In early 2014 we introduced a completely new diverter concept to the slackline community with the Zilla 3. Basically, we left the realm of cylindrical shapes behind and did a step forward to a more sophisticated approach of anchoring slackline webbings.
With the current introduction of the Lynx 4 we refined the Evolve diverter concept even more, thus leaving some questions about the basics, functionality and effectivity of the concept in the slackline community.
From the start Landcruising was involved in the evolution of slackline "bananas", based on Scott Balcoms Slackdog. We set the kickoff to manufacture the first steel "banana" together with Heinz Zak back in spring 2007. Later on in 2008 Michi Aschaber took the design and introduced it to a wider audience. In spring 2010 we set the next step by introducing the push-button-concept and the direct shackle attachment to the slackline weblock market for the first time. Two features which are used in nearly every weblock nowadays.
Naturally we did a lot of break tests with a wide collection of webbings and different weblocks, including chainlinks, rings, bolt lockers and "bananas". You can read more about break strength efficiencies on our SlackLab website. In 2010 we designed a big weblock called Revolve, using the capstan principle which will be explained shortly. The Revolve was specially designed for our high-end dyneema webbing Aeon,allowing us to anchor the webbing safely at very high tensions.
So we were always in search of more efficient but yet handy weblock designs. The main question was about how we achieve a superb break strength efficiency of the webbing inside the weblock, while keeping the overall dimension and weight as small as possible.
Premise 1: Webbing strength reduction inside banana like weblocks relates mostly to the diameter size of the main diverter. The bigger the diameter is the more homogenous the webbing is loaded through its thickness, e.g. the load on the inside vs. the outside fibers converges. Ok that's easy to understand.
Now we step one level up. We are going into the theory of friction mechanics. Ever heard of the "Euler-Eytelwein" formula (in english language commonly known as capstan equation)? Here it is:
Premise 2: So basically the equation gives us the relation between the load reduction in the webbing and the sling angle over a cylinder. One major parameter is the webbing to webbing friction coefficient. The higher the sling angle the lower the load. The outcome of this principle you can observe everywhere in the real world (climbing belay, marine rigging etc.).
Now we put the premise 1 (bigger diameter = higher strength retention) and premise 2 (higher sling angle = lower load) together. And what we get is our Evolve shaped diverter. With an increasing sling angle on the diverter, the load on the webbing reduces resulting in a smaller curvature radius of the diverter. Ideally the resulting diverter shape looks a little bit like an evolvent (a mathematical curve), that's why we called this diverter design "Evolve". A more simple approach is to cut a full cylinder into half and round the edges. However maximizing the reduction of curvature radius uses the full potential of physics.
In practice for example, we have an approximately webbing-webbing friction coefficient of around 0,15 to 0,3. This gives with a sling angle of 40 degree a load reduction of around 10-20%. Now with our extended knowledge of webbing break strength parameters, we know that webbing A will break at this force with that diameter and so on. So basically we can design an optimized diverter. We reduce the curvature radius with increasing sling angle. Its logical that we choose the webbing which suffers the most from strength reduction on a small cylindrical shape, a relative thick webbing with low stretch properties. This is our "shape design webbing".
In the following picture you see the result: cylindrical main diverters of the former generation with Evolve shaped diverters of the new generation.
Obviously the diverter sizes are becoming smaller and even more efficient at the same time. Thats double magic! Furthermore the whole weblock design benefits from a smaller diverter. The sideplates can be designed smaller too. The distance between frontpin and main diverter can be drastically reduced , improving the weblocks strength and weight. In addition the handling (pretensioning of line) and the high-load slipping behavior is enhanced too.
Of course, we approved the function in practice with lots of webbing break tests. We compared the Zilla 2 (cylinder diverter)and Zilla 3 (evolve diverter) with Core 1 webbing. And we compared Lynx 3 (cylinder diverter) and Lynx 4 (evolve diverter) with Core 2 HS webbing. In following you will find the results:
Test series 1:
Core 1 strength 43,8 kN (we used for all tests the same webbing batch, all tests with single wrap and stopper knot).
|Test||Weblock||Breaking Strength||Failure Mechanism|
|1||Zilla 2||39,12 kN||slipping of Core 1|
|2||Zilla 2||39,70 kN||break of Core 1 at test machine grip on opposite site|
|3||Zilla 2||39,60 kN||break of Core 1 inside Zilla 2 at main diverter|
|4||Zilla 3||42,60 kN||break of Core 1 at start of diverter|
|5||Zilla 3||42,00 kN||break of Core 1 at start of diverter
After this tests we improved the diverter geometry of Zilla 3 at the webbing inlet additionally, so for the serial batch the weakest point regarding webbing strength is at the frontpin.
Test series 2:
Core 2 HS strength 45,4 kN (we used for all tests the same webbing batch, all tests with single wrap)
|Test||Weblock||Breaking Strength||Failure Mechanism|
|1||Lynx 3||31,13 kN||minor slipping starting at 20 kN, fiber melt and break|
|2||Lynx 3||32,74 kN||successive slipping starting at 20 kN, fiber melt and break|
|3||Lynx 3||34,85 kN||successive slipping starting at 20 kN, fiber melt and break|
|4||Lynx 4||40,09 kN||no slipping until break|
|5||Lynx 4||39,51 kN||no slipping until break|
|6||Lynx 4||40,44 kN||no slipping until break
In case of the Lynx 4 we could improve the break strength efficiency by over 21% and simultaneously reduce the weight by nearly 40%, also because of the use of lighter aluminium!
We have to mention that the results of webbing break tests can scatter widely. Every webbing is different, depending on yarn material, yarn density, weave style, overall webbing construction, treatments etc. The test method has its boundaries too. So we have no absolute values, but we have relative results. We compared the different weblocks with the same webbing, same testing method and same boundaries.However this relative comparison gives us a good validation of the theoretical background.
The Evolve diverter geometry, which is patented by Landcruising, is the start of a new era of high end weblocks. This principle enables us to create lighter and stronger weblocks with increased safety and higher performance, compared to the traditional weblock design.
We are proud to equip our two premium weblocks Lynx 4 (coming soon) and Zilla 3 with this innovative technique.