Moderator: Tim White
fuzzy-hair-man wrote:Aluminium definately provides more braking than steel, I have tried both stainless steel and aluminium racks and the steel ones are a lot faster.
That said I use a steel carabiner as my brake krab because it is a friction surface and steel will not wear as fast as aluminium. If you need the extra braking then go aluminium but if not I'd go steel.
If you are likely to be doing high wear trips then I'd definately go for a steel brake krab.
What I'm trying to say is to not worry too much about the material for the braking carabiner with respect to the amount of friction it provides itself - consider weight (seel is heavier), price on how long the braking carabiner will last (steel is more resistant to wear).
and materials and structure and temperature...hunter wrote:It's also worth remembering that friction is a factor of both surface area and force.
hunter wrote: Just because something has a smaller area of surface contact with the rope doesn't mean it has less breaking.
paul wrote:Sure - but my main point, put another way, is that to increase the braking effect on a bobbin-type descender you pull harder on the controlling rope. By adding a braking carabiner, the effect of pulling on the controlling rope is increased as the carabiner is acting like a pulley (albeit a not very efficient pulley!) thus supplying a mechanical advantage.
paul wrote:I bet even if you used a pulley in the same place as the braking carabiner, there will be more braking effect provided by the descender when pulling upwards on the controlling rope!
NZcaver wrote:paul wrote:Sure - but my main point, put another way, is that to increase the braking effect on a bobbin-type descender you pull harder on the controlling rope. By adding a braking carabiner, the effect of pulling on the controlling rope is increased as the carabiner is acting like a pulley (albeit a not very efficient pulley!) thus supplying a mechanical advantage.
Nice idea - but I contend that a braking carabiner does not really supply any mechanical advantage.
If you are referring to the wide "V" formed in the rope as it leaves the descender, goes through the braking carabiner, and then to your hand - that's not mechanical advantage. It's just a simple 1:1, with a change of direction. Not only that, but you are braking by pushing the rope away from your body. This is not nearly as effective as applying force by pulling down or toward you.
NZcaver wrote:But I do agree the difference in practical braking force between an alloy and a steel carabiner is probably negligible. Although rope generally produces more friction against alloys than steel, a single turn around a carabiner is hardly any surface area at all.
paul wrote:Mind you, I don't push the rope away from my body, I grip the rope so that the rope leaves the bottom of may hand towards the braking carabiner and descender. To apply more friction to slow down, I raise my arm upwards and grip harder on the rope pulling upwards at an angle to the horizontal.
potholer wrote:When I started caving, I was nearer his weight and caving on 10mm basically all the time, and it took me a while before I started using a braking crab...
I imagine that someone of a larger build than me *may* find they move uncomfortably fast even with a lot of weight beneath them, and so would have the problem of having to lift a heavy rope in order to use the braking krab.
tchudson wrote:I use steel as they last longer than aluminum, and on the dirty, muddy ropes that most TAG cavers seem to have, that says a lot. In fact, I had some tubular steel bars that a friend made especially for me - extra thick. Unfortunatly, that rack is lost somewhere in the wilds of Arizona. Anyway, it's never been an issue of which was faster, but which lasted longer.
Uncle Muddy wrote:Choice of descending devices not withstanding, a steel carabiner can also be used for a munter hitch for short drops.
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