Author Topic: Prusik Loop Knots  (Read 7640 times)

xarax

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Re: Prusik Loop Knots
« Reply #15 on: October 04, 2011, 10:19:29 AM »
   @knot4u

   My question was not about the knots discussed in this thread, or bowlines. It was a general question, about the evaluation of strength in knotting, using an abstract, hypothetical situation to facilitate the discussion. It was not about strength consideration being the most important or not, security of specific knots, etc.. It was a general question, about the evaluation of strength in knotting. With modern materials and everyday life s applications, strength is never an issue any more. So, should it be considered as a factor when we choose knots,  or not ?
   I asked this question in the most general way I could, and you have answered - to something else - in the most specific way you could... :)
This is not a knot.

Dan_Lehman

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Re: Prusik Loop Knots
« Reply #16 on: October 04, 2011, 07:02:47 PM »
The article is an interesting to read.  Unfortunately, the article uses sloppy language.  For example, on page 5, the article says:

Quote
However, up until the present time no research has been carried out to determine the actual
strength of friction hitches when used in the doubled rope system adopted by arborists. There
are specific concerns about the strength of friction hitches following wear associated with
descents. Of particular interest is the amount of wear and subsequent loss of strength that a
friction hitch can receive in fast descents or extended use.

Right there, the use of the word "strength" is sloppy.  I believe they should have said "point of failure", instead of "strength".

I find the statement perfectly sensible : to what degree does
the usage of the knot reduce its strength --no ambiguity in this.

Quote
if we include these other knots in our comparison, then we can do a lot better with strength than the [Strangle noose] or the Alpine Butterfly.

On what do you base this assertion?
(From some tests of the former, there really isn't "a lot"
left to do!)


--dl*
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knot4u

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Re: Prusik Loop Knots
« Reply #17 on: October 04, 2011, 07:16:07 PM »
The article is an interesting to read.  Unfortunately, the article uses sloppy language.  For example, on page 5, the article says:

Quote
However, up until the present time no research has been carried out to determine the actual
strength of friction hitches when used in the doubled rope system adopted by arborists. There
are specific concerns about the strength of friction hitches following wear associated with
descents. Of particular interest is the amount of wear and subsequent loss of strength that a
friction hitch can receive in fast descents or extended use.

Right there, the use of the word "strength" is sloppy.  I believe they should have said "point of failure", instead of "strength".

I find the statement perfectly sensible : to what degree does
the usage of the knot reduce its strength --no ambiguity in this.

It's sloppy language because the test results in the article are related mostly to security, not strength.
 
Quote
if we include these other knots in our comparison, then we can do a lot better with strength than the [Strangle noose] or the Alpine Butterfly.

On what do you base this assertion?
(From some tests of the former, there really isn't "a lot"
left to do!)

My educated guess is that there are fishing knots that can be tied in rope that are stronger than the Strangle Noose and the Butterfly Loop.  To be clear, by "strength", I mean the propensity to resist rope breakage.  I have no hard data, but who does?  If I had to put my money on strongest hitch, I'd put my money one of the fishing knots if they're up for consideration.  The Berkley Braid versus the Strangle Noose, that's not even fair.  Do we even have to run a test for which is stronger?
« Last Edit: October 04, 2011, 07:37:47 PM by knot4u »

Dan_Lehman

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Re: Prusik Loop Knots
« Reply #18 on: October 04, 2011, 08:59:52 PM »
In other sources, you can find some contrary results:
what do you know, then?

Dan, I have no personal experience with testing these loops.  I guess I was just accepting statements like:
The Alpine Butterfly is generally considered to be one of the strongest and most secure loop knots.
which is found on
http://www.layhands.com/Knots/Knots_SingleLoops.htm
I think that I have seen similar statements elsewhere. 
Live and learn.

Mike, even so, you should consider this :
1) the butterfly eyeknot is asymmetric,
so a different structure obtains in loading its 1st end
than loading its other end;
2) there are at least three ways of dressing/orienting
the eye legs of the knot --crossed one way, crossed the
opposite way, and uncrossed (probably the most often
pictured).
.:.  That amounts to SIX distinct cordage constructs that
might be seen by the test device, without consideration
of the differences between materials tested (softish,
compressible line vs. firm round line (think, caving cordage),
vs. ... .

Has any test report ever disclosed the first aspects?
(The cordage usually IS described.)

So, my point is to try to awaken people to be critical of
information rather than so accepting of it ; we need to
gain better information vs. propagating the easy nothing.

--dl*
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knot4u

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Re: Prusik Loop Knots
« Reply #19 on: October 04, 2011, 09:15:21 PM »
Here's another example of sloppy language on page 12:
Quote
In these latter cases, a test bed with two metres of
pull would probably have resulted in a failure, as the heat generated by slippage causes fusing
and reduced strength in the friction hitches.

Based on the context of this sentence within the rest of the page, I'm fairly certain the author meant to say "security" instead of "strength".  The author is talking about the knot slipping (security failure).  When someone says "strength" while talking about knots, it means something different than "security".  For my purposes, the difference is important.  I shouldn't have to analyze the context of the terms to discover what the author really means.
« Last Edit: October 04, 2011, 09:26:45 PM by knot4u »

Dan_Lehman

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Re: Prusik Loop Knots
« Reply #20 on: October 04, 2011, 09:26:25 PM »
My educated guess is that there are fishing knots that can be tied in rope that are stronger than the Strangle Noose and the Butterfly Loop.  To be clear, by "strength", I mean the propensity to resist rope breakage.  I have no hard data, but who does?  If I had to put my money on strongest hitch, I'd put my money one of the fishing knots if they're up for consideration.  The Berkley Braid versus the Strangle Noose, that's not even fair.  Do we even have to run a test for which is stronger?

"Educated" --how so?
The highlighted rhetoric suggests otherwise.
(Of all the knots to choose, BB is one rather like
the supposed inferior noose.  And, with nooses, one must
consider the hitched object, too --relative diameter, i.e..)

--dl*
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knot4u

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Re: Prusik Loop Knots
« Reply #21 on: October 04, 2011, 09:31:50 PM »
My educated guess is that there are fishing knots that can be tied in rope that are stronger than the Strangle Noose and the Butterfly Loop.  To be clear, by "strength", I mean the propensity to resist rope breakage.  I have no hard data, but who does?  If I had to put my money on strongest hitch, I'd put my money one of the fishing knots if they're up for consideration.  The Berkley Braid versus the Strangle Noose, that's not even fair.  Do we even have to run a test for which is stronger?

"Educated" --how so?

...by analyzing test results from Knot Wars and drawing reasonable conclusions.  I hate to burst your bubble, but this is not quantum mechanics.  How are you educated on the issue of strength for these knots?

knot4u

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Re: Prusik Loop Knots
« Reply #22 on: October 04, 2011, 09:39:18 PM »
(Of all the knots to choose, BB is one rather like
the supposed inferior noose.  And, with nooses, one must
consider the hitched object, too --relative diameter, i.e..)

For this thread and the posted  article, the hitched object is a carabiner or other climbing anchor with a similar diameter.  Also, I find it odd you say the Berkley Braid is similar to the Strangle Noose.  I find these knots to be obviously different in multiple ways.
« Last Edit: October 05, 2011, 12:49:17 AM by knot4u »

SS369

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Re: Prusik Loop Knots
« Reply #23 on: October 05, 2011, 03:57:37 AM »
Another grip and slide method to consider that will work is using the Prohaska hitch, aka Blake's hitch.

I have not personally tried this knot in rock climbing, but it worked during the recreational tree climbs that I have done. It was used to facilitate ascending up the rope using the end of the rope I climbed.
It has the advantage, should you not have prusik cord, of being a grip and slide hitch that works with the same diameter as the parent rope.

SS

alpineer

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Re: Prusik Loop Knots
« Reply #24 on: October 05, 2011, 04:20:26 AM »
1) the butterfly eyeknot is asymmetric,
so a different structure obtains in loading its 1st end
than loading its other end;
2) there are at least three ways of dressing/orienting
the eye legs of the knot --crossed one way, crossed the
opposite way, and uncrossed (probably the most often
pictured).
.:.  That amounts to SIX distinct cordage constructs that
might be seen by the test device, without consideration
of the differences between materials tested (softish,
compressible line vs. firm round line (think, caving cordage),
vs. ... .

Has any test report ever disclosed the first aspects?
(The cordage usually IS described.)

So, my point is to try to awaken people to be critical of
information rather than so accepting of it ; we need to
gain better information vs. propagating the easy nothing.

All good points. Lots of work to be had, in order to get it right.

alpineer

Semperviren

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Re: Prusik Loop Knots
« Reply #25 on: October 05, 2011, 11:18:07 PM »
It has the advantage, should you not have prusik cord, of being a grip and slide hitch that works with the same diameter as the parent rope.

It depends on the type of rope you use. I've used the blakes hitch with 11.2 mm dynamic line, and it had a tendency to slip. I've heard 9mm PMI ezbend is great for blakes, but i've never tried it myself.

SS369

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Re: Prusik Loop Knots
« Reply #26 on: October 05, 2011, 11:43:33 PM »
Hi Semperviren and welcome.

Yes I am sure it can depend on the rope used. I suspect that some static ropes are just too hard and stiff for the Blake's hitch. Then the rope or cord used can influence all knotting and the decisions to make concerning the task at hand.

Can you tell me the brand of dynamic 11.2mm rope you tried this with?

I suspect that this hitch, the Prohaska/Blake's will work with more ropes than not. Tree surgeons and recreational tree climbers use many brands of rope and this method of ascending is widely employed.

The Blake's?Prohaska grip and slide hitch is not what the OP asked about, but I threw it in to expand his database.  ;-)

SS

Dan_Lehman

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Re: Prusik Loop Knots
« Reply #27 on: October 07, 2011, 07:43:15 AM »
It has the advantage, should you not have prusik cord, of being a grip and slide hitch that works with the same diameter as the parent rope.

It depends on the type of rope you use. I've used the blake's hitch with 11.2 mm dynamic line, and it had a tendency to slip. I've heard 9mm PMI ezbend is great for blakes, but i've never tried it myself.

One shouldn't consider the knot to be set in stone
re its structure --i.e., one can vary the number of
wraps in it.  Heinz Prohaska, (one of) its inventor(s),
 gives the following advice:

If the knot slips because the rope is too stiff,
make an extra turn on the half with the tail tucked;
if it slips because the line is too slippery, make an extra
tuck at the other end (which wraps only the object line)


I.e., there might be redress to the slippage you encountered;
I'd recommend adding the turn at the part of the knot wrapping
its tail.  (And one could add two extra turns (but at some point,
extra becomes excessive).)

--dl*
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