Talk:Additional equipment for vertical caving

From Ukcaving.com wiki

I would debate the point about the safety-link from cental maillon to top jammer MUST by made from dynamic rope in case of shock load. Mainly because you are attached via the safety-link to the main rope by a jammer which will cut the rope at forces way below those which would snap a static safety-link due to its lack of shock-absorbance. Having a single static cord making up the footloop and safety-link using knots which can be unndone after loading such as bowline (for the footloop) or bowline-on-the-bight (for the attacment to the central maillon) means a reasobly long piece of cord is vailable in case of emergency. Paul

Reply: As I understand it, the point of using dynamic (ie stretchy) rope is not that SRT rope isn't strong enough, but in order to somewhat reduce the sudden shock load if you take a fall - too high a force could indeed (as you say) cause the jummar to cut the rope. Anything to reduce this force - by a stretchy safety link is a good thing. It also reduces the force on the caver when brought to a sudden (or with dynamic rope, slightly less sudden stop). Bear in mind that in certain (admitedly worst case) circumstances, you could fall twice the lenght of the safety link - generating a fall-factor 2 fall which is as bad a fall as you can get! If you fall from 1/2m above the jammer to 1/2m below this is a fall-factor 2 which is v. bad! Admitedly you shouldn't get into this position, but you could. In summary the stretchyness is to protect everythign else, rather than the link itself. A fall-factor 1 fall is quite plausible if you climb up so that top jammer is a waist-level - even this is a bad fall

I've added words on this, but perhaps could do more as many people do use SRT rope for this eg the other end of footloops - but I think it is wrong, or at least not ideal, to do this. It's fine unless you fall !

I'm also a bit skeptical about undoing a long-used knot to get a spare bit of string for some other purpose. After being on my rig for a while, knots tend to be well-stuck in my experience. I'd pinch a bit off the end of the rope under these circumstances, but usually have a sling or two in any case.

I'd also have some misgivings about using the same knot (if single footloop / safety) used for footloops - subject to repeated friction and wear every step climbed - but then be a very vital knot indeed if subject to a potentially serious high-fall factor fall.

Does this make sense ?

Cheers

Hywel

Hywel - I understand your points made above, which have also been promoted by others in the past, but I would add: You SHOULD NOT put yourself in a position where you could fall onto the Safety Link whatever the Fall Factor! Its purpose is to be a back-up in case the chest jammer slips or becomes detached during normal prusiking and if that were to happen you would probably simply sit down in your harness as usual and find your weight was taken by the top jammer via the Safety Link or at worse start sliding down the rope as the chest jammer slips.

Since a relatively small force is required to cut a rope under tension with a jammer, having a dynamic rope as Safety Link is unlikely to make a lot of difference as even after absorbing the shock of a fall there may still be enough force to cut the rope - I don't know what force would be needed without actually carrying out tests. It is better not to rely on the Safety Link in case of a fall - that's what Cows Tails are for...

Your point about being able to undo knots - suitable knots CAN be undone after being tensioned - even after many months of use. I suggest a Bowline-on-the-Bight for attaching to the top jammer via a krab. And - yes, I have been doing this for many years and can still undo the Safety Link/Footloop if needed. This was suggested to me by a CIC. And I know of at least one case where having the few metres of cord thus available came in very handy during an on-rope rescue. However, I think this is probably not the best place to continue the discussion seeing as we have both put pur 2p's worth! :) Paul

Paul - fair enough points, though I remain unconvinved and naturally enough still prefer my way :-). That said and unclipable safety as part of footloops also gives you an option to rig a 2-1 pulley substitute too. Still, I want stretchy rope on anything which might conceivably take a fall.

Perhaps you can put some updates in describing your points so that the wiki can properly show the alternatives ? I tried to do this with my "stop" versus "simple" words for the abseiling section, whilst remaining neutral (though I'm a stop man myseelf). There are other things in this nature eg tie in top-jammer or clip in, etc. Needs to cover all (reasonable) views if the wiki thing is going to work - and I've written far too much already.

Cheers

Hywel