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General Climbing Discussion

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Half Ropes 16-Jun-2006 At 11:02:24 PM JamesMc

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Nick Kaz wrote:
>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.

Actually Nick, I reckon there's heaps of friction between a krab and a rope if there is a lot of contact pressure. Take your abseil example. All the energy from the abseiler's loss of height goes into heat. Some in the abseil device, some into the rope, and a bit into the air. I don't know the proportions.

Also imagine belaying a lead fall where the rope goes through a pulley with zero friction. The belayer would feel a harder pull than if the rope just went through a krab. The difference is due to the friction in the krab. The harder pull would mean less heat going into the rope at the pulley, and more at the belay device.

However the rope is rigged, the energy loss from a falling climber loosing altitude turns into heat. The way to minimise the heat in the rope would be to increase the size of the karabiners and belay device, in order to get a greater heat sink effect. Using 2 krabs would help make a better heat sink. Ten krabs would be better still. I couldn't be bothered with the weight as I think the heat issue is too small to matter.

James Mc

(PS I don't know the answer, I just a skeptic thinking out loud)