Highline Tensioning

[jdcalamia]

What's your go to method without a dynamometer?

[FiremanLyman]

Feild math using the Rule of 12/18 (12 for 7/16th and 18 for 1/2 inch rope).

With 7/16 (11mm) rope if we retain 100% strength, using say a tensionless hitch, you have a 6000# MBS. Rule of 12 with 7/16 rope says; MA * number of people pulling stays at or less than 12.

With 1/2 inch (12.5mm) rope, 100% MBS 9000#. Rule of 18 with 1/2 inch says; MA * # on haul team less than or equal to 18.

Both these rules are based on the average person pulling 50lbs based on average hand strenght. So 3x haul team bubbas on a 4:1 gives you 12. 12 * 50lbs per equals 600# or a 10:1 SSF on a 6000# MBS 7/16 rope.

Works same for the 1/2inch rope, 4x haul team bubbas on a 4:1 gives you 16, or 3x on a 5:1, or 6x on a 3:1... none break 18. 18 x 50# per gives you 900#, or a 10:1 SSF on the 9000# 1/2inch rope.

That and a critical anchor based on load and anchors.

[MichaelXYZ]

This forum is blessed to have you on board Drew

[Rescue 2 Training]

Feild math using the Rule of 12/18 (12 for 7/16th and 18 for 1/2 inch rope).

With 7/16 (11mm) rope if we retain 100% strength, using say a tensionless hitch, you have a 6000# MBS. Rule of 12 with 7/16 rope says; MA * number of people pulling stays at or less than 12.

With 1/2 inch (12.5mm) rope, 100% MBS 9000#. Rule of 18 with 1/2 inch says; MA * # on haul team less than or equal to 18.

Both these rules are based on the average person pulling 50lbs based on average hand strenght. So 3x haul team bubbas on a 4:1 gives you 12. 12 * 50lbs per equals 600# or a 10:1 SSF on a 6000# MBS 7/16 rope.

Works same for the 1/2inch rope, 4x haul team bubbas on a 4:1 gives you 16, or 3x on a 5:1, or 6x on a 3:1... none break 18. 18 x 50# per gives you 900#, or a 10:1 SSF on the 9000# 1/2inch rope.

That and a critical anchor based on load and anchors.

The 12's and 18's apply to a loaded highline with the load at it's center point, where the most force will be felt by the anchors. It also assumes that the haulers are using a hand over hand tensioning method and not wrapping the rope around their hands and heaving on the haul line.

Using this tensioning method, you will get around 3kN of force on each anchor for a one person load.

Highlines really only need to be tensioned enough to clear obstacles in the way of the rescue package. If you can get away with less tension than the 12's or 18's, then do so.

Here is a paper with a little bit of history and some good guiding principles from the guys at Rigging for Rescue. RfR was started by Arnor Larson who, incidentally, was the guy who drove forward the Kootenay Highline System when it was developed.

http://www.paci.com.au/downloads_pub...Paper_1997.pdf

[servantleader]

To elaborate, the 12/18 guidelines mentioned above are designed to maintain a 10:1 SSSF: 3 kN maximum tension in an 11 mm track line (30 kN unknotted tensile strength) and 4 kN maximum tension in a 12.5 mm track line (40 kN unknotted tensile strength).

The RfR paper at the link in the above post is highly recommended reading.

[FiremanLyman]

Highlines really only need to be tensioned enough to clear obstacles in the way of the rescue package. If you can get away with less tension than the 12's or 18's, then do so.

Here is a paper with a little bit of history and some good guiding principles from the guys at Rigging for Rescue. RfR was started by Arnor Larson who, incidentally, was the guy who drove forward the Kootenay Highline System when it was developed.

http://www.paci.com.au/downloads_pub...Paper_1997.pdf

Agree 100%, rule of 12/18 is what is not to be exceeded, there is no need to force more tension into the system than is needed to complete the operation. Original question was what to use in the field in lieu of a dyno.

The KHS paper is a great read, thanks. Added to the collection.

[Rescue 2 Training]

Agree 100%, rule of 12/18 is what is not to be exceeded, there is no need to force more tension into the system than is needed to complete the operation. Original question was what to use in the field in lieu of a dyno.

The KHS paper is a great read, thanks. Added to the collection.

Yeah, I forgot to emphasize that in my post. If you stick with 12's and a one person load, the need for a dyno is lessened because the hit on the anchors will remain roughly in the 3-4kN range using the KHS guidelines.

[jmatthe2]

We teach a pre and post tensioning method. A 2:1 with one puller (pulling as hard as they can) is used to pre-tension; the rules apply for post-tensioning should more tension be needed in the rope to clear an obstacle.

Many institutions teach pre-tensioning using the rules and/or with a 4:1 MA. This simply places too much tension on the system and can drop you down to a pretty low SF if your not careful. The problem with this tensioning method is that, yes, you can guestimate your input tension into the system. However, you will always have a variable of your load mass. Not all rescuers weigh the same and the span length. Both will affect the angle at center span.

[Rescue 2 Training]

The problem with this tensioning method is that, yes, you can guestimate your input tension into the system. However, you will always have a variable of your load mass. Not all rescuers weigh the same and the span length. Both will affect the angle at center span.

If your input force is the same, it doesn't really matter what the load mass is. If it is too large, you simply will not be able to raise it while it is at center span. This means you will have the required sag to keep the forces on your anchors low.

I'm generalizing, but: if a 12:1 (the constant in the equation) will get you to 170 degree highline with 100kg, it will only get you to 150 degrees with 200kg, 120 with 300kg, etc...

The numbers aren't correct, but he concept is. You can only raise a load so much with a constant input force.

[jmatthe2]

DC - I don't think we are on the same page. The comment you quoted was not related to post-tensioning with a center span load. It is with regard to pre-tension with no load. I agree with your generalization in a post-tension application and that is the beauty of the rules Arnor Larson developed.

If I pre-tension with too much power, I make a guitar string tight system. If I then move a load across that guitar string tight track, leg tensions will be higher.

Vice versa, if I PRE-tension the system with a small MA (2:1) and then move my mass across the span I can apply the Rules of 12/18 to raise or lower the system with confidence that I won't overload. This is where your generalization example will apply.

The spirit of my post is the more tension you begin with on an UNLOADED trackline, the more leg tension you will end with when you move the load across the span.

I don't get on here very often so I hope that makes sense...It's late and been a busy shift...I just spent more time correcting typ-o's than writing!!!! Sorry If I missed any!!

[Rescue 2 Training]

You're right, I was misreading your post. I didn't know you were talking about tensioning an unloaded trackline.

We're on the same page now!

[sfdtruck1medic]

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