treeMOTION bridge replacement?

moss said:
I looked around for the 8:1 sheave diameter recommendation for KMIII but couldn't find anything. Probably didn't try hard enough ;-) It's all about the core not the cover for a static kernmantle so this is about the nylon core and construction right? Curious to know more, is it about the Nylon or is is about the core construction and the Nylon? Very interesting.
-AJ
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I’m with you, Moss. I’ve talked with manufacturers who have said that there is some loss of strength due to bend radius, but not enough to warrant fear of failure. The other interest I’ve had is the difference between xstatic and drenaline. According to Rob’s argument, it would seem that the wider drenaline would need a larger bend radius than its slightly smaller counterpart, but we know that drenaline is considered ddrt compatible.
From my understanding, the greatest issue/argument against static lines as ddrt lines is reduced elongation when doubled. The funny thing is, there are double braids out there that have less elongation than some “static” kernmantles. The only thing left to explore, in my mind, is the reaction of the core fibers to a dynamic load while doubled over a sheave/rings. Perhaps the parallel fibers are somehow more prone to failure? Inquiring minds want to know!
 
Well, a kernmantle with a sewn eye is exposed to a small bend radius, and the hardware in it moves back and forth over a very small section of the rope... I would think that such an arrangement would be at least as prone to failure as using the same rope for a harness bridge if it was a core issue. Most 16-strand ropes have a parallel core, some are even nylon. Hmmm. I'm starting to think this might be a "we haven't tested it for this so don't do it" escape clause kind of thing.
 
Crimsonking said:
Perhaps the parallel fibers are somehow more prone to failure? Inquiring minds want to know!
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I think you're getting there. We'll need some of our advanced rope technology theorists to weigh in here. The original TM bridge, formerly known as Globe 3000, has a braided Dyneema core. In a tight bend radius scenario the issue is that the core fibers on the outside of the bend are heavily loaded and in effect "leveraged". The core fibers on the inside of a tight radius bend are taking very little load. As I read in some rope manufacturer's document on the subject, the outside core fibers can fail and zipper under heavy loading. I'm guessing, but we'll need a several hundred word expert treatise on the subject to clarify [joke], that with a braided core the fibers are moving in and out of the "hot zone" on the outside of a tight core bend. Looking at it that way a braided core may be more resilient in tight radius bending than a parallel core construction. With parallel core the same lengths of fiber on the outside are taking all the load throughout the bend area, making that core construction less resilient to a tight bend radius. Just a theory.
-AJ
 
Question is, what is the average bend radius for a bridge with say a ring on it? It's not really based on the diameter of the ring cross-section, the two legs of the bridge are never "parallel" unless a climber has an absurdly long bridge. I run a fairly short bridge so the maximum angle is probably never less than 80-90°. The exception being on limb walks when you're facing away from the trunk and the ring or swivel moves to the furthest end of the bridge. That's probably when you're going to get the tightest bend radius on the bridge cordage. There is less load on the bridge anyway as the climbing line angle gets flatter on limbwalks, climber weight is shared with the limb. So many variables. All I know for sure is that a 4 year-old very well used braided Dyneema core stock TM bridge broke in the range of 9700-10,000 lbs in a basket pull break test (both ends anchored, broke in the middle). Dyneema has very good flex fatigue characteristics in addition to its outstanding strength, makes sense that Teufleberger went that route for the original TM bridge.
-AJ
 
And lastly one more question/comment, I need to go to a job site! The leading harness makers are being super quiet about their current bridge sourcing/construction. What cordage is Petzl using for the current Sequoia harnesses? Same for the new TM, what's the deal on their new bridge cordage? Always questions.
-AJ
 
The original bridge has the double overhands that were also sewn to prevent untying. Should I run a couple of stitches as well?
 
ATH said:
The original bridge has the double overhands that were also sewn to prevent untying. Should I run a couple of stitches as well?
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On the original TM bridge the stitching has three functions, the tight rows of stitching through the cover and core are to prevent the notoriously slippery Dyneema core from sliding through the double overhand stopper, the resulting stiffened section of tail will also be more difficult to slip through the stopper. The other stiching which you see as a single piece of red thread going over the double overhand is I believe a visual indicator that shows that shows the knot is stable. If for example on inspection you notice the indicator thread is gone or has shifted you want to verify the tail after the stopper isn't getting sucked into the knot. The reports from the field from those of us who replaced our TM bridges with 10mm Globe 3000 is that once the bridge stoppers are well set there's no way anything is going to slip through the stopper knots. Even so it's easy to do, there's no reason not to put a few stitches into the tail after the stopper to fix the core to the cover.

Since the core and cover are already intertwined in the Platinum line used for the NT Onyx bridge, no need to stitch.
-AJ
 
I’ve thought of switching over to those. They seem to be the most widely (hardware) compatible webbing bridge out there.
 
no, just throwin it out there. i grew up on fat webbing, sometimes webbing and leather and some just webbing. just feels right when fibres line and roll with a stitch.
Climb "On Rope" and roll on a web.
 
As opposed to the "expected" failures?:rayos:

I don't know the answer, but it is a good question. Mine isn't in bad shape, but is showing a little wear. Simple and cheap enough to replace. I'm trying to avoid being in either the expected or unexpected categories - whether a pioneer or following a well-blazed trail in either.
 
As opposed to ones that were blatantly obvious, like trashed or cut. But even then, I'm not sure that I have ever heard of even one of those.
 
Well, the bridge is in basket mode, so the forces aren't huge. Plus, most of the time you're not fully weighting the thing. You've usually got other points of contact with the tree. Oddly enough, this old Komet Butterfly harness I've been fiddling with surprised me in that the original webbing bridge looks nearly new condition, while the saddle looks well used and slightly crispy. There's a thin, chafe sleeve over the webbing, and even that looks real good. I would have thought it would wear out before the rest of the saddle, but that's not the case. I think UV and rubbing on bark does more damage to the saddle than a ring or 'biner does to the bridge. Not what I expected.
 
RopeShield said:
no, just throwin it out there. i grew up on fat webbing, sometimes webbing and leather and some just webbing. just feels right when fibres line and roll with a stitch.
Climb "On Rope" and roll on a web.
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Is that web bridge double or triple thick?
 
DSMc said:
Has there ever been an unexpected treemotion bridge failure?
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None that has been reported. The cover wears through first before any core deterioration happens. The idea of hidden core damage on that bridge is a myth. Anyone who does have the core showing through the cover on that bridge cordage hasn’t changed out their bridge in a loooong time ;-)
-AJ
 
DSMc said:
As opposed to ones that were blatantly obvious, like trashed or cut. But even then, I'm not sure that I have ever heard of even one of those.
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I know people who kept climbing on their TM bridge with the core showing, not a healthy practice but the bridge didn't fail by the time a replacement was installed, not naming names ;-)
-AJ
 
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