Joining unequal diameter ropes for rappel.

Bill Lawry wrote: That depends on the difference in the two diameters and possibly on the rap device. I've had a 6 mm cord travel when married with a 10+ mm rope on a basic ATC. And the results can be fatal if rapping near the tails.

Has anyone rapped with, say, a 6mm and 10mm but using a fig8 rather than a modern belay device. I'm guessing that maybe because the two ropes are wrapped around each other within the fig8 the thinner does travel faster than the thick rope.

David Coley wrote: Has anyone rapped with, say, a 6mm and 10mm but using a fig8 rather than a modern belay device. I'm guessing that maybe because the two ropes are wrapped around each other within the fig8 the thinner does travel faster than the thick rope.

I'd think the opposite. Since the different diameters get wrapped around each other, probably less chance for movement.

ATC isolates the strands. You get the full effect of the difference in friction.

I rapped on a 6mm pull cord paired w a 9.5 off Guides Wall in the Tetons. Noted the knot pop thru the big rap ring. Contolled the friction on each cord separately (one hand on each rope). Wasn't a deal but not recommended.

Brian in SLC wrote: I'd think the opposite. Since the different diameters get wrapped around each other, probably less chance for movement. ATC isolates the strands. You get the full effect of the difference in friction. I rapped on a 6mm pull cord paired w a 9.5 off Guides Wall in the Tetons. Noted the knot pop thru the big rap ring. Contolled the friction on each cord separately (one hand on each rope). Wasn't a deal but not recommended.

We agree. I missed a word out in my post, it should have read:

.... the thinner does NOT travel faster than the thick rope ....

Sorry

rgold wrote:The strands shown below are 6mm and 8.5mm.

Mammut pro cord? That stuff is rough...hard pulling? I'd imagine if your hand slipped on it, might take a chunk of flesh...

Nice photo's!

I always use the EDK with the stopper knot. IMO i think it's the most streamlined knot. I've never used it on ropes with vastly differant diameters, but i do always make sure the rope with the more abrasive sheath has the stopper knot in it.

David Coley wrote: Rick, Just in case you didn't know, there is a potential failure mode for this knot. See the photos near the end of: people.bath.ac.uk/dac33/hig… This doesn't mean the knot is no good, just something to be aware of.

I did not know that, seems solvable if stopper knots are used. The part about potentially losing one of the ropes seems more likely and little bit comical. Seems the flat fish sandwich is better all around.

Thanks David!