By Michael Tain
Slide lines, also commonly called zip lines or speed lines, have a wide variety of uses in multiple fields, both professional and recreational. In the tree care industry, they are primarily used to move material, limbs, branches or even pieces of wood from one location to another. This movement may be required by obstacles or hazards beneath the tree being worked on, or may simply increase the efficiency of the particular job by eliminating a long, tedious “brush drag.” Slide lines may also be used in specific aerial rescue scenarios to move a victim and rescuer to a better spot for ground access and subsequent patient care. But their primary application is in rigging operations. They may be, and often are, used in conjunction with other rigging methods and techniques such as spar pole, limb balancing, or knotless rigging. However, due to the inherent complexity of properly setting up and using a slide line, and the attendant gear requirements, their benefit can quickly be exceeded by their cost in time and labor requirements. But in the appropriate situation and scenario, knowledge of slide lines and their use can make rigging operations both safer and more efficient.
Slide line: The rope chosen to be used as the slide line itself should be carefully examined for factors such as strength, elongation and melting point, as all of these will have an impact on the slide line’s performance and ease of use. For example, a rope with a great deal of elongation will require that much more input force and energy to be made taut enough to support the load as it slides down it to the desired landing zone.
Anchor points: The anchor points for the slide line must be evaluated for strength and placement. The slide line itself is going to have a great deal of tension on it, particularly after the load comes to bear on it. Thus, anchoring one end of the line to the tree the climbing arborist is in can create a bending moment with very unsatisfactory, if not catastrophic, results. One of the best options is to anchor the upper end of the slide line into a separate tree, thereby putting no undue force on the tree being worked on. Unfortunately, this is not always possible. However, the creative use of redirects can often be employed to lessen the forces generated near the climbing arborist to a great extent.
Slide line tension: The rope being used for the slide line should never be under tension when the load is brought to bear on it, let alone dropping a load into a tensioned slide line. This fairly common practice is, in short, a recipe for disaster; and will sooner or later result in catastrophic failures of trees, anchor points, gear and ropes. In a dynamic rigging situation where the load is going to drop some amount, a secondary line should be used to absorb that force. Then the load may be attached to the slide line, the slide line brought under tension, and the load sent on its merry way. The use of fiddle blocks, tensioning kits with Prusik minding pulleys, or a device such as the Good Rigging Control System will make tensioning and slacking the slide line much more user friendly. The use of motorized equipment, such as trucks or skid-steers, to tension the speed line should be avoided as it is an excellent way to break trees, anchor points, and ropes.
Control line: For all but the smallest and lightest of loads, a control line should be used to manage the speed of the load’s descent. And even for those supposed smallest and lightest of loads, a control line is highly recommended. Gravity is the law no matter where one is located, and the sight of numerous 1-inch- and 2-inch-diameter branches approaching at a high rate of speed down a slide line can be more than a little disconcerting to even the most hardened and experienced ground crew member. The slide line system can often be set up in such a fashion that the line that caught the load prior to the slide line being tensioned can also be used as a control line on the load’s descent.
Traveler(s) or carriage(s): The traveler or carriage is the method that the load is attached to, and travels down, the slide line. There are a wide variety of items used for this application, from simple non-locking carabiners to double sheave pulleys such as the Petzl Tandem, with a wide variety of friction levels between them. Users should evaluate whatever traveler they choose for strength and ease of use with the loads they intend to subject it to. Keep in mind that multiple travelers may be desired, and in fact required, if the load in question needs to be kept in a particular position during its descent. Having multiple carriages on hand will also speed the slide line process, as it allows the climbing arborist to be preparing another load while the earlier one completes its controlled descent.
As can be seen from this admittedly brief description, slide lines are a gear- and prep-time-intensive project, and will often not be the most efficient way to complete a job. Yet in the appropriate situation or scenario — one with no shortage of delicate obstacles beneath the tree or no access — knowledge of their use can mean not only finishing a job more quickly, but knowing that the job can be done in the first place.
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 firstname.lastname@example.org