Author Topic: Prusik Loop Knots  (Read 8494 times)

Mike in MD

  • Full Member
  • ***
  • Posts: 40
Prusik Loop Knots
« on: October 02, 2011, 07:30:33 PM »
A friend who is learning rock climbing has asked me to recommend a Prusik-type loop knot.  So I am not going to consider the Mark Adams illustrations which are not tied from loops. 

I tried the Prusik, Bachmann and Klemheist initially with two wraps of slippery Dyneema 3/16 (4.8 mm). I used two variations of the Bachmann and Klemheist: the working loop-end at the top with the SP at the bottom (towards the load) and the reverse.  It is interesting that Budworth shows the Bachmann in the first configuration, but has the Klemheist in both, as if he didn't have a preference. 

With two wraps, the Prusik easily slipped.  The Bachmann slipped with the SP at the top and was tighter but still slipped intermittently with the SP at the bottom.  The Klemheist was tight with two wraps in both orientations.  With three wraps, all were tight, but I was left with the conclusion that the Prusik is best avoided if you know the others.  And that the SP should be at the bottom, towards the load. 

After tying the Prusik, Bachmann and Klemheist I have concluded (as a non-climber who has never tried these knots for real) that the Klemheist with the SP at the bottom is the easiest to tie and the most secure, but the Bachmann has a carabiner to hold the structure of the knot in place (which would be comforting if my life depended on holding that structure).  However, the carabiner also reduces the gripping surface of the Prusik cord.  So I have tried tying the version in the picture.  What do all you real climbers think of this?  What do you use? 

Please ignore the cheap carabiner in the picture.  It is what I have here for the picture. 

For a real Prusik loop (if I were really climbing), I would probably use Bluewater 5 mm Perlon and put it through a 10 mm carabiner with the knot version in the picture, wrapped around a 10 or 11 mm climbing rope.

Any thoughts positive or negative ?

Thanks,
Mike

knot4u

  • Sr. Member
  • *****
  • Posts: 1076
Re: Prusik Loop Knots
« Reply #1 on: October 02, 2011, 07:46:47 PM »
After tying the Prusik, Bachmann and Klemheist I have concluded (as a non-climber who has never tried these knots for real) that the Klemheist with the SP at the bottom is the easiest to tie and the most secure...

Have you compared the secured of the Klemheist with the standing part at the top?  In my relatively brief testing, I have found the Klemheist also performs well in this configuration.

xarax

  • Sr. Member
  • *****
  • Posts: 2781
This is not a knot.

Mike in MD

  • Full Member
  • ***
  • Posts: 40
Re: Prusik Loop Knots
« Reply #3 on: October 02, 2011, 10:06:00 PM »
Have you compared the secured of the Klemheist with the standing part at the top?  In my relatively brief testing, I have found the Klemheist also performs well in this configuration.

Yes, I tried both ways for the Klemheist.  I agree that it worked well both at the top and at the bottom.  The difference was that, with the SP at the bottom, the loop end at the top was larger which made it easier to finish the knot.

SS369

  • Global Moderator
  • Sr. Member
  • *****
  • Posts: 1939
Re: Prusik Loop Knots
« Reply #4 on: October 02, 2011, 11:24:14 PM »
Hello Mike,

I climb and I use a Prusik cord sized to the rope I am using. Yes, I have a few different slings available for me to use.
The smallest is 6mm and the largest is 8mm and these cords are specific to prusiking.
Preferably I use the largest because it releases the easiest and has not failed to grip during ascension. I rarely use a Prusik for belay/rappel backup, but for that I would use the smaller diameter cord because it will dig in and lock faster.

I use the standard 6 wrap Prusik and have yet to have a failure.
Yes, the knot influences, but technique of use goes a very long way to insure survival.

The Dyneema is not the best test specimen for exploring grip and slide knots. Get some true Prusik cord and see the difference it makes.

All this may be contrary to published data, but real world experience has value.


SS

P.S the link given by xarax is worthwhile reading.

Mike in MD

  • Full Member
  • ***
  • Posts: 40
Re: Prusik Loop Knots
« Reply #5 on: October 02, 2011, 11:36:27 PM »
P.S the link given by xarax is worthwhile reading.

Hi SS,

Yes, I have given the paper a quick read.  The most fascinating conclusion is on page 21 where they say:
"The half double fishermans tested out stronger than the bowline, with the Alpine Butterfly being the weakest of the different methods of terminating the climbing line."
I had thought that the Butterfly was the strongest loop.  I now know otherwise.

Mike

SS369

  • Global Moderator
  • Sr. Member
  • *****
  • Posts: 1939
Re: Prusik Loop Knots
« Reply #6 on: October 03, 2011, 12:30:25 AM »
Hi Mike,
yes the conclusions were the best part of the read. ;-)
Some of them different than what I expected.

So much about climbing and the rope use within that "genre" is subjective to many variables. Each climber and his circumstances and equipment play large roles in methods and practices.
Good basic stuff should be the base from which to climb. (Pun intended)

You or your buddy should experiment more on what will work, feel correct and be what you can do in most any scenario before committing to the adventure. Practice with eyes closed, one handed-ly and all that wax on, wax off stuff. lol

As for what's the strongest loop? Start a thread. Or search to see if there is one already.

SS

knot4u

  • Sr. Member
  • *****
  • Posts: 1076
Re: Prusik Loop Knots
« Reply #7 on: October 03, 2011, 04:14:39 AM »
P.S the link given by xarax is worthwhile reading.

Hi SS,

Yes, I have given the paper a quick read.  The most fascinating conclusion is on page 21 where they say:
"The half double fishermans tested out stronger than the bowline, with the Alpine Butterfly being the weakest of the different methods of terminating the climbing line."
I had thought that the Butterfly was the strongest loop.  I now know otherwise.

Mike

I agree with SS that these numbers do depend on context.  However, all other things being equal besides the knot, I would have guessed the half double fisherman (HDF) is the strongest of those three.

Side note, I consider the HDF to be a hitch, rather than a loop.  Specifically, the HDF is a noose, and I consider all nooses to be hitches.  I'll take an educated guess that a Uni Knot or other fishing knot is even stronger than a HDF.  As you know, a fishing knot is typically some sort of noose with multiple coils.
« Last Edit: October 03, 2011, 04:33:37 AM by knot4u »

SS369

  • Global Moderator
  • Sr. Member
  • *****
  • Posts: 1939
Re: Prusik Loop Knots
« Reply #8 on: October 03, 2011, 04:28:21 AM »
What I am unsure of is why the climber, whoever it will be would elect to use a split tail for prusik use? Unless they are the tree service industry.
You would have to use two biners for clip-in purposes and have two potential knots to fail unless these are spliced eye tails.
Just make a sling using prusik cord with the best bend possible, use the tested grip and slide hitch and go for it.

But, if one uses the tied loop split tail method, half the load  (approx.) will be on each loop. I am sure we can find loops with added security around here.

SS

Dan_Lehman

  • Sr. Member
  • *****
  • Posts: 3989
Re: Prusik Loop Knots
« Reply #9 on: October 03, 2011, 06:53:50 AM »
The most fascinating conclusion is on page 21 where they say:
"The half double fisherman's tested out stronger than the bowline, with the Alpine Butterfly being the weakest of the different methods of terminating the climbing line."
I had thought that the Butterfly was the strongest loop.  I now know otherwise.

In other sources, you can find some contrary results:
what do you know, then?

And, even in this one source, do you know how the knots
were tied?  The butterfly is asymmetric, so it differs in
loading from one end vs. the other : we don't know what
was tied & tested in most cases.
(But the degree of difference shown in some of this report's
cases is certainly surprising!)

Finally, knots are not strong or not ; only knotted cordage
is, and one needs to keep that in mind.  E.g., you might
conclude (though still in disregard to above) "Now I know
that knotting this rope with a butterfly is ..."
--leaving unknown how some different cordage might behave.

--dl*
====

Mike in MD

  • Full Member
  • ***
  • Posts: 40
Re: Prusik Loop Knots
« Reply #10 on: October 03, 2011, 03:26:54 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

knot4u

  • Sr. Member
  • *****
  • Posts: 1076
Re: Prusik Loop Knots
« Reply #11 on: October 03, 2011, 07:06:18 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

To be accurate, the author of Layhands.com is NOT including knots like the Half Double Fisherman (HDF) in the category of "single loops".  Those knots on that page are all FIXED single loops.

Again (see my last post), the HDF is NOT a fixed loop and NOT in the same category as the Alpine Butterfly.  The Half Double Fisherman is a noose, specifically, a Double Overhand Noose.  If you're (wrongly) putting the HDF in the same "single loop" category as the Alpine Butterfly, then you should also include these knots in the same category:

-All nooses
-Most fishing knots

For the sake of argument, if we include these other knots in our comparison, then we can do a lot better with strength than the HDF or the Alpine Butterfly.  It would be good then to borrow some knowledge from fishermen, who are obsessed with knot strength.  If strength were the only consideration with a knot, then we'd all be tying large, impractical contraptions.  This brings us full circle to the concept of strength NOT being the only consideration.  Outside of fishing, I can't remember strength ever being the most important consideration for me.
« Last Edit: October 03, 2011, 08:13:57 PM by knot4u »

knot4u

  • Sr. Member
  • *****
  • Posts: 1076
Re: Prusik Loop Knots
« Reply #12 on: October 03, 2011, 08:21:19 PM »
http://www.paci.com.au/downloads_public/knots/14_Report_hitches_PBavaresco.pdf

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 say this because the test results in that same article are directed more generally toward the point at which the tested knots fail.  That means either a security failure (rope slippage) or a strength failure (rope breakage).

When talking about knots, it's important to be precise in the use of these terms, especially when you're publishing results of testing.  "Strength" means the propensity of a knot to resist rope breakage.  "Security" means the propensity of a knot to resist rope slippage.  It's back to the fundamentals we go...
« Last Edit: October 03, 2011, 08:36:16 PM by knot4u »

xarax

  • Sr. Member
  • *****
  • Posts: 2781
Re: Prusik Loop Knots
« Reply #13 on: October 03, 2011, 10:09:58 PM »
Outside of fishing, I can't remember strength ever being the most important consideration for me.

   Let s say we want to choose one of two bends, that :  they can be set and dressed quite easily in about the same time, they consume about the same amount of rope, they are 100% secure with the material we use, they do not jam, and their strength is absolutely sufficient to withstand loadings 5 to 10 times the maximum loading we expect. However, let s say that you happen to know  that the first of them can withstand 80% of the maximum allowed rope strength, while the second can withstand "only" 40%. Would this knowledge you have - on the back of your mind - make you to choose the first bend and not the second - or not ? I mean, ceteris paribus ( :)), is the strength of a knot, as a quality, a consideration we should take into account when we choose a knot out of our toolbox, even if we do not expect to load the knotted material near its breaking point ?
   
« Last Edit: October 03, 2011, 10:14:41 PM by xarax »
This is not a knot.

knot4u

  • Sr. Member
  • *****
  • Posts: 1076
Re: Prusik Loop Knots
« Reply #14 on: October 03, 2011, 11:12:23 PM »
Outside of fishing, I can't remember strength ever being the most important consideration for me.

   Let s say we want to choose one of two bends, that :  they can be set and dressed quite easily in about the same time, they consume about the same amount of rope, they are 100% secure with the material we use, they do not jam, and their strength is absolutely sufficient to withstand loadings 5 to 10 times the maximum loading we expect. However, let s say that you happen to know  that the first of them can withstand 80% of the maximum allowed rope strength, while the second can withstand "only" 40%. Would this knowledge you have - on the back of your mind - make you to choose the first bend and not the second - or not ? I mean, ceteris paribus ( :)), is the strength of a knot, as a quality, a consideration we should take into account when we choose a knot out of our toolbox, even if we do not expect to load the knotted material near its breaking point ?
 

I said I can't remember strength ever being my most important consideration outside of fishing.  Strength is a consideration, but it has not been the most important.  My most important consideration has been security, followed by jam-ability.  Strength is relegated to being a theoretical discussion after I get the knot tied.

Even in your hypothetical, strength is not the most important consideration.  Security is.  You said both bends are 100% secure.  In other words, security is so important that you made it a given.  Also, note your hypothetical is misplaced.  Security is definitely not 100% in the knots discussed in this thread.  We've discussed friction hitches, Bowlines and nooses, among other knots.  You can't assume security is a given in any of these types of knots.

Last but not least, the longest threads on this forum are related to improving Bowline security.  In contrast, knot strength is what it is, and has always been good enough in my applications.  So, there's not much there for me to consider.
« Last Edit: October 04, 2011, 07:13:31 AM by knot4u »