UKC

What size / thickness cord is reasonable for transferring the weight of the fallen climber using a Prussik-munter-mule-overhand to the belay whist escaping the system?

Is 5mm cord (5kN) to thin for this bearing in mind at one point in the escape it is all thats holding the fallen climber?

What do others use for this?

Thanks

In reply to anon60521:

"... bearing in mind at one point in the escape it is all thats holding the fallen climber?"

Perhaps I've misunderstood the scenario, but aren't you able to tie a figure eight on the bight on the rope with a bit of slack as a back up? I would say 5mm is probably fine in terms of tensile strength when new, but personally it is getting a little thin. With deterioration due to age and abrasion, I'd be looking at 6 or 7mm really.

In reply to anon60521:

At least one texts description of escaping the belay involves tying a FoE and clipping it to the anchor before you go through the procedure, presumably incase some point goes pear shaped - the climber will then fall the distance of however much slack you opted to allow between the FoE and your belay device.

I'd not mind if my partner used 5mm cord.

(One way of considering the security of 5mm cord is, how many people are willing to rap off it?)

In reply to anon60521:

Although your prussik cord will be at some point be holding all the weight, it should always be backed up by the rope.

Interesting side note...

http://www.hamradio.si/~s51kq/photo_album/Climbing_and_Mountaineering/pdf_c...

That table of diameter and minimum strength, fits the formula diameter^2 / 5.

(
map(lambda x: x**2./5, range(4,9))
[3.2, 5.0, 7.2, 9.8, 12.8]
)

In reply to needvert:

I use 5.5mm, which doesnt seem to be allowed by uiaa as it is not an integer

In reply to anon60521:

Of course its strong enough. Its not over an edge and in any case its doubled up in a loop. The scenario you are talking about is so rare that it won't happen to the majority of climbers in their lifetime. Not worth worrying about.

In reply to needvert:


Assuming you can reach the anchor of course.

In reply to GrahamD:

Well, you're probably right. But it's like practicing a fire drill isn't it.

In reply to Jonny2vests:

In which case you need another bit of cord or a sling to set up another prussic on the ropes running between your harness and out of reach belay anchors...

In reply to anon60521:

5mm is fine. It's really very strong.

If you're worried, then use 6mm. The weight won't kill you

In reply to anon60521: It is possible to escape the system both in reach of the anchors and out of reach without leaving someone attached to just a prussic. I generally try and teach people the idea that a prussic is half a point and they need one point or more for any rescue to be safe.

5kn is about a 500kg breaking strain, so it should be ok, but like I said never leave someone hanging on only that. Often a italian hitch tied off makes a suitable back up.

youtube.com/watch?v=CsnZVl9EMdE&

In reply to Jonny2vests:


No harm in practicing these things of course but far better on concentrating on things that are much more likely to go wrong than a piece of cord which can hold a car snapping under body weight.

In reply to GrahamD:

Oh, I thought you meant escaping the system was rare, which is the fire drill I alluded to.

In reply to Mark Reeves:

cool, cheers.
good point re It hitch.
From reading some yank's bigwall techniques book (cant remember the name or author), the self rescue stuff has tied off Italian hitch for systems & backups.
makes sense in that you can always lower/slacken off under load;
if you end up with some >80kg dead weight on a fig8 that'll be a total ball ache to free up.

In reply to Gavin:

Why not just lock the plate off, then take the free end back to the out of reach anchors?

In reply to GrahamD:

If it's 5kN it definitely can't hold a car...

In reply to anon60521:

Slightly intrigued if that is your default method for escaping the system.

Most climbers I know in the UK tend to carry short prusiks so default to other methods. This is re-enforced by these methods being the ones described in the official MLT Handbook.


If it is the only thing holding the climber, then IMO you need to learn a better method of escaping the system. The way most UK climbers tend to escape the system, as jezb1 has already said, the prusik is backed up with the rope.


I don't.

However, I do use 5mm cord for the two or three short prusik loops I carry and I don't have any concern about their strength given how I would use them.

In reply to anon60521:

Surely it is not the width of the cord which is critical, it is that it is a prussik - and therefore not to be relied upon?

In reply to anon60521:

Easy to always say thicker is safer, but prussiks only work when they are thinner than the rope they grip. Up to 8mm cord if fine for 11mm rope, but on modern half ropes then 6mm must be the maximum, and different cord grips differently on different ropes especially when new.

In short, 5mm is fine for all single climber rescues: if it starts to slip (around 3kN) then something is wrong

In reply to Jonny2vests:

My reading of the original problem was that you had the weight of the climber on the rope, so wouldn't be able to lock the plate and walk back to the out of reach anchors until you'd got yourself out of the system.

Putting the second prussic in means that when you come untie you'll have the fallen climber held on the prussic that was in front of the belay plate and also tied off as a back-up to the intermediate anchor formed using the second prussic.

In reply to kestrelspl:

Being a pedant, you have two strands in a loop. 10kN is just about enough for a small car. Certainly very much more than the static weight of a climber which is the real point.

No actually the real point is if you can't work this out for yourself, should you really be putting you and your partner in a situation where you need to be able judge far more significant forces in the system ?