how dangerous is misusing krabs?

[Charlie]

this thread http://ukcaving.com/board/index.php/topic,6949.msg93749.html#new got me wondering about how dangerous misuse of krabs actually is.

the link from that thread http://www.onrope1.com/Myth2.htm seems to suggest that krabs under tri-point load break at about 85lbf [40kg or 0.4KN] whereas this
http://www.alpinets.com/carabiner.html suggests it will be similar to cross gate loading [7-9KN]

I have seen no data on how much strength is lost under tri-point load, torsional load or any of the other different ways we are warned to not use krabs.

Does anyone have any data? or recommendations of where to get some? [preferably nothing too difficult, I dont care all that much - just want to know to satisfy my curiosity]

Cheers
Charlie

 

[graham]

Well, I once used one as a drift, with a large rock as a hammer, to push a rusted bolt out of a cave gate. It wasn't dangerous at all, as we'd already promised to buy the owner a new one if it bent.

 

[Peter Burgess]

What, a new krab, or a new gate?

 

[graham]

New krab (which we bought from Mr Rat shortly after). The gate was only improved by our actions.

 

[AndyF]

If there was any way to break a krab under 3 point load at 40kg, there would be lots of dead bodies splattered around the crags.

It has to be a figure approaching the cross-gate stength

 

[Charlie]

If there was any way to break a krab under 3 point load at 40kg, there would be lots of dead bodies splattered around the crags.

I had serious doubts about that figure, and several others on the site - the "using a double loop knot reduces the strength of your krab by 1/3 because the load is away from the spine" - sounds false to me as well.

still interested in the other things marked in the instruction leaflets with a nice friendly skull and crossbones [except the quickdraw ones about how the rope comes out through the gate, I understand those]

 

[Hughie]

I've used a krab as a central connecting point on a cow lifting harness lifting weights in excess of 600kg with no apparent damage.

Also used for securing gates occasionally - no significant risk of damage there.

One of our vets nicked one of mine to use in in-utero embryotomyies - only real danger there is being shat on.

I reckon - but it's only my opinion - that a krab with the screwgate done up, is a lot stronger than people give them credit for.

 

[Stu]

This will teach me not to throw my journals away!!

The Association of Mountaineering Instructors (www.ami.org.uk) did some ad hoc testing on krabs, specifically HMS types, where the krab had three clove hitches in it (a common enough site on the crags and one which had caused some concern about this type of krab being used as some kind of central point for belays due to its shape).

The krabs were breaking at about half their stated main axis breaking strain. The weren't exactly cross loaded in the recognised sense of across the gate. The conclusion being that stacking lots of knots onto the wider part of the krab was poor practice.

 

[docfunk]

I`ve managed to break 2, 22kn screw gates back to back whilst pulling a huge tree stump out of the ground with the landrover, they went off like a shot gun BUT... the 10mm mammut static rope doubled up never snapped!!