The Ripple

Jessica Cofer Blog

By Tony Tresselt

As an organization, NATS is seen as a guiding force in the Tree care industry.  One example of this is we are often asked to consult or review training materials.  Recently, Tchukki Anderson, staff arborist at TCIA asked me my judgement on a small section she is working on for the newest version of their rigging manual.  (For reference, you pronounce Tchukki’s name Chuckie, just like the horror movie icon.  Her description, not mine!)  This is fairly normal as Tchukki and I maintain a fruitful professional relationship and often consult each other.

I thought it would be a fine example to show you the original paragraph Tchukki asked me about, my long winded response (careful what you ask for!), and my revision of the original.

The idea here is to get you all thinking, not about rigging, although you certainly can, but about our concept of the ripple, how it flows out, how we produce it and the effects it can have in our industry and our world.

The original paragraph Tchukki sent

Add Friction

Peak forces in negative rigging can multiple quickly. It is common to be working in the range of 1 1/2 times the weight of the piece to then suddenly 4 or 5 times the load weight. Try to control load weights to about 1 1/2 – 2 times the load weight zone. To work in the ballpark of 1 1/2 times the load weight, there should be friction at the rigging point and a long slow deceleration. Experienced rope runners can certainly accomplish smooth, controlled descents with tree wraps (see chapter 4) but use of lowering devices ensures that the friction level is the same regardless of tree species. Adding friction in the canopy of the tree will also reduce forces placed on the tree.

My response

On your question, what you wrote is technically correct, although I tend to stay away from numbers any more. About as close as I will get is to state that doubling the force is easy to do and increasing from that point is not too difficult either. Perhaps I have had to battle “number semantics” too many times and I have been worn down. Perhaps I am just a math-phobic turning rapidly curmudgeon?

The same holds for adding friction at the rigging point. While generally speaking, it does dissipate force. (Again I never say decrease as gravity is a constant.) In certain instances friction at the rigging point can be advantageous; at other times, it can be detrimental. (Of course, there is always friction, I am referring to intentionally increasing it.)

For many years we applied friction at the rigging point every time. This was the ‘ol natural crotch rig point. Still perfectly acceptable today, but with limitations. The obvious being damage to trees and rope. Secondarily, the ability to predict how much friction as it changes tree to tree, branch union to branch union. Ironically, the reason friction at the rig point worked so well was it gave us a margin of error we needed because we were restricted on where our rigging points could be. We could not move them.

Most seem to forget this limitation. Our original term for a rigging block is very telling to our mindset at the time. To this day many still refer to a block as a “false crotch.” We moved away from friction at the rigging point in favor of better rig point positioning. We also gained predictability in friction application. A low friction block “false crotch”, along with a lowering device (at the base), worked the same from tree to tree day to today. What changed was the load, the rope, and the amount of rope in the system. These were all things we can control.

Fast forward to today where it seems we have combined the best of both worlds, movable, “friction-generating” rig points. Again with a certain amount of irony and symmetry, we have turned an advantage into a possible disadvantage. Natural crotch rigging is limited by rig point placement. We can only rig from where the tree has unions. The hidden gem is we are automatically rigging with/into the strength of the tree.

Unless you choose a weak branch union, (generally does not happen as the weaker unions have poor structure for rigging i.e V” shape, cracks, splits, etc.), natural crotch rigging puts rig points at the strongest structures of the tree, in alignment with the tree form. The best single piece of tree removal advice I ever received was from Dr. Kim Coder. He told me over lunch one day, “Tony, if you are going to take a tree apart, take it apart the way it was put together.”

Natural crotch rigging forces us to do just that. Use tree structure as a basis for dismantling and rigging. With the advent of friction-generating “false crotches,” I use the old term very specifically to highlight my thinking we can now apply friction to rigging points anywhere in the canopy big enough to slap a sling on. We can, in effect, rig against the natural strength and structure of the tree. The same is true of using low friction blocks, but we have the margin of error that low friction gives us. See how the tables have turned?

On one hand, low friction at the rig point allows us to dissipate force faster with more predictability, but anywhere in the canopy. Friction added rigging points allows us to dissipate force through heat and friction, but are “slower” and can be set to load the tree in undesirable ways.

Neither is bad, not good, there are only choices. An arborist can rig poorly with great equipment just as fast as a rig well with poor equipment. The key is understanding the subtleties of trees and kit and making sound judgments.

I shall give you an example. In 2018, I along with two other curious arborists got together to do a bit of tree guy “research.” I was presenting at Expo on the topic of friction in top-down rigging scenarios. We knew from other testing and just sound logic that adding friction at the rig point displaced force. The question was where did it go? Heat? Abrasion? The answer to those two is yes, but not in great quantity. Yes, the rope did abrade more, in the Safe-bloc (our aerial friction device we tested), but not significantly. Yes, the Safe-bloc did get hotter than the DMM impact block (our control), but again while significant in difference, the temperatures were not damaging to the rope and could be managed from becoming so.

That left stem deflection. We theorized that the increased friction at the rig point would pull the stem forward as the added friction slowed the dispersion. We surmised the block would have less of an effect if both pieces were allowed to “run” or use equal amounts of deceleration.

I used the term “research” because obviously, I am not a scientist, we did not have instruments to calibrate, there were numerous values we could not control and math is a religion I refuse to believe in. I am a dyed in the wool math atheist.

We tried though. We discovered a few things. First, we discovered that if we wanted the answer we were after, it could not be had in Rick Denbeau’s back yard. I know, imagine our dismay! As a side note, we did approach some real scientists from NASA. They totally agreed with our hypothesis and we were working on a plan to hire them to test it for us, but it fell apart with funding. You never know we may revive the project!

In this process, we also discovered something much more tangible and the main reason I caution arborists in using friction at the rigging point in top-down scenarios specifically, and to further select any type of rigging based on advantages and limitations of kit and tree, not based on what is new, cool, shiny or the dreaded “should” work factor!

As the short video clip shows when a block is released from the stem, with the block the slack is absorbed back into the system either through gravity (lots of rope on the fall side of the block) or by the grounds person physically pulling it in. (A skilled ground worker will do this sweating or pulling of the lowering line to absorb the slack intentionally. It is one way to tell adequate from good grounds people.) This keeps slack out of the system which is always desirable in top- down rigging.

Pretty much the exact opposite happens when you use an aerial friction device in top-down rigging. The slack cannot fall or be pulled through the rigging point fast enough and the piece loads the system it cannot be decelerated as smoothly. This is why we were getting higher peak force measurements at the rig point with the Safe-bloc as opposed to the impact block. (All things being as equal as we could make them of course!)

So…. having said ALL that… If I were to write the paragraph…

Peak forces in negative rigging can multiple quickly. Doubling the force is easy to do and increasing from that point is not too difficult either. Always employ as many sound measures as you can to dissipate force in your rigging system. Manipulate the amount of rope in the system, the amount of elongation as necessary. Decelerate the pice slowly if possible and decrease the size of the piece to lesson wright if there are any doubts. Using friction at the rigging point is an option, but one that comes with considerations. While friction at the rigging point dissipates force, the rigger has to ask, “where is it going?” and develop a sound plan based on that assertion. A long slow deceleration is always desirable. Experienced rope runners can certainly accomplish smooth, controlled descents with tree wraps (see chapter 4) but use of lowering devices ensures that the friction level is the same regardless of tree species. Adding friction in the canopy of the tree will change reduce forces placed in and on the tree. It is on” the tree that should guide your decision.

The Ripple

As all of you that have attended trainer or Empower the Educator will know, the ripple is a valuable allegory for NATS mission of serve, share and support.  I am honored to be given the opportunity, by Tchukki, to share my knowledge and experience. I am honor bound to do so by the lesson of the ripple.  We do not have the right to take ourselves out if we have value to add, knowledge, and experience to share.  I encourage you all to look for opportunity and take it no matter how small when it arises.

Please follow and like us:
Visit Us
Follow Me