Author Topic: square knot or double sheet bend?  (Read 13200 times)

edt71

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Re: square knot or double sheet bend?
« Reply #15 on: October 25, 2014, 08:46:49 AM »
Oooops, sorry guys. Didnt clarify well. I meant that about the reef knot.

Dan_Lehman

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Re: square knot or double sheet bend?
« Reply #16 on: October 27, 2014, 05:57:41 AM »
As a new recruit myself Im not quite sure what they call the rope, but its brown and not the natural version. I think they call it "polypropylene manila rope" the most common size our shop seems to use for everything is about 1 inch.

They use if for everything and can be found everywhere in the yard and other shops rely on it for other things.
Wow, 1" rope --even 3/4, 1/2"-- seems mighty big
for much of "everything" that might want tying up
(or down)!  E.g., in the commercial-fishing areas I've
seen, tie-down cordage tends to be about 5/16 - 3/8"
(polypropylene or "PolyDAC").

And is the UNtying of these knots something that
comes easily enough?


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Twine

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Re: square knot or double sheet bend?
« Reply #17 on: October 28, 2014, 10:12:43 AM »
Wow, 1 inch twisted polypropylene manilla imitation.. I agree with Dan that it sounds a bit like overkill. And how expensive it must be, to use that for every purpose!

Anyway, edt71, since you use that kind of rope, I retract my suggestion that the double harness bend could be a replacement for the reefknot-based bend they use right now. The double harness bend would be good for braided stiff line, but not for the soft, twisted polypropylene you describe. There are so many ways to make a substandard double harness bend in your synthetic manilla that mistakes would be inevitable. You need to make the variant of the double harness bend where the tails come out on the same side, the tails need to be crossed in such a way that it results in the "shorter" version of the bend, and first of all, you need to take care how you start the knot (left-handed or right-handed) depending on the lay of the rope. So many ways to go wrong, and only one way that's safe.

Twine
« Last Edit: October 28, 2014, 10:27:47 AM by Twine »
"Simplicity is the ultimate sophistication" - Leonardo da Vinci

Dan_Lehman

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Re: square knot or double sheet bend?
« Reply #18 on: October 28, 2014, 09:29:12 PM »
you need to take care how you start the knot (left-handed or right-handed)
depending on the lay of the rope. So many ways to go wrong,
and only one way that's safe.
Really?!
On what basis are your assertions made?!
(One could say much the same re the squaREef
which is their currently used end-2-end knot.)


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Sweeney

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Re: square knot or double sheet bend?
« Reply #19 on: October 28, 2014, 10:18:59 PM »
........ but not for the soft, twisted polypropylene you describe.

I have never come across imitation manila rope - imitation hemp is quite common (one  trade name is "Hempex"). It is usually hard laid unlike fine spun polypropylene which is extremely soft. Other than that I agree that it's overkill but if it's just lying around then that may not matter so much. Manipulating stuff like this is not easy so although I wouldn't use a reef knot it is relatively easy to tie and with a couple of half hitches probably safe enough. The difference between the real world and the theoretical one maybe?

Barry

Twine

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Re: square knot or double sheet bend?
« Reply #20 on: October 29, 2014, 02:10:22 AM »
On what basis are your assertions made?!
(One could say much the same re the squaREef
which is their currently used end-2-end knot.)

Yes, I guess it is true even for the reef knot, but there are more twists in the double harness bend, so the shortcomings of a wrong-way start get more pronounced.

The basis: When I learned that edt71 used laid rope, I tried it out with 8 mm, three-strand, soft, laid polypropylene, and the knot slipped open just from the pull of my hands when I tried the long version of the double harness bend with tails on the same side. When the knot is started the right way, the tails tend to automatically cross themselves the right way, but when you start the wrong way, the tails twist themselves the wrong way maybe one third of the time, forming the long version of the bend, which slips in this material. Also, even the short version of the bend (when started in the wrong way) tends to untwist itself slightly inside the knot and then the knot transforms into some kind of long/short hybrid with the ropes untwisting themselves inside the knot. It's very ugly, but hard to describe. I'll take some pictures, and also write a bit more about my observations of this wirebend that's called a double harness bend in English. I have much to say about it. One thing is that it seems to me that it's perfectly safe in stuff like stiff, braided line or wire, no matter how you tie it, but for soft, laid line I can only recommend one of the totally eight variants that are possible (or four variants if we exclude the variants with tails going in opposite directions).

Twine
"Simplicity is the ultimate sophistication" - Leonardo da Vinci

Twine

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Re: square knot or double sheet bend?
« Reply #21 on: October 29, 2014, 02:39:23 AM »
........ but not for the soft, twisted polypropylene you describe.

I have never come across imitation manila rope - imitation hemp is quite common (one  trade name is "Hempex"). It is usually hard laid unlike fine spun polypropylene which is extremely soft. Other than that I agree that it's overkill but if it's just lying around then that may not matter so much. Manipulating stuff like this is not easy so although I wouldn't use a reef knot it is relatively easy to tie and with a couple of half hitches probably safe enough. The difference between the real world and the theoretical one maybe?

Barry

I too have no experience of synthetic manilla, but I have seen and handled synthetic polypropylene hemp, 12 mm and 36 mm, and I thought they were both very soft and not at all like real hemp, so I assumed that synthetic manilla would differ from real manilla in the same way. Maybe edt71 can tell us how soft his rope really is.

The secured reef knot, is, as you say, probably safe enough, but I wouldn't use it. I'd use the Zeppelin bend instead.

When I first mentioned the double harness bend, I was trying to come up with something as easy to tie as their old bend, but more secure. And it would have been too, if they would only have used stiffer, braided lines. Now it looks like Dan Lehman's double lapp bend is the strongest contender so far.
"Simplicity is the ultimate sophistication" - Leonardo da Vinci

edt71

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Re: square knot or double sheet bend?
« Reply #22 on: October 29, 2014, 12:38:12 PM »
Sorry guys but I think I may have been incorrect on the size of the rope. It may be in the size of 5/8 of an inch. ( I havent asked anyone or measured it yet...and no one seems to know besides management) Im not sure what the rope is really called, so doing a search on the internet comes up with something they call "pro-manila" 3 strand (looks exactly like the rope we use)

Truthfully I dont like the rope. Once its cut, the strands easily unwound apart after some use and just gets real messy. So alot of the guys will simply put tape on the rope then cut it to keep the ends tight. Its not like some of the other synthetic rope where it can be real slippery as it does have some grip. The only reason I can guess why the company uses it, is probably due to its tensile strength compared to regular manila rope which shrinks or rots.

Im not sure what is meant by how hard or soft a rope is? Are we talking about its flexibility? If such is the case, then its not too hard. Easily bendable and when tying applications, (as one of the the more experienced riggers had mentioned to me) they always leave a foot of end line in case of slippage.

I forgot to mention that the yard also uses another type of rope. A synthetic strap rope that is fire retardant they call "white lightning". Its shaped more like a flat looking ribbon type and is also used around the yard for smaller applications. (such as hanging lines or electrical boxes within areas of the ship when its under repair) You can usually find a spool of the stuff on many of the forklifts for tying down smaller items onto pallets. Since its flat shaped, knots are much easier to tie and they dont slip much.

However, since many have used the "white lightning" for applications not specified for its tensile (probably because its so much easier to obtain than the proper rope sizes) Our shop now tries to encourage the use of the larger size synthetic manila just to be sure.


Dan_Lehman

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Re: square knot or double sheet bend?
« Reply #23 on: October 30, 2014, 05:46:24 AM »
On what basis are your assertions made?!
(One could say much the same re the squaREef
which is their currently used end-2-end knot.)

Yes, I guess it is true even for the reef knot, but there are more twists in the double harness bend, so the shortcomings of a wrong-way start get more pronounced.

The basis: When I learned that edt71 used laid rope, I tried it out with 8 mm, three-strand, soft, laid polypropylene, and the knot slipped open just from the pull of my hands
...
 One thing is that it seems to me that it's perfectly safe in stuff like stiff, braided line or wire, no matter how you tie it, but for soft, laid line I can only recommend one of the totally eight variants that are possible (or four variants if we exclude the variants with tails going in opposite directions).

Twine
Hmmm, you might have this backwards : that
in fact the softer (more flexible) rope should be
more secure --if set snugly--, and that the stiff
stuff while secure seeming initially could slip at
high loads as the stiffness has prevented the knot
from drawing up fully (and while at lower loads
the stiffness is sufficient to resist the bending
that will spill the knot, when "push comes to shove"
at high loads, the openness & spilling vulnerability
will be manifest!?  (perhaps?)
(How slick was your PP?  --slicker I'd think would
be surer, in this case.)

In any case, I haven't suspected the harness bend
of any form to be unable to be set well and hold,
in common materials.  (But everything seems suspect
in that HMPE stuff EStar was testing!  :o   :P  )


:)