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Universal Flag (Safety) Line Replacement Ideas

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evan
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Re: Universal Flag(Safety) Line Replacement Ideas

Postby evan » Mon May 31, 2021 8:37 am

The common mistake between most manufacturers is that they make the bungee too short and/or the outer Dyneema too loose so all load is then on the stitching of the bungee which will fail sooner or later nullifying the springiness of that flagout line.

OzBungy
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Re: Universal Flag(Safety) Line Replacement Ideas

Postby OzBungy » Tue Jun 01, 2021 3:31 am

evan wrote:
Mon May 31, 2021 8:37 am
The common mistake between most manufacturers is that they make the bungee too short and/or the outer Dyneema too loose so all load is then on the stitching of the bungee which will fail sooner or later nullifying the springiness of that flagout line.
The bungie has to be short. It's job is to take up the slack when you pull the trimmer. If it's not short then there's no tension to pull in the slack.

When designing the bungie length you have to stretch it out so that it is just short of the rest state then the trimmer is fully pulled. When you release the trimmer the trim bracket moves away and tensions the bungie to its maximum stretched length.

The ultimate problem is bungie cord simply isn't designed for the job it's being used for. Bungie is usually used on things like boat covers with a big knot in the end. The sheathing has no real structure to sew into and the rubber itself is not good to sew into. That's why you get those complicated loopy end attachments.

What works is to feed the bungie out, around and back, then wrap ribbon and sew through that. The bungie is clamped by the sewn ribbon and the ribbon fabric holds the stitches. That takes up length and can make for a bulky attachment point. It will still break eventually. The break point just moves further down inside the line.

evan
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Re: Universal Flag(Safety) Line Replacement Ideas

Postby evan » Tue Jun 01, 2021 6:48 am

I didn't mean the total length, but the relative difference between the outer Dyneema and the bungee inside. Most of the time the Dyneema has still some slack when the flagout line is fully loaded with all the tension on the bungee inside making it snap.

You want all the tension on the outer Dyneema, but it takes more effort to design this well with the right combination of materials and has smaller tolerances with manufacturing.


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