I am probably a liar, and this is not a Practical Knot.

[xarax]

This knot is the only double loop I know that is both symmetric and has loops that don't communicate.  Still, I can't think of an application in which I'd prefer this knot over some other double loop knots I know.  If someone knows of an application, please share so we can discuss, thanks.

 I have thought of this loop only after a quarrel with knot4u, about the Karash bowline-like loop, in the "theoretical"   discussion about the bowline. As a sailor, there is only one thing I really fear while at sea : a man falling overboard. In such a case, which has never happened to my boat - and I almost "pray" not to happen ever - a double loop, tied on spot and quickly, might be of some help. Learning how to tie a simple double loop as a rescue harness, is a safety measure for the psychology, at least, of the inexperienced crew. I believe that this loop can serve this purpose sufficiently well, because, as I have said, it is the simplest possible double loop and the most easy to memorize - essentially just a double line overhand knot .
   See the video (1) for an application proposed for the Karash bowline-like loop. (1) Exactly the same thing can be tied with the even simpler double loop presented in this thread.

1) http://www.youtube.com/watch?v=6EyfYyJkZss

[xarax]

only now in gazing at these images does it occur to me that one can see this as the twin ends *pouring* material into a (horizontally oriented, here) twin piece (with bight ends) that then ties an overhand knot around the twin ends!

 The same loop was also presented by me some time ago, with an explicit reference to the fact that it might well be considered as the simplest possible double loop, as it is nothing more than a double-line overhand knot. I had even published two pictures showing this (see the attached pictures). I hope that each time somebody succeeds in getting me banned from the forum, somebody else will succeed in re-discovering something I have already said...    Peace on the Forum !   

[knot4u]

I have thought of this loop only after a quarrel with knot4u, about the Karash bowline-like loop, in the "theoretical"   discussion about the bowline. As a sailor, there is only one thing I really fear while at sea : a man falling overboard. In such a case, which has never happened to my boat - and I almost "pray" not to happen ever - a double loop, tied on spot and quickly, might be of some help. Learning how to tie a simple double loop as a rescue harness, is a safety measure for the psychology, at least, of the inexperienced crew. I believe that this loop can serve this purpose sufficiently well, because, as I have said, it is the simplest possible double loop and the most easy to memorize - essentially just a double line overhand knot.

You brought up life saving.  So, a full vetting of your assertion is in order.  I'm curious what others think about the Bipod being used as a quickly tied rescue harness in comparison to other double loops.

In theory, the Bipod appears like I should be able to tie it quickly.  However, in practice, it's not a quick tie compared to other double loops like the Butterfly Double Loop or the Karash Double Loop.  Thus, the Bipod does not come to mind when I think about tying a double loop "on spot and quickly".

Also, as others have noted above, the Bipod may require securing the working end to the standing end in order for the Bipod to work properly.  This addition places the Bipod in the complex category and, of course, increases tying time.

[xarax]

You brought up life saving.

   I would better describe the original idea as : "What is the most simple, most easily memorizable double loop, that can be taught to an un-experienced crew, tied easily and quickly, and offer some psychological - mainly - feeling of security ? Because, real life saving, and real security on board of a ship, is a greatly bigger issue, and I  am not qualified at all to offer any advice on it... 

   However, in practice, it's not a quick tie compared to other double loops like the Butterfly Double Loop or the Karash Double Loop.

  I guess it depends on tying experience and dexterity. I have not tied the double loops you mention so many times, as the one described here, to be able to compare the tying times of all those loops objectively. Also, and that is the most important point, I think that, conceptually, this "double-line overhand knot based loop' is simpler than either the Alpine butterfly or the Karash double loops.
   For the Karash bowline-like loop, which, of course, is a very secure knot, I have observed that, 1,  it may happen  to pull the wrong segment of the double eight knot by mistake, and, 2,  after the pull, the knot does need some careful dressing, to be set properly. The Alpine butterfly double loop is easy to tie with a number of different techniques, but it is not that simple : The inexperienced tier can learn one method by heart, but, as he can not follow the paths of the ropes inside the knot s nub, he can not have a simple mental picture of the knot, so he will probably forgetthe method after a while.
   On the contrary, with this simple double loop we are talking about, once one understands the main concept, gets the "double-line overhand knot" mental picture of the loop, he would probably remember it for a longer time, and it would be easier for him to tie it under stress, in a short notice. That is nothing else than my 2 pence opinion, of course, I can not prove it ! Only experienced. long time rescue teachers could possibly say something we could depend upon here...

Also, as others have noted above, the original knot may require securing the working end to the standing end in order for the knot to work properly.  This addition places the knot in the complex category and, of course, increases tying time.

1st. With marine ropes, a further connection of  the two ends together, is seldom necessary. I do not tie this connection - but perhaps I will, if I will have enough time at those crucial moments...The original loop would probably be deformed a little, under heavy loading, but it will not slip altogether !   
2nd. As you have noticed in the video I am referring to, to tie the complete rescue harness, one has to tie an additional knot,  even in the case of the Karash bowline-like loop.

[certainlysyrup]

Isn't this a three-part crown?

http://www.Layhands.com/Knots/Knots_DoubleLoops.htm#TripleCrown

[xarax]

Isn't this a three-part crown?

  It looks like a three-part crown, ABoK#1097, indeed. Tie both those double loops, and see their front and their back side, to notice their differences.