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 Post subject: How to use Snatch Blocks
PostPosted: Mon Nov 15, 2010 4:09 am 
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Location: Denver, CO
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Snatch blocks are a great way to get more pulling power from your winch. If you have an 8,000 lb winch then you can roughly double or triple your pulling power with the below setups.

Single Line pull. Goes straight from the winch to the tree. If you have an 8,000 lb winch you can get roughly 8,000lbs of pull
Image

Double line pull. Notice how the winch line goes around the pulley and anchors back onto the bumper. In this case you can get around 16,000 lbs of pull (8k + 8K = 16k)
Image

Triple line pull. In this case the line goes from the winch around the first pulley on the tree, around the 2nd pulley on the rig, and anchors on the tree.
In this case you can get roughly 24,000 lbs of pull (8k + 8k + 8k = 24k).
Image

If you were to use a third pulley in the same manner you can create 32,000 lbs of pull (8k + 8k + 8k + 8k = 32k)

Alternately if you have enough anchors around and winch line you can change the configuration to create 64,000 lbs of pull with three snatch blocks.

Image

Just so you know the actual pulling power doesn't work out quite this neatly. There are a lot of factors that cause loss of pulling power. The more layers of winch line you have on your winch drum the less pulling power you have. If you are unspooled your winch line to the point that you are pulling off the bare drum then you will have the rated pulling power of the winch. For every layer of winch line you lose roughly 10% of the pulling power. BTW you should never have less than 6 wraps of line around your drum or you could unspool your winch line right off the drum! Winch lines are not secured on the drum at the factory.

You also lose pulling power by creating angles in the winch lines. In the single line and double line pulls the angles are good and you don't lose pulling power because there are not any angles in the line. In the example with the triple line pull you are losing pulling power from angles because the line anchored to the tree is at an angle. Remember vectors in high school? Well looks like your teacher was right, it is useful in the real world :bonk:

You also lose power from friction in the pulleys.


Here's a good setup if there are no trees around. If you don't chock the wheels you may only get a few hundred pounds of anchoring from each rig on ice. Closer to 1,000lbs of anchor if you are on dirt. If you dig holes to chock the wheels you can get thousands of pounds of anchoring per vehicle.


In this case the silver rig and the red rig don't need to chock the wheels but the green and tan ones do.
Image

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 Post subject: Re: How to use Snatch Blocks
PostPosted: Thu Sep 15, 2011 6:45 am 
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Location: Australia
Hey I've been following your post since last 3 or 4 months and I must say I got so many information from here so thank you very much for sharing it with us.

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 Post subject: Re: How to use Snatch Blocks
PostPosted: Tue Jan 17, 2012 2:14 am 
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Location: Australia
The snatch block is a pulley block with a side plate that swings open. Because the side plate opens up, you don’t have to thread your winch cable through the opening; instead, you open the side plate, fit the cable over the pulley, and then close the side plate.

A snatch block has two primary functions in recovery winching. One is to change the direction of your winch cable when the anchor point is offset. The second is to increase the pulling power of your winch.

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 Post subject: Re: How to use Snatch Blocks
PostPosted: Mon Dec 16, 2013 12:15 am 
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Location: Vancouver Wa
one thing id just like to add here, be careful when using a snatch block to "double" your pulling power, make sure your gear is rated for it. some of us have 9 or 9.5k winches, and some snatch blocks are only rated to 16k or 18k.... well if you have a 9k winch double that is 18, and if your snatch block is only a 16k, you could destroy the snatch block. or if you use two snatch blocks, and you only have a 8k winch, thats still 24k of pulling power, and you could damage your system, rip your bumper off, pull the tree over ect... so be smart about this stuff. also the more snatch blocks you use the shorter your effective "pull" becomes or your line becomes you basically at least half the line length each time you use a snatch block.

working in SAR, and being a rope tech and high angle rescue tech i have seen systems that are "over built" and could very easily rip the guts out of the system if the even a "mild" force was applied to it.

another great use for a snatch block is a change of direction pull... say someone has slid off the trail to the right side of the trail. well you cant pull them strait back and the can not go forward, the only way they can go is sideways back up the way they went down.... but you cant get a truck in there cause the trail is too tight or what ever... you can run your line to the left side of the trail anchor and snatch block to a tree, or another rig (i prefer trees or other large "none movable" objects) run your line through the snatch block and pull that way... -feel free to reverse the sides in correlation as needed


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 Post subject: Re: How to use Snatch Blocks
PostPosted: Mon Dec 16, 2013 1:24 pm 
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I took physics in high school and college which means my knowledge is more dangerous than useful, so here I go showing how little I know of this...

I thought the point of the pulley system (snatch blocks) was to distribute the force of the mass being pulled upon (so each block would only take a portion of the total load). Thus lowering the total force or "pull" required to move an object.

Example/Question: If my vehicle were to weigh 3 tons and I had 2 snatch blocks hooked similar to the last diagram, then wouldn't each length of line have half the weight of my vehicle applied to it (static/non-pulling)? Which means my winch would only have to pull just over 1/2 of the weight instead of the full 3 tons? (In a perfect/non-existent world)

I understand that the applied force to each snatch block could compound quickly in a complicated pull, but maybe only if the vehicle were truly "stuck" and not just being pulled over/off something?

Sorry, probably didn't word that very well. I'm VERY new to the winching world and would rather ask now then have an unwanted/dangerous incident.

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 Post subject: Re: How to use Snatch Blocks
PostPosted: Mon Dec 16, 2013 2:49 pm 
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Location: Vancouver Wa
i get what you are saying, and i took the same physics and geometry level classes too so dont take me as an expert physicist or anything like that.


lets say you have a 9k winch, but its mounted on a earthroamer xv-lt expo truck(if this is you, your an idiot, cause you paid at least $250k and couldnt pony up $2500 for a nice 16.5k winch or higher...?) anyhow the earthroamer is rated at 17,950 gvwr(lets call it 18k to make things easy.

now lets take that truck and get it stuck in the mud for sake of this argument. now every situation will be different, as variables such as how much weight or gear you actually have with you, how stuck are you, -is it just i cant get traction, or am i to the frame in the bog ect., and are you on level ground, down hill, or up hill ect ect ect. but for scenario lets just say flat/level ground, stuck to the axles in mud. so now you need to pull yourself out, but your vehicle weighs 18k and you only have a 9k winch. you are going to need a snatch block to double that 9k power to 18k. that means that every part there is going to be taking on the full 18k weight. that single line, its having to do all the work(there is no second line, and second winch, yes you have doubled the line over, but all you did was basically change the gear ratio. that stanch block just took the load for the motor in the winch. so you start to pull and all things being ideal you have only 6 wraps on the drum of the winch so you are getting max pulling power, and the mud is not sticky so its not creating a suction or holding power -ill cover this in a bit. so you are pulling your 18k truck with your 9k winch and its working. but is your winch line rated to pull that -sure it can, but is it rated to do so? and just cause it can once, how many times do you want to trust that it will keep doing that? and again is your snatch block rated to do that? no, ok but your are stuck and its all you have, so you give it a shot, and it works. great, but do you want to trust it again and again to be over loaded every time you have to use it?
maybe you should get a bigger snatch block. -i would not own a snatch block that is under half the load of my winch, unless you plan on only using it for a change of direction. -now i have a snatch block that is only a 16k sntach block and i have used it with my 9.5ti winch, to where the winch bogged down and almost stopped, had the truck almost completely off the ground. -i was pulling a tree over at my parents house and had anchored my 1985 toyota pickup to another tree behind me and using the winch to pull the tree in the middle of their yard out, and no my snatch block did not fail(and i did not tear the frame in two). so yes it can be done of needed, these things are under rated, but why do this if you can avoid it. i have sense bought a 18k snatch block and keep both of them with me at all times in my rig. i will use the smaller one for change of directions only. i would never put the smaller one into a compound system knowing that i have already over stressed it, that would be asking for a disaster.

so now to cover issues with snow, sand or mud... all of these elements can get you stuck, and when winching out of them your actually might be pulling more weight than the rig itself weighs. that is because these elements will cause a suction or vacuum if you will, and the can and will fill into all the small crevices and openings at or below their level. thus the initial pull will require more force or effort to get the vehicle moving or unstuck than will be required once the vehicle starts moving to keep it moving. so lets say our same rig the earthroamer xv-lt is stuck to the doors in a mud bog and the bumper is half under mud, the axles are completely covered, and the frame is buried along with the transmission transfer-case ect. so we get out our 18k snatch block, and our cable, and we start rigging uo our system to pull out the truck, get it all set up and go for it. and the winch just bogs down... no pull nothing. so we are now needing more power to pull the truck on level ground that we would need to pick it vertically up in a parking lot.... that is the power of suction. and i have experienced this in snow and sand as well. some would say well just toss in another snatch block... ok well hold on, not so fast. you might only need another 1000lbs of pulling power, so that might work, but your are creating the ability to now pull 27k lbs so anything between 18 and 27k lbs you will be able to move, but your snatch blocks are only rated for 18.... so moving 19 or 20k might be doable -remember these are undrated, but by how much, and again thats always in optimal conditions never used before ect., but 27k is not gonna work. -well you say thats no biggie, i got me two of the Warn 24k lb snatch blocks, we will just use those... ok so now your snatch blocks are good for it, but is your bumper and how its mounted? or the winch and its mounts? -the drum might not be able to take that kinda abuse, because while the motor is only pulling 9k the drum and line have (up to) 27k lbs on them... and i know the line on a 9k winch will not hold a load of 27k... sorry not gonna happen.

so in short yes snatch blocks are great, but dont get ahead of yourself and rip your system apart.

i have seen videos of 2 or 3 guys rip the guts out of a rope system moving a huge truck. they literally broke pulleys and shredded the rope they had it so built up.

im trying to find some images or videos of such disasters, but but right now i can not. now i could be wrong on my thinking, but i know i have seen systems fail that seamed like they would work, but didnt because one or more of the items it the system were not rated high enough. and if i remember correctly the only thing that the power or load rating does not matter on, is the unit doing the work ie the motor, that can be as small as it wants, you will just have to over come that with gearing(pulleys/snatch blocks) -also the more you gear down or every snatch block you use cuts your length of pull in half and the distance of the the pull. if you have just one snatch block, and you pull in 10' of line you will have only moved 5', say you have pulled in 15' of line, but you have two snatch blocks, well you only moved 5' still... cause you have 3 lines.

a note to the admins... this thread or group of post might be nice to be added to the general section board index under winching and recovery tips and techniques as well as here. just a thought.


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 Post subject: Re: How to use Snatch Blocks
PostPosted: Mon Dec 16, 2013 5:11 pm 
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Joined: Sat Sep 11, 2010 9:16 pm
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Rick
I think I'm picking up what you are throwing down.

The way I think of it is...

Lets say you are stuck and you do a straight line winch pull on your 8k winch. You are pretty stuck and your winch is still pulling but is really bogging down but not stalling. You (in theory) are pulling close to 8k.

Same scenario but you do a double line pull thru a snatch block. There is the same pulling force on the winch mount and the anchor.

New scenario. Lets say you are really stuck and you do a straight line winch pull on your 8k winch. You are really stuck and your winch is stalling out and will not pull. You do a double line pull and the winch is bogging down but pulling you out slowly. You (in theory) are pulling close to 16k. This pulling force in directly on the winch mounts, anchor, snatch block loop/ shackle/ tree saver. The winch line will only have half the force so you could actually (in theory) do a 16k pull with an 8k winch line.

There is good news. These situations where a rig is this stuck usually happen in the mythical stuff called MUD. Something I avoid.

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 Post subject: Re: How to use Snatch Blocks
PostPosted: Mon Dec 16, 2013 5:45 pm 
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Location: Denver, CO
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Rick wrote:
Example/Question: If my vehicle were to weigh 3 tons and I had 2 snatch blocks hooked similar to the last diagram, then wouldn't each length of line have half the weight of my vehicle applied to it (static/non-pulling)? Which means my winch would only have to pull just over 1/2 of the weight instead of the full 3 tons? (In a perfect/non-existent world)

Yep, you got it. Just remember that although the line that goes around the pulley has half the load, the yank strap that you have going from the pulley to the tree (and rig) has double the pull of the winch line.


Normally the reason for a pulley is to change the direction of the line pull or to multiply the pulling power. For example lets say you were given an ATV winch for your rear bumper and it was rated at 1.5k lbs. It probably wouldn't be enough to pull you out of some deep stuff unless you used a snatch block.

In the snow a common reason for needing more line pull is in those cases where you can't or won't dig out the area in front of your wheels. It's better to dig a ramp into the snow though. Less stress and potential to break stuff.

Sometimes the area in front of the wheels is so steep that the winch is essentially trying to pull the rig and all of the earth in front of it. A gentle slope up to get the rig out of the snow or mud = less line pull. A vertical wall or worse, undercut and you need a ridiculous amount of line pull. It's not hard to get in a situation where you need double or triple the vehicles weight in power to get a rig unstuck. That's why an 8k lbs winch is really on the low side for what we need in our rigs.


Here's an example of how to set up to get a stupid amount of pull. I've been meaning to draw this up for a long time. I usually get nodding heads in agreement along with that glazed look when I try and describe this setup. A picture is worth...

In the below setup you could literally pull out a semi tractor if you had the line strength and the hardware for it. I took some time on this on for ya Rick. Even color coded the tree trunks and labeled Snatch Block 1, 2, and 3. How's that for showing a little love? :cheesey grin:


Image

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 Post subject: Re: How to use Snatch Blocks
PostPosted: Mon Dec 16, 2013 5:57 pm 
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I always knew that H2s were heavy, 32k!

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 Post subject: Re: How to use Snatch Blocks
PostPosted: Mon Dec 16, 2013 9:09 pm 
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Joined: Sat Jul 02, 2011 1:07 pm
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Location: Vancouver Wa
ok in that scenario i could see that working... but what i was refering to was if you would be hooking your snatch blocks to the same tree, and to the same spot on the bumper or just back to the same vehicle, when you use a different anchor each time, yes the load will be spread out

drawing key;
(t) = tree
>O or O< = snatch block and anchor
[TRUCK] = truck or vehicle
c = shackle
--<-- or -->-- = direction of winch line being pulled
*** means nothing

(t)>O------>-------[TRUCK] truck/winch
****------<------O<[TRUCK]
****------->-------
(t)>O------<------c[TRUCK] line anchored back to the truck


that is what i was thinking of with the use of 3 snatch blocks, and that system would be placing all the forces on all of the components and not really spreading out the load.

sorry for my crude letter/symbol drawing


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