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autoblock on rappel

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Re: autoblock on rappel

Postby ajkagy » Tue Nov 13, 2012 10:26 pm

never used an autoblock, but i've used a prusik. Works the same way, but the auto "block" i figured just means that it's going to block the rappel device from going any lower on the rope if the tension on the autoblock knot doesn't grab the rope first.

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Re: autoblock on rappel

Postby DaveSwink » Tue Nov 13, 2012 10:30 pm

The autoblock friction hitch takes the place of your brake hand, in the event your hand releases, so it is positioned right where your brake hand rides, several inches below the belay device. Conveniently, your brake hand can hold the autoblock in "released" position while performing its braking duties too.

If an autoblock was configured above your belay device, that would require holding at least one hand above the device while rappeling, to keep the hitch released. That would be possible, but awkward. If it did grab while rappeling, it seems like getting it to release again while your weight was on it could be challenging too. :shock:
Last edited by DaveSwink on Tue Nov 13, 2012 10:35 pm, edited 1 time in total.

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Re: autoblock on rappel

Postby GregMiller » Tue Nov 13, 2012 10:33 pm

I'd figure it's because if you set the length on the autoblock too long, and it slips out of your hand, it'd be no fun to try to climb back up the rope to retrieve it.
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Re: autoblock on rappel

Postby DaveSwink » Tue Nov 13, 2012 10:34 pm

ajkagy wrote:never used an autoblock, but i've used a prusik. Works the same way, but the auto "block" i figured just means that it's going to block the rappel device from going any lower on the rope if the tension on the autoblock knot doesn't grab the rope first.


No, an autoblock is just another friction hitch like the prusik. It releases easier though. If the rappel device hits the autoblock, it will keep the autoblock from engaging, and down you go. :oops: That is why the rappel device is extended off of the harness, to create a bit more distance between the rappel device and the harness leg loop that the autoblock is attached to. I use a couple of half-length slings to extend my rappel device.

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Re: autoblock on rappel

Postby DaveSwink » Tue Nov 13, 2012 10:41 pm

aaron479 wrote:Just seems like the extension from the belay loop (for room) and the limited room (between the leg loop and the rappel device) could pose problems too. Just seems, from a function point of view, that above may be "cleaner."


That is a good observation, and above an auto-locking ATC belay device is where you put a prusik hitch if climbing the rope, with the ATC taking the place of the second climbing prusik. But the best way to picture the function of the autoblock when rappeling is that it is waiting to take the place of your brake hand, below the rappel device.

Added: Extending your rappel device will seem a bit awkward the first time you do it, but it becomes comfortable quickly. It is very helpful if you have to attach someone else to your rappel in a rescue.

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Re: autoblock on rappel

Postby Doug Shaw » Tue Nov 13, 2012 11:28 pm

dswink wrote:If an autoblock was configured above your belay device, that would require holding at least one hand above the device while rappeling, to keep the hitch released. That would be possible, but awkward. If it did grab while rappeling, it seems like getting it to release again while your weight was on it could be challenging too. :shock:


While a below-the-device friction hitch is a little easier and safer to work with, releasing a locked-up above-the-device friction hitch is not that hard:

Raise one foot and wrap the rope around one foot 3-4 times.
Stand up on that foot, which raises your body and unloads the friction hitch.
Loosen the friction hitch by sliding your hand down from above it.
You are still standing on your foot - transfer your weight back to the rappel device (making sure to have a hand on the brake strand!)
Shake foot a few times to free your foot.
Continue rappel.

One of the big advantages of a below-the-device friction hitch versus one above the device is that with an above-the-device backup you must slide your free hand down above the knot as you descend, or else the hitch will load and lock up. More importantly, in a crisis you must have the presence of mind to do exactly the opposite of what instinct tells you to do: let go of the rope!. Instinct will have you death-gripping the rope to try to stop your fall, and that gripping free hand will slide the hitch and keep it from locking up and you'll take it all the way to the ground with you.

With a below-the-device hitch, your brake hand will automatically slide down the rope above the hitch, which is generally rigged off of a leg loop. If you let go with your brake hand (which will generally be one of the more common loss-of-control scenarios), the autoblock should automatically begin to lock up by virtue of your brake hand not continuing to slide it down the rope. This resolves a lot of the instinctual problem as if you've got a grip on that brake strand you're probably not really out of control. As has been mentioned, though, if the autoblock is long enough to extend up to reach the descender itself it can cause it to not be able to reach maximum extension and fail to lock.

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Re: autoblock on rappel

Postby d_baker » Wed Nov 14, 2012 4:33 am

Make sure you test your autoblock before going on rappel, as part of your double-check for safety.
The Baron had some things to say about autoblocks and extending them a few years ago when I asked the question.

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Re: autoblock on rappel

Postby TomPierce » Wed Nov 14, 2012 5:56 am

IMO the below-device autoblock is a relatively recent technique, maybe the last 10-15 years? I don't recall seeing it mentioned much prior to that, but maybe I missed that. Personally I'm old school and use the above-device method. As Doug mentions getting it unstuck is pretty simple, and setting it to extend the correct distance from the harness is extremely easy (like...if the attaching sling/cord is longer than your arm, not good, duh...). Not that there's only one way to do it; like almost everything in technical climbing, we could articulate pros/cons to both systems. I almost always rappel first and I occasionally need to stop mid-rappel to get the ropes unstuck and if I use an autoblock (I rarely do, I usually just use a leg wrap, but it depends on the terrain and conditions) I like seeing the knot directly in front of me. Just me.

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Re: autoblock on rappel

Postby Brian C » Wed Nov 14, 2012 6:16 am

TomPierce wrote:...I almost always rappel first and I occasionally need to stop mid-rappel to get the ropes unstuck and if I use an autoblock (I rarely do, I usually just use a leg wrap, but it depends on the terrain and conditions)...


I'm like Tom. It's nice on certain types of rappels to have a third-hand especially when rapping first. That said I don't use it all the time, really depends on the scenario. But, I always use it below my ATC and use a prussik knot. My 'rescue' loops are short and just enough length to use for this purpose. I find that the prussik feeds smoother more of the time (I know the opposite of what the books say) and is always the right length. This is a pretty crucial skill to know how to do effectively, especially if involved in a rescue scenario.
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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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