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Single rope technique (SRT) has become increasingly popular in the tree care industry as an ascent method; and has even led to the development of some tools and methods that allow climbing arborists to work the tree safely and securely off a single line, instead of having to switch over after ascent to a conventional dynamic (two moving parts of line) system.

Single Line Ascent Techniques: Why Use Two When One Will Do?

By Michael “House” Tain


Single rope technique (SRT) has become increasingly popular in the tree care industry as an ascent method; and has even led to the development of some tools and methods that allow climbing arborists to work the tree safely and securely off a single line, instead of having to switch over after ascent to a conventional dynamic (two moving parts of line) system. Any tree care professional that has struggled for what seems an interminable amount of time to isolate a branch or tie-in point (TIP) for a static secured footlock or dynamic ascent can quickly see the advantage of ascending on only one part of the line: no isolation required. In addition, safer, more controlled aerial rescue techniques are available with a properly configured single line system. However, as with any tool, technique or method, there are attendant limitations with the advantages that single line ascent brings to the tree. Learning, understanding and working with both the advantages and limitations of single line ascent will help assure tree crews of not only a quick efficient ascent into the canopy, but also a safe and secure one.



Single line ascent systems, by their nature, are static systems, meaning the line or rope is secured and is not moving as it would in a conventional dynamic system; and this static nature gives them much greater efficiency. Dynamic systems provide an inherent mechanical advantage requiring climbers to only lift roughly half their weight as the weight is split between the two parts of line, but with this advantage comes the attendant negative fact that the climber must move his/her hitch over twice as much line. In short, because the load is split between the two parts of line and both parts are moving, a 200- pound climber is only pulling up 100 pounds but has to move two feet of line — one foot from each part of the line — to ascend one foot. Static systems, such as SRT, mean the user has to deal with his/her entire bodyweight, but ascend at twice the speed as a dynamic system; or one foot of ascent for every one foot of line moved.


Line placement


An SRT ascent/hybrid system properly backed-up. Once aloft, the hitch, properly backed-up, could be used for a floating anchor point with no load on the framed ascender. In addition, note the use of a Port-a-wrap to allow ground personnel to lower the climber and their system to the ground in the event of an emergency.As mentioned previously, the use of single line ascent techniques eliminates in large part the need for the climbing arborist to isolate a specific branch or TIP prior to ascending. As long as the line is over a suitable branch or through an appropriate TIP, its isolation is typically immaterial to whether SRT may be used. In fact, in many cases, climbers using single line ascent techniques will have their line over multiple branches/TIPs with little or no negative effect on the speed, safety and efficiency of their ascent. However, with this ease of line placement comes one concern that users must be aware of and consider; the forces at the tie-in point have changed dramatically due to the use of a static single line. As mentioned, a dynamic system splits the user’s weight between the two parts of line, thus the TIP sees no more than the weight of the climber plus whatever magnification occurs through bouncing, bumping and dropping on the two parts of line. A single line static system that goes over a branch or through a TIP and returns to the ground to be secured, in effect doubles the weight and forces of the climber at the TIP. Using the earlier example of a 200-pound climber, the single part of the line being used in ascent will see two hundred pounds, but the other part of the line secured back at ground level, will also experience 200 pounds, meaning the branch or tie-in point will experience at least twice the climber’s weight, or 400 pounds (once again dependent on the magnification from bouncing, bumping and dropping). Although this inherent disadvantage is certainly not a reason to avoid single line ascent, it is one to be aware of when deciding which branch or TIP is appropriate. This doubling of forces can be avoided by securing the single line to the branch or TIP itself, instead of passing over it, by sending up a Running Bowline; but this will require isolating the branch with the line, and will necessitate removal before descent — unless the climber wishes to leave their rope in the tree in perpetuity. Another option, one that is removable from the ground, is the use of a midline knot such as the Alpine Butterfly, where one end of the line is passed through the loop formed by the knot, then the knot advanced up to the branch, cinching it in place — yet this also requires isolation of the TIP.


Rescue options

If the non-working end of the single line is returned to the ground, the use of a friction management or belay device, appropriately anchored, can enable ground personnel to lower an injured or even unconscious climber — provided enough rope is available. Equipment such as the Petzl Gri-gri, ID, or Buckingham’s small Port-a-wrap, along with others, are all appropriate in this application. Whichever device is employed, it should be securely “backed-up” to avoid unintended slippage or loosening during the climber’s ascent. But its presence, with enough rope, will allow crew members to lower the climber’s entire rope and system to the ground safely in the event of an emergency.


Ascent tools/methods

There are a wide variety of tools and methods available for ascending single ropes — ranging from complete systems like Sherrill’s Tree Frog to the simplicity of the secured footlock requiring only an appropriate Prusik loop. Many manufacturers offer both single- and double-handled ascenders that will work well on single lines, along with ascenders for the feet, such as the Petzl Pantin. The Mar-bar system, designed and developed by Washington state climbing arborist Paul Sisson, not only provides ascenders and handles for both hands and feet, but also works on both single and doubled lines. Regardless of which ascender(s), system, or combination of tools is used, there must be some form of “back-up” to the climbing arborist’s primary means of support — particularly if the primary means of support is a mechanical device. In addition, users must remember that whatever device, knot, or hitch they use is going to experience their full body weight, not the half it would experience in a dynamic system; thus it may function radically differently, and require adjustment to provide true security and safety.


Hybrid systems

A previous column discussed the use of floating anchor points as movable TIPs; and these are certainly appropriate for use on single lines. A dynamic system “piggy-backed” on a static ascent system can be called a hybrid system since it contains elements of both. The climber who chooses to use such a hybrid system has the advantages provided by the single line ascent methods, while being able to quickly begin work on the dynamic system attached to the floating anchor point. Once again, factors such as forces at the tree’s TIP, security of the floating anchor point, and the appropriateness of the device/hitch being used as a floating anchor point must all be considered and evaluated prior to use of such a hybrid system.


Working systems

Traditionally, single lines in the tree care industry have been used mainly for ascent, but climbers and manufacturers have continued to work on, and develop, tools and methods that would allow arborists to safely and securely ascend, work and descend all on a single line. Two options that are currently available are the Unicender from Thompson Tree Tools, a device that works on both single and doubled lines in the ascent, canopy movement and descent; and the F8 Revolver system developed by climbing arborist Kevin Bingham of Michigan, which allows for smooth secure canopy movement and descent on a single line.


Single line ascent techniques can make for a quicker, more efficient ascent into the canopy, where the work actually begins; and, once fully understood and practiced, will become a trusted, safe and invaluable tool in an arborist’s mental toolbox. Further exploration, evaluation and training in hybrid and single line working systems will only increase the value and applicability of single line use in the tree care industry providing the true desired end result: easier, safer and more efficient methods and techniques.


Michael “House” Tain is a contract climber, splicer, educator and writer associated with North American Training Solutions www.northamericantrainingsolutions.com and Arbor Canada Training and Education www.arborcanada.com  He is currently located in Lancaster, Ky., and can be reached via e-mail at house@houseoftain.com

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