mconnell wrote: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).

Need a picture.

Ben Beckerich wrote:

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

It works really well. You start your rappel the standard way with your brake hand by your butt and if you find you need more friction, simply pull up with your brake hand and you'll engage the biner on your leg loop. I don't think rigging the second biner with a munter hitch would be a good idea; unnecesary complication and it would likely be too much friction.

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

Two biners make the rope take sharper bends as it goes through the ATC.

See here: http://www.canyoneeringusa.com/techtips/black-diamond-atc-rappelling/

Edit to add: See the above link for picture and discussion.

MoapaPk wrote:

mconnell wrote: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).

Need a picture.

+1

TimB wrote:

MoapaPk wrote:

mconnell wrote: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).

Need a picture.

+1

Follow coldfoot's link above to see how it is set up.

If one believes the capstan equation there is a trivial difference between the configuration with two carabiners vs. one. The capstan equation factors out the frictional surface area, and two 90 degree turns over two carabiners reduces to one 180 degree turn. A turn of (say) 190 degrees produces a very small increase in friction.

On the other hand, a run through a leg-loop carabiner can add a lot, if the rope is pulled up away from the leg. Or a double munter adds an extra tight turn.

I have rap'd off 6mm countless times. The problem is not friction in the ATC. Well, it is as most are used to ropes autoblocking anymore. If you want more friction you just wrap it around a biner several times if you feel like it on the UPHILL side of the ATC, figure 8, etc. So it goes, anchor, rope, biner with rope wrapped around, once ore more with biner tied to your harness main loop, rope, atc, figure 8 etc, around your body, firm grip. No more of this typed moronacy of pulling UP to brake. Though you could just as easily tie several biners together on your harness before the atc, fig 8 and then wrap the rope around them before going back up through the atc, but getting out of that scenario has got to be a nightmare.

Have a nut job for a friend who raps off of 2.3mm static line. The guy is gonna die doing that, but as he points out it has a 600lb breaking strength. To rap on the stuff, you just wrap it around a biner a whole bunch of times before going through your rap device. Can just leave the rap device home really if you use 2 such biners.

Those claiming pain... sigh. Not true unless pansy or against skin, of course that is true of large ropes as well. Wrap completely around the waist if right handed and then wrap a leg if one so desires. Hardest part of small diameter rapping is keeping a firm grip in your hand. Gloves are near mandatory. Especially when it is hot out(sweat) or rope is wet(snow). Always be prepared to wrap around your thigh.

Beware if using 6mm in conjunction with +9mm climbing rope. The 6mm will pay through your belay device faster than the larger rope and you MAY rapel off the end of the 6mm line! TIE THEM TOGETHER!!! Pay ATTENTION for this extra slippage and hold the 6mm a bit tighter as you rappel.

Try this at home FIRST. Get comfortable with it. Make sure you know how much extra friction you need when the rope is WET.

I seriously have to wonder how many who replied to this thread have actually rapelled with small line.

Accidents can happen with fat lines as well, especially when you are using a figure 8. Had another friend who got stuck on rappel while using a figure 8 on fat ropes and he had to be rescued half way up a wall. The figure 8 twisted the rope as he went down creating too much friction between the two lines until he couldn't descend any more.