There is a discussion going on over at
SuperTopo that is directly related to a rappelling fatality in Yosemite last week. There are many posts on the technical aspects of rappelling with one lead line and one "pull" line of a small diameter, when the anchor consists of rap rings.
Petzl has a
diagram of how they suggest a single line rap should be done. Their method is safe enough to keep you alive, but it too has problems with the knot possibly getting through the rap rings and then becoming un-retrievable from below . I've suggested that the clove hitch method be used and is the safest method available in this scenario.
The relevant technical posts start
here in the thread.
There is some really good info in that thread and is worth your time to read it and understand it.
Clint Cummins has just added a great presentation of
Yosemite style anchors and which rap set up will allow or not allow the knot to pop through the anchor rings.
Posts
Thanks for that...excellent. The one thing that I simply do not get about all this (and the tragedy) is these techniques make little to no sense in the front country. Especially where the punishment for carrying an 8mm tag or even another 10.2 is 5 minutes of walking.For most mere mortals, I don't thing the risk is worth the reward.
ReplyDeleteI think it is also a case of you use what you are used to since that is your "set up". I use a 70 meter skinny lead line (9.2?) and have a matching 70 meter 7mm trail line. The knot profile is very small, but that is what I use and know its limitations and pitfalls. I do not use this set up for standard cragging, and use something a bit larger for the lead line, and whatever rope others in the party have for the trail/pull line.
ReplyDeleteThe key advantage to having the skinny trail line long routes, be it front country or not, is not only weight but package size. Something like a 7mm can be stored in a very small pack or worn while climbing with it not being obtrusive.
That being said, any legit system is safe when used correctly and you understand the limitations and the dynamics of the system and stay on top of your game until you safely get back to the car.
I'll also add... I have never liked the "knot block" system of rappelling, and in fact I can't remember the last time I used it. When I'm doing multipitch stuff and running my set up from the above comment, we always have at least one ATC style device, and usually a GriGri. If anyone is single line rapping, I set up the rappel like normal through the links and then clove off the single line directly to the rings or anchor. The GriGri person raps the "fixed" single line. Once they are secured at the lower station, I undo the fixed line clove, and set up to do the standard rappel mode, using both ropes, with my ATC and rap off.
ReplyDeleteThanks.....I end up rapping both lines with the trail line as well. To me there is a certain security that I'm used to and as you stated, know its limitations. Having said that....knowing the feed speed of the skinny line takes careful consideration.
ReplyDeleteIf I'm thinking the skinny line is going to shift a fair amount, I'll do the clove block method on the fat line, but still rap both lines.
ReplyDelete