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Backup Extender – length calculation

Hello community,


In that objective, I developed the Split connection, allowing to get it with standards lengths of webbing (50m or 100m), whatever the webbing is used for mainline or for backup. This is much more versatile than having really long continuos strands, or than having different sizes of strand depending if the webbing is dedicated to be  a mainline or a backup.

This is working very well but we are receiving quite often the same question from our customers which is : « Which length should I use for my extendor ?»

This is difficult to answer without any other info as this extender length is depending on the mainline elasticity, the static tension of the line, your practice (only walking, surfing, bouncing, amplitude…).

Bigger loops of backup are more confortable to walk as they will stabilize the line, but if the loops are too long, the shock in case of backupfall can be extremely violent, and the rider can sometimes fall down to the ground before to be catched by the backup… !

Shorter loops are a pain to ride as on dynamic, if the backup get tight you cannot enjoy the full behavior of the mainline.

In my opinion, the best length for a backup is the shortest one that still allow to bounce like a machine without getting the backup tight.

I so decided to develop a simple calculator based onto physical laws and experience that you can find THERE.

We noticed that usually, the ratio between static and maximum dynamic load on a highline is almost fix and not depending on the webbing properties or weight of the rider. With the biggest amplitudes it goes down to 0.6. 

The calculator is based onto this ratio and the laws of physics. You will only need to fill :

-The length of your splits (50m, 100m or any special length)

-The elasticity value of your mainline

-The static tension that you use to rig, with you sitted in the middle of the line. If you don’t have a dynamometer, just use the formula T=L*P/4/s with :

T= Tension (kg)

L=  length of the line (m)

P=  your weight (kg)

s=  sag (m)

And the calculator will give you the best suitable length for your extender.

Enjoy !

Florent BERTHET