UKC

I have a 7.5 "skinny" which is a few years old and a newish Mammut Genesis 8.5. The older rope has furred up somewhat and the two ropes feel similar and look the same.

I know that it is not recommended to use different diameter ropes with an overhand knot for abseiling but when does it become an issue? Has anyone any practical experience of this?

In reply to GridNorth:
I've read that too but in the few places I've seen it stated they never gave an explanation, just stated that you shouldn't use an overhand but a double fisherman's instead.

I've thought about this before with a few friends and the best I could come up with was that the thicker rope might not bend enough to grab the thinner one which could then slip out of the knot. This is just my thought, no way of backing it up or any kind of scientific thought behind it really.

Also the guys I was talking about it with were very experienced and knowledgeable climbers and they'd never heard of it and had tied a 9.1mm rope to a 10mm or 10.5mm (I forget which) for an abseil before with nothing bad happening. Not that that's particularly proof that it's fine to do.

Personally I'd use a double fisherman's for joining those two.

In reply to GridNorth: Yes. It works fine. There is some test data on the web (BD?) of an overhand on a 10.5/8.5mm pair I think.

You might get the thinner rope creeping through your belay plate more rapidly than the thicker rope on some raps. So go slowly, keep an eye open in case you get to the end of one rope before the other - and always tie a knot or knots in the ends.

In reply to GridNorth:

I tried a few out at our local wall. When well 'dressed', I could hang on a 6mm accessory cord attached to a 10.5mm wall rope connected with an overhand. Convinced me that slightly dissimilar ropes are fine.

In reply to GrahamD:
You may want to be more wary on iced ropes ofcourse. I've had an overhand roll on iced ropes before (fortunately only one roll on to the other overhand backing it up!)

In reply to GridNorth:

Whilst I'm surprised that someone such as yourself should ask this, I must admit that I've pondered it myself. But the issue that I had was more the relative stiffness of the two ropes - I was tying together a quite stiff 10mm static that had been hanging on a crag for several weeks and a supple 8.2mm dynamic, using an overhand. It occurred to me that the thinner rope could pull through the knot due to the thicker one not tightening, so I added a stopper (I suppose another overhand) tied in the thin rope over the thicker one. In retrospect I'd have been better off adding a second overhand, or indeed just tying a fig 8 in the end of each and clipping them together with a screwgate as there was no possibility of the knot getting stuck.

In reply to jon: Why are you surprised I have asked this question? I have no personal experience of usind different diameter ropes. My common sense tells me that my two ropes will be fine but I thought that others may have more personal knowledge. Indeed one person referred me to a BD page which seems to re-inforce this..

In reply to GridNorth:
Do you happen to have a link to the BD page? I'd like to read it but couldn't find it on their website.

In reply to GridNorth:

I apologise, you surprised me. I just naturally assumed that someone of your experience would have that knowledge or at least hold an opinion. It was in no way meant to be derogatory. As I said, my sense tells me it's more to do with the stiffness of the ropes...

In reply to ElBarto:
Not BD, but just as good:
http://user.xmission.com/~tmoyer/testing/EDK.html

In reply to ElBarto: Try this: http://web3.bdel.com/scene/beta/qc_kp_archive.php#123008

In reply to GridNorth:
Thanks guys! I'll have a read of them both.

In reply to GridNorth: Also see myth 5 here: http://www.geir.com/mythbuster.html