Rebelay etiquette

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Rebelay etiquette

Postby Chads93GT » Feb 13, 2012 3:11 pm

Dug open a new pit to a known cave that was buried. The rim of the pit is full of old implements and wire fencing. We cleaned out the area to rig a rope to a tree then I had to set a bolt for a Rebelay straight down into the pit through breakdown. No bolt would mean dozens of rub points. That led to another offset ledge with jagged fluting all over. Another bolt was required.

Now. What is the rule of thumb for how many bolts per Rebelay? I've seen many drops in tag with only one bolt for a Rebelay. I did that here since I literally only had two hangers. I am currently out. Due to the nature of the pit I have to leave several feet of slack. I am comfortable on one bolt but should another be added for safety? We have a good half a dozen surveys left plus monitoring a bat colony there over the long term so I want it to be safe.

But when is it acceptable to just have 1 bolt? Not so deep well has 1 bolt Rebelay for a 250' drop and plenty of slack is needed there as well. Theoughts?
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Re: Rebelay etiquette

Postby BrianC » Feb 13, 2012 3:52 pm

If you put the bolt in, was it a bomber? If the rock is solid and the bolt went in properly, the weight it can hold is the question. Most bomber bolts can hold many hundreds of times the most weight that the bolt would be under load. What is the sheer strength of the bolt? and what is the Kn rating of the hanger?
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Re: Rebelay etiquette

Postby Scott McCrea » Feb 13, 2012 3:57 pm

There is always a "better" way to rig a pit. It depends on who you ask. Ultimately, you and the users have to decide if you feel safe.

There is also the old rule of thumb, "Rig for rescue." In a rescue, it's a good idea to have a back-up anchor for spots where hauls will be rigged. However, some times (usually) it is faster and safer to bypass the rebelays and just haul the package straight out with some guidance from rope attendants at the rebelays. It would be fun and educational to do a dry-run haul with an empty Ferno or Sked to see how it would work.

If a single bolt is installed properly in good quality rock, MBS would say that many other components of the vertical system would fail before the bolt.

If you placed it, I'd inspect it, but I'd use it.
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Re: Rebelay etiquette

Postby ian mckenzie » Feb 13, 2012 4:19 pm

Theory is, the backup for the rebelay bolt is the anchor above it. Most rebelays I've seen have been a single bolt, natural feature, or really good chock.
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Re: Rebelay etiquette

Postby Chads93GT » Feb 13, 2012 4:56 pm

Rock is solid and bomber. Sheer strength is around 4800lbs. I forget. The hangers are fixe 3/8 30kn??
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Re: Rebelay etiquette

Postby hunter » Feb 13, 2012 6:47 pm

This is a question fraught with different opinions. My personal view is that if I am uncomfortable on one bolt and all other things are equal (conservation, enough equipment, time, etc...) it costs me less than 5$ to add another bolt so I usually do.

Theory is, the backup for the rebelay bolt is the anchor above it.

In this context it is good to ask, if the bolt failed would the next anchor function as a good backup? Is there an edge sharp enough to cut the rope or are you comfortable ascending the pitch once w/o the rebelay? Would someone swing enough to hurt themselves or dislodge loose material that could hurt them? etc...

I would also keep in mind that a generally accepted rule is to always have two anchor points and there isn't really an exception for one being bomber. This could be the upper anchor but if that isn't a good idea for some reason the bolt being bomber isn't really an excuse for only one anchor point.

Anyway, just my .02
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Re: Rebelay etiquette

Postby Chads93GT » Feb 13, 2012 7:00 pm

On the upper Rebelay it needs another bolt to back it up. The lower can be backed up to a massive breakdown boulder with a sling. Provided of course I can get it all the way around and provided I can climb up high enough to do it but a second bolt may be safer. For fear of dislodging a Mankiller.
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Re: Rebelay etiquette

Postby paul » Feb 14, 2012 7:22 am

In the UK the usual rule is start with two bolts at the top of the pitch then if there's enough rope above each rebelay to absorb the shock should the lowere rebelay fail, use one bolt otherwise use two rigged in equal tension.

As already said: the backup for the current rebelay os the one immediately above.

Regarding "bomber" anchors: on popular pitches, we generally use resined-in stainless steel rods bent in half with an "eye" at one end which serves as the attachment point. These are regularly tested with a test rig to pull horizontally out from the rock. There's a cave near me where such an anchor had been regularly used and tested and is still firmly attahced to the rock. Unfortinately, the rock, with the bolt, is now at the borrom of the pitch...
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Re: Rebelay etiquette

Postby chh » Feb 14, 2012 8:12 am

I'm sure you thought of this and made the appropriate decision, but would a redirect work instead of a rebelay?
Your words of caution are no match for my disaster style!
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Re: Rebelay etiquette

Postby Chads93GT » Feb 14, 2012 8:47 am

chh wrote:I'm sure you thought of this and made the appropriate decision, but would a redirect work instead of a rebelay?


If there was something to wrap a sling around for a redirect, s ure, but the walls are sheer fluted walls with no flakes. Its a collapsed dome so there are large boulders above the main drop once you get underground, but getting up to them would be difficult and dangerous to rig up a long permanent sling. Ive just basically always wondered why sometimes in TAG I see 1 bolt rebelays, and other times I see two bolt rebelays. We have another project nearby where I rigged 2 redirects so I am definately familar with that option, its just in this case, it wasnt there. Thanks for the help.
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Re: Rebelay etiquette

Postby chh » Feb 14, 2012 9:16 am

I really meant placing/using single bolts for redirects instead of rebelays, or wondering if your current rebelay bolt would work as a redirect also, though this doesn't usually seem to happen.

Anyway, for me it's the rock quality and type/age of bolt that makes my comfort level. I've hung quite happily on single bolts, but have also been at 2 bolt anchors that gave me a sphincter factor of about 9.5
You know the rock and bolt. Seems to me you're the one most qualified to make the distinction. I think I would probably leave well enough alone unless I heard a complaint, or saw that people were adding bolts. Then all you have to decide is whether or not you care... :grin:
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Re: Rebelay etiquette

Postby caverdoc » Feb 15, 2012 1:35 am

Chad
I sent you a PM about this. "Have Bosch, will travel" to paraphrase an old western.
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Re: Rebelay etiquette

Postby Chads93GT » Feb 15, 2012 10:03 am

Image

This is the rebelay. as you can see it comes over a long ways from the entrance shaft. a redirect would = hellacious rope rubbing on jagged stuff everywhere.
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Re: Rebelay etiquette

Postby ek » Apr 17, 2012 8:50 pm

hunter wrote:I would also keep in mind that a generally accepted rule is to always have two anchor points and there isn't really an exception for one being bomber.

I (and many other cavers, climbers, rescuers, professional rope users, and so forth) disagree. Provided, that is, that our meaning of "bomber" is sufficiently robust.

Suppose you come upon an enormous, well-seated rock that isn't going anywhere. I'm talking something the size of an SUV. (I could go considerably smaller in my example, but this way is the most illustrative.) Suppose you're considering rigging to it in one or the other of two ways:

(1) Tie the rope around the whole thing.

(2) Put two bolts in the front of it, and clip the rope to the bolts.

Unless the rock is sharp at the edges where you'd put the rope around, there's effectively no way that option (2) is safer--in terms of risk of anchor failure--than option (1). If you put bolts in, you could make a mistake judging the quality of the rock you're drilling, you could make a mistake drilling, you could make a mistake putting them in, you could make a mistake and overtighten the nuts attaching the hanger to the bolt...or undertighten them. (Unless you're using one-piece glue-ins...then you couldn't make that specific mistake.) You could make no mistake, but there could be a hidden fracture or weakness you were unable to detect by visual and auditory inspection (though that only very rarely happens). You could put the two bolts too close together (I see this mistake in a very large fraction of horizontally separated bolts placed in walls of northeastern caves). That's a bad thing because (according to Alpine Caving Techniques), when you put a bolt in the rock fractures a little bit around it, rendering it unsuitable for a placement very close to it.

You could make a mistake tying the big knot around the rock...but then, you could make a mistake tying the more complicated double-loop knot (or if you prefer, pair of single-loop knots) to attach the rope to the bolts.

If the bolts were there in the first place, then they could be corroded where you cannot inspect, or they could have been subjected to an extreme situation (like hitting the hangers really hard with a hammer by accident), or the washers could have been manually overtightened by another party after they were placed.

So, in terms of likelihood of anchor failure, I think it's pretty clear that rigging around the whole boulder has a lower chance of failure than rigging to two bolts on the front of the boulder. And yet you will notice that, by the conventional meaning of the term "redundant" as used in discussions of anchors and rigging, rigging to the whole boulder is non-redundant, and rigging to the two bolts is redundant. After all, rigging to the whole boulder gives you one anchor point, and rigging to the two bolts gives you two anchor points. As you can see, even the number of anchor points you have in any particular situation is not always so clear, when you think about it hard enough.

So what should you do? Well, it might be that you should rig to the bolts. If they're already there, it's more convenient. If they're not, but you have a bolting kit and bolting skills but want to save rope, then you might consider putting them in (though you should ask yourself if doing so is consistent with your conservation ethic and the wishes of other parties). It might even be safer to rig to them--they might make the rope run at a better angle, or keep it out of some water. But the likelihood of anchor failure is not a reason to use the bolts in this situation (except in the specific case where part of the boulder's surface is dangerously sharp).

You might say, Eliah, this is a contrived example. But is it, really? How many situations are you in where an event likely to lead to the failure of one anchor would not also likely lead to the failure of another anchor? Most bolts are in the same rock feature, after all. And even if not, if rock turns out to be bad in one place, doesn't that suggest that the natural processes that made it that way might have acted the same way on the wall on the other side of your Y-hang? If you're having a bad day and making mistakes putting one bolt in, aren't you likely to have placed the other bolt on the same day, too? (The same thing goes for a rigger who is just chronically bad at placing bolts--they're the same person for each bolt they place.)

Even if you decide that you really have totally independent, redundant anchors, ask yourself this: How many combinations of any number of anchors are really less likely to fail than a large live tree, rigged around reasonably close to the base? I'd suggest that virtually no anchor is better than this, and that no combination of bolts--except maybe multiple glue-ins placed professionally in previously inspected industrial concrete in the light of day with experienced co-riggers observing followed by frequent formal engineers' inspections--is ever that reliable.

So I agree we should be very, very reluctant to trust a single bolt in a situation where someone could be hurt or killed if it (and no other part of the system) failed. But I think we shouldn't rush to decry nonredundant anchors. Some of the best anchors are nonredundant.
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Re: Rebelay etiquette

Postby chh » Apr 18, 2012 7:29 am

That's an excellent post Eliah, but we're talking about a rebelay, not the primary anchor. I don't think anyone is suggesting we intentionally rig or use a single bolt as our primary anchor. And, as you stated, bolts CAN be better under some circumstances, i.e. when you need to alter the rope line in such a way that using or finding natural anchors is not possible. If a natural anchor is available why not use that? I've backed up 2 bolt climbing achors with natural gear just because it was there and easy to do, so, why not?
So the question is 1 or 2 at a rebelay? Again, I think rock quality plays a part. I also agree with you that when you clip an unknown bolt you are putting a lot of faith in the stranger who placed it and that the number of bolts this individual placed at the station may not be the most crucial part of the equation. Is injury possible if a single rebelay/redirect bolt fails? Absolutely. But it's possible at any time during the trip. I'd say that for the most part you face a greater challange mitigating risks in other aspects of caving.
But I think that perhaps you posted just to get people to think about what they are doing critically which is admirable, and a necessary capability in a rigger.
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