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majid_sabet
Jul 3, 2008, 3:51 PM
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Great work aric
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adatesman
Jul 3, 2008, 4:05 PM
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Roasta
Jul 3, 2008, 4:09 PM
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Nice work Aric.
Interesting that the blue line commonly broke more than the red?? Maybe the nephew liked chewing on blue ;-)
Does the test rig 'pull' in a linear fashion or do you load - stop - increase load - stop etc etc?
Looking at the threads - would you say there was about an inch of slippage/lengthening of the knot prior to failure?
I would be interested to see what the 9/16 would break at in an end to end test with overhand or fig 8 knots at each end. Rabbit runner style - spoke with a guy recently that liked using 9/16 in this fashion, I believe it to be too weak a configuration myself. Theory would suggest breakage at about 1600-1700 lbf.
Nice work.
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adatesman
Jul 3, 2008, 4:23 PM
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majid_sabet
Jul 3, 2008, 4:34 PM
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aric
can you do a test on square knot. some fire rescue services use webbings to build harnesses in SOL situation and they use square knot to tie the ends. even due there are backups after the square knot but still ,the main core is a square knot.
Thanks
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Arrogant_Bastard
Jul 3, 2008, 5:43 PM
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I can't say I've ever tied a 2X Fisherman in webbing, but it looks slightly different than how they look in cordage -- mine anyway. The way the retuck slides between the wraps, and then finishes with an extra tuck under the start of the wrap. I can't tell, perhaps it's just because of using webbing?
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adatesman
Jul 3, 2008, 6:55 PM
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Arrogant_Bastard
Jul 3, 2008, 7:58 PM
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adatesman wrote: Yeah, it looks a bit goofy in webbing since its so wide and can slide over itself. There's also 2 options for the last tuck... I rather arbitrarily chose to put the last tuck on the same side as the webbing started on because I thought it would dress nicer. Alternatively you could twist it around the other side. I don't know if one would be stronger than the other and I'm out of webbing, so maybe I'll give it a try (and MS's square knot as well) when I get home. -a.
Yeah, I think that's the difference, I'm used to twisting it an extra half loop around the other side.
Regardless, interesting data. Nicely done.
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knudenoggin
Jul 8, 2008, 7:39 PM
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Hooooorayyy!!!!!, finally we get to SEE test specimens, and some novel
items among them, instead of some mere quote of force values!
I have some comments on these tests, which are a nice start, but just that.
1. re color of broken tape: that shows tape from one batch/spool breaking
more than another; it MIGHT show something re color, additionally.
--good eye!
2. My Symmetrice Water Knot: ... wasn't all so symmetrically dressed, judging
from the pics. At the bottom (as oriented here) of the knot, the red/blue tapes
should be completely UNoverlapped; but at the top, one or other should nearly
cover the other--it is in this way that each tape shifts from lying exterior
(which was what was conjectured enabled cyclical slippage) to go interior
and be locked (in theoretical hope).
The resulting knot thus is more "thin", longer along the axis of tension, and
less bulky laterally, than the common Water Knot in tape; and, my guess
was that it might be a little weaker--but that seems not really the case.
(A corresponding loopknot exists, and can be tied-in-the-bight [g-h-t].)
We should note that this knot is less easily formed as tape's dimensions go
less flat, such as is the case w/9/16" and "dental floss" HMPE tapes.
3. Note that the Grapevine breaks the material as it enters through the tight
turn, NOT within that hard turn!? --similar results were seen for the "half
a Grapevine" (better: "Strangle knot") noose hitch used by cavers/arborists.
Soooo, in response to Aric's pertinent point about various placements of the
ends in this knot,--to wit:
adatesman wrote: Yeah, it looks a bit goofy in webbing since its so wide and can slide over itself. There's also 2 options for the last tuck... I rather arbitrarily chose to put the last tuck on the same side as the webbing started on because I thought it would dress nicer. Alternatively you could twist it around the other side. I don't know if one would be stronger than the other
of a protective padding against the tight nip of the opposing SPart.
And it would also be interesting to see what effect reorienting the Dbl.Overhand
knot from a Strangle into an Anchor Bend had, as this would make the SParts
wrap fully before u-turning at knot ends, and so might lessen the tight
constriction at the entry point (though bulk rather oddly, otherwise).
--noting that, to such musings for improvement, the breaks were already at
such high loads as to leave little to be desired!
(And I concur in Aric's guess that the rated strength isn't matched to what his
device reports--truly or nominally.)
4. In one specimen of the Water knot, note that although the blue tape broke,
on the companion knot the red tape is visibly breaking, and well inside of
the knot, where it makes a u-turn!?
5. On the more novel bends of mine, which fared not so well (lardbutts beware!),
the hope was to bend the tape completely flatly--i.e., w/o any sort of
warping. But I realized that this is only effected by wrapping around
the relatively soft material itself, and at high forces (push comes to shove),
things were probably going to get distorted.
HOWEVER, I hold the ace of this design goal close to the vest, and I'll need
to tie those knots myself, for starters, anyway.
--either w/A-supplied like tapes, or presumed compatible locally.
(What is the desired inner length of the specimen sling?)
Moreover, we've yet to explore sling-2-sling joints, and there are some
appealing ideas on that to be tested.
*kN*
ps: I concur in Majid's rec. for testing the SquaREef bend, as indeed it sees
use in tapes (one can easily wrap & tuck ends back through center of knot,
if slippage seems a problem).
pps: Geesh, Aric, MASON LINE qua marker bits???! Are you devoid of simple
thread (which sews in much more easily, surely)? That mason line can do some
actual decent work (whipping rope ends, e.g.). [;)
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knudenoggin
Jul 8, 2008, 7:55 PM
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In reply to: knudeNoggin's Double Water Knot [not!] Some data knudeNoggin has seen suggests that creep in the Water Knot happens mainly with the piece of material on the outside of the knot. By using two water knots it is possible to have both pieces of material inside the knot ...
Yes, verbally: but note that in fact your shown specimen is bassackwards
--the exterior part contains each end, rather than the interior.
Do Not Pass Go!
(You have it CORRECT at top, decorative image (short ends/SParts),
but note that it's reversed, alas, in actual tested material. The BLUE tape
should enter a BLUE knot and finish in a RED knot ('cause it finishes on the
INterior).)
One should not expect this double-knotted structure to be just like the regular
Water Knot, for each knot here is loaded on 1-vs-twin parts, not 1-v-1.
And in such cases, loopknots (essentially what is here, load-wise) are stronger
than corresponding bends.
In these actual test cases, both broke on blue, INterior strands, and
with nearly equal results;
had the double-knotted one been correct, there would've only been
EXterior (entry) strands at this point--stronger, at that alone?
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tradrenn
Jul 9, 2008, 6:56 PM
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This:
adatesman wrote: You know, I didn't even notice that the blue broke more frequently. Interesting.... Both of the spools that the webbing came off and both were labeled with the same strength rating. Plus with such a small sample size and variation in dressing its probably just how it ended up.
and that:
knudenoggin wrote: 1. re color of broken tape: that shows tape from one batch/spool breaking more than another; it MIGHT show something re color, additionally. --good eye!
got me thinking.
About the way it is set, so I have a question and a suggestion.
Are you (adatesman) having red webbing on a hook or something similar and pulling on a blue webbing ?
I would suggest that you reverse your set up and have a blue webbing on a hook and pull on a red webbing.
I think if you were to do that, you will see red webbing breaking more.
HTH
P.S. Thanks for doing all this, very good read.
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jeremy11
Jul 9, 2008, 7:05 PM
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Great work!
How about the figure 8 for webbing?
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jeremy11
Jul 9, 2008, 7:10 PM
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how about water knots with the tails sewn down? I've done this on a few items (cam slings) just to keep the tails from creeping
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adatesman
Jul 9, 2008, 8:24 PM
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shorty
Jul 9, 2008, 8:49 PM
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Thanks for doing the testing and reporting the results. IMO the 3-per-knot test is pretty valid (although a larger sample size would be a better), especially since you did not seeing a huge variation within each knot type. This is quite similar to some results I saw from Blue Water many moons ago.
This reaffirms my preferred knot use with webbing -- water knot if you want to untie the webbing at some future time, double fisherman if you don't.
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adatesman
Jul 9, 2008, 9:02 PM
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adatesman
Jul 9, 2008, 9:16 PM
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adatesman
Jul 9, 2008, 9:20 PM
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adatesman
Jul 9, 2008, 9:27 PM
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trenchdigger
Jul 9, 2008, 9:41 PM
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Out of curiosity... Are you rating % loss against the rated strength or the actual strength? Did you test the actual (unknotted) strength?
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ja1484
Jul 9, 2008, 10:38 PM
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Damn fine work. Looks like the 2fish is still the champion.
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knudenoggin
Jul 9, 2008, 10:41 PM
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As he indicates, RATED STRENGTH is the basis for the % values.
(How to measure its real strength, without big bollards?)
In reply to: knudeNoggin's Symmetric Water Knot ... I thought I matched your diagram, but its quite possible I goofed somewhere.
the "bottom" (long edge) of the knot that faces each other,
top & bottom knots: THERE one should see COMPLETELY
unoverlapped red beside blue tape parts; but in fact we see
the red mostly overlapping the blue (as it does even in the topmost
pic). This knot is to be (as its name suggests) SYMMETRIC!
(but this is a little fiddly dressing)
As for the revised Grapevine w/Anchor hitches, yeah, one
ties that hitch of each end 'round the other, with ends still
running away from knot center.
--tried this today, and unlike in rope, dang, the tape will overlap
itself and really defeat the wrapping-away aspect I'd hoped for;
but it's still worth a try.
Oh, and a like knot to try is the angling Blood Knot (bend).
Incidentally, is it the case that device's total force is yet
limited such that e.g. one might have trouble breaking
1" tubular tape? (double 2-ton loads)
Cheers,
*kN*
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trenchdigger
Jul 9, 2008, 10:53 PM
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With webbing, you shouldn't need that big of a bollard to create a tensionless hitch with no strength loss. Most sources claim 8-10 times the diameter of the rope as the minimum to prevent strength loss. With a half-inch rope that would be a 4" diameter object - like a steel pipe. Because of the construction of webbing, I'd presume you could get away with something much smaller than that to test webbing.
Nice work on this, guys. Keep it up.
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ja1484
Jul 9, 2008, 10:56 PM
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trenchdigger wrote: With webbing, you shouldn't need that big of a bollard to create a tensionless hitch with no strength loss. Most sources claim 8-10 times the diameter of the rope as the minimum to prevent strength loss. With a half-inch rope that would be a 4" diameter object - like a steel pipe. Because of the construction of webbing, I'd presume you could get away with something much smaller than that to test webbing. Nice work on this, guys. Keep it up.
My personal thoughts: Why bother with real strength when rated strength is already more than enough?
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