belay plates on cave rope

[hunter]

Then 9mm should lock fine too, so long as the belay tube permits 9mm dynamic rope, right?

Right. I mentioned the Reverso because it is the only one I know the manufacturer does not rate for smaller than 10.

I hope it was semi-static!

I don't remember real well now. It was black and seemed about as stretchy as your average caving rope.

James

[NZcaver]

Of course if your standard caving descender is a Stop (or similar), you could just belay with that.

I've used a Petzl Stop as a fixed brake lower with 9mm cave rope. It slipped a lot--I had to tie it off to keep it from slipping. I'd be worried about its ability to catch a load in time on thin cave rope.

As you know, most descenders and belay devices - particularly those with automatic functioning components - can be very diameter-specific when it comes to rope. I was envisaging using 10mm or perhaps a supple 11mm rope with a Stop in this application. But often I've found the Stop can be a real pain to belay with (back-feed), so try just using a Munter for those rare in-cave static rope belay situations. Just a suggestion.

[ek]

I hope it was semi-static!

I don't remember real well now. It was black and seemed about as stretchy as your average caving rope.

It was probably Sterling SuperStatic, which is a semi-static rope that usually comes in black and is advertised for use in climbing gyms as well as the usual uses for semi-static ropes.

Traditionally, cavers use semi-static (low stretch) rope rather than static (very low stretch) rope. This is also by and large the safest practice. To reduce bounce, stretch, and abrasion, some cavers, especially in the US, use static rope that stretches less than steel cable.

Dynamic rope is OK with falls up to factor 2. Semi-static is OK with falls up to factor 1 (but of course, get it wet and it's less shock absorbing, when it's old it's less shock-absorbing...best to avoid a factor-1 fall if at all possible). By OK, I mean that not only does it not break but the peak impact force is no higher than 12kN at most.

Static (very low stretch) rope is OK with falls up to factor 0. More than that could rip things out. Not a good idea even to have a bouncy rappel or ascent.

[hunter]

Makes sense. I've always heard ropes as static vs dynamic but I expect that everything I use is actually semi-static by your def...

Oh, NZs post reminded me that the Gri-gri is the other device I know that the manufacturer says should not be used with 9mm. A number of people have been dropped while lead climbing as a result of narrow diameter ropes and incorrect gri-gri usage.

James

[ek]

Yes, the minimum rope diameter for the Grigri's locking assist action to function properly is 10mm. Unofficially, the Grigri supports ropes of lower diameters, but if you have to maintain the brake hand on the rope at all times, and hold it in the braking position, as with a belay tube.