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  #11  
Old 06-22-2009
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Thank you all for the great responses.

Sway, the math really helped, thanks for taking the time to write all of that out.

I think I may be okay, the load is actually less than 1000lbs, more like 600lbs, I was being conservative and wanted it to use 1000lbs for a safety margin. Now I see that the working load on the equipment already has a safety margin built into it at 5-to-1 or even 10-to-1 to estimated break, I just hadn't read the fine print and didn't know they were already being conservative. The load won't be lifted more than about 60 degrees from vertical, and the rings I am looking at now are forged steel rated over 3000lbs WLL and are 10-to-1, rated over 30000lbs to break, that should more than do it (famous last words).

Edit - follow-up question, is there a resources somewhere that says what the estimated holding power of various knots and splices, etc, are for lines ? I would assume that the goal in using most knots would be to have the rope break before the knot, but I don't like assuming things, so it would be nice to find out what chances there are of various knots slipping.

Edit #2 - I forgot to say why rings since that might come up, the reason is that I need to attach the load to the rings in multiple places, not with a single line, so I need some surface area to work with and the rings would let me attach the load with a number of lines. I think the shackles might be too cramped though you guys have totally convinced me that is the better route to go if possible.
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Last edited by wind_magic; 06-22-2009 at 07:17 PM.
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  #12  
Old 06-22-2009
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If you want something that's easily opened, D-shaped screw gate carabiners will be stronger for the same weight that any other shape.
There's a long and interesting history behind the design of carabiners, some of which is covered here:
ATS Resources for the Recreational Canyoneer - Carabiners


Quote:
Originally Posted by wind_magic View Post
Dog, what I want to do in the abstract is to have a load that has two rings on it, one on either side, and to lift that load with ropes on either end pulling horizontally so that the load is suspended in the air and is between two ropes as if it was suspended over a river with the ropes tied at either shore.

I'm starting to think that screw links like the ones that climbers use might be better able to hold a load instead of something round like a metal ring.

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Any knot or hitch will part before the line does. Any time you place so much as an overhand knot in a line you weaken it. If memory serves me right you can expect to lose about 50% of the strength of a line with a knot, hitch, or bend. A properly made splice will retain 90% of the line's strength.
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Old 06-22-2009
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Have a look at the bottom of this page:

Hamilton Marine 2009 iCatalog - page 133

I think the "weldless rings" or the "weldless sling links" might be what you're looking for. 3/8" sling link will handle 1000 # and cost about $7.00
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