Sorry Oscar,
I really should not use TLA's (three letter acronyms).
USP is a marketing term -- Unique Sales Point -- it is also an acronym that is starting to take on a meaning all of its own, vis "that which is special about the subject".
As for the dressings. Your knot really tickled my interest, because, after discovering that it was simply a double cord slipped overhand with a twist, I realised that quite simply it should not be capable of doing what it was doing -- a slipped overhand should slip -- yet this little beastie had a definite ratchet built into it.
I first became interested in the mechanisms involved in knots gripping or slipping after having been introduced to the infamous Grief Knot AKA the Whatknot -- see roo-two's excellent site for details
http://www.geocities.com/roo_two/reefknot.html The Whatknot can either lock solid, or at the twist of the ends, it can flow like rope through a pulley. From this knot, I discovered that components within a knot can act either as a ratchet or as a cog, the ratchet locks movement while the cog encourages it. Tie this lovely example of knot mechanics for yourself and watch how one dressing sets the knot up with ratchets, while the alternative dressing creates two lovely cogs which run freely against one another.
When I come across a new knot, my first two exercises are usually to slacken out the knot in order to see the internal structures it contains, then to progressively 'deconstruct' it to seek alternative ways to tie it. Doing this you immediately see that the 'Lyndy' is based on a slipped overhand with an additional twist. This offered a simple way of tying the Lyndy 'in line'. The trouble was, that when I tied the Lyndy this way it did exactly what a slipped overhand should do -- IT SLIPPED. There must have been something special about the way you had tied it that I had missed which was conferring its ability to grip.
The Lyndy is 'in essence', four cores running parallel through the heart of the knot, surrounded by four gripping turns. On one side of the knot, two of the cores emerge as the two load lines and the other two connect to the 'adjuster' loop. On the opposite side of the knot, two of the cores connect to one of the load loops, the other two to the other load loop. Dressing the knot allows the connections of one side to the other to be varied and which is connected to what makes all the difference in functionality. Only two of the cores pass right through the knot connecting the adjuster loop to one side of each of the two load loops. The other two cores are fixed to the knot and cannot slide under load. When loaded, the four outer wraps are tensioned and squeeze the central cores and increases the friction between the cores and the wraps and between the cores themselves.
Consider for a moment the situation with only one of the cores being able to slide.
In this diagram, the grey ring represents the external wraps under load squeezing the four cores together. If B,C and D are fixed to the knot and cannot slide and 'A' is the only core that is free to slide, then you will see that it is firmly gripped on all three sides by surfaces that do not move. The surface contact of 'A' with the other cores and the ring is about 3.5 diameters and the Lyndy is about 4 diameters long, so we have a working frictional area of ca 14 diameters square. If 'A' and 'C' are connected to a load loop holding say 100 lb, then 50lb would be transfered by 'C' into the knot and 50lb would be applied to 'A' which works out to about 3.5lb tension per square diameter of contact area. If the intrinsic friction of the cord system is high enough it might not slip, but in most nylon braids it will slip easily.
In the case of the doubled slipped overhand (with a twist), there are two load loops, consider A-C is one loop and B-D is the other.
This time the load is shared across all four cords with A and B holding 50lb between them. The frictional contact area has gone up so the tension on the contact surface has come down to about 2.5lb per square dia. It should grip better than the single core -- but! A and B are effectively joined by the 'cogging' surface marked in green. Because they are different cords, A and B will rarely be the same length, so the load will often be biased more onto one than the other. If this causes one of the cords to be loaded above its slipping point, then some of its motion transfers a force into the B cord, inducing it to slip as well. The two cord surfaces 'cog' one with the other to create a mutual inducement to move. Despite the increase in frictional contact area, this knot is highly prone to slipping.
Now consider the 'resistant' Lyndy format.
In this configuration the adjuster loop is connected to cores A and D, with the load loops as before on A/C and B/D.
Three things have happened. First, the frictional density has dropped still further to 1.7lb per square diameter. Second, there are no 'cogging' surfaces to induce sympathetic movement and third, the two load loops are connected up 'opposite handed'. Any slippage in the A/C loop will tend the rotate the load anticlockwise, feeding the force of this movement into the fixed 'B' leg of the other loop, while any slippage in the B/D loop rotates the load clockwise and this time the fixed 'C' leg resists the load. This is 'ratcheting' where one part of the knot takes up and resists movement in another part. Although in extremely low friction cord this knot will still slip, in 'normal' braids it easily holds to breaking strain. The only 'tell' that you have tied this variant is the presence of one of the fixed cords entering the top of the knot
between the two adjuster loop lines. The 'tell' is shown in red in this image.
As this post is now quite large, I will cover the two intermediate variants in a new post.
