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#164402 - 01/22/09 04:45 PM Re: Paracord...how much is too much? [Re: ]
Mike_H Offline
Addict

Registered: 04/04/07
Posts: 612
Loc: SE PA
Just like to know the limitations of some of the equipment that I carry with me.

I know that paracord doesn't like sharp jerks/bounces and tend to fail under those conditions with too much stress applied.
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#164423 - 01/22/09 05:35 PM Re: Paracord...how much is too much? [Re: jamesraykenney]
lifeview Offline
Journeyman

Registered: 05/09/06
Posts: 80
Loc: Nashville,TN USA
Quote:
You do want to be sure that you get the REAL para-cord though...
A lot of what is sold does NOT have the inner strands that are each made up of two even smaller strands.
Some just has the fibers(unstranded) inside of the outer covering. This CAN be strong, but there is no guarantee...


Any store that sells true mil-spec paracord should be able to provide a certification letter from the mill that manufactured it. A great deal of what's sold is commercial grade paracord. It's usually less expensive and available in many colors, but is not subject to the rigorous manufacturing standards and testing of mil-spec 550 cord.
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#164451 - 01/22/09 06:44 PM Re: Paracord...how much is too much? [Re: Mike_H]
scafool Offline
Pooh-Bah

Registered: 12/18/08
Posts: 1534
Loc: Muskoka
Originally Posted By: Mike H
Just like to know the limitations of some of the equipment that I carry with me.

I know that paracord doesn't like sharp jerks/bounces and tend to fail under those conditions with too much stress applied.



OK, this is going to be a bit long winded, mostly because I am bored and not much is happening here right now.

With cordage they tell you its breaking strength. From there you start applying your safety factors.
Safety factors are simply how much stronger you need to make things for safety, they are not like gambling odds where you say it might break one out of so many times.

A safety factor of one is no safety factor at all.

If your cord says it is good for 550 lbs them a safety factor of two says only try 275 lbs.
As the cord degrades from use you might want to increase the safety factor. If what you are doing with it is more critical you increase the safety factor again.

Scaffolders built scaffold with a safety factor of 4, so everything is built at least 4 times as strong as it needs to be according to the ultimate material strengths.

Safety rigging where MY life might depend on it gets a safety factor of 10.
( ie. Massive overbuild)


So if the cord is a bit shabby, factor 2, if it matters add that, maybe not so important if it fails, so safety factor 3, jerky load, safety factor 5.
So your paracord might be trustworthy for a 110 pound load under those conditions.
If you figure a safety factor of ten because what you want it to hold matters more to you, then you are saying you trust holding 55lbs on a brand new piece of 550lbs line.

(Usually safety factor 4 is good.)

Shock loading?
You need to calculate how hard you are hitting the end of the line.
You need to understand that the Kinetic energy of a moving load can be very high and increases at the square of the speed, but only directly with the weight.
The equation, if you want it is 1/2(Mass* Velocity^2)
So the weight times the square of the speed and then divide by 2 to get how much energy needs to be absorbed when it hits the end of the rope.
The way to balance Kinetic Energy is through Force times Distance. (fp Foot Pounds energy, foot pounds torque is a different measure)
In other words; shock absorbers.

Nylon is stretchy (10% strain is normal) so it actually absorbs shock loads pretty well, but it needs to have enough length of nylon to stretch and absorb the shock.
I have seen bungee cords used as shock absorbers (think of bungee jumpers).
Climber's safety harnesses sometimes use shock absorbing links that are flat webbing folded over itself and sewn with stitches meant to tear out. It is meant to reduce the shock loads to the point a human body can withstand them.
In the pictures in this link http://www.safetysupplies.co.uk/trolleyed/21/ you can see the shock absorber in the fall arrest lanyards. It is the white block on the yellow webbing, notice it is missing from the restraint harnesses. (screamer is the slang term for the shock absorbing lanyard, the fall that stretches it and the the person that ends up dangling from it. You have about 15 minutes to get him down after he stretches his harness. After 20 minutes he might be dead from compartment syndrome.)

Oh yes, all load ratings are for new material so keep that in mind.

Then come all the rigging points, knot weaknesses and angular loads.
It can get pretty complicated if you are not careful so with rigging KISS is important.

Safety factor 2,000?

(fishing line is different. because competition test weight ratings means it is guaranteed to break at the stated test weight instead of carrying at least that weight when new.
Eight pound test fish line is supposed to break before it has eight pounds of load on it.)

Edit:
Note what paracord was designed for. You don't get much more bounce than a parachute opening with a fully equipped footsoldier hanging below it.


Edited by scafool (01/22/09 08:11 PM)
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#164461 - 01/22/09 07:12 PM Re: Paracord...how much is too much? [Re: TeacherRO]
Brangdon Offline
Veteran

Registered: 12/12/04
Posts: 1204
Loc: Nottingham, UK
Originally Posted By: TeacherRO
Am I the only one who carries little or no para cord?
I carry a little, and I've never needed to use what I carry. It's the same with duct tape; I've been carrying some every day for years and never had a need for it.

I expect it depends on your lifestyle. The area I live in is populated quite densely; why build a shelter when there are so many buildings around?
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#164524 - 01/22/09 10:22 PM Re: Paracord...how much is too much? [Re: lifeview]
jamesraykenney Offline
Enthusiast

Registered: 03/12/04
Posts: 316
Loc: Beaumont, TX USA
Originally Posted By: lifeview
Quote:
You do want to be sure that you get the REAL para-cord though...
A lot of what is sold does NOT have the inner strands that are each made up of two even smaller strands.
Some just has the fibers(unstranded) inside of the outer covering. This CAN be strong, but there is no guarantee...


Any store that sells true mil-spec paracord should be able to provide a certification letter from the mill that manufactured it. A great deal of what's sold is commercial grade paracord. It's usually less expensive and available in many colors, but is not subject to the rigorous manufacturing standards and testing of mil-spec 550 cord.


The stuff I was talking about as REAL para-cord, is the stuff you get from a parachute rigging supply house...
I would imagine that is is BETTER tested than the mil-spec stuff, because: ONE, it is not 'lowest bidder' and TWO, the liability. shocked

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#164530 - 01/22/09 11:20 PM Re: Paracord...how much is too much? [Re: Glock-A-Roo]
ironraven Offline
Cranky Geek
Carpal Tunnel

Registered: 09/08/05
Posts: 4642
Loc: Vermont
I think it is four strand, might have been five. I don't have any here other than some that was gutted for a braiding project. I've got a lot of core lines in a ziplock that have turned into a snarl, I might sort it out some day. *laughs*

Best bet is to call or email them.
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When a man dare not speak without malice for fear of giving insult, that is when truth starts to die. Truth is the truest freedom.

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#164532 - 01/22/09 11:22 PM Re: Paracord...how much is too much? [Re: Mike_H]
ironraven Offline
Cranky Geek
Carpal Tunnel

Registered: 09/08/05
Posts: 4642
Loc: Vermont
For water work, given my druthers, I'd go with something other than nylon- it is heavier than water. :P I've got some marine utility cord, braided, about as thick as p-cord. It floats, I think it is polypro but I'm not sure. I got it for a lanyard project, but it is at my folks in my braiding box.
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When a man dare not speak without malice for fear of giving insult, that is when truth starts to die. Truth is the truest freedom.

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#164567 - 01/23/09 01:37 AM Re: Paracord...how much is too much? [Re: ]
Desperado Offline
Veteran

Registered: 11/01/08
Posts: 1530
Loc: DFW, Texas
Originally Posted By: IzzyJG99
Originally Posted By: Glock-A-Roo
Originally Posted By: IzzyJG99
Tragically the eyelets on my Bates GX-8's won't take paracord.


Try the 4-strand (but sometimes 5-strand; watch your sources) Type II cord, which is constructed the same but is a bit narrower in diameter.


I was able to get the 7 strand to work in my GX-8's. The problem was just making the burnt off ends small enough and slightly pointy for threading. The Desert Camo paracord I have actually looks great on the tan boots. Coyote would've been too dark.

Each lace was 5 feet, so I cut two lengths that're a smidge over 5 feet long. So that gives me 10 feet (160 feet total, really) of cord.


Get a soldering iron with a really fat tip to cut the 550 cord with. It lets you shape the ends without shaping the ends of your fingers.

I like this one.
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#164655 - 01/23/09 03:50 PM Re: Paracord...how much is too much? [Re: ironraven]
Mike_H Offline
Addict

Registered: 04/04/07
Posts: 612
Loc: SE PA
Originally Posted By: ironraven
For water work, given my druthers, I'd go with something other than nylon- it is heavier than water. :P I've got some marine utility cord, braided, about as thick as p-cord. It floats, I think it is polypro but I'm not sure. I got it for a lanyard project, but it is at my folks in my braiding box.


Was more of a what-if thought as opposed to an actual need. grin
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#164657 - 01/23/09 03:51 PM Re: Paracord...how much is too much? [Re: ]
Mike_H Offline
Addict

Registered: 04/04/07
Posts: 612
Loc: SE PA
Originally Posted By: BigDaddyTX
Heh, I don't know the math behind it, but I used it a lot when I was moving, we had an L shaped entry and I tied it across the rails on the sides of the L to make it like a triangle, and I didn't have a problem dropping a heavy couch on it, so I'm guessing there wouldn't be a problem with a person.


Ahhh... real world usage. I love it.
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