Tree Climbing Multicenders: Akimbo, Unicender (Uni), Rope Wrench (RW), Hitch Hiker (HH2 & HHX), Rope Runner (RR), ZigZag/Chicane (ZZ) & the BullDog Bone (BDB)

Technical tree climbers have a growing number of mechanical SRT multicending tree climbing devices to choose from. SRT (single rope technique or static, fixed or stationary line climbing) has transformed recreational tree climbing, enabling climbers to ascend into and maneuver within the canopies, using the least amount of wasted energy.

In the last twenty years new climbing products and innovations like professional grade multicenders, or devices that combine ascending and descending functions into one device, within the SRT framework have become available. Choosing which device is best suited to beginners or advanced users depends on a number of personal preferences.

In case you didn’t already know, the main difference between single-rope-technique (SRT) and doubled-rope-technique (DdRT) is that with DdRT, you pull two times, or double the length of a moving rope, going up and around a limb and back down. The climber, controls both ends of the moving rope and has a 2:1 mechanical advantage. That makes it easier to lift oneself up a climbing line, but it only advances the climber half as far, when compared to SRT’s 1:1 advantage. Ascending SRT on a stationary climbing line, using a multicending device, together with a foot and knee ascender creates a Ropewalking climbing system. This puts a climber’s weight on both legs and not the upper body, enabling one to capture progress with each leg independently and literally be able to walk up the rope, almost like a ladder.

The Rope Wrench and the Hitch Hiker both use hand-tied friction-cords, aka: prusik cords, tied into rope-grabbing hitch knots. The effectiveness of either device can vary, based on the quality and type of friction hitch, the type of friction cord, as well as, its direct relationship with the climbing line and the climber.  The friction cord’s diameter must be less than the rope’s diameter, in order to properly perform. Once the friction hitch is properly tied, dressed and set, these devices are as effective as the mechanical multicending devices, except for more sit-back that occurs each time the hitch knots are weighted. Most hitch knots also have a tendency to bind and can generally become more difficult to manage, when loaded.

Friction hitches or rope grabbing knots, although they can become tightly bound, are gentle on ropes and well suited for dissipating heat, compared to the metallic friction points, or way more abrasive teeth on certain types of hand, feet, knee or chest ascenders. These teeth, when shock loaded, can strip the cover off a rope. Friction cords are also economical and easy to replace, compared to the cost to replace or retool a worn out mechanical multicending device.

A major concern among hitch cord users is, or should be, knowing when to retire a used cord. While many commercial grade friction cords are heat rated for climbing, excessive friction may cause scorching on the cord itself. By rubbing the cord back and forth against tree bark, it may be possible to scrape off the scorched material.

The Unicender, Rope Runner, BullDog Bone, ZigZag/Chicane and the Akimbo  are completely mechanical multicending devices. They eliminate the use of friction cords altogether. These devices eliminate much more of the sit-back, common among hitch-knot users. Overall efficiency depends on climber’s size, rope width, type, make and condition of climbing line and even weather conditions, but they all seem to perform well with static 11.5mm to 12.5mm (or 1/2 inch) diameter climbing lines.

I began climbing with a Rope Wrench, using a dependable 5-wrap Michoacan (aka: Martin) friction hitch/knot on a 28″ sewn eye-and-eye Bee-Line prusik cord and a Hitch-Climber pulley. While this device is dependable, keeping a close eye on the friction knot and adjusting it periodically to be sure it grabs and releases the rope when needed is always mission critical. Based on my weight, I tried a number of different prusik cords and hitch knots, until finding ones that were better suited to grabbing and releasing my weighted climbing line.

The Rope Wrench itself is incomplete without a recommended eye & eye hitch cord, a hitch tending pulley, 12″ stiff tether and a locking carabiner. The Rope Wrench itself is positioned on one end of tether, above the hitch knot, creating a bend in the climbing line. A hand spliced or sewn spliced eye & Eye prusik cord connects the to the pulley and carabiner, creating an effect that is similar to a DdRT climbing system, but with the benefits of an SRT system. The Rope Wrench’s effect places a bend in the rope, which reduces tension on the hitch knot, similar to DdRT, making it less likely to bind. A tending device, connects the tether to the climber’s chest harness, neck loop, or an over the shoulder lanyard.

The Rope Wrench has the distinction of being the only multicender that’s  for SRT climbing, only. However, the Rope Wrench and tether are mid-line attachable. When changing from SRT to DdRT, one would remove just the Rope Wrench‘s slic pin and detach the tether, while leaving the hitch tending pulley and prusic hitch in place. Just be careful not to drop the slic pin from the Rope Wrench, while up in a tree.

The Rope Wrench, when used in combination with the ZigZag or the Chicane/ZigZag, offers a hitch cord alternative, while providing the mechanical strength and consistency needed for SRT climbing systems. Unlike other multicenders, the ZigZag is not mid-line attachable and that may be challenging when advancing and or alternating between climbing lines. The tests in the following video confirm the integrity and strength of the the ZigZag and proves how it’s relatively safe to use a ZigZag in place of a hitch cord, with a Rope Wrench in an SRT system. Petzl has now released their new 2019 Zig Zags with, or without the built-in swivel. These updated devices are now more rugged and sturdy than their predecessors.

The RopeTek Hitch Hiker 2 is a personal favorite and possibly the best multicending device ever. It’s noted for its overall strength, simplicity and for being compact and efficient when used at different climbing angles. Unlike the Rope Wrench which uses an eye & eye cord, the Hitch Hiker 2 uses a friction cord that’s threaded through a dog-bone like metal bar, secured with a fisherman’s  or other suitable stopper knots on both sides. A steel carabiner and the dog bone add friction to the Hitch Hiker 2’s climbing line when weighted, enabling the prusik knot to perform smoothly and reliably.

A Hitch Hiker 2 can be augmented for tending with a piece of  throw line, a short 5″ rope with two sewn eyes, or my favorite, a holster made of molded plastic. This enables the Hitch Hiker to attach onto the climber’s chest harness, neck loop or over-the-shoulder-lanyard and self-tend the Hitch Hiker while ascending.

Installing the hitch cord on any Hitch Hiker is a bit more tedious than other devices, but tying stopper knots on the ends of the friction cord is simple to learn and once the friction hitch is dialed in, sit-back is minimal and the hitch performs to the satisfaction of a growing number of tree climbers. It’s a very efficient, compact, rugged, reliable and economical multicender.

Both the Hitch Hiker and the Rope Wrench are mid-line attachable. Because prusik cords are economical, easily available and rope-friendly, both of these devices are very popular multicending contenders for hitch knot users. They can take some getting used to, in terms of getting your preferred cord and hitch knot properly tied, dressed and set. The Hitch Hiker is the least expensive to own and operate, compared to other multicenders and it’s built like a tank.

As shown in the above video, Climbing Innovations is now selling a variation of the Rope Tek Hitch Hiker 2, using a Tree Quickie, in place of the original steel carabiner. The Hitch Hiker X no longer has riveted bumps on it’s sides, leaving smooth surfaces on both sides for the Tree Quickie to move more freely. For this reason, I found it impractical to use the Tree Quickie in place of the carabiner on my Hitch Hiker 2, at least without using the plastic tending holster. I’ve also tried using a piece of rubber (BigShot) tubing on the friction knot and it works beautifully.

When friction knots are properly tied, dressed and set using either the Rope Wrench or Hitch Hiker, they perform adequately with minimal sit-back. A friction cord under load and heavy use will eventually wear out, causing it to lose integrity, mainly due to heat build-up and friction.  Friction hitch/knots are not recommend solely for use as a primary repelling device on SRT, unless its being integrated into one of these two devices.

The Unicender is a compact, fully self-contained and mid-line attachable ascending and descending device. It works well on both SRT and DdRT climbing systems. There’s a slight transitional bump or jerkiness that happens when transitioning to and from ascent to decent, but getting used to that is easy. Wrapping the rope around the Unicender on descent is strongly advised, rather than pinching the two outside arms together with your hand and holding on for dear life. The later option is dangerous under any condition and should be avoided.

The risk of an object or falling limb striking the Unicender’s or Akimbo’s upper arm, or any multicending device for that mater, may cause an unintentional or accidental release from the climbing line. Some multicender manufacturers warn against using hand ascenders with foot loops, but when I am on a ropewalking system with a foot and knee ascender, I also like to use a hand non-foot-looped hand ascender, because my hands prefer holding onto a hand ascender, versus the rope itself..

Based on the high friction demand placed on the Unicender, especially due to factors that may include an unwashed climbing line causing abrasion, and through normal wear and tear will eventually take it’s toll. Equipment of this caliber is usually dependable for maybe three years, depending on each individual’s climbing characteristics.

I’ve climbed on my Unicender many times with no slippage, but I am seeing some signs of friction wear on the anodized finish. Although the Unicender has no replaceable parts, there are two options to address signs of excessive wear. For about $200, versus the $300+ replacement cost, you can get the device restored and refurbished through Rock Exotica. In comparison, the Rope Runner has wearable bollards and other components which can easily be replaced with available replacement parts. This may be the one of the most notable differences between the various mechanical multicenders.

For someone like myself who climbs strictly for recreation, home gardening or much less than someone like a tree care professional who regularly hauls cutting and rigging equipment into the trees, from a beginner’s standpoint, the Unicender remains a top contender because of its overall user-friendliness, being mid-line attachable, compactness and especially for being fully self-contained, with no removable pins or parts.

I’m curious about how well all these devices perform in side by side comparisons, with regard to friction, heat retention and dissipation, namely on descents that are 200′ or longer. Changing over to a descender from a  multicending system is no longer necessary, but when rappelling from heights that may reach 200′ or more, a climber may opt to use a Petzl Rig, or another similar type of mechanical positioning or descending device that may incorporate an anti-panic feature, or be designed more specifically for longer, heavier, and/or more controllable descents. Always keep in mind, these devices are all subject to the same laws of physics, friction and heat retention.

Friction and heat build-up can scorch and actually start to melt a polyester covered climbing line, especially if a climber is ripping around and not being attentive enough to their gear. A scuba-diver is subject to embolisms when ascending too quickly, whereas a descending climber depending on a friction knot and or mechanical device may overheat and melt a polyester climbing line when rappelling too quickly for a long duration.

Richard Mumford at has designed a Unicender accessory to mitigate friction, known as the Drum and it looks like it makes things a lot better for Unicender users because of the way it helps improve both friction-management, reduces wear and tear and provides for an easy lock off.  Richard demonstrates its installation and use in the following video.

How the Drum may effect the overall performance of the Unicender, for better or worse, is uncertain, but it does alter the original design in an attempt to make it more durable and functional. I’m not aware of any formal response from the inventor Morgan Thompson, or Rock Exotica who manufacturers the Unicender, with respect to them possibly sanctioning the Drum, or any such modifications to the original design.

The Rope Runner, as demonstrated below, uses a mechanical hitch, very similar to the Rope Wrench, but without any friction cord. It has two auto-locking removable slic pins and uses a carabiner to guide the rope through the device and secure it onto a climbing harness. With proper care, by replacing warn our slic pins, nuts, and the spring from becoming overly worn, a climber can maintain a Rope Runner almost indefinitely.

The Rope Runner performs on a wide variety of ropes between 11mm and 13mm. It’s a top choice for a mechanical multicending device, especially for production climbers. The device requires the use of a tending device like a chest harness, or an over-the-shoulder lanyard. The device’s built-in pulley enables very smooth tending, especially when using a RAD system or when limb walking. The Rope Runner can be augmented with a 4SRT Birdflap, to give the device’s bird a bigger area for the climber to grip onto when descending.

The Rope Runner is comprised of several components: the body, the bird assembly, the tether assembly, the tender-pulley assembly, the lever assembly with the axle spring, two slic pins and the retaining washers. Installation is relatively simple with rope guides etched directly onto the device. The rope is secured between the bird assembly with a slic pin and with the friction bollard in the level assembly using a slic pin. A carabiner secures the tending pulley assembly and connects onto the climber’s saddle.

On a personal note, I know a successful competitive tree climber who prefers using the Rope Runner with a worn down upper slic pin. He is hesitant to replace it, especially after winning a speed climbing competition. He says it gives him added efficiency and control, but the manufacturer may suggest otherwise. While the design may seem rather simplistic, unrefined and clunky, the Rope Runner is affordable, efficient and serviceable.

Singing Tree, makers of the Rope Runner sold the RR’s rights to TreeStuff, who were then bought out by SherrillTree. According to Kevin Bingham, the inventor of the Rope Runner, the Rope Wrench and founder of Singing Tree, the original Rope Runner is well suited for commercial use because of its component based design that vastly extends its longevity when properly maintained.

While new designs do exist, the market eagerly awaits an updated Rope Runner, perhaps with a better tending system, more user-friendly bird design and other overall refinements. If a Rope Runner 2 is more expensive and less serviceable than the original, it may not be able to compete with itself. To my knowledge there are no immediate plans to release a revised Rope Runner, like Petzl does with certain items, but many climbers are optimistic.

Initially I discovered the BullDog Bone with a buy-and-use-at-your-own-risk disclaimer, available through a private party who makes and sells these. The BullDog Bone is a forerunner to the Akimbo which is collaboratively based on the initial design concept. A search on the TreeBuzz forum using the keywords, “BullDog Bone“, may provide access to the individual who sells these.

Like the Unicender and Rope Runner, the BullDog Bone is a fully mechanical, self contained multicending device that has the appearance of being a top contending option, but the BullDog Bone isn’t a mass marketed product and for that reason, it falls outside of my personal comfort level when it comes to testing and researching new products of this magnitude. If it were to become available on a retail level, my ability to compare this to other similar products would be less biased.

The Akimbo became available, as of January 25, 2019. It is both SRT and DdRT friendly,  aesthetically pleasing, compact, adjustable for use on static climbing ropes on specific “approved” ropes between 11.5mm and 13mm diameters. It uses no external locking pins and it doesn’t rely on a friction cord.  It uses two adjustable bollards, to assure better conformity with different size climbing lines. The tending system is unique and includes a wire gated hook. This may take a bit of time for climbers to get adjusted to and hopefully come to appreciate.

In the following video, the Akimbo’s creator, Jaime Merritt, shows a couple tending methods, using a climbing lanyard. My preference is the Petzl Torse Croll Harness, a lightweight adjustable webbed suspender-like 1″ strap that attaches the the Akimbo’s wire-gated tending system using a micro-carabiner, or something similar. Having the ability to control tension when remaining attached to the wire gate tending system gives me more mobility, especially when I pause for a rest during a long ascent.

Finding the proper bollard settings is required every time a climber uses their Akimbo and different climbers may have different settings on the same or similar ropes. Using ropes under 11.5mm on the Akimbo may cause slippage and Rock Exotica has published their list of approved weight rated ropes, some with a 220lb weight limit, and some with a 286lb weight limit.

The Akimbo’s approved rope list appears on Rock Exotica’s web site and is expected to grow over time as more ropes get tested and new ropes become available. My personal experience when trying several non-approved ropes has been less than favorable when it came down to not being able to dial into functionally safe and usable bollard adjustments. For that reason, I bought a new 150′ hank of Drenaline by Teufelberger, which runs great for me. I now enjoy the Akimbo on an approved rope and feel more secure and confident doing so.

Perhaps the Akimbo will someday evolve and include self-adjusting bollards that work on a broader variety of rope sizes, or maybe adapt to using a non-breakaway tending point. Despite the set up time, hard to see bollard pin settings and the unique learning curve, the efficiency and compactness of the Akimbo, when used properly, puts it in a class of its own.

I initially began climbing with the Rope Wrench and then the Unicender, once I became better trained and understood the fundamentals of climbing. The Uni has no sit-back and tends so much better than the Rope Wrench‘s friction hitch, its like day and night. I then acquired a Hitch Hiker 2, which I enjoy for the sake of its compactness and rope-friendly efficiency. Eventually, I then acquired the Akimbo, and was one of the first to receive shipment, having been one of the first to place a pre-order. At that point, the temptation to buy a steeply discounted Rope Runner became too unbearable, so I bought a Rope Runner to add to my collection.

Over time it turns out that the Rope Runner has become my favorite mechanical multicender, with the Hitch Hiker taking a close 2nd overall and being my top choice for hitch based multicenders. If I find myself climbing in foul, wet or during inclement weather, the Hitch Hiker 2 is my preference.

I’ve gone full circle. I’ve come to appreciate and deeply respect the overall benefits of rope-friendly friction cords, in comparison to less rope-friendly mechanical ascending products that flatten and/or use teeth like cams to grip the climbing line. I’m also comforted knowing how we all can totally rely on each of these multicending SRT devices, when used responsibly and safely, in accordance with the manufacturer’s guidelines.

Given the diversity of static climbing ropes, it’s becoming apparent that certain ropes perform better than others, depending on the specific multicending device. The Akimbo is geared toward ropes in the 11.5mm-13mm range, while other multicenders also work on smaller diameter ropes. Of all the available static climbing ropes, some devices may or may not work properly, so be sure you are buying a rope that is properly suited to your climbing system/s.

In conclusion and based on feedback from others, I recommend the Rope Wrench, Hitch Hiker and/or the Rope Runner for daily production work. The Akimbo and the ZigZag/Chicane are also solid viable options, especially for more experienced climbers with different preferences, but unfortunately the ZigZag remains non-mid-line attachable. The Unicender is the most user friendly, with no removable components, but it eventually wears out. The Akimbo has a tendency to wear out too and although it’s light and compact, it loses some of its appeal because of it’s finicky bollard settings and restricted usability, except on manufacturer approved ropes.

The ZigZag is non-mid-line-attachable, but the Chicane is. This combination ZigZag/Chicane combination is an SRT friendly mechanical replication of the Rope Wrench with the mechanical ZigZag hitch in place of the Rope Wench. It’s a solid alternative to using more finicky hitch cords with the Rope Wrench, but since it’s feasible and economical for climbers to combine a ZigZag with the Rope Wrench, thereby replacing the Wrench’s hitch cord with the ZigZag, this is another SRT multicending option, as well.

Seasoned and old-school climbers may prefer the Hitch Hiker or Rope Wrench, when the weather sucks, but will likely favor using a mechanical multicender when the conditions are optimal. The Rope Runner and the Hitch Hiker both have replaceable components which make them my two top picks for both rec and production climbers, but the adjust-ability, compactness and efficiency of the Akimbo also makes it the most promising multicender to emerge on the scene, once the climber gets it everything properly dialed in.

This article is updated periodically, as needed to hopefully keep up with new products and industry standards. Please leave a comment. Your feedback is appreciated.

Related Information: My Gear Bag, Where to Buy Tree Climbing Gear & Tree Climbing Gear for the Fully Autonomous Recreational Tree Climber