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The Climbing Club • View topic - Strongest Rappel Knots

The Climbing Club

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 Post subject: Strongest Rappel Knots
PostPosted: Mon May 03, 2010 1:01 am 
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One Armed Wonder
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http://www.blackdiamondequipment.com/en ... appel-knot

I find it interesting that the author still uses the euro death knot. From other things i've read the ring bend is easy to get out after weighted and strong...

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PostPosted: Mon May 03, 2010 10:30 am 
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Tenacious Lee
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PostPosted: Mon May 10, 2010 2:29 pm 
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As the engineer says, the Euro Death Knot - EDK, is plenty strong when used to join two ropes for rappelling. The reason why I prefer it is that is provides a flat bottom to slide across rock features. The Ring Bend does not slide across rock ridges, rock fins, etc.

The EDK slides most easily when pulling across an acute edge of rock.

Some people use the Figure-8 with tails on the same end. This also provides a flat bottom to slide easily across rock. However, it's taller and therefore seems to flop down on its side which then does not slide easily. I think people who prefer the Figure-8 with tails on the same end to the Overhand with tails on the same end (EDK) feel better about the Figure-8 rather than the Overhand. Tests have shows they fail at similar loads; the failure mode is the same, they knot rolls over itself when overloaded. It successive time the knot (either the Figure-8 or Overhand) rolls over itself, the tails are much shorter. Ultimately, if the knot performs sufficient rolls, the knot will roll off the ends of the ropes.

That's why it's wise to leave long tails on the EDK. Long tails allow the possibility of the knot failing once or twice before the knot rolls off the ends. 10-inch tails are generally considered minimum.


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PostPosted: Mon May 10, 2010 5:40 pm 
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Cap'n Wingspan
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What about the square knot backed up with double fishermans? I read about this in an older copy of Knots for Climbers by Craig Leubben and have been using it since, with great results. The knot is ridiculously easy to tie and cannot become tightened (which makes it great for winter climbing when the rope gets iced up and you've got gloves on). The strength should be the same as the rope itself un-knotted, since it's actually just looped through the other rope, but I admit that I haven't actually seen any numbers. It doesn't have the same flat area for rolling over sharp edges that the EDK has, but I think it's a much lower profile knot, and is less likely to get caught in constrictions, which seems to me the bigger problem.


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PostPosted: Mon May 10, 2010 11:55 pm 
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I have the same book, Knots for Climbers, Craig Luebben, 1995, page 23:
Joining two ropes for rappelling using s symmetrical square knot backed up by a double fisherman's on each side.

This certainly has an advantage over the EDK in that the primary knot joining the two ropes will be easy to untie after loading. Especially if the lines are 9.2mm or thinner!

This has a great disadvantage under the EDK in that it presents 3 different knots to get hung up going over edges, fins and constrictions (cracks). This would be a nightmare in many occasions where the EDK would nimbly and smoothly glide right over.

If you don't believe me and can't visualize it, I suggest practicing pulling various knots over a 90-degree edge and make sure the pulling rope is directly below the edge's lip. In general when pulling the rappel ropes it's best to back away from the face as far as possible, but sometimes you're hanging from a pair of bolts or webbing and you can't change your location; you gotta pull your ropes and you're not able to move. And when you need to pull that joining knot over a lip way way up above your position, the type of knot you use may be the difference between a smooth pull and one of the climbers ascending the rope all the way back up to re-rig the system. Or, maybe the other end of the ropes is out of your grasp when the joining knot gets hung up on an edge.... then you can't climb the pulling rope because while climbing the rope you're risking the knot eventually sliding over the edge and you take the big ride.

The choice of knots used to join ropes for rappelling is a topic of discussion that precedes the EDK by many decades and I'm sure the discussion will never loose steam :)


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PostPosted: Tue May 11, 2010 11:33 am 
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Longshanks
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PostPosted: Tue May 11, 2010 1:22 pm 
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Dr. Crevasse
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PostPosted: Sat Oct 19, 2013 9:15 pm 
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One Armed Wonder
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Hi Friends,
Came across this randomly searching for climbing safety info. Says similar things: EDK is 'ok' Figure 8 is BAAAD. The author does not use
http://user.xmission.com/~tmoyer/testing/EDK.html

Its an old site ('99) that performs tests. Perhaps unsurprisingly, the EDK with wet rope is really REALLY bad idea it seems.

I'll still use an EDK +backup+tail, unless the rope is wet. Then I might use a double fishermans (tied asymmetrically to avoid getting stuck).

Any further thoughts?

Hope all are well with their climbing and always using autoblock technique for rappelling!

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