Rope strength question

[Eithieus]

Of the two: climbing SRT butterfly with a ring or a U-saver in the top canopy, does anybody know what is my loss in the strength of the rope? I am 260lb with gear. Is it safe to run the butterfly with the ring instead of the U-saver as I prefer the butterfly? Thank you in advanced,

Eithieus

 

[Tuebor]

Yes

 

[evo]

A butterfly is one of the stronger knots. Additionally using it to choke with a ring (or naked) takes loading off the knot due to the friction of the choke. Think of a portie take a few wraps and then cleat it off, the half hitched on the cleat take very little load. The strength loss in a choke configuration comes from the bend of the rope that makes the choke

 

[Eithieus]

Thanks guys

 

[agent_smith]

A butterfly is one of the stronger knots.

This is actually a nebulous concept. There is no load that a single climber (in the act of climbing and being mobile in the tree canopy) can generate that will reach the MBS yield point of (any) knot.
What is more important (with hand tied knots) is stability, security and resistance to jamming.
Same goes for human rated ropes used in life critical applications (EN1891, EN892, etc)... there is no load that a climber can generate that will reach the MBS yield point of the rope.
Note that I am careful to type 'life critical applications' (and not hauling/hoisting logs, pulling trucks, pulling tree stumps, etc).

So in the case of the original poster, with his body weight being 'orders of magnitude' less than the MBS yield point of both the rope and the knot, the main variables of concern would be sharp edges, cyclic loading and reliability of the anchorage point. Sharp edges can usually be managed... the cyclic loading of rope caused by vertical mobility (ie act of climbing and moving around) can also be mitigated.

Rope access operators (ISO22846) use twin ropes - they are never reliant on a single rope strand. But, the tree climbing industry prefers to distance itself from being deemed a form a 'rope access'. Be that as it may, rope access operators and tree climbers both haven't figured out how to isolate gravity - it affects them equally.

 

[TheTreeSpyder]

i think if the load leg goes over a branch, then B'Fly around main leg leaving a retrieval handle with other end of B'Fly is about same as ring in same position as B'Fly?
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The most loaded deformity is the bend around branch support, actually then buffering load to the B'Fly or ring position; but as far as real degrading efficiency; the ring made shears across the Standing Part/most loaded part/load leg. (As Evo)
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Tree folk do dive into a 2is1, 1isNone world on 1 overhead support tho, for there are many more obstacles to multi line paths thru trees, especially when needing to move around. But, tree climb is more meant to be a positioning than catching system, and has lanyard to side D's as 2nd rope system, angled from overhead support line; allows sit in nice V pocket for positioning squarely to target. And tree itself; at many points easier scaffolding than in mountain/rescue. Tree folk totally different kind of crazy tho, have 1/2" synthetic ropes; that then run 68mph chain of 600 teeth per second w/900 degree muffler next to and in between ropes confidently, to then cut and swing weight right next to ropes, saw, self etc. Different game, different sharp edges(chain) that we carry with us, amongst the round limbs surrounding. Different kind of what normal earth walkers would call stupid.

(These are on the ground risks, multiplied in air)
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SRT entrance to tree newer evolution, but not necessarily mainstay of whole tour.
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Tree folk will ask about strength of line/setup/knot even if all strengths many times self, for might use about same or less rig on next cut that weighs many more times than self and know will receive impact multiplier that must account for in elasticity or slip reliefs etc. whole system then taking rest of brunt of loading. So a constant topic in brain, that you then seat yourself into. It is a good habit to inspect and wonder, a mental exercise whose built strengths and observations can overflow to other areas. Your own life, hanging in own contraption, seems good time to really get in touch with what is going on, that affects all else we do in that climb and the next.

 

[evo]

This is actually a nebulous concept. There is no load that a single climber (in the act of climbing and being mobile in the tree canopy) can generate that will reach the MBS yield point of (any) knot.
What is more important (with hand tied knots) is stability, security and resistance to jamming.
Same goes for human rated ropes used in life critical applications (EN1891, EN892, etc)... there is no load that a climber can generate that will reach the MBS yield point of the rope.
Note that I am careful to type 'life critical applications' (and not hauling/hoisting logs, pulling trucks, pulling tree stumps, etc).

So in the case of the original poster, with his body weight being 'orders of magnitude' less than the MBS yield point of both the rope and the knot, the main variables of concern would be sharp edges, cyclic loading and reliability of the anchorage point. Sharp edges can usually be managed... the cyclic loading of rope caused by vertical mobility (ie act of climbing and moving around) can also be mitigated.

Rope access operators (ISO22846) use twin ropes - they are never reliant on a single rope strand. But, the tree climbing industry prefers to distance itself from being deemed a form a 'rope access'. Be that as it may, rope access operators and tree climbers both haven't figured out how to isolate gravity - it affects them equally.

Understood. The OP asked for the strength of the knot. And a alpine is one of the stinger knots.

 

[Tony]

This is actually a nebulous concept. There is no load that a single climber (in the act of climbing and being mobile in the tree canopy) can generate that will reach the MBS yield point of (any) knot.
What is more important (with hand tied knots) is stability, security and resistance to jamming.
Same goes for human rated ropes used in life critical applications (EN1891, EN892, etc)... there is no load that a climber can generate that will reach the MBS yield point of the rope.
Note that I am careful to type 'life critical applications' (and not hauling/hoisting logs, pulling trucks, pulling tree stumps, etc).

So in the case of the original poster, with his body weight being 'orders of magnitude' less than the MBS yield point of both the rope and the knot, the main variables of concern would be sharp edges, cyclic loading and reliability of the anchorage point. Sharp edges can usually be managed... the cyclic loading of rope caused by vertical mobility (ie act of climbing and moving around) can also be mitigated.

Rope access operators (ISO22846) use twin ropes - they are never reliant on a single rope strand. But, the tree climbing industry prefers to distance itself from being deemed a form a 'rope access'. Be that as it may, rope access operators and tree climbers both haven't figured out how to isolate gravity - it affects them equally.

A thorough post save two variabilities, misconfiguration of anchor assembly and remote inspection. These must be considered for any life support anchor.

Tony

 

[agent_smith]

The OP asked for the strength of the knot. And a alpine is one of the stinger knots.

The MBS yield (ie strength) of the #1053 Butterfly is irrelevant. People use a Butterfly because it is jam resistant (in biaxial through loading profile), its 'TIB', it can exist mid-line, and has multiple loading applications. There are lots of eye knots that have similar MBS yield (but again, this is more for academic interest).
What matters most is security, stability and resistance to jamming (there are other factors too - I'm simply identifying factors of high significance).

Warning - commentary ahead!
Unfortunately, many people conceptualise knots used in life critical applications only in terms of MBS yield. I think this has been historically propagated by the military and to a large extent, knot book authors. And it has then been passed on by word of mouth to other users - including climbers, canyoners and rope access technicians, etc.
You'll often see knot book authors listing various knots and assigning 'efficiency' % ratings to them. Readers often assume that authors of knot books are 'authorities' (subject matter experts) - and so the notional concept of 'efficiency' is associated with 'strength'.

There is no load that a single climber working in a tree canopy will generate that will reach the MBS yield point of a lifeline rope or a hand tied knot. You can even tie a simple overhand loop and it would work within the nominal loads of a single climber. Realistically, the concern would be contact with power tools, sharp blades and abrasion damage.
Pulling trucks, tree stumps and dragging logs is a different matter - because human rated ropes used for fall-arrest would not normally be employed to pull a truck or drag a big log.

 

[TheTreeSpyder]

Using something that is more efficient; takes more towards full capacity load,
can be like working a chain hard without a kink in it.
Can take you longer immediately with more Max Headroom and over longer term, more confident life from less stress as any other.
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The strength numbers are a barometer also to measure and grow by. Just as car racing is not very road real, but does advance road safety. It also allows us to keep in a safe powerband/SWL by knowing these limits a bit, and what lowers the ceiling. Tho, once again agree that single or in rescue double body weight load will not break our systems, arbos are a different kind of crazy; might use same strategy on 5xBodyweight load, that is more slammed into a 3/4" rope and slipped thru a rope brake for forgiveness/peak steam relief from system to keep peak forces lower. It is all thus just part of the same study of concerns always weighing and measuring for as good habit only now butt is sitting in, for more thinking. i always thought of it as this is how the load feels, this is what this angle of pull feels like to load etc. Data is king, at least google thinks so; seems to work fer thems. In short thinking about numbers is better than not thinking; and numbers give us something to chase that does give growth; other things are harder to quantify the same to excite the blood and lead the charge.
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Have L-earned a lot, simply watching and playing with dragging logs.
>> Pull wrong log w/Running Bowline and log flips around like wildcat flipping from side to side trying to get collar off as the Bowline pulls from the side while dragging forward
>> throw Half Hitch pre-fixxer on the nose and raging wildcat turns to purring kitten and follows nicely
All the same forces, just illuminated different ways, to develop feel, imagery and understanding of what is going on, beyond what a typical eye sees/decodes from same shituation.
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By the book, i think are systems are built for positioning rather than fall arrest.

 

[Bart_]

A related conundrum is attaining 5x or 10x life support strength, but items like shock absorbing thread-ripping links to dampen down the lack of elasticity created by the large initial system strength. Some ascent/descent devices actually tout the advantage of reduced " strength" of support i.e. if you drop the device skids a bit damping/dissipating out the energy while in some people's eyes perhaps violating its "hold" strength requirement.

I was reminded of a sometimes mentioned human spine limitation (much lower force than life support MBS) when I was wiggling up through some pine limbs on my Arbscender and didn't cleanly pass my shoulders past a few. Felt like a wrestler was torturing my lower back. I imagine a poorly landed drop into a slack system might feel similar. I know a drop into a rope walking SRT ascent configuration is a non-event. It's like landing on your feet after jumping off something, with adequate rope elasticity.

too hot to work today

 

[TheTreeSpyder]

Most correct that elastic dampening response is from how far invades MBS.
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This is so true that 2/1 pulley on load raises capacity so reciprocally reduces elastic dampening response in trade. Even tho more rope in the system, it is not accounted for as more rubber band to take shock like if used 2x rope for longer drop.
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Very key model/point to me, ty!

 

[Brocky]

Perhaps strength is a frequent concern because it isn’t something the average person can test. Knot security, stability and jam resistance can be arrived at by trial and error in a low and slow method to find answers by most.