If you’ve ever worked a simple removal job, I’m sure you’ve gotten to the point once or twice where you’ve needed to pull over a high stump. The tagline set, you rappel down the stem, take off your spikes, and contemplate the next move for whatever the reason: back-lean, added control/security, not wanting to cut any more spar while aloft, wedges won’t do it, ya da ya da ya da. Pulling over a high stump is a pretty common situation, yet one in which the complex mind can thrive if we let it. And if you are working alone, there are typically two or three options: you can either set a notch and back cut and walk out of the drop zone and deliver a strait pull on the tagline, knock on the door to get your client for a helping hand, or you can set up a simple mechanical advantage system when there is anchoring potential.

As it is with life, so it is with tree work, some choices are better than others.

The choices we make when pulling over high stumps can ultimately tend to define us. If we back up those choice with a few simple pieces of information mostly pertaining to physics, it won’t feel so lonely out in that backyard anymore staring up at the only thing standing between you and a shot in the big leagues.

Set up the mechanical advantage, and walk away.

Literally though, with a 3:1 advantage classically known as the Z-Rig, you have the benefit of continuing to walk away from the falling spar as you pull. This is something a simple 2:1 redirect may not offer, at least not as efficiently. Also, if you have to set the felling cut and pull the high stump over, a 3:1 mechanical advantage will allow for a thicker hinge when that holding strength is needed for say a side-leaning or back-leaning spar, because of the increased pulling power you’ll have to overcome the hinge strength and bring the spar into the desired lay.

You don’t need thousands of dollars in hardware or rope to make life easier when building a mechanical advantage system for pulling over high stumps either. What you do need to know though, is that size matters, especially when it comes to pulleys and how they work.

This idea came to me while reading Chapter 10 in On Rope entitled Vertical Potpourri. It contains a good bit on pulleys and their application in simple and compound systems. One particular bit of information, which I’m sure is very basic jargon to the master rigger is this:

“Every time rope is bent, friction and resistance are generated, and work is performed. When rope goes through a pulley, it is best to use the largest diameter pulley available. A 2-inch pulley with 7/16 inch supple rope generates about 85% efficiency while a 4-inch pulley with 7/16 inch supple rope about 95% efficiency. This is compounded with the type of pulley used. An oilite (bushing) type pulley delivers about 85% efficiency while ball bearing pulleys deliver about 95% efficiency” (245).

So, the bigger the pulley, the more efficient that pulley is. And a pulley with  ball bearings versus a bushing is all the better. So then, let’s get back into the back yard where we are setting up the famous Z-Rig, a great and simple mechanical advantage system for pulling in arboriculture operations. Chances are, in some of the more basic gear cases out there, two pulleys may be different sizes and different builds. And that’s all there is. What’s important to consider when trying to milk the most efficiency out of a  mechanical advantage system limited to two pulleys is that how you arrange those pulleys in the system could make a big difference, and by big I mean 10 or 15%.

To put that in perspective, calculate how much more money you’d make by increasing your yearly earnings by 15%. My point exactly.

On Rope tells us “the most efficient pulley should be placed closest to the hauler because its efficiency gets multiplied through the entire system. Placing it on the load will have little consequence if attempting to lighten the load for the haulers” (244).

This can be a little confusing, but the pulley at the anchor is not necessarily the closest pulley to the hauler (even though when standing out of the drop zone and using a 3:1 Z-rig the pulley on the anchor tree actually may be the pulley physically closer to the hauler). The closest pulley to the hauler can be found by tracing the rope in the system from the hauler (you pulling on the tagline) to the closest pulley you come to in the system. See the diagram included for better detail. That pulley should be your best pulley.

So then, if you only have two pulleys to choose from when building a mechanical advantage for pulling over a high stump in someones backyard, always use the most efficient (bigger) pulley second when building the system. For instance, if you are building the mechanical advantage into the tagline itself, then at the anchor (located out of the drop zone) install your less efficient pulley (smaller, bushing, whatever). Install the rope through this pulley then move back up the tagline towards the spar. With a prussic or other progress capture device, install the second, more efficient pulley onto the tagline, install the rope through it and then proceed back towards the anchor and out of the drop zone for safe pulling.

Of course, there are so many factors to consider just in pulley choice alone, and I won’t even get into the use of beckets for the sake of this conversation. Just because the pulley is bigger may not make it more efficient, either. A bigger pulley with bushings may be less efficient than a smaller pulley with ball bearings. A dirty pulley, a damaged pulley, a pulley that spins no more. Know thy pulleys, and how they are constructed.

But to make things easier to imagine for this discussion, let’s assume that you have each one of DMM’s Pinto Pulleys: a Pinto Rig pulley and a Pinto pulley.

The Pinto Rig Pulley is larger, and it also has pre-lubricated sintered bronze bearings. The smaller Pinto Pulley has oilite bushings. The efficiency ratings are 95% and 71% respectively. If setting up a 3:1 mechanical advantage with these pulleys, the most efficient system would be to place the smaller Pinto pulley at the anchor and attach the Pinto Rig pulley on the prussic or progress capture device further up on the tagline. This places the Pinto Rig pulley, which is the more efficient of the two because of it’s larger diameter and ball bearing construction, closer to the hauler. In turn, this simply multiplies the force better by mere arrangement.

I feel as though especially with rigging equipment the arborist is forced to apply gear in such a multitude of different ways because of the changing landscape that we work in and the variable subjects we work in, on and around. Just by arranging hardware in minor ways, the work we do can get easier because we give that gear the best potential with consideration of its design and engineering. One arrangement yields 15% more efficiency, another arrangement and we get 10%, another and we get 8%. So then, in this light we can see that gear placement in a system can have a drastic effect on how well that gear performs. With the proper arrangement, the arborist can get more results from the same effort.

Maybe in 2018 we won’t define ourselves by the size of our pulleys or the depth of our gear bag, but in how we arrange the rigging systems we build.