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Author
More or less friction for belay devices?
Wighty
15/05/2011
10:53:03 PM
I've had this discussion with a couple of mates in the last year or so and am keen to try and settle this once and for all.

Does adding a second screw gate through the rope when using a belay plate create a more or less controlled lower (i.e. more or less friction)

I was under the impression that the second biner creates a larger angle which enables the rope to slide through the device easier.

Mates believe that by having the second biner more rope touches metal creating a slower and more controlled lower due to more friction.

Any thoughts?

nmonteith
15/05/2011
11:40:24 PM
It creates more friction and a slower and more controlled descent.
Decoy
16/05/2011
8:11:44 AM
Depends on whether the second one is attached to you belay loop or not.

This article explains what I mean (about half way down):

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

patto
16/05/2011
8:28:16 AM
It really depends on a few factors. Friction is lowest when the rope making a smooth broad curve around the 180degrees. Narrow profile biners cause a sharp curve and increased friction. Two fat biners cause a fat bell shaped wiggle around the two biners and cause increased friction. A single big fat smooth round 12mm biner will pretty much give minimum friction.

Two DMM sentinals attached to belay loop give LESS friction than one due to their narrowness.
egosan
16/05/2011
9:08:59 AM
Jim Titt's in depth analysis of braking forces is here:

http://www.paci.com.au/downloads_public/equipment/19_Belay_Device_Theory.pdf

Very interesting reading.

nmonteith
16/05/2011
9:23:16 AM
Intriguing! I've only ever used the two biner method a couple of times when abseiling on a single strand of a half rope. I didn't think much about what biners I was using but obviously my random choice of biner type worked to slow me down. I'm glad I didn't choose the 'go faster' biners!
kieranl
16/05/2011
10:07:29 AM
Agreed, a very interesting read.
The ability, more correctly inability, of most devices to hold long falls is sobering stuff.
Perhaps people not using Grigri-type devices (or Munter hitches!) need to go back to the practice of wearing gloves while belaying or abseiling. It might even cut down the incidence of people being dropped in short falls by inexperienced belayers.

miguel75
16/05/2011
10:20:57 AM
Has anyone found a need to use the double Munter (I've heard/read of it being called the Monster Munter) referred to in the article Egosan referrenced? Wendy or other guides/rescuers?

I found this video of it interesting from around 6 minutes;

http://youtu.be/6ulTTrhfCvs

ajfclark
16/05/2011
10:39:59 AM
Here's some stuff from KP @ BD too: http://www.blackdiamondequipment.com/en-us/journal/climb-qclab/qclab/qc-lab-autoblock-misuse/
egosan
16/05/2011
4:18:26 PM
The ol' Monster Munter has more friction than a munter, but does not twist the rope. If your HMS Biner is big enough and you are rapping on a munter, the Monster Munter makes for nice coiling of the rope later.
Wendy
16/05/2011
4:25:54 PM
On 16/05/2011 kieranl wrote:
>Agreed, a very interesting read.
>The ability, more correctly inability, of most devices to hold long falls
>is sobering stuff.


I'm curious as to what becomes the sort of fall that most devices aren't able to hold? I can't remember holding a single fall that either gave me rope burn or I thought I might not be able to hold on.

A few months ago, I held Sol on a big whipper of the top of Wasp on his 7.8mm doubles - or more precisely, on one of them - with my ATC guide. He fell from the last holds to quite low in the initial corner. I'm guessing somewhere around10m, not quite at the end of a 20m pitch. I'd walked downhill as he sketched out to put more rope into the system, so he may have had 21m out, and I went up pretty much everything I'd walked down. But holding a .5 ish factor fall, with a heavy climber on a skinny rope wasn't an issue. Not for me anyway; Sol was a bit shaken! I'm thinking this is because being a mobile belayer absorbs lots of force? Hence why I have no recollection of any problematic to hold falls in 20+years? Admittedly, no one has gone anything near factor 2 on me though.
kieranl
16/05/2011
4:46:53 PM
I think Jim is saying that you can start having issues on long falls of about factor 1. Probably don't want to encounter one of these on a single pitch climb unless it starts from a ledge that the leader can fall past. I don't know that he said what he would consider a long fall; my feeling is that it would be greater than 10 metres. I can't justify that, it's just a guess.
What does length have to do with it? The length of the fall doesn't change the theoretical impact force : a 10 metre factor 1 theoretically generates the same impact force as a 20 metre factor 1. I don't really know but it's certainly a complication and maybe contributes a randomising factor to the situation.

Miguel75
16/05/2011
4:56:32 PM
Thanks for your input Sol. Aside from anchoring the pig (or practicing an emergency belay plate-less rap) I haven't used it much.
grangrump
16/05/2011
5:10:31 PM
On 16/05/2011 egosan wrote:
>The ol' Monster Munter has more friction than a munter ....
Yeah but you have to pay more for the Munter??
Ebay
Kong Bonaiti - Screw Lock Carabiner
The size and shape of this carabiner make it popular for many uses: connecting a belay device to a harness, belaying with a Munter hitch (sold separately) and as a multi-purpose carabiner for use at belay stations.
Compact, lightweight and easy to handle. Colour: Blue ...
mikllaw
16/05/2011
5:20:29 PM
On 16/05/2011 kieranl wrote:
>I think Jim is saying that you can start having issues on long falls of
>about factor 1. Probably don't want to encounter one of these on a single
>pitch climb unless it starts from a ledge that the leader can fall past.

I had trouble holding a 20m factor 1.8 fall on a waist belay, and I heard that Warwick Baird went an extra 15m on Bluff Mountain till a tangle jambed their belay device

>What does length have to do with it?
A short factor 2 fall may get an extra bit of 'stretch' as knots tighten and bodies slump in harnesses and come tight on belays etc. I think this might add up to a total of 250mm, which would make a short factor 2 quite soft, and would make no difference to a 20m factor 2 fall
Jim Titt
16/05/2011
10:02:49 PM
As you point out, what one could think is a factor 2 is reduced by all the extra give in the system and for short falls this helps a lot to remove energy from the system, once you take bigger falls the energy concerned is enormous and some of it will be going into your hand as the rope slips, too much and your in deep trouble.

No doubt hundreds of people will be along to say they held the whipper of all time and the rope never slips but all the testing shows that it does, just it wasnīt noticed. This is the official view of the UIAA amongst others and in theory slip must occur unless you pre-tensioned the rope on the belaying side sufficient to hold the fall and most people arenīt strong enough or fast enough. Even a Grigri slips a bit!

Jim

There are 16 messages in this topic.

 

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