Question about a concept in art and science of practical rigging

L

Lupin_IV

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St Paul
In said book, the author advocates for pulleys over natural crotch. With the pulley, the low friction at the rigging point allows the entire length of rope in the system to absorb the energy. With natural crotch, the friction at the crotch increases the force on the working end and it is not absorbed fully through the length of rope after the rigging point.

Fast forward to modern riggings tools I.e rigging rings and aerial friction - does anybody know how this works and why many folks choose aerial friction? My guess was with rings and such the friction is predictable and generally minor relative to the load, not preventing the energy absorption throughout the entire rope.

Maybe overthinking but want to hear more experienced thoughts.
 
Not an expert on rigging, but as I understand it, witz aerial friction you get less load on the anchor point, because the forces would double when using a pulley, with more friction added, you get less load on the anchor point. You would get more shock absorption with using a pulley, so provided your anchor point is sufficiently strong to handle 200% of the load, you can get a softer catch of your piece when using a pulley.
 
In practice, I mostly find folks using aerial friction devices due to a lack of trust of help on the ground. Or access to the base of the tree is treacherous and this allows for pieces to be caught by hand, no portawrap.
 
Wrangler said:
If you’re rigging point is not the best and you want to keep forces applied to it to a minimum then aerial friction is the way to go. When a block is installed at rigging point mechanical advantage increases forces at that point
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This is an oversimplification. allow me to explain. I have no intention to discuss the actual numbers or force measurements so let's keep this all fairly conceptual. Deal?

Depending on the amount of friction at the rigging point, the rope available to absorb energy from loading may be limited. Think of your rigging line in its two parts, the lead, rigging point, to load, and the fall, rigging point to the ground. The fall is generally same the same length, the lead will vary as the piece travels down/up. The rigging point is where the line changes direction. Friction at the rigging point can divide these areas of rope and cause uneven loading. Worst case scenario, there is so much friction at the rigging point that only the lead of the line is loaded. Best case, there is no friction and the whole line can absorb the load. Making sense?

In the case of a natural branch union, this friction could be substantial. In the case of aerial friction, it is far less and far more predictable.

While there is a slight decrease in load on the rigging point when using aerial friction, there is a corresponding increase in reactive force. So if a piece is loaded into an aerial friction point and is pulling forward as it falls, the rigging point will be pulled forward as well, more so than with a rigging point with less friction. Again most cases, this changed reactive force is minimal. and proper ancho selection negates it.

The force is not so much decreased as it is changed and partially dissipated. For in-field calculation, I think it is fair to assume that aerial friction devices or pullies the rigging point is going to be loaded roughly the same. Having said this there may be many reasons to add friction at the rigging point, some already mentioned. There are also some situations where the increased friction at the rigging point could be a really bad idea.

Moral of the story? Make rigging equipment selection decisions based on a firm grasp of the principles and an understanding of how the equipment follows those principles. Make good anchor point selection through inspection and good experience. Err on the side of caution and always use as many of the 5 ways to manage force (also mentioned in the book) as you can.

Wrangler, your blanket statement while not false, is also not true in many scenarios. It does not take into consideration all the other factors that must be looked at, hence the oversimplification. It would be rather easy to implement an aerial friction rigging device and generate more force in worse ways. The same is true of a block, or natural union.

Tony
 
my version:
Dialable trade off betwixt dropping amount forced past friction buffer of redirect (thus reducing load support)
Or
Employing rest of line as more part of elastic rubber band concept of same rope.
Or choice range tradeoff between these 2 absolute benchmarks. Hybriding together some of each(d)effects into scenario, trying to pick best combination to load, rope length, elasticity, frictions, crew, run-able length, support strength, support iron rigidity vs. elastic dampening and other considerations in support chain etc. and event timing .
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Devices tho tend to offer smoother surface than tree bark against rope w/more consistent frictions AND heatsink. Both factors increasing 'running' at least part of load force, only encountering that force that is resisted.
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The geometry determines the potential force pattern setup, the support frictions buffer is just a volume adjustment knob in that schematic. Support texture, thermal insulator/heatsink are attributes at that point in the geometry as like rope texture, elasticity, tensile etc. More friction also can help give greater sweat/swig region and rope purchase secure capture. Less friction easier for climber position to help pre tighten to potential of 2xEffort + bodyweight as another pair of trade offs.
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These support redirect friction choices are antagonistic reciprocals, whereby increase of 1decreases other to the sum of the whole elastic dampening reduction vs. friction reduction.
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True Art i think is not letting accelerate, for speed is a squared factor/unless purposefully pushing thru etc. But otherwise smooth, consistent , low impact etc. motion.
So softer catch/elongated, less brutally impacting stop.
Or run /walk slowly last 250# force to 'snub' out on ground absorption.
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To me, more proper to view as energy in(lossless) system is always same, but expresses forces differently?
Model as like child's swing breathless pendulum stall at each extreme end of no force expressed, but still same energy all the time I think; even as most force expressed at midpoint/bottom, energy in lossless system = SAME.
The initial pull back being only time force expressed at extreme end of lossless pendulum swing.
Vert rather than horiz model would be lossless spring, same Zer0 force stall before recoil, same midpoint force peak.
Peak to 1Zer0 side as like a 90, full travel 1 sweep as stroke plus return as a full cycle. And so following, change pattern more to a cosine waveform as a pulse, than a static arithmetic scale of change. These I think are 2 best simple motion models, for horiz/vert 'expressions'.
 
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Per Donzelli (and I got the same value) the tension ratio on a 180 through a rigging block is 1.2 which means the log side tension is 1.2x higher than the down side rope. He spotted it because he was expecting and didn't get the mythical 200%. So with a block you're already de-rating use of the down side rope's spring/damping shock load energy absorption. If you further redirect at the base of the tree something like a 90 degree turn through another block would be a tension ratio of about 1.1.

I think the quantity of friction employed at the tip is the most important issue. You know best case your ratio is 1.2 with a block and you can choose the make it higher. I think rigging rings was 1.4, 1 1/2 wraps on a belay spool about 4.0 and a morgan block about 5. I'd feel nervous about anything beyond 5 as you might accidentally put a transient tug into the control side and get it multiplied way up "large" where you don't want it to be. Of course the limit to this is snubbing off, worst case at the tip by crazy high friction force (likely through mishap), next worst is snubbing off at the tree base porty, next is more rope involved but snubbing at a remote. After that is any degree of controlled run, whatever the configuration. IMO

So basically I think everybody's right. Good discussion.

For Tony - a morgan block at a 5 ratio means the control side is only 1/5 or 20% - total at tip 120% definitely drastically reduced. 120% applies to transient "log weight " too e.g. decel at 3G, 120% x 3G
 
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i think of friction as a buffer, that favors the lesser, control/less active side.
It is the stronger pull side's burden to be able to pull thru the friction buffer, like a load against hold thru the helpful friction buffer. But if try to be the larger force, and lift thru the friction buffer then it works against you instead of helps as it does in hold/lower. If a Round Turn(540 degrees) of nylon on aluminum yields the quoted 10x factor, that is like a 10x lever of help to the lesser side to hold/control the load as in 20# of Effort to hold 200# Load.
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The co$t of conversion, deformation etc. of the arc MUST have friction;
nothing gets by untaxed; w/o friction.
(or the Kennedy bullet would still be flying theory)
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A larger pulley sheave to same bushing/bearing size on same size axle
>>sheave is then a larger cranking leverage ratio over those frictions around axle.
>>so more efficient return from Load to Control side.
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Pulley on load increases load capacity and aids pretightening
>>but gets less elastic dampening response
The stronger system, just as a stronger rope now does not have it's (Max)'headroom' invaded as much,
>>so yields/screams out less elastic dampening in response.
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Hard use of the elastics, rope is not the same rope for a while, minutes or hours depends on factors; before the rope is truly itself again. Same trick might not go the same on the 2nd or 3rd successive round, on the now temporarily (tho can go to permanent) stiffer line.
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180 arc segments are king for friction, can be listed radially on a Porty or even a linear list of arcs on a rappel rack, comes out as all the same maths. 180 arcs commit the whole unit to pull the same direction as one, and employ any sideforces as well. A deformation like a squared corner (don't do) or rounded corner or full 180 arcs are the only time that ALL rope tension force used to seat to host that then gives the controls of friction, nip and in opposing pairs grip. In the corners only over a small range, but in 180 arc thru the whole range delivers the key seating of rope to host to get the controls over Load. Other rope parts with more linear pulls of ends pulling in opposing DIRECTIONS, only use the lesser side force to seat to host(while main force dedicated to support of the load), to then yield any much more nominal frictions, nips, grips.
The 180 again is total king of this, and the counting units of capstan theory of all collective radial frictions compounding into each other. i think in terms of the 180 arc pulling load direction, then the next 180 opposing in opposite direction (this is only point of full rope force used as grip).
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Perhaps defacto standard of capstan theory that grinded thru over for years sifting things out
>>now can only find on way back machine @web.archive goldmine(link)
then made
Flat to converted to radial frictions spreadcheat w/calculator too. (and more maths) extension of above study(link)
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Metal is a heat sink for frictions vs. wood thermal insulator
>> each with higher heating synthetic rope racing around.
Natural fiber more friction, but more heat worthy too.
Nylon gives more rubber band dampening than polyester
>>but not as strong, nor heat resistant as polyester and can soak up more water.
75 fahr standard rope work temperature, most stable for nylon.
Nylon rope try to keep below 200degrees in usage.
 
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Bart_ said:
Per Donzelli (and I got the same value) the tension ratio on a 180 through a rigging block is 1.2 which means the log side tension is 1.2x higher than the down side rope. He spotted it because he was expecting and didn't get the mythical 200%. So with a block you're already de-rating use of the down side rope's spring/damping shock load energy absorption. If you further redirect at the base of the tree something like a 90 degree turn through another block would be a tension ratio of about 1.1.

I think the quantity of friction employed at the tip is the most important issue. You know best case your ratio is 1.2 with a block and you can choose the make it higher. I think rigging rings was 1.4, 1 1/2 wraps on a belay spool about 4.0 and a morgan block about 5. I'd feel nervous about anything beyond 5 as you might accidentally put a transient tug into the control side and get it multiplied way up "large" where you don't want it to be. Of course the limit to this is snubbing off, worst case at the tip by crazy high friction force (likely through mishap), next worst is snubbing off at the tree base porty, next is more rope involved but snubbing at a remote. After that is any degree of controlled run, whatever the configuration. IMO

So basically I think everybody's right. Good discussion.

For Tony - a morgan block at a 5 ratio means the control side is only 1/5 or 20% - total at tip 120% definitely drastically reduced. 120% applies to transient "log weight " too e.g. decel at 3G, 120% x 3G
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Bart, thanks fpr the numbers and the clarification. These discussions inevitably turn to the numbers, and I appreciate accurate well explained ones.

My initial pint still holds regardless of the math. While there is force reduction it does not happen in isolation. To achieve it many other factors are necessary.

No tool we use is a magic bullet. Tools , techniques and systems must be chosen and designed with all components, (human included) to reduce force. Numbers, while important, can cause some to lose sight of this. They are but one factor to keep in mind when you are in the field rigging tree parts to the ground.

Tony
 
Will stein said:
I'll still use my fiorri ring when we get into the big wood. I feel it gives us more wiggle room as to how many wraps on the portawrap. We love the rings.
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That ring looks so awesome, glad you commented on it, I been wanting one but haven’t heard any feedback on them yet.
The really large ring is the one I’m referring to....
 
Wrangler said:
That ring looks so awesome, glad you commented on it, I been wanting one but haven’t heard any feedback on them yet.
The really large ring is the one I’m referring to....
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It is really awsome. One ring with many configurations. We mainly use it to negitive rig trunk sections down. Using the ring with one wrap on the Porty can easily lower 600-750lbs with the amount of contacr/surface area on the ring. If you under judge the weight "ie. not enough wraps" you still have control unlike a block/pully where your just Plain screwed. Let me know if you have any questions. Purchased mine from wesspur.com
 
Will stein said:
It is really awsome. One ring with many configurations. We mainly use it to negitive rig trunk sections down. Using the ring with one wrap on the Porty can easily lower 600-750lbs with the amount of contacr/surface area on the ring. If you under judge the weight "ie. not enough wraps" you still have control unlike a block/pully where your just Plain screwed. Let me know if you have any questions. Purchased mine from wesspur.com
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Thanks man, I’m going to go for it. There’s just so many applications it can be used for and it looks easy to deploy. Tying on big blocks sucks up time and energy, l’d
love to have something lighter to work with when possible .
 
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