International Guild of Knot Tyers Forum

General => Practical Knots => Topic started by: luis peaze on January 10, 2014, 08:35:36 PM

Title: What knot to use as a backup extra savety to hold floating piers (see image)?
Post by: luis peaze on January 10, 2014, 08:35:36 PM
Hello Folks,
I have been asked to suggest a knot as a back up and/or extra savety to hold floating piers in case the original straps (as per image in attached) fail. The knot will probably be done on a spectra 10mmm line on the bars where the actual straps (green and brown) are.

After a lot of thoughts given I came up with a simple suggestion that is a bowline knot on one end, then after the other end going around that bar and through the eye of the bowline knot finished with three or four half hitch. What do you say? Hey, no much tension required, again, it is an extra savety/back up in case the straps fail. Thanks for you help. Luis Peaz? www.luispeaze.com and Greeting from Rio.
Title: Re: What knot to use as a backup extra savety to hold floating piers (see image)
Post by: Dan_Lehman on January 12, 2014, 01:55:11 AM
What is the nature of the original straps?
They look to be quite strong.

You've moved me to discover my first "invention"
of the new year, 2014, and maybe I've found a
complementary-strands hitch that will prove to
be very strong in HMPE --or maybe HMPE will
prove my knot to be woefully short of friction
to hold through such imagined forces!

But I must wonder who thinks that 10mm Spectra
is the right way to go about backing up this structure?
I'm presuming that you actually mean "(pure) Spectra"
--and not some combination rope in which HMPE is
combined with another material, usually that put in
the sheath!?  (Rockclimbers, e.g., don't use pure
HMPE cordage (though in a practical sense, the interwoven
nylon? in tape I think is less an adulteration than the
sheathing of HMPE kern fibres with a mantle of polyester).

In some tests, bowlines have been shown to simply
come untied upon loading, in HMPE ropes; and, otherwise,
they are so much weakening as to beg the question I put
at the start : why "Spectra" (HMPE cordage) ?!

Given HMPE, my thinking runs to seeking a way to tie
only hitches in the weakened-by-knotting cordage.
And, thus, I was led to discover a way to hitch the two
ends at one bar, jointly, leaving their SParts completely
UNtouched --for pure strength !!!  (But one might learn
my offered caution about requisite friction in this sooo
slippery material! It looks good, but looks are for the showroom.


--dl*
====
Title: Re: What knot to use as a backup extra savety to hold floating piers (see image)?
Post by: luis peaze on January 12, 2014, 07:20:22 PM
Dear Dan,
first of all thank you so very much for taking the time and to elaborate way more than I would expect although honestly wish.

I must admit that this request came to me on last Friday and with some urgency, having a lot on my plate this weekend, while I am setting up the collection of the Museu dos N?s (Knots Museum) and my new atelier naval, I?ve made a post lacking of inputs. The matter of fact I don?t have much of that. The party has briefed me over the phone and has mentioned a double Spectra 10mm line of about 2m lenght.

I dumped on him at first a lot of points of concern such as: why to add an extra savety attachment to the floating docks, presumably done by an accredited engeengineering design? how this would be secured, meaning who would get this done, by the supplier or the client, pro or amateur? how often this would be done? environmental consideration should be made, such as salt water imersion for long period, plumes, sediments, shocks, colision, friction up against metal, sun exposure, etc...

Well, it turned out to be simpler than I thought: the third party client?s wants to show extra care about risk of failure; those flat straps are indeed strong enough (although I have suggested to care about friction action and also attention to sun degradation of stitches on those straps); then I was reminded the Spectra 10mm will be doubled so the 4,5 ton would be then close to 9 tons load capacity; apparently the Spectra was chosen for less elasticity and the extra back up line any way would have no tension, meaning, the attachment will be done with a slack/belly under those iron bars of the floating docks.

So I took two wooden round 12" pieces of wood (of a thickness of an oar) and set three options knots as a prototype or study case for my friend to make decision from, all of them variations of double bowline with half hitches.

Now, I am curious about your invention. And again, many thanks.

Luis Peaz?

Title: Re: What knot to use as a backup extra savety to hold floating piers (see image)?
Post by: [Inkanyezi] gone on January 13, 2014, 09:08:41 PM
One particular knotting problem with HMPE is its extraordinarily low friction. Much before approaching its breaking strength, knots slip, and they can slip severely. Therefore, I would not use Spectra for such a contraption. HMPE also lacks all elasticity, being less elastic than steel, and in jerking movement as in violent swell or waves, hardware for attachment might be ripped loose.

The standard method to avoid sun degradation is to have an outer shell that protects the inner core, and most lines are of a type with an inner core either braided, loosely twisted or straight. Materials used for moorings mostly are polyester or polyamide, and in some applications polyethylene or polypropylene are used. Preferences for polyamide and polyester partly is because of their resilience. They can elongate rather much without losing strength or breaking and return to original shape also after shock loading. The slings shown in the image probably is made from one of those materials.

So adding a slack HMPE strap would be akin to a likewise slack chain. When it is engaged, there will be a hard jerk on its attachment points. Imagine the weight of the pontoon, and the speed it can have attained in a swell, and stop that movement at zero length. Steel wire rope, chain, or HMPE might not be among the best options. What about another sling, like the two shown, but heavier gauge and a bit longer, as security in case those break? However I think it is very unlikely for them to break, provided care is taken to check them for wear and ageing now and then.
Title: Re: What knot to use as a backup extra savety to hold floating piers (see image)?
Post by: luis peaze on January 13, 2014, 09:26:29 PM
Dear Inkanyezi,
Thank you very much. I heard your points. I just came from a meeting with this friend who asked me an advise to full fill a demand from one of his client. Thing is, I am with the impression that nor him either his client are too fussy about anything else than the knot to be done, and probably I must to blame myself on that one because I have told them so much about the importance of knotting, proper knotting, that "there is no such thing as a nearly right knot..." and so on. Then I felt awkward stressing points such as yours and the ones from Dan Lehman, plus vectors of force, actions, environmental & aging factors etc... and again felt I wasn?t being heard. Fortunately at least I ended up with the idea that the "colloquium" was such that time (say couple of weeks or month or so) will make my remarks to them salient enough, probably filtered and hopefully useful. Again, thank you very much for interacting.
Luis Peaz
Title: Re: What knot to use as a backup extra savety to hold floating piers (see image)
Post by: Dan_Lehman on January 14, 2014, 08:52:05 AM
... have told them so much about the importance of knotting, proper knotting,
that "there is no such thing as a nearly right knot..." and so on.
Alas, this utter nonsense from Ashley so appeals
to those wanting a black & white world, of Good vs. Bad,
and easily seen distinctions.  (It would've been a good
statement to have mis-quoted, perhaps!   ;) )


--dl*
====
Title: Re: What knot to use as a backup extra savety to hold floating piers (see image)?
Post by: luis peaze on January 14, 2014, 11:09:07 AM
Dear Dan,
thank you for your interaction, although it seems that you have threw yourself off the curve. The statement that annoyed you I?ve made within a context, to stress a point, as an additional adjective. FYI I think Good vs Bad is a reductionism thinking (as such "to have a gun and shoot, or not have a gun, know or not when to shoot etc), I rather choose a shade somewhere in between among eficiency & practical, economical & lasting, etc. "But" if I go on it would be an off topic chat, already is actually. Bottom line, this friend of mine was happy and I now am curious to see how the thing will work.

My encounter with him was a nice afternoon with his team playing knots, teaching procedures and care with lines, and this friend went on asking me to suggest knots for another interesting application. In the end I shaked his hand went to my car in his garage to find out he had asked on of his employees to throw in my trunk a giant bag of lines of all sort, from 30mm to 20mm to 3mm as a donation for the Museu dos N?s. What gentleman!
Luis Peaz
Title: Re: What knot to use as a backup extra savety to hold floating piers (see image)?
Post by: [Inkanyezi] gone on January 14, 2014, 12:41:51 PM
Seria interesante algun dia de ver aquel museo de nudos. Espero que se ubica en Portugal?
(It would be interesting to some day see that museum of knots. I guess it is in Portugal?)
Title: Re: What knot to use as a backup extra savety to hold floating piers (see image)?
Post by: luis peaze on January 14, 2014, 01:09:46 PM
Rio de Janeiro, Brazil, Inkanyezi. We are still setting up the collection and installation, soon I will publish a link with pictures. Best
Title: Re: What knot to use as a backup extra savety to hold floating piers (see image)?
Post by: [Inkanyezi] gone on January 14, 2014, 01:20:47 PM
One more reason to go there, apart from applauding the sunset at Ipanema. ;-)
Title: Re: What knot to use as a backup extra savety to hold floating piers (see image)
Post by: Dan_Lehman on January 14, 2014, 06:06:16 PM
... those flat straps are indeed strong enough
Of what material are they?  I think that polyester
might be best, for abrasion & UV resistance.  Although
that will be quite inelastic --but how elastic, really, is
even nylon, when put in tape, and after many cycles
of usage loading?  (Hmmm, recalling Tom Moyer's
report of differences when he tested these materials,
there was enough to be noticed.)

Quote
(although I have suggested to care about friction action and also
attention to sun degradation of stitches on those straps)
To address this concern of wear & ageing, one
could inspect and rotate/adjust-position of the
slings, to move the contact point into new material,
and change what parts are exposed to direct sun.

Quote
... ; then I was reminded the Spectra 10mm will be doubled so the 4,5 ['4.5' for Americans]
tons would be then close to 9 tons load capacity;
Is 9_000# the safe working load?  --I think not!
It's closer to what a tensile strength would be for
some composite rope of HMPE (core & sheath).
And (as Inkanyezi notes) knots perform poorly in
this material --beyond slipping, the breaks come
at surprisingly low forces relative to tensile strength
(e.g., I had 5 eyeknots tested : best ~=40%)

Quote
Now, I am curious about your invention. And again, many thanks.
It's a musing about how jointly hitch the two ends
of a line to the same bar, with the ends wrapping
around in opposite directions so that their tails can
be tucked out beneath the wraps so that the wraps
will be drawing the tails ever tighter (as, e.g., in the
Prohgrip / Blake's hitch).  And the SParts will be
UNtouched in their approach and wrapping; there will
be the securing later along, in the securing of the
tails.

A shortcoming for this use of yours is that I've not
developed a structure to stay snug when slack.
Conceivably, this would be done with some sort of
put-on binding in a separate material.


--dl*
====
Title: Re: What knot to use as a backup extra savety to hold floating piers (see image)?
Post by: luis peaze on January 14, 2014, 06:50:29 PM
Thanks Dan.

All your iputs considered.

Right now I am feeling "almost" like the character played by Daniel Day-Lewis in the film The Age of Innocense. At the end he says to Michelle Pfeiffer (her character):  "You gave me my first glimpse of a real life. Then you asked me to go on with the false one"

Meaning: I don?t have much more information about the whole thing, and if I ask the source I will turn out to be a bug; it is not a job or order, although I am dying to follow it up, but must to wait. You know.

If I understood your "musing about..." you dealt with a single line, it must be with double and noap, sorry, no such "put-on binding in a separate material", only line and knotting.

I?ll stay put now, thanks again, I really appreciate your support on this one. Goes on record when opportunity pops out. All the best. and thank you too again Inkanyezi. Luis Peaze
Title: Re: What knot to use as a backup extra savety to hold floating piers (see image)?
Post by: luis peaze on January 15, 2014, 02:52:12 PM
Hi,
I was able to dig out important inputs about this project and I am convinced the old and reliable bowline is the way to go, provided it is well done and finished with extra half hitches, but I accept suggestions:

- the iron bars are 1-1/2" diameter;
- from the center of each other measures 26-5/8"
- the rope once tensioned (it does not tension so much) reaches 10mm, it is very soft (no core) and without tension =  11mm or 11,5mm
- I asked a pic of the rope in action (I?m hour and half from the place) and a worker sent me the pic in attached (I asked him to tie up on something so third party viewers can have a better idea of how the rope behave).
- but again, as I took very serious the task of giving my best recommendation (I could not do in other manner anyway) my friend highlighted with capital letters that "it must be as easy as possible, simple, nothing complex at all";
- that?s why (after playing with several options/alternatives) I suggested the bowline --- and believe me or not (if you knew Brazil you would belive) even the would-be so wellknown bowline in the boating environment is considered not so easy/simple (I am always amazed but this is another story).
- finally, the straps are Polyester cord strap strapping (PES), but this is not an issue at all, since the end interested party is serious about adding a rope as an extra set up.

Thanks for any interaction
Title: Re: What knot to use as a backup extra savety to hold floating piers (see image)?
Post by: luis peaze on January 15, 2014, 02:54:09 PM
sorry, one more thing:
the rope will be doubled and the entire length must not surpass 3m
Title: Re: What knot to use as a backup extra savety to hold floating piers (see image)?
Post by: [Inkanyezi] gone on January 15, 2014, 06:56:35 PM
I would use the ABoK #143 anchor bend for such a task.

http://web.comhem.se/~u77479609/anchor_bend.html

http://web.comhem.se/~u77479609/anchor_bend_es.html

It is a knot that is very easy to learn and it holds well. It also minimises wear, as it will not rub much against the surface where it is attached.
Title: Re: What knot to use as a backup extra savety to hold floating piers (see image)?
Post by: luis peaze on January 15, 2014, 07:20:45 PM
Inkanyze,
Thanks. My first shot was exactely the anchor bend AboK#1843, I think it is easy yes, but again, easy for whom?

Today, after going over several options annoyed by why and how come they do just go with a bowline, I became attempted to suggest the following options:
1 - a double fisherman?s bend #294;
2 - a double overhand bend #339;
3 - a double hobble knot, for if it holds a crazy donkey, it will certainly hold a pier.
Title: Re: What knot to use as a backup extra savety to hold floating piers (see image)?
Post by: DerekSmith on February 20, 2014, 12:46:57 PM
Quote
Today, after going over several options annoyed by why and how come they do just go with a bowline, I became attempted to suggest the following options:
1 - a double fisherman?s bend #294;
2 - a double overhand bend #339;
3 - a double hobble knot, for if it holds a crazy donkey, it will certainly hold a pier.

Hi Luis,

The major problem with the cord you are planning to use is that it has a very low self friction.  This means that although it might exhibit a modest friction against some other surface, within a knot, it just slides over itself as if you had smeared the cord with grease.

This means that it really won't matter which knot you choose, because they will all simply slide open when a load is applied.  Even a knot able to incapacitate a donkey driven crazy by brutal humans will be no match for the force of a large wave, amplified by the leverage of the length of the pontoon and delivered into a knot made in one of the slipperiest cords made - it will just slide through itself...

The elements of the solution you will need are - a knot whose strangle grip increases with load, and a stopper which cannot slide open.

The Packers knot has the necessary strangulation property and has the advantage that you can use it to preload the cord before tying off the knot http://notableknotindex.webs.com/butcherknots.html (http://notableknotindex.webs.com/butcherknots.html)

However, conventional stopper knots will simly pull through themselves.  The normal solution is to use a stopper splice.   Thread the cord back through itself - open up the braid and pass the end of the cord straight through the braid, one side to the other.  Sometimes a solid object such as a round stone is incorporated inside the braid before it is spliced back into the braid.  Then splice the braid back into itself again at the same point, but this time at 90 degrees to the first splice, making a cross splice in the cord... Finally, lock the splice stopper using a liquid penetrating adhesive such as Superglue.

If your cord is ever called upon to do any work, you will find the packers knot drawn tight and hard as steel rope, and the stopper slice jammed rigidly into jaws of the strangling loop

Good luck