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nooj
Jan 7, 2008, 4:46 AM
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Does it matter if you tie the knot above or below your device? Because I've been reading some of the threads here and some mention tying it below.
Could someone help a poor beginner figure out the pros/cons and why it's done?
[edit] The climber I'm climbing with taught me to use the kleimheist (hence the title) above the descending device and I'm not second guessing him, I just want to learn a little more.
(This post was edited by nooj on Jan 7, 2008, 5:19 AM)
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moose_droppings
Jan 7, 2008, 5:23 AM
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nooj wrote: Does it matter if you tie the knot above or below your device? Because I've been reading some of the threads here and some mention tying it below. Could someone help a poor beginner figure out the pros/cons and why it's done?
The reason for tying it below is because its easy to release it after weighting it. If its above the rap device, you'll need to take your entire weight off of it to release it. I used to keep it above until I was showed how easy it was to release it below. Try it both ways and you'll find what is right for you.
(This post was edited by moose_droppings on Jan 7, 2008, 5:38 AM)
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nooj
Jan 7, 2008, 5:51 AM
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In reply to: The reason for tying it below is because its easy to release it after weighting it. If its above the rap device, you'll need to take your entire weight off of it to release it. I used to keep it above until I was showed how easy it was to release it below. Try it both ways and you'll find what is right for you.
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penoyar
Jan 7, 2008, 6:09 AM
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My understanding of the safety difference would be 1. load on the backup knot vs. 2. getting the backup too intimate with your belay device. If there's any concern of the strength or grabbing power of the back-up, then obviously below the device is better, as it will see significantly less load. But as you may discover when trying it below your device, unless you're pretty careful with lengths, the back-up knot will bump up into the belay device, rendering it useless. You've probably seen other climbers either extend their belay device on a sling or attach a very short back-up knot to their leg loop, both of which are pretty well accepted as OK. IMO, the safest would be below the device, as this tends to give you more options and control. Or walk off...
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pro_alien
Jan 7, 2008, 7:13 AM
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I use a 30 cm sling to get the belay device a little out of the way + backup below the device. Works for me.
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tarsier
Jan 7, 2008, 9:36 AM
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If you have a friction knot attached to your (brake-hand-side) leg loop, you definitely want it to grab the rope below the belay device. Far enough that it doesn't jam, but the belay device still has to be close enough to control. Girth-hitch the (belay device) extending sling to your belay loop as per pro alien's suggestion. While feeding rope to the belay device you have to hold the friction knot open, which can take some practice.
(This post was edited by tarsier on Jan 7, 2008, 10:03 AM)
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clemsonscooby
Jan 7, 2008, 1:52 PM
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It should always be below the device. The prusik or backup is only meant to put your device into the breaking position and not to hold your weight. If the backup is above your device it is holding your weight and that is not what 5mm cord is intended.
As a further note, AMGA teaches only to use the prusik or autoblock below the device when descending. Dyneema has too much slippage and this is why it does not tie good knots.
(This post was edited by clemsonscooby on Jan 7, 2008, 4:10 PM)
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livinonasandbar
Jan 7, 2008, 2:05 PM
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Nooj, find out how to set up an "autoblock" with a 22" or 24" nylon sling (dyneema has too low a melting point, from what I've been led to believe) attached to a locking carabiner clipped to the leg loop of your harness. If you wrap the sling completely around the rope (probably six wraps), there won't be enough slack to risk getting it stuck in your belay device. (And, if concerned, you can simply extend your belay device a bit by doubling another sling through your belay loop and belay- device biner.)
Wrap your hand around the autoblock (a normal position for rappeling) and you'll find you can easily control feeding the ropes through both the autoblock and your belay device by applying downward pressure on the block. If you release the downward pressure, the block will "seize up" on the ropes and stop your descent. To get back underway, just re-apply downward pressure on the block and it will release.
As mentioned previously, the problem with applying a back-up above your belay device is encountered when trying to release it under load. Consider a rappel down an overhanging face when you are hanging in the air. To unload such a back up, you'll have to manage a one-hand pull up on the ropes while you use the other hand to "unseize" the back-up, pull up the slack, and lock off your belay device (to avoid weighting the back-up again before you get underway). A major pain in the ass...
The autoblock is, in my simple mind, the way to go.
(This post was edited by livinonasandbar on Jan 7, 2008, 3:40 PM)
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billl7
Jan 7, 2008, 2:54 PM
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When done correctly including appropriate material and knot (these can differ depending on the option chosen) ...
above device:
* pros - completely backs up the break hand as well as the belay device.
* cons - a pain if, when loaded, the knot gets out of reach; and unloading the friction knot while free hanging is time consumnig ... and risky if you are unfamiliar/unprepared for the procedure;
below the device:
* pros - easy to unload; and backs up the break hand;
* cons - can get stuck in belay device if there is not enough clearance between the two; and the friction knot of choice may not be a sufficient backup to the belay device; in other words, a lighter duty friction knot (e.g., autoblock) could be used below the device since it normally only sees the force required to brake the belay device and does not usually see body weight.
Notes:
* Neither of the above methods eliminates the possibility of completely rapping off the rope ends although the latter is worse in this regard.
* Avoid the habit of completely relying on a friction knot; in the above applications, the friction knot is a backup and is not a primary; if you decide to go hands free then do something like a leg rap so the friction knot is still a backup.
I know that repeats some of what has been said and other parts are more than you asked for. But hopefully it is a fairly complete picture of the issues.
Bill L
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reg
Jan 7, 2008, 3:30 PM
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here's a pic of an extention set-up. i almost always extend and place a prussic below.
always tie stopper knots (as a habit ) even if you see the ends on the ground.
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scotchie
Jan 7, 2008, 4:02 PM
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livinonasandbar wrote: Nooj, find out how to set up an "autoblock" with a 22" or 24" nylon sling (dyneema has too low a melting point, from what I've been led to believe) attached to a locking carabiner clipped to the leg loop of your harness. If you wrap the sling completely around the rope (probably six wraps), there won't be enough slack to risk getting it stuck in your belay device. (And, if concerned, you can simply extend your belay device a bit by doubling another sling through your belay loop and belay- device biner.)
I've found it's possible to use dyneema for friction hitches, but you have to increase the # wraps to compensate for the reduced friction of the sling (*). The diameter of the rope also affects the amount of friction. If there's too much friction, however, it can be very difficult to loosen the hitch in order to continue the rappel. So it's imporant to learn the right number of wraps for your combination of equipment before doing it on an actual climb.
(*) in spite of my experiments with dyneema slings, I still prefer to use 5mm cord for autoblock below the belay device and 6mm cord for a prussik-ascender system.
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livinonasandbar
Jan 7, 2008, 4:13 PM
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Scotchie, you're probably right about the reduced friction of dyneema. I've been cautioned, however, not to use it because of its lower melting point. I'm not sure the sling would burn through during a rappel, but perhaps the build up of heat might affect the slings integrity--in terms of strength--for later use.
We'll have to let the experts weigh in on the matter, I suppose.
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shoo
Jan 7, 2008, 4:58 PM
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clemsonscooby wrote: It should always be below the device. The prusik or backup is only meant to put your device into the breaking position and not to hold your weight and that is not what 5mm cord is intended. As a further note, AMGA teaches only to use the prusik or autoblock below the device when descending. Dyneema has too much slippage and this is why it does not tie good knots.
This is simply not true. A 5mm prussik is more than capable of holding your weight, provided you are using an appropriate cord, rope, and a well dressed prussik. Prussiks are used in almost every self-rescue scenario imaginable to hold body weight and then some.
I agree that using high tech cords (like dyneema) for prusikking may be slightly worse on the basis that they are stiffer and slipperier and thus are less likely to catch the rope. However, this is not the case with nylon, which is a far more common and recommended prussik cord material.
Also, I completely agree with everything in Bill7's post.
(This post was edited by shoo on Jan 7, 2008, 5:01 PM)
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roy_hinkley_jr
Jan 7, 2008, 4:59 PM
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The AMGA is once again giving poor knot advice. The autoblock is the easiest of all the friction knots to screw up and die. It requires a dedicated sling of just the right length or it will not grip sufficiently to stop you -- improvising without prior testing is a dangerous idea. OTOH the klemheist, or better yet, the Hedden works with any sling length. The Prusik is inferior to either of those but still safer than the autoblock.
Unless you are doing gonzo speed rappels, there is no danger using dyneema webbing or sling for a backup. With webbing, a few extra wraps are recommended.
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billl7
Jan 7, 2008, 5:39 PM
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First time I've considered the Hedden. It does look like it could be superior to an autoblock below the device: simple, more compact under load, and probably a better grip. How does it compare in tending/loosening in this application (i.e., below the device)? How about compared to the klemheist?
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roy_hinkley_jr
Jan 7, 2008, 6:38 PM
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The Hedden is just a klemheist upside-down, which gives it better grip. Both are easier to release than a Prusik but YMMV.
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livinonasandbar
Jan 7, 2008, 6:50 PM
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So, Nooj... are you sufficiently confused, yet?
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clemsonscooby
Jan 7, 2008, 8:23 PM
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shoo wrote: This is simply not true. A 5mm prussik is more than capable of holding your weight, provided you are using an appropriate cord, rope, and a well dressed prussik. Prussiks are used in almost every self-rescue scenario imaginable to hold body weight and then some. I agree that using high tech cords (like dyneema) for prusikking may be slightly worse on the basis that they are stiffer and slipperier and thus are less likely to catch the rope. However, this is not the case with nylon, which is a far more common and recommended prussik cord material. Also, I completely agree with everything in Bill7's post.
5mm cord is rated for your weight statically, but is only okay for a hard catch.
I agree with its use for pickoff's and other rescue scenarios.
(This post was edited by clemsonscooby on Jan 7, 2008, 8:30 PM)
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j_ung
Jan 7, 2008, 9:14 PM
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roy_hinkley_jr wrote: The AMGA is once again giving poor knot advice. The autoblock is the easiest of all the friction knots to screw up and die. It requires a dedicated sling of just the right length or it will not grip sufficiently to stop you -- improvising without prior testing is a dangerous idea. OTOH the klemheist, or better yet, the Hedden works with any sling length. The Prusik is inferior to either of those but still safer than the autoblock.
I agree that the klemheist, prussik or Hedden will work just fine, but there's nothing inherently more dangerous about the autoblock. It's a fine addition to any bag of tricks, and in the context herein, it's my preferred option, just as it is for thousands of other climbers. Also, the assertion that you need a dedicated length of sling is incorrect. You can autoblock till the cows come home with any 24" nylon runner.
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scotchie
Jan 7, 2008, 9:58 PM
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The reason the autoblock sling needs to be the right length is to keep it from getting jammed in the belay device. But it's easy to shorten any sling - just tie an overhand. Thus you can improvise with cordelettes or longer slings if necessary.
The reason to use 6-7mm cord above the belay device or 5mm cord below is to provide just the right amount of friction. It isn't because of cord strength.
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shoo
Jan 8, 2008, 12:33 AM
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clemsonscooby wrote: 5mm cord is rated for your weight statically, but is only okay for a hard catch. I agree with its use for pickoff's and other rescue scenarios.
http://www.northwashoutfitters.com/...Prod&productId=9
5mm nylon cord rated at 1250 lbs. This is a whole lot more force than you could conceivably generate as a rappel backup. There is absolutely no reason in terms of strength why you wouldn't use it as a rappel backup above your rappel device.
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philbox
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Jan 9, 2008, 1:16 AM
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Here is a scientific study as to the effectiveness of various friction knots for backing up abseils.
http://www.chockstone.org/...otectingAnAbseil.htm
Note that the autoblock 4 and 5 turns using 6mm nylon always worked on a single 11mm rope. Please review the evidence for other configurations. The evidence does not support the efficacy of the Klemheist to protect a rappel.
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Adk
Jan 9, 2008, 1:53 AM
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I use a prusik knot with the attachment point coming from a biner from one leg of the harness to the rope. When I use a 10.2 rope and use three wraps on a 5 mm cord and when I let go I stop. If I'm flying down on a rap and let go, I stop.
If I have a lot of rope out to rap I have to work the prusik to move due to the weight of the rope. The rope weight almost creates a fireman's belay type situation.
I'm a pretty light guy but no pip-squeak.
Hope this helps.
Nice data at Chockstone.
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philbox
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Jan 9, 2008, 3:27 AM
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5mm will definitely hold better than 6mm. 7mm is crap at holding.
In conjunction with those tests by Dr. Ron Farmer we instituted a series of tests to see how the Autoblock performed in various configurations during a rappel/abseil.
We settled on extending the rappel device away from the belay loop and then connecting the autoblock directly to the belay loop. This effectively gave a common rotational point such that the autoblock can never rotate into the abseiling device.
This is now the preferred method we teach in the circles I frequent. It is definitely THE most effective method on which to base various rescue scenario setups.
Do I use this method all the time? No. It depends (tm).
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oldsalt
Jan 9, 2008, 3:53 AM
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A couple years ago, I participated in one of these discussions and strongly supported the brake below stance, for all of the right reasons expressed above.
I later changed my mind and recommend and practice having the brake above the rap device for one simple reason....
If you somehow rap off the end of your rope, or off a single strand of an unsecured two-strand setup, the end passing through your hand is your first notice of a problem. You basically have no way to stop the rope at that point.
A Prusik, Auto-block, whatever, will still have your strand or strands in its grip.
One of the reasons that rappelling is so dangerous is that the margin of error in such situations is too small to generate a rational response. My way, above the device, still fails if you grip the wrapped rope or sling so that it can't bite the rope.
My way is my preference, but neither side is guaranteed to catch if you make the fundamental error of rapping off the end of your rope. Tie knots in the end, stay vigilant, stay in control, and DON'T BE IN A HURRY.
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