Double rope rappel?

Is there a limit on what size ropes can be tied together. I have a Mammut Infinity Doudess 9.5, and considering buying a Beal 8.5 to lighted the load. Am I missing something, or is there an issue I'm not seeing?

That combination will be just fine as a double rope rap. THey will join together with an EDK or DF just fine. If the difference in diameters is too great the smaller rope will have less friction at the rap device and will travel through it faster, potentially causing the rope(s) to move through the anchor. But I have routinely used ropes with that kind of diameter difference, with no issues.

ChaseSmallwood wrote:Is there a limit on what size ropes can be tied together.

Yes there is a limit with many knots, especially the EDK. But that sort of difference is not an issue.

To my knowledge there isn't much knowledge/research on where this limit lies, but I wouldn't expect 11mm rope to work with 2mm rope on an EDK.

A bit more realistically, if you start using 6mm and 11mm then I'd start to think a bit more about the appropriateness of the knot you are using.

I've rapped on a 9.5 and 7.8 with no issues. When joining them with an EDK just make sure to have the smaller strand underneath the larger one so it won't be able to roll as easily and it's probably not a bad idea to have a backup knot just in case.

Jake Jones wrote:You don't actually have to rap both lines. You can use the 8.5 as a tag line and just rap on the single 9.5. Look up "reepschnur rappel".

The reepschnur rap has limitations. Don't use it on slabs or rings spaced apart. Slabs present too much friction. Same thing with rings spaced apart. I witnessed a knot get pulled through one ring and not the other because of the friction.

patto wrote: Yes there is a limit with many knots, especially the EDK.

I've tested the largest difference in diameters that exist in climbing and found no concerns. I joined 11mm with 6mm in an EDK and pull tested the sample (results are on MP). The 6mm failed without the knot rolling once. I even tested 11mm and 4mm for fun. Same results. I also tested 11mm and 9mm, again the knot dident even roll. The key is pretighting the knot well and leaving 24" tails. If you do that, you can join any combination of diameters that exist within the climbing realm.

As far as using one as a tag line, there is not much benifit in doing that unless you plan to tie the tag back to the lead line. If you're doing a carabiner block at the top on the tag line or something of the sort, thread both through your ATC, even if the tag is a tiny 5mm. It improves friction and safety as now you're not relying just on the carabiner block, but also the tag line directly. I've used 6mm tags since before I can remember, and I always rap on both strands, even if it's 10.5mm and 6mm. As far as the knot moving around at the top because the difference in friction down at the ATC, it doesent happen--it cant. That's because you thread the lead line through the anchor, not the tag, and so the bias would be for the lead line to travel down with you as you rap, but that cannot happen as the knot will stop it from pulling through the anchor.

OP: This topic has been covered a billion times, you're best bet is to just use a search. The only thing that's going to conclude from this thread is the exact same information posted in all of the last 10 threads talking about this topic.

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