I don't understand how this holds

"Mechanical advantage only exists when something is moving"? I guess that all that time I spent studying Statics was all fictional!!

Sailor here. My understanding is that when a halyard is being raised and a deck hand is reaching up to grab the line at a high point and letting their weight pull own on the halyard, that is called "jumping the line." When you pull sideways to add the last bit of tension with the help of a person "tailing" (like you did in the video) that is called "sweating."

This is really similar to some 3rd year engineering dynamics final exam questions. Especially the question of "why does the system's advantage change inversely proportional to the systems ability to hold or progress capture when the coefficient of friction is the independent variable?" The coefficient of static friction between the rope and the biner is always higher than the coefficient of kinetic friction after the rope has started to slide. As far as the system is built the slack tail of the rope is not in the system under static conditions, as the tension at the anchor does not exceed the total sum of friction. Although the friction from the final carabiner after the piston dyno is included, but less influential than the biners that have a 180 degree contact with the rope. The higher the coefficient of static friction between the biner and the rope, the more tension it will hold before slipping. Then when adding force normal to the pulley system you are doing 2 things. The first is wrapping more rope around more of the carabiner thus increasing the surface area that friction is acting on. The second is that you are adding potential energy into the rope's elasticity, and getting closer to the impending slip. When you relax the system while pulling the slack through, you are using the stored potential energy in the elasticity of the rope and the lower coefficient of kinetic friction, which is why it works like a progress capture.

If I set up a 5:1 pulley system, in order to lift 100lbs, I have to pull with more than 20lbs of force. Once the load is at the desired height, I can't let go, nor do I have to apply 100lbs of force to keep the load raised. I do have to apply exactly 20 lbs of force (including any friction)

Sailor here. Our traveling 420 team used this trick all the time to tie up halyards on masts before strapping the masts to a trailer and hitting the highway. The masthead block and the bail ring were the “anchors” and we used some clever bowlines for everything else. No carabiners necessary.

So here's the thing; mechanical advantage is still relevant to this system even with the friction involved; in fact, especially with the friction involved. Without mechanical advantage you wouldn't be able to put any serious tension into the system just pulling by hand. The mechanical advantage doesn't disappear jus because there is also a friction force that masks it, and is necessary in order to enable a human to be able to tighten the system up adequately. Useful video in all practical terms, but I felt like the theory needed a litle clarification.

There is a difference between static friction, that must be overcome to start something moving, and kinetic friction, the force required to keep it moving. Although the kinetic friction seen by the rope sliding over the carabiners is greater than if they were replaced by pulleys, it is not so great as to completely overcome the mechanical advantage, so the hitch does amplify the force you are able to exert. When movement stops, the static friction is great enough to capture the progress. The vector pull aids in adjustment of the hitch because it helps to overcome the static friction.

So I might be wrong here but, I feel like this dives into semantics really quickly. It's ideal mechanical advantage would still be 3:1 because ideal mechanical advantage is theoretical in a system with no friction, basically the setup with pulleys. The flip side of that is the actual mechanical advantage which is, as the name implies, an actual number that takes into account friction and real world issues. The system with those carabiners and the rope used creates enough friction to offset the theoretical advantage. So basically it's either a 3:1 or a 1:1 depending on which type of mechanical advantage you want to use. Changing variables that would change the friction would still change the AMA, not the IMA though.

Very similar to the Trucker's Hitch and the Versatackle, just with carabiners instead of fixed loop knots.

Yeah he is wrong. Its an inefficient 3:1. Just because it has so much friction that it is effectivly a 1:1 doesn't change the definition mechanical advantage. Nothing is a true 3:1 at most will be a 2.99999999:1 .

I used this exact system to set pipes exactly in place because this setup works wonders in its adjustability.

It's called "sweating" a line. You're speaking Swedish.

I learned this knot arrangement for securing anything, using non binding knots to fully secure ocean bound materials. Also, it was very helpful in my rigging work on stages. Sans the ‘biners. I added loops to the line to be able to created the resistance or opposite side of each pulling point. These days I primarily rely on it for cargo transport atop my vehicle when transporting sheet goods and similar items for my work. The same high quality lines (rope) I bought in the 90s is still serving me as though they were brand new. Properly stored a good high tensile material can last indefinitely. I wouldn’t rely on climbers lines, since they have a much greater life and death concern.

Hysteresis is what holds the tension. You can put pulleys in some of the turns and it will still work, gonna play with it tonight.  I used to have an illustration I did from playing with the VooDoo of where pulley(s) worked before "failure". Will remake it to share or hopefully dig it up.

You count the supporting ropes. If there are 3 ropes in the center vs one on either end, it is a 3 to 1 mechanical advantage LESS the friction of the turns. If you were using well lubed pulleys or blocks, snatch blocks, etc, is is about 5% loss per turn. Slippery beeners maybe higher. I have been using a truckers hitch, utilizing 4 hole boat cleats (functionally similar friction to beeners) for more than 50 years. As you are noting,, I call it a magic knot, you call it voodoo,, because it can be tied in the middle of a rope, and when released it disappears, nothing to untie. With 4 hole cleats I secure the end with a simple cleat hitch,, every sailor, on every sail trim uses. Functional equal to the clove hitch, but open, you don't have to untie anything. I did note the 'perfection loop' at the bitter end. Well done !

“vector pull” is a useless term and whoever coined it doesn't sound as smart as they think they do. Applying a force in a given direction is a vector, but calling it a vector in no way suggests the direction the force is applied. “Apply perpendicular tension” would sound similarly educated but would actually mean what it says.

This is the coolest video I've seen from yall! Awesome stuff!

Super interesting to see! Especially since I like to use a similar system (variation of the poldo tackle) for Spacenets. Thanks man!

Sweating is in fact the correct term for vector loading in sailing parlance. Fascinating system for sure!

This reminded me of something a professor once said about worm gears (worm gears generally have a lot of friction). If a worm gear cannot be back-driven (the majority of worm gears can't be back-driven), then it is less than 50% efficient. Without going through the math, I suspect the same is true of this rope arrangement. Without the pulleys it is less than 50% efficient, so it holds. With the pulleys it is more than 50% efficient, so it doesn't hold the load.