ian mckenzie wrote:I should think the opposite - because there is so much rope used up in knots, plus the harness, connectors and other slack, it'd be impossible to even achieve FF2. I understand your point, though, that chains can generate higher than FF2, but most cowstails don't have more than one biner in a row so there is no chain effect.
I am not talking about chaining together two biners. In this case the issue is that a greater % of the total length of the system is made up by static connectors.
If you have a 19" lanyard with a maillon on one end and a biner on the other you now have 24" of total length. If you were to then climb 24" above your last point of protection and fall, you would fall 48" onto 19" of rope. I agree that the knots etc. would absorb more than a corresponding length of dynamic rope - this seems to be what testing shows. But using the common definition of Fall Factor, 19/48 is greater than 2.
Again, whether or not this corresponds to impact force can be debated. As Derek mentioned the reports linked to so far don't seem to isolate the shock absorbtion of knots other than to show in a general sense that knots are better than sewn connections. But the reports allude to the fact that Fall Factors are not the best way to judge impact force when dealing with short lengths of rope. I also agree that with the harness and dynamic nature of the human body you will probably encounter lower impact forces than what is shown in testing where steel plates or some other static load is used - other testing has provided evidence for this. But people don't normally account for harness/body when calculating fall factors.
The point is, fall factor aside, impact forces can be suprisingly high with cowstails. I certainly would not want to subject myself to the 7-10 kN that some of those tests show for commonly used cowstails(steel plate testing issue duly noted). So whether or not you use static or dynamic rope it would seem that the best bet is to keep your point of attachment as high as possible.
Anonymous_Coward wrote:Actually, I've decided to do one more cave trip. It's kind of a large one, so I am starting to shop for the trip now. Tomorrow I am making a run down to Spectra Depot. Need me to pick anything up for you?
Could you pick any Hitler Spectra up for me Andy? I need to use it to attach my six extra QAS that I use in my unorthodox high attachment vertical system I wear while caving without a helmet. Also, I think three sources of light is ridiculous and manilla rope suits me just fine. Backsights are for ninnies who can't read instruments(Did I miss any hot topics?).
Wait, you have a Spectra depot in Utah?