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farmer's hitch

PostPosted: Apr 19, 2012 3:01 pm
by ek
I was recently asked about the farmer's hitch in caving. Scattered around the web are claims that it is an acceptable knot for caving. I replied that I'm not familiar with it, and, when shown it, I replied that I couldn't see any advantage it would give over the alpine butterfly.

One of the websites claiming that the farmer's hitch is acceptable for caving is this. Please note that I am not endorsing that page--it contains some misleading and downright inaccurate advice about some of the other knots which I do know about. I think this page might be the source (cited or not) of most Internet claims that the farmer's hitch is suitable for caving use.

Does anyone know if there is reason to think knot is safe for caving use? In particular, does anyone know if it has been established as safe through extensive use and/or laboratory testing?

Also, does anyone know if there is any reason to prefer it over the alpine butterfly? The alpine butterfly is one of the more complex knots that cavers learn to tie...but the farmer's hitch looks even more complicated.

Re: farmer's hitch

PostPosted: Apr 19, 2012 3:23 pm
by Stridergdm
Better question might be, "what about it would make it unsafe?"

(I may have to get some rope out later and see if I can make sense of the diagram and tie it a few times.)

Re: farmer's hitch

PostPosted: Apr 19, 2012 3:45 pm
by ek
Good question.

Even though we don't generally need to look at knot strength figures to choose between approved knots in a particular application, it is still possible to have a knot that should never be used because it is so weak. (I believe that the double-loop and directional/inline figure-nines--unlike the regular figure-nine--are examples of this.) For all I know, this might apply to the farmer's hitch. After all, it does seem to have a remarkably sharper bend in it than is found in most knots. (That doesn't necessarily make it unsafe. My understanding is that knot strength is determined much more by how much the rope is compressed in the knot than by how sharp a bend it goes around...though those factors may interrelate.)

Besides that, if it were found to be prone to slipping, or if it were found to be tied incorrectly a significant percentage of the time due to complexity, or if it were extremely difficult to inspect for correctness, these are all factors that could contribute to it being evaluated as unsafe for caving use.

I am not claiming any of these negative things about the farmer's hitch. I am asking about them, though.

[Edited to fix minor spelling error.]

Re: farmer's hitch

PostPosted: Apr 19, 2012 3:52 pm
by Phil Winkler
I just tried it several times and I like it! Fast and easily done.

I often find myself needing to tie a loop in a fixed line when tying something down in a trailer or on a boat and this works a dandy and is quite easy to untie even after being loaded quite heavily.

Re: farmer's hitch

PostPosted: Apr 19, 2012 3:58 pm
by Scott McCrea
Maybe I'm doing it wrong, but I can't get the knot to end up symmetrical. There is a wad of rope on one side. It looks a messy butterfly. I don't see any benefit over a butterfly. Do you?

Re: farmer's hitch

PostPosted: Apr 19, 2012 4:01 pm
by NZcaver
Curious. I can't recall ever seeing or hearing about this one. New mission for you, Eliah. Thoroughly test it, and report back. :big grin:

ek is still possible to have a knot that should never be used because it is so weak. (I believe that the double-loop and directional/inline figure-nines--unlike the regular figure-nine--are examples of this.)

I agree there are knots which are inappropriate and/or unsafe for certain applications, and I also don't know if this applies to your Farmer's hitch or not. I assume if it does the same job as a Butterfly but is slightly more difficult to tie, it would rate as little more than a curio knot to me. [Edit] Just saw Phil's reply which looks encouraging. Will have to play with this.

I am puzzled about one thing though - why would you think a double-loop figure 9 (not inline) should never be used because it is so weak? Do you have data on that?

Re: farmer's hitch

PostPosted: Apr 19, 2012 5:33 pm
by Stridergdm
I'm curious too (about data on the inline Figure-9).

I'd say in general, if you're worrying about knot strength in your system, you've probably got other issues. ;-)

It dawns on me, I wonder if this is the knot I've heard some people call a "false-butterfly". None of them were able to show it to me though.

Re: farmer's hitch

PostPosted: Apr 19, 2012 9:49 pm
by ek
Unless there is more than one knot that people call the false butterfly, the farmer's hitch is not the same as the false butterfly.

I have seen the farmer's hitch tied, and I am able to tie the false butterfly (as the term "false butterfly" is used in Alpine Caving Techniques). They are not the same. The false butterfly slips quite a bit, which in caving use is its purpose. While I have heard of people using the false butterfly as a rigging knot, I don't know of any reason to recommend it for that. Unlike the butterfly (a.k.a. alpine butterfly), the false butterfly will slip enough under load to--supposedly--absorb energy. Alpine Caving Techniques recommends the false butterfly for the bottom of rebelay loops when either (1) the rebelay is very close to the anchor above, so its failure could produce high fall forces or (2) very thin ropes (8 mm, or even 7mm) are being used, which potentially would not tolerate the impact of a rebelay failure very well (maybe because they could be cut against an edge).

According to Phil Winkler's post, the farmer's hitch doesn't slip. Whereas the false butterfly has slipping as its most important property.

The alpine butterfly is typically very easy to untie after it is loaded on each side of the loop, but very hard to untie after the loop is loaded. Were you able to tell if the farmer's hitch is easy to untie even when the loop is loaded, as by a caver climbing on ascenders? (I suppose I can pretty easily test this myself...though I won't get a chance to do so for another several days.)

@Stridergdm, NZCaver
I'll try to get you a citation for the claim that the inline/directional figure nine and double-loop figure nine knots are so weak as to be dangerous to use in rigging.

Re: farmer's hitch

PostPosted: Apr 19, 2012 10:14 pm
by ek
At the risk of getting off the topic of the farmer's hitch, here's the text from Life on a Line, 2nd Edition by Dave Merchant (page 43), claiming that the inline/directional and double-loop figure nines are too weak to use:
A Directional Figure-9 exists, as shown in the photo, but is not to be used. Contrary to common sense, it’s weaker than a Directional Figure-8 when end-to-end shock-loaded - the problem is that the emerging rope (heading left in the photo) doesn’t follow the entire pattern, and just bends around one turn as it leaves. Combined with the extra slip inside a Figure-9, this makes a rope-on-rope rub point at the worst position. The loop of the knot is fine, it’s what it does to the straight-through strength of the rope that’s the dangerous bit, and if the loop itself isn’t loaded first the knot can be damaged by a severe shock load.

Also in the same “nice but deadly” camp is the Double Figure-9 (the Bunny-9). You’ve probably never seen one, but it exists (and here’s a photo!). As with the Directional knot, it’s impossible to make the inter-loop turn of rope follow the pattern of the knot, and it creates a very slippy rope-on-rope rub point. The Bunny-9 under a careful, equal load is the same strength as a Bunny-8, but if one loop is slack and the knot is shock-loaded, it can melt.
[color highlighting in original]

I don't know if those conclusions about the directional/inline and double-loop figure nine knots are the results of the knot testing Dave Merchant did. He did do extensive testing, and I do believe his book is an excellent resource overall. But if his reasoning about these knots is not based on actual rigorous testing, then I'm not sure we should believe him. After all, there are all sorts of ideas about knots based on some theory or other, that might not match up with reality. In particular, and as has been previously discussed here on Cavechat, Dave Merchant maintains that tying a figure-eight on a bight "backwards" reduces its strength by 10% and makes it considerably harder to untie after it is loaded. I have never seen any source to substantiate this idea, and Bruce Smith has published a refutation of this notion arguing from theoretical grounds.

If I find other sources for the idea that the inline/directional and double-loop figure nines are too weak to use, and I think they're probably not just restatements of Merchant's claims, I'll try to post them.

In the mean time, while I am not absolutely convinced that the inline/directional and double-loop figure nines are too weak to use, I see no compelling reason to think Merchant is wrong, and I don't intend to start using them or trusting rigging that uses them. (Fortunately, it doesn't seem like anybody ever uses them, which makes sense, since there is no reason to think they'd be in any way preferable to the inline/directional figure-eight and double-loop figure eight.)

Re: farmer's hitch

PostPosted: Apr 19, 2012 10:39 pm
by NZcaver
Thanks for following up, Eliah. I certainly learned something, though I'm a little skeptical about the assertions there.

I can't say I've ever used an inline 9, but I'm one of the apparent few who many years ago regularly used a double loop 9 in place of a figure 8 bight. Following the old advice of Warild's Vertical, the 9 was rated 'stronger' than the 8 and some of us felt double loops were always better than single. The knot always seemed a little easier to undo than the 8 too, and was especially preferred for thinner ropes and cords.

We now know Warild's old figures bear little relevance to results from the ropes we use today, and double loops are seldom a necessity for most uses. I'm not sure we ever pull tested the double loop 9, but I'll ask around. If the knot is properly dressed and the loops adjusted appropriately, I don't see why there would be critical amounts of nylon-on-nylon friction between the loops if the knot were to be shock loaded or slow-pull tested. And I certainly don't see how the result would differ greatly from the double loop 8.

As I recall, the single cord, double footloop arrangement on my frog system is 5.5mm Spectra tied with a double loop 9. Perhaps I should be afraid.

Re: farmer's hitch

PostPosted: Apr 19, 2012 10:41 pm
by ek
If you plan to take big falls on your Spectra footloop, I think you should be afraid. :tonguecheek:

Re: farmer's hitch

PostPosted: Apr 19, 2012 10:49 pm
by NZcaver
ek wrote:If you plan to take big falls on your Spectra footloop, I think you should be afraid. :tonguecheek:

I generally prefer other people take the fall instead of me. :shhh: :rofl:

Re: farmer's hitch

PostPosted: Apr 20, 2012 7:45 pm
by Stridergdm
Thanks for the follow up. I to question the reasoning on the double-9, etc. What little results I've seen from Anmar's rope pulling (which is highly non-scientific!) is that "there's a LOT of variables and it's hard to predict".

That said, I think there's a good reason to try to stick to a small standard group of knots and it has little to do with 10% here or there (because honestly, if your system relies on that extra 10% just to be safe, I might want to use someone else's system ;-)

The reason is, everyone in your party should be able to cleanly and clearly recognize the knots used. I hate walking up to a rigging point and looking at it and scratching my head and saying, "what the heck is that?"

Re: farmer's hitch

PostPosted: Apr 23, 2012 10:48 pm
by chh
Spent some time tying the farmer's hitch and the butterfly, which you can tie in a similar fashion, i.e. 3 coils over the hand. Butterfly is still faster for me, and easier to identify. Would I use the farmer's hitch? Sure. Would I CHOSE to use it in lieu of something else? Probably not.

Re: farmer's hitch

PostPosted: Apr 23, 2012 10:54 pm
by chh
Subsequently, as a sticking point, I call the butterfly knot the butterfly knot. Whereas the "alpine" butterfly is when the loop of the butterfly captures a rope join of some kind. Don't know if that's correct or not. Also, don't really care. My wife calls the butterfly the "alpine butterfly", or sometimes the "alpine moth" but I think this is mostly because she is enamoured of the word "alpine" and likes to use it whenever possible. :laughing: