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Snatch/yarding block differences?

Postby Low_Sky » Thu Aug 11, 2016 5:10 pm

Does anyone know if there are any differences in the China-made cast-style, fixed-bail blocks that are available from various sources?

Warn's 33,000 lbs block, $165 (https://amzn.com/B0002Z9SWE)

looks identical to

Smittybilt's 36,000 lbs block, $99 (https://amzn.com/B004XG3KT0)

looks identical to

This painted yarding block, $73 (http://www.westechrigging.com/block-import-toggle-pin-6.html)

looks identical to

This galvanized yarding block, $53 (http://www.riggingwarehouse.com/default.aspx?page=item+detail&itemcode=201-BLOCKYB06&catlist=4434)

They all appear to be the same, but I suppose there could be minor differences that aren't readily apparent in pictures (bearings, finish/smoothness of the sheave). As far as I can tell, these are the only blocks rated for our trucks/winches that aren't $$$ professional rigging equipment. The "HD" snatch blocks from the off road companies with flat side plates are rated by ultimate strength, and don't give enough of safety factor to have a place on my truck. I'm looking to put together a recovery kit with two blocks, and I don't want to waste money shipping and returning crappy blocks to/from Alaska.
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Re: Snatch/yarding block differences?

Postby Cactus Red » Thu Aug 11, 2016 6:35 pm

I've been using 20K pulleys for years. That's a very decent safety factor for a 15K winch. No point on a pull will exceed the capacity of the winch if rigged properly, and 20K exceeds the strength of the cable in any respect.
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Re: Snatch/yarding block differences?

Postby Low_Sky » Thu Aug 11, 2016 8:07 pm

Cactus Red wrote:I've been using 20K pulleys for years. That's a very decent safety factor for a 15K winch. No point on a pull will exceed the capacity of the winch if rigged properly, and 20K exceeds the strength of the cable in any respect.


Cactus Red, I'm not a rigging or recovery expert, but I am a mechanical engineer with too much time to read and think about this stuff. I'm sure that you have put more feet of cable through 20k pulleys than most anybody, but I just can't get on board with the math.

A block needs to be rated to twice the winch capacity, because a doubled pull (assuming 15,000 lbs for the PW winch getting enough current) can transmit up to 30,000 lbs through the block to the anchor. A safety factor would then need to be applied to that 30,000 lbs maximum pull. The off-road industry doesn't seem to have a standard for how safety/design/fudge factors are applied to recovery gear, but it appears that ARB and Warn use approximately 2.0 SF. In the case of Warn's "33,000 lbs" block, it's clearly a 6.5T WLL yarding block (it's actually cast into the housing).

6.5T * 2000 (lbs/T) * 5.0 SF (rigging industry standard) = 65,000 lbs ultimate rating

65,000 lbs / 2.0 SF = 32,500 lbs (Warn's rating, I wonder if it's a coincidence that they re-brand and sell a block rated to a doubled pull from their strongest winch?)

Granted, a rig will never see the winch's maximum pull unless the load is so badly stuck that the winch motor stalls out with the winch line paid out to the last layer, but I believe the recovery gear should still be rated for that worst case scenario.

As a hypothetical worst-case recovery scenario, an 8000 lbs PW mired up to the frame (3.0 resistance factor), pulling up a 45-degree slope (0.75 resistance factor) needs a 30,000 lbs pull to get out (or so says the Army's recovery field manual).

(3.0 + 0.75) * 8,000 lbs Loaded Weight = 30,000 lbs Pull

*EDIT* I corrected "last wrap" to "last layer". Pulling from the last wrap makes for a very bad day!
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Re: Snatch/yarding block differences?

Postby Cactus Red » Thu Aug 11, 2016 9:10 pm

Again, the load can't exceed the rating of the winch at any attachment point. The physics are straight forward. You do get a theoretical 30K of load, but it"s split between two points, the pulley and the anchor point. That's just the way it works. Here's some mathematics that show it better than I can explain it.

http://www.engineeringtoolbox.com/pulleys-d_1297.html

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Re: Snatch/yarding block differences?

Postby Low_Sky » Thu Aug 11, 2016 9:15 pm

Take a closer look at the page you posted, under the "moveable pulley" header ;)


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Re: Snatch/yarding block differences?

Postby Low_Sky » Thu Aug 11, 2016 9:24 pm

Cactus Red wrote:Again, the load can't exceed the rating of the winch at any attachment point.


If this is true, then crane companies have been wasting money on all those expensive blocks and way too much wire rope.

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Re: Snatch/yarding block differences?

Postby Cactus Red » Thu Aug 11, 2016 9:58 pm

So, the load on each line is no more than the rating of the winch pulling in the cable, but the load at the moving hook is higher. In our case, the pulley is fixed to a tree or PulPal. The moving load is the truck itself with only one point fixed as it were.

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Re: Snatch/yarding block differences?

Postby Low_Sky » Thu Aug 11, 2016 11:29 pm

Try thinking about it as if nothing is moving. Imagine that the truck is fixed too, and is just using the winch to exert tension on a static rig. I'm bored tonight, so I drew pictures :D

Anchors are black dots, Power Wagons are blue dots, and single blocks are red dots. The winch exerts W pounds of tension. For easy math, all winch lines are parallel except for the last example. No friction from the blocks.

1. The first diagram is a straight pull. The Power Wagon is experiencing a pull of W, and the anchor is experiencing an equal and opposite pull of W.

2. The second diagram is also a straight pull. This is the scenario that people sometimes "think" gives them a double advantage, but does not. The only benefit to this rig would be to get line off the drum to get down to the last wrap. The Power Wagon is experiencing a pull of W, the anchor right next to it is also experiencing a pull of W in the same direction, and the anchor with the tree strap and block is experiencing an equal and opposite pull of 2W to keep the system in equilibrium.

3. The third diagram is a double pull. The winch line goes through the block, and back to a tow hook on the Power Wagon. Two connections to the winch line means the Power Wagon experiences a pull of 2W. The anchor experiences an equal and opposite pull of 2W.

4. The fourth diagram is a redirected single pull. The placement of the anchors just happened to work out for really easy math. Lucky me! The Power Wagon experiences a pull of W. The right anchor, connected to a single leg of the winch line also experiences a pull of W. The anchor connected to the block is connected to two legs of winch line at 45-degree angles and feels a pull of 1.4W. The higher the angle between the two winch line legs, the less pull the block anchor would feel. The lower the angle between the two legs, the more pull the block anchor would feel. If the angle between the two legs was zero, we'd be back at scenario 2. If the angle was 180, we'd be back at scenario 1.

In every scenario except #1, the block, tree strap and shackles between the two need to be rated for more than the winch rating. You get more rating out of your tree savers if you rig them with a basket hitch versus a choker hitch. I won't even get started on rigging for triple pulls, especially since that would be done using more hardware rated for double pulls. No need to go shopping for 1" shackles :)
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Re: Snatch/yarding block differences?

Postby Low_Sky » Thu Aug 11, 2016 11:30 pm

And if anybody knows anything about yarding block quality, or where to get the cheapest 6.5T WLL yarding block if they're all the same, I'd love to hear about that too!
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Re: Snatch/yarding block differences?

Postby Colibri » Fri Aug 12, 2016 7:18 am

Not necessarily the cheapest, but certainly competitively priced, and very good quality and customer service

http://www.awdirect.com/snatch-blocks-and-accessories/

Been using them for years for commercial quality rigging equipment and other hard to find stuff.
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Re: Snatch/yarding block differences?

Postby Ducky's Dad » Fri Aug 12, 2016 9:16 am

No need to go shopping for 1" shackles :)

Interesting. I was just shopping for 1" shackles before I read this post. Since I now have a Pull-Pal RW14000, I was planning to hang a 1" shackle on it and just leave it there rather than packing with the other recovery gear.
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Re: Snatch/yarding block differences?

Postby Low_Sky » Fri Aug 12, 2016 9:47 am

I'll be getting 7/8" 6.5T WLL shackles when I finally pull the trigger on building a recovery gear kit. If you never intend to rig a triple pull or don't think the pull pal or ground would stand up to a 45,000 lbs triple pull, a 1" shackle would be overkill. A 1" shackle also has a 1-1/8" pin, how big is the shackle pin hole at the end of your pull pal?
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Re: Snatch/yarding block differences?

Postby Cactus Red » Fri Aug 12, 2016 6:37 pm

This is my kit. All three pulley's are 20K rated, the shackles are (5) 3/4" and (3) 7/8", all rated at 6.5T. Don't over think it - these have done multiple double line pulls, dozens of single line pulls, and many redirected pulls. The snatch blocks are: Smitty Built 20K, ARB 9000 20K, Warn 88899 20K. If I'm going to load the system really heavy, the ARB is my #1 choice. Two ARB tree savers, one WinchLine.com 50' extension, one 10' rigging strap, two rope bones, one ARB 3" x 30 tow strap, and a couple safety vests. If we know we're heading into really bad conditions, I take the gear out of the JKUR which doubles what's shown here.
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Re: Snatch/yarding block differences?

Postby Ducky's Dad » Fri Aug 12, 2016 6:41 pm

A 1" shackle also has a 1-1/8" pin, how big is the shackle pin hole at the end of your pull pal?

Good point. The hole in the RW14000 is 1-1/8", but I thought it was larger until I went out and measured it.
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Re: Snatch/yarding block differences?

Postby nts007 » Fri Aug 12, 2016 8:35 pm

Low_Sky wrote:I'll be getting 7/8" 6.5T WLL shackles when I finally pull the trigger on building a recovery gear kit. If you never intend to rig a triple pull or don't think the pull pal or ground would stand up to a 45,000 lbs triple pull, a 1" shackle would be overkill. A 1" shackle also has a 1-1/8" pin, how big is the shackle pin hole at the end of your pull pal?


Keep in mind because even though you've created this amount of pull force you will still only pull as much as you need to get unstuck. A single snatch lock will cut the load on the winch by half. That's more the point not increasing the pull force. If 12k lbs isn't pulling you out then 24k is just gonna break things. For example if your axles are so buried that it takes more than the 12k winch you're likely gonna bend your control arms or something else. Not saying that increasing the pull with a snatch is bad but a person needs to have good knowledge of the situation. I know most of you guys aren't dumb enough pull your truck apart but you know what I mean. Part of the reason the cranes use a multi block system is to allow more force with a lighter hydraulic motor. But keep in mind every loop doubles the amount of cable on the drum. If they had an unlimited amount of winch power they could do it with a single line because the total weight the boom can handle doesn't increase just because there are more snatch loops.

I always wanted to hang my old PW on a big aframe by its winch. Woulda been awesome. Just not sure how well the fluids woulda liked that lol
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Re: Snatch/yarding block differences?

Postby Colibri » Fri Aug 12, 2016 8:51 pm

I would pay to see that shit lol. It would be epic
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Re: Snatch/yarding block differences?

Postby Low_Sky » Fri Aug 12, 2016 9:39 pm

If you look hard enough you can find videos of people dumb enough to do this on YouTube, usually with jeeps. Getting the jeep in the air is the easy part. Getting it down is harder because almost any way you do it the jeep wants to come down on its roof.




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Re: Snatch/yarding block differences?

Postby Low_Sky » Fri Aug 12, 2016 11:50 pm

https://youtu.be/YD5uAJPKasI

This is part one of a two-parter. It's not worth watching the whole thing. Just skip ahead a few minutes at a time and you'll get the gist of it :)


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Re: Snatch/yarding block differences?

Postby Bill2014 » Wed Oct 19, 2016 6:08 pm

Low_Sky wrote:https://youtu.be/YD5uAJPKasI

This is part one of a two-parter. It's not worth watching the whole thing. Just skip ahead a few minutes at a time and you'll get the gist of it :)


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Re: Snatch/yarding block differences?

Postby Reloaderguy » Fri Oct 21, 2016 1:33 pm

Low_Sky wrote:https://youtu.be/YD5uAJPKasI

This is part one of a two-parter. It's not worth watching the whole thing. Just skip ahead a few minutes at a time and you'll get the gist of it :)


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