Author Topic: Prusik knot with two ropes/cords of equal diameter  (Read 13845 times)

jamesk

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Prusik knot with two ropes/cords of equal diameter
« on: March 24, 2011, 12:08:40 PM »
I am trying to find a knot that will perform the same as a prusik, ie, will allow me to tie one rope/cord to the other and keep it's position on the main line under tension of the secondary line but that can be easily moved along the main line without untying the knot.

Can a normal prusik knot be used for this?  Everything I've tried so far shows a smaller cord being used to attach to the main line, but I don't have smaller cord (I don't have any cord yet, but when it comes I'd like to know the right knot to use!).

Thanks,

James

SS369

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Re: Prusik knot with two ropes/cords of equal diameter
« Reply #1 on: March 24, 2011, 01:44:03 PM »
Welcome to the forum jamesk.

There are quite a few friction hitches that could do the job you're asking about, some better than others.
The one that comes to mind most readily and has a proven track record, with arborists and recreational tree climbers at least, is the Blake's hitch.
Here is a link to an article about it. http://en.wikipedia.org/wiki/Blake%27s_hitch
It would be my choice for same line size need.
Of course choice of knot(s) is sort of conditional to the materials used, loads to be encountered, angles , etc. So if there are more particular needs let us know.

Hope this helped.

SS

jamesk

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Re: Prusik knot with two ropes/cords of equal diameter
« Reply #2 on: March 24, 2011, 01:53:54 PM »
Hi, loads are not very heavy, but angle of load will be up to 45 degrees from perpendicular :)

I would think that this knot will be fine, if, when I try it at the weekend, it fails, I'll be sure to post back!

Thanks very much!

James


Andre

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Re: Prusik knot with two ropes/cords of equal diameter
« Reply #3 on: March 24, 2011, 04:26:57 PM »
Hi, James,

I'm a climber and we have a nice solution to a similar problem when climbing up a fixed rope. It's the Bachmann, and we use two of them, alternating the load, stepping on one as you move the opposite carabiner up. Unfortunately it does use extra gear - carabiners. I don't remember seeing reliable knots for this purpose, grabby and easy to untie at the same time, using rope alone.

http://en.wikipedia.org/wiki/Bachmann_knot

Not sure if it works with large diameter ropes (10 mm), but it will do with 7 mm or so.

Sorry if I got the question wrong.

Andre.

Dan_Lehman

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Re: Prusik knot with two ropes/cords of equal diameter
« Reply #4 on: March 24, 2011, 06:40:30 PM »
James, greetings!

You probably should try what is commonly called "Blake's Hitch"
(and which I like to call "ProhGrip").  This is a knot intended to
join a line to another of equal diameter.  It's standard form has
4 turns, with the tail tucked beneath 2 of these; it can be adapted
to particular materials by adding turns with the tucked end if the
cord is stiff, or adding turns w/o the tucked tail if the line seems
especially slippery and is flexible.

How easily the hitch can be moved will depend on various factors.

--dl*
====
« Last Edit: March 25, 2011, 03:59:00 AM by Dan_Lehman »

knot4u

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Re: Prusik knot with two ropes/cords of equal diameter
« Reply #5 on: March 25, 2011, 12:49:31 AM »
Try a Klemheist if the tension is constant and the knot doesn't need to withstand too much vibration.  A Klemheist is easier than a Prusik to loosen after loading.  Here's a cool video:

http://www.youtube.com/watch?v=tEiDIhHGs0c
« Last Edit: March 25, 2011, 08:55:54 PM by knot4u »

Bob Thrun

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Re: Prusik knot with two ropes/cords of equal diameter
« Reply #6 on: March 25, 2011, 06:58:01 AM »
All of the friction hitches hold better if the sling rope is smaller than the main rope.  Does your application require that the hitch hold when pulled in either direction?   The Prusik Knot and Helical Knot are symmetrical.  Some hitches, like the Bachmann, work better in one direction.  I have not tried the Blakes Hitch upside down.  The Klemheist is somewhat directional.  It works slightly better tied upside down, when it becomes a Hedden Knot. None of the hitches will hold even half the strength of the rope.  All will slip at several hundred pounds when loaded parallel to the main rope.  If there is some perpendicular component, they will hold much better.  You want a six-coil Prusik, not the normal four.

jamesk

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Re: Prusik knot with two ropes/cords of equal diameter
« Reply #7 on: March 25, 2011, 11:23:03 AM »
Hey folks,

Thanks for all your help.  I think I will be fine with the Blake's Hitch but I am getting quite enthusiastic abotu learning knots so I will be looking at the others too!

I tried Blake's Hitch with a small scrap of cord I have and it worked fine.  I applied considerable pressure to the knot and it did not slip.  This pressure (my full strength) is, in my opinion, way more than it will ever need to hold for this particular purpose!

Thanks!

James

knot4u

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Re: Prusik knot with two ropes/cords of equal diameter
« Reply #8 on: March 25, 2011, 11:58:39 PM »
Regarding a Hedden versus a Klemheist, the jury is still out for me.  I can't say one is more secure than the other.  Had I tested these knots without my ears being tainted by comments from others, I would have said a Klemheist is more secure.  I'm talking about using the same number of wraps (3 or more wraps) for each knot.

Shift gears.  At least one source has said a single wrap is all you need with a Hedden.  However, the single wrap Hedden has proven for me to be less secure than a Klemeist having 3 or more wraps.  A single wrap Hedden may be OK for lightweight applications, but I'd be uncomfortable using a single wrap Hedden in something critical like supporting a human body.


Hedden Knot (single wrap)
« Last Edit: March 26, 2011, 08:51:51 PM by knot4u »