PHOTOS BY MICHAEL (HOUSE) TAIN.
A hybrid system (dynamic on static) properly backed up and being used as a floating anchor.

Climbing arborists have a wide variety of systems, methods, devices and options available to them for ascending, descending and working within the canopy of trees. Tree care professionals hopefully choose their respective systems and methods for safety, speed and efficiency, finding the ones that work best for them given their individual work styles and practices, yet provide optimum safety and security in use. Climbers should, when making these choices and decisions, be fully aware of not only what forces individual climbing systems generate on their tie-in points, but also what forces they, as users, must generate within systems to move around. Knowledge of these forces will not only help them climb and work more efficiently, but also more safely.

Dynamic climbing systems

A dynamic climbing system is one in which both parts of the rope are moving when in use. Although this system will work with the rope simply running over the bark of the tree in an appropriate crotch or branch attachment point, it will be much more efficient with greatly reduced friction if a device such as a leather cambium saver, friction saver or rope guide is used. All of these devices reduce friction at the tie-in point to varying degrees, saving wear on the rope, wear on the tissue of the tree and, by reducing friction, wear on the user. This means the climber is able to move more quickly and efficiently while using one of these devices, simply by reducing the effect of friction on the system. The use of a dynamic system means that the climber’s body weight will be roughly divided between the two parts of rope. This division makes it easier to ascend in this system, as the user only has to generate enough force to move half their body weight, but it is accompanied by an inherent inefficiency in the ascent. The division of body weight between the two parts of rope means the climber has to move twice as much rope in the ascent. For example, to ascend 1 foot, a climbing arborist has to pull 1 foot of rope down on the running end of the line, and 1 foot of rope up on the working end. Yet, this inefficiency in the ascent is what gives climbing arborists more control and precision when descending and working the canopy of the tree in a dynamic system, their chosen climbing hitch or device only has to control half their body weight, thus allowing them to fine-tune their movement for smoothness and control. Forces at the tie-in point of dynamic climbing systems will typically only be the weight of the climber themselves, multiplied only by any drops into the system experienced during the climb, although gravity will significantly increase the forces experienced by the tie-in point during these drops.

SRT ascent system secured to Port-a-Wrap III for disabled climber rescue.

Static climbing systems

A static climbing system is one in which no part of the rope is moving when in use. Static climbing systems may be used on both parts of rope or on a single leg of the climbing line, typically called single rope technique (SRT). An additional refinement is a hybrid system, in which a dynamic climbing system is piggybacked onto a static climbing system. Each of these systems will generate a variety of forces and all need to be evaluated for the appropriateness of their use in any given situation. In general, static climbing systems will be more efficient for use in the ascent, but do not provide as much control and precision when used in the descent or for movement around the canopy. Their efficiency in the ascent is due to the fact that the lines do not move, eliminating the need to move 2 feet of rope to ascend 1 foot. In addition, this also explains their lack of control in comparison to dynamic climbing systems. All of the climber’s body weight is on the hitch or device in a static climbing system, as opposed to half their body weight in a dynamic system, thus the hitch or device is attempting to control much greater forces than it would in a dynamic system. Hitches or devices that are perfectly safe and acceptable for use in a dynamic climbing system are often unsafe, unacceptable and, in fact, dangerous when used in a static system. Simply put, it is not the hitch or device, but the system that is being used. Static climbing systems using SRT generate much different forces at the tie-in point than comparable static systems. SRT involves using only one part of the climbing line to ascend or work; the other part is tied off or otherwise secured to an appropriate anchor, usually at ground level. The use of a long enough climbing line and lowering device as an anchor with this technique can allow for the lowering of an incapacitated climber from the ground. With the single rope technique, all of the climber’s body weight is on one part of the line, which then goes up and over a tie-in point, returns to the ground and is secured in some manner, thus the tie-in point experiences twice the climber’s body weight and must be evaluated and chosen accordingly. Hybrid systems in which a dynamic climbing system operates off of, or in conjunction with, a static climbing system will generate approximately the same forces as when operated individually. However, prior to using a static system as a floating anchor or tie-in point, the climber must back up the static system with an appropriate knot or hitch properly secured. Once again, just as in SRT, a dynamic system piggybacked onto a single part of a climbing line passing over a branch then back to the ground will generate twice the weight of the climber at the branch.

An endless loop formed in a Prusik for ascent on two parts of a line in a static system.

There are obviously many more climbing systems and techniques than those discussed here, but hopefully a basic knowledge of some of the forces that these systems can generate and require will assist tree care professionals in making better, safer and more efficient choices.

Michael (House) Tain is a contract climber, splicer, educator and writer currently located in Lancaster, Ky. He can be reached at house@houseoftain.com.