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General Climbing Discussion

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Half Ropes 16-Jun-2006 At 9:46:14 PM Nick Kaz

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On 16/06/2006 JamesMc wrote:
>Does anybody have any evidence that two ropes going through the same biner
>and stretching differently is a real problem, or is it just theoretical
>or just urban myth?

I haven't ever herd anything about it actualy happening but thoreticaly its very possible.

>My thought on it is that the energy going into heat from friction between
>the ropes would be negligible compared to the energy going into heat from
>the friction between the ropes and the krab.

The surface of the krab is smooth and radiused so that there is minmum friction between the rope and the metal so not much energy would be dissapated into the biner, think of how hot a crab gets after abseiling say just 10m, warm but not hot enough to melt the rope. Now think about the rope surfaces. both are relatively rough and against each other there is high friction thus much energy will be dissapated here. The result? Try rubbing two lengths of prussic together under load, you will be supprised how little it takes to melt one...

>For a given lead fall, would the belayer feel a smaller load if the ropes went throught the >same krab rather than two krabs next to each other? If there's no difference then there's no >point having seperate krabs.

>James Mc

The ropes would feel half the force each, the belayer feels the sum of these minus the energy lost to friction etc in the system. Two crabs is a good idea if you plan to clip a single placement with both ropes after seperating them.