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  #11  
Old 12-22-2010, 05:14 PM
John D John D is offline
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Join Date: Sep 2006
Location: Richmond, California, USofA
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Default More on Soft Shackles

Cam,

Thanks for the link. Lots of neat solutions are shown there.

Peter,

You can practice with any hollow single braid rope with a good hand. If you have any Regatta Braid or Tenex lying around you could use that. However using UHMWPE (Ultra High Molecular Weight PolyEthylene [Dyneema, Spectra, etc.]) for soft shackles makes sense both because of the physical properties (strong and slippery) and the cost.

OK, I can hear you saying "Sure, strong is good and slippery makes it easy to open and close a soft shackle hundreds of times without it binding up. But cost? That stuff is very expen$ive"

UHMWPE rope is only expensive when you are comparing it to a nylon or polyester rope of the same diameter. If you compare a UHMWPE rope to other ropes with the same strength, the prices are close and often the UHMWPE is less expensive. As a rough rule of thumb UHMWPE is as strong as polyester with twice the diameter.

Less rope is needed to create a soft shackle with 5mm (3/16") UHMWPE than with 10mm (3/8") polyester because you need more rope to tie the diamond knot in the larger diameter line. And four UHMWPE soft shackles will weigh less than one polyester soft shackle of the same strength (and UHMWPE floats while polyester sinks).

If you wander down to the dinghy section of your local chandlery you can find 3mm, 2.5mm and even 2mm single braid. Iíve used the 2.5mm to make some super skinny soft shackles to hold my power cord where it hangs from the lifelines at dock. The 2.5mm is only rated at 1,500 lbs. (giving a SWL of 300 to 750 lbs, depending on your safety factor) which limits where it can be used, but the material cost per shackle was less than a buck.


Kohlhoff, the German rigging company, has a slightly different method of making their soft shackles (Kohloff calls them loop shackles or twin loop shackles). Rather than passing the rope into itself (splice style), they pass the rope through itself (like beginning a brummel) and have two parallel legs for the length of the shackle. From the pictures they appear to finish with a locked brummel and a diamond knot. Take a look at http://www.loopblock.com/docs/Loop%20Shackles.pdf


John D.
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  #12  
Old 01-05-2011, 12:15 AM
allene allene is offline
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Quote:
Originally Posted by John D View Post
Cam,

Kohlhoff, the German rigging company, has a slightly different method of making their soft shackles ... they appear to finish with a locked brummel and a diamond knot.

John D.
I have made some soft shackles both ways and a section of the same line with eye splices on each end. I intend to pull on it until something breaks. I want to find out which of these soft shackles is stronger, or if they are both stronger than the line they are made of. I will post my results. In the mean time, I made a "how to" page including an animated gif on how to tie a diamond knot. I hope someone finds it useful for all the work it took.
http://l-36.com/diamond_knot.php. If it isn't clear, let me know and I will change it.



Allen
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  #13  
Old 01-24-2011, 10:34 AM
allene allene is offline
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I completed the strength testing on the soft shackles. I tested both styles of soft shackles made from 1/8 inch Amsteel. To get a calibration point I put a straight section of Amsteel between the two soft shackles. Just to make it interesting, the straight section had a brummel eye at one end and a straight bury and stitched eye at the other. The test was made and the Amsteel broke in the middle away from the splices. Neither soft shackle broke. My test setup had 100:1 mechanical advantage and I had to pull almost as hard as I could to break it. Incidentally, there were no grommets on the eyes but they still held.

So, while I didn't actually test the ultimate strength of the soft shackles I did verify they are stronger than the line they are made of. For my application, that is enough and that was the goal of my test.

I now have 6 web pages devoted to soft shackles including one that has a video of the test. I was amazed how hard it was to break the 1/8 Amsteel.
http://l-36.com/soft_shackle_intro.php



Allen
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