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#266796 - 01/22/14 10:46 PM Re: Testing the strength of cordage [Re: clearwater]
hikermor Offline
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Registered: 08/26/06
Posts: 7324
Loc: southern Cal
Why on earth would you want to do this?
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#266800 - 01/23/14 12:38 AM Re: Testing the strength of cordage [Re: hikermor]
clearwater Offline
Old Hand

Registered: 03/19/05
Posts: 1163
Loc: Channeled Scablands
Sustainable, provides jobs in poor countries like Bangladesh, can be used as tinder, bits left around decompose quickly, processing the plants just takes water.

Hemp is hard to come by, don't know how it works as tinder, also don't know how "green" industrial hemp manufacturing is.

Figure I need about 80 lbs breaking strength as force on tarp cords attached to tarps of silnylon in high wind gusts generally do not exceed 40 lbs.

I'll bet jute comparable in size and weight to 550 cord would be strong enough.


Edited by clearwater (01/23/14 12:43 AM)

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#266802 - 01/23/14 01:46 AM Re: Testing the strength of cordage [Re: gonewiththewind]
ireckon Offline
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Registered: 04/01/10
Posts: 1629
Loc: Northern California
The jute is going to be a lot less stretchy the synthetic nylon (e.g., most paracord). That's something to consider if you're tying down a tent, tarp, etc. You may get the jute taught. Then, the wind blows the wrong way, and suddenly there's slack in the line. That's just something to keep in mind.
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#266805 - 01/23/14 03:36 AM Re: Testing the strength of cordage [Re: ireckon]
clearwater Offline
Old Hand

Registered: 03/19/05
Posts: 1163
Loc: Channeled Scablands
Just want to try it out. I currently use 1mm polyester and it works great and has little stretch. Paracord is way overkill. The parachute nylon of the tarp is super stretchy and would limit dynamic loading just as a climbing rope limits strain on wire stoppers.


Edited by clearwater (01/23/14 03:38 AM)

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#266807 - 01/23/14 04:06 AM Re: Testing the strength of cordage [Re: clearwater]
hikermor Offline
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Registered: 08/26/06
Posts: 7324
Loc: southern Cal
Natural fibers like jute and manila are obsolete for rope and cordage. They degrade more quickly and unpredictably than synthetics and in every respect are inferior.

I'll bet the force exerted on a tarp in high winds can easily snap jute in the size range of paracord. Actually, there are now better materials than paracord for light cordage suitable for shelters and similar. I've got some stuff that is one half the size and twice the strength of 550 - "ironwire" is what the supplier calls it. It's actually pretty hard to beat braided mason's twice for most uses.


Edited by hikermor (01/23/14 04:06 AM)
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#266811 - 01/23/14 05:20 AM Re: Testing the strength of cordage [Re: ireckon]
AKSAR Offline
Old Hand

Registered: 08/31/11
Posts: 1195
Loc: Alaska
Originally Posted By: ireckon
The jute is going to be a lot less stretchy the synthetic nylon (e.g., most paracord). That's something to consider if you're tying down a tent, tarp, etc. You may get the jute taught. Then, the wind blows the wrong way, and suddenly there's slack in the line. That's just something to keep in mind.
Originally Posted By: hikermor
I'll bet the force exerted on a tarp in high winds can easily snap jute in the size range of paracord.
Big gusts can pull out stakes, bend or break poles, blow tents away, and cause all sorts of havoc. A strong gust could easily break jute.

One trick I learned is to tie a short loop of shock cord through the tie in points on your tent or fly. Then tie the guys in to that, and stretch them snug. The shock cord keeps the guys tight, and creates a bit of give when the wind gusts hit. Less wear and tear on the tent or fly. And you sleep better with less distraction from a flapping fly.
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#266818 - 01/23/14 04:40 PM Re: Testing the strength of cordage [Re: AKSAR]
clearwater Offline
Old Hand

Registered: 03/19/05
Posts: 1163
Loc: Channeled Scablands
Unless you use very heavy shock cord, it will provide too much stretch and increase the sawing motion on stakes etc. You need to pre-stretch the fabric to keep flapping to a minimum.

Check out these tarps backpackers are using made from shrink wrap and tape.

http://www.backpackinglight.com/cgi-bin/...le_pagination=1

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#266820 - 01/23/14 06:16 PM Re: Testing the strength of cordage [Re: clearwater]
AKSAR Offline
Old Hand

Registered: 08/31/11
Posts: 1195
Loc: Alaska
Originally Posted By: clearwater
Unless you use very heavy shock cord, it will provide too much stretch and increase the sawing motion on stakes etc.
You use stout shock cord and very short little loops (perhaps 2-3" in diameter). Because they are loops, you effectively have double shock cord. When you set up the tent, you pull the guys snug, so the shock cord is stretched slightly. When wind gusts hit, it stretches a bit more, but softens the jerk.

The method has worked quite well, in my experience. Way better than tying the guys directly to the fly.
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"Toto, I've a feeling we're not in Kansas any more."
-Dorothy, in The Wizard of Oz

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#266868 - 01/26/14 12:29 AM Re: Testing the strength of cordage [Re: gonewiththewind]
Steve Offline
Journeyman

Registered: 05/29/04
Posts: 84
Loc: North Carolina
The excellent book "On Rope" by Bruce Smith and Allen Padgett (about North American vertical rope techniques, published by the National Speleological Society) has a section on measuring rope strength, and here are a few points it mentions:
  • There is a U.S. test standard: 191A, Method 6016
  • It involves wrapping rope around two cylinders that are pulled apart at a fixed rate. All the parameters/dimensions are spelled out.
  • Lots of factors affect strength, and lots of different things can be measured as "strength"
  • Practical, real-world values may be significantly different from what is measured in a lab
From my own brief experience measuring Nomex thread strength in a university Textile Engineering lab, ideally what you might like to get is not a single number, but a graph of the relationship between elongation and pulling force.

Steve
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#266869 - 01/26/14 01:42 AM Re: Testing the strength of cordage [Re: gonewiththewind]
Pete Offline
Veteran

Registered: 02/20/09
Posts: 1372
Montenero - I like the suggestion of suspending a steel drum and filling it with water. You can calibrate the height of the water level against the total weight (drum plus water). You can suspend the drum with extra strength paracord, and then you only have to loop the cordage you are testing through the paracord.

good luck,
Pete

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