Redundant Bridge vs. Second Bridge
- Thread starter Njdelaney
- Start date
Nah. Stick with polyester....those tech cordage do not belong on bridges.
moss
Been here much more than a while
- Location
- Carlisle, Massachusetts, U.S.
Except the gone but not forgotten 10mm Globe 3000 with polyester cover and Dyneema SK75 braided core, the classic TreeMotion bridge cordage.
I built my own by stripping the core out of Sterling HTP 10mm then replacing it with a Dyneema core stripped out of 9mm Samson Warpspeed II. On my second bridge from that build, is sewed to my TM front D's. The polyester Sterling cover is burly, the Dyneema core reliable. My primary bridge is the TM replacement bridge (Globe 3000).
It was more to prove a point after Globe 3000 by the foot was pulled from the retail market. Climbers can safely implement made for the purpose bridege cordage by the foot. When my last Frankenstein Dyneema bridge is retired I'll go back to the OG TM replacement bridge for my second bridge.
Going around in cricles I've posted all this in the past ;-) For my primary bridge using the small DMM Axis swivel. It is great for hooking up two lines while traversing, Captain Hook'ing. and a stable positioning "platform" while working, with my short lanyard and main system sharing the bridge swivel. Two separate lines on two bridges can be usable but it is not as stable/efficient as hanging from two lines on one swivel/bridge.
For advancing above my initial anchor point I really like two bridges, much easier to manage alternating two SRT or DdRT systems on separate bridges working my way up.
-AJ
treebing
Been here much more than a while
- Location
- Detroit, Mi.
I absolutely love having two bridges with two swivels. Two separate points of attachment that are independent and don't get tangled.
Will they still stay untangled if you do a 360 under them?
treebing
Been here much more than a while
- Location
- Detroit, Mi.
You can do 180s. It is much much easier than managing two ropes with rings. And two bridges allowed you to position between the ropes.
The rabbit holes of redundant safety seem to be never-ending. Two climbing lines can be fun and practical at times, but two bridges just feels clunky to me.
Camp Gyro 3 keeps two lines free from tangles superbly while still keeping one simple bridge.
Camp Gyro 3 keeps two lines free from tangles superbly while still keeping one simple bridge.
Muggs
Been here much more than a while
- Location
- Canuckistan
I use 2 bridges as well, one has a swivel, the other has a ring and a gyro 3. I will often use both, but sometimes I hang 2 systems off the one. All depends on the situation. Like everything else, it doesn't have to be 100% this or 100% that. Be deliberate, stay flexible, do what works in the moment. Be a hybrid...
treebing
Been here much more than a while
- Location
- Detroit, Mi.
If I would have picked one, I would still be climbing on that one. I still haven't found one that I'm happy with.
Willber
New member
- Location
- Milford, NH
Why does the bridge cordage need to be Dyneema or such techy material. Wouldn't a good cordage be at least 13mm, high braid count and very stiff.
moss
Been here much more than a while
- Location
- Carlisle, Massachusetts, U.S.
It doesn't need to be Dyneema. This keeps going round and round, people talk about best bridge cordage, then start speculating on various high density/strength fibers like Kevlar, Technora etc. Then people warn about flex fatigue problems with the brittle/stiff fibers in the "hi tech" fibers. Dyneema is exceptional in that it has excellent flex/fatigue properties compared to other high molecular density fibers. It has poor resistance to heat and surface abrasion so it needs to be protected within a supple cover, braided polyester for example.
Polyester double braids make good bridges. the caveat is that since the strength is shared between cover and core it will start losing strength more quickly than a Dyneema core/polyester cover bridge due to surface abrasion on the cover braid.
As always regular inspection of your bridge is key to keeping things safe.
Manufacturer recommended bridges make the most sense though it's good to understand the what and why of bridge cordage. Ignorance is never bliss in tree climbing.
-AJ
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Willber
New member
- Location
- Milford, NH
@moss
That’s good to hear that Dyneema does not fatigue from rapid flexing and can survive the abrasion of slight cover on core movement.
Then possibly an ideal bridge cordage could be made, that has a poly cover tightly woven over a 100% Dyneema core, causing the core to be compressed within the cover, then we’d have a lightweight, flat resistant bridge cordage.
I was told by a rope manufacturer, that Dyneema and polyester (or nylon) core would not be advisably developed, because even the slight movement of the poly against the Dyneema in the core, will cause the Dyneema to abrade.
Also, given Dyneema’s poor heat resistance, would it detrimentally heat up, if used on a pulley, during heavy use in MRS?
Other poly/nylon ropes don’t seem to heat up, during heavy MRS pulley use.
But, what about the fine sand particles that eventually end up in/on a rope’s core, would they cause the Dyneema core to abrade prematurely?
That’s good to hear that Dyneema does not fatigue from rapid flexing and can survive the abrasion of slight cover on core movement.
Then possibly an ideal bridge cordage could be made, that has a poly cover tightly woven over a 100% Dyneema core, causing the core to be compressed within the cover, then we’d have a lightweight, flat resistant bridge cordage.
I was told by a rope manufacturer, that Dyneema and polyester (or nylon) core would not be advisably developed, because even the slight movement of the poly against the Dyneema in the core, will cause the Dyneema to abrade.
Also, given Dyneema’s poor heat resistance, would it detrimentally heat up, if used on a pulley, during heavy use in MRS?
Other poly/nylon ropes don’t seem to heat up, during heavy MRS pulley use.
But, what about the fine sand particles that eventually end up in/on a rope’s core, would they cause the Dyneema core to abrade prematurely?
moss
Been here much more than a while
- Location
- Carlisle, Massachusetts, U.S.
Building bridge cordage specs on potentially false assumptions will get in the way of achieving the goal. There is zero problem if a bridge cordage flattens somewhat under load. It will flatten (somewhat). Some flattening will likely improve the strength of a bridge as the loading will become more equalized for fibers at the bend. With a "perfect" round cordage at the bend there is unequal loading between the wider radius at the top of the bend and the lower radius at the bottom of the bend over the bridge ring or swivel hardware.
It is true that the inside of the polyester cover will abrade the surface of the braided Dyneema core over time. If you dissect the stock TreeMotion OG bridge (10mm Globe 3000) you'll see there is an intermediate very thin soft polyester sleeve (PEZ). It effectively protects the Dyneema braid from surface abrasion. For my homemade Dyneema bridge I did not have a PEZ intermediate sleeve. After 2 years of use there was a slight surface fuzzing of the Dyneema braid core. Probably something in the range of 5% or less of the total Dyneema braid effected. Illustrative of why the PEZ sleeve is included in the OG TM bridge construction.
For bridge use there is not sufficient movement/fiction effect to heat up the Dyneema core through the protective polyester cover. Are you referring to a Dyneema core overheating in MRS use when a Dyneema core is used for a climbing line?
Sand penetrating into climbing lines is a potential issue for caving, in tree climbing not really a consideration. With double-braid polyester lines I can imagine soil/sand getting into the looser more supple cover braids. For true kernmantle lines the cover braids are woven heavy and tight and exclude sand quite well.
-AJ
Will you be using your bridge for 12 years? I hope not. Do you drop your saddle in the sand when you take it off? I hope not. Are you climbing trees in the desert? Probably not. Replace that bridge every six months and no worries about sand inside.
BTW, you have a flattening fetish like no one I've ever known.
moss
Been here much more than a while
- Location
- Carlisle, Massachusetts, U.S.
99% of the problem is defining terms and use goals. The only reason for me to want to use a Dyneema core bridge cordage is because the OG TM bridge install openings require 10mm or less cordage to fit (except maybe the 11mm Platinum line some people successfully jammed through?). The only way to get the strength numbers that make the ABS numbers good for 10mm bridge cordage is to use a Dyneema core. For everything else where 11mm or 11.5+ diameter works the double-braid polyesters are excellent.
Maybe not that deep of a rabbit hole after all.
-AJ
I was going to say what is with your obsession with flattening, it's ridiculous we're climbing ropes that we want to be flexible not steel.
I said that to try and free you up from having to explain any of this again, not because I had any problems with your rationale. I must have missed the mark!
