I’m pretty sure I’ve invented/discovered a new bend. I’ve scoured all the online knot-tying resources I could find without seeing anything resembling what I created, but I’d like to appeal to the collective expertise of the IGKT community. Has anyone come across this before? If it’s new, I’m calling it the “Ren Bend.”
I’ve been thinking a lot about what contributes to a knot’s efficiency (percentage of MBS retained) and wanted to develop a bend that minimizes strength loss. I know the primary reduction in strength comes from narrow bend radii at points of high stress. Looking at knots known for retaining high percentages of MBS — like the Blood Knot and the Berkley Braid Knot — I noticed they share characteristics with friction hitches (aka slide-and-grip hitches): plentiful wraps that constrict and maximize friction on the loaded strand. Applying this insight, along with my knowledge of various friction hitches, I tested numerous ideas and settled on this knot, which maximizes friction on the loaded strand while minimizing bending where the rope is under higher stress.
Counterintuitively, a truly symmetrical version (both strands with identical wraps) causes both tails to tuck through the center in the same direction. You can modify this by giving one tail an extra half turn and tucking it from the opposite side to create opposing friction—but in practice, once the knot is properly set (by pulling on both tails before loading), I haven’t observed any slippage, so I prefer the symmetrical form.
Setting the knot:
Pull both loaded strands in opposite directions,
then pull each tail and the other loaded strand.
This bend combines the advantages of a VT-style weave with the principles of a Blood Knot. The alternating weave applies lateral forces to the loaded strand—similar to a rappel rack or termination plate (also known for high MBS retention)—but thanks to the higher friction coefficient of most ropes (UHMWPE excepted), it achieves more friction with less deflection (i.e. a larger bend radius). Because the deflections alternate, the strands within the core can equalize, further reducing internal strain. By the time each end wraps back toward the center, most of the load has already been dissipated by friction, allowing the knot to carry more before failure. My hypothesis is that the combination of minimal bending at high-stress points and the high friction of multiple woven strands will yield an efficiency exceeding that of the Blood Knot.
I plan to do pull testing with a dynamometer and produce a video tutorial on tying the Ren Bend (I’ll post the pull-test videos too). But first, I’d love to know if anyone in IGKT has seen this knot written up anywhere before. Please let me know what you think!
After loading, it’s still fairly easy to untie. It doesn’t clamp around the tails too badly, and because it’s fairly long, you can flex it back and forth to loosen the center a bit. Once you get the tails pulled out of the middle, it loosens up everything else, and you can get the weave undone without much issue. It’s not as easy to untie as a something like a bowline, but maybe somewhere between a bowline and a figure-eight.
Let’s specify what sort of “loading” you’ve done
–per material(s) & force.
I will surmise that this knot so tied as shown
above will see the S.Parts pull straight and
put all turning into the remaining parts which
will clump up.
A Blood Knot names the angler’s one with a U-turn
and then wraps around both S.Parts to the tucking out
of Tails in the center point (do note : the sometimes
shown case where the S.Parts wrap going past each other
and have Tails make a long reach from the ends of the
knot back to tuck out in the center point is NOT what
anglers use, and a mistake re that (and one that in
heavier cord/rope might see the form roughly sustained,
with now dubious nipping of the Tails!),
or the Strangle knot, for its rumored use in tails
of whips to help draw blood.
Decades ago, I tried to fashion something along the
thinking given in this knot’s rationale :: to make
gradual deflections (yep, even like that term!) in
the S.Part before it faced the hard U-turn at knot’s
end. And I had it tested, tied in 1/4" laid nylon
(think “stretch”). Ironically --ya gotta chuckle–
the knot pulled S.Parts straight (perhaps with some
taking of force), and there was a quite blood-knot-like
1dia turn of S.Parts each end; BUT it was the strongest
of my tested knots, and decently so (70%?). But the
break can >>at, not IN<< the 1dia U-turn --i.e., of the
S.Part passing through that hard turn. This sort of break
is like that found for the Strangle noose-hitch, and for
the Grapevine/multiple-fisherman’s knot. Meanwhile,
Stanley BARNES found in nylon the break came in the
center of the knot, in one S.Part or the other,
passing around the tucked tails. !?
Seemingly not exactly the same, but a “blood knot” and “improved blood knot” does much the same thing, typically tied in fishing line if you are wondering about similar knots.
Yes, it is similar to the blood knot, in much the same way that a Zeppelin/Rosendahl is similar to a Hunter’s/Rigger’s. It’s similar in function and the initial tying steps, but decidedly different. Blood Knot, Surgeon’s Knot, and Ren Bend all start with the twisting of the two strands, but they are all finished differently. My hypothesis is that the additional friction caused by the lateral force of the alternating weave pattern will lead to higher efficiency than the blood knot. For something like fishing line, the added complexity of the Ren Bend might mean the Blood Knot is still the preferred choice. On the other hand, for something like making a loop out of accessory cord for a climbing anchor, or joining two climbing ropes together, The Ren Bend might be preferable to something like a Double Fisherman’s for both it’s MBS retention and it’s ease of untying.
I’ll be doing some break tests soon with 5mm accessory cord, so that should give us some data to look at.
Yes, with smaller cord, you are correct. I tried it with cheap 7-strand P-cord from the dollar store (it’s basically a sheath with almost nothing inside), and at >1kN the loaded strands did pull straight.
I would imagine something similar might happen to larger cord/rope at higher forces, but I have not had a chance to apply such high forces yet. I have a Ren Bend tied in some 7mm PMI Tuff-Cord that I have been cyclically loading at >1kN (the kids and I have been swinging/bouncing on it for days), and so far the form has remained stable.
I have noticed that as the form starts to compress, the bends in the loaded strand past the center point become more pronounced, thereby increasing the friction before the first U-turn. In theory, that means the force required to cause further deflection grows in a compounding (more-than-linear) fashion as the knot continues to compress. In a rigid cord or rope that resists flattening, the force needed to completely straighten the loaded strands could even exceed the rope’s MBS.
The only way to know for sure it to test it. I’m looking forward to applying some hydraulics to that 5mm accessory cord. This is the 5mm after cyclic loading of >1kN:
As noted above, no, the angler’s Blood Knot pulls together
without any attempt at friction gripping --that
“which maximizes friction on the loaded strand while
minimizing bending where the rope is under higher stress.”
Which itself can be a challenge to dress & set
even with identical ropes (e.g., making a round
sling), having to judge how much deflection is
needed --enough / too much–, AND to defeat what
might be called a “race condition” in which the
one joined end makes tighter nipping-gripping
on the other, thereby even differing in their
tensions, the latter choked from delivering
an equal tightening around the other.
But is pure strength figuring --for real-- in practical
uses? Note that in testing the Grapevine for strength
that often a round sling is formed, and the tester
presumes to attribute to the knot half the force
sustained; but in fact the knot’s material yield
via compression upon increasing force will give
imbalanced loading to the sling, movement on
the anchoring pin(s), and a break often NOT
in the knot but at the pin!
I just did some quick & dirty testing of the
knot in 6mm-ish kernmantle tied to a marie
diamond braid. Upon perhaps some 250# force
the knot was about 8" (20cm) in length; then
some further pulling on the line (i.e., pulling
outwards from the axis of tension --sweating)
reduced its span to 17" (17.5cm), S.Parts doing
some sliding through. Quite easily untied via
looseness/space at the tucked-Tails center
(but the nipping of them seemed decent).
Agreed, breaking force is not the be-all and end-all. I have seen quite a few break tests where the loop broke where it went over the carabiner/shackle/ring instead of the knot. Presumably, the internal stress from cord/rope going over a ~1 cm-diameter carabiner is greater than 50% of the force that the knot sees (in a loop, each side carries ~50% of the load, so the knot only sees half the load, whereas the carabiner sees 100%). If the knot reduces MBS to 50%, but the sharp bend over the carabiner reduces MBS to even 90%, then the rope is going to break at the carabiner because it sees twice the force of the knot, and the knot strength is irrelevant.
Knot strength is far more important when you don’t have a loop, like when joining two climbing ropes together. Yes, we assume large safety margins in climbing gear as our lives depend on stuff not breaking, so a 50% reduction in MBS is fine in most circumstances, but I could see some situations, like a rescue or hauling gear, where forces could potentially get multiplied, significantly reducing safety margins, and using something like a Ren Bend would be beneficial.
All that being said, if you are getting anywhere near 50% MBS on a double fisherman’s, you are never getting it untied, whereas I think a Ren Bend will be substantially easier to untie (with the added benefit of higher MBS retention).
Putting aside considerations of breaking strain and deformation under tension; does anyone dispute that this may be a new knot? It is clearly related to many fishing type knots, but to me it looks new. However I’m not the authority, the community here is.
This question sounds all too laudatory of “new”.
There are zillions of knots to be discovered,
and as I noted somewhere among these forums
some few of us have probably put into the record
over 3_000 “new” knots --to what benefit/purpose
might be questioned. (Well, I should qualify that
MY record is so far pretty private w/some few
sharings hither & yon.)
This knot I think probably hasn’t appeared in print
or e-print; perhaps some others have come up with it
or the like --and my note re “Blood Knot” and its
sometimes misreprentation as coils going outwards
shows a way goophs can yield “new”.
