Author Topic: Beefed up KC Hitch  (Read 12383 times)

DerekSmith

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Beefed up KC Hitch
« on: October 08, 2006, 06:33:38 PM »
The KC Hitch could be accused of one fault - it can be just tooo powerful.  Its leverage can bite into the surface of the object it is gripping .  Taking a lesson from history in the form of ABOK 1758, we can produce a modification to the KC hitch which offers improved load distribution and abrasion resistance.

This is achieved by tying the KC Hitch using a loop of cord, then instead of tying it off, pass the end of the loop through starting loop.




The result could be called the Double KC Hitch, or perhaps the KC Sling Hitch.

Because it is a sling, it can be discarded if it is damaged by abrasion and it can be fabricated from a material more likely to withstand damage and abrasion, leaving the towline to just perform the function of pulling. 

Because the closure of the two spirals does not feature any 'knots', it is impossible for it to lock up and therefore remains easy to remove and is potentially even easier to tie than the KC Hitch.

Because contact area is doubled, overall friction is increased and the load density reduced both by doubling the contact area and by requiring less leverage to be applied in order to transmit the force into the load object.

The same rule applies, that enough turns should be used to ensure that when fully loaded, the last two turns (the anchor turns) do not open.  This is necessary to ensure that all of the in-line force has been transferred to the load before reaching the anchor turns.  If any residual in-line force is allowed to reach the anchor turns, it is possible that this force could move the anchor forward and this in turn will allow the whole knot to slip.  If sufficient turns are utilised to ensure that the grip exceeds the breaking strain of the cord, then there is no means of making the knot slip.

As before, it will be valuable if members of this forum would use this knot, then feed back their observations as a form of peer review.  That way if anyone spots any problems they can at least be shared with everyone.  Of course, if anyone comes up with a particularly useful or novel application, then again sharing it with members will be much appreciated.

Derek

Mike

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Re: Beefed up KC Hitch
« Reply #1 on: September 08, 2009, 03:15:15 AM »
Hi Derek,   Would there be any advantage in starting in the middle of the sling and wrapping both sides back and forth while swapping the over/under orientation  (e.g. A over B than B over A )

Mike

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Re: Beefed up KC Hitch
« Reply #2 on: September 14, 2009, 01:11:16 AM »
Hello, anyone there? ???

Dan_Lehman

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Re: Beefed up KC Hitch
« Reply #3 on: September 14, 2009, 06:44:22 AM »
Hi Derek,   Would there be any advantage in starting in the middle of the sling and wrapping both sides back and forth while swapping the over/under orientation  (e.g. A over B than B over A )

I think that what you are describing is to e.g. orient the sling such that
it crosses under the object and those sides are spaced apart (each crossing
point  -- left & right, if the bar is horizontal as Derek shows) -- , and then
you bring the top and bottom far reaches of the sling in opposite directions
to wrap inwards around it, alternating which side goes within (resp.
around) the other.  This knot is known and has been shown in some books,
with the finsihed-wrapping points of the sling then clipped with a carabiner.
It seems to waste the wraps on the load side of the attachment, with the
away wraps doing more of the gripping.

Relative sizes matter in alternating crossings, for each rise to cross over
takes that part off of the surface to be gripped; whereas if one side is
always under its contact grips w/o interruption:  relatively large
diameter objects will give ample run between crossings so this won't
matter (and damNear any sort of wrapping will grip); relatively small
diameter objects will be hard to grip with alternating crossings, with
much air in the hitch.

 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
NB:  Although Derek presents a version without a tie-off/knot at the
entry point, it could have one (Bowline on a Bight, or Eskimo orientation
or ...).  Without one, there is some difference in mechanics -- the S.Part
strands can be tensioned into the structure w/o matching tension from
the collaring side strands -- w/o exact matching, any way (this would
be seen as the point of the S.Part strands that starts in contact with
the collar moving out away from it, which if there were a knot joining
them couldn't happen).

One point where such a hitch might find popularity is wherever those
"stoppers" are used for heavy ropes, assuming that the heavy ones
are of non-hi-mod fibres and the stopper sling is of say Technora-sheathed
Dyneema SK-75:  high strength in the stopper but in smaller diameter to
effect this tenacious gripping; and lightweight for easy handling.
In the form Derek shows here, the "collar" might best be a metal ring,
to reduce abrasion!? 

--dl*
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DerekSmith

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Re: Beefed up KC Hitch
« Reply #4 on: September 14, 2009, 06:46:12 PM »
Hello, anyone there? ???

Hi Mike,

Apologies for not reading your suggestion sooner.

What you are describing is the original mode of tying the straight KC hitch - starting in the 'middle' (i.e. at the anchor end) and wrapping both ends front to back, back to front etc.

The over under order/sequence is not important, because once the loops have been closed up and the ends tied off, the gripping action is created when the load is applied and the loaded loops start to open under load.  This increases the diagonal length of the cord around the bar and the tension rockets - feel how 'hard' the cord gets when the load is applied.  The tension travels up the cord to the anchor end and grips tightly so long as at least the last two wraps are not pulled open.

The 'Beefed Up KC' version was created to simplify the wrapping process and does not need an 'over - under' sequence - again, so long as the loops are closed up before the load is applied.  Using a loop like this makes it ultra simple to 'wrap up' the hitch as easily as possible, and if you start with the 'end' of the loop, then you know where the tie off is going to be because you start there.

Have you tried putting the beast to work yet?

Derek

Mike

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Re: Beefed up KC Hitch
« Reply #5 on: September 15, 2009, 12:47:18 AM »
No, I have not tried it yet.  I do, however,  think it will  be a very good hitch for pulling 10'-20' sticks of copper tubing (5/8 to 1-5/8 diameter) up on a roof.

dfred

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Re: Beefed up KC Hitch
« Reply #6 on: September 15, 2009, 03:55:07 AM »
The KC Hitch could be accused of one fault - it can be just tooo powerful.

I don't think it's a fault, per se, but another vulnerable point of the KC hitch is the first turn.  If this is moved towards the strain, the entire hitch moves.  Recently I had reason to beef the KC hitch up in another way to address this issue...

Earlier this summer I helped my cousin's family secure their hanging tomato plants.



Their original plan was that the frame which the "upside down" tomato planters were to hang from would be made from otherwise unsecured steel tubing.  However, it quickly became apparent that the friction of the threaded fittings was not enough to stop the frame from falling over with even the slightest provocation.  Even without the tomato plants, this steel frame was very heavy and dangerous if it were to fall on someone.   This was the point I was called.  :)

Rather than drilling holes for anchor points, I decided to try friction hitches first.   I was especially concerned about unintentional (or naively intentional) movement of the friction hitches and took some measures to secure them; I used a modified KC hitch as the anchor, but starting with a heavily tightened constrictor knot for the first "turn".

The ends of the pipes were about 1ft (30cm) into the ground and were also prevented from moving towards the center as they were abutted against raised planting beds.  The friction hitches on the downward legs were reeved prusik-like hitches, again secured against the unwary untying or loosening them.  The system was tightened by having one person press on the apex of one side, which produced slack in the down-ropes of the other side which could be tightened by sliding.  This was iteratively repeated until everything was tight.  After the tomatoes were hung and sat for a day or two everthing was retightened.  All the pictures were taken about 6 weeks later, and nothing has needed adjustment since...


KC started with a constrictor, after six weeks.


The friction hitch securing the down ropes.

[EDIT: Fixed links to intermediate sized images rather than originals.]
« Last Edit: September 17, 2009, 04:58:16 AM by dfred »

DerekSmith

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Re: Beefed up KC Hitch
« Reply #7 on: September 15, 2009, 05:46:48 PM »
Hi Dfred,

That is a novel example, and your cousin has great garden.

Quote
I don't think it's a fault, per se, but another vulnerable point of the KC hitch is the first turn.  If this is moved towards the strain, the entire hitch moves.

If by the 'first turn' you are referring to the turns on the right in the following image, then these are the anchor turns and indeed, they must not move...  move the anchor and you allow the knot to move to a new location relative to the anchor.



It is interesting that you 'beefed up' the KC by starting with a Constrictor - that is exactly where I started when developing this knot to make as solid an anchor as possible.  Later on, I discovered that the Constrictor actually reduces anchor grip slightly although the cause of this reduction is not immediately obvious.  The anchor grip is created out of pure tension in the cord around the tube with no inline tension reaching it.  The cord tension is created by the first two / three turns being scissored open by the inline load.  By pulling the loops into those long spirals, the cord is stretched by the considerable leverage of pulling the coils sideways.  The vice like grip of the coils increases the contact friction and the in line tension is all transferred to the tube in the opened coils.  Provided the end coils do not open (i.e. all the load is shed before reaching them) then this knot will not slip(unless there is so little friction that the coils do not even open).

As the 'tightness' of the cord increases, its grip on the bar increases and so does its frictional resistance to sliding along the tube.  If you load the KC then feel the cord, you will see how hard it has become because of the great tension it is under.  There is far more tension in these wraps than there is in the load line, because of the leverage advantage of the scissor action as the coils open.

You will notice in the example above, the two base or 'anchor' coils have not opened.  This is key to ensuring the grip of the KC.  If the last coils start to open, then you need to make the KC with more turns until you can load it with the last two remaining closed.

Going back to our starting point, if you put a Constrictor in that very first wrap, it not only makes tying a little more complicated, but it also impedes very slightly the flow of tension around the last anchor coil and so reduces it potential to grip (but this is a very slight reduction).

Of greater importance perhaps is the old 'law' of relative diameters.  The gripping cord diameter should not be a significant fraction of the gripped surface diameter.  As far as I know, this is true for all of these gripping knots - Prussics?  The cord you have used is probably a bit on the thick side to perform well, even though it very much 'looks the part'.  You would probably have achieved a more secure job with a double strand of 3mm Polyprop, it is deceptively strong at 100kg breaking strain, but would not have looked as good as the job you created.

I hope the tomatoes are good and thanks for bringing this real application to the Forum.

Derek

dfred

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Re: Beefed up KC Hitch
« Reply #8 on: September 15, 2009, 07:14:54 PM »
Thanks for the comments, Derek.  Unfortunately even with the fancy knotting, the tomatoes were a bit of a bust.  Two of them had to be replanted due damage sustained when the frame fell and the others never really took off probably due to the very cool summer we had.  I'm not entirely convinced of the effectiveness of those hanging planters.   The cherry tomatoes growing in the ground were quite yummy, though.

Your points are well taken regarding the size of the rope used for this task.  This was initially intended to be a temporary stabilization of the frame until they could get something else, but it functioned well enough that it became permanent, at least for the summer.  I just used whatever line I had in my car that day, which was a 100' hank of so-called "diamond braid" from the hardware store which I keep to use basically as disposable utility line.  It is a braided sheath around a core of mixed of bulk fibers.  It doesn't hold up too well under repeated use and it handles terribly.  But it is really cheap, holds knots well, is reasonably consistent in structure (no big splices/flaws), and comes with a listed SWL of 100kg.   It's the kind of stuff I can help people lash stuff to their cars and not worry about asking for (or wanting :)) it to be returned.

That is interesting about the behavior of the anchor wraps.  The one issue with this rope is that it is not slippery at all.  I was mildly concerned that the tension would fail to tighten the anchor loops enough to prevent unintentional movement (e.g. someone putting there hand on the frame while bending over to pick vegetables).  But I definitely agree with your reasoning for going with plain wraps in general.  And regarding the initial wraps needing to stay together, you'll notice in the wide view shot the distant KC Hitch held up better -- however the only close-up I took of that hitch was out of focus.


Dan_Lehman

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Re: Beefed up KC Hitch
« Reply #9 on: September 16, 2009, 08:00:55 PM »
[GEEESH, DFred, what size are those images?  -- beyond my dial-up!  A smaller size,
for the board here, helps.  (that 100kb attchment)]

Of greater importance perhaps is the old 'law' of relative diameters.  The gripping cord diameter should not be a significant fraction of the gripped surface diameter.  As far as I know, this is true for all of these gripping knots - Prussics?

And it depends on the materials.  The ProhGrip (Blake's Hitch) works on equal diameters
in ropes (and can work in unequal diameters with hitching line thicker, even).

--dl*
====
« Last Edit: September 16, 2009, 08:20:21 PM by Dan_Lehman »

dfred

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Re: Beefed up KC Hitch
« Reply #10 on: September 17, 2009, 05:02:36 AM »
[GEEESH, DFred, what size are those images?  -- beyond my dial-up!  A smaller size,
for the board here, helps.  (that 100kb attchment)]

Very sorry about that.  I just fixed this.  The forum automatically inserted code to reduce the displayed size, so I hadn't realized I'd linked the originals and not the intermediate sized images.  The new images are about 40x smaller, that should help!  Thanks for mentioning it...




Dan_Lehman

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Re: Beefed up KC Hitch
« Reply #11 on: September 17, 2009, 07:31:40 AM »
Earlier this summer I helped my cousin's family secure their hanging tomato plants.

You know, I think that this made more sense before I could view the photos!
(Thanks for the fix.)

Quote
I was especially concerned about unintentional (or naively intentional) movement of the friction hitches and took some measures to secure them; I used a modified KC hitch as the anchor, but starting with a heavily tightened constrictor knot for the first "turn".

And I'll 2nd Derek's rejoinder that the Constrictor isn't such a good friction
knot, nor the tightest binder -- the Clove is (but doesn't hold the higher binding
force so well).  Consider, the two ends (which in this case are two S.Parts,
bearing load into the knot) run unimpededly around the object in the Clove
hitch, but must cross each other in the Constrictor (and if tensioned by pure
opposed pulling -- i.e., S.Parts in a straight line -- there is this bit of lifting
of their continuations where the round object curves away from the tangent;
this can be anticipated by sort of pulling around the object, but the
Clove doesn't have this problem in delivering tension into the knot).

Quote
The friction hitches on the downward legs were reeved prusik-like hitches, again secured against the unwary untying or loosening them.  The system was tightened by having one person press on the apex of one side, which produced slack in the down-ropes of the other side which could be tightened by sliding.  This was iteratively repeated until everything was tight.

I'll venture to assert that these Prusik variations show a poor understanding
of the mechanics of that knot.  (Or, it might be that this venture shows that!)
That the extra wraps do more good in the away half vs. the near
half of the knot.  The problem (this came to light in the 2nd edition of On Rope,
where editors turned some images upside-down) is that the away coils will
(like the ProhGrip, Klemheist, KC knot) grip by extending/"stretching" their
reach a bit, and tightening their grip in the process; the other half has to
tighten in place without such movement; BUT as the away half extends,
its S.Part bears into the near coil and breaks its grip, as Ashley e.g. notes
for moving the Rolling hitch -- similar mechanics.  Of course, Prusik hitches
DO grip, and have been put to the test in much usage.
But the problem was writ large in the On Rope case because
the away "half" was a single turn, which never gripped, and so
perpetually pushed the near coil.

Also, why not feed the Prusik from an eye knot?!  I'll surmise you were
tying it tight from the start, hence the 37 Half-Hitch (Reversed Hitches
("Hitch Sequence")) finish? 
 ::)
--  though feeding from an eye can bring problems of tension balance
on the two legs into the Prusik.  argh

"Away"-gripping knots seem to be problematic with tightening, as its
hard to push them into that extended gripping; they work better being
set and letting the line be pulled against their every tightening (but
with some extension) grip.

Here, I think I'd go for a combination structure:  the immediate friction
coming from a simple turn/Half-Hitch or double, and then the end
secured with some friction hitch.

Or maybEven running one line from side to far side, Prusik near the
center of the cross beam, and a 2nd rope for the 2nd pair of legs.
In theory the shove from one end makes slack at the opposite
end which would weaken your center-gripping hitches; but that's
theory; praxis would shrug.

--dl*
====

dfred

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Re: Beefed up KC Hitch
« Reply #12 on: October 01, 2009, 06:51:49 PM »

You know, I think that this made more sense before I could view the photos!
(Thanks for the fix.)

Heh heh, this is what I get for posting mere makeshift knotted contrivances... :)


Quote
I'll venture to assert that these Prusik variations show a poor understanding
of the mechanics of that knot.  (Or, it might be that this venture shows that!)
That the extra wraps do more good in the away half vs. the near
half of the knot.  The problem (this came to light in the 2nd edition of On Rope,
where editors turned some images upside-down) is that the away coils will
(like the ProhGrip, Klemheist, KC knot) grip by extending/"stretching" their
reach a bit, and tightening their grip in the process; the other half has to
tighten in place without such movement; BUT as the away half extends,
its S.Part bears into the near coil and breaks its grip, as Ashley e.g. notes
for moving the Rolling hitch -- similar mechanics.  Of course, Prusik hitches
DO grip, and have been put to the test in much usage.
But the problem was writ large in the On Rope case because
the away "half" was a single turn, which never gripped, and so
perpetually pushed the near coil.

Interesting, I'll have to take a look at On Rope.   Somehow I've missed that in my reading, it looks good.  I must admit most of my personal experience with friction hitches is for static holding where the hitch can be carefully set and tightened.  The subtleties of how they behave when moved, shock loaded, cycled, etc. is something I could stand to understand better.  I've done some light rock/gym wall climbing and earlier this year took a recreational tree climbing course (fun!), but in terms of actual experience I mostly come from a boating and general utility knot usage background.

Quote
Also, why not feed the Prusik from an eye knot?!  I'll surmise you were
tying it tight from the start, hence the 37 Half-Hitch (Reversed Hitches
("Hitch Sequence")) finish? 
 ::)
--  though feeding from an eye can bring problems of tension balance
on the two legs into the Prusik.  argh

I was sloppy in describing this as a Prusik-like knot.  It's really an extra-wraps magnus/rolling hitch; only the upper of the two emerging lines is really loaded.   I was tying it with the end, and not particularly tight but with some tension to hold the KC-ish hitch steady.  The real tightening was done after the knots were tied by iteratively pushing the frame sideways and sliding the slackened lines down on the other side.  I'd say about half the downward deflection of the horizontal beam was from pretensioning -- it was pretty darn tight before the plants were rehung.

The "37" HHs were to take up extra line I'd left in case it later needed to be readjusted/redesigned (it never did) and to discourage fiddling and untying -- as was the double constrictor seizing of the end added when it was clear no changes were needed.   If you remember my Foucault Pumpkin project, I used similarly "excessive" hitching on some knots that were in easily accessible places.

Quote
"Away"-gripping knots seem to be problematic with tightening, as its
hard to push them into that extended gripping; they work better being
set and letting the line be pulled against their every tightening (but
with some extension) grip.

Here, I think I'd go for a combination structure:  the immediate friction
coming from a simple turn/Half-Hitch or double, and then the end
secured with some friction hitch.

Or maybEven running one line from side to far side, Prusik near the
center of the cross beam, and a 2nd rope for the 2nd pair of legs.
In theory the shove from one end makes slack at the opposite
end which would weaken your center-gripping hitches; but that's
theory; praxis would shrug.

Yea, there are a number of other stay arrangements which would have (perhaps) obviated the need for such dependence on friction hitches, or at least made the pull on them approach the perpendicular.  Tensioning by trucker's hitch/versatackle style arrangement across the full width would also have been a more controllable option at the cost of tidiness, less head clearance in the center (which was useful before the garden had filled-out like it is in the photos), and possibly somewhat more rope.

The main thing to remember is that literally the moment the frame was stable and in an upright position my "client" started rehanging the plants on it and was having none of my "hmmm, how about we try redoing it this slightly different way" intimations.   I won't be losing too much sleep about my choices as I made them.  It stood all summer without any adjustment or other maintenance...   Though I will say that even in a simple little project like this there are seemingly countless ways to solve a given rigging problem.

Mrs Glenys Chew

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Re: Beefed up KC Hitch
« Reply #13 on: October 02, 2009, 05:02:54 PM »
Hi Derek,

Please may I ask what the bend is you show in the first image?  It looks familiar, but I can't place it.

Regards

Glenys
Mrs Glenys Chew
1 Corinthians 15:10

DerekSmith

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Re: Beefed up KC Hitch
« Reply #14 on: October 02, 2009, 10:11:41 PM »
Hi Glenys,

Do you mean this image?



Please don't say that you have seen it elsewhere, I thought I had created it, so named it the 'Beefed up KC Hitch'.

However, when I first posted the concept, I think it was Dan drew our attention to ABoK #1755 and #1758 - the cross lashed straps.  They are almost identical in form but differ in the mode of application - the KC relies on the loops being closed and then as the applied force opens them, the line tension is ramped up and the hitch grips - the last two turns must not open in order to ensure that no inline force reaches the all important anchor turns.  Whereas is the cross lashed straps, grip depended purely on the coarseness of rope on timber, because the cross lashings started open so could never develop grip.

Is this the structure that you might have seen?

Derek