Questions on Cobra Vs. Treesave

[FBerkel]

Questions to anyone and everyone:

1) Have these two had their respective dampeners tested when properly installed? In other words, does the dampener for the x-lbs tensile strength system actually break at x lbs? How about relative longevity of the two?

2) The Cobra blurb in the Sherrill catalogue says "...less suitable for taut support of unbraced crotches with included bark." Less suitable than what?

3) Does this mean it is less suitable for "taut support" in guying applications than some other system?

4) Treesave dampener looks less reliable than Cobra's, due to wrapping the rope around it, instead of internal placement in Cobra. Is this a valid impression?

5) Does anyone have more detailed info about how these two test out, compared to each other?

I need to (temporarily, not permanently) guy a fairly large tree that had roots cut; Do you have an opinion on what system works better for this application? (Ruled out Guardian, as too inflexible)

 

[Tom Dunlap]

#3 From what I understand, the material that Cobra is made from is not suitable for a constant load. All fibers have a characteristic called "creep" where the fiber stretches like a gob of bubblegum being pulled out. The fibers stretch but don't contract.

Can't help with any of the other points.

Tom

 

[Tobe]

No rope is (very) suitable for constant load. Of course it depends on how high the load in comparison to the rope's tensile strength. A 1 ounce weight on a 30,000 pound rope doesn't qualify as much of a load, even though it's constant.

Unlike bubblegum, rope creep has it's limit, but true, it will elongate by some (small) degree. So, on to your answers;
1) The shock absorbing "dampeners" bare no load and have no strength rating. They are designed to displace the rope fibers in a manner that causes the rope to contract some distance while compressing the soft member, affording a dampening effect prior to stopping at 100% fiber support. Longevity of the two is virtually equal. They are made of the stuff that covers roofs and lines fish ponds and has perhaps the highest UV resistance of any synthetic material known to man, EPDM.
2) Than static support (steel wire). No movement wanted. Situations may vary.
3) No. Evidence shows that synthetic systems (that aren't overloaded) hold up extremely well for many years in trees, but more importantly, provide the type of "effect" most suitable for both the tree and the support system in the dynamic environment. If it were in support of a tower or stiff building, everything would be modled differently.
4) No. TreeSave HAS a shock dampening core for that runs the full length of the line designed for general loading. The external dampener (derrived from the marine industry) is only used when necessary (depending on the situation) and is highly reliable and less of a failure influence than inserted materials (Cobra shock) since it doesn't displace fibers.
5) Nothing significant. Our industry is truly weak in this area. Little is being done to review (not just these) many products. Some ask why we don't do more ourselves, but who would be convinced of GM products if GM conducted the testing.
TreeSave with dampner core for sure. Minimal elongation is not so bad in this situation but will indeed, not help in training the tree. The amount of leverage that the tree will have on your cable and anchor will be high due to the angle. Perhaps consider multiple guys and/or a tree to tree (low to high) attachment. Remember the 50% rule and avoid canopy cabling until after the root plate is set (if possible). Best of luck. Good questions.

 

[FBerkel]

Tobe,

Thanks for the response. Got everything but your reference to the "50% rule", if you get a chance.