As production arborists, we are often in a position where rigging is needed to lower tree parts. Whether we are preventing damage to the tree or the surrounding landscape or property, making the job more efficient by cutting larger pieces and/or lowering them into a more convenient place or managing risk, rigging is an intrinsic skill that has many methods.
Often the simplest approach is the best. Generally speaking, placing the lowering device (LD) on the tree we are working on is a simple, effective and best-
practice option. However, there are good reasons to move the LD and increase our options. This article will focus on seven good-sense reasons you may choose to relocate the LD on the job site.
There are two main options when it comes to relocating the LD. First is the most obvious, attaching the LD to another appropriate anchor. (Diagram 1)
This causes the rigging line to enter the rigging point at an angle. The second method is to redirect the lowering line from the base of the tree being rigged to the relocated LD. (Diagrams 2 and 3)
Each method produces a different outcome, each with distinct benefits and, in turn, limitations. However, regardless of the method, the principle remains the same. The intention is to move the LD away from the base of the tree where the work is being completed.
1. Moving the rope handler away from the drop zone
The simplest and most obvious reason to relocate the LD is to keep the ground crew out of the drop zone and/or clear of overhead hazards. With the LD at a distance, the risk of a struck-by decreases. Deadwood, structural failure, wildlife (read bees) and even the load being rigged all present possible hazards to the rope handler when lowering. Putting distance between these hazards and the worker is an engineered solution that lowers risk and mitigates hazards.
2. Improve visibility to climber and rigging load
Tree work is teamwork. The cutter aloft and the ground crew, especially the rope handler, need to work in concert to achieve the best results. Moving the LD and, hence, the position of the rope handler can improve visibility in both directions. The ground crew can see the climber/aerial-lift operator and the rigging load more clearly. The cutter aloft can see and better communicate with the rope handler.
When feasible, the load should be allowed to decelerate slowly over as much distance as possible. This greatly reduces the load into the rigging system. A relocated and thus improved vantage point allows this to be much easier for the rope handler.
The worker in the tree also can be sure the ground crew is clear of the drop zone and ready to proceed.
3. Protect friction device from impacts
When lowering tree parts, even the best-rigged piece can do unexpected things. Furthermore, drop zones and lowering zones may be restricted and tight. When this happens, the rigged piece and the equipment used to control it may need to occupy the same space.
Slamming a large piece of wood or limb into any LD never creates a good result. Even if the LD withstands the impact, the rope may be damaged. If the load impacts the device, at the very least the ability of the rope handler to exert maximum control will almost certainly be hampered.
Some rigging systems require components to be “in the line of fire” as the system is utilized. Vertical speed lines that restrict the movement of pieces after they impact the drop zone are one example. Redirecting the load line through a smaller and possibly more impact-
resistant redirect can protect the LD and the rope handler.
4. Facilitate addition of mechanical advantage
Some rigging scenarios may require the ground crew to exert lifting or pulling force into the rigging system to lift and/or balance pieces. Not all rigging jobs require a crane! The ability to add a mechanical advantage to a ground-based lowering system is a great benefit. A come-along or fiddle-block set is much easier to deploy and activate when it is set up close to the ground in a horizontal configuration. (Diagram 4)
In this type of setup, the crew can safely apply more force as a cut is being made, if necessary. The ground crew also can lock off the rigging line and then reset the mechanical advantage if it “two-blocks,” but the job is not complete. (Two-blocking is when the mechanical-advantage system is fully compressed and can no longer be used because all the scope in the system is used up.)
5. Increase rope in the system
One excellent way to manage force in a rigging system is to increase the amount of rope in the system itself. This, on one hand, physically puts more cordage and rope material in the system to handle the loads. It also allows for better rope elongation. As a rope elongates, it absorbs energy and lessens the total load on the system. The more rope in a system between the load and the friction-management device, the more energy absorption. To put it simply, the more rope that bears load, the more elongation or “stretch” in the system.
Furthermore, in the setup where the rigging line is redirected (Diagram 2), there are more anchors to help dissipate and redirect load forces. There are more friction points to help absorb force as well.
6. Open the angle at the rigging point to reduce forces
Another excellent way to reduce force in the rigging system is to change the angle at which the rigging line enters and/or exits the rigging point. As the angle becomes greater, the total amount of force the rigging point experiences decreases. In Diagram 5, if we assume a starting point where both lead and fall of the rigging line hang straight down from the rigging point, the rigging point will see approximately 2x the load. At 60 degrees, the rigging point will see 1.73x the load weight. At 120 degrees, the rigging point will experience 1x the load weight. When the LD is relocated, as it is in Diagram 1, this opening of the load angle can be significant.
7. Change the reaction force at the rigging and redirect points
Our last example showed us we can reduce the force at the rigging point by opening the rope angle. There is another aspect to changing the angle at the block beyond load reduction.
As the angle of the line at the block changes, the reaction force also may change. When a system is loaded, the force of load and added friction at the LD are segmented at the rigging point. If the lead and fall of the rigging line are parallel, the reaction force at the rigging point is straight. Think bow and arrow. Just as the arrow segments the bowstring evenly to force the arrow in the desired direction, so will the angles of the lead and the fall of the rigging line. The direction of the reactive force can be predicted by the bisecting of these angles, just like an arrow’s direction when the bowstring is released.
In the rigging scenario shown in Photo 1 (page 46), the LD was moved back to another tree. This not only lessened the force on the rigging point, but it also loaded the leaning hemlock (Tsuga canadensis) in compression along its main stem (green arrow). This change in reaction force of block loading helped reduce the risk of the rigging forces causing the tree to continue to uproot. It also simultaneously removed the rope handler from a hazard zone, added a bit more rope to the system and allowed the ground crew to better see the rigging operation.
If the lowering device was placed on the trunk of the hemlock (Photo 2), the reactive force would have been much more likely to add force to the root system of the tree.
It bears noting that, were it possible, moving the LD forward into the lean (Photo 3) would increase the load on the root system of the tree! This is to be avoided and shows how application of force and reaction-force manipulation can be used poorly.
There are many ways to design and implement a lowering system. Often, the most straightforward method is the best. However, many times a crew will have to make decisions and alter the plan. Displacing the LD is one quick and effective way to manipulate not only the proximity to drop zones of the crew but also communication and load forces.
Understanding the principles behind block loading and reaction force can allow arborists to apply many methods to manage risks, mitigate hazards and make the rigging operation safe and more efficient.
Anthony Tresselt, CTSP, is a consultant serving as director of safety and training for Arborist Enterprises, Inc., an accredited, 31-year TCIA member company based in Manheim, Pennsylvania. He is also a writer, philosopher, student of gravity and independent trainer based in Manheim. His writing and thoughts can be found on his blog, gravitational
anarchy.com. His books can be found on Amazon. He is a co-founder of The Arborist Boot Camp (thearboristbootcamp.com), a transformational training experience for new tree workers. He is also a co-founder of Leadership Performance Mastery, an online, self-paced, transformative leadership course for anyone looking to improve his or her leadership, regardless of whether they lead one or a thousand (valuebasedleadershipjourney.com).