In reply to Greasy Prusiks:
> OK thanks Jim. I've had a look at your research (much appreciated by the way) and through the climbing grape vine understand you know one end of a belay device from the other.
Jim certainly does (far more than me), but all of his tests are static, not dynamic drop tests (because you need a drop tower etc and it is hard/expensive - I am grateful for the tests that Jim has done voluntarily and kindly provided to the public!). The massive unknown is whether a FF2 fall on the MegaJul, and consequent slippage, will result in:
a) catastrophic failure, continued slippage, and death for all involved, or
b) the slippage reducing as the energy of the fall is absorbed and the climber eventually coming to a halt.
It is almost certainly dependent on rope diameters, as the MegaJul will fail to hold bodyweight for certain ropes (single strand 8.5mm in my case, but static 9mm is fine).
I _don't_ trust my MegaJul to hold a fall unless I am holding the brake rope correctly, and I expect it to slip if subjected to a large enough force. But equally I don't trust myself to hold a FF2 fall - I have absolutely no experience of holding such dramatic falls and I don't intend to if I can possibly avoid it; it may very well be that having a belay device that will, for the correct choice of ropes, eventually lock up may stop a FF2 fall that I wouldn't have held myself. Or not. Who knows, unless someone does some dynamic drop tests? :P
Slippage can be good (the alternative usually being tearing a rope). When tying off a Petzl ID (industrial belay device/descender, bit like a big Grigri - which you don't normally need to tie off as they lock off but it is an option) you are supposed to leave at least 1m of slack rope downstream as in a big fall the rope will slip and absorb the energy of the fall, and if you don't leave the slack then the knot hits the device before the slippage has finished and Bad Things happen.
All of the above can be ignored - I'm just not sure Jim's results mean you should run out and buy yourself a new belay plate, when there is so much more shiny gear in the world to buy :P
Post edited at 21:15