Dynamic vs Static Cable Systems, in the upper canopy

jim1nz

Im interested in your thoughts on this. Im going to back dynamic systems and this is why,

Reasons for using dynamic bracing systems as opposed to static;

By installing a static cable into the upper canopy (2/3), this is removing the natural crown movement and stress distrubition.

By installing a static cable into the upper canopy (2/3), this massively reduces any adoptive growth/reaction wood growing to strengthen the weak union. I realise included forks will never be as strong as normal forks.

With out sufficent felxability in the canopy, wind energy is unable to be distrubited effeciently. Stresses, instead of traveling throughout the tree and down the trunk into the ground can be multiplied/isolated through the cable.

Have you ever been up a tree with another climber and shaken a tree to see and feel how it reacts with static cable systems installed? Its obvious whats going on.

All i seem to see here is guys backing the static systems.....

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Eric Frei

Funny that, I asked here and we have some responses.

http://www.treeworld.info/f6/wiresto...html#post23559

Critters are chewing through dynamic systems.

Jim, what is the stretch factor of dynamic systems? In other words lets say the system (dynamic cord) can take 10tonne, how much will it stretch before it breaks. Now in the rock climbing rope world for instance figures of 50% crop up, with say static rigging lines like we use it's only about 10% (to breakage that is) and under normal use only around 3%

So what I'm trying to figure out is you have a dynamic system installed across a span of say 10m and it will stretch how much before it breaks? Maybe 5m which means the leader would have broken, please, save me Googling and researching I'm sure the manf of dynamic systems have to provide this data.

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hartley

The cobra system uses a static, specially designed rope with a relatively open lay. The system is made dynamic by the insertion of a rubber shock absorber. This is pushed inside the rope making it look like a snake after a big meal. as a stem/branch moves and puts more tension on the system the bump is squeezed by the rope trying to equalize the tention across the whole of its self.

It is a dynamic system, but with relatively little stretch, enough to let the tree react with growth but restricting it enough so as to give support.

Very clever and very easy to install

treeseer

I think it's kinda simple--rigid to reinforce unions that are split or cracked (when you do not want movement), otherwise dynamic (when you do want movement).

jim1nz

Yea true, but if this is the case then why dont you install static systems lower in the tree? (1/3 up the canopy from the split) This allows movement in the canopy plus support of the weak union. I do realise this multiplys the forces on the cable though.

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jim1nz

It varies slightly between what size rope your using. At max breaking strength of the 4ton system, its 17% stretch.

If your using the rubber shock absorber, this adds 20cm stretch to the span.

The strength loss over time is calculated and tested to be 2% per year.

Soo if you have a 10m span, the system its self is going to stretch 1.7m at MAX breaking strength. In the tree, each leader is going to move 0.85m apart from each other. In a wind storm at the top of the tree thats not actually a whole lot.


The thing is with cobra, its a support system. Its not ment to do the trees energy distrubition for it, what the system is going to do is provide support and additional strength from what the tree already had before an arborist decided a brace needed to be installed.

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Eric Frei

I think installing it lower on it's own could lead to whiplash and that point becoming the place it breaks. However installing a dynamic further up would eliminate that risk a lot.

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JohN Dee

Whilst I've never braced/cabled a tree, I do know a little bit of theory on it..

With the static, if it is installed near cracked and split unions... The tree will always depend on the static line being there and never grow to support itself.

Where as dynamic cabling further up will make/allow the tree continue to support itself aswell as providing a fall arrest if it doesn't overcome the problem.

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TrevMcRev

Dynamic cables in the canopy, done lots of cobra and just tried the yale type.
Unsure about it yet, i think cobra is better but the other is much cheaper.

Steel for Rod bracing at union when needed as well but maybe only 1 in 20 Cabled trees i do get that as well. Usually smaller less hazardous trees, more about preserving structure that averting a hazard.

Anyone else run cobra off a central ring system before? We did. I know cobra suggest bracing from stem to stem to stem to stem but... its done with steel so why not.

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jim1nz

Yea i dont think thats necessarily true, installing the brace 1/3rd from a split fork acts as the fork its self not so much as a static brace so tree movement oscillation is close to normal. Im just thinking this because a tree moves so much less lower down.

Here are some photos of dynamic and static systems used together, sorry i should have included this in the poll...


This English oak is around 300 years old, lives just out side Stockholm Sweden. It got a 5% weight reduction on the tips and a full deadwood/standard tree care. Big tree, good fun climbing!

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jim1nz

Great photos trev!

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jim1nz

Here are some more photos now i have how to do it sorted...

This is a Horse chestnut also in Sweden although much smaller than the Oak above. Recieved a light thin, lift and a 10% reduction over road and from a building + standard tree care.

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