/ Abseiling on two different diameter ropes.

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womblesi on 04 Feb 2013
Hi,

I have read an article that you should not abseil on two ropes that significantly different in diameter, such as 11mm and 8.4, as the thicker rope will create more friction and pass slower through the plate than the thinner rope. But apparently this is not such an issue with two ropes of a similar diameter.

Has anyone got any experience on abseiling on a 9.8 and an 8.6 and if this would be OK or not.

Thanks

Simon
colina - on 04 Feb 2013
In reply to womblesi:
8.6 seems a bit thin but I guess the only way to see if it works is set it up in a safe environment and see what happens.id have thought it would be ok but you need to make your own risk assessment.
IPPurewater on 04 Feb 2013
In reply to womblesi: I used to abseil on an 11/9 pair without problems. If I was abseiling from a bolt for instance, I would put the 11mm rope through and then knot it to the 9mm. Theoretically, if the 9mm was then too slick, the knot would rest against the bolt and move no further.

One thing to do is tie the ropes together at the bottom before dropping them, so you can't abseil off the end of one causing the other to pull through the anchor.

Also if you tie a loop close to where the ropes join, in the thinner rope, then clip a crab into this and clip it around the thicker rope, below the anchor, it would not be able to pull through the anchor. You then need to retrieve the ropes by pulling the thinner one. In caving, I know this as "The Yorkshire Rope Trick".

womblesi on 05 Feb 2013
In reply to colina:

Thanks Colin,

Yea, my next plan was to set something up at my local wall and have a play about with it.
womblesi on 05 Feb 2013
In reply to IPPurewater:

Thanks,

I am planning on doing a 4 x 25m multi pitch route, to get off the guide says a that two 60m abseils are required. I was planning on climbing the route on a 70m rope but taking a 50m half rope with me.

My idea is to join the two ropes with a double over hand knot then descend 10m ab over the knot before completing the rest of the descent to the belay station.



jkarran - on 05 Feb 2013
In reply to womblesi:

> Has anyone got any experience on abseiling on a 9.8 and an 8.6 and if this would be OK or not.

I've never had any issue with it.

Generally you can get away with big differences by giving a little thought to positioning the knot so it jams should the thin one run a little more freely. The alternative is a single rope ab pulling the thin one to retrieve. All of which is overkill for two ropes that are pretty similar like yours.

jk

GrahamD - on 05 Feb 2013
In reply to womblesi:

I've never had a problem with doing this. Just take it slowly and carefully. I'm not sure what article you read ?
David Coley - on 05 Feb 2013
In reply to womblesi: The difference in diameter when this becomes an issue depends on the angle of the rock/friction, the speed you rap and the belay plate. With a 7.7mm twin and an 11mm it can be a big problem. If you keep the knot the correct side of the chain you should be ok. Going slowly will really help and you must use knots in the end of the rope.
womblesi on 05 Feb 2013
In reply to GrahamD:
> (In reply to womblesi)
>
> I'm not sure what article you read ?

Thanks for the advice Graham. The article is:

http://www.ukclimbing.com/articles/page.php?id=167

Look under the heading "What is the best rope to use for abseiling?"

Thanks again

Simon.
womblesi on 05 Feb 2013
In reply to all:

Thanks for the advice I will definitely make sure I go slow, and practice at my local wall before I head off and give it a go outdoors.

Regards

Simon
GrahamD - on 05 Feb 2013
In reply to womblesi:

Interesting article - Bob, when he posted, used to be more pragmatic !

Its true to say that its more awkward with a thick and thin rope and, as you descend, the thin rope will stretch more but its nothing you can't deal with with practice.
rgold - on 06 Feb 2013
In reply to womblesi:

> I am planning on doing a 4 x 25m multi pitch route, to get off the guide says a that two 60m abseils are required. I was planning on climbing the route on a 70m rope but taking a 50m half rope with me.
>
> My idea is to join the two ropes with a double over hand knot then descend 10m ab over the knot before completing the rest of the descent to the belay station.

Everyone is saying you shouldn't have a problem. Maybe not, but sure wouldn't want to bet on it. If the ropes run unevenly, which is certainly possible even though their diameters are close, then the knot could be pulled back up to the anchor, in which case your thin rope will be 20m shorter than your thick rope. It is very hard to notice uneven running of the ropes while rappelling. You could end up rapping off the thin rope and end up hanging on the thick rope, supported by the knot wedged against the rings at the anchor. I know personally of two instances, one fatal, in which such a knot has pulled through the rings.

At the very least, you have to have knots in the ends of your ropes so you can't rap off them. It is conceivable, if the ropes are uneven, that you could let the shorter rope's knot jam up against the rap device and continue rappelling, letting the device pull the shorter rope down and thereby even out the ropes. I wouldn't want to count on this working without multiple experiments in a safe environment first.

Something you can do to mitigate uneven slippage is to feed the rappel lines into the device hand-over-hand, rather than just letting them slip through your hand.

You haven't addressed passing the knot on rappel. There are a range of ways to to this, from extremely simple with virtually no extra gear to absurdly complicated with ascenders, aiders, and multiple steps. You will certainly want to have that process dialed before having to use it anywhere consequential.

If I had to do something like this, here's what I'd do. I'd clip a quickdraw between the ropes so that they can't slip for the first person down. (The second person down better remember to undo this or you're screwed!) Once the first person is down and off rappel, they anchor the thin rope so that it can't be pulled up by differential running.

rgold - on 06 Feb 2013
Addendum:

Another thing you could do to keep the ropes from moving, something which wouldn't require the second to remove anything, is to set up a carabiner block on the thin rope at the anchor. This is a common canyoneering stunt but is less well-known among climbers. You simply install a carabiner on the thin rope next to the anchor by tying a clove hitch on the solid side of the carabiner. This serves to block the thinner rope from being pulled through the anchor ring. It is best to use a large old carabiner, since it will be dragged down the rock when the rappel is pulled.
womblesi on 07 Feb 2013
In reply to rgold: Hi,

Thanks form the advice, I will be knotting the ends on the rope together so I can't ab off the end.

To pass the knot I am going to use this method:

http://www.ukclimbing.com/videos/play.php?i=490

It looks pretty straight forward.

In relation the thinner rope running faster than the fatter rope I will set up something at my local wall to practice and see what happens. I will also practice passing the knot to make sure I have it well versed before I have to do it on the route.

In relation to the canyoneering set-up it defiantly looks worth having in as part of the system as an extra back up just in case.

Thanks for the advice.

Simon
henwardian - on 07 Feb 2013
In reply to womblesi: Passing a knot is a chore, if you want to use a 70m and a 50m, I'd suggest setting up the abseil as normal and then just locking your 50m rope and abseiling the first 10m by letting out 20m of your 70m rope, then abseil as normal. Job done.

I've rarely abseiled on different diameters of rope but it's never caused a problem. Even if you do end up letting more through on the thin one than the fat one and reach the end of your abseil (knots in end of ropes obviously for a 60m abseil) with mismatched rope lengths, just continue to abseil by letting the longer length through while the shorter length is against the belay plate (practically speaking you are essentially lowering yourself off a toprope).

If you did end up somehow jamming the knot then you prussic back up and free it (unless of course you abseiled down an impossible overhanging wall, only reached the next anchor by flipping upside down at the end of the ropes, clipping in and then essentially falling onto it by releasing one rope end and THEN the knot sticks... Then the fun begins).
Pero - on 07 Feb 2013
In reply to womblesi: I can't quite get my head round this. Abseiling is dangerous enough without abseiling over a knot and having ropes of different lengths and different diameters.

There's too much to go wrong in my view. Keep it simple: buy 2 x 60m ropes of the same diameter and you're safe.
In reply to womblesi: There are many ways of doing this...

1. Join the ropes at one end, and ab with both ropes through the abseil device.

2. Abseil on one rope only, retrieve it by pulling the other rope. you need to connect the abseil rope through the belay via a krab tied onto the end of the belay rope i.e. abseil rope is tied onto a krab, it then runs up through the belay anchor and down back through the krab. You then attach the thin rope by a knot to the krab too. This works well for e.g. two vastly different diameter ropes, or if you have 2 ropes and one is badly damaged, or if you, say, want ot go light and take a half rope of 60 m with 60 m of 4mm cord.
rgold - on 08 Feb 2013
In reply to womblesi:

The knot-passing method in http://www.ukclimbing.com/videos/play.php?i=490 is standard but a bit slow and cumbersome. Here is what I think is a better way that doesn't involve any prussik knots.

Pull up the rappel lines, install your atc directly under the knot, tie it off releasably, and clip it to your harness belay loop.

Girth-hitch a sling to your harness the same length as the one used for the upper prussik in the video, install a munter biner, and clip the the rappel ropes near the anchor to that with a munter hitch. Rappel down using the munter hitch until your weight comes onto the installed and tied-off atc.

Now comes a cute trick: even though the munter hitch is at least partially weighted, you can pop the munter biner off the rope. You are now hanging from your atc below the knot. Release the atc tie-off and continue rappelling.
needvert on 08 Feb 2013
In reply to Pero:

Cavers abseil and pass stuff (rebelays, redirects, knots) lots, and they're not all falling to their deaths. (They do it in a darker environment than most nights too!).

Guess what I'm trying to say is, abseiling and knot passing, like most other things, are not that dangerous for the prepared.

The feeding through the longer rope to avoid knot passing seems a good idea, will give it a go when the need arises.

GrahamD - on 08 Feb 2013
In reply to rgold:

Knot passing - like 'escaping the system' and various other things that regularly crop up on forums as essential life skills are, in reality, only ever needed once in a blue moon. Fundamentally, 99.99% of people do not need to worry about them and those that do are capable of working it out for themselves.
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Pero - on 08 Feb 2013
In reply to needvert: So, abseiling is perfectly safe? And not the most dangerous part of mountaineering?
rgold - on 08 Feb 2013
In reply to GrahamD:
> (In reply to rgold)
>
> Knot passing - like 'escaping the system' and various other things that regularly crop up on forums as essential life skills are, in reality, only ever needed once in a blue moon. Fundamentally, 99.99% of people do not need to worry about them and those that do are capable of working it out for themselves.


I agree, most of those skills are never going to be used and are over-rated in terms of the applicability in real emergencies. But for better or worse, the OP is contemplating a specific scenario requiring knot passing---did you happen to read the posts I was replying to? This is someone who, if he doesn't do the more sensible thing of re-equipping, will have to pass a knot several times during a descent.

"Working it out for yourself" is a prescription for a long epic with possibly dangerous hiccups to boot and no guarantee of arriving at the most effective procedure. When multitudes of climbers around the world have experimented with various options and found effective solutions, reinventing the wheel (and quite possibly ending up with a square one) makes absolutely no sense.

Moreover for your 0.01% who have to pass a knot for some reason (e.g. ropes nicked by rockfall with damaged section tied off, or tying a pair of half ropes together for a 400 foot rappel to the ground in an emergency), the very fact that no one does this regularly argues for knowing the absolute simplest possible system with the fewest steps and least amount of equipment, which is what I posted.
GrahamD - on 08 Feb 2013
In reply to rgold:

I still reckon working it out on the fly is the way to go. For a 60m abseil on a 70m + 50m rope I'd (personally) just allow the ropes to slip and equalise through the anchor which at the end of the pitch would leave you the equivalent of a 60m abseil. Given that pitch lengths are advisory at best (even in our beloved rockfax) getting too prescriptive is likely to lead to dissapointment !!
summo on 08 Feb 2013
In reply to needvert:
> (In reply to Pero)

> Guess what I'm trying to say is, abseiling and knot passing, like most other things, are not that dangerous for the prepared.

curious, but I've seen lots of very unprepared people ab off places like Tremadog/Sheperds etc., purely because they are unprepared, they can't be bothered to walk round (even though it'll take them 30mins to ab), they don't want to walk in stickies, they don't know the way etc.. etc.. Many don't know just how far down it is in places, there are plenty of trees to snag on, other climbers to knock stuff off.

Sometimes the most unprepared folk and most likely to need it!
Jonny2vests - on 08 Feb 2013
In reply to rgold:
> (In reply to GrahamD)
> [...]
>
> Moreover for your 0.01% who have to pass a knot for some reason (e.g. ropes nicked by rockfall with damaged section tied off, or tying a pair of half ropes together for a 400 foot rappel to the ground in an emergency), the very fact that no one does this regularly argues for knowing the absolute simplest possible system with the fewest steps and least amount of equipment, which is what I posted.

Yeah, practicing it regularly is probably not going to happen, but nothing wrong with having a simple recipe in your back pocket. Doing it on the fly might work for Graham, but its hardly good advice.
GrahamD - on 08 Feb 2013
In reply to jonny2vests:

Disagree. Understanding the underlying principles of abseiling and being able to improvise is far better than having a recipe which falls apart as soon as one of the ingredients is missing !
rgold - on 08 Feb 2013
In reply to GrahamD:

A false dichotomy. There's no reason not to understand underlying principles and be able to improvise AND still have a simple and effective recipe that, in this case, will work in almost all situations. I'm tempted to say all situations, but it doesn't work if you have to pass more than one knot during a rappel.

Moreover, the person who, when the chips are down, actually turns out to be good at improvising is the one who knows many different ways to do something. The guy who thinks he's going to wing it when the critical moment arises is almost certainly going to fare worse, especially if the conditions are stressful.

The decision to drag 20m of rope through the rappel rings under bodyweight would, in general, depend on the nature of the intervening terrain. Someone who understood underlying principles might, in some circumstances, opt to pass the knot instead.
needvert on 08 Feb 2013
In reply to Pero:
> (In reply to needvert) So, abseiling is perfectly safe?

I didn't say that.

> And not the most dangerous part of mountaineering?

No, it's not.


Lets look at the Accidents in North American Mountaineering numbers, from 1951-2003 for US+Canada. [I'm reading the extract in the back of Climbing Self Rescue by Andy Tyson and Molly Loomis.]

Of the accidents, most happened on the ascent - 2735+555 rather than the descent - 2152+352.

Number one immediate cause was 'Fall or slip on rock', 2887+273.

Rappel Failure/Error is way down the list, 252+44.

[They included a footnote explaining what rappel failure/error meant - 'These include no backup knot - so rappelled off end of ropes, inadequate anchors, rope too short, improper use of descending device, inattention of belayer when lowering']

Number one contributory cause was 'Climbing unroped', second was 'Exceeding abilities'



Do you have anything to substantiate your stance?
summo on 08 Feb 2013
In reply to needvert:
> (In reply to Pero)

> Do you have anything to substantiate your stance?

most stats don't differentiate between walking un-roped and climbing, so an abseiling incident is very hard to separate. Plus, correlation and causation?

However, when abbing, it is often the only time when many folk rely on only 1 point of contact with the rock. Single anchor or krab at the top, perhaps only 1 to the harness and no prussik. Single rope running through what ever. So if anything goes wrong, you have an oversight etc.. it's going to hurt.

Skills - self rescue isn't not a fixed recipe. It's made up of about 4 or 5 different actions, like escaping the system etc. which can be used in many different orders, depending on the recipe; you can just escape and walk off, descend, up or down past a knot, rescue someone as you descend etc. Learning something as a set piece is fine and a good start. But, if you envisage 20,30,40 years on the crags, better to expand your skill set beyond pure cragging, as one day yours or your climbing buddies life 'might' depend on it.

summo on 08 Feb 2013
In reply to rgold:
> (In reply to GrahamD) I'm tempted to say all situations, but it doesn't work if you have to pass more than one knot during a rappel.

not sure if you are implying that you need to leave kit behind when passing a knot, it's a simple 5mins procedure that requires nothing extra beyond what a climber carries anyway and certainly doesn't need kit abandoning or left fastened to the rope.
rgold - on 08 Feb 2013
In reply to summo:

Nothing is either abandoned or left fastened to the rope in the procedure I described.

It shouldn't take anywhere near 5 minutes to pass a knot.
summo on 08 Feb 2013
In reply to rgold:
> (In reply to summo)

> It shouldn't take anywhere near 5 minutes to pass a knot.

I was thinking in terms of zero preparation and for somebody who isn't practicing very often. Personally, I'd expect to do it in 1 or 2.

I was referring to your quote that you can only pass 1 knot per abseil.
rgold - on 08 Feb 2013
In reply to summo:

If you read the process described, you'll see why it only works on one knot per abseil, and you'll also see that nothing is left behind.

Of course, if you bring out the prussiks and improvise, you could reuse the procedure for multiple knots, but at that point the savings in time and simplicity (which, by the way, entail an increase in safety) would be lost and you might as well just use the "hang from a prussik and reattach the belay device" method.
needvert on 08 Feb 2013
In reply to summo:
> (In reply to needvert)
> [...]
>
> [...]
>
> most stats don't differentiate between walking un-roped and climbing, so an abseiling incident is very hard to separate. Plus, correlation and causation?

He said mountaineering, rather than climbing. [He also attempted a strawman argument :P]

I think the argument that abseiling is the most dangerous part of mountaineering has no substance to it.
summo on 09 Feb 2013
In reply to needvert:
> (In reply to summo)> I think the argument that abseiling is the most dangerous part of mountaineering has no substance to it.

I think the jury is out on specifics, but the individual and what he does towards the end of the day, when he is tired is the most dangerous aspect. The usually involves decending in one form or another. Be it navigational errors, or clipping the wrong thing whilst abseiling, both can ruin an otherwise fun day out.

The difference is when abseiling, you don't usually get chance to make multiple errors, the first one will get you!!
Pero - on 09 Feb 2013
In reply to needvert: I'll let the BMC state my case:

"As with all methods of descending abseiling is dangerous; but it is particularly unforgiving of any mistakes or failures.

For most experienced climbers abseiling is an activity to be avoided unless it is the only way of getting off a climb or down a mountain - for the unwary it can be a fast introduction to discover the quickest way to reach the ground."
jon on 09 Feb 2013
In reply to needvert:

> I think the argument that abseiling is the most dangerous part of mountaineering has no substance to it.

Plas y Brenin used to have an old American textbook in its library called simply (I think) 'Rappelling'. Rich may have come across it...? Inside the front cover somewhere, it stated < Rappelling transcends validity > So there you have it.

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