UKC

I've read up about this technique [Andy Kirkpatrick's Site]. Anyone out there who's used this method and have any practical advice and the pros and cons: particulalrly on the abseiling part?
There seems to be two ways of joining the ropes together, one involving using a locking carabiner and the other tying the ropes together using two figure of eight knots - this would seem to increase the chance of the rope snagging on retrieval - is this a problem in practice?
The Dyneema has some problem that the sheath and core can stretch differently? If I buy 50 m of 5.5 Dyneema [which seems to be a special order], do I need to do anything special to the ends?

In reply to John Workman:

I don't know anything about the technique, but I do remember reading an accident report: http://www.rockclimbing.com/cgi-bin/forum/gforum.cgi?post=2332405;sb=post_l...

Seems it's fine if you set everything up correctly, maybe like http://www.canyonwiki.com/wiki/index.php/%27biner_block

In reply to John Workman: I've used this system successfully in the Alps with 40m dyneema and 40m single rope. I ended up abseiling about 16 pitches with it off the Grandes Jorasses!

There are many things to go wrong with it and I don't think it is worth it. However, I'll write up all the pros and cons plus how we set it up when I get back from the Alps on Monday.

Mike

In reply to Mike Pescod:

Thanks Mike

In reply to John Workman:

some info...

Pros... Rope work is simpler, therefore faster.
combination of 9.1mm single and 6mm dyneema is lighter than 2 8mm half ropes (i think)

cons.. Usual issues like rope drag potential etc.

Also i think fig eight knot is BAD even if doubled. Double overhand works, but i have been told this is bad if the ropes are different diameters... I'd appreciate some clarification on that too...

In reply to Paulcmountain: when i was in scouts we useda knot calla sheet bend simialr to a reef knot this was used for tying together two ropes of unequal thickness we have thought about this method of abseiling and would like to here mikes views on this

stuart

In reply to Paulcmountain:
Paul
See this link to Andy's website which tells you about how he recommends joining the ropes

http://www.andy-kirkpatrick.com/articles/view/ropes.

I've tried the figure-of-eight and carabiner method in a 'controlled situation'. This seems to work well enough, but is likely to be more prone to snagging when pulling down when retrieving?

In reply to John Workman:

I've used the single-rope/spectra system several times using a few different joining methods - jury is still out on which is best. One tip I would suggest however is to buy your dynemma with a few extra metres of length (10%?). Because it has lower stretch you'll still be able to make full use of your single rope's length for abbing.

dave

In reply to daveholl:
Thanks Dave. Good point.
This 'thing' about the Dyneema core stretching differently from the sheath or being not 'connected' to the sheath? Does one have to 'do' anything about this [apart from the set up at the abseil point - as described by Andy Kirkpatrick] - from your experience?

In reply to John Workman:

Use this technique successfully on pull through caving trips.

Joining the rope: I use an overhand loop with a 20cm or so tail(small loop). Attached to this is a small locking crab. This crab is then attached to the line I'll descend (pretty much as others have said or linked to). I then attach the retrieval cord to this crab.

In reply to John Workman: The system I used was the locking karabiner method - I tied the skinny rope and the fat rope together in a single overhand loop. I clipped a karabiner in the loop and onto the fat rope. We then abseiled down the fat rope and used the skinny rope to retrieve everything.

I would not trust a sheetbend or the usual overhand knot. Even if there was a good knot to use the skinny rope would go through your abseil device much faster than the fat rope so it would be very difficult to abseil on the two ropes together I think. Mind you, I didn't try it out.

The advantages of the dyneema system are that you have a single rope to use for the climbing which is easier when you are moving together or changing from moving together to pitching regularly. The dyneema weighs very little and is no problem at all to carry.

The disadvantages are many and I chose the system because I thought there was going to be very little abseiling. If I was planning to do lots of abseiling I'd take two half ropes.

As Dave says, the dyneema does not stretch. I clipped the end of the dyneema to my harness so I didn't lose the end and a couple of times I weighted it - there was no stretch at all! The dyneema is very easily tangled, blown away and generally is a bit of a faff.

Clipping a karabiner back into the abseil rope is great but beware of the knot pulling back over the anchor sling making it impossible to retrieve. Having the abseil rope through a maillon is best.

The biggest problem is the greater chance of the ropes getting stuck. The knot is big and bulky, easy to catch on an edge or in a crack. The usual overhand knot used for abseiling on matching topes sits on one side so there is no extra resistance from the knot. In the dyneema system, not only is there a big knot but there is a karabiner being dragged down under the abseil rope, scratching away on the rock the whole way down. It is easily possible for this alone to make too much resistance to pull the ropes. Certainly if there is an edge or corner to go over, it will be very difficult to retrieve the rope.

Of course if the ropes do get stuck you are stuffed - you can't prussick up the dyneema in case it releases and because it is too skinny and you don't have the climbing rope to lead on. You can't lead on the dyneema either because it does not stretch and because it is too skinny to belay.

Lastly, the system takes longer in multi-pitch abseils as you can not thread the next anchor when you are pulling down the ropes.

So, as I say, I'd only choose the system if I was planning few abseils and lots of moving together. I used it to traverse the Rochefort Arete and Grandes Jorasses where there are only three abseils down to the Col des Grandes Jorasses. I practiced the system beforehand as well to get used to it.

Unfortunately, at 5am in the bivi hut on the col, we had a thunder storm which forced us to retreat from the col instead of going over the Jorasses! This involves abseiling a wall that's maybe 400m high! The dyneema system worked perfectly but there were some very tense moments and some very strong tugging on the rope! John (my paying client!) asked me what we would do if the ropes got stuck. I answered "We'd call a helicopter, we'd be stuffed!". Since the ropes did pull every time we both enjoyed the experience but only after we were down.

This year I managed to complete the traverse with John (pictures here - http://www.flickr.com/photos/abacusmountaineering/sets/72157624471427233/ ) and I chose two half ropes. Ironically we got the ropes stuck on the abseil down to the col! It was also a right faff trying to move together with two half ropes. However, as it is quite a serious place to be, I'm happy with my decision to take two half ropes. After all, it's only a couple of hundred grams of difference.

Hope this helps.

Mike
IFMGA

PS I didn't do anything special to the ends, just cut the dyneema with a hot knife as per usual. Didn't have any problems at all.

Mike

In reply to Mike Pescod:
Mike, Thanks for info. Jeepers. That sounds like a right faff. If you're not planning on doing much abseiling, I'd just use the one rope and have no dyneema cord and accept doing shorter abseils.
Just had one 60m 8mm rope on GJ Traverse and that was fine.

In reply to TonyM:

I've used this method quite a few times. I don't particularly like it, but it's useful where having double ropes wouldn't be appropriate e.g. big wall climbing, where realistically you need singles for jumaring etc.

In contrast to Mike, I join the ropes using a double overhand knot rather than using a krab. I prefer the idea of using a krab since you're effectively rapping off the one good line, but I've always been wary of pulling a lump of metal down onto myself and anyone below me; I'd be interested to hear Mike's experience on this. I ALWAYS tie the ends of both ropes to my belay loop, so that the difference in stretch is not going to catch me unawares (well it might, but I won't go off the end). To avoid a wind-driven clusterf*ck, if it's windy then I never throw the skinny rope; one climber gets lowered down carrying the end of both ropes.

I'm always a bit nervous using a skinny tagline - boy does it seem skinny when you're 4 pitches up - but it's a useful tool when the climb demands single rope method.

In reply to Captain Fastrousers:

I should also add that climbing is dangerous and I'm just a bloke on the internet etc, so make sure you try anything I tell you out on the ground first

In reply to Captain Fastrousers: The karabiner is just about all the way down to you (if not completely down) before the rope falls so it's not usually a problem.

Mike

In reply to Mike Pescod:

Ah yes, that makes perfect sense now that I think about it. Thanks.

In reply to Mike Pescod:
Mike
Thanks for the very informative reply. I hadn't thought through the problem of what to do if the ropes hung up on an abseil. This will need to be considered!
Some good photos.

John

In reply to John Workman:

No problem. Where are you off to?

Mike

In reply to Mike Pescod:
Hopefully a short trip to Cham - next summer - nothing to big and bad. Might also try on some easier local winter stuff.

In reply to John Workman: I've use the system Mike describes on two big expeditions where weight was critical (Spitsbergen and Afghanistan) and like Mike found it a faff and a bit slow. As he says it needs very careful rigging to avoid jams but I found using a DMM revolver as the krab reduces the friction appreciable on steep ground.
Al