Self-locking descender for rappelling

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Re: Self-locking descender for rappelling

Postby NZcaver » Jul 8, 2008 4:08 am

Scott McCrea wrote:
NZcaver wrote:
Scott McCrea wrote:A properly configured and used rack will stop or slow down when you let go.

Or, more likely, cause you to plummet just like most other non-autostop descenders. Have you tried letting go completely while descending on a rack? (Why would you?) And (like Hank was saying) a nice clean flexible 10mm rope is likely to perform differently, as a micro or other U rack might versus a J rack.

Yep, I tried it. It works on any variable friction device. Racks are configurable on the fly so it can be adapted to preform differently.

Scott, some day I'd like you to show me how to configure one of my micro racks to stop me when I let go of the rope completely (with both hands, feet, and other appendages) while rappelling with no additional rappel safety. It seems to me the amount of friction to make this possible would mean I would need to painstakingly "feed the micro rack" just to rappel somewhat normally. And we know that's a no-no.

To keep this on-topic, basically I'm a little skeptical when I hear racks being promoted as self-locking descenders (the title of this topic). There are many reasons to prefer a rack design over other descender choices, but without an external hitch or shunt I don't see a "let-go-safely" feature as being one of them. Of course I could be wrong.
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Re: Self-locking descender for rappelling

Postby Scott McCrea » Jul 8, 2008 9:43 am

NZcaver wrote:Scott, some day I'd like you to show me how to configure one of my micro racks to stop me when I let go of the rope completely (with both hands, feet, and other appendages) while rappelling with no additional rappel safety. It seems to me the amount of friction to make this possible would mean I would need to painstakingly "feed the micro rack" just to rappel somewhat normally. And we know that's a no-no.

To keep this on-topic, basically I'm a little skeptical when I hear racks being promoted as self-locking descenders (the title of this topic). There are many reasons to prefer a rack design over other descender choices, but without an external hitch or shunt I don't see a "let-go-safely" feature as being one of them. Of course I could be wrong.

U-shaped racks (including micro-racks) are not true variable friction devices. They do have some variation through spreading the bars, but you can't really add or remove bars. A U-rack is somewhat variable, a J-shaped rack is almost infinitely variable (total amount of friction is limited by the number of bars available).

To get a standard J-shaped rack to stop you, you need to be actively and physically holding the bars apart—spreading them while rappelling. If you let go while doing this, the bars will naturally un-spread and increase the friction. If you are careful to always be holding the bars spread, it works. Sometimes, we get lazy and find it easier to vary the friction with the rope on their hip. Then, letting go will not be a good thing. In my experience and observation, very few people use J racks optimally.
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Re: Self-locking descender for rappelling

Postby hunter » Jul 8, 2008 10:04 am

:rofl:
Some how I find this ironic. To stop you have to ... drum roll ... let go! The primary objection of all the rabid rack using anti-Stop folks is that the auto-lock feature doesn't work if you instinctively grab. Perhaps Scott the reason that so few people use the J-rack optimally is because it teaches bad habits :tonguecheek: . I'd hate to see a bunch of newbie rack users cratering because they panicked and grabbed the rack, preventing it from locking.

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(and before I get slammed that was a mostly sarcastic post)
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Re: Self-locking descender for rappelling

Postby ek » Jul 8, 2008 11:46 am

I think that objection to the idea that racks can be configured for autostop has to wait in line.

During a rappel, more friction is progressively needed. The caver adds bars to the rack to maintain control (a complex, non-automatic action that quite a few beginners actually have trouble with). If you slow down by letting go, and then you slide down (albeit slowly) far enough, then suddenly you are in a place where you would want more bars on even if you were gripping the brake end of the rope.

Suppose you are about to add a bar and that's when you let go completely? :yikes:

Furthermore, if the rope-rack interface changes--say, by a change in dirtiness or wetness of the rope--then the "guaranteed" nature autostop function goes out the window as well.

The advantage of descenders with built-in brake handles is that when they are configured to autostop--a configuration that is default and that is obvious and clear to the user and which does not unconfigure itself mid-rappel--and you do let go completely, they do stop, or at least slow down in such a way that you will always be sliding slowly (not just far enough to when you'd want to add another bar before plummeting you at breakneck speed to your death).
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Re: Self-locking descender for rappelling

Postby Scott McCrea » Jul 8, 2008 3:29 pm

The let-go-and-stop feature only works when the bars are being actively, forcibly, physically held apart. If you're pushing them together while rappelling and let go, you die. Of course, the let-go-and-stop feature should only be used when you unintentionally let go. Normally, to stop, you push the bars together.

The goal is to adjust your friction throughout the rappel so that the bars need spreading in order to move down the rope. Since a J-shaped rack is very adjustable, this is possible.

To add a bar during a rappel, a caver should stop by pushing the bars together. Then add the bar.

All I'm saying is, don't discount the standard J-shaped rack as not being a safe device. IMO, the safest.
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Re: Self-locking descender for rappelling

Postby OpenTrackRacer » Jul 8, 2008 5:16 pm

It's kind of nasty inside... rat droppings, bats, lots of dust. Besides... sleeping in a dusty mine in a sleeping bag on a pad versus sleeping on a nice soft bed in an air conditioned trailer with a bathroom and shower is a pretty easy equation to solve for me!

ek wrote:Perhaps you could camp in the mines...


I don't think you can compare a rack to a auto-stop descender in terms of safety if something goes wrong and you lose the rope in your brake hand.
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Re: Self-locking descender for rappelling

Postby Scott McCrea » Jul 8, 2008 5:37 pm

OpenTrackRacer wrote:I don't think you can compare a rack to a auto-stop descender in terms of safety if something goes wrong and you lose the rope in your brake hand.

Sorry to keep stirring the pot, but I just want things to be clear.

A properly used rack does not require the rope to be in a "brake hand." It only requires that the bottom one or two bars are managed properly. The "brake hand" can be used as an emergency brake, but it is not necessary for normal, safe operation.

BTW, "Brake hand" is not the best term for J-rack use. "Off hand" is more appropriate. "Brake hand" is a perfect term for fig 8s, ATCs, bobbins, etc.
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Re: Self-locking descender for rappelling

Postby Amazingracer » Jul 8, 2008 6:59 pm

Found this thread kinda late.

But as a Stop user it seems to be the way to go. Another recommendation is a steel braking carabiner for the Stop. It not absolutely required, and just a personal opinion. With that I can control the friction of the device a little better. I have used the Stop on many occasions including muddy swollen dome ropes to a 402' rappel.

Like everyone else said you just have to watch what you are doing. The device is not deadly or flawed, just people using it wrong.

And as the others have said it will not auto-stop every single time. It will slow you down nearly every time you let go but not a guarantee auto-stop every time.

I know every one else has already said all of this, just representing for the Stop, as I have found that many people are anti-Stop.
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Re: Self-locking descender for rappelling

Postby NZcaver » Jul 8, 2008 10:56 pm

Scott McCrea wrote:A properly used rack does not require the rope to be in a "brake hand." It only requires that the bottom one or two bars are managed properly. The "brake hand" can be used as an emergency brake, but it is not necessary for normal, safe operation.

:shock: In a personal sense, I think we'll just have to agree to disagree on this. Regardless of the descender, I'm simply not comfortable with removing my lower control/brake hand (or whatever you prefer to call it) from the rope using virtually any type of descender - unless it's locked off, held by a hitch or shunt, or I'm in an otherwise secure position on or off the rope. Any other regular users of J-racks out there care to comment about "proper use" with the rope hand removed?

Mike - sorry if it seems like some of us keep hijacking your discussion! This happens here sometimes. :wink: Please let us know how you do with your Stop and/or any other gear you end up using in those mines.
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Re: Self-locking descender for rappelling

Postby hank moon » Jul 9, 2008 11:59 am

NZcaver wrote:Any other regular users of J-racks out there care to comment about "proper use" with the rope hand removed?


The "brake hand" reflex should be learned and mastered by any vertical caver, regardless of device used. While it is true that with a properly set-up J-rack (and compatible rope) the brake hand is seldom used for braking, it should always be there as a backup. A friend was once edging over a pit lip when his footing (a chunk of lip) broke away underneath him, sending him swinging down and into the wall whereupon a bar or two popped off his J-rack. Brake hand (and leg) saved the day.

Sometimes the brake hand is used when the other is pushing off a wall, lip, etc. or when the passage is too tight to maintain a hold on the bars. I think it would be confusing to use different terminology for J-racks (i.e. "off hand") when "brake hand" is still very relevant to J-rack use and to vertical work in general.

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Re: Self-locking descender for rappelling

Postby OpenTrackRacer » Jul 10, 2008 1:56 am

Well surprise surprise... I took my daughter, niece and nephew to the local climbing gym today. I got to talking with one of the guys and he said it would be fine if we brought our rope and rappelled off a fixed anchor they have on one wall above a ledge. So, once we have the new gear we'll be able to test it out in a very controlled environment on belay.

Most excellent!
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Re: Self-locking descender for rappelling

Postby ek » Jul 10, 2008 2:00 am

Perhaps that would also be a good time to practice whatever emergency ascending techniques you have prepared in case those wooden ladders break.
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Re: Self-locking descender for rappelling

Postby OpenTrackRacer » Jul 10, 2008 2:13 am

We will indeed. We're all getting frog ascending systems. That's more for open shafts but we will be using the Croll as a safety backup on the ladders. They're not continuous so even if one section breaks it doesn't effect the rest.

ek wrote:Perhaps that would also be a good time to practice whatever emergency ascending techniques you have prepared in case those wooden ladders break.
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Re: Self-locking descender for rappelling

Postby ek » Jul 10, 2008 2:20 am

If their condition is generally good and the maximum length you'd need to climb due to a single failure is small then you might want to use a single-ascender technique for that, and leave most of the components of your frog system behind when accessing those particular shafts.

Also, if you use your upper ascender (or any ascender styled like a Petzl Ascension or Petzl Basic), clipped around the rope and with a carabiner clipped through the top holes, and around the rope, and to your harness, then you can eliminate the chest harness from your self-belay system. The carabiner also serves to decrease the likelihood that the safety catch--which it mostly occludes--will be operated by the environment and the user disconnected from the rope. And if you attach the ascender to the end of a lanyard (best tied of dynamic rope--I use a cowstail for this) and run the lanyard over your shoulder then the ascender is kept high enough up that there is no significant shockload in a fall, but still above you enough that it is easy to thread a descender below it (if the ladder breaks). This technique is recommended in Alpine Caving Techniques.
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Re: Self-locking descender for rappelling

Postby Chads93GT » Jul 11, 2008 11:51 am

With all this talk about autostops and racks letting you fall out of control if you let go of the rope...........do none of you use a Prusik or autoblock backup when rapelling, no matter what device you use???
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