We've all seen them, many of us will have hung off them, and most will have wondered how strong they are! I did as i carefully sat on this one in Horne's Gully in Titan.

I was feeling at least a little bit happier that the ~20m long rope up to the next single bolt was a little bit tight to this single bolt. Also that myself and Henry had already prussiked up this route 30 minutes earlier.



It snapped when i was about 1m below the bolt, causing me to freefall ~4m before the rope above kicked in, slowing my impact with the floor enough that i was not hurt.

A few lessons from this:
[list type=decimal]
[*]Gooey krabs may be very weak
[*]Abseiling has potentially more loading than prussiking, so slide smoothly
[*]Tight rigging is good when rigging single bolt rebelays
[/list]

That is very scary and definitely makes you think 

Yeah, and he's not exactly Lard-lad. Good to know you're OK Rob...

This is the result of preferential electrolytic corrosion where an aluminium carabiner has been in extended contact with a steel or stainless steel anchor. The real moral of the story is that if you are placing anchors for long term use, all of the components of the system must be stainless, and in particular do not leave aluminium krabs on stainless anchors.

Nick.

Rob said:

It snapped when i was about 1m below the bolt, causing me to freefall ~4m before the rope above kicked in, slowing my impact with the floor enough that i was not hurt.

Click to expand...

Blimey - sounds like a bowel-loosening moment !
A salutory lesson - I wouldn't have expected a breakage even if the surface did look furry.
Thanks for posting.

Good that you're OK Rob,  do others now need to be aware that the top section of rope has now had a shock load ?.

Rob - Good that you're OK.
A couple of things spring to my mind -
1. This should maybe be on the "equipment" thread
2. If that picture is the actual krab you used, did you really think it could hold you? and was it a good idea to hang off it?
3. If the price of your life is less than leaving a ?5 krab on a pitch, then you're undervaluing yourself.


[gmod]Moved to Equipment as suggested above[/gmod]

I wouldn't use that crab to hang my washing off!

Can't say I have ever hung off a crab like that though, I have gone past some deviations that are of that vintage (which require a rock to operate).

Burt said:

Rob - Good that you're OK.
A couple of things spring to my mind -
1. This should maybe be on the "equipment" thread
2. If that picture is the actual krab you used, did you really think it could hold you? and was it a good idea to hang off it?
3. If the price of your life is less than leaving a ?5 krab on a pitch, then you're undervaluing yourself.


Moved to Equipment as suggested above

Click to expand...

"3. If the price of your life is less than leaving a ?5 krab on a pitch, then you're "undervaluing yourself" 
Alas, that is the situation " up North"  , can you really get a decent stainless steel crab for a fiver down where you are ?

I've got stainless maillons. Can't remember how much they are/were, though.

Caving Gear have them for about ?7.50 (compared to ?2.50) http://www.caving-gear.co.uk/products_tn.asp?id=62

I think Burt was suggesting using a replacement alloy krab (or the original rigger putting a steel krab in instead of an alloy)

Mike

mikem said:

I think Burt was suggesting using a replacement alloy krab (or the original rigger putting a steel krab in instead of an alloy)

Mike

Click to expand...

Nick is quite right is spot on.

nickwilliams said:

This is the result of preferential electrolytic corrosion where an aluminium carabiner has been in extended contact with a steel or stainless steel anchor. The real moral of the story is that if you are placing anchors for long term use, all of the components of the system must be stainless, and in particular do not leave aluminium krabs on stainless anchors.

Nick.

Click to expand...

So how should replacing with another alloy be any sort of a answer?

Jopo

One thing that has not been asked is "how long has this crab been there?", another question or two may be "who put it there?", "was it a temporary measure?" etc. etc.

Been there a maximum of 14 years but could be considerably less.

I think most keen Peak cavers have hung off 'jelly' krabs at one time or another - for example if you want to go up Cliff Cavern in peak and explore the side passages the traverses all look a bit like this......

Something to consider is things left rigged are generally left rigged as they are up pitches - therefore you often don't know the state of the krabs until you are hanging on them.....

Jopo said:

So how should replacing with another alloy be any sort of a answer?

Jopo

Click to expand...

By replacing dodgy gear to ensure your own safety (i.e. not long term use), if you're doing the pitch regularly or intending to make it safer for other explorers then you'd go for the more expensive option...

Mike

Nick is right about the (potential) cause of the corrosion.
Galvanic Action between dissimilar metals is well known. However, the statement that it may have been in place for up to 14 years might well suggest that the most likely cause might just be plain old water, especially after the protective Anodised layer has been abraded off
  Aluminium and it's alloys react very fast to corrosion, like point nothing of a second after exposure to Air/Moisture an Oxide will form, and this, itself can inhibit corrosion, but when it is subjected to an almost permanently damp or wet environment the trace elements in cave water will most defiantly accelerate it's progress, and not just by itself. Nick named Electrolytic Corrosion as the probable culprit, and the water is, in this case the Electrolyte, rather like the acid in a car battery, it is the medium by which the electrons will be exchanged by the two metals if differing potential.
The amount of Exfoliation of the alloy seems to suggest that this damage had either gone unnoticed, or replacement deferred, so in light of the
"Something to consider is things left rigged are generally left rigged as they are up pitches - therefore you often don't know the state of the krabs until you are hanging on them" comment, NOW might be a good time to have a good look at them.

We all learn from our mistakes....so Rob, I bet You and Henry won't be hanging off of any others like this ....too soon.

I have sometimes found myself in the situation of having gone up a fixed rope and found something like that at the top. I always came down leaving my own krab/maillon behind. I'm not saying I donated a brand new stainless one, just something safer than I found.

Maybe in a few years time we'll all be hanging off these 

http://www.crabdev.co.uk/Design%20of%20a%20composite%20carabiner%20for%20rock%20climbing.pdf

Did some work about 10 years ago using an impact modified nylon with a 40% kevlar content. material was supplied by Dupont and was developed to replace structural steel part for the automotive industry. Only a matter of time folks before we're all hanging off plastic!!

manrabbit said:

Maybe in a few years time we'll all be hanging off these 

http://www.crabdev.co.uk/Design%20of%20a%20composite%20carabiner%20for%20rock%20climbing.pdf

Did some work about 10 years ago using an impact modified nylon with a 40% kevlar content. material was supplied by Dupont and was developed to replace structural steel part for the automotive industry. Only a matter of time folks before we're all hanging off plastic!!

Click to expand...

Way to go guys!

Jopo

Hi Manrabbit, thanks for posting a most enjoyable read.