Author Topic: Examining slippage of bends: Lapp, Sheet, Double Sheet, Simple Simon Under  (Read 5432 times)

Seaworthy

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I am testing out the following simple bends for slippage amount:

Lapp bend
Double Lapp bend version 1 (Don called this the jammable version)
Double Lapp bend version 2
Single sheet bend
Double sheet bend #1434
Double sheet bend #488
Asher's Simple Simon Under


Knowing how much a bend can slip before it sets is very useful information, if only to tell us how long a tail we need to leave.

This is dependent not just on the particular bend, but on the material and diameter/diameters selected for the line. My particular interest is finding the best simple bend when double braided polyester lines are used and are different in diameter. 

Note: The amount of initial slipping does not necessarily tell us anything about knot strength. A knot could slip substantially before it bites well.

My testing resources are unfortunately limited so this is just very preliminary work, but not much information currently seems to be available and curiosity has got the better of me.

As a side issue, I will also comment later on how easy I found the bends to undo after the load was applied (surprising results).

I will copy a few posts over from the other thread to fill in what prompted all of this. I have done one test on each today so I will then post photos of the 7 bends dressed and then after load has been applied (may be slow as internet is weak).
« Last Edit: June 21, 2014, 08:38:04 PM by Seaworthy »

Seaworthy

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I am querying how the double sheet bend is best tied. I think it is possible that the current method that seems to be commonly taught is not the best one.

All diagrams I have come across show ABOK #1434 and give the description of tucking the tail under the first loop over (ie tying a single sheet bend first) before proceeding to loop the tail around the bight a second time and tucking it under again.

When tying any knot, I try and snug it down so it sets neatly and slippage is avoided. For years I have given the first turn of the standard Double Sheet Bend (ABOK #1434) a bit of a push to do this. I have assumed that when the knot is under load it would often slip into this position naturally anyway (wrong assumption by the way). If it did not, I think the knot would not grip as well.
What I end up with is ABOK #488.

Ashley called both of these a Double Sheet Bend.

At some point I started tying the DSB differently so that this push was not needed to get from #1434 to #488. I do not tie a single sheet bend first, instead I make the second turn away from the apex of the bight before bringing the tail under both turns.

I could only perform a highly unscientific trial (unknown variable force with few tests, please don't crucify me for my rough and ready methods) tightening up the knot by tying one end on a cleat and winching the other end, but my longstanding impressions about the 2 versions look to be possibly correct.

#1434 seems much worse, as in my trials there was always considerable slippage of both lines. I was hesitant to apply any more force to see if the slippage eventually stopped.

It was suggested on Cruisers Forum that the slippage was occurring as I had not tightened the knot before putting load on it. The problem was that with older salty stiffer line, the knot instantly loosened as I let go and a tight fit was not achievable.

So my big questions are:
"Is #488 a better version of the double sheet bend than #1434, which is currently in use?"
and
"If so, why is the worse version taught everywhere or illustrated as the version to use (as in all books I have seen and even in this guilds section on knots for Sea Cadets)?"

Seaworthy

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This post prompted me to check out the Lapp bend (or knot as it is also referred to):

Referring to the double sheet bend, Don Lehman recently made this interesting comment that caught my attention. I had not come across the Lapp knot previously:

Discard them both!
Try this similar knot, intead:
looking at #488, follow the path of the
thinner (hitching) line from the tail
through the knot --it reaches across the
bight (not through it),
turns around it fully,
then turns around again but is tucked through
the bight.
So, with this vision, tie $488 in reverse
(tails are SParts & vice versa --which keeps the
"same side" relationship (tail & tail, SPart & SPart)).
BUT on both turns around the bight, tuck the
working end (of thinner line, in your example)
through the bight (otherwise, you'll have a jamming
knot!).  You might even make another turn,
and the tail can be further tucked out through
its own initial turn around the bight.
(If the diameters are much different, this becomes
problematic to secure, as the large-roped bight will
see too much space for the small hitching line to
be nipped.)

Consider this an extension of the Lapp bend
which itself is the (same-side) SB reversed.

Seaworthy

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I had a particular request for testing the slippage of the Simple Simon Under, so will also test this out again later using new line and perhaps also using a thinner diameter, comparing that to the best performer of the other six bends:

Hi Seaworthy,
That was an interesting thread.
Maybe you already know Asher's Simple Simon Under.
Here it is ; a loose an a dressed version.
Are you able (time, interest) to test it with your gear?
I would love to know it's behavior vs the Double sheet bend. (slipping, jamming)
ths.

Seaworthy

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So these are the nitty gritty details. Skip this if all you are interested in are the results later:

Equipment used:
Two speed manual Lewmar 54 self tailing sheet winch
Old double braided polyester 16 mm and 10 mm (sailors very rarely use new line, so this is useful information for us).
Calipers
Camera

Measurements taken:
18 were taken for each test:
- To judge the amount of stretch in the thinner line (and therefore get a rough idea of the load applied) three sets each of the length of the line between two points was measured before and under the final load applied
- Three sets each of the length of the tail of each line before and after.

Method:
- A loop was tied in the middle of the thinner line so that I could throw it around the drum of a nearby winch. Initially a midline bowline was used, but that seemed to need care so that it did not elongate too much under load, so I switched to an Alpine Butterfly loop (grrrrrrr, more about that later)
- Bends were tied and dressed and photographed
- The lines were transferred to the winch with 4 turns of the thicker line around the winch (within half a metre of the location they were tied), but the lines left slack and the bend tightened as carefully and as much as I physically could
- I took measurements as described above
- Load was slowly applied by turning the handle on the higher gear. I continued to turn the handle until no further movement was possible (two hands)
- the length between the chosen two points on the standing line was measured 3 times again, the load removed and the length of the tails measured.

I plan to do at least 3 lots of measurements, 5 if enthusiasm persists.

If anyone can see any improvements I can make in technique, please let me know. Too late to change for this trial, but if I do any more it will help.
« Last Edit: June 21, 2014, 04:57:07 PM by Seaworthy »

Seaworthy

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Lapp bend (knot) before and after load applied:

Seaworthy

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Double Lapp bend version 1 (Don Lehman called this the "jammable version"):

Only a photo on the winch after load is applied is available from this trial, the first photo is the one I posted previously:

Seaworthy

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Double Lapp bend version 2 (supposedly able to be untied) before and after load was applied:

Seaworthy

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Sheet bend (single) before and after load applied:

Seaworthy

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Double sheet bend #1434 before load applied (forgot to take one after, will pist this after the next trial):

Seaworthy

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Double sheet bend #488 before and after load applied:

Seaworthy

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Asher's Simple Simon Under before and after load applied:

Seaworthy

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For those of you reading this with bated breathe waiting for the results, this is how it stands after the first lot of trials on each bend:

First place : Ashers' Simple Simon Under bend and the Double sheet bend #488 neck and neck

Third place: Double Lapp bend version 2 (supposedly able to be untied)

Fourth and fifth place: Double sheet bend #1434 and Double Lapp bend version 1 (supposedly not able to be untied) are pretty close

Sixth place: Sheet bend (single)

Seventh place: Lapp bend (single), but close to the Sheet bend

Well, so much about my long waffle in the other thread about how good the Lapp looked :).
It will be interesting if results are reproducible.

« Last Edit: June 22, 2014, 09:26:18 AM by Seaworthy »

enhaut

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Thanks for the effort Seaworthy,
Looking for the conclusion of your study.
Glad to see Simple Simon Under in the lead for now :o