dark_storm83 wrote:Just curious how most people rig their ropes for the first descent into a cave.
What I do is one way of many, and I certainly would not represent it as necessarily the best. That said...
In caves with thick, living trees near them that can be accessed easily without falling in the hole, I usually rig of such a tree with a 2 or 3 wrap tensionless hitch, wrapped downward (so the loop knot is at the end of the lowest wrap) with the wraps free of one another, and with the loop attached to the line with a locking carabiner, with the gate locked and the gate opening facing the line going into the pit. If it is a D or offset-D carabiner, I keep the gate on the bottom, as I have found that otherwise the 'biner tends to flip and put the gate opening away from the pit line.
I put the gate opening toward the pit line so that in case it were to slips (or, in case I manage to mess up the rigging) so that the knot gets weighted, *and* it turns out to be necessary to untie it under load, the pit line would only have to be deflected to the gate opening, and not to the center of the carabiner (to flip the 'biner and then remove it). This may seem insignificant...and maybe it is. I've never had to take the load off a tensionless hitch, much less one with the knot weighted. But I've practiced doing so, and I've found it much easier when the gate opening toward the pit line.
If I have twice as much rope as I need or more and am rigging with a tensionless hitch, I usually leave half at the top. This makes it easier to pull the rope up and provides more rope to send down in case of emergency, or use in some other capacity, and (usually) makes it possible to lower someone (very carefully!) by partially untying the hitch and allowing it to slip in a controlled fashion.
When leaving rope at the top of a drop in the winter, I usually keep it in a bag to minimize the likelihood that it will get wet, freeze up, and become less useful. Otherwise, I usually throw the bag end down into the pit, because that is a lot easier and faster than flaking out the rope and more likely to keep out tangles (I don't know about anybody else but I can certainly pack a rope in a bag more properly than I can flake it out). If there is something fragile (e.g. a formation, a person) at the bottom of the drop, or it's an unknown cave, I usually take the rope down with me in a bag hanging off my descender by a tether long enough to keep it under my feet (which in a pinch can be tied with the piece of webbing that I'm not using to rig the rope, see below).
Ralph E. Powers wrote:Sometimes there's a nice stout stunted cedar to rig to but other times one has to use webbing wrapped 3-pull 2 around a BFR because there are no trees.
If the only thing you're attaching to your anchor is the pit rope, why not just tie a bowline (properly backed up) or rethreaded figure-eight around the BFR? If the anchor needs not to slide up or down on the rig point, the bowline or figure-eight could be tied on a two-wrap coil (run around the anchor point two full turns instead of one). If the top end of the rope is in use, a "double bowline" (a bowline tied on a bight of rope) could be tied.
Then that piece of webbing and carabiner could either be available for use should the need arise, or left home for convenience.
If there is no single bomber anchor point but multiple anchor points that *should* each individually be strong enough, I rig a load-sharing anchor when it is practical to do so, but know that what looks like 50%/50% might really be 99%/1% when it's being used. For example, off two bolts, I would tie a double figure eight or a double bowline. I'm not talking about any fancy self-slipping thing, but rather:
http://www.chockstone.org/TechTips/BunnyEars.htmYou've got to keep the angle between the anchor points less than 120 degrees at the absolute most, or each anchor point feels more force than you're hanging on the anchor system. *Way* less than 120 degrees is ideal. I've heard that most bolt hangers are designed to be weighted not more than 45 degrees away from the vertical (suggesting 90 degrees as a maximum angle for bolts).
Given two bolts that are vertically far apart, I might use an alpine butterfly and a figure-eight on a bight, or a directional figure-eight and a figure-eight on a bight (or really lacking rope, a long-tail bowline and a Yosemite bowline) to rig an anchor that (probably) doesn't load-share but still maintains minimal extension.
For natural anchors that are *very probably* all individually good enough (e.g. strong-looking rock outcroppings, smaller live trees near the base), I would rig a load-sharing anchor around two or more of them with a separate rope or some webbing. This makes a whole lot of sense when you see a diagram, and absolutely none by verbal description. When I find a good diagram on the web, I'll post a link. But this may be the spiderweb-like anchor type that you've seen used.
Lacking any anchor points that are individually sufficiently strong, potentially I might create my own by setting rock (or ice) protection. I've never actually encountered a caving situation where I've felt comfortable doing that. Failing that, I would probably go find another cave, or a more experienced caver for help--I don't have the knowledge, experience, or hardware to put in bolts, and I don't trust myself to correctly rig a safe dynamic load-distributing anchor.
EDIT (everything after this point added--no sense double-posting):
fuzzy-hair-man wrote:This is a red flag to me that they should have already tried it out in a SRT practice session. In my opinion is all new or unfamiliar gear should have been practiced outside a cave where mistakes are less serious.
Agreed! There is no effective technical solution to somebody else not knowing what they're doing.
I know someone who began to rappel into her first vertical cave with her rack attached to her harness by her gear loop! I can't think of any way the drop could have been rigged to prevent that... (And it is a miracle she survived.)
There is surely no substitute for knowing understanding how your gear works and being well-supervised when you're inexperienced. Still, I am interested in the idea of rigging simple drops with fixed brake lowers (e.g. tied-off racks). Sure, it wouldn't be as strong as a tensionless hitch...but in sport caving, that rarely matters. I've belayed people down ladders with Munter hitches and then tied off the hitches and rappelled on the rope. Does anybody know any reason *not* to rig with a fixed brake lower for single-person loads, besides that it requires more gear (minimally, one HMS carabiner)?