"As I pondered weak and weary, upon a midnight dreary, over many a volume of quaint and forgotten lore"

I ran across Knot for Climbers, by Craig Luebben,(1993) a very decent reference. The square knot, backed up with a double fisherman's knot, is his preferred choice for joining two rappel ropes together(!, over a double fisherman's and a figure eight. Luebben is an excellent, experienced rock climber and his choices have worked well for him. So you guys are not going to die after all!

Just be careful out there (with any knot). I still have reservations about the square knot - it is real easy to tie improperly, especially if you are a bit tired. Luebben does repeat the information that a rope tied with a square knot retains 45% of its strength.

The double fishermans knots as backups would greatly add to the security of the square knot. I would say those would make it as secure as it would ever need to be. Without backup knots of some kind - whether they be double fishermans or simple overhand knots - the square knot is NOT secure.

But theses backup knots would NOT add to the STRENGH of the square knot one bit. Your climber person here has come up with a secure knot, I'll give him that. But why would he use a knot that is less strong than others (like just using a double fishermans as the bend in the first place)? With modern ropes, sure, having a square knot eat up half of the ropes original strength is adequate for rapelling. But why would one go to the trouble of tying a square knot, and then two double fishermans knots as backups when they could have just tied one double fishermans in the first place and come out with a stronger knot that is just as secure as the odd square knot contraption?

I'm not sure how you'd tie a double fishermans as a backup knot anyway, since you need both running ends of the ropes to tie this knot. The climber guy probably meant a double overhand knot rather than a double fishermans.

A picture is worth a 1000 words, so I will try and scan the illustration in the book - it is basically a double fisherman's with a square knot right in the middle. The stated advantage is that it is easier to untie compared to a double fisherman's, something that has not been a problem for me.

When I am rappelling on a double rope, I really, really want the joining knot to be secure. Even if it should be a bit tough to take apart, that is a trivial problem.

I will try to come up with a picture......

Even after my years in the Boy Scouts, I do everything to avoid even attempting a square knot. I must have severe knot dyslexia because I don't ever seem to get that one right.
I am a pretty fair hand at bowlines though, go figure...

Nice of you to say as much Hikermor. Mighty big of you.

Tying Swiss seats, the norm before the sewn seats were widely available, and a major step up from the venerable swami or bowline on a coil, uses a square knot for the final knot. It was backed by a half-hitch on each tail. It had been tied that way for roughly 80 years before I learned it.

Square knots are okay but they need to tied correctly, dressed, and backed up. Failure of any of those steps can be catastrophic. Square knots are good but you can't fudge it and get away with 'close enough'. It is one of those knots where it is either absolutely correct or an invitation to disaster.

For joining ropes in climbing I have shifted to a Flemish knot, essentially a back-fed figure eight. (Not to be confused with a double figure eight or, ominously named, the EDK.) The Flemish is robust, easy to tie and untie, and tolerant of both abuse and inexperience. Novices can easily handle a figure eight and back feeding the other line to match is intuitively obvious. Errors stand out so they can be corrected.

The current favorite with rescue workers for joining lines seems to be a fisherman's knot with three wraps on each end. It is a solid knot with a lot going for it.

1993; is a long time ago. Way outdated material.
Most climbers these days use a simple overhand knot. Yes a simple overhand knot with no back up just plenty of tail.
If you are rappelling one rope length it may not matter but if you have ever done multiple rappels down a cliff you know that any "mess" of extra knots is a surefire way to get them stuck when you pull them.
An overhand with a lot of tail will not come undone accidentally, you will have no trouble untying it and it is less likely to get stuck in a crack, tree etc.

For non climbers it may sound scary but it is proven ask any AMGA guide. I am sure Craig would agree.

As for rescue thing may vary but in an alpine environment the overhand is favored.

A lot of my rope work has been mountain and vertical rescue, including numerous victims of rappelling accidents. The record in Yosemite is that rappelling is as hazardous as lead climbing. A lot of details can, and have, tripped people up, usually with very bad results.

Remember square not strong,

Granny knot,, weak!!

(no offence to any grandmothers who read this post)

A backup to the overhand knot is a good idea. Single overhand
knot has been reported to fail.

Link with good picture.




http://www.psychovertical.com/?abseilknot

There is a slightly more comprehensive review of applicable knots:
http://www.needlesports.com/advice/abseilknots.htm

Scan down to comments and note that at least one person claims that the single overhand can slip. I worry about any knot that is only considered 'safe' when you leave long tails. IMO a knot that slips is one that will eventually give up. Which tells me that if you use an overhand you need to double it. Doubled you lose some of its apparent advantages.

I'm also bothered by the emphasis on a knot being easy to untie. It is a useful trait but in a survival situation if a knot welds shut I simply use this high-tech device known as a knife. If you don't simply butcher outside the entire knot you less than a foot of one of the ropes. The ends, where you tying and untying all the time, wear out so trimming back a little is good. Sailors do this sort of trimming as a matter of course. Ropes are expendable and sailor use it without getting romantically involved like climbers seem to.

If you scan down to the Bushwalkers wilderness Rescue Squad the correct link is:
http://www.bwrs.org.au/?q=research

The PDF "Preferred Knots for Use in Canyons" is quite good.

IMHO it backs my opinion that there are several choices that are good. The Fisherman's knot and "Rethreaded
Figure 8", what I know as a Flemish bend slip least are strongest and are otherwise sound. They catch edges more than the double-overhand but in rescue and survival use this is less a concern. Florida is pretty flat and on shorter climbs simply whipping the line slightly clears most snags. Everyone has to make their own choices.