Climbing System Compatibility: A Theoretical Approach

March-April 2012

Most climbers, myself included, started on the most basic climbing system (tautline on a closed system, remember?). Then we began building on it by adding equipment to create a more efficient system, a micro pulley here, an eye-to-eye there, and soon we have a completely revamped system. When doing this, you’re adding complexity to a system or in other words, links to a chain. Concern arises when the links in the chain don’t fit together properly and the chain can break due to lack of compatibility. Improper compatibility can, at minimum, create ergonomic and efficiency issues and, at maximum, cause system failure and bodily harm.

Basic Definitions
For clarity, I would like to highlight the terms compatible and compliant. Both words are used throughout, and although similar, the differences are important:

compatible adj. 1 a able to coexist: well-suited, mutually tolerant b. consistent; 2 (of equipment etc.) capable of being used in combination.

compliant adj. disposed to comply; yielding obedient, in compliance to a command, etc.

For the sake of this article, compliant equipment means it is properly rated and fit for the purpose of use, i.e., carabiners rated at 22.24 kN for life support (ANSI Z133.1-2006 (8.1.11)). Compatible equipment is in regards to gear working together in a succinct and functional system. For example, it is possible for a completely compliant climbing system to not function properly or reliably due to compatibility issues.

Explaining climbing system compatibility is difficult due to so many different compliant pieces of equipment available combined with climbers’ individual styles, techniques and body types. It is ill advised to make any blanket statements since there are too many variables present. If the climbing gear is being used appropriately in a proper system then the configuration of that system is the climber’s preference. Therefore, the goal of this article is to make you think objectively and look into your own gear bag and mental toolbox to make sure that you are working with the safest and most efficient system possible.

Climbing lines can generally be categorized into three types: 16 strand, double braid and kernmantle. Although all categories pass for climbing lines, the way each performs in a climbing situation can vary greatly. Caution must be taken that the rope is used in a compatible manner. 

16 strand has been used as a popular climbing line in the arborist industry for years. Its great strength, handling, wear resistance and knot-ability make it an excellent line used by many climbers. With an average diameter of 13 mm (1/2”), 16 strand can sometimes have issues with some modern ascent and climbing equipment (i.e. ascender and belay devices). Some of these devices were designed for smaller diameter rope and although will still accept a 13 mm, there may be some friction and bunching issues. The characteristics of this rope make it ideal for DdRT (doubled rope technique). Although I always recommend the use of a friction management device, 16 strand is tolerant of natural crotch tie in points (TIP).

Double braid is constructed as a rope within a rope and usually consists of 24 strands rather than 16. The diameter of double braid is usually smaller compared to 16 strand (Samson’s new Vortex is an exception). Double braid was and will continue to be developed to adapt to modern climbing techniques and styles, therefore it is compatible with mechanical ascender and belay devices. The double braid’s tighter braid and smoother surface will tend to wear aggressively if run over a natural union TIP and it is recommended to utilize a friction management device. 

Kernmantle rope has been making its way into the climbing realm as a crossover from the mountaineering and caving fields. As SRT (single rope technique) becomes more prominent, a growing number of climbers are turning to this low stretch line. Climbers must be aware of the intended use, characteristics and limitations of kernmantle. It is not typically considered a suitable rope for a dynamic DdRT system. Kernmantle is compatible with cammed ascenders and a variety of belay devices. Since this is a static rope and is tightly woven, running over a natural union is undesirable.

Splices & Knots 
Depending on the system used, the chosen termination connection can make a large difference in your system’s compatibility. With some of the newer configurations, using a knot can make the system “crowded” and can get in the way of hitch responsiveness. Likewise, some splice designs can create rigid sections just adjacent to the splice and this too can create an unpredictable rope response. When inspecting climbing systems, climbers should try different knots and splices to find the most reliable system.

Hitch Rope Interface
With well over 20 different types of climbing lines with all different characteristics, as well as at least a half dozen varieties of hitch cordage, the possible combinations are endless. As a rule of thumb, your hitch cordage should not be larger than your climbing line. Also consider that the compatibility between hitches and the climbing line can change over time with the abrasion and wear inflicted on the cordage. If switching hitch cordage, be aware that you may need to adjust the tying of your hitch (more/less wraps) to acquire proper friction. The length of the hitch cordage can also create large variables in the hitch and therefore in the system’s responsiveness and compatibility.

Just like cordage, arborist hardware is plentiful and few steadfast rules apply in the proper selection of which to use. Certainly one rule that must be followed is to only use hardware rated for at least 22 KN (approx. 5,000 lbs.) when in a life support situation. Also, hardware is either for climbing or rigging, but never both.

Selection of hardware and how it interacts with the rest of the climbing system is mostly trial and error.

Carabiners. Carabiner size and shape can affect compatibility. While large biners, e.g. Petzl’s Williams, is easy to open and large enough for multiple attachments, it can be bulky and it won’t centre your load the way an oval biner like Petzl’s OK can. No matter what type of biner or climbing system is used, always be aware of side loading potential.

Most modern climbing systems use alum alloy carabiners that have replaced steel carabiners and snaps. When using steel hardware, check for compatibility with connections and pairing a soft metal with a hard metal, which can wear aggressively.

Pulleys. Most climbers have incorporated a micro pulley into their climbing system to fair lead the hitch. These micro pulleys can be clipped under the hitch with a key chain biner or be fully integrated into the system as with a micro pulley with multiple attachment points. It has been my experience that the design of the micro pulleys (size, shape and width between side plates) can affect the responsiveness of the climbing system. Also be aware of side load issues as certain brands of pulleys have large attachment holes that can wander over a carabiner’s gate.

Parting Remarks
It is important to note that the assurance of a compatible system must fall solely on the shoulders of the climber. Although managers/foremen and suppliers all have input, only the climber himself can be responsible for using climbing equipment in a compliant and compatible system. This is done by researching and understanding equipment characteristics and limitations, talking to colleagues and industry professionals and always modifying or incorporating gear in a controlled fashion. Remember, low and slow. Lastly, if it increases safety and efficiency, only then is it a worthwhile link in the chain that is your climbing system.  

About the Author
Matt Logan is owner/operator of Logan Tree Experts based in the Peterborough/Kawartha area. He is an ISA Certified Arborist/Tree Worker ON931-AT as well as a Certified Tree Risk Assessor CTRA721 and trainer for ArborCanada.

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