topcat said:

The split pitch yes?  As it seems common to have problems here, do you know if the issues arise when not splitting the pitch, or does the rope tend to jam even if you split at the ledge?

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A karabiner is only required when belaying the rope round a scaffold pole or a wooden beam as it allows the the rope to lock when tightened. When using P-bolts, however, a karabiner become a liability as it can rise up and get jammed on the P-bolt.

All one actually needs is a very thick knot which won't pass through the bolt. The bigger the knot, the better...

We have never had even a momentary problem since dispensing with karabiners about ten years ago.

I've used a big knot on it's own and it works well.  To be safe though it is a good idea to clip in a krab as well, just in case the knot were to force through the hole.

Another way is to tie two knots, either side of the anchor.  Use a maillon (the 7mm long work well) from the loop of the knot on one side to jam up against the knot on the other side.  Another refinement, if you have one try a small pulley to jam up against the knot, the small hole of the pulley is good for jamming and makes pulling through the rope much smoother. 

This practice has found favour with rope access trainers in recent times.  You can also bridge the two knots with a wire strop so that the weight of the person is on the strop, not the rope.  Very useful if your pull through anchor has sharp or abrasive edges.

Hope that makes sense.

Badlad said:

I've used a big knot on it's own and it works well.  To be safe though it is a good idea to clip in a krab as well, just in case the knot were to force through the hole.

Another way is to tie two knots, either side of the anchor.  Use a maillon (the 7mm long work well) from the loop of the knot on one side to jam up against the knot on the other side.  Another refinement, if you have one try a small pulley to jam up against the knot, the small hole of the pulley is good for jamming and makes pulling through the rope much smoother. 

This practice has found favour with rope access trainers in recent times.  You can also bridge the two knots with a wire strop so that the weight of the person is on the strop, not the rope.  Very useful if your pull through anchor has sharp or abrasive edges.

Hope that makes sense.

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And it's always a good idea for the last one down to give the setup a quick check that the rope still free to be pulled down.

Badlad said:

Hope that makes sense.

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No. I don't follow that at all  :-[

I'm clearly missing something as the way I'm picturing it with one knot each side of the anchor, it's never going t pull through whichever way you pull it, which obviously isn't what you mean...

Can you draw a diagram?

I tend to use a rack, with one end of the rope through each side and no knot*

* except one knot to tie the ends together at the bottom in case one side decides to go faster than the other 

Badlad said:

I've used a big knot on it's own and it works well.  To be safe though it is a good idea to clip in a krab as well, just in case the knot were to force through the hole.

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This is how I do pull-throughs, since moving from a rack (when I did similar to Pete) to a simple: a butterfly with a crab in it (which is then clipped round the other side of the rope to avoid tangling when the rope is pulled down).

I'm afraid I don't follow the rest though... Like Pete, I'm struggling to visualise it, and how it can be possible to pull the rope down if there's a knot either side of the anchor... A picture of some sort might help

Loads of pictures here:

http://dyeclan.com/outdoors101/canyoneering101/?page=rigging-a-retrievable-rope

Yes, sorry, I didn't make it clear but my thinking had moved on to other types of anchors such as poles, beams, threads, flakes etc.

One of the considerations of pulling through around a scaffold pole or other anchor of small diameter is the force placed on the krab.  With this sort of loading the krab can fail at surprisingly small loads and is not good practice.  My coffee cup shows the sort of thing.



Around a wider diameter anchor such as a coal bucket this is much less of a problem.



There may be a problem of the rope binding round certain anchors such as threads, flakes large bosses etc.  Both may be solved by putting a knot in and using something of smaller diameter to 'lock' against it like a maillon or a pulley which also allows for a smoother retrieval.



If there is concern over abrasion of the rope on the anchor, or the anchor is sharp then you can use a wire belay or strop between the two knots which is shorter than the rope.  Therefore the weight of the caver is on the wire not the rope.

I am only adapting some of the techniques and thoughts processes we use in the rope access industry to caving.  Most of the time our standard caving method will see us through. As Kevlar has shown there are many options for canyoneers.  Same too for the industry.  Here's a video of one of many double rope methods;

https://www.youtube.com/watch?v=cdEbE8Qzg7M

Aha, thanks - I had assumed you were still talking about P-hangers. Makes sense now!

Kevlar said:

Loads of pictures here:

http://dyeclan.com/outdoors101/canyoneering101/?page=rigging-a-retrievable-rope

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I'd never realised there were so many different methods!

Kevlar said:

Loads of pictures here:

http://dyeclan.com/outdoors101/canyoneering101/?page=rigging-a-retrievable-rope

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FFS KISS !

topcat said:

FFS KISS !

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We just tie a butterfly then thread the rope through the bolts and back through the butterfly. I presume we are all going to die soon?

I guess, Andrew, this is just a pain in the arse with a 100m rope. It also may rub the rope a bit when you pull it down, but I haven't worried about it because the rope's not weighted?

andrewmcleod said:

We just tie a butterfly then thread the rope through the bolts and back through the butterfly. I presume we are all going to die soon?

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I remember someone doing a double rope pull-through like this from the top of the Humber bridge down to the road deck. When the Alpine Butterfly knots reached the ground both the knot loops were worn half way through!!

Best to use a small Maillon Rapide as any miss-loading will generally only ever result in deformation whereas a carabiner could very easily break.

I witnessed a 35kN alloy carabiner, rigged as in Badlad's coffee cup example round a 6" steel pipe, break at 375kg. A heavy caver doing a bouncy descent could easily apply similar loads to this!!!

Mark

When it comes to double-P-hanger pull-throughs, I typically use a knot with a crab in, and clip the crab into the 'other' hanger when rigging, with it to be sorted out by the last person down.

That means even if someone tried to descend the wrong rope, it would still be attached (at least, to one of the hangers).
It can also make it a bit easier to use the pull-down side of the as a temporary traverse line

From Petzl...

Re Mark's comment about rubbing of rope, https://www.youtube.com/watch?v=VWaIQhEuPds&feature=youtu.be might be of interest. 

Bob Mehew said:

Re Mark's comment about rubbing of rope, https://www.youtube.com/watch?v=VWaIQhEuPds&feature=youtu.be might be of interest. 

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It beats watching paint dry, though not by much...

Seriously, I was impressed that the first rope survived well over 400 cycles, when the outer sheath had failed at ~200.  If you had prussiked to a pitch head and found the rope in that condition (ie outer sheath gone), you'd be horrified, but perhaps you wouldn't have been as close to death as you'd thought.

Have used a double rope through my rack, also a fifi hook with a bungee and prussik knot tied to it and tensioned on the main rope. When you unload it and give it a flick, it comes down.

Last time I abbed off a mug I fell 20 metres. Fortunately I landed in a deep pool of cold tea, so I survived, but it wasn't pleasant. It put me off trying to do it off a bucket, I regret to say. 

Bob Mehew said:

Re Mark's comment about rubbing of rope, https://www.youtube.com/watch?v=VWaIQhEuPds&feature=youtu.be might be of interest.

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possibly slightly supports my contention that class B rope is probably better than class A rope at 9mm (more sheath?) although a single result doesn't really count as evidence...

if only 11mm rope wasn't so heavy!

Also for a pull-through there really shouldn't be cyclical rope rub, and movement right at the top of the pitch should be minimal, so I reckon just putting the rope through a knot _ought_ to be OK and as someone else stated using a crab can lead to dangerous crossloading...

This option seems safe and easy:

Best to use a small Maillon Rapide as any miss-loading will generally only ever result in deformation whereas a carabiner could very easily break.

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