What is a « Anti-Projection » design?

For our second article of this technical section, we choose to present you the concept of our « anti-projection » designs. Obviously, this is refered to all our products.


The risk

When a slackline is tensioned, that create streching into the webbing which accumulate some élastic energy. You don't have to be a rocket scientist to understant that if the sling breaks for example, every of the metallic parts will be projected. And unfortunately, this projection will be oriented to the middle of the webbing, in other words to the people riding the slackline !

Some basis rules

The first rule is ti be intelligent. When you rig, you should always anticipate the risk. Before to attach your slackline to a shutter hinge pin, ask yourself the right questions : « Is it strong enough ? What will happens it it breaks ? » To answer the second question, it is getting to the point of the backup. If you do not understand what it is about, please reffer to the Slackimoufle or Mini Double’s manuals. The fird rule applies to designers, and that is what we gonna develop on this article. It is extremely important to design the products in order to limit as much as possible the damages if its breaks. Let me assure you that at Slack Inov’, this step is complusory as the following sections will show you.


Case of banana

A weblock can break at several locations :

Example with the Slackibloc 3.1 : We can wonder if it would be suitable for itto break at 1, 2 or 3 ?

1 : If it breaks at 1, the weblock will not be hold anymore by the shackle. Il will thus fly in direction of the rider. Not so good…

2 : if the weblocjk breaks at the second location, same conclusion, still bad…

Last solution, n°3 : Then, the webbing will be liberated (perhaps cut, dependind on the configuration) but the weblock will stay in place.

« Anti-Projection » Weblock
(For the Slackibloc 3.1 and Slackibloc Jump, the front pin will break first. Same conclusion.)
Exemple of badly designed weblock, the break involve a projection of the body.


On Slack Inov’ pulleys (Slackimoufle + Mini doubles), the rope break first. That does not prevent the pulley to be projected, but the multiples redirections of the rope inside the sheaves induce inertia which limit a lot the projection compared to a break in the connexion eye. If used with the STAUP, the rope will slip on the brake far before the break on the gear (6kn on the rope strand).

What about the fatigue behavior ?

In many circumstances, a mechanical fatigue’s braek will not occurs at the same location as a simple loading break. This is notably due to the fact that the metal will be diformed before break thus the geometry and the location of high stress zones will be modified.

before/ after, we notice that the piece is deformed

Also parts subjected to shear stress will endure a specific behaviour in fatigue sollicitations. That is why, for example the Slackibloc jump is weaken between the two pins. The aim is to warranty that in any cass of break, this will occurs on the front part of the weblock and not on the tail.

Conclusion : Don’t worry !

This design rule does not replace at all a backup. However, that limit significantly the risks of accident in any configurations. I don’t know for you, but personally, that helps me to feel « slack. »

Florent Berthet

Mechanical Engineer

Designer of Slack Inov’ products


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