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autoblock on rappel

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Re: autoblock on rappel

Postby climbing_rob » Wed Nov 14, 2012 9:43 am

Good discussion. couple of points: I find that the autoblock (the below version) does jam up the rope in the belay device, at least the ones I've tested, so this would stop a fall if you released your brake hand. I think it depends on the number of wraps and length of prussik used for the autoblock and of course your belay device type.

One of the main purposes of either backup, as I see it, is to have a separate, independent attachment to the rope. People fall and die on rappels because they forget to finish their rappel tie-in properly (even experts, like Lynn Hill, who thankfully survived her 75' fall). If you include an autoblock in your setup (or a trailing prussik), that's another connection (your leg-loop to the climbing rope), and if you screw up your primary tie-in, you'll be embarrassed when you start your rap and you flip sideways, but you won't fall and die.

On canyoneering trips, you might have a half dozen raps per canyon, multiplied by 8 canyons in the weekend, that's a lot of rappels and I have found myself getting lax over double/triple checking my setup and using an autoblock. This is a recipe for disaster. I wish I used a backup on every rap. I keep telling myself to do so, but no one else I do canyons with does this and I bow to peer pressure. Bad.

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Re: autoblock on rappel

Postby DaveSwink » Wed Nov 14, 2012 9:59 am

climbing_rob wrote:I find that the autoblock (the below version) does jam up the rope in the belay device, at least the ones I've tested, so this would stop a fall if you released your brake hand. I think it depends on the number of wraps and length of prussik used for the autoblock and of course your belay device type.


Rob, if I am understanding you correctly, the autoblock setup is not correct and could fail. If you let go with your brake hand(s) while rappelling with an autoblock, the autoblock should fully engage and pull down on the rope below the rappel device to stop you (just as your brake hand would do). If the autoblock is allowed to touch the rappel device, it may not fully engage and stop you. So, if you are experiencing the autoblock jamming up the rappel device, you may also be very close to experiencing failure of the backup altogether.

Are you extending the rappel device away from your body a foot or two with slings? Is the autoblock attached to your leg sling? Both of those steps are usually required to get the necessary distance between the autoblock hitch and your rappel device. Sorry if I am misunderstanding your post. Visualizing this stuff from text is not always easy. :oops:

I completely understand about peer pressure to not use a backup. I work to have my autoblock gear always ready (rides on the rear loop of my harness) and be able to set it up quickly (about a minute) to avoid the disdainful looks. :lol:

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Re: autoblock on rappel

Postby ebnhils » Wed Nov 14, 2012 10:19 am

My concern with an autoblock above the belay device is once it is activated now all your weight is on the 6mil cord (or whatever you are using for the autoblock) which is much weaker than your climbing rope. With the autoblock below the belay device you weight will always be on your rope. Could be important in an emergency which is most likey the case if the autoblock is activated. The autoblock should never contact the belay bevice.

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Re: autoblock on rappel

Postby Brian C » Wed Nov 14, 2012 10:27 am

ebnhils wrote:... now all your weight is on the 6mil cord (or whatever you are using for the autoblock) which is much weaker than your climbing rope...


Still a 6mm cord has a breaking strength of close to 8KN. You can drink alot of beer before your body weight will break that. The only problem of having it above is if you don't know how to unweight it. Not a problem if you're used to it and have practiced it. I have seen people battle with a loaded prussik above their belay device for a LONG time on more than one occasion.
Brian in the Wild
Lists of John
"Nature never did betray the heart that loved her." - Wordsworth

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Re: autoblock on rappel

Postby pvnisher » Thu Nov 15, 2012 4:12 pm

I think that the "above-the-device" crowd has a fair argument on it being slightly easier to set up. And since ease of setup and speed could be factors in deciding to use a backup, that might make it safer. Like how if your helmet is heavy and uncomfortable, you won't wear it, even if it offers great protection, and is thus less safe than a light, comfortable one that you actually wear.
It's also easier to take an unknown setup (a different harness, borrowing someone else's cord, etc) and make it work.

But the main advantage of the "below-the-device" argument is, for me, that if you let go of your brake then it uses the device itself to add friction and stop you, vice simply using the knot's own friction properties. That, and the "I'm falling, I'll grab the rope" instinct which would negate the benefit in the "above-device" setup, but would strengthen your brake grip in the "below device" setup means that I vote in favor of using it below the device.

I'm also definitely in favor of extending the device in all raps.

That said, I generally don't do a backup when I'm not first on the rope. But I know I should. ](*,)

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Re: autoblock on rappel

Postby crossfitter » Thu Nov 15, 2012 4:30 pm

- A mountain is not a checkbox to be ticked
- Alpinism and mountaineering are not restricted to 14,000 foot mountains
- Judgment and experience are the two most important pieces of gear you own
- Being honest to yourself and others about your abilities is a characteristic of experienced climbers
- Courage cannot be bought at REI or carried with you in your rucksack


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Re: autoblock on rappel

Postby Dancesatmoonrise » Thu Nov 15, 2012 4:39 pm

Brian C wrote: You can drink alot of beer before your body weight will break that.



:-D

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