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WLL question

Discussion in 'Winching and Recovery' started by rc51kid, Sep 13, 2017.

  1. rc51kid

    rc51kid

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    I ordered a few Crosby items from a rigging shop to repasr some old steel line to use as a extention.

    Looking at the rigging sights web page i saw a few things i would mind having.

    I understand most of our off road gear is raited at the weight it will fail. Most rigging gear usses WLL. From what i see most things fail raiting are about 4-5 times there WLL but some are as low as 3X there WLL. Am i right so far?

    Looking at my 3/4 shackles i see a WLL of 4 3/4 tons, about 9000 pounds. I never really hear about shackles failing, do you? It made me think that in general if i stick with a min WLL from a rigging shop of around 9000-10,000 i should be pretty good.

    Just as info i have a M12,000 with 3/8 amsteel on it. I think my lune has a fail point of 19,000 or so. Much less than a WLL of 10,000.

    Is my logic bad or about right? I know there is no 100% fool proof with vehicle recovery. Things go wrong and fail and you need to always be in a safe position if somthing brakes. But am i about right with a WLL number?
     
  2. Steve83

    Steve83

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    No, it's exceptionally rare for any manufacturer or retailer to publish a number at which catastrophic failure is LIKELY to occur. Virtually everything (from trash bags to tug boat ropes) is rated with a safety factor; a multiplier that encourages consumers to NOT approach the point of failure. The lowest SF is probably 1.5x, meaning failure is likely at 1.5x the published rating number.
    That's more in the range of overhead lifting & carrying live humans. But some things have an even-higher SF.
    It's uncommon because large shackles (with SUBSTANTIALLY-higher WLL than necessary) are so inexpensive, and popular for the look (I'm guilty). But it DOES happen.
    It depends on exactly what rigging components you're talking about, and exactly how you use them. The most-stressful recovery (on the equipment) is a snatch - especially when using a NON-elastic connection (like chain or cable). Winching is generally the least-stressful.
    If that's what's advertised, then it's probably still actually a WLL. But you could find out... Google or WikiPedia the YIELD strength (in Ksi or x,000psi) of the Amsteel material (possibly tempered UHMW), and then try to calculate the actual cross-sectional area of your rope. Area x yield strength = yield force. If it comes out to ~19,000lbs, then they didn't apply any SF.
     
  3. half k cruiser

    half k cruiser

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    @rc51kid I've not seen or heard of a shackle failing. I would say 9000lbs is an ultra conservative rating for something built of solid steel like that. I have a steel carabiner I carry at work that's rated at 56Kn or 224x56 for 12,544lbs, its only 1 lb of steel and way thinner than a 3/4'' shackle. My cloth recovery gear is all from a overhead lifting supply company. Its all tagged with ratings for single pull, basket, and cinch.
     
  4. rc51kid

    rc51kid

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    What WLL do you go for when you select gear?
     
  5. Steve83

    Steve83

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    A better way to think of it is: don't pull harder than your rigging can take. If you have a 3/8" shackle, you can use it to pull a truck out. But don't jerk it, because the shackle could break. If you're using a 5/8" shackle, it can take more abuse.

    But a 3/8" shackle is NEARLY as strong as 3/8" chain (which is pretty stout). And it's probably stronger than a 3/8" cable, because the shackle has 2 3/8" sections made of weaker cast steel, compared to the cable's single 3/8" section with air gaps made of better steel.

    A 5/8" shackle is NEARLY as strong as a 5/8" hitch pin, which is strong enough to drag a travel trailer across the continent at 90mph on highways & 20mph on the roughest roads.
     
  6. half k cruiser

    half k cruiser

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    I would have to look at my slings again but I believe my 30ft eye to eye are 20,000lb straight pull, obviously more is better. My 6ft bow slings are only around 6k a piece but they are used as an arrestor in case I lose a tow point or shackle. The one piece of rigging that always worries me the most is the pulleys. Its expensive for a true overhead rated pulley. The ones from ARB and Harbor Freight look like they come from the same factory in China, and I'm just not sure if they have my best interests in mind.