Snatch Block rating

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CruisinGA

CruisinGA

Joined
Mar 27, 2003
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I need a couple of snatch blocks. One for my 40 w/ 8274 and synth line and another for my 80 with an XD9000i and steel cable.

When a snatch block is rated as a "20,000 lb" snatch block, I assume that is the total pulling force it can take, ie, shouldn't be used with a winch rated over 10K lbs.

Is that right?

Also, Some of the cheaper snatch blocks I see listed on Ebay claim "good for cable up to 1/2". Seems to me like this is not necessarily a "one size fits all" item.

:beer:
Bailey
 
Most of the consumer stuff is rated at it's breaking strength. If they don't give a SWL (and give the safety factor) and specify it as such, figure it's the ultimate strength.
 
Since I don't want it breaking on me, I guess I ought to stay way below the ult. strength.

Think a "20,000lb" snatch block would be appropriate for an 8274, XD9000i, or neither?
 
Well, you can double the force your winch is putting out with a single block, so the force on the block is up to twice your line pull. Given that you are normally running close to your ultimate line strength on these winches (5/16 7x19 steel cable is 9800lb, 3/8 7x19 steel cable is 14,400lb, 5/16 amsteel is 10,500lb, and 3/8 amsteel is 15,500lb), you can see there is virtually no safety factor here at all, so a 9000lb winch with 5/16 cable and a 20,00lb block is an interesting thing... they are all right at their ultimate strength, with the hope that the winch gives up the ghost first!
 
That's what I was referring to, that much of the time I use a block, the force on it will be double the tension in the line.

I've snapped 5/16 amsteel blue with my XD9000i. It was not a pleasant experience, luckily no one was hurt.

Seems to me I would be better off with a snatch block rating above 20k lbs. I often find myself winching at the limits of my equipment.

Thanks for the help.

I am a mech. engineering student, but Ga Tech doesn't like to teach much that isn't useful to someone pursuing a PhD:rolleyes:
 
CruisinGA said:
That's what I was referring to, that much of the time I use a block, the force on it will be double the tension in the line.

I've snapped 5/16 amsteel blue with my XD9000i. It was not a pleasant experience, luckily no one was hurt.
snip
Click to expand...

what was the unpleasant part, given that the synth is not supposed to whip. Did the truck move? Or did it whip anyway?
 
It was a long pull, there was a strap between the cable and the truck being pulled, I was anchored to a tree at the top.
When the amsteel let go, the strap flung a d-ring and the severed end of the amsteel so far I couldn't find it. I learned pretty quick that just using synthetic won't keep you safe if anything in tension stretches.
 
Okay, back to snatch blocks, I was in an arborists supply shop the other day and saw this on their wall; Bailey's - CMI 3/4" Stainless Steel Block
Pricey, yes, but beautifuly made, light and compact and 40,000 lb breaking strength.
 
Here's a link to a good explanation of SWL and WLL (I think that's what you meant by WWL?). Basically the same thing, but they use WLL (working load limit) now to avoid liability...
ProffessionalDiary: SWL or WWL (Rigging Terminology)
Normally in rigging, you look at the type of lift, or pull (lifting, pulling, manned, unmanned, overhead...) and apply a suitable and appropriate safety factor to the weight involved and you will get the minimum ultimate strength of the components you must use.
So their 40,000lb ultimate strength divided by 5 (an acceptable safety factor for overhead lifting) equals 8000lb WLL (or SWL in oldspeak).
 
roalco said:
Here's a link to a good explanation of SWL and WLL (I think that's what you meant by WWL?). Basically the same thing, but they use WLL (working load limit) now to avoid liability...
ProffessionalDiary: SWL or WWL (Rigging Terminology)
Normally in rigging, you look at the type of lift, or pull (lifting, pulling, manned, unmanned, overhead...) and apply a suitable and appropriate safety factor to the weight involved and you will get the minimum ultimate strength of the components you must use.
So their 40,000lb ultimate strength divided by 5 (an acceptable safety factor for overhead lifting) equals 8000lb WLL (or SWL in oldspeak).
Click to expand...

Excellent information - thank you!
 
CruisinGA said:
I need a couple of snatch blocks. One for my 40 w/ 8274 and synth line and another for my 80 with an XD9000i and steel cable.
Click to expand...



ARB 209.


I have three in my truck and have used all of them at the same time.


Will work well for you and last a long time.


:beer:
 
snatch blocks don't "double" winch power

CruisinGA said:
That's what I was referring to, that much of the time I use a block, the force on it will be double the tension in the line.

I've snapped 5/16 amsteel blue with my XD9000i. It was not a pleasant experience, luckily no one was hurt.

Seems to me I would be better off with a snatch block rating above 20k lbs. I often find myself winching at the limits of my equipment.

Thanks for the help.

I am a mech. engineering student, but Ga Tech doesn't like to teach much that isn't useful to someone pursuing a PhD:rolleyes:
Click to expand...

Your snatch block should be plenty strong. Many people misconceive how snatch blocks work. They do not double the strength of the winch so there is not double the tension on the line. When you have a full drum of cable on a 9000lb winch you do not have a full 9000lbs pulling power until you only have 1 wrap of cable on the drum. So if you have 5 wraps you may only have 6000lbs of pull(just throwing a number out there). The snatch block allows you to pull out more cable off the drum to give the winch less cable on the drum allowing it to pull closer to it's maximum capacity. Once you are down to one wrap on the drum you have 9000lb pulling power. Even with a snatch block your winch is only capable of 9000lbs. I don't mean this to seem like rant, but my buddy argued with me on this point for about an hour till he went and researched it and realized I was telling him the truth. Point is if your snatch block has a working load of 20,000 lbs it should be good. Your line probably snapped because of a fray or weakness in the synthetic, its common when maxed out.
 
You may want to rethink that example, homebuiltcruiser.
If you use a double line pull, that is line out from winch, around an anchored block, and back to the winch vehicle, the strain in the line will be the same on both legs, and, can be up to the max power your winch can develop. This means the strain on the block and the anchor rigging (shackle, straps etc) and the anchor will be twice the strain developed by the winch, In this case it could be up to 18,000lbs, very close to the ultimate strength of the block, and does not consider any dynamic loading.
Blocks can be used to either redirect the line of pull, or when compounding the line (like above), to increase the net force applied between the winch and the anchor point.
By the way, a 9000lb winch with 3/8" line will pull 9000lb on the first wrap, 7,300lb on the second wrap, 6200lb on the third wrap, and 5400 lb on the fourth wrap.
 
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