Author Topic: Looking for a knot that can be tensioned.  (Read 12063 times)

awtchi

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Looking for a knot that can be tensioned.
« on: March 06, 2014, 02:52:25 PM »
Hi all,

First of all, thanks for taking the time to read my topic.

I am a complete newbie in the art of knots, my knotting knowledge is limited to tying my shoe laces ... This i why i came here, i need help with a project i?m working on.

I need two knots, here is a drawing (expertly made in Paint) to explain my need:



The poles that are going to be tied are much thinner than what i drew, maybe about 5/16" give or take. And the rope width will vary between 1/16" and 1/2".

The rope will be a Dyneema rope (i don't know if this will influence the knot much, but still, better mention this).

Fixed End: This is auto explanatory.

Tensioning End: This end will be used to tension the rope between the poles. I need a knot that can only be tensioned and stay at that tension for a long time, maybe forever if possible.

Both knots need to be able to handle a huge amount of tension.

Thanks for your time and your help!

« Last Edit: March 06, 2014, 03:37:44 PM by awtchi »

roo

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Re: Looking for a knot that can be tensioned.
« Reply #1 on: March 06, 2014, 04:00:17 PM »
Hi all,

First of all, thanks for taking the time to read my topic.

I am a complete newbie in the art of knots, my knotting knowledge is limited to tying my shoe laces ... This i why i came here, i need help with a project i?m working on.

I need two knots, here is a drawing (expertly made in Paint) to explain my need:



The poles that are going to be tied are much thinner than what i drew, maybe about 5/16" give or take. And the rope width will vary between 1/16" and 1/2".

The rope will be a Dyneema rope (i don't know if this will influence the knot much, but still, better mention this).

Fixed End: This is auto explanatory.

Tensioning End: This end will be used to tension the rope between the poles. I need a knot that can only be tensioned and stay at that tension for a long time, maybe forever if possible.

Both knots need to be able to handle a huge amount of tension.

Thanks for your time and your help!

If the rope is slick, you may need to use a Slippery Eight Loop as a tensioner:

http://notableknotindex.webs.com/slippery8.html

...or a Versatackle:

http://notableknotindex.webs.com/Versatackle.html

(second diagram)
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[Inkanyezi] gone

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Re: Looking for a knot that can be tensioned.
« Reply #2 on: March 07, 2014, 09:50:51 PM »
If it shall withstand lots of tension, maybe the versatackle at both ends might be an answer, but it is a tricky problem, as HMPE rope is not prone to stay knotted when tension is applied. There has been discussions on the board about loop knots that hold in HMPE, and I think thorough testing should be done before walking on a tightrope of the material. Sometimes I think the H is for Houdini and the E Escape, fill in for the letters between.

When approaching about half of the rope's breaking strength, most knots slip.

Spliced eyes might be needed to do the job, and spliced eyes with versatackle for tensioning might be the answer.
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SS369

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Re: Looking for a knot that can be tensioned.
« Reply #3 on: March 07, 2014, 10:45:02 PM »
Hi all,

First of all, thanks for taking the time to read my topic.

I am a complete newbie in the art of knots, my knotting knowledge is limited to tying my shoe laces ... This i why i came here, i need help with a project i?m working on.

I need two knots, here is a drawing (expertly made in Paint) to explain my need:



The poles that are going to be tied are much thinner than what i drew, maybe about 5/16" give or take. And the rope width will vary between 1/16" and 1/2".

The rope will be a Dyneema rope (i don't know if this will influence the knot much, but still, better mention this).

Fixed End: This is auto explanatory.

Tensioning End: This end will be used to tension the rope between the poles. I need a knot that can only be tensioned and stay at that tension for a long time, maybe forever if possible.

Both knots need to be able to handle a huge amount of tension.

Thanks for your time and your help!

Hell awtchi and welcome.

I think before a real meaningful answer can be given you should provide us with more information. What is the purpose of this construct? Will the rope just be a guide line? Will it have something else attached to it? Will this be a permanent thing?
How many poles in all?

Your poles are not all that substantial and your rope/cord is very substantial. I would think that any tension between the poles will bow them toward each other and you will be adjusting the tension till they touch!

I would not go so far as to say, as you have, that the fixed end is auto explanatory. You show an eye knot, but this can slide up or down and might need to be a tight hitch instead. Or the rod(s) may need a through hole(s).

We can go from here with some more data.

SS


Dan_Lehman

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Re: Looking for a knot that can be tensioned.
« Reply #4 on: March 08, 2014, 07:57:54 AM »

The poles that are going to be tied are much thinner than what i drew,
maybe about 5/16" give or take.
And the rope width will vary between 1/16" and 1/2".

The rope will be a Dyneema rope
(i don't know if this will influence the knot much, but still, better mention this).


...
I need a knot that can only be tensioned and stay at that tension for a long time, maybe forever if possible.

Both knots need to be able to handle a huge amount of tension.

I think before a real meaningful answer can be given
you should provide us with more information.
...

Your poles are not all that substantial and your rope/cord is very substantial.
...
Ditto/+1 to SS369's concerns.
And --goodness!!!-- what an odd set-up,
such as it's been so far presented : HMPE
super-static/-strong cord varying in size
from 1/16" to 1/2" :: that's about 30times
breaking strength (interpolating the missing
1/16" value from the table of strengths given
here : http://phillystran.com/product-catalog/12-Strand-Braids-Spectra-Dyneema
(I tried to figure a rough factor from doubling diameter :
about 2.8 or so.)

And "forever" is a long time.

!!!! ?-?-?-?   :o

Cheers,
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SaltyCracker

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Re: Looking for a knot that can be tensioned.
« Reply #5 on: March 11, 2014, 01:19:37 AM »
There is a way, using the simple crossing knot, to pull effective tension between the two poles/spars. Don't have the time to do a video or sequential diagrams but essentially it involves forming a crossing knot, pulling excess slack out of the the line between the two poles by pulling the tailing/working end toward the "fixed end" pole then pulling back away from it, inverting the crossing knot over the top of the "tensioning end" knot's pole. This effectively cinches taut the "standing" line between the two poles/spars. Can then wrap around the tensioning end pole crossing knot, locking it in place by crossing over the crossing knot, pinning it in place, and using half hitches to secure. Wish I had more time to show but some of the knot wizards on the forum will probably understand, can clarify and improve upon... or, as is the custom, challenge the solution. Sometimes we complicate our solutions.
« Last Edit: March 11, 2014, 01:50:38 AM by SaltyCracker »

Dan_Lehman

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Re: Looking for a knot that can be tensioned.
« Reply #6 on: March 11, 2014, 05:54:23 AM »
Don't have the time to do a video or sequential diagrams but
... words can work, but we must sharpen them.
Quote
essentially it involves forming a crossing knot,
To clarify : the line runs around 2nd pole,
turns around itself,
goes *back* around pole,
Quote
pulling excess slack out of the the line between the two poles
by pulling the tailing/working end towards the "fixed end" pole
then pulling back away from it,
inverting the crossing knot over the top of the "tensioning end" knot's pole.
to be hauled upon (towards 1st pole)?

I'm lost, now, with "then pulling back away from it"
[= 1st pole]?!  For one thing, that seems like a LOT
of pulling back --i.e, maybe I'm e.g. a half-metre from
the 2nd pole in tensioning it by pulling towards 1st,
and now to "pull back" I must cover all that ground
(with slack!) and then again (the extent of material
in my grasp) before I gain tension in the opposite
direction. !??  --something's not right, here.

Also, I find that in the first pulling, if it takes enough
material --there's an issue re initial tension--, the
crossing knot will be capsized --a familiar sort
of thing, e.g., with rockclimbers belaying : they are
pulling IN for a following ("2nd") climber but if
she falls, she pulls OUT and flips the mezzo barcaiolo
(Munter hitch)
.

Quote
This effectively cinches taut the "standing" line between the two poles/spars.
Hmmm, weil, something I tried did work, around
my finger; but a smooth pole I think will see the
structure rotate, if one releases the tail.

.:.  I think another stab at words is needed,
but we should be closer, now.  Thanks,


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xarax

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Re: Looking for a knot that can be tensioned.
« Reply #7 on: March 11, 2014, 08:02:24 PM »
There is a way, using the simple crossing knot, to pull effective tension between the two poles/spars.

   Yes, there is, but we have to use TWO crossing knots, the one next to the other. See (1), and the attached picture.
I have not found any other way - and I bet there isn't any !  :)

1. http://igkt.net/sm/index.php?topic=4819.msg31391#msg31391
« Last Edit: March 18, 2014, 02:00:57 PM by xarax »
This is not a knot.

DerekSmith

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Re: Looking for a knot that can be tensioned.
« Reply #8 on: March 13, 2014, 09:01:04 PM »
Well, it doesn't look like Awtchi is coming back to answer the questions in a hurry, so in the meantime, how about we consider how we would do it if we were doing it for ourselves. 

Lets presume that those anchor poles are fixed to some rigid enough frame so that they can take the load that the Dyneema is capable of sustaining - then how would you fix the rope and how would you tension it?

Derek

DerekSmith

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Re: Looking for a knot that can be tensioned.
« Reply #9 on: March 13, 2014, 09:14:40 PM »
To start the solutions rolling, I will offer an anchor for the LHS pole.

First I would tie (yes, you guessed, a KC hitch) as the base of my anchor.  I would then lead the Dyneema into a multi turn around the pole.  The number of turns will depend upon the coefficient of friction between the Dyneema and the pole material but must be able to shed virtually the whole load into the pole at full rated Dyneema load.

The advantage of using multiple round turns is that a) the rope does not loose any strength in the fixing and b) sufficient turns can be utilised to guarantee that the Dyneema cannot pull out of the anchor knot.

Now I have to tension the rope and anchor it on the RHS pole.

DerekSmith

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Re: Looking for a knot that can be tensioned.
« Reply #10 on: March 13, 2014, 09:34:34 PM »
To tension the rope, I cannot expect any knot to function both as an anchor and as a tensioning device, so I would split the job into two.

Tensioning.  I would start by tying four VT friction hitches onto the end near the RHS anchor pole and connect each via pulley to a pulley anchor to create enough MA to allow the rope to be tensioned to the required force.  I would use a fifth VT as a 'third hand' to retain and sustain the tension while I then anchored the end of the tensioned rope.

Naturally, the first part of my anchor is going to be the same number of round turns I used to shed the load into the LHS post.  But now I need a tensioning hitch to supply the small load necessary to lock the capstan turns in place and allow them to generate the full loaded tension when the pulleys are slacked off.

Any ideas?

Derek

SS369

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Re: Looking for a knot that can be tensioned.
« Reply #11 on: March 13, 2014, 09:46:50 PM »
Yes, disappointing that we've not read back from awtchi. Maybe he'll check in and contribute.

Since the poles won't come close to handling the tension we can induce using Dyneema, at any diameter indicated, I'll just throw in what I would do in any case.

Since we need an anchor knot that will have a right angle pull and needs to grip the pole so it doesn't slide up or down potentially, I would most likely use something that wraps the pole a couple of turns.
Maybe a Ground Line hitch (ABoK# 1680) and take it one step further with this slippery material and add a stopper knot.
Though a two round turn with half hitches knot and a stopper would probably suffice.

For the next pole, assuming there will not be anymore, I would consider using the double slipped prusik  ;) as presented here> http://igkt.net/sm/index.php?topic=4813.0. With the tail pulled through the last slip bight or with the lock suggested in that thread.

With the project in hand I might try other things too. (Of course.)

SS

DerekSmith

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Re: Looking for a knot that can be tensioned.
« Reply #12 on: March 14, 2014, 01:20:52 AM »
Hi Scott,

The OP required the RHS knot to be capable of tensioning the suspended rope.  How would you apply tension with the tie off you proposed?

SS369

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Re: Looking for a knot that can be tensioned.
« Reply #13 on: March 14, 2014, 02:58:18 AM »
Hi Derek.

By hand of course.   ;)
Pull the cord/rope between the poles and at the same time take the slack with the other hand after the round turns and working part pass over. Like a Munter hitch and belaying, then complete the knot when the tension is adjusted.

With 5/16" poles I don't feel any force multipliers (versatackle, etc.) are needed.
Yes, I am still addressing the original post conditions, just in case.

SS

Sweeney

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Re: Looking for a knot that can be tensioned.
« Reply #14 on: March 16, 2014, 10:40:24 PM »
In terms of the fixed anchor at least the following would seem to fit the bill - being specifically tested in Dyneema: http://igkt.net/sm/index.php?topic=4756.msg30713;topicseen#msg30713

Barry