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autoblock on rappel

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autoblock on rappel

Postby aaron479 » Tue Nov 13, 2012 11:18 pm

Having never used this system ... I have a question. Why does this configuration need to be placed below your device? I have re-read Freedom of The Hills, and checked all avail. resources. Seems like it would function fine if attached above too. Answers??? Thank you.

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Re: autoblock on rappel

Postby ajkagy » Tue Nov 13, 2012 11:26 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 11:30 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 11:35 pm, edited 1 time in total.

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Re: autoblock on rappel

Postby GregMiller » Tue Nov 13, 2012 11:33 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 11:34 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 aaron479 » Tue Nov 13, 2012 11:35 pm

thanks for the replies...
I guess I kind of was thinking along the same lines as far as use goes. 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."
again,
thanks

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Re: autoblock on rappel

Postby DaveSwink » Tue Nov 13, 2012 11:41 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 aaron479 » Tue Nov 13, 2012 11:44 pm

10-4 ... probably will not come into play with me, just did not make sense. Thanks again

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Re: autoblock on rappel

Postby Doug Shaw » Wed Nov 14, 2012 12:28 am

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 5:33 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 6:56 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 7:16 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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