Something to ponder

[Antman]

I was just over on Pirate and a question came up and was discussed viciously.


If you put a pulley to a tree and hook the winch line back to your jeep, what is

the advantage and why. Some said none as a pulley doesn't double the force.

Others said yes it 2 timesed the force and was an advantage. Other said you

need two pulleys to get an advantage.

Any discussion? Also on a single pulley, what forces are on the pulley?


:sifone:

[Allen]

9000 lb winch single line 9000 lbs of pull
9000 lb winch double line pull (there and back using pully block) 18000 lbs pull!

9000@ 2:1 reduction!



why do you think big sailboats have 4 and five wheel pullies? so they can pull up the sailcloth at 10:1 reduction!

[04jeeptj]

9000 lb winch single line 9000 lbs of pull
9000 lb winch double line pull (there and back using pully block) 18000 lbs pull!

9000@ 2:1 reduction!


That was my thought, but wasnt sure how to explain it.

[Henthorn]

We've pulled HMMWV's out of sand with 5 people with a couple of pullies. These are up-armored ones at that.

Pullies do great things as far as recovery gear!

[nolimits4x4]

Ive heard some stuff on this and kind of understand it a little some people say it doubles some say it just helps the winch work to its fullest potential i think its a little of both first Ive heard the more line you have out the closer you get to your winches rated power this is just what Ive heard and makes sense when using one pulley. i know that using more than one pulley gives you a hole lot more just like the guy above me said you have enough snatch blocks and rope you can pull almost anything out thats just my 2 cents though im no engineer

[AZLugz]

Singly pully is 1:1
double pulley is 2:1

Unless the pulley is set up in a moveable pulley mode.

The advantage of a single pulley is that you can change direction.


In basic. If you hook a pulley to a tree and run you winch cable to it and back to another jeep to pull him out, you gain no advantage except to change direction.

If you have a winch on the stuck jeep and run it out thru a pulley attached to the tree and back to your jeep (same jeep as winch is on), you gain a 2:1 advantage as you made a "moveable Pulley" setup even tho the pulley is not what truley moves.

Its a crappy drawing but I am not the best in MS Paint!!! This should help see it tho


All that to say, you do get a 2:1 agavantage out of a snatch block BUT ONLY if it is hooked up right (which a lot of people dont)

http://www.virtualjeepclub.com/attachment.php?attachmentid=19291&stc=1&d=1205070860


http://www.howstuffworks.com/pulley.htm

http://en.wikipedia.org/wiki/Pulley

[Sedona Jeep School]

That is a perfect drawing that explains it perfectly!

There was a recent thread here relating to this. The pulley (aka snatch block) can double your own pulling power OR align your cable for a pull when you cannot otherwise get directly in line with the other vehicle.

[Billy 4 hp]

Pretty basic stuff, Freshman High School science I believe...

I'm surprised this was a heated debate over at Pirate.... Cabin fever must be setting in to our "snowbound" friends in the rest of the country....

[AZLugz]

A lot of people have the misconception that just because you put in a snatch block that it makes a double line pull when in fact, it is only true if the cable originates and terminates at the same point, otherwise it is a standard single line with a change in direction. Yes, pretty basic but amazing how many people miss it.

[Billy 4 hp]

A lot of people have the misconception that just because you put in a snatch block that it makes a double line pull when in fact, it is only true if the cable originates and terminates at the same point, otherwise it is a standard single line with a change in direction. Yes, pretty basic but amazing how many people miss it.

I have never had an opportunity to use an snatch block any other way, what scares most people when they do use a snatch block for the first time is how it cuts the line speed in half when attached in this manner. So they abort using the snatch block thinking something is getting damaged or their winch is screwed up...

[TRobertsRN]

OK here is why there is such a contraversy at priate.

All that have responded here are incorrect so far.

You can take the word of a retired pipe rigger and crane operator (me) or you can do some research about block and tackle or how stuff works dot com or where ever.

There is no mechanical advantage when one pulley is used.

The diagram is correct but the wrong conclusion is made.

If you need to move something 100 feet with no pulley or one pulley (no mater how attached) you have to pull the rope 100 feet.

Only when you properly use two pulleys do you get a 2:1 advantage such that you will have to pull 200 feet of line to move the object 100 feet.

In fact beause you have spooled out more of your line using only one pulley will reduce your pulling capasity compared to using no pulley.

[drroadie]

No, that only explanes why your line speed is cut in half. If you pull from two points on the same Jeep,( the winch its self, and the hook that you you have hooded to) you have doubled you pulling power. That only requires a single snatch block.

[mingoglia]

If you need to move something 100 feet with no pulley or one pulley (no mater how attached) you have to pull the rope 100 feet.


Yeah, but that's exactly why you get a 2:1 mechanical advantage with one pulley if it's attached back to your vehicle. You pull out 100' of cable but each leg is 50'. So now for the same 50' of vehicle movement you're moving 100' of winch line. That's reduction right there. Add a second snatch block and you're spooling out that much more cable... but your vehicle is still only traveling 50' when it's all said and not...

Look at it this way: Let's say your winch pulls in at 50' per minute. If you're doing a straight pull and you've spent out 50' of line it will take 1 minute to pull your vehicle the 50' (this of is for arguments sake as winch load dictates speed...but bare with me here). Let's now say you put a winch snatch block in there. You attach the snatch block to the tree, loop the line through it and attach it back to the vehicles recovery point. You now have 50' of line heading up to the snatch block, looping back around, then another 50' leg heading back to the vehicle. For a total of 100'. If you winch is pulling at 50' per minute (once again assuming your winch will sustain 50' per minute), it's now going to take 2 minutes to pull the very same distance. That's reduction. That's mechanical advantage. If it takes you twice as long to do work when the amount of power supplied stays the same that's mechanical advantage. :) Regardless of how you try to envision this, the fact remains the same that you're taking twice as long to do the same amount of work.... and since the winch is moving at exactly the same RPM (for this example), it's just like moving up to a larger sprocket on the back of a bicycle. :)

Mike

Mike

[mingoglia]

No, that only explanes why your line speed is cut in half. If you pull from two points on the same Jeep,( the winch its self, and the hook that you you have hooded to) you have doubled you pulling power. That only requires a single snatch block.

Yep, you posted that while I was typing. It's all about the line speed and the fact that you've cut it in half because you now have two legs moving at the same time... I think I need to host another recovery workshop. :) Anyone notice on Extreme 4x4 what they did wrong when using a high lift as a make shift winch? :angel:

[Billy 4 hp]

Not going to get into a long debate on how it works and why...

But this explains it pretty easily....

http://www.technologystudent.com/gears1/pulley8.htm

The moving pulley "snatch block" doubles the effort...

Class dismissed...

[AZLugz]

OK here is why there is such a contraversy at priate.

All that have responded here are incorrect so far.

You can take the word of a retired pipe rigger and crane operator (me) or you can do some research about block and tackle or how stuff works dot com or where ever.

There is no mechanical advantage when one pulley is used.

The diagram is correct but the wrong conclusion is made.

If you need to move something 100 feet with no pulley or one pulley (no mater how attached) you have to pull the rope 100 feet.

Only when you properly use two pulleys do you get a 2:1 advantage such that you will have to pull 200 feet of line to move the object 100 feet.

In fact beause you have spooled out more of your line using only one pulley will reduce your pulling capasity compared to using no pulley.


I can only assume you did not look at the websites posted in support


http://www.howstuffworks.com/pulley.htm

http://en.wikipedia.org/wiki/Pulley



See diagram 2 in the second link.


Diagram 2 - A simple pulley system - a single movable pulley lifting weight W. The tension in each line is W/2, yielding an advantage of 2.

[mingoglia]

I guess I'll post one more time as I've extensively experimented with different recovery techniques as I have a strange fascination with getting "unstuck". For any of us that have used a snatch block (and I use mine more often then not as it truly makes the equipment last longer on shorter pulls where your winch line is piled on top of each other) we've all noticed that you get "unstuck" at half the speed when using a snatch block. Half the speed = mechanical advantage because winch speed is more or less a constant. :)

[Billy 4 hp]

I guess I'll post one more time as I've extensively experimented with different recovery techniques as I have a strange fascination with getting "unstuck". For any of us that have used a snatch block (and I use mine more often then not as it truly makes the equipment last longer on shorter pulls where your winch line is piled on top of each other) we've all noticed that you get "unstuck" at half the speed when using a snatch block. Half the speed = mechanical advantage because winch speed is more or less a constant. :)

Now don't go throwing real world experience and logic at it....

:banghead:

[TRobertsRN]

I can only assume you did not look at the websites posted in support


http://www.howstuffworks.com/pulley.htm

http://en.wikipedia.org/wiki/Pulley



See diagram 2 in the second link.


Diagram 2 - A simple pulley system - a single movable pulley lifting weight W. The tension in each line is W/2, yielding an advantage of 2.


Movable pully only applies when the moving pully is on the weight being moved as in the diagram you site.

When you are using the winch on your jeep to tie to a tree with no pully on the tree or with a pulley on the tree there is no multiplication of force.

If the jeep stays stationary and you are pulling the tree toward the jeep then and only then is there a mechanical advantage. Or if the winch was on the tree and there was a pulley on the jeep there would be a multiplication of force.

The simple way to determine if force is multipled is to compare how far the weight is moved to how much line must be pulled. If they are the same there is no advantage.

I promise these are the facts of it.

[TRobertsRN]

I guess I'll post one more time as I've extensively experimented with different recovery techniques as I have a strange fascination with getting "unstuck". For any of us that have used a snatch block (and I use mine more often then not as it truly makes the equipment last longer on shorter pulls where your winch line is piled on top of each other) we've all noticed that you get "unstuck" at half the speed when using a snatch block. Half the speed = mechanical advantage because winch speed is more or less a constant. :)

Winch speed is generally only a constant with a hydrolic winch. What appears to be half speed to you may be due to the increased resistance of having a pulley and that by playing out more winch line you have changed the final ratio of your winch, much like using a different size tire with the same gear set up.

[mingoglia]

Movable pully only applies when the moving pully is on the weight being moved as in the diagram you site.

When you are using the winch on your jeep to tie to a tree with no pully on the tree or with a pulley on the tree there is no multiplication of force.

If the jeep stays stationary and you are pulling the tree toward the jeep then and only then is there a mechanical advantage. Or if the winch was on the tree and there was a pulley on the jeep there would be a multiplication of force.

The simple way to determine if force is multipled is to compare how far the weight is moved to how much line must be pulled. If they are the same there is no advantage.

I promise these are the facts of it.








See diagram 2 in the second link.


Diagram 2 - A simple pulley system - a single movable pulley lifting weight W. The tension in each line is W/2, yielding an advantage of 2.[/QUOTE]

How do you explain that my Jeep moves half as fast when using a snatch block? If it's moving half as fast and the winch is moving the same speed where is all the speed going? If this goes on much longer I may have to go outside with the video camera and post some videos. :)

[AZLugz]

Movable pully only applies when the moving pully is on the weight being moved as in the diagram you site.

When you are using the winch on your jeep to tie to a tree with no pully on the tree or with a pulley on the tree there is no multiplication of force.

If the jeep stays stationary and you are pulling the tree toward the jeep then and only then is there a mechanical advantage. Or if the winch was on the tree and there was a pulley on the jeep there would be a multiplication of force.

The simple way to determine if force is multipled is to compare how far the weight is moved to how much line must be pulled. If they are the same there is no advantage.

I promise these are the facts of it.


interesting, not sure how it can be different if the tree is moving and not the Jeep when the hook up, forces and directions are all the same but.......

[mingoglia]

Winch speed is generally only a constant with a hydrolic winch. What appears to be half speed to you may be due to the increased resistance of having a pulley and that by playing out more winch line you have changed the final ratio of your winch, much like using a different size tire with the same gear set up.

If I changed the final ratio of my winch then that means mechanical advantage, sir. :smug:

...and I of course was being very general when I was referring to a constant winch speed. That was to illustrate the point. My 9.5ti will run at 65'/min without a load and probably single digit ft/min under full load.

[AZLugz]

dup

[Billy 4 hp]

If I changed the final ratio of my winch then that means mechanical advantage, sir. :smug:

...and I of course was being very general when I was referring to a constant winch speed. That was to illustrate the point. My 9.5ti will run at 65'/min without a load and probably single digit ft/min under full load.

And line speed varies depending on what "wrap" your on as it's changing the pulley diameter (drum spool)...

Anyways internet battle as you want....

I know what works for me..... :aagh:

[Antman]

:lurk5::whistling:

Ok, now that I got you thinking, if your pulling a 4,000 lb jeep with a pulley

attached to a tree, and back to the jeep. How much force is applied to the

pulley? :sifone:


(Much better than drama school)

[Billy 4 hp]

Movable pully only applies when the moving pully is on the weight being moved as in the diagram you site.

When you are using the winch on your jeep to tie to a tree with no pully on the tree or with a pulley on the tree there is no multiplication of force.

If the jeep stays stationary and you are pulling the tree toward the jeep then and only then is there a mechanical advantage. Or if the winch was on the tree and there was a pulley on the jeep there would be a multiplication of force.

The simple way to determine if force is multipled is to compare how far the weight is moved to how much line must be pulled. If they are the same there is no advantage.

I promise these are the facts of it.



And a average snatch block used in this manner (vehicle is it's own attachment point for the winch cable) cut's the line speed in half, so if I am feeding in 1 foot of cable, my Jeep moves 6 inches.... Therefore I just doubled (mechanically) my winching strength...

Just so well all know what a snatch block is...

http://www.warn.com/truck/accessories/snatch_blocks_.shtml

Another tidbit...

http://www.behold-the-rage.com/images/VEX-winchdynamic-1.jpg

Tom's point is (I believe) that the mechanical advantage occurs only at the snatch block end (moving pulley), but if I have 12,000lb's of load on my front bumper twice (at the winch and at the cable attatchment point) don't I actually have 24,000lb of load (pull)??

[TRobertsRN]

interesting, not sure how it can be different if the tree is moving and not the Jeep when the hook up, forces and directions are all the same but.......

I guess my schooling and work didn't teach me anything??????


What matters is whether the pulley is moving. If the pulley is not moving you don't have a moving pulley and therefore no mechanical advantage. When the pulley moves the amount of work (movement) left to do is not just shortend by how much line has been pulled but also by the pulley movement shortening the distance.

Here is another way to look at it that may or may not help. Imagine a steel beam above the ground. You are standing on the beam. There is a 100# weight on the ground you wish to lift. If you attach a rope to it and pull, you will need 100#'s of force to lift it. If you put a pulley on the weight and run a rope back to you it will only take 50# to lift it.

If you stand on the floor and there is a pulley on the beam it will still take you 100# of force to lift it.

[Antman]

Here's the link tp pirate for those that want to get really confused. It starts about
Ian from Extreme 4X4 doing something on the show.

http://www.pirate4x4.com/forum/showthread.php?t=664814

[TRobertsRN]

If I changed the final ratio of my winch then that means mechanical advantage, sir. :smug:

...and I of course was being very general when I was referring to a constant winch speed. That was to illustrate the point. My 9.5ti will run at 65'/min without a load and probably single digit ft/min under full load.

Unfortunately you have weakend your mechanical advantage when you spool out more cable. Winched are rated at pull when the spool is full. When spooled out they are less powerfull.

[mingoglia]

:lurk5::whistling:

Ok, now that I got you thinking, if your pulling a 4,000 lb jeep with a pulley

attached to a tree, and back to the jeep. How much force is applied to the

pulley? :sifone:


(Much better than drama school)

It depends. A vehicle stuck on it's frame (assuming the tires are off the ground) will require approximately 3 times the weight of the vehicle to move it off the frame. so in that case the d-shackle that's attached to the pulley that's attached to the tree strap is going to see up to 12,000lbs of force (this folks is why a 9,500lb winch can stall with a Jeep even on the first wrap of your winch drum). On the other hand, a 4,000lb Jeep will require approximately 10% of the weight of the vehicle, or 400lbs to move it on a level paved road. This is why a single person can push a vehicle that ran out of gas to the gas station.

In the case of the 12,000lbs of fource on the d-shackle, that would translate to 6,000lbs on each of the 2 legs coming from snatch block.

Although I haven't opened it yet, these approximate figures are in my TM 5-725 Rigging Army Tech Manual that I have in front of me. :) I did a heck of a lot of research on recovery before I taught that class. :beta1:

Mike

[mingoglia]

Unfortunately you have weakend your mechanical advantage when you spool out more cable. Winched are rated at pull when the spool is full. When spooled out they are less powerfull.

It's just the opposite sir.... they're rated at the last layer of the drum and are less effective when the line is piled with multiple wraps.

[Billy 4 hp]

:lurk5::whistling:

Ok, now that I got you thinking, if your pulling a 4,000 lb jeep with a pulley

attached to a tree, and back to the jeep. How much force is applied to the

pulley? :sifone:


(Much better than drama school)

Depends on how much load is keeping the Jeep from moving or what your trying to move at the end snatch block end, the weight of the vehicle is not the only factor...

[TRobertsRN]

[QUOTE=Billy 4 hp;308451]And a average snatch block used in this manner (vehicle is it's own attachment point for the winch cable) cut's the line speed in half, so if I am feeding in 1 foot of cable, my Jeep moves 6 inches.... Therefore I just doubled (mechanically) my winching strength...



While this may appear to be true when doing it it is not. With a simple single none moving pulley for each foot you pull the rope the weight will mobe one foot.

[TRobertsRN]

It's just the opposite sir.... they're rated at the last layer of the drum and are less effective when the line is piled with multiple wraps.

I admit you may be correct on that, I was going on memory.

I still stand by the fact that a simple non moving singe pulley offers no mechanical advantage.

[TRobertsRN]

interesting, not sure how it can be different if the tree is moving and not the Jeep when the hook up, forces and directions are all the same but.......

It makes no difference whether it is the tree or jeep moving in general. Specifically what is important is whether the pulley is moving.

Pulley moves equals mechanical advantage.

Pulley not moving equals no mechanical advantage.

[Antman]

Depends on how much load is keeping the Jeep from moving or what your trying to move at the end snatch block end, the weight of the vehicle is not the only factor...

Assume the vehicle weight is the only factor.

[Antman]

It's just the opposite sir.... they're rated at the last layer of the drum and are less effective when the line is piled with multiple wraps.

Mike is right!

You guys are too fast! On the keyboards that is.

[AZLugz]

What matters is whether the pulley is moving. If the pulley is not moving you don't have a moving pulley and therefore no mechanical advantage. When the pullye moves the amount of work (movement) left to do is not just shortend by how much line has been pulled but also by the pulley movement shortening the distance.

Here is another way to look at it that may or may not help. Imagine a steel beam above the ground. You are standing on the beam. There is a 100# weight on the ground you wish to lift. If you attach a rope to it and pull, you will need 100#'s of force to lift it. If you put a pulley on the weight and run a rope back to you it will only take 50# to lift it.

If you stand on the floor and there is a pulley on the beam it will still take you 100# of force to lift it.



Well, I have also worked with weights and measuring equipment for over 20 years and I am sorry, but you are off the mark. As more proof of my point, I went to Warn who most seem to think is the leader in winches and accessories and they validate my point.

See page 17 of the guide:
http://warn.com/corporate/images/90/UserManualSRC.US.readers.pdf

http://www.virtualjeepclub.com/attachment.php?attachmentid=19306&stc=1&d=1205082617



Warn also states in their ATV winch manual:

MOVING PARTS ENTANGLEMENT
HAZARD
Failure to observe these instructions could
lead to minor or moderate injury.
General Safety:
• Always know your winch. Take time to fully
read the Installation Guide and the Basic
Guide to Winching Techniques in order to
understand your winch and its operation.
• Never operate this winch if you are under 16
years of age.
• Never operate this winch when under the
influence of drugs, alcohol or medication.
• Never exceed winch or rope capacity listed
on product data sheet. Double line using a
snatch block to reduce winch load.

[mingoglia]

Assume the vehicle weight is the only factor.

I think I might see where you're going with this (btw, did you see my reply about how much force is required to move an object). If you're saying that regardless of how many pulleys are in place you're still only causing 4k of force? If so, power has to do with how much work can be done over a period of time. That's where mechanical advantage comes in. If that's not the point you were trying to make then disregard.

[Billy 4 hp]

And a average snatch block used in this manner (vehicle is it's own attachment point for the winch cable) cut's the line speed in half, so if I am feeding in 1 foot of cable, my Jeep moves 6 inches.... Therefore I just doubled (mechanically) my winching strength...



While this may appear to be true when doing it it is not. With a simple single none moving pulley for each foot you pull the rope the weight will mobe one foot.

I think we're confused on what another is saying (and it also depends on the diameter of the snatch block pulley by the way)... I am talking about a moving pulley to move an object... My jeep is on the snatch block end, not the "dead manned" vehicle...

[Antman]

I think I might see where you're going with this (btw, did you see my reply about how much force is required to move an object). If you're saying that regardless of how many pulleys are in place you're still only causing 4k of force? If so, power has to do with how much work can be done over a period of time. That's where mechanical advantage comes in. If that's not the point you were trying to make then disregard.

I do rigging in the tower industry, or used to. i am now an instructor. If you run
a line to a single pulley and back to your vehicle that weighs 4,000 lbs, I saw
somewhere on Pirate in a diagram someone got somewhere, (need to go
retrieve it), there is twice the force applied to the single pulley, thus 8,000 lbs.

I'll go look for it.

[mingoglia]

I do rigging in the tower industry, or used to. i am now an instructor. If you run
a line to a single pulley and back to your vehicle that weighs 4,000 lbs, I saw
somewhere on Pirate in a diagram someone got somewhere, (need to go
retrieve it), there is twice the force applied to the single pulley, thus 8,000 lbs.

I'll go look for it.

Oh, okay. Yeah, didn't know where you were originally going. That thing on Pirate would be wrong then. The only time though that that could be true is if for example the 4k lb vehicle being pulled was stuck up to the hubs in mud...then that extra drag could translate to 8k lbs on the pulley. It is also true though that if you had 4k on the pulley that each leg of the winch line is then carrying 2k lbs.

[AZLugz]

Unfortunately you have weakend your mechanical advantage when you spool out more cable. Winched are rated at pull when the spool is full. When spooled out they are less powerfull.

You have that backwards

[Antman]

Check this out:

http://www.thecrosbygroup.com/productcatalog/Calculators/Calculators/snatchblockrigcalc.htm

Single line, like from your jeep to a pulley and then to another jeep.

Turn number 2 upside down and its: from your jeep to a pulley and back to
your jeep.

Also look at number one and see how much force is applied to the block or pulley.

:):):)

[TRobertsRN]

Check this out:

http://www.thecrosbygroup.com/productcatalog/Calculators/Calculators/snatchblockrigcalc.htm

Single line, like from your jeep to a pulley and then to another jeep.

Turn number 2 upside down and its: from your jeep to a pulley and back to
your jeep.

Also look at number one and see how much force is applied to the block or pulley.

:):):)

Only #1 applies to a Jeep with winch to a stationary pulley and it clearly shows it will take 100#'s of force to move 100#'s of weight.

#2 does not apply even upside down as the pulley moves. With a single pulley attached to a non moving object as in a Jeep with winch to a pulley on a tree the pulley is fixed.

Only #1 applies to what we are talking about.

[ollllo4x4ollllo]

:aagh:hmm if it works and gets ya unstuck isn't that all that counts?? we're not trying to build skyscrapers here just pulling jeeps off rocks:drummer:

[Antman]

:aagh:hmm if it works and gets ya unstuck isn't that all that counts?? we're not trying to build skyscrapers here just pulling jeeps off rocks:drummer:

Well no. We're having a discussion on something that we use when we go wheeling, and i think it's a healthy discussion so far. If you want to read
a mud slinging side of this go over on Pirate.

I have already learned a few things here and even if we don't all agree, I
bet the next time we winch, we will be thinking about it and maybe do some
experiments on it to see how the effects work.:)

[Antman]

Only #1 applies to a Jeep with winch to a stationary pulley and it clearly shows it will take 100#'s of force to move 100#'s of weight.

#2 does not apply even upside down as the pulley moves. With a single pulley attached to a non moving object as in a Jeep with winch to a pulley on a tree the pulley is fixed.

Only #1 applies to what we are talking about.

Tom, all I can say is in the real world I have been to a point where my winch

won't pull any more from snow build up under the vehicle, or lodged in a ditch,

and know that doubling my line back through a pulley to the frame of my truck

gets the job done.

[TRobertsRN]

Well, I have also worked with weights and measuring equipment for over 20 years and I am sorry, but you are off the mark. As more proof of my point, I went to Warn who most seem to think is the leader in winches and accessories and they validate my point.

See page 17 of the guide:
http://warn.com/corporate/images/90/UserManualSRC.US.readers.pdf

http://www.virtualjeepclub.com/attachment.php?attachmentid=19306&stc=1&d=1205082617



Warn also states in their ATV winch manual:

MOVING PARTS ENTANGLEMENT
HAZARD
Failure to observe these instructions could
lead to minor or moderate injury.
General Safety:
• Always know your winch. Take time to fully
read the Installation Guide and the Basic
Guide to Winching Techniques in order to
understand your winch and its operation.
• Never operate this winch if you are under 16
years of age.
• Never operate this winch when under the
influence of drugs, alcohol or medication.
• Never exceed winch or rope capacity listed
on product data sheet. Double line using a
snatch block to reduce winch load.

There is mechanical advantage in the 2 line if the weight being moved is not the illustrated jeep. 2 line is an advantage if the jeep pictured is stationary and is moving another jeep or dragging something.

In a self rescue situation such as attaching your stuck jeep to a tree with a snatch block there is no machanical advantage over just a straight line attached to the tree.

[Antman]

I have even rigged my line up hill (90*), around a big rock and back to my rear

hitch, then while winching, spun the tires on the truck to go sideways back on

the trail. I was over the side on a steep drop off and the truck was stopped

from going farther down the slope by a rock. I winched myself back on the

trail.:eek:

[TRobertsRN]

I think we're confused on what another is saying (and it also depends on the diameter of the snatch block pulley by the way)... I am talking about a moving pulley to move an object... My jeep is on the snatch block end, not the "dead manned" vehicle...


I do see what you are saying here. If the jeep being rescued has the snatch block on it and the other jeep that is stationary has the winch then there is a mechanical advantage.

If someone is doing a self rescue with the winch on their jeep to a stationary object there is no advantage to a snatch block.

In this case of a self rescue you would need 2 snatch blocks one on the jeep and one on the tree to have a mechanical advantage. This would require runing the cable through the tree snatch block, then through the jeep snatch block, and then back to the tree.

[TRobertsRN]

Only #1 applies to a Jeep with winch to a stationary pulley and it clearly shows it will take 100#'s of force to move 100#'s of weight.

#2 does not apply even upside down as the pulley moves. With a single pulley attached to a non moving object as in a Jeep with winch to a pulley on a tree the pulley is fixed.

Only #1 applies to what we are talking about.

Correction, #2 could apply to what we are talking about but only if there were 2 jeeps and the one being rescued had the pulley on it and the other had the winch.

[AZLugz]

There is mechanical advantage in the 2 line if the weight being moved is not the illustrated jeep. 2 line is an advantage if the jeep pictured is stationary and is moving another jeep or dragging something.

In a self rescue situation such as attaching your stuck jeep to a tree with a snatch block there is no machanical advantage over just a straight line attached to the tree.



Wow, I sure wish Warn knew what they were talking about!!!! :laugh2:


Sorry, anyway.....one is stationary and one is moving, everything is hooked up the same and the cable goes thru the same......how can it be any different????

As long as the wing and the tie point are on the same vehicle and the pulley is on the other vehicle (or tree), the load vectors and forces are identical. you can not change the basic principal of the formula.

I will listen tho if you can mathmatically prove the difference

[TRobertsRN]

http://www.swe.org/iac/lp/pulley_03.html

This may be helpful.

It does a better job than I on explaining the difference between an moving and non moving pulley in a single pulley system.

In a self rescue it is a single non moving pulley and there is no mechanical advantage.

In being rescued by someone else with a winch and you have a snatch block on your jeep it is a moving pulley and there is a 2:1 mechanical advantage.

So a single snacth block can be a mechanical advantage just not in the way described in the beginning of this post which is a self rescue.

Tom

[AZLugz]

Correction, #2 could apply to what we are talking about but only if there were 2 jeeps and the one being rescued had the pulley on it and the other had the winch.


ok, why does it matter which one has the winch and which has the pulley?

[TRobertsRN]

ok, does it matter which one has the winch and which has the pulley?

Yes. There will only be a mechanical advantage it the jeep with the pulley is the one that is stuck.

Example #1

Jeep A is stuck. He has a winch. He hooks himself to Jeep B who has a D ring and a snatch block. It makes no difference if he just hooks to the D ring of jeep B or loops back to himself using the snatch block on jeep B he will only have the power of his winch to pull himself out.

Example #2

Jeep B is stuck. He has a D ring and an attached snatch block. Jeep A has a winch. If they use the snatch block on Jeep B double the pulling force of the winch will be available.

As before the snatch block must move in order to have a mechanical advantage, so yes it matters which jeep has the pulley on it

[mingoglia]

Tom,
Myself and others have argued our points. I can't rephrase anything any better than I already have so I'll just sit back and see if anyone can do a better job than me. Regardless of the forumulas of what's moving where all I can say is, well, nevermind. I'm tired. ;)

Mike

[AZLugz]

Yes. There will only be a mechanical advantage it the jeep with the pulley is the one that is stuck.

Example #1

Jeep A is stuck. He has a winch. He hooks himself to Jeep B who has a D ring and a snatch block. It makes no difference if he just hooks to the D ring of jeep B or loops back to himself using the snatch block on jeep B he will only have the power of his winch to pull himself out.

Example #2

Jeep B is stuck. He has a D ring and an attached snatch block. Jeep A has a winch. If they use the snatch block on Jeep B double the pulling force of the winch will be available.

As before the snatch block must move in order to have a mechanical advantage, so yes it matters which jeep has the pulley on it

You still have not supported that argument. As I said before, the force vectors are identical as are the loads and the moving cable. Whether the winch moves, or the pulley moves in irrelevant. Again I reference back to the documents I have already provided including the Manual from Warn that supports my point.

[TRobertsRN]

Wow, I sure wish Warn knew what they were talking about!!!! :laugh2:


Sorry, anyway.....one is stationary and one is moving, everything is hooked up the same and the cable goes thru the same......how can it be any different????

As long as the wing and the tie point are on the same vehicle and the pulley is on the other vehicle (or tree), the load vectors and forces are identical. you can not change the basic principal of the formula.

I will listen tho if you can mathmatically prove the difference

It is not a matter of mathmatical proof. One has a moving pulley and one does not. In our example of a jeep with a winch and a snatch block on a tree the pulley does not move. If you could attach the winch to the tree and the snatch block to the jeep then the pulley would move.

[TRobertsRN]

Tom, all I can say is in the real world I have been to a point where my winch

won't pull any more from snow build up under the vehicle, or lodged in a ditch,

and know that doubling my line back through a pulley to the frame of my truck

gets the job done.

I believe you 100%

What is happening there is that when you spool out more cable you have a stronger winch.

I incorrectly stated this the other way around in a previous post.

Your winch is much stronger with a couple of wraps on the spool than with most of the cable on the spool.

[TRobertsRN]

You still have not supported that argument. As I said before, the force vectors are identical as are the loads and the moving cable. Whether the winch moves, or the pulley moves in irrelevant. Again I reference back to the documents I have already provided including the Manual from Warn that supports my point.


The warn manual does not state whether you are moving the jeep with the winch or the object the jeep is attached to.

Here again is the illustration of the difference that a movable or non movable pulley makes. Figure #1 and #2 specifically.

http://www.swe.org/iac/lp/pulley_03.html

Using a snatch block in the #1 situation can get you more power with a winch but it is not due to mechanical advantage it is due to not having as much cable on your winch and therefore you have changed the final ratio of the winch.

[AZLugz]

It is not a matter of mathmatical proof. One has a moving pulley and one does not. In our example of a jeep with a winch and a snatch block on a tree the pulley does not move. If you could attach the winch to the tree and the snatch block to the jeep then the pulley would move.


OK, then again I ask if you are saying that the diagram and information provided by Warn is incorrect, in the picture it is a pole tree or similar that the block is attached to:

http://www.virtualjeepclub.com/attachment.php?attachmentid=19306&stc=1&d=1205082617

Please do not take this as me being ugly or upset in any way, I am enjoying the debate and I hope it does not come off wrong.

[Antman]

I believe you 100%

What is happening there is that when you spool out more cable you have a stronger winch.

I incorrectly stated this the other way around in a previous post.

Your winch is much stronger with a couple of wraps on the spool than with most of the cable on the spool.

Quote from WARN:

"Because pulling power decreases
with the number of layers of wire rope
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.
Start by feeding out enough wire
rope to free the winch hook. Attach
the hook to your vehicle’s frame/tow
hook and run the wire rope through
a snatch block.

Was a Picture here


Disengage the clutch and, using
the snatch block, pull out enough wire
to reach your anchor point. Do not
attach hook to mounting kit.
Secure to the anchor point with a tree
trunk protector or choker chain. Attach
the clevis/shackle. Attach the shackle to
the two ends of the strap/chain, being
careful not to over tighten (tighten and
back-off 1/2 turn)."

Obviously there is quite a bit of difference with a empty spool over a

full spool on our winches.:confused:

[David C]

:jester: He he, uhh... he he he... you guys just said 'snatch block'! ...he he...he he he...:aagh:

[Antman]

:jester: He he, uhh... he he he... you guys just said 'snatch block'! ...he he...he he he...:aagh:

David, go to your room!:)

I can't resist. Naw, I deleted it.:sifone:

[TRobertsRN]

OK, then again I ask if you are saying that the diagram and information provided by Warn is incorrect, in the picture it is a pole tree or similar that the block is attached to:

http://www.virtualjeepclub.com/attachment.php?attachmentid=19306&stc=1&d=1205082617

Please do not take this as me being ugly or upset in any way, I am enjoying the debate and I hope it does not come off wrong.


No ugliness taken or intended.

It is refreshing to be discussing something Jeep related.

As to whether it matters if the pulley is stationary or moving I refer back to the excellent site you referedced.

http://www.thecrosbygroup.com/productcatalog/Calculators/Calculators/snatchblockrigcalc.htm

Entering 100# as the weight shows the difference between #1 which is like our tree example and #2. The difference is #1 is a fixed pulley, and #2 the pulley moves with the load.

I checked out some of the discussion on Priate and while informative at times just very rude. I may go there from time to time for information but I don't think I would care to ask or answer a question there.

[AZLugz]

More to support my 2:1

http://www.ec4wda.org/4x4score3.asp

http://www.geocities.com/~landroverpty/winching.htm

http://www.leisurewheels.com/Modules_FE/layout1/displayFullNews.asp?newsID=17

http://www.ocalajeepclub.com/Jeep%20Tech/off-road_dictionary.htm

[AZLugz]

One other point.

If the snatch block does not give the 2:1, what good does it do in this example....nothing and if that is true, what is the sense of doing it!!

[TRobertsRN]

One other point.

If the snatch block does not give the 2:1, what good does it do in this example....nothing and if that is true, what is the sense of doing it!!

It still increases the pulling power of the winch by reducing the amount of cable on the winch.

[TRobertsRN]

More to support my 2:1

http://www.ec4wda.org/4x4score3.asp

http://www.geocities.com/~landroverpty/winching.htm

http://www.leisurewheels.com/Modules_FE/layout1/displayFullNews.asp?newsID=17

http://www.ocalajeepclub.com/Jeep%20Tech/off-road_dictionary.htm

Sorry,

They are all incorrect.

[TRobertsRN]

OK, some information has come to my attention that if true may change my opinion about this.

Forget exacty where I found this today but it follows

The drum of the winch is the 2nd (mobile) pulley and is why the load is cut in half.

EDIT: And just to clarify why the snatch block on the tree does not halve the load, for every foot of movement towards the tree there is a foot of cable through the pulley, and a foot of cable back towards the vehicle. The winch itself, namely the drum, is effectively a 2nd pulley and why a foot of cable wound back onto the WINCH, not through the snatch block, results in 6 inches of movement.

So the above got me thinking and I found this stuff below at http://www.dodgepowerwagon.com/glovebox/snatch.html


And in #2 above, if the bitter end of the line is *not hooked to the winched vehicle* but is hooked to a tree or rock next to it, for each pound of winch force applied, the block will be under *twice* the load, while the line strain will be equal to the line pull. So if you apply a full 12,000 pounds of pull, you are putting 24,000 pounds of stress on the block/anchor. If, however, the bitter end *is* attached to the winched vehicle, the block becomes a "traveling block", even though it is attached to a solid object, because the vehicle itself is actually doing the "traveling", and the load on the *line* is halved, since you are using two lines to "support" the load. In this case, the mechanical advantage is 2/1, so you get 2 pounds pull for each pound of winch effort. Now, since you have two lines splitting the load, let's say it's 10,000 lbs. (you're *really* stuck), the line load is halved to 5000 lbs per line, but the *block* load is still 10,000 lbs because of the parallel line angle factor of 2. As you can see, while the load on the winch is cut in half, as is the line speed for winding, the load on the block is *not*, and is equal to the total line load.

If this is true, and my mind begins to think it may be then using a snatch block on a tree as in our original example would indeed have a 2:1 mechanical advantage plus the greater pulling power of not having as much cable on the drum.

It appears it is possible that in this situation there are 2 pulleys, one of which is the winch itself.

I am not convinced but I am now more open than when I absulutely viewed this as a one pulley system.

[TRobertsRN]

Singly pully is 1:1
double pulley is 2:1

Unless the pulley is set up in a moveable pulley mode.

The advantage of a single pulley is that you can change direction.


In basic. If you hook a pulley to a tree and run you winch cable to it and back to another jeep to pull him out, you gain no advantage except to change direction.

If you have a winch on the stuck jeep and run it out thru a pulley attached to the tree and back to your jeep (same jeep as winch is on), you gain a 2:1 advantage as you made a "moveable Pulley" setup even tho the pulley is not what truley moves.

Its a crappy drawing but I am not the best in MS Paint!!! This should help see it tho


All that to say, you do get a 2:1 agavantage out of a snatch block BUT ONLY if it is hooked up right (which a lot of people dont)

http://www.virtualjeepclub.com/attachment.php?attachmentid=19291&stc=1&d=1205070860


http://www.howstuffworks.com/pulley.htm

http://en.wikipedia.org/wiki/Pulley


I am beginning to believe that what you have with the jeep with winch/tree with snatch block/back to same jeep set up if diagramed is illustrated by example #3 in the wikipedia.org above. This would only be if the winch was considered a pulley in this system by the laws of physics.

But if this is assumed it would mean that it provides not a 2:1 mechanical advantage but rather a 3:1 advantage by that wikipedia site.

[Antman]

Thanks guys for all the input, and for keeping it a discussion and not a Pissin
match.:):)

[TRobertsRN]

:lurk5::whistling:

Ok, now that I got you thinking, if your pulling a 4,000 lb jeep with a pulley

attached to a tree, and back to the jeep. How much force is applied to the

pulley? :sifone:


(Much better than drama school)

8000 pounds, which is why your snatch block should be rated for over twice the power of your winch, as I learned today.

[Antman]

8000 pounds, which is why your snatch block should be rated for over twice the power of your winch, as I learned today.

I learned the same thing Tom!:)