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Tech Tip: Rapping

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Re: Tech Tip: Rapping

Postby TomPierce » Wed Feb 20, 2013 2:21 pm

So Brian, with your Flemish knot it looks like you just do the first half of a figure 8 knot in one line, then use the other line to retrace the first knot? I don't think I've seen that before (although I haven't really looked to replace the dbl fisherman's). Interesting!

Fuego: I too rarely use a rap backup, really only on sketchy rappels (over loose rock, etc. that might come loose and bop me in the head) or when I know I'll need to use my hands to fix snags in the rappel line (behind a flake, tangled in a tree, etc.), but even then I'll do a copious leg wrap and a prussik brake.
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Re: Tech Tip: Rapping

Postby Brian C » Wed Feb 20, 2013 2:52 pm

TomPierce wrote:So Brian, with your Flemish knot it looks like you just do the first half of a figure 8 knot in one line, then use the other line to retrace the first knot? I don't think I've seen that before (although I haven't really looked to replace the dbl fisherman's). Interesting!


That's it! Really, really easy to visually inspect if it has been tied correctly. Also, it's MUCH easier to untie after rappelling, which is very nice after making multiple rappels in a row.
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Re: Tech Tip: Rapping

Postby Stone_man » Fri Feb 22, 2013 6:09 pm

Brian -- Can the Flemish bend invert itself? You didn't mention backup knots on the tails so I'm assuming this would have a low probability....

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Re: Tech Tip: Rapping

Postby Brian C » Fri Feb 22, 2013 7:49 pm

Stone_man wrote:Brian -- Can the Flemish bend invert itself? You didn't mention backup knots on the tails so I'm assuming this would have a low probability....


I've rappelled on it alot and with various rope diameters and never seen it move even in the slightest. I leave tails but not super long like a double fisherman, just like tying in (but not with a backup as this increases the knots profile dramatically).

EDIT: So I did a bit of digging after a friendly PM about stats and came up with a few things worth sharing on knots used to join ropes. I know this is not what the original article posted was about. Sorry Tom!

1) Here is an article that was done on the stats of knot failures including both breaking and capsizing. EDK Knot Testing
http://user.xmission.com/~tmoyer/testing/EDK.html

2) The article showed the the "flat figure 8" if tied incorrectly and not well dressed can begin to capsize at a very low weight threshold, lower than the EDK.

3) I think it's important to note that the "flat figure 8" is in the same family as a EDK (flat overhand) and is different from the Flemish Bend. The Flemish Bend is similar to the double fisherman as to how the weighted strands pull against each other. See photos below...

Flat Overhand with another as a backup. Should be set a bit better though.
Image

Flat Figure 8 - are these tails too short?
Image

Double Fisherman
Image

Flemish Bend - These tails should be longer!!!
Image

4) It is VERY important to dress your knots correctly as well as set them. Improperly dressed knots are significantly weaker on all of the tests in the article. It always amazes me when I see other climbers tying ropes together or even tying in with very poorly-dressed knots (happens in the gym all the time). Knots are not 2 dimensional, they must be 3 dimensional to be tied correctly.

This is a 2 dimensional knot. It is not properly dressed, and the tail is too short.
Image

Although this one is 3 dimensional, this is also not dressed correctly. The strands on the ends cross each other instead of running parallel.
Image

This is properly dressed and appears to be well-set.
Image
Last edited by Brian C on Sat Feb 23, 2013 8:10 pm, edited 1 time in total.
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Re: Tech Tip: Rapping

Postby TallGrass » Fri Feb 22, 2013 9:43 pm

Remember reading something %s and strengths like this... "When knotted rope is strained to its breaking point, it almost always fails at the knot or close to it ... Relative knot strength, also called knot efficiency, is the breaking strength of a knotted rope in proportion to the breaking strength of the rope without the knot."
http://en.wikipedia.org/wiki/Knot#Strength

and a chart something like this:
Strong Knots
Blood Knot 85–90% (Barnes); 80% (Day)
Flemish Bend 81% (Frank and Smith)
Figure Eight Loop 80% (Frank and Smith)
Double Fisherman’s 79% (Frank and Smith)

Moderately Strong Knots
Butterfly 75% (Frank and Smith)
Bowline 60% (Day)
Overhand Knot 60-65% (Luebben )

A Weak Knot
Overhand Bend (My guess is less than 50%)

Sources: http://www.bethandevans.com/pdf/8_strength.pdf http://allaboutknots.blogspot.com/
Not sure if I'll do more 14ers. The trip reports are too tiring. :wink:

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Re: Tech Tip: Rapping

Postby Dancesatmoonrise » Fri Feb 22, 2013 10:58 pm

So, Brian, of the knots shown, it looks to me like the Flemish and the Fisherman's would each pull through obstacles well, though I'd tip my hat to the Flemish - the more rounded edges presented by the bend look like they would be less likely to hang up, versus the more squarish nature of the double fisherman's. Has that generally been your experience?





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:wft: (I have no idea what this is but it's hilarious...
a method for closing the ends on a braided rope? )

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Re: Tech Tip: Rapping

Postby Brian C » Sat Feb 23, 2013 7:46 am

Dancesatmoonrise wrote:Has that generally been your experience?

Jim, I've never gotten either a EDK or a Flemish Bend stuck while pulling, but I did get a doublefisherman stuck once. Probably just bad luck though.
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Re: Tech Tip: Rapping

Postby tenpins » Sat Feb 23, 2013 9:11 am

flemish bend. EDK. figure eight follow through. all the same _knot_, applied differently. For the non technical folks, the EDK has been used in the technical climbing world for at least 30 years. It's reputation as the least hanging up knot used to join the ends of two ropes is well established by millions of uses. Which also speaks to its safety.

If I can suggest to those using the double fishermans, try a double sheet bend. Its a bowline used to join the ends of two ropes. Load it all you want, still unties with the ease of a normal bowline. Add backups if you like. It's really not any more bulky than a double fisherman. Bulky, or not bulky. They are both bulky.

If you want to play in the roped/technical climbing world - which rappelling is - you need to know more than one knot. Nobody should be 'surprised' by an unfamiliar knot. The climbing world has settled on relatively small group of knots. You should really know them all. I started climbing 22 years ago and havent found a silver bullet knot, technique, style or piece of hardware yet. I keep them all in my bag of tricks. Something that is often lost in threads like this where the 'best' is bandied about. Tom Moyer has been publishing testing results and data for a long time. Very cool, very educated and practical person Ive had the pleasure of meeting once or twice.

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Re: Tech Tip: Rapping

Postby Brian C » Sun Feb 24, 2013 7:17 pm

One last post on this, I promise!

I got thinking more about friction hitches and rappel backups, and ended up writing a short article on summitpost about different hitches used in climbing. I think it is related enough to the original content of this thread to post.

Climbing Hitches
http://www.summitpost.org/climbing-hitches/840016
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"Nature never did betray the heart that loved her." - Wordsworth

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