Snatch block recovery

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bigndn said:
See page 16.

http://www.warn.com/corporate/images/90/TechGuide_PN62885-A2.pdf
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XFACTOR.....see above.


x factor said:
block and tackle: Definition from Answers.com

One of the references.
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This reference is great if you have huge pulleys and unlimited amounts of rope. Typically, our winches are rated for 1.5X the vehicle weight at a minimum, so a double line pull would be effective in a high percentage of situations.

Scenario 1: Stuck vehicle has a winch. Attach snatch block to fixed point and run cable from winch thru snatch block, back to stuck vehicle. Double line pull.

Scenario 2: Recovery vehicle has a winch. Tie off recovery vehicle to fixed point. Attach snatch block to stuck vehicle, run cable from recovery vehicle thru snatch block on stuck vehicle, back to recovery vehicle. Double line pull.
 
x factor said:
If you are willing to try the experiment that I have done, you will
1) directly lift a weight with only a fish scale (mine was 30#s of lead)
2)attach a sigle pulley to ceiling, attach cable/string to the lead weight, run cable through pulley and attach to the fish scale, pulling down on the fish scale to lift the lead off the floor took 30# of force to lift the weight (NO DOUBLING EFFECT)
3)attach one end of the cable to the ceiling, run cable through the pulley that is now attached to the weight directly and the other end to the fish scale and lift, it now only took 16# of force to lift the weight (REDUCED THE FORCE REQUIRED BY HALF)

This was the start of the experiment and does explain the fixed verses moving block I spoke of.

As I stated before I have read conflicting reports on this subject and did the experiment in real world application with the affor mentioned results. This said I feel reading more contradictory statements without real world proof redundant.

Block and tackles have been used for a very long time and what I found from the research I did on those systems is what compelled me to do the testing. Say what you will but results are results.
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You simply are not understanding this. In your example you have not double line anything. All you have done is changed the direction of the pull when you anchored the pulley to the rafter. How may lines are going to your load in this example? only ONE. This is not a double line pull. This is not the same as running a winch line out to a pulley on an anchor and BACK TO THE RIG.

What you have done is akin to parking beside a stuck rig and running your line to a pulley out in front of both rigs to pull the stuck rig forward. This approach has it's uses, but it is still a single line pull.


You comment about "reading more contradictory statements without real world proof"... If you are referring to the replies of those of us trying to correct your misunderstanding, then this is uninformed and offensive... Some of us have been recovering rigs under adverse conditions using a wide variety of winches and rigging for probably longer than you have been driving. My statements are contradictory to yours because yours are wrong. Mine are based on real world experience... as well as simple understanding of common sense.... Not playing with a lead weight and a fish scale in the garage while not understanding basic physics like your comments are.


Mark...
 
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Cruiserdrew said:
....

To muddy it further for the original poster--We recovered a truck last year using the truck to the rear of the truck being recovered forward. The winch line went out, past the stuck truck, then doubled back through a pulley, pulling the truck in front. Because the ends were attached to different objects, the pulley block only changed the direction but not the force of the pull.
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A second block would have been useful on that recovery, the winch was way to low power and the truck it was mounted on was way to light. Both situations call for as much mechanical advantage as possible.
 
Somewhere around here I have a picture of three '40s making our way over a deteriorating snowmachne trail in late spring. The last one in the line has broken through the crust where some overflow is making it sodden. The surface did not permit the manuvering of the other rigs, and there were no anchor points besides the rigs.

The winch from the front end of the middle rig is running cable to a snatch block on the back of the front rig. The cable was then run under the middle rig and back to the front of the stuck rig at the back of the line. Worked well at getting the line where it needed to be to extract the rig. Of course the front rig had to anchor twice as much pull this way so it was being pulled back a bit. But the stuck rig was in wet slush so there was not a lot of resistance to the extraction. It just could not climb out with the zero traction provided by the slush.

I often use a snatch block and a double line pull just to ease the load on the winch, even when I have the power to make a single line pull. Ratpuke has a shot of my '40 from this summer extracting another '40 from a Tundra bog. The load was strong enough that the location of the OEM PTO winch, just barely above the frame centerline was enough to lift the rear end until the suspension was unloaded and virtually all the weight was on the front axle. I'll have to get her to post it here later.


Mark...
 
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x factor said:
If you are willing to try the experiment that I have done, you will
1) directly lift a weight with only a fish scale (mine was 30#s of lead)
2)attach a sigle pulley to ceiling, attach cable/string to the lead weight, run cable through pulley and attach to the fish scale, pulling down on the fish scale to lift the lead off the floor took 30# of force to lift the weight (NO DOUBLING EFFECT)
3)attach one end of the cable to the ceiling, run cable through the pulley that is now attached to the weight directly and the other end to the fish scale and lift, it now only took 16# of force to lift the weight (REDUCED THE FORCE REQUIRED BY HALF)
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The experiment (2) above is not the same as the double line pull shown below from the Warn document. Your experiment (2) is the same as "how to change the pulling direction". The difference is that in the double line pull, both the end of the winch line and the winch are attached to the same bumper. The winch has to pull in two feet of rope to move the bumper forward by one foot, and therefore a doubling effect is achieved. To simulate this in your experiment you would need to "attach" the fishscale end of the rope back to your lead weight. I think if you did this you would see that fish scale would read 15#, not 30#. This is because the weight is being support by two ropes, each holding one half the weight.

In other words "double line pull" means that two lines are pulling on the bumper...
winching.webp
 
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At this point, I'm gonna have to say that any more posts on this topic would be considered :deadhorse:

If Xfactor doesn't understand, it's not because it hasn't been explained. :meh:
 
bigndn said:
At this point, I'm gonna have to say that any more posts on this topic would be considered :deadhorse:

If Xfactor doesn't understand, it's not because it hasn't been explained. :meh:
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I think he understood all along, there was just a breakdown in communication.
 
craptabulous said:
go find a 250 tonne crane with a 8 part line , it has been working on them for 100's of years .
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Yup, been rigging crane for the Air Force for 20 years.

winch capacity X parts of line= load capacity
(not to exceed line tensil strength)
 
2mbb said:
The experiment (2) above is not the same as the double line pull shown below from the Warn document. Your experiment (2) is the same as "how to change the pulling direction". The difference is that in the double line pull, both the end of the winch line and the winch are attached to the same bumper. The winch has to pull in two feet of rope to move the bumper forward by one foot, and therefore a doubling effect is achieved. To simulate this in your experiment you would need to "attach" the fishscale end of the rope back to your lead weight. I think if you did this you would see that fish scale would read 15#, not 30#. This is because the weight is being support by two ropes, each holding one half the weight.

In other words "double line pull" means that two lines are pulling on the bumper...
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THANK YOU
From this explenation I can see how the it would in effect make the vehicle the moving block even though the block is not attached to the vehicle. This does give me a way to test this also. In #2 the fish scale would in effect be a tree or other ancoring point with applied force coming from the weight.

"DOUBLE LINE
Because pulling power decreases with the number of layers on the winch drum, you can use a snatch block to double line out more wire rope. This decreases the number of layers of wire rope on the drum, and increases pulling power." Quoted from Warns page.

This could be accomplished without the snatch block by taking the winch line to a further away ancoring point. This proved nothing as far as the block being required for the mechanical advantage that was provided by the winch layers. This is also a veriable gear reduction and not a constant. This is part of the contradictory info that made me want to test this.
 
Not quite right yet, if you want to see the 2x effect with a scale, in 2nd case. One end of scale would attach to wieght instead of one of the lines, then that line would go to other end of scale. By looking at it setup that way you would guess scale would read half the wieght. Therefore something pulling other end of line attached to wieght could pull twice as much since it only sees half the wieght.
Luv beating a dead horse. Now if someone has seen the movie Animal House, where is the chain saw. :-)
 
And now having gone through this and being proven wrong I found the easiest testing method to be a comealong with the hook on the end of the of the wire rope that can be attached or removed from the main body and one pulley for doubling.
 
I'll explain where I'm coming from....I've been rigging concerts, singage, and almost everything else that's come into work at the stampede grounds here in Calgary for the last 6 years. I'm also a rope access/rescue technician. I have been studying the effects and physics of pulley systems for the last 3 years.

In the warn example where the vehicles are about 90* from each other, the rigging on either the stuck vehicle is not as important as where the pully block (change of direction) is. If the angle is 90*, then the forces on the block/pulley are 1.41 times the force on the cable. This is due to the physics on the rigging. So...lets say that the winch is pulling at 6500lbs, then the force on your pulley block is almost 9200lbs. Please be cautious with these kind of recoveries as this is where equipment will fail!

If (for example) you're going to use your winch to pull something into a tree to hang it (I dunno....maybe a moose). The force on the pulley and branch in the tree will actually be double whatever the weight is what's hanging. So...the moose weighs 300lbs, you hook your winch up, pass the cable up through the pulley and back down to the moose and start winching. The winch pulls with 300lbs force (pulling down), and the moose weighs 300lbs (also pulling down), hence the doubling of weight and the pulley gets 600lbs of weight hanging on it.

The angle between where winch (or whatever is doing the pulling) and the load is critical. At 0* (like pulling a moose up into a tree) the load "on the pulley" is double whatever the weight is of what is being lifted. At 90* it's 1.41x, and obviously when the angle is 180* (or the line is not re-directed) the load is whatever is being pulled.

For a two-to-one advantage system, you're very right. The pulley has to be attached to the load, and is moving. In the above example where someone attached the pulley to a tree, and ran the winch cable to the tree and back to the vehicle, this would be a 2:1. The tree has to be treated like the moving object here...(I know, it's not moving). The reason I say it is like this, is due to the fact that your winch is not moving in relation to where the cable is connected back to the vehicle. Also, for every 1' of cable that is spooled back onto the winch, you only move 6". ie...2:1.

I do hope that I don't come across the wrong way, but I have seen people get the wrong impression when it comes to pulley systems. If you want something to get confused over, when pulley systems get into compound and...even better, complex pulley systems. I don't mean to offend, but I do hope that it clarifies a little....
 
300 pounds? Ya'll got some small moose over that way. ;)


Good point about the increased load on an anchor point used to change the direction of a pull. People tend to forget that. It is usually not going to be a major concern, but it is well worth staying aware of.

Mark...
 
yycranger4x4 said:
I'll explain where I'm coming from....I've been rigging concerts, singage, and almost everything else that's come into work at the stampede grounds here in Calgary for the last 6 years. I'm also a rope access/rescue technician. I have been studying the effects and physics of pulley systems for the last 3 years.

In the warn example where the vehicles are about 90* from each other, the rigging on either the stuck vehicle is not as important as where the pully block (change of direction) is. If the angle is 90*, then the forces on the block/pulley are 1.41 times the force on the cable. This is due to the physics on the rigging. So...lets say that the winch is pulling at 6500lbs, then the force on your pulley block is almost 9200lbs. Please be cautious with these kind of recoveries as this is where equipment will fail!

If (for example) you're going to use your winch to pull something into a tree to hang it (I dunno....maybe a moose). The force on the pulley and branch in the tree will actually be double whatever the weight is what's hanging. So...the moose weighs 300lbs, you hook your winch up, pass the cable up through the pulley and back down to the moose and start winching. The winch pulls with 300lbs force (pulling down), and the moose weighs 300lbs (also pulling down), hence the doubling of weight and the pulley gets 600lbs of weight hanging on it.

The angle between where winch (or whatever is doing the pulling) and the load is critical. At 0* (like pulling a moose up into a tree) the load "on the pulley" is double whatever the weight is of what is being lifted. At 90* it's 1.41x, and obviously when the angle is 180* (or the line is not re-directed) the load is whatever is being pulled.

For a two-to-one advantage system, you're very right. The pulley has to be attached to the load, and is moving. In the above example where someone attached the pulley to a tree, and ran the winch cable to the tree and back to the vehicle, this would be a 2:1. The tree has to be treated like the moving object here...(I know, it's not moving). The reason I say it is like this, is due to the fact that your winch is not moving in relation to where the cable is connected back to the vehicle. Also, for every 1' of cable that is spooled back onto the winch, you only move 6". ie...2:1.

I do hope that I don't come across the wrong way, but I have seen people get the wrong impression when it comes to pulley systems. If you want something to get confused over, when pulley systems get into compound and...even better, complex pulley systems. I don't mean to offend, but I do hope that it clarifies a little....
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Awesome. That's exactly what we've been saying. :cheers:

Welcome to Mud. :flipoff2: <<<OFFICIAL MUD WELCOME>>>
 
Mark W said:
300 pounds? Ya'll got some small moose over that way. ;)

Mark...
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Yeah, we kinda frown upon people shooting moose "calves". ;)
 
LOL...haven't shot any moose, but now that I think about it, that was a pretty light guess.

228 lb is = 1 KN
 
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