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The ultimate guide to Stationary Rope Technique (SRT) climb systems
I have personally spent lots of time with these devices and found that any of these (when set up correctly) can be used to effectively perform safe and efficient tree work. There are certain factors/features however which make a significant difference in usability. The following are my primary considerations and the pros and cons of each device.
If you don't want to read this whole article you can get the gist of it from this video: (If you want to go deeper keep reading!! there is lots more in this article than in that video)
The features that matter
Certifications:
Some of the devices released in the US over the last few years have little to no “official certification” This may not matter to you personally so long as they have been tried, tested, and proven to be safe when used correctly. However, employers might not allow equipment without some official stamp of approval.
Tolerance of contamination on ropes:
This is critical because a clean rope may not always be available. All these systems work well on a clean fresh rope, but work in the trees exposes lines to dirt, pitch, and other contaminants. For example, the Akimbo is one of my all-around favorite devices, and I use it almost exclusively when I have new ropes, but as soon as those ropes have ANY sap on them the akimbo goes back in the toolbox to be replaced by a system that won't lock onto the rope when it encounters a little pitch.
Ease of installation midline:
Many climbing techniques require repositioning the climb system in the tree and if that can be done efficiently without fumbling parts or pieces then that saves time and effort. Conversely, if the whole rope must be threaded through the device (ZigZag) or if removing creates loose gear (OG rope runner) time will be wasted. On the other hand, the fixed nature of the ZigZag on the rope may inspire confidence in those who are more concerned about their device failing, so this compromise may be acceptable to some.
Length and ergonomics:
When working on a spar it is often best for the device to be close to the climbing anchor, and if the climb system is too long or worse, both long and rigid then it can force a climber out of ideal position because of that limitation.
Smoothness of releasing:
Many movements within the canopy require precise balance, and the climb line is a primary point of contact. A smooth and consistent release of friction is necessary to balance and move efficiently in the tree. A device that has jerky, inconsistent, or two-handed release will be irritating and inefficient.
Rope Walking Compatibility:
The rope walking technique is the most efficient way to make a long ascent without a powered ascender, so anytime frequent rope ascents are necessary within the canopy it is best to avoid using a device or system (like most rope access descenders) that cannot easily be integrated with a rope walking system.
Hitch Cord, Rope Wrench, Tether and Pulley SRT Climb System
The performance of this type of system depends on which combination of hitch cord, climb line, wrench and tether are used. Each combination has its compromises, and some are better than others. The adjustable wrenches like the ISC Apex and the Notch Flow have some extra adjustability which can be nice (I’ve never wanted more adjustability myself but I am only 170 lbs plus gear) and there are a variety of tethers some soft and some rigid. Overall, these pros and cons are consistent through most configurations.
Pros
Less new gear needed
Use familiar hitch cord combinations
Uses familiar techniques to MRS closed systems
Easy switch between SRT and MRS
Can replace hitch cord if sappy or burnt
Easy to adjust for different climb lines
Easy to inspect
Cheap to replace hitch cord
Easy to bend and resists cross-loading (with soft tethers)
Midline attachable
Cons
Hard to know when to retire the cord
Inconsistent performance because of lots of variables
Long make for tricky positioning
Slow to install or uninstall
Easy to misconfigure
Can be more expensive over time to replace hitch-cord
Long sit-back
Rope Runer
Pros
Consistent Friction
Adjustable to accept different climb lines
Fairly tolerant of contaminated rope
Tested to relevant CE and EN standards
Simple to install
Midline attachable
Easy to switch between SRS or MRS
Compatible with rope from 11mm-13mm
Easy one-handed use
Easy to inspect.
Cons
Loose components that can be dropped
Somewhat slow and tedious to remove mid-line
Easy to side-load
Somewhat long making for challenging positioning
Known Mild failure potential under a fairly common condition (dirty or damaged spring on the bird )
Hard on fingers to release under load
Not the most consistent in release, and difficult to adjust
Tends to flatten ropes with repeated descent and then creep
Zigzag with Chicane
Pros
Incredibly consistent performance
Easy to find and common
Approved by relevant CE and EN standards
Very tolerant of rope contamination
Easy to learn/train when transitioning from hitch-cord
Built-in Pulley allows for easy 3:1 rescue lift or V-Rig
Simple, obvious installation (difficult to misconfigure)
Built-in swivel prevents tangling with a MRS
Very smooth operation
Compatible with rope 11.5mm - 13mm
Can be used for a two-person descent with additional friction
Cons
Requires specific carabiner to use
Easy and dangerous to cross-load
Difficult to inspect
Not mid-line attachable
Not repairable
Wears out quickly on dirty ropes
Long and clumsy in SRT
Difficult to pull slack through device
Akimbo
Pros
Easy to adjust
Very compact
Easy to inspect
Easy and fast to Install midline
Easy to switch between SRS and MRS
Easy one handed use
No loose parts
Cons
Jams severely with sap/pitch on the rope
Drags on ascent
No built-in Swivel
Limited rope selection
Not certified to conform to current standards for Industrial use Ascenders, or Descenders
Expensive
Rock Exotica Unicender
Pros
No Sitback
Tends easily
Consistent performance
Easy to install or remove midline
Easily switch between MRS and SRS
Tolerates a rope with contamination
Short and difficult to cross-load
Functions well with a wide variety of rope diameters.
No loose parts
Cons
Difficult to use one-handed
Difficult to modulate friction
Not smooth while learning
When in SRS a panic can easily result in an uncontrolled descent.
Tending slack is awkward
Expensive
Lacking EN, ANSI or CE certification
Taz Lov2/3
Pros
Easy and fast to install or remove midline
Minimal sit-back
Drags when tending
Consistent performance
Compact and difficult to cross-load
No loose parts
Can be used with a 200kg Load with added friction in a rescue scenario
Cons
Limited to 10-11mm ropes
Requires two-handed use
Is difficult to operate smoothly
Unusual to find in the US
HitchHiker XF
Pros
Use familiar hitch cord combinations
Easy switch between SRT and MRS
Easy to replace hitch cord if sappy or burnt
Easy to adjust for different climb lines
Easy to inspect
Cheap to replace hitch cord
Easy to bend and resists cross-loading (with soft tethers)
Midline attachable
Cons
Hard to know when to retire cord
Inconsistent performance because of variables inherent to friction hitches
Slow to install or uninstall
Easy to misconfigure or tie wrong
Can be more expensive over time replacing hitch-cord
Long sit-back
Slack tending can be rough.
Lacking CE, EN, or ANSI certifications.
Rope Access Descenders
(Petzl ID, EDELRID Megawatt et. al.)
Pros
Smooth controlled descent
Most have anti-panic features
Minimum sit-back
Long history of safe use in rope access
Easy to install midline
Clear documentation for testing and certifications
No loose pieces
Most can be used to perform a rescue with 200kg load on one device with added friction.
Cons
Most have narrow rope diameter compatibility
CANNOT be used in a rope walking system
Must use a RAD system or similar to ascend
Can be difficult to pull slack through device