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

Over at TreeBuzz I started a conversation-thread to see what seasoned and experienced tree climbers were using, in terms of the latest and greatest mechanical SRT tree climbing devices. SRT (single rope technique or static, fixed or stationary line climbing) has transformed recreational tree climbing, enabling climbers to ascend and get the maximum results with 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.

The Rope Wrench and the Hitch Hiker both use hand-tied friction-cords, aka: prusik cords, tied into rope-grabbing hitch knots which connect directly to these devices. The effectiveness of either device can vary, based on the type of friction knot being used.  Once the friction hitch is properly tied, dressed and set, these devices are almost as effective as their fully-mechanical competitors, except for the sit-back that occurs each time these hitch knots are weighted.

The economics of replacing a friction cord are favorable, compared to the cost to replace or retool a worn out mechanical multicending device. Wear and tear is subject to each climber’s individual climbing characteristics, prusik cord preferences and frequency of use.

The Unicender, Rope Runner, BullDog Bone and the Akimbo  are completely mechanical multicending devices. They eliminate the use of friction cords altogether. These devices eliminate the sit-back, common among hitch-knot users.  The efficiency can vary, depending on climber’s size, rope width, type and make of climbing line and even weather conditions, but they all seem to perform well with static 11mm/7/16″ climbing lines.

As a beginning SRT rec-climber, I opted to start using the Rope Wrench with a dependable Michocan (aka: Martin) friction 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 mission critical.

The Hitch Hiker is noted for it’s compactness and its ability to work effectively at different climbing angles. Unlike the Rope Wrench, it requires that an unspliced friction cord be tied securely to both sides of the Hitch Hiker. Once properly installed, this device performs very well.  Both the Rope Wrench and the Hitch Hiker are favored multicending devices among many old-school climbers, mainly for it’s efficiency and reliability.

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 wear out, causing it to lose integrity, mainly due to heat build-up and friction.  Friction knots are not recommend solely for use as a primary repelling device on SRT, unless it’s being integrated into one of these two devices.

While many commercial grade friction cords are heat rated for climbing,  excessive friction may cause scorching on the cord itself.  Hand-massaging the cord and if needed, by rubbing it back and forth against tree bark, it is possible to scrape off the excess material caused by scorched rough spots or damaged areas on the cord, but eventually it will wear out.

The Unicender is a compact, fully self-contained and mid-line attachable ascending and descending device. It works well on both SRT and DRT 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 Uni 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.

A concern for production climbers more than recreational climbers is the risk of an object striking the Uni’s upper arm, or any multicending device,  and causing an unintentional or accidental release from the climbing line. This may occur as a result of falling debris or improper use and while it may only have a temporary effect while the pressure is being exerted, once it’s gone, the device should re-engage.  However, the end result may potentially cause a shock-load to you and your climbing system.

Using the Unicender on a daily basis and/or based on the high friction demand placed upon it, over time it may tend to wear out quicker than other similar products, creating the potential for it to slip on the rope.  For about $200, versus the $300+ replacement cost, you can get the device restored and refurbished through Rock Exotica, but for daily production work, many production-climbers prefer the Rope Runner’s or the Rope Wrench’s  consistency and durability. For someone like myself who climbs for recreation maybe once a week, the Unicender is a top contender and offers a lot of bang for the buck.

Each device certainly has its pros and cons for specific uses in specific climbing situations and there are a lot of great things to say about all these devices, once you get everything nicely dialed in. What I’m curious to know is how well all these devices perform on descents that are 200′ or longer.  Changing over to a Petzl Rig or other similar mechanical breaking devices may be preferred for longer descents, so keep in mind, these devices are all subject to the laws of physics.

Friction and heat build-up can scorch and even melt a climbing line, especially if a climber isn’t being attentive enough to their gear when descending on any repelling device. 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 long durations.

Richard Mumford at has designed a Uni accessory to mitigate friction, known as the Drum and it looks like it makes things a lot better for Uni 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.

Another recent addition to the multicender family is the Rope Runner. As demonstrated below, it uses a mechanical hitch, very similar to the Rope Wrench but without any friction cord. It has two auto-locking removable pins to guide the rope through the device, but is otherwise fully self-contained.

Singing Tree, makers of the Rope Runner are rumored to have a Rope Runner 2 coming out at some point. Perhaps it’ll be a more efficient and rope friendly version of the original, without any removable parts. Rumor has it that Singing Tree may keep the original Rope Runner in production while adding the newer Rope Runner 2 to their line of multicenders, costing about $100 more. It will, no doubt, be warmly welcomed into the family of multicending devices.

A prototype product has come to my attention, available through unconventional means and involves a buy-and-use-at-your-own-risk disclaimer.  Even under these circumstances, this is a highly regarded multicending device, favored among many production climbers. A member of the TreeBuzz group sells it and the product is known as the BullDog Bone. It too, like the Unicender and the Rope Runner, does not use a friction cord. It is a compact, self contained multicending device that has the appearance of being a top contending option and with that being said, I am uncertain why this product isn’t already being sold over-the-counter on a retail basis. Possible usability issues being addressed and/or further ongoing refinements to make the device efficient on different size ropes are speculations on my part.

Here’s a preview video of the Akimbo. There’s already quite a stir in the tree climbing community about this innovative product. It is both SRT and DRT friendly,  aesthetically pleasing, compact, adjustable for use on different width ropes, using no external locking pins and it doesn’t rely on using a friction cord.  Unfortunately it’s still in the initial R&D/production phase and not expected to hit the shelves until maybe sometime in 2018.

As a newbie I think I made a good choice by starting with the Rope Wrench and then upgrading to the Unicender, once I became better trained and understood the fundamentals of climbing. I’d also rather not be as reliant on temperamental hitch cords, but at the same time I’ve come to appreciate the overall benefits a friction cord has, in comparison to less rope-friendly mechanical ascending products that use teeth like cams to grip a climbing line. I’m comforted knowing I now have access to two dependable multicending SRT devices in my gear bag.

In conclusion and based on the group’s feedback, I recommend the Rope Wrench or the Rope Runner for daily production work, otherwise the Unicender may be a better option for climbers who climb less frequently, or who can afford and don’t mind replacing a worn out device more often. Of course, this may all change when the Akimbo becomes available, so please stayed tuned.  has published a description, a video and photos. They say Rock Exotica’s Akimbo will be out later this spring.




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