We bought a Cinch which was great (and is a really good backup when ascending a fixed line as it self feeds) but did need a totally different technique and you couldn't just pass it to someone and expect they'd be familiar with it.
Tl:dr: Grigris don't kill people, belayers do
The device requires tension in the rope to engage the cam, so if this tension isn't present or is low enough, you won't engage the braking assistance.
I don’t agree with that interpretation. The device works on friction between rope and cam. The faster the rope is moving the more potential it has to engage the cam, if it touches it. The problem is holding the rope and device, as in the video, where the rope isn’t touching the cam sufficiently. Acceleration does have a role, in that it is more likely to disturb the path of the rope out of a poor position, but it’s not acceleration that engages the cam, it’s friction. Hence why in the vid the cam does engage eventually.Unlike drag in air or water, solid-on-solid friction does not simply increase with speed, so the critical thing is the quality of the contact between the rope and the cam. Hence why a slow pull will engage the cam if things are in contact, but a fast one may not. But we tend to get in the habit of trying to minimise the contact for clipping. When I tested Shunts as used for fall arrest in shunting or rope access back up, we found the behaviour at low speed was not representative of that at falling speeds, where the device required a higher load to start slipping than it did to continue slipping. But grigris don’t slip once engaged in my experience.
Just hold onto the rope
"Keep a hand on the brake rope"However, from now on, I'll be using the finger under the lip method and 3 fingers on brake rope. , but only for that moment they need quick slack.
I think many accidents/near misses are essentially a result of people who treat belaying as a break between their own activity.
"Keep a hand on the brake rope"Yes, obv.. but isn't that the issue? (I certainly find it a problem), that its hard to quickly pay out slack without using the thumb on cam method, which entails not having your hand properly on the brake rope.
This is what Petzl recommend.
I think the danger with the forefinger under device method is that under stress, we grab, and it’s possible to clamp the cam open in this position as thumb and finger are opposed.A finger under the flange is offset from the thumb on an insecure feature to hold. It’s unlikely you’d exert enough force to keep the cam open in a fall this way.