Author Topic: Gripping Hitches: A Proposed Rating System  (Read 28727 times)

knot4u

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Gripping Hitches: A Proposed Rating System
« on: February 22, 2012, 07:01:49 PM »
Friction is obviously the key for a gripping hitch on a pole. However, what really makes one hitch "better" than another? Can the rating of a gripping hitch be quantified? Efficiency and elongation can be quantified. Other characteristics (e.g., simpleness) are a lot more subjective, but still important. I put "better" in quotation marks because desired characteristics of a gripping hitch are application-dependent. For example, a particular application may not require the coils to remain as circular as possible.

Efficiency

Efficiency is the number of coils needed for the hitch not to slip on the pole under maximum loading. A coil is one rope strand traversing 360 degrees around the pole. I'm assuming the hitch has enough coils to prevent slippage along the pole. If the hitch slips on the pole, then coils must be added before you even get to talking about elongation. If the hitch slips regardless of the number of coils, then the hitch receives an overall rating of ZERO (i.e., lowest possible rating), and it goes straight to jail without passing Go.

Elongation

Elongation is the amount by which the coils move from being as circular as possible under maximum loading (i.e., as much loading as the user can give it). In other words, elongation is the tendency for a gripping hitch to resist spreading out. Here's the formula...

Elongation = Average shift distance of coils = (Sum of shift distance of coils along pipe) / (Number of coils)

Simpleness

Simpleness is the ease with which a hitch can be tied, untied, and remembered. This category is subjective. Nevertheless, for some people like me, simpleness is rather important. For other people, simpleness is not so important.

Overall Rating

It depends. Again, some of these characteristics are more important in some applications. If we limit the discussion to one particular application and rope type, then we can more accurately compare two different gripping hitches. When comparing a hitch, we are to assume the same application and the same rope type. It doesn't matter what they are. Just make sure to define what the application and rope type are. For example, it's not fair to claim a particular gripping hitch sucks if all you did was test monofilament, while the particular application involves pulling a 6" diameter lead pipe out of the ground.

For me, the deciding factor has been simpleness. I have not found there to be much difference in performance among friction hitches. We can compare efficiency and elongation all day. However, if those characteristics come at the expense of sacrificing too much simpleness, then I won't be using the hitch anyway.

=====

Here are some related threads:
http://igkt.net/sm/index.php?topic=1889.msg12943#msg12943
http://igkt.net/sm/index.php?topic=3794.msg22204#msg22204
« Last Edit: February 24, 2012, 09:30:18 PM by knot4u »

xarax

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Gripping hitches
« Reply #1 on: February 22, 2012, 09:05:19 PM »
  "Efficiency" . So, we will characterize more "efficient" a gripping hitch that has the same gripping power than another, but uses a smaller number of coils. Economy of coils (?).
  "Effectiveness". So, we will characterize more "effective" a gripping hitch where the coils remain more circular than the coils of another, when they are equally or maximally loaded. Equally, or maximally (?). ( With "maximal loading", I mean the maximum loading under which the hitch does not slip alongside the pole ).
   "Simple-ness".  Let me refer here to some thoughts I have already tried to express in this forum.  There are two, rather distinct, things that can be described by this term, as regards the "easy-ness to be remembered" part of it. A hitch may be simple (A) to remember, because its structure/form/shape/image is simple. Or. it may be simple to remember, because, although it is not simple (A), it is simple (B) nevertheless : i.e. there is a simple logic/rule/law/idea/mechanism that, when followed, produces the hitch. A hitch, as any knot :
   1. Can be simple (A) but not simple (B). It can be a not-so convoluted knot, with a few only tucks, but one has to learn it by heart. If one will forget a single thing, he will not be able to tie it, because there is nothing that can lead him from the one stage to another, there is no coherent logic/rule/law/idea that connects the individual parts of this knot. I think that many of the gripping hitches shown by Ashley at ABoK 1734- ABoK#1746 are simple (A) but not simple (B).
   2. Can be simple (B), although it is not simple (A). It can be a very convoluted knot, with many tucks, but
a. one has only to learn the logic/rule/law/idea that dictates their presence. once this is well understood, the knot is easy to be reproduced, without a flaw.
b. one has only to combine two or more well-known, often-used knots, the one after the other.
    So, even if one forgets the overall structure/form/shape/image of this simple (B) hitch, he can
a. reproduce it on spot, by following the"ratio" behind its construction, or
b. tie the one well-known knot after the other, and complete the final compound knot. 
I think that many of the gripping hitches I have proposed are simple (B), although not simple (A).

   I believe that the overall rating should also depend upon the overall security of the hitch, measured with the help of a tug-of-war type of test between pairs of hitches. I also believe that the gripping power of each hitch is very sensitive to the relative diameters of the ropes and the poles. So, we should not only test different materials, more or less slippery and more or less springy, on more or less slippery poles...but also large diameter ropes tied around small diameter poles, and vice versa. In short, I see much work before we can have any thumbs-up / thumbs-down result !  :)
« Last Edit: February 22, 2012, 09:08:17 PM by xarax »
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Benboncan

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Re: Gripping Hitches: A Proposed Rating System
« Reply #2 on: February 22, 2012, 09:25:39 PM »
I agree with this.
Quote
Other characteristic are a lot more subjective, but still important. I put "better" in quotation marks because desired characteristics of a gripping hitch are application-dependent. For example, a particular application may not require the coils to remain as circular as possible.

This is contradictory to the first quote.
Quote
I will define effectiveness as the amount by which the coils do not move from being as circular as possible.

??



knot4u

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Re: Gripping Hitches: A Proposed Rating System
« Reply #3 on: February 22, 2012, 09:35:21 PM »
I recognize that a hitch can be easy to remember, but difficult to tie, and vice versa. However, I want to keep the "simpleness" category combined in order to have subjective characteristics in one place.

Again, simpleness is subjective. It does no good to force somebody to accept how a hitch is simple when the hitch might be complex according to how the person's brain works. If you believe dyslexia is real, then you can understand how different brains may be wired differently.
« Last Edit: February 22, 2012, 10:25:24 PM by knot4u »

knot4u

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Re: Gripping Hitches: A Proposed Rating System
« Reply #4 on: February 22, 2012, 09:36:58 PM »
I agree with this.
Quote
Other characteristic are a lot more subjective, but still important. I put "better" in quotation marks because desired characteristics of a gripping hitch are application-dependent. For example, a particular application may not require the coils to remain as circular as possible.

This is contradictory to the first quote.
Quote
I will define effectiveness as the amount by which the coils do not move from being as circular as possible.

??

Efficiency and elongation are quantifiable. Simpleness is subjective. So, the overall rating is subjective because of the simpleness characteristic. When comparing hitches, again, I'm assuming the application and the rope type are established.
« Last Edit: February 23, 2012, 03:26:22 AM by knot4u »

Sweeney

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Re: Gripping Hitches: A Proposed Rating System
« Reply #5 on: February 22, 2012, 10:27:46 PM »
I cannot see how distortion of the coils in a gripping hitch has anything necessarily to do with effectiveness.  To my mind effectiveness is measured by the load which can be applied before overall movement of the hitch in the direction of the applied force occurs (ie not movement within the hitch as elongation is almost bound to occur for the hitch  to work). If the rope and application are standardised so as to eliminate different coefficients of friction in the materials then the hitch which bears the greater or greatest load is the most effective. If however a hitch has to elongate considerably before gripping then its efficiency may be called into question - I would prefer that as a measure rather than how much rope is consumed which is largely irrelevant usually. However how much rope is consumed may be a factor in considering simpleness so that it is not totally subjective.

Barry

knot4u

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Re: Gripping Hitches: A Proposed Rating System
« Reply #6 on: February 22, 2012, 10:33:47 PM »
To my mind effectiveness is measured by the load which can be applied before overall movement of the hitch in the direction of the applied force occurs (ie not movement within the hitch as elongation is almost bound to occur for the hitch  to work).

The problem with saying that is once a gripping hitch is set (i.e., coils are made as tight as possible before loading hitch), I have found there to be zero overall slippage with any legitimate friction hitch I've tested. So, there is nothing to compare there. If others have other results, then please describe your testing.

If for whatever reason there is any overall slippage, I give that gripping hitch an overall rating of ZERO for that particular application and rope type.
« Last Edit: February 22, 2012, 10:46:36 PM by knot4u »

knot4u

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Re: Gripping Hitches: A Proposed Rating System
« Reply #7 on: February 22, 2012, 10:39:10 PM »
If however a hitch has to elongate considerably before gripping then its efficiency may be called into question - I would prefer that as a measure rather than how much rope is consumed which is largely irrelevant usually.

To prevent confusion, I changed the word "Effectiveness" to "Elongation" in the original post.

Also, I disagree with you about your point about how much rope is consumed (efficiency). It is a factor. It's not the only factor, but it is one factor that does tell us something about the hitch. For example, if I throw 100 coils on a hitch, there's a pretty good chance I can get it to be secure no matter what. If you don't care about how much rope is used, then you can't complain if a hitch requires 100 coils to make it secure. I personally would give that hitch a low overall rating.
« Last Edit: February 22, 2012, 11:01:08 PM by knot4u »

xarax

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Re: Gripping Hitches: A Proposed Rating System
« Reply #8 on: February 22, 2012, 10:42:41 PM »
I recognize that a hitch can be easy to remember, but difficult to tie, and vice versa.

I was speaking about knots easy or difficult to remember, but for different reasons. A simple picture may be difficult to remember, because there is nothing coherent in the arrangement of its components, and a complex picture may be easy to reproduce, because all its elements are connected, following a certain logic.

different brains may be wired differently.

Veeery true. However, when there is a certain logic behind something, when we manage to understand this logic, we can "follow" it and remember the relevant object much easier.
« Last Edit: February 22, 2012, 10:43:24 PM by xarax »
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knot4u

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Re: Gripping Hitches: A Proposed Rating System
« Reply #9 on: February 22, 2012, 10:52:38 PM »
In the original post, I changed the word "Effectiveness" to "Elongation".

xarax

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Re: Gripping Hitches: A Proposed Rating System
« Reply #10 on: February 22, 2012, 10:58:15 PM »
I cannot see how distortion of the coils in a gripping hitch has anything necessarily to do with effectiveness.

   It turns out that it has, indeed...So, the main thing we can do to improve those hitches, is to keep this distortion as small as possible - by the pre-tensioning of the coils I have proposed.

effectiveness is measured by the load which can be applied before overall movement of the hitch ...not [by the] movement within the hitch

To a degree, that is correct. However, at the very end, it is the angle between the axis of the poles and the coils that will determine the gripping power of the hitch - because an angle much less than 90 degrees, mean very oblique coils, so the possibility of much space between the coils and the pole, that always means slippage.

I have proposed one more objectively measurable element to the overall formula ;

the overall rating should also depend upon the overall security of the hitch, measured with the help of a tug-of-war type of test between pairs of hitches.
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xarax

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Re: Gripping Hitches: A Proposed Rating System
« Reply #11 on: February 22, 2012, 11:05:51 PM »
In the original post, I changed the word "Effectiveness" to "Elongation".

Good. It is more precise. You should also define WHEN this elongation is to be measured. Under maximum loading, just before the hitch slips, or under working loading, within a margin of maximum loading ?
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knot4u

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Re: Gripping Hitches: A Proposed Rating System
« Reply #12 on: February 22, 2012, 11:46:47 PM »
In the original post, I changed the word "Effectiveness" to "Elongation".

Good. It is more precise. You should also define WHEN this elongation is to be measured. Under maximum loading, just before the hitch slips, or under working loading, within a margin of maximum loading ?

It's elongation under maximum loading. I have changed the original post.
« Last Edit: February 23, 2012, 12:01:42 AM by knot4u »

xarax

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Re: Gripping Hitches: A Proposed Rating System
« Reply #13 on: February 23, 2012, 12:00:00 AM »
Have you ever completely set a knot and have it slip?

   You mean, set, dress and tighten a knot, and then load this knot and force it to be untied, without any (partial or not) rupture.  Of course !  :) Most simple knots will slip before they break - and also some more complex ones, I should say. Otherwise, we would not have been considering the security issue at all, would we ?

the discussion here assumes that the user is using enough coils (efficiency) such that the hitch does not slip.

 I was talking about slippage alonside the pole here. Is there any other word we should use, so we do not confuse the two kinds of slippage ? 
 I ment that you should count the elognation just before the hitch slips alongside the pole.

under maximum loading (i.e., as much loading as the user can give it).

...before the hitch "slips" alongside the pole !  :)
« Last Edit: February 23, 2012, 12:04:38 AM by xarax »
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knot4u

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Re: Gripping Hitches: A Proposed Rating System
« Reply #14 on: February 23, 2012, 12:05:15 AM »
I'm assuming the hitch has enough coils to prevent slippage along the pole under any amount of load (i.e., rope will break before hitch slips on pole). If the hitch slips on the pole, then coils must be added and tightened before you even get to talking about elongation.

If the hitch slips regardless, then I give the hitch an overall rating of ZERO (i.e., lowest possible rating) for the particular application and rope type. It doesn't matter if you have an emotional attachment to the hitch, too bad. If we don't make this stipulation, then the efficiency factor is a lie at the beginning.
« Last Edit: February 23, 2012, 12:26:01 AM by knot4u »