I suspect that if such a minor change in form really produced a difference that mattered to the safety of the user, the knot would have been pulled from life support applications quite some time ago.
Roo: I agree that the (potential) slight difference in strength between a "weak" and "strong" fig. 8 knot does not really affect its use in life support applications (by trained experts with a proper design factor etc etc). Perhaps the "weak" version is 65% efficient, rather than 75%; both are adequate for the task. I do wonder what you mean by "pulled" from life support applications. Is there some governing authority on knot use that could do such a thing as stop all the people that currently use the fig.8 loop from using it?
is that they were just copying each other
Xarax, it is posible that there is a bit of "knot book echo chamber effect" going on here, but....
so many people were so much wrong
I don't think that ANY of these authors are "wrong" They all reported the facts as they knew them. Even on the point of contention, the different sources agree on more points than they disagree, and the disagreement is over a (relatively) small percentage. Each of these authors I cited touch upon the figure 8 loop (briefly) within the larger context of the greater work they authored, be it caving, SRT, rope rescue, or strength of rope. (ie they had bigger fish to fry)
It is interesting to me that we find this information about the fig 8 (potential) difference in strength in books and articles about fields where knots are used, but no book about knots mentions it (as far I yet know)
Also Xarax, I agree that the only way to (possibly) settle the matter would be destructive tests. I hope to be able to do them (someday... sooner rather than later I hope)
How about we say one might be a bit more right than the other?
Z: I suppose "strong" and "strong
er" versions of the figure 8 loop would be the most appropriate names, but perhaps a bit confusing. I'll stick to Dan Lehman's "weaker" and "stronger" monikers for the time being I think.
Speaking of Mr. Lehman
AMGA
who's that?
Lyon Equipment, doing contract work for the UK's HSE,
did test some version of my "strong/weak form" and
concluded that for the fig.8 it didn't matter
I'd love to see a copy of this testing, should anyone know where to find it.
Egadz, you're again going ambiguous :: please, people,
understand that there are TWO editions of On Rope;
Sorry about that. I'm not planning on buying the first edition just to find out what the differences are. And I don't usually cite which edition of the ABOK I have (for instance) but I take your point.
BUT NO NO NO :: Rob Chisnall clearly illustrates what
I call "the perfect form"...
whereas Merchant introduces another form...
Ok, to summarize what you're saying (i think): Chisnall and Merchant both assert that there is a 10% difference depending on if the standing part follows the outside or the inside "parallel" (giving a larger or stronger bend) but they show the fig 8 loop
dressed differently. I've attached two pictures of two of the most common dressings of the the fig loop (thanks Xarax, I stole them from your postings) [1] this dressing is what I've learned through multiple professional trainings, and I would say it is the consensus opinion, in my field, of the "best" way to dress a fig 8 loop. [2] this dressing is very similar, and I consider it adequate, if not perfect, and it is what Merchant shows in his
Life on a Line. So DL, is [1] your "perfect" form?
I have no evidence to support this, but IMO, one of the great qualities of the fig 8 loop, is that it is still secure, strong, and reliable, even if you haven't dressed it "perfectly". It had been my working assumption, that while different sources show different dressings, that these do not crucially affect knot strength and security. And that different authors showing a dressing other than [1] we're wrong (IMO) but not seriously, a difference of better vs best. Moreover, I had not considered the dressing of the knot as part of the question of the "weaker" vs the "stronger" forms. The crucial difference between the "weaker" and "stronger" forms (as asserted by Merchant and others) is which path the standing part takes in the knot, and the hypothesis is that the standing part taking the "outside" path yields a more gradual first bend in the knot, and thus a stronger knot.
Of course how you dress the fir 8 may effect strength as well, I suppose that's up for discussion.
IMO the best way to dress the fig 8 is [1], and I find that a commonly held assertion in my field.
(I think that Grog has this in
his on-line presentation, and with "strong form" loading)
Grog does indeed show this [1] dressing, with the "strong" form of loading here:
http://www.animatedknots.com/fig8follow/index.php?LogoImage=LogoGrog.jpg&Website=www.animatedknots.com#Figure8LoopCould a like-named article appearing in Off Belay
only a year later (nominally, by publication date)
be different?!
It's my working assumption that this is the same article, but I did order that issue of
Off Belay just to be sure
Heinz, I will hope, is yet reachable via snailmail
if no other way. (It's been a while since we've
exchanged correspondence --I'm way behind.)
I would be greatly interested in hearing Mr. Prohaska's views on the strong vs weak form of the figure 8 loop. Perhaps you could ask him on my behalf, or Private message me a way to reach him. Thank you
The website OnRope1.com asserts that there is no difference between the two versions [6]
And Bruce's notion there of "two versions" should be
pointed out as not likely matching either Chisnall's or Merchant's
I had assumed that OnRope1.com was connected to Bruce Smith, but wasn't certain. Here is what his website says on the topic:
Myth #6: A Figure 8 knot tied "backwards" is 10% weaker.
Truth: Absolutely incorrect. The second a load is applied to the 'outside' loop. It will be forced to the inside of the course the lines take as they trace the knot. All efforts to keep the load line at a greater radius will only result in the load line taking the path of the lesser radius.
after which is shows an incredibly unhelpful depiction of a figure 8 loop dressed flat, with no tail visible (good grief!) But what the text says is very interesting. That when tied in the "strong" form, and loaded, the standing part slips under the tail part, and finds the tighter radius bend regardless. I have seen this for myself as well! Both 'in the field' and in break testing, here is a link to a video of a break test:
http://tinyurl.com/ABKbreakingVideoThe figure 8, on the right, is tied in the "strong" form "perfectly" dressed, and you can see how the standing part behaves.
Another observation I've made of the "perfectly" dressed [1] knot is that the "inside" path appears to take a
wider bend than the outside path. It's not much of a difference, but you can see it on Grog's depiction fairly well. It's not apparent in Xarax's pictures [1] because I think the knot wasn't set as you would set a fig 8 loop (Xarax pics are clearly fig 8 bends). This difference is slight, but by the "wider radius bend" theory, the "weaker" form should perform better! Of course neither of the pictures show a heavily loaded 8 either, and I'm sure the behavior would change under extreme loading.
Ok, final thoughts (for today):
1) I can only really settle this issue of strength with break testing, which I'd like to do, but my break test rig is temporarily down
2) while the theory of why one form may be stronger than the other seems valid, I personally see inconsistencies in the application of the theory (ie does the "stronger" form really result in a wider radius bend in the standing part)
3) if there is a slight difference in strength, both forms are adequate and safe for life safety applications (when used appropriately by trained personnel of course)
4) despite that, it sure would be interesting (and possibly useful!) to know what the difference in strength is