[CNY]

This thread is dedicated to all things about winch cables, whether it be wire rope, safety, usage, maintenance, or synthetic rope.

I am not a cable expert. What I post in this thread is from either reference material I have found, observation, or my opinion!

This thread was spurred by my off-topic posts in this thread:
http://www.jeepforum.com/forum/f27/winch-fixed-removable-326130/

I'll start us off with some info from that thread:


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[CNY]

Originally Posted by Pantheus

....{winching backward}... I was able to use two snatch blocks and multiple D-Rings and tree savers, and let the winch on the front do the job. Once I used a log between the front bumper and the winch line and went underneath to the rear and got out that way. [NOT recommended ! - DON'T do it, unless it means not getting home !]......

Originally Posted by chim

How did you rig this? I'm trying to visualize it, but can't come up with anything that wouldn't result in trying to "stretch" the Jeep...................chim

For the cost of 8 snatch blocks, you can buy a second winch!

[CNY]

Winch cable (wire rope)

I did a bit of research on this a while ago, and had a good thread on it, but it was General Discussion, and looks to be gone.

Here's some info from another thread http://www.jeepforum.com/forum/f27/snatch-block-theory-205210-post1549255/........
The working load rating on a 8,000 lb winch cable is only 1,960 lbs. Did I say that loud enough?

Yup, all these winches are running cable rated for about 1/5th the capacity of the rest of the parts. And when you snatch-block it, the load at the pulley is about double the load of the pull. Now you're putting 16,000 lbs of load on a cable whose working load is 1,950 lbs (and its breaking rating is about 9,800 lbs!). (1)

If you find it hard to believe that winch manufacturers are selling winches rated for loads that are dangerously close to the breaking strength of the cables, believe it.

Let's not forget, breaking strength is determined in testing conditions on new, undamaged cable, in a controlled testing environment.

Safe working load (SWL) for pulling is determined by dividing the breaking strength (straight-line pull, lab conditions, undamaged cable) by 5. This is called a safety factor of 5.

To use a snatch block with an 8,000 lb winch, you'd want to be running cable rated for 16,000 x 5 = 80,000lbs to stay within the SWL of the cable.

That would be a cable about 1 inch thick.(2)

References:
1) http://www.rigging.net/wire.html
2) Area of a circle (I know wire rope isn't a true circle) pi * r2


....the BREAKING load rating on 3/8" cable (common on winches over 9000 lbs) is about 14,000 lbs, and the safe working load (SWL) is 2,880 lbs (yes, that is right, 2,800 lbs).

Size (Inches) ......SWL (Lbs.)
3/32 ....................... 200
1/8 ......................... 400
5/32 ....................... 560
3/16 ....................... 840
7/32 ...................... 1000
1/4 ........................ 1400
5/16 ...................... 1960
3/8 ........................ 2880



This is one of those winching subjects that I think everyone should be aware of.

Here is a great source of info:
http://www.pirate4x4.com/tech/billavista/Recovery/index.html

[CNY]

http://www.masterpull.com/cpage.cfm?cpid=197

Originally Posted by Jerry Bransford

........ You're basing everything you say on a 5X SWL for a breaking strength and if that was even close to being valid for a winching application.........

OK, let's not use the 5X SWL safety factor, let's use the published SWL information from the US Navy:

WIRE ROPE SAFE WORKING LOAD
The term safe working load (SWL) of wire rope is used to define the load which can be applied that
allows the rope to provide efficient service and also prolong the life of the rope.
The formula for computing the SWL of a wire rope is the diameter of the rope squared, multiplied by 8.

D x D x 8 = SWL (in tons)

Example: The wire rope is 1/2 inch in diameter.
Compute the SWL for the rope.
The first step is to convert the 1/2 into decimal numbers by dividing the bottom number of the fraction into the top number of the fraction: (1 divided by 2 = .5.) Next, compute the SWL formula: (.5 x .5 x 8 = 2 tons.) The SWL of the 1/2-inch wire rope is 2 tons.


So if we plug our 5/16" wire rope into the Navy's formula:

Wire rope is 5/16 inch in diameter.

convert the 5/16 into decimal numbers = 0.3125

Compute the SWL formula: (0.3125 x 0.3125 x 8 = 0.78125 tons.) The SWL of the 5/16-inch wire rope is 1562.5 pounds.

[CNY]

Originally Posted by crownhilldigger

.......My questions is if this is true why aren't their more issue reported relative to injuries during winch use and from a liabilty only stand point why would any manufacturer set themselves up for a lawsuit?

Because :

* the cable is being used within its breaking strength of 9,800 lbs
* Most winching operations aren't done on the first wrap of the drum (the only place you can come close to an 8,000 pull (on an 8,000 lb winch)).
* Most people aren't injured, even if the cable fails

I'll admit, that a lot of factors have to line up for someone to get hurt by a parting winchline, but that doesn't change the fact that the SWL of a 5/16" cable is less than 2,000 lbs.

Go down to your local farm supply store, and look at the 5/16" cable they have on display. You won't see a working load listed anywhere near 8,000 lbs.

[CNY]

Originally Posted by mrblaine

First off, your premise is flawed. The 5-1 WLL is for overhead hoisting. Let's get rid of that piece of non applicable info right now. For our uses, we should actually be using a 3-1 WLL as it's more realistic even though it's difficult for offroaders to comprehend and accept, it's still the best. We operate outside the accepted industry standard of 5-1 for overhead and if we're lucky and run synth, we wind up with 2-1 which is much better than we used to get.

The only time I use the industry standard of 5-1 is when I need to compare the breaking strength of recovery devices like shackles to find their breaking strength and then compare than back to the breaking strength of my line.

Your points about folks not understanding are valid, but you need to get better versed in all of your facts and how they apply before you start your seminars on safe recoveries.

Your animation, although cute, won't work. No matter how many snatch blocks you use, you can't create more than you have as far as line travel goes. The only thing you've drawn is a very fancy way to lift your rig off the ground if the front and rear anchor points are higher than the bumpers, or you're looking for a cheap way to make your rig longer.

Your comment about the line seeing 16,000 pounds of load in a multiple snatch block situation is also bogus. The line never sees more load than the winch is capable of producing, nor will the winch see any load higher than it can produce. The snatch blocks themselves will see the higher loads as will the attachment points you hook the blocks to on the frame and the anchor points.

btw- switch your terminology to Working Load Limit so folks can compare it to what the catalogues use. WLL.

. .

[CNY]

Originally Posted by mrblaine

....btw- switch your terminology to Working Load Limit so folks can compare it to what the catalogues use. WLL.

OK!

Originally Posted by mrblaine

First off, your premise is flawed. The 5-1 WLL is for overhead hoisting. Let's get rid of that piece of non applicable info right now. ........

For overhead use. WLL is 10:1 ratio based on ultimate yield point. Which means WLL for overhead lifting is 1/10th breaking strength. (on our 5/16" cable, that equals 980 lbs).

Also, the one warning that does come with all winches is that they are not to be used for overhead lifting.

I know you didn't say they should be, but my point is that no component on a winch is spec'd for overhead use.

Originally Posted by mrblaine

..........if we're lucky and run synth, we wind up with 2-1 which is much better than we used to get. ..............

Only if you've gone to 3/8" synth (or larger).

Originally Posted by mrblaine

.....Your animation, although cute, won't work. No matter how many snatch blocks you use, you can't create more than you have as far as line travel goes.........

It's not my pic, just a link to one I found.

Go get some sting and your favorite model Jeep; rig this up at home. Simulate reeling in at the front bumper, while keeping the anchor points as in the diagram. You'll see that this is a viable rigging for winching backward.

Originally Posted by mrblaine

.......Your comment about the line seeing 16,000 pounds of load in a multiple snatch block situation is also bogus. The line never sees more load than the winch is capable of producing, nor will the winch see any load higher than it can produce. The snatch blocks themselves will see the higher loads as will the attachment points you hook the blocks to on the frame and the anchor points. .......

I will admit that I'm not clear on this point.

I did say (as you mention) ...when you snatch-block it, the load at the pulley is about double the load of the pull. . But then I make the leap (assumption) that Now you're putting 16,000 lbs of load on a cable.

I would love to understand this point better.

What follows is based on my understanding and assumtions. I don't have enough eveidence to say this is all fact. If anyone has references to material that explains this better, please let me know.


I understand that the work done by the winch in a single-block-with-the-end-of-the-cable-attached-to-the-pulling-vehicle is one half the weight pulled.

Let's use an example of an 8,000 lb winch, doing a 16,000 lb pull.

Load at winch and end of winch cable = 8,000lbs each.

Load at anchor point of snatchblock = 16,000 lbs.

What is the load on the cable, at the apex of the turn on the block? Some of the strength of the cable will be supported by the friction on the snatch block pulley, but what is the force at the apex? Isn't it 16,000 lbs?


As a test of this, I picture this:

Take a piece of string, and keep hanging weight to it until it snaps. Let's say it broke at 65 lbs.

Take a piece of this same string, hang it from a pulley. Add 60 lbs to each free end of the string. Think it will break? It sure will, because at some point on the pully, the string is feeling 120 lbs.

[CNY]

OK now, talk amongst yourselves...

[mtngoht]

Dam, you should have your own forum..........

[mrblaine]

Originally Posted by CNY-like posts

OK!

For overhead use. WLL is 10:1 ratio based on ultimate yield point. Which means WLL for overhead lifting is 1/10th breaking strength. (on our 5/16" cable, that equals 980 lbs).

http://www.thecrosbygroup.com/productcatalog/body_236.htm

Crosby is one of the most respected suppliers of rigging in the industry. Read about tail chains and apply what they say to what we do and then compare the WLL. BTW- I hadn't read this until I found it. So my use of the 3-1 WLL didn't come from there.

Also, the one warning that does come with all winches is that they are not to be used for overhead lifting.

Does it not make sense that we then have to apply some common sense to our uses and ratings we use in order to buy and acquire the correctly rated gear?

I know you didn't say they should be, but my point is that no component on a winch is spec'd for overhead use.
Only if you've gone to 3/8" synth (or larger).

Isn't that all the reason you need to run 3/8" synth?

It's not my pic, just a link to one I found.

Go get some sting and your favorite model Jeep; rig this up at home. Simulate reeling in at the front bumper, while keeping the anchor points as in the diagram. You'll see that this is a viable rigging for winching backward.

I'll make you the same offer. My way will be done here in the next few months when we get together with Jon out in JV with a video camera and put together a few things to show what works and doesn't.

I will admit that I'm not clear on this point.

I did say (as you mention) ...when you snatch-block it, the load at the pulley is about double the load of the pull. . But then I make the leap (assumption) that Now you're putting 16,000 lbs of load on a cable.

I would love to understand this point better.

The load is seen from the center of the rotating sheave away from the line and to the hook on the block. Whatever force the winch produces is what the line sees divided by the number of lines as long as it is anchored back to the bumper. A block used to change the angle of the line and not anchored back to the bumper but over to the side will only see the straight force of the winch.

What follows is based on my understanding and assumtions. I don't have enough eveidence to say this is all fact. If anyone has references to material that explains this better, please let me know.


I understand that the work done by the winch in a single-block-with-the-end-of-the-cable-attached-to-the-pulling-vehicle is one half the weight pulled.

Let's use an example of an 8,000 lb winch, doing a 16,000 lb pull.

Load at winch and end of winch cable = 8,000lbs each.

Load at anchor point of snatchblock = 16,000 lbs.

What is the load on the cable, at the apex of the turn on the block? Some of the strength of the cable will be supported by the friction on the snatch block pulley, but what is the force at the apex? Isn't it 16,000 lbs?


As a test of this, I picture this:

Take a piece of string, and keep hanging weight to it until it snaps. Let's say it broke at 65 lbs.

Take a piece of this same string, hang it from a pulley. Add 60 lbs to each free end of the string. Think it will break? It sure will, because at some point on the pully, the string is feeling 120 lbs.

Your premise is flawed. You've done the equivalent of using two 60 lb winches one on each line. You only have 60 lbs to work with. Thats the force that gets divided by the number of lines used.

You've created a scenario to support your flawed premise. Say your winch had a max pull of 60 lbs. Now what?

[CNY]

Originally Posted by mrblaine

.......You've created a scenario to support your flawed premise. Say your winch had a max pull of 60 lbs. Now what?

That's a good point.

In my example, the string fails at 65 lbs (breaking strength just a little more than the 60 lb winch you mention).

So now, is it possible to break my 65 lb string (using a pulley system), without ever exceeding 60 lbs of force from the winch? If no point on the string ever has more force on it than 60 lbs, the winch will stall, before the string ever breaks.

[mrblaine]

Originally Posted by CNY-like posts

That's a good point.

In my example, the string fails at 65 lbs (breaking strength just a little more than the 60 lb winch you mention).

So now, is it possible to break my 65 lb string (using a pulley system), without ever exceeding 60 lbs of force from the winch? If no point on the string ever has more force on it than 60 lbs, the winch will stall, before the string ever breaks.

The string will never see more than the load being put on it by the winch in a perfect world. In the theoretical we are dealing with, we have to discount the anchor points slipping under load or the rig doing something stupid to impart an impact load, so theoretically, yes the winch will stall before the string breaks discounting friction and such.

[mylt1]

not to get somehthing started but i want to know how that 8 pully pull worked. i can for the life of me figure it out even with the animation. how are you gonna pull something one way while pulling the opposit way as well?

[chim]

Originally Posted by CNY-like posts

That's a good point.

In my example, the string fails at 65 lbs (breaking strength just a little more than the 60 lb winch you mention).

So now, is it possible to break my 65 lb string (using a pulley system), without ever exceeding 60 lbs of force from the winch? If no point on the string ever has more force on it than 60 lbs, the winch will stall, before the string ever breaks.

In lieu of two 60# weights, run the string up from a fixed point and through the pulley and back downward. The attach that end of the string to a 60# weight. That would be more like a winch with a 60# pull......................chim

[r_w]

Originally Posted by TeamCNY

I will admit that I'm not clear on this point.

I did say (as you mention) ...when you snatch-block it, the load at the pulley is about double the load of the pull. . But then I make the leap (assumption) that Now you're putting 16,000 lbs of load on a cable.

I would love to understand this point better.

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

This web site does a decent job explaining pully principles.