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A lot of elite climbers carry a thin (~5mm) static tag line for hauling and rappelling. I think the standard ATC specs require a rope of at least 7.7mm diameter. So how do those climbers set up the rappel?

Not something I'll be doing any time soon.. I'm just curious.

Well I'm no elite climber, but I frequently carry 6mm for rapping while solo. I'm not sure if I've rappelled off 5mm, but I fully intend to get a coil of some 5mm titan at some point- it's actually stronger than my 6mm.

There are descenders for skinny cord. I don't have any first hand experience with them. I used a Petzl Reversino for a while, then finally modernized to the current iteration of the Reverso, which is good from 7.5 to 9 something, I think.

For 6mm, I do have to hold on tighter during free-hanging vertical raps. I've actually wrapped the cord around my back and braked with my left hand, just for the added control, and I've also run the brake line through the legs and around my thigh. I think I've done two carabiners in the loop through the Reverso also, but it's not necessary. Anything that offers just a bit more friction pretty much makes up the difference.

Do you use autoblock? Both strands of 6mm seems much scarier to me than one strand of skinny rope.

I'd rather be lazy and have a rich luxurious rappel.

Regarding an auto block, it is very easy. It's basically three raps around the rope with both ends attached.

http://www.youtube.com/watch?v=gqBTV16dpN0

No, I don't use an autoblock. But you can. 5mm wrapped around a couple strands of 6mm will hold, if it's dressed right.

Comrade, in the scenario you are describing it's not a matter of rappelling on the 5mm only. If the tag line is used for a double-rope (full length) rappel then you are really rapping on the climbing rope (so normal diameter) as well as the 5mm tag line. Not a big deal. If you are doing a rap on a single line you would just rap on your climbing rope.

Make sense?

To rephrase what's said above - you're effectively only rapping on the climbing rope. The thin static is there to be used as a pull line to retrieve the rope(s).

I've rapped off of a 6mm line using both "body wrap" and an ATC. For the body wrap, don't. It hurts like hell with a thick rope. With a 6mm, it is questionable whether just jumping would hurt less.

With an ATC, I used multiple biners to increase the friction. Work's OK.

Thanks for the replies, everyone. That makes sense.

Can someone explain how to use multiple biners to increase friction like mconnell said? I'm sure this is basic stuff and you can RTFM me if you point to the manual!

Set up your ATC rappel just like you normally would. Instead of using one locking biner, you can use multiple. More surface area, more friction.

Re using multiple biners to increase friction. Another technique is to attach a biner through the harness leg loop that is on your brake hand side. Rig for rappel through your descending device as usual, but then clip the rope through the biner on your leg loop as well. Note that when descending using the friction on the leg loop biner, you will be braking holding the rope in an upward direction.

If we believed the capstan equation analysis, it's the number of tight turns that counts, not the surface area for each turn.

Correct, MoapaPk. Multiple biners increases the angle/number of the turns. Instead of the rope going straight into the ATC, around the biner, and straight back out, the rope needs to make 2 turns (assuming the diameter of the biners is wider than the opening in the ATC).

Mcconnell,
that is interesting. I may have to give that a try one of these days.
A related question: how do the 'figure eight' type devices work with skinny(6-7mm) ropes? Thus far I have only used an ATC Guide for abseils.

Augie Medina wrote:Re using multiple biners to increase friction. Another technique is to attach a biner through the harness leg loop that is on your brake hand side. Rig for rappel through your descending device as usual, but then clip the rope through the biner on your leg loop as well. Note that when descending using the friction on the leg loop biner, you will be braking holding the rope in an upward direction.

Nice... superior to rope-burning the thigh of your climbing pants or jacket. I wonder if muntering to the second biner would be too much