International Guild of Knot Tyers Forum

General => Practical Knots => Topic started by: dmacdd on July 25, 2010, 03:09:49 PM

Title: Lapp knot
Post by: dmacdd on July 25, 2010, 03:09:49 PM
What is the Lapp knot (a bend) good for?

A Lapp knot has the same structure as a sheet bend, but the roles of working end and standing part of the cord that wraps around the U cord are interchanged.

video here (45 seconds) : [1. Sorry, url now corrected]:

         http://www.youtube.com/watch?v=AF_8VKLo2W8

[2. Note added after the exchanges below: I believe the above video is either simply incorrect, or that it shows an extremely unreliable version of the Lapp knot. Contrary to the video, the two working ends must come out of the knot on the same side.]

I just load tested it in 1/16" / 1.6 mm nylon braid.  It slipped to failure under moderately heavy load.

It is very easy to tie quickly, whether slipped or unslipped.  A slipped Lapp knot is particularly easy to tie when the two working ends are too long for easy reeving through the knot.

So, a light duty bend?, especially for tying slipped with long ends?
Title: Re: Lapp knot
Post by: roo on July 25, 2010, 08:13:57 PM
video here: http://www.youtube.com/watch?v=6EyfYyJkZss
Better re-check your link.

Then again, wouldn't a clean, small, illustration suffice?  Is the attached image the form you have in mind?
Title: Re: Lapp knot
Post by: knot4u on July 25, 2010, 09:07:20 PM
What is the Lapp knot (a bend) good for?

A Lapp knot has the same structure as a sheet bend, but the roles of working end and standing part of the cord that wraps around the U cord are interchanged.

video here: http://www.youtube.com/watch?v=6EyfYyJkZss

I just load tested it in 1/16" / 1.6 mm nylon braid.  It slipped to failure under moderately heavy load.

It is very easy to tie quickly, whether slipped or unslipped.  A slipped Lapp knot is particularly easy to tie when the two working ends are too long for easy reeving through the knot.

So, a light duty bend?, especially for tying slipped with long ends?

Yeah, that link is for "New Rescue Knot, for Fire, Rescue, Mountaineers", which would be interesting if I could figure out all the knots he's tying.

Also, what do you mean by "slipped to failure".  That's a bad thing, right?
Title: Re: Lapp knot
Post by: dmacdd on July 25, 2010, 09:21:48 PM
What is the Lapp knot (a bend) good for?

A Lapp knot has the same structure as a sheet bend, but the roles of working end and standing part of the cord that wraps around the U cord are interchanged.


video here (45 seconds) : [Sorry, now corrected]

             http://www.youtube.com/watch?v=AF_8VKLo2W8
Quote
Also, what do you mean by "slipped to failure".  That's a bad thing, right?

A working end slipped progressively right out of the knot. Yes, it's a bad thing. But there can be useful applications for less than perfectly secure knots if they have other useful attributes.
Title: Re: Lapp knot
Post by: dmacdd on July 25, 2010, 09:30:13 PM

Better re-check your link.

Thanks. Sorry. I just modified the original post to correct the link error:

      (45 seconds):       http://www.youtube.com/watch?v=AF_8VKLo2W8

Quote
Then again, wouldn't a clean, small, illustration suffice?  Is the attached image the form you have in mind?

Yes, that's it,  but I couldn't find one. Did you make this one you posted?
(http://igkt.net/sm/index.php?action=dlattach;topic=1955.0;attach=1547;image)

I suppose I could have made a photo.
Title: Re: Lapp knot
Post by: dmacdd on July 25, 2010, 10:04:44 PM

Then again, wouldn't a clean, small, illustration suffice?  Is the attached image the form you have in mind?

Yes, that's it,  .... Did you make this one you posted?
(http://igkt.net/sm/index.php?action=dlattach;topic=1955.0;attach=1547;image)

Or is it? (Should it be?) The video shows the RH standing part coming out of the knot on the same side of the knot as the LH working end, which is consistent with the description of the Lapp Knot as having the structure of the sheet bend with the roles of the RH WE and SP exchanged.
Title: Re: Lapp knot
Post by: roo on July 25, 2010, 10:09:44 PM
Yes, that's it,  but I couldn't find one. Did you make this one you posted?
I just cropped and darkened an internet image.

I'm not a big fan of the Lapp Knot (either form).  Sometimes it holds OK, but then sometimes it settles a different way and allows the U shape to straighten and slip out, as you noted.  It's probably instructive to play with different rope types and combinations.

Another thing that makes me uneasy is that it's so close to the Sheet Bend that it may cause people to get muddled on their tying or recognition of the Sheet Bend if they become familiar with both knots.  

I'm not ruling out the possibility that someone may have some use for it, but I can live without it.
Title: Re: Lapp knot
Post by: dmacdd on July 25, 2010, 10:40:39 PM

Yes, that's it,  .... ?
(http://igkt.net/sm/index.php?action=dlattach;topic=1955.0;attach=1547;image)

Or is it? (Should it be?) The video shows the RH standing part coming out of the knot on the same side of the knot as the LH working end, which is consistent with the description of the Lapp Knot as having the structure of the sheet bend with the roles of the RH WE and SP exchanged.

I just tested the two configurations 4 times each, with 1/16" braided nylon, with startling results.

When tied as in the video, with the RH SP coming out of the knot on the same side as the LH WE, the knot is completely unreliable in my test rig. (Slips to failure every time.)

When tied as in the above diagram, with the RH SP coming out of the knot on the side opposite the LH WE, the knot is completely reliable in my test rig.  (And easy to untie after heavy load, by the way.)

This means that the Lapp knot should not be characterized (as perhaps no one but me ever did) as having the structure of the sheet bend with the roles of the RH WE and SP exchanged.

It also means that that video is hazardous.
Title: Re: Lapp knot
Post by: dmacdd on July 25, 2010, 11:02:18 PM
So, like the sheet bend, the two working ends (or the two standing parts) of a Lapp knot should come out of the the same side of the knot.   But it's much more important for the Lapp knot -- essential, in fact.
Title: Re: Lapp knot
Post by: dmacdd on July 25, 2010, 11:53:05 PM
Here's a (trivial)  application for the Lapp knot for which I will try the Lapp knot. I carry a shoulder bag with a long shoulder strap, because I like to carry the bag right down on my hip.  The strap is too long to use to suspend the bag from most chairs, and using it to tie the bag onto the chair is often not practical. The bag has no other built-in means of hanging it from a restaurant chair.  I keep an 24 inch length of cord cow-hitched to the strap anchor to fasten the bag to restaurant chairs.  Sometimes I need the whole length of the cord and sometimes not, depending on the structure of the restaurant chair.   The slipped Lapp knot seems to me to be a good knot to close the cord into a loop around a suitable part of the chair. It is very fast, and if tied slipped, which is entirely appropriate anyway for the application, nothing needs to be reeved through the knot if I only need, say, eight inches of the 24 inch cord -- wherever I need to grip the two WEs relative to their bitter ends to make the knot, I can tie the knot with equal convenience, (and always the same way) and this would be true no matter how long the WEs were.
Title: Re: Lapp knot
Post by: roo on July 26, 2010, 12:11:39 AM
When tied as in the above diagram, with the RH SP coming out of the knot on the side opposite the LH WE, the knot is completely reliable in my test rig.  (And easy to untie after heavy load, by the way.)
One form may be less stable than the other, but I have observed slippage in both forms, even when the correct side of the U is loaded.  The slippage doesn't always occur by the same mode, either.
Title: Re: Lapp knot
Post by: Dan_Lehman on July 26, 2010, 08:50:27 PM
What is the Lapp knot (a bend) good for?

Many things.  It's the base of a fine set of bight hitches (in which
category I include the Sheet bend, and maybe should include
the SquaREef knot(!).

Quote
A Lapp knot has the same structure as a sheet bend,
but the roles of working end and standing part of the cord that wraps around the U cord are interchanged.

Exactly -- and as was later remarked, it's the particular structure of
the same-side Sheet Bend : tails on same side.

The origins of being used by Lapplanders or other northern, icey-area folk
is that it was tied in leather *webbing*, we might say -- i.e., a relatively
rigid flat-cross-section material.  Consider the two loadings (Lapp v. Sheet)
in such material, and I think you'll prefer the former.  One can also try
nylon (etc.) woven webbing, but this unlike leather is compressible.
Still, it seems that cord hitched to a webbing bight is better when in
the Lapp vs. Sheet orientation.

Quote
Contrary to the video, the two working ends must come out of the knot on the same side.

YES, spot on.

Quote
I just load tested it in 1/16" / 1.6 mm nylon braid.  It slipped to failure under moderately heavy load.

Dang, you and that measly little cord again.  Even so, I'm not getting that result.
One needs to set the knot carefully, pulling on all ends and being esp. sensitive
to getting the hitching side (i.e. the non-bight (hitched to, you see) side) snug.
BUT, I won't argue in favor of its use in this form, even so (even though I think
it should be holding; I might be missing transformations in the geometry as
load peaks.  Again, this doesn't concern me for I use a variation, anyway, for
anything serious.

NB:  this Lapp orientation is that of a ring-loaded Bowline !  Which is
why the so-called (by Ashley and his echoes) "Left-handed Bowline" is more
secure in such loading.


I use the simple Lapp, w/slipped hitching-side tail, for a quick release knot,
sometimes -- as pulling the slip-tuck spills the knot completely free.


Now, the obvious variation(s):

1) make a turn around the two SParts with the hitching tail and 2nd tuck;
this anchors the structure to remove the dangerous slippage, as
the full turn will bear down on its SPart;

2) repeat this wrapping, and then tuck the hitching tail out under the
initial turn of the hitching SPart (so, parallel to the bight legs);
this becomes ineffective if the bight is much larger than the hitching
line, as the *ravine* between bight legs will be too *roomy* for
nipping the tail.

These knots have the beneficial characteristic of being secure-when-slack
unlike the Sheet bend -- nothing to sneeze at!

NB:  one can make the initial wraps around both bight legs,
but the knot will be difficult to untie; making the wraps around only
the bight's SPart (or, even if loading is in the dangerous-for-Lapp
orientation, then the tail) will allow for some hope of forcible
loosening
-- by pulling the bight tail to pry out some hitching-SPart
material, and enable further loosening.  YMMV with materials & load.

It also strikes me that the structure is more secure when joining two
ends than joining end to eye (what I've called a "closed bight"),
as if the bight legs have equal loading from the setting, the knot
doesn't seem to close (snug up) as securely -- something one can bias
in dressing/setting, to imbalance eye legs to sort of simulate an
end-2-end geometry.


.:.  The Double Lapp knot -- the best unsung new knot!

--dl*
====
Title: Re: Lapp knot
Post by: dmacdd on July 26, 2010, 09:53:17 PM
I have just further tested the Lapp knot and what I will call, for the nonce, the anti-Lapp knot  multiple times with my 1/16 inch 1.6 mm cord and my test rig (foot bar and dowel handle with rings and substantial  rope leads to shorten the test specimen).

The Lapp Knot:
(http://igkt.net/sm/index.php?action=dlattach;topic=1955.0;attach=1548;image)

The anti-Lapp knot is very similar except that the RH standing part comes out of the knot, contrary to the Lapp knot, on the same side of the knot as the LH working end.

In every case I

set the knot carefully, pulling on all ends and being esp. sensitive
to getting the hitching side (i.e. the non-bight (hitched to, you see) side) snug.

I tested the Lapp knot a further 10 times. In no test did it fail. In each test I exerted enough force to stretch the cord substantially, about 25%.  It did not slip _at all_ in any test. It was easy to untie every time.

I tested the anti-Lapp knot a further 8 times.  It slipped to failure every time in a load considerably less than I am able to exert with my test rig,  with relatively little stretching of the cord.

I believe these results condemn the anti-Lapp knot as unsuitable for a great many applications.

Title: Re: Lapp knot
Post by: roo on July 26, 2010, 10:50:06 PM
I believe these results condemn the anti-Lapp knot as unsuitable for a great many applications.
Another evil impostor scenario, although I think users should be cautioned not to expect a lot from the Lapp Knot anyway.  It's a step down in performance from the general utility Sheet Bend.

As an aside, it's good to properly set knots, as Dan mentions, but that does rapidly become more difficult as rope diameter increases.   
Title: Re: Lapp knot
Post by: roo on July 27, 2010, 03:48:53 AM
One attempted justification for using the Lapp Knot is using the slipped version as a quick release bend, as mentioned before.  Now, I can see not having end access to the rope for the knot on one side, since you may want to release it from a distance, possibly, but it seems unlikely for this to be the case on both sides.

In the likely event that we have end access for the future "U" shaped rope, then the slipped version of the Sheet Bend becomes an easy and familiar solution.

One way of doing this is tying and collapsing a Halter Hitch around the rope with end access to force it to assume that "U" shape.

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

Don't try this with the Siberian Hitch, by the way.  Anyway, other less gimmicky, more standard sheet bend/bowline methods with a draw loop would work as well.

P.S.  This can be done without any end access, as shown by the new image at the bottom of the Halter Hitch page, but at the cost of some simplicity.
Title: Re: Lapp knot
Post by: Dan_Lehman on July 27, 2010, 05:54:24 AM
I have just further tested the Lapp knot and what I will call, for the nonce, the anti-Lapp knot  multiple times with my 1/16 inch 1.6 mm cord and my test rig (foot bar and dowel handle with rings and substantial  rope leads to shorten the test specimen).

The Lapp Knot:
(http://igkt.net/sm/index.php?action=dlattach;topic=1955.0;attach=1548;image)

The anti-Lapp knot is very similar except that the RH standing part comes out of the knot, contrary to the Lapp knot, on the same side of the knot as the LH working end.

Whoa, this is an easy change to state :
the LH SPart is the upper strand instead of the lower
(and thus the two tails are on opposite sides).  The reader
can SEE this at once -- just loading the other end.  Your
words coerce a re-tying of the "RH" side to be seen.

As for Roo's limited vision on value, he should read my post to its end,
and realize the considerable value of the simple, "obvious" extensions
(neverminding whether someone has put them in a book or on-line
(well, they are on-line now)).  And lapp it up!

.:.  The Extended (or "Multiple") Lapp Bend -- the best of new knots!


--dl*
====
Title: Re: Lapp knot
Post by: roo on July 27, 2010, 03:03:29 PM
As for Roo's limited vision on value, he should read my post to its end,
and realize the considerable value of the simple, "obvious" extensions
(neverminding whether someone has put them in a book or on-line
(well, they are on-line now)).  And lapp it up!

.:.  The Extended (or "Multiple") Lapp Bend -- the best of new knots!

If the justification is some double version or versions (yet to be diagrammed) of the Lapp Knot, it had better have some very good justification beyond novelty or modest increase in security/stability.  Otherwise you'll end up unwittingly promoting the single version to a whole host of people who may not realize its problems.
Title: Re: Lapp knot
Post by: dmacdd on July 27, 2010, 03:33:15 PM
The Lapp Knot:
(http://igkt.net/sm/index.php?action=dlattach;topic=1955.0;attach=1548;image)

The anti-Lapp knot is very similar except that the RH standing part comes out of the knot, contrary to the Lapp knot, on the same side of the knot as the LH working end.

Whoa, this is an easy change to state :
the LH SPart is the upper strand instead of the lower
(and thus the two tails are on opposite sides).  The reader
can SEE this at once -- just loading the other end.  Your
words coerce a re-tying of the "RH" side to be seen.

I agree. My description of the anti-Lapp knot, while correct, was not as kind to the reader as yours above.   An alternative reformulation: "The anti-Lapp knot is similar, except that the horizontal U of the LH cord is turned upside down, so that the standing parts come out of the knot on opposite sides."

And a drawing or photograph would have been even better.  So see the attachment.