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prussic KN?

J

Jokerswild

Active Member
Joined
Dec 11, 2019
Messages
163
So this may be a dumb question......

Ropes, devices, carabiners all in that 22 and above KN ratinge

Cord for prussics- 11, 14.

System only as good as its weakest link?
 
There are 2 strands supporting you on the Prusik, so double it. Except for knots, they are close.
 
A prussic is really only one strand forming a loop. Not sure you can double the strength for that calculation.

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WannaBMonkey said:
A prussic is really only one strand forming a loop. Not sure you can double the strength for that calculation.

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Click to expand...
One strand, yes, but the loop has 2 strands. The load is distributed over these 2 strands so there is half the load on each strand.
 
Where your caribiner hangs in the loop, it's one strand curved around the caribiner, so, I could be wrong, but I still believe that you only have the strength of one strand. The "two strands" are not independently supporting the load and not independently attached to where if one side breaks, the other still holds. I'm no engineer, but I'd like to hear some other's opinions on this. Like I said, I could be wrong. Anyone? Now I am truly curious. Not trying to start an argument, but I would really like a third opinion.

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I run two Prussics on my safety tether while on stand and run a 4 wrap Klemheist loop and a Prussic when I 1stick.
 
Jokerswild said:
So this may be a dumb question......

Ropes, devices, carabiners all in that 22 and above KN ratinge

Cord for prussics- 11, 14.

System only as good as its weakest link?
Click to expand...

But you are using two strands to hold the weight.
This might not double the rating but my gut says it matters.

climbing gurus?
 
WannaBMonkey said:
Where your caribiner hangs in the loop, it's one strand curved around the caribiner, so, I could be wrong, but I still believe that you only have the strength of one strand. The "two strands" are not independently supporting the load and not independently attached to where if one side breaks, the other still holds. I'm no engineer, but I'd like to hear some other's opinions on this. Like I said, I could be wrong. Anyone? Now I am truly curious. Not trying to start an argument, but I would really like a third opinion.

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Click to expand...

this is partly why I attach with 2 scaffold knots
 
WannaBMonkey said:
Where your caribiner hangs in the loop, it's one strand curved around the caribiner, so, I could be wrong, but I still believe that you only have the strength of one strand. The "two strands" are not independently supporting the load and not independently attached to where if one side breaks, the other still holds. I'm no engineer, but I'd like to hear some other's opinions on this. Like I said, I could be wrong. Anyone? Now I am truly curious. Not trying to start an argument, but I would really like a third opinion.

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Click to expand...

a counter point by example

imagine a loop of elastic instead

the elastic would generally stretch uniformly at any specific section thereby distributing the force across the length evenly
 
WannaBMonkey said:
Where your caribiner hangs in the loop, it's one strand curved around the caribiner, so, I could be wrong, but I still believe that you only have the strength of one strand. The "two strands" are not independently supporting the load and not independently attached to where if one side breaks, the other still holds. I'm no engineer, but I'd like to hear some other's opinions on this. Like I said, I could be wrong. Anyone? Now I am truly curious. Not trying to start an argument, but I would really like a third opinion.

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Click to expand...
Yes, you are thinking. On a rope, the load is distributed equally along it's length. If each strand has 100 lbs of load there has to be 100 lbs on the strand over the carabiner.
 
A sewn loop has a slightly higher mbs than a single strand, but not near double. Look at the specs for a beal jammy vs the regular beal cord. Hitches that have 2 connections to the carabiner (aka basket configuration) will more closely double the mbs of the cord (minus strength lost to knots). This is why I like sewn double eye cords, plus there are a bunch of different hitches you can use and customize them to you specific setup...
 
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While i can appreciate your concern about the durability of your gear, I think you're focusing on only one aspect while not really considering the whole picture. That being, if your body took the 11kn of force it would take to reach the breaking strength of your prusik in a fall, at a minimum, you'd probably snap your spine. It would probably be much worse than that. Look at it this way, most traditional rock climbing protection (med/large nuts, hexes etc.)can take 10-14kn. The rock its placed in would usually fail before the piece of protection would.
 
davecarp said:
A sewn loop has a slightly higher mbs than a single strand, but not near double. Look at the specs for a beal jammy vs the regular beal cord. Hitches that have 2 connections to the carabiner (aka basket configuration) will more closely double the mbs of the cord (minus strength lost to knots). This is why I like sewn double eye cords, plus there are a bunch of different hitches you can use and customize them to you specific setup...
Click to expand...

Hmm...this might be of interest.

stringandpulley

isaac.exploratorium.edu
 
Im not doubting the safety of a 11kn cord. This is the same prussic gear that pros use. Just curious on "the math," and the huge difference.
 
WannaBMonkey said:
Where your caribiner hangs in the loop, it's one strand curved around the caribiner, so, I could be wrong, but I still believe that you only have the strength of one strand. The "two strands" are not independently supporting the load and not independently attached to where if one side breaks, the other still holds. I'm no engineer, but I'd like to hear some other's opinions on this. Like I said, I could be wrong. Anyone? Now I am truly curious. Not trying to start an argument, but I would really like a third opinion.

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Click to expand...

Correct with an actual Prusik knot. But with a hitch such as Schwabisch or Distel there are two independent connections to the carabiner, thus spreading the load equally between both causing each connection to hold roughly half of the load.
 
CharlieTN said:
Correct with an actual Prusik knot. But with a hitch such as Schwabisch or Distel there are two independent connections to the carabiner, thus spreading the load equally between both causing each connection to hold roughly half of the load.
Click to expand...

Right. But that is fouled thinking. It one of the connections somehow broke, the hitch cord would (COULD) simply come unwrapped and let you fall. So it does t actually pay to double it on a hitch like that.


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trailblazer75 said:
Right. But that is fouled thinking. It one of the connections somehow broke, the hitch cord would (COULD) simply come unwrapped and let you fall. So it does t actually pay to double it on a hitch like that.


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Click to expand...
Not to get into a debate, if each connection is holding roughly half then that would greatly decrease the chance of failure. Of course that assumes knots are tied correctly and checked often. So i would argue that it is a great benefit to have the double connection on a hitch like that. In addition, those hitches I listed are so much easier to work with in the majority of the applications we use over the actual prusik knot which tends to lock up tight as a drum.
 
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