for big tree climing is super, but maybe I am missing something.

comments?

Chris, thanks for the BD report. The tip on webolettes alone was worth the read. As a relative beginner with only prior military climbing training, I really appreciate the info I glean from the more experienced posters. When hiking I usually carry a Beal Rando 8mm x 30m rope, 4m of 11mm which can double as a swiss-seat etc.., and a very basic rack (one each D-ring, locking biner, quick draw, nut, ATC, sling) for adding some safety to any non-vertical obstacles along my route. I am always looking for clever ways to multi-use my climbing gear.

We usually carry some abseil gear on our walking trips into Wollemi NP: there are a LOT of cliffs.

35 m of 6 mm nylon kernmantle line is fine for a careful abseil – much better than Spectra or similar. The likes of Spectra are just too hard to hold onto, and too slippery. Seriously dangerous imho. If you slip on it, you will find NO stretch, and it will snap you neck off (or feel like it).

We do NOT carry a figure-of-8 descender. These things mangle the core of a kernmantle rope badly. I reckon they should be taken off the market. When canyoning we carry a rack (like the Petzl one) as this gives a straight line with no twists. The difference on subsequent abseils is enormous. Walking we carry something like a BD ATC. Light, but once again the rope does not get twisted.
A couple of 4 mm slings to turn into a waist loop as needed, and one locking Alloy crab.
Ah yes – plus a pair of riggers leather gloves! They take the heat.

Cheers
Roger Caffin
Australia

Things to to keep in mind.

Bad things-

Low melting point of spectra/dyneema , it is polyethylene. I would check with Bluewater or
whoever makes the rope, for their use recommendations.

Slipperyness, some recommend using triple
fisherman’s knots for tying ends together or for slings, double
fisherman’s slip at about half the breaking strength.

IE-I don’t know if I would use a European death knot
for joining 2 ropes for rappel if either has a spectra core.

Good things-

Spectra’s properties should make it absorb very little water, less than nylon or polyester. It probably
would float even with a nylon sheath.

Unlike aramid fibers and wire cable it should withstand repeated kinking and knotting very well.

I would mention that neither an i'D nor a gri-gri will lock on an 8mm cord. I'd also mention that if you get in touch with Petzl USA, and you're connected with some sort of university study or similar, you might just be able to get a version of the i'D that works with 8mm cord.

Massive Edit. Please see post below…

I routinely use mammut 5mm pro-cord to rappel off of during solos. This a specialized rope, and one of the few I am comfortable rapping on by itself. There are multiple considerations when selecting thin rappel cord.
First off the cord must be supple enough to be run through a rappel device, nylon is by far the most suitable for this. Second, your rope must have a high breaking strenth due to the fact that under load a nylon cord this thin will stretch somewhat, creating some impact force. This force increases the more rope there is between you and your anchor.Third, the sheath must comprise a significant portion of the rope(abrasion).And most importantly there must be 0 sheath slippage!This is what makes spectra and kelvar core ropes unsuitable.Pro-cord is unique in that the sheath and core are actually braided together making it very strong and eliminating sheath slippage.However, rappeling on thin cord is dangerous bussiness.5mm cord can be easily severed especially under tension.Care must be taken to avoid abrasion and sharp edges as well as heat buildup in the belay device.The sheath must be examined, the rope recoiled and thougholy dried after every use.I suggest using thin cord by itself only to make shorter decents(40-50ft).For alpine climbing I couple my 63m 5mm cord with my 60m 9mm rope(always using a euro death knot). Thereby alowing me to climb and decsend full rope lengths.
NOTE: 80% of climbing accidents happen on decsent. Thin ropes are prone to twisting. Always practice first. Pro – cord is not waterproof and as far as I know not avertised for this use.
If expecting sharper rock… go thicker.
DISCLAIMER:Climbing can kill you, on second thought you probably shoud't go.

Adam,
Here's a lighter, safer alternative:
Ideally for this system rap rings or chains/links are at each rap point. If not, bringing rap rings is helpful (although you can tie a loop in your rappel sling to pass the rope through if you don't have rings)

With 10mm rope you can pass the upper end through the rap ring and tie a double figure 8 loop which will not pass through the common SMC steel rap ring. Even more so for the smaller diameter aluminum Omega Pacific ring. Tie the upper end of a 63M 3mm 15oz cord through the fig8 loop in the 10mm cord. Rap single strand on your 10mm and thread the 3mm retrieval cord through the other side of your ATC or through a biner clipped to your harness to keep it captive as you rappel on the 10mm. At the end of the rap pull on the 3mm to retrieve both cords.

I have done this with cords as thin as 9.1mm but at that size you are flirting with the knot pulling through the rap ring. To deal with this, a locking biner (which will bounce all the way down upon retrieval)or another rap ring can be tied into the double fig8 loop to back-up the knot if it pulls through.

An even better solution is a .5oz, .190" thick, 46mm diameter, 6061 aluminum plate I made with a 9mm hole in the center. Pass the 9mm rope through the anchor rap ring and then through the rap plate.
Tie a double fig8 loop on the back side of the plate. Now the knot cannot pass through the rap plate and the rap plate cannot pass through the ring. The plate is tied into the dbl fig8 loop with a keeper cord and the 15oz 3mm retrieval cord is also tied into the loop.

Using the thin cord as a retrieval cord allows it to be much lighter and to be uninvolved in the strength of the rap line.

Of course every solution creates it's own set of problems:

0)3mm cord tangles easily.
0)It can be difficult to pull on, especially without gloves.
0)On retrieval, if either cord jams once the rap line ascends above your position you are stuck on a wall with only a 3mm cord. (Are you prepared to prussik up a questionably anchored 3mm cord with your shoelaces per James Bond?? – Damn these velcro slippers!)
0)On retrieval, once the rap line pulls free if you don't catch it you will have a 3mm line attached to your rap line somewhere below. If either line hangs up as you pull up on the retrieval line…see above.
0)Rappel plate is larger than euro death knot or double fisherman which may make it more likely to hang up upon retrieval (it's also harder than a knot which may make it more likely to scrape along rock rather than catch on it.)
0) Plate bouncing down rock could be compromised (6061 is incredibly strong and much more ductile than 7075 often used in tent poles, stakes and trekking poles – also BD tested biners that Todd Skinner and Paul Piana dropped 2k' off the Slathe Wall and they failed beyond rated strength.)

Other than this, it's a walk in the park!

These are worse case scenarios and will rarely happen (if at all) if you pick the proper terrain and venues to use this on. The consequences of being stuck on a wall in August in Yosemite Valley are very different than in the middle of the Sierra in October. I have used this system several times with no problems yet.

Let's face it. Rappel retrieval is one of the diceiest, least predictable activities that climbers regularly engage in. Even with 2, 11mm ropes you can have retrieval nightmares.

In case there is any confusion, this is cilo / crackers…i didn't realize till today that i had two accounts on my different computers. d'oh!

After this discussion, and some others, I followed up with several manufacturers. I did several tests in my neighbors parachute tower to determine the temperature of a belay device in different rappelling situations. We also reviewed the literature, unpublished (aka proprietary data) documentation and discussed the situation with folks from all aspects of the business.

The very short version is that there are multiple and varied modes of potential failure for Dyneema/technora/kevlar accessory cord in a rappelling environment, especially when actively used in the rappell. It can get damaged by a hot belay device. It could cut through the knot attaching it to another cord. It could experience sheath separation.

If you must use an specialty fiber accessory cord, don't run it through or near your belay device. And don't bounce unnecessarily on the rope. And inspect the sheath often for any signs of separation. And replace it after 5 uses.

There are no known concerns of loss of strength from flexing in these ropes.

Using 5-7 mm nylon cord is much preferred. Replace often.

Graham, I agree with you that rappelling on Spectra/Kevlar lines is a bad idea, but what I've heard of is Kevlar TechCord being used as a retrieval line paired with a skinny single or double that you rappel on single strand allowing full length rappels. The retrieval line DOES NOT go into your belay device, rather you either feed it out with you as your rap, keep a hand on it, or use a carabiner off your harness to keep it with you.
The reason for that is the strength of the line when pulling (I could easily break 3mm cord trying to unstick a stuck rope), and the fact that the stiffer Kevlar is easier to handel in the wind.
Again the Kevlar is the RETRIEVAL line are DOES NOT go anywhere near your belay device, the rappel is on a dynamic (of if your pushing it and taking risks, a skinny static line).

I was wondering if you could talk to that? I've been looking into getting a RETRIEVAL line and am torn between a skinny double, 5.5 TechCord or 6-7mm Accessory Cord. I'm thinking the cheapest will win out though.

Rob:

From my above post…
"If you must use an specialty fiber accessory cord, don't run it through or near your belay device. And don't bounce unnecessarily on the rope. And inspect the sheath often for any signs of separation. And replace it after 5 uses."

that's for retrieval lines. For my $0.02 –ie the value of my life– I'm going with nylon from here on out. If i'm going for a climb that will end up in Alpinist, well, I'll consider one of the smaller, thinner cords as an acceptable risk factor

>…the rappel is on a dynamic…

What about the knot? That's part of the problem.

Thanks Graham, its made for a really good discushion on rope systems.

what I've done is feed my lead line all the way through the anchors and at the end tie an alpine butterfly or fig8, and use a locker to clip the knot back to the lead line so its not going anywhere.
Tie your retrieval rope to the loop formed by the knot, and rappel on the dynamic single strand feeding out the retrieval line as you go down.
When your at the next anchor pull the static and hopefully the carabiner/knot wont get stuck somewhere coming down. I use the single locker b/c I feel that its less likely to hang up then two reversed and opposed carabiners.

lol, me thinks doubles might be the better option!

But thats how I do it anyways.

The critical temperature of HMPE (Spectra/Dynema) is 150 F. Critical Temperature is the temperature at which the fiber degrades due to temperature alone. Sampson Rope has a good table of rope fiber characteristics. http://www.samsonrope.com/site_files/Fiber_Characteristics_and_Rope_Construction.pdf
Kevlar does not like to be bent. When I was on oceanographic ships the recommended pulley tread diameter was 20x the kevlar rope diameter. The standard for all other fibers was 8x.