Author Topic: A fixed loop for springy polypropylene rope  (Read 17173 times)

Sweeney

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A fixed loop for springy polypropylene rope
« on: March 17, 2012, 05:12:08 PM »
I have a problem and although I have a possible solution it may not be the best.  I am tying a fixed loop in 6mm split film polyprop. This loop must be fairly quick and esy to tie and - here's the unusual bit - I want it to be as difficult to undo as possible. The bowline and variations tend not to hold well in this stuff as it's so springy and in any event they are, by their nature, relatively easy to undo. Splicing takes too long and I am not a fan of splicing this stuff anyway. I have access to the working end and the standing part but not the end of the standing part.

What I came up with was this: tie a loose overhand knot in the standing part at the point where the loop knot is required. Now tie double overhand (ie a scaffold knot) through the overhand over the crossing part so that instead of a noose when tightened the initial overhand knot stops the double overhand from sliding. The load on the rope is likely to be less than 5% of its breaking strength so knot strength is largely irrelevant. And it certainly jams tight! Anybody got a better idea?

Barry

SS369

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Re: A fixed loop for springy polypropylene rope
« Reply #1 on: March 17, 2012, 06:31:26 PM »
Hello Barry.

There are a few modified bowlines, secured, that could work, see  http://igkt.net/sm/index.php?topic=19.15 thread #19. Just pull all the legs tight while hold the knot body, the tail last.

But what comes to mind is that many fishing loops would work like magic. I like the Double for slick cord. http://www.fishing-khaolak.com/knots/plaiting_a_double_steps.html . You will knot need to braid as much as shown for it to be a strong loop.

Hope this helped.

SS

Sweeney

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Re: A fixed loop for springy polypropylene rope
« Reply #2 on: March 17, 2012, 06:48:04 PM »
Thanks Scott. I have a copy of Geoff Wilson's fishing kots book and I've tied double braid in monofilament but never in something this thick - I'll give it a go. Your lock for the bowline interests me as well but I'm not sure how much it resists untying (not lack of security - I'm tying a loop that a child aged say 12 - 14 cannot untie easily for safety reasons). Again I'll give it a go. The fact the end points back along the standing part is handy.

Barry

SS369

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Re: A fixed loop for springy polypropylene rope
« Reply #3 on: March 17, 2012, 07:51:51 PM »
I'm glad the mental nudge was handy, some of us (me) could use a few time and again. ;-)

As for the untying, as you must know, any industrious individual can probably make work of it and do it, but I think you'll be pleased with the difficulty. That stuff you're working with is slippery and once crushed in the knot should deter long enough for a un-dared/not motivated child to lose interest.

Could use a dollop of adhesive too, though I doubt that will be necessary.

SS

knot4u

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Re: A fixed loop for springy polypropylene rope
« Reply #4 on: March 17, 2012, 09:15:15 PM »
Since you want it to jam, why not use an adhesive (per SS369 above) or a flame to burn things together?

Sweeney

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Re: A fixed loop for springy polypropylene rope
« Reply #5 on: March 17, 2012, 10:22:28 PM »
Thanks again Scott and Knot4U - I have now tried the bowline lock and it does indeed tighten well with no sign of loosening in poly rope.  Adhesive is a good idea and I had thought about using a hot melt gun but as polyprop has a low melting point I dropped that idea - as with applying a flame etc it is very difficult to control. However thinking along those lines it struck me that as the WE runs parallel to the SP a cable tie pulled tight enough to clamp the SP and WE would deter all but the most determined. Any knot can be undone given enough effort (and maybe a rusty nail!) - in the case in point I think the cable tie and a tightly drawn up knot will suffice to deter most kids.

Although not what this is about I have noticed lifebelts along the local beach where the rope is not actually attached to the lifebelt (polyprop again) because some idiot has undone a splice or knot. Those I've seen I've retied with a scaffold knot (triple overhand) pulled up tight around the edge of the lifebelt. You do wonder at the mentality of some people.

Barry

SS369

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Re: A fixed loop for springy polypropylene rope
« Reply #6 on: March 17, 2012, 10:44:32 PM »
Glad that worked for you Barry, but now you have my curiosity peaked. What may I ask is the loop to be used for?
Inquiring minds and all that..  ;-)

SS

Dan_Lehman

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Re: A fixed loop for springy polypropylene rope
« Reply #7 on: March 18, 2012, 05:13:51 AM »
Rather surprised at the responses.

Quote
But what comes to mind is that many fishing loops would work like magic. I like the Double for slick cord

Somewhere the criterion for quick-tying was lost,
and, frankly, I doubt this is all so secure in lesser
lacing (and quite expensive in material)!

Quote
Any knot can be undone given enough effort ...

Good luck w/those rosy glasses, mate!  Apparently, the term
"welded" hasn't come your way w/knots; it has, for many.

My first thought ran to a double overhand eyeknot
(i.e., like the overhand loop but w/a strangle (or more));
that's quickly tied and firmly set.  Your idea is along these
lines for a component, and should suffice.

Looking to fishing knots for inspiration, I take the
old favorite, the blood knot, and work an eyeknot
out of it, as follows (with orientation of SPart running
away leftwards, eye to-be-formed at right, horizontally
disposed working) :

1. make an ample 270deg anti-clockwise loop, and form
a bight --the size of desired eye-- at the closure of this
loop (i.e., where it crosses the SPart) and have bight
cross OVER SPart; a bit of tail stays above SPart, and
to left of other bight leg;

2. Wrap tail back around SPart to up now on right of
bight-crossing.

3. Now, this big loop (not the eye bight, but the first-formed
ample loop) will be material you can easily increase/decrease
with which to essentially make a common whipping
wrapping of the SPart & eye bight with, turning it
back-downUNDER-forward-up ... a few times;

4. Then haul the SPart to set this whipping wrapping
tight against the eye-bight's single turn.

(The general idea came to me from seeing in Barnes
the joining of a short bight's tails to a line using the
blood knot working --2 strands vs. 1.  It occurred
to me that were one to fuse the single-line's (SPart's)
tail to one of the bight's tails, you'd have a normal
eyeknot (with one tail), TIB (Tiable Inthe Bight), too!)

The same knot could be tied beginning at though to
tie a double strangle knot and just modifying the
finish to be with the one-turn-secured end bight.

Then, again, a simple, overhand loop is considered
pretty jamming --the tying is simple, you just need
to give it a hard setting, well beyond what kids will
have means to untie.


--dl*
====

Sweeney

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Re: A fixed loop for springy polypropylene rope
« Reply #8 on: March 18, 2012, 02:11:31 PM »
Thanks Dan - I will try experimenting with some local Scouts and see how they get on attempting to undo various knots. Makes a change from trying to teach them to tie them!

Barry

Sweeney

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Re: A fixed loop for springy polypropylene rope
« Reply #9 on: March 20, 2012, 07:00:33 PM »
What may I ask is the loop to be used for?
Inquiring minds and all that..  ;-)
SS
Sorry, I forgot to reply to this. The loop is at the seaward end of a means to anchor a kids inflatable to the beach. There will be relatively little force on the loop but I don't want bored kids playing with it and trying to undo it (stupid as that would be, it'll happen). Some of the winds and tides here can have toy boats etc floating out to sea before adults, who should be supervising, notice and it's another job for the inshore lifeboat at best. At the moment I'm experimenting with loads etc. including any danger to swimmers and other beach users (though this is designed to be used in very shallow water close inshore).

Barry

SS369

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Re: A fixed loop for springy polypropylene rope
« Reply #10 on: November 25, 2012, 04:39:06 PM »
Good day Barry.
Reading through posts I find some that just are left hanging, for one reason or another. I am wondering if you settled on a solution to your challenge.
Or did summer come and go with time lost?

SS

X1

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Re: A fixed loop for springy polypropylene rope
« Reply #11 on: November 25, 2012, 09:33:24 PM »
This loop must be fairly quick and easy to tie and - here's the unusual bit - I want it to be as difficult to undo as possible.

   The most difficult to undo knot I had ever come across , is the "Oyster" bend ( M. B 5 ). When tightened, it becomes a rigid sphere, that is awfully difficult to untie ! Try it as a loop knot, it might suit to your purpose. ( See the attached pictures ).
« Last Edit: November 25, 2012, 09:37:32 PM by X1 »

Benboncan

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Re: A fixed loop for springy polypropylene rope
« Reply #12 on: November 26, 2012, 12:09:07 PM »
The most tamperproof solution in my opinion would be to splice followed by heatshrink tubing over the splice. You don't have to use a flame for the tubing, a soldering iron or similar presented near the tubing does the job in a controlled manner. Simple and elegant.

X1

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Re: A fixed loop for springy polypropylene rope
« Reply #13 on: November 26, 2012, 12:17:38 PM »
Simple and elegant.

  Simple, in a looose sense of the word, it might be, indeed. However, it is not elegant ! I have never thought that the word "elegant" would be used for a melted thing !  :)

Benboncan

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Re: A fixed loop for springy polypropylene rope
« Reply #14 on: November 26, 2012, 01:02:42 PM »
Heatshrink should not be melted, it is heated so that it shrinks back to it's original diameter. Melting is not an option, there is a clue in the name.

Edit
An example of heatshrink used extensively on arborists equipment these days, this one is sewn first.

http://outdoorxscape.co.uk/store/arboriculture-rope/rope-marlow-split-tails-13-5mm-dia-x3.html
« Last Edit: November 26, 2012, 02:13:40 PM by Benboncan »