Wire Rope vs. Aircraft Cable

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Wall Township, NJ
I went to the local supply store and they carry aircraft grade cable in both 5/16" and 3/8", but the ratings on the cables are not very high 9,000lb for the 5/16" and around 14,000 for the 3/8". They mentioned that the cable is just wrapped strands, but "wire rope" has a straight strand that runs down the middle and then has strands wrapped around it and holds a much stronger rating.

Does anyone have any input on this? Looking at replacement steel cable online everything seems to be aircraft cable, but with the strength rating being at 9,000lbs for 5/16" I am hesitant about putting it on my 9,000lb winch. Won't I exceed its load capacity as soon as I throw a snatch block in the mix?
 
Go with synthetic rope and your problems are solved. Once you use synthetic you will be glad that you don't have to screw with steel cable anymore. Synthetic is stronger than steel. The only problem with it is heat and UV rays, and both are easy to avoid.
 
I've considered synthetic, I'm leaning towards some cable because of frequence of use, cost, and nastalgia...I like the steel cable on my 20+ year old viking worm drive winch.
 
This is the dirty little secret of the winch industry... 5/16 cable is working right near the BREAKING strength when on a 8000 or 9000 lb winch..... there is high strength cable, look for a local rigging shop (where the loggers or crane operators shop) and ask around. I run 5/16 on my Warn 8274, but you just have to know your limits and take precautions. Yes rope is nice and has a higher breaking strength when new..... but there are down sides to rope too (mainly UV/heat/abrasion issues) it is a lot nicer to handle though :p
 
Wire rope is the more correct term for cable, it may have a fiber core, an independent wire rope core or a core the same construction as the outer strands.
The important thing is the grade of steel and the layup of the strands (strength VS flexibility).
And yes, the breaking strength rating of small size wire ropes are right at the advertized "vehicle" winch capacities, leaving you almost no safety factor at all (actually pretty much the same as synthetic).
If you value your rig and your safety, go to a real rigging shop, get real (not offshore made) wire rope, get told the breaking strength, and go up a size (say 5/16 to 3/8), that will cost you a wee bit more than "aircraft" (yeah, right) cable from the local farm supply, but will be much safer...
Be safe!
 
Wire Rope vs Aircraft Cable

The difference per this website :

How does aircraft cable differ from wire rope?
Aircraft cables are available in smaller diameters than wire rope. For example, aircraft cables are available in 3/64 in. diameter while most wire ropes begin at a 1/4 in. diameter.

There's also illustrations of the construction of Aircraft Cable sizes.

On this website You get the info and illustrations for Wire Rope.

BTW, my Ramsey Winch owners manual specifies: "Use only 5/16 inch (8MM) 7x 19 Aircraft Cable". Now, my winch is a REP8000 and the owners manual has a 1986 date on it. But, I don't think this has changed. I don't see the 7 x 19 construction pattern on the Wire Rope page, only on the Aircraft Cable page. The 7 x 19 means there are 7 strands and 19 wires in each strand. Now you can get 2 grades of Aircraft Cable: galvanized and stainless steel. And basically 3 grades of wire rope: bright, galvanized and stainless steel. Except for my winch info, all of this information and more comes from different pages on the website: www.lexcocable.com/. HTH
 
Get proper 5/16 lifting cable its good for over 10k swl my 5 tonne shop crane runs 5/16 . A snatch block doesn't put double the weight on the cable just on the block
 
check with local 4wd clubs/forums. people that have gone synthetic are always selling their cable, often brand new. craigslist is also a good source (that's where i sold my new wire rope ;) )
 
A snatch block actually cuts the load on the cable in half, with exactly half of the load on each line of cable running from the truck to the block, and the block gets the full load.

Debunking the "aircraft grade" myth: it is a marketing ploy. Like "aircraft grade" aluminum, it is simply a marketing ploy to sell that particular brand or item. In the materials engineering world, for example, regular 6061 T6 aluminum is the SAME, with NO DIFFERENCE than the supposed "aircraft grade 6061 T6 aluminum." Same tensile strengths, capabilities, etc., just a few more words in the description.

The reason the "aircraft grade" wire ropes have more diameters and start smaller is because of the trade off of weight vs. strength in the aviation industry. You select, based on forces required and necessary safety factors, the wire rope that satisfies your criteria and that's it, no more. Finer graduations of sizes (and therefore strength) allow the required strength without excess weight.

Hopefully that helps.

Brian
 
A snatch block actually cuts the load on the cable in half, with exactly half of the load on each line of cable running from the truck to the block, and the block gets the full load.

Debunking the "aircraft grade" myth: it is a marketing ploy. Like "aircraft grade" aluminum, it is simply a marketing ploy to sell that particular brand or item. In the materials engineering world, for example, regular 6061 T6 aluminum is the SAME, with NO DIFFERENCE than the supposed "aircraft grade 6061 T6 aluminum." Same tensile strengths, capabilities, etc., just a few more words in the description.

The reason the "aircraft grade" wire ropes have more diameters and start smaller is because of the trade off of weight vs. strength in the aviation industry. You select, based on forces required and necessary safety factors, the wire rope that satisfies your criteria and that's it, no more. Finer graduations of sizes (and therefore strength) allow the required strength without excess weight.

Hopefully that helps.

Brian

Speaking of debunking myths - a snatch block only truely benefits the winch. Yes, you have split the load on your winch line in half from winch to snatch block and from snatch block to hook. Also on the winch itself and the point that hook is secured to. But as you mentioned, the snatch block is carrying the full load as is part of the winch cable that is in the snatch block. At some point in the winch line the load is split into 2 halfs, when run through the snatch block. It is at that point, that the full load is applied to the winch cable. This point moves as the cable moves through the snatch block, but there's no magic in this. You still need to heed the rating, considering the full load, on your winch line using a snatch block.
 
Speaking of debunking myths - a snatch block only truely benefits the winch. Yes, you have split the load on your winch line in half from winch to snatch block and from snatch block to hook. Also on the winch itself and the point that hook is secured to. But as you mentioned, the snatch block is carrying the full load as is part of the winch cable that is in the snatch block. At some point in the winch line the load is split into 2 halfs, when run through the snatch block. It is at that point, that the full load is applied to the winch cable. This point moves as the cable moves through the snatch block, but there's no magic in this. You still need to heed the rating, considering the full load, on your winch line using a snatch block.

Huh? If you assume no friction at the pivot point (snatch block)- then the full pulling capacity of the winch is literally doubled. ie. a 9000lb winch becomes capable of moving 18,000 lbs. ergo your winch rope (aircraft or otherwise ;)) needs to be strong enough to tolerate this. (have a high enough WLL)
 
Huh? If you assume no friction at the pivot point (snatch block)- then the full pulling capacity of the winch is literally doubled. ie. a 9000lb winch becomes capable of moving 18,000 lbs. ergo your winch rope (aircraft or otherwise ;)) needs to be strong enough to tolerate this. (have a high enough WLL)

Correct. We're saying the same thing, just differently.

A snatch block actually cuts the load on the cable in half, with exactly half of the load on each line of cable running from the truck to the block, and the block gets the full load......

Read this carefully. I interpret this as: Using a snatch block will allow you to have half the stress on your winch cable, and only the block gets the full load. This is misleading. As I said before, only the winch will benefit when using a snatch block. Using 1 snatch block will allow the winch to pull double it's rating. And like you said also, your winch rope needs to be strong enough to tolerate this. (Have a high enough WLL)
 
Speaking of the actual strength of some things we assume are big enuf...

I was in the local big farm box store to get some paint for the M101. I happened past the section that has cable and other such items. Saw the 3/8" cable, which they sell by the foot.

Nice thing is that they very clearly indicate the WLL of each item. Now, I assume they are using the same WLL as I've been told to interpret WLL, i.e. it's for an overhead lift, so for the typical horizontal pull that offroaders do, multiply by a factor of 4.

I can't recall exactly what the WLL of their 3/8" cable is, but it was under 5k. I'm remembering that it was actually 2,9xx pounds. Struck me as rather low, given that you usually find 3/8" cable on winches bigger than 8k.

Not sure that does anything to clear up confusion about which standard to use for comparison of rigging, but the fact that the store was rigorous about including it easily for the consumer's buying decision is interesting.
 
Correct. We're saying the same thing, just differently.



Read this carefully. I interpret this as: Using a snatch block will allow you to have half the stress on your winch cable, and only the block gets the full load. This is misleading. As I said before, only the winch will benefit when using a snatch block. Using 1 snatch block will allow the winch to pull double it's rating. And like you said also, your winch rope needs to be strong enough to tolerate this. (Have a high enough WLL)

You do not need a WLL of 18000lbs on your line in order to double line a 9000lb winch. And yes the line also benefits from double lining, just not to the full effect the winch does. The line does loose some of it's "doubling" strength going through the pulley. The amount varies with the type of line, actual pulley size and angle.

Yes, friction on the pulley (among other things) will take away from the full x2 effect of double lining your winch. But you also have to consider that you are using more winch line and there for are going to be using a lower wrap on the winch drum, which increases the winch's mechanical advantage.

I run a 30 ton winch truck for a living and spend 90% of my time double lined with 1" line. I have also double lined 75 ton winches with 1 1/4" line. I have broke many lines, sling, clevis's and even snatch blocks, not to mention equipment in the process, but I have never broke a double line.

Use a double line, long before you reach the max capacity of your equipment. It will extend it's life as well as yours.
 
You do not need a WLL of 18000lbs on your line in order to double line a 9000lb winch. And yes the line also benefits from double lining, just not to the full effect the winch does. The line does loose some of it's "doubling" strength going through the pulley. The amount varies with the type of line, actual pulley size and angle.......
What's the formula, then???

"Just not to the full effect the winch does" is not good enough! "The amount varies with the type of line, actual pulley size and angle" leaves too many variables!

.........Yes, friction on the pulley (among other things) will take away from the full x2 effect of double lining your winch. But you also have to consider that you are using more winch line and there for are going to be using a lower wrap on the winch drum, which increases the winch's mechanical advantage......
Here we go again, more variables. Also, most of us are aware that a winch will only pull it's full rating on the first wrap of the spool and the effective rating goes down as the wraps increase.

.......I run a 30 ton winch truck for a living and spend 90% of my time double lined with 1" line. I have also double lined 75 ton winches with 1 1/4" line. I have broke many lines, sling, clevis's and even snatch blocks, not to mention equipment in the process, but I have never broke a double line.

Use a double line, long before you reach the max capacity of your equipment. It will extend it's life as well as yours.
Come on, you do this for a living and you're not quoting a formula? Never say never! Famous last words.

I hear and appreciate what you're saying. But you're not contributing positively to this dilemma. Yeah, the winch and part of the cable benefit from a "double line". It's the part that's in the pulley that is in doubt.

I know that with the snatch block that the load on the winch and the two ends of that doubled cable is half of the load on the snatch block. But, I also know that it is 1 cable and those halves add up, so some part of the cable is exposed to somewhere between full load and half load, depending on all the variables. If I'm figuring capacity, for safety's sake, I'm going to err by choosing to go with WLL of the full load.
 
exhibit a

cc12600xi1.jpg


this crane lifts 1750 tonnes we had it on the last job site , if i remember right it has a 20 or 24 part line on the block of approx 2" cable , are you telling me that 2" steel cable lifts 1750 tonnes ? in one section around the shiv on the block .

im sorry but you can take the same cable and keep snatching it till you run out of cable . as long as the winch can't break the cable in a 1 part pull then your fine .

if you shop for cable anywhere that involves the word farm please stop , i have a 5/16th cable that will hold more then your 3/8" cable any day .
 
................im sorry but you can take the same cable and keep snatching it till you run out of cable . as long as the winch can't break the cable in a 1 part pull then your fine ............

Yeah, I've heard that, too. Even seen it demo'd on a few U-tube winch guides. There's got to be more to the physics than the "just keep adding snatch blocks till your winch can pull it" mentality. I've been googling snatch block, block and tackle, all sorts of stuff and the closest I can come to what I'm talking about is the Capstan Equation. The material is above my pay grade, but at one point they're referring to "Forces on cordage in general" and the accompanying drawing is not applicable, but illustrates the forces that I'm talking about on a winch line with a single snatch block.

What bothers me is basically very simple. Say you have your 8K rated winch set up with 1 snatch block and your winch line doubled back to your rig. The 5/16 wire rope that you're using has a 9.8K WLL rating on it. The force required to get unstuck this time is 14K lbs. So the force on the snatch block is 14K, and 7K on each half of your doubled winch line. Now the winch line runs from the winch, through the snatch block pulley and back to the tow hook on your rig. We've determined that there will be a 14K load on the snatch block and 7K load on each half of the winch line. What bothers me is this: the winch line is 1 piece of wire rope from winch to hook. We've split the load from winch to snatch block and from snatch block to hook. But there's still a section of that 1 piece winch line that's running around the pulley in the snatch block. The winch line is not physically attached to the snatch block. You've got 7K on one side and 7K on the other of 1 piece of cable. That, to me, adds up to 14K of stress on that winch cable where those two 7K forces meet. I don't think that the snatch block pulley is magically strengthening the winch cable. I can see the mechanical advantage for the winch and 2 exposed sections of the winch line. It's like gearing in a tranny, transfer case or axle diff. The engine, like the winch motor spins more revs to cover the same ground. But, in either case, you still need to respect the load. The axles, gears and drive shafts are still exposed to the same stress.
 
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Originally Posted by 80t0ylc
"What's the formula, then???"
*To make a formula you will first need to determine every variable.

""Just not to the full effect the winch does" is not good enough! "The amount varies with the type of line, actual pulley size and angle" leaves too many variables!"
*Sorry you dont like variable but they are all legitimate factors. For example the larger the diameter of the pulley, the less stress on the line. Not to mention synthetic rope is obviously more flexible and has more tolerance then wire rope for short angle changes. What about your snatch block? is the pulley pivoting on bearings to reduce friction?


"Here we go again, more variables. Also, most of us are aware that a winch will only pull it's full rating on the first wrap of the spool and the effective rating goes down as the wraps increase."
*Not sure what your argument here is. If you know it true then you know its a legitimate factor. Besides how else are you going to use more line on a short pull in order to access the lower wraps on your drum.


"Come on, you do this for a living and you're not quoting a formula? Never say never! Famous last words."
*I don`t have time to figure out all of the ever changing variables to do a formula every time I run my winch. But here are a few general guide lines for you;
- deduct 10% from the total pulling capacity for each snatch block used (due to line friction on pulley, and pulley friction on pivot point)
-0 degree angle (2 parts of line running parallel) of line on pulley is a multiplying factor of 2
-45 degree angle of line on pulley is a multiplying factor of 1.8
-90 degree angle of line on pulley is a multiplying factor of 1.4
-180 degree angle (straight line) is a multiplying factor of 1
As for the never say never, your right but I have been doing this for 15 years and I can assure you that a properly maintained line is rarely the weak point in the double line equation.

"I hear and appreciate what you're saying. But you're not contributing positively to this dilemma. Yeah, the winch and part of the cable benefit from a "double line". It's the part that's in the pulley that is in doubt."
*
Just because I am not supporting your theory does not mean I am not making a positive contribution.


"I know that with the snatch block that the load on the winch and the two ends of that doubled cable is half of the load on the snatch block. But, I also know that it is 1 cable and those halves add up, so some part of the cable is exposed to somewhere between full load and half load, depending on all the variables. If I'm figuring capacity, for safety's sake, I'm going to err by choosing to go with WLL of the full load."
*What you are not understanding is the load is consistent over the entire length of line whether it is going through the snatch block or not.
 
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...........*What you are not understanding is the load is consistent over the entire length of line whether it is going through the snatch block or not.

So what you're saying is that I can hang 500 Lbs on a 250 lbs. rated line by using a single line attached in one place to the load, and run the line over a securely mounted pulley and attach the other end to this same load. There's not going to be 500 lbs of stress on the line at the pulley - just 250 lbs?

Why don't I believe this?

Now if you ran 2 separate 250 lbs lines and secured them to a common point - to share the load - that would be believable. A single line has to support the full load at some point along it's length. Isn't it like a tug-o-war? Pull on one end of a line with 250 lbs of force and some one else pulls on the other end with 250 lbs of force - doesn't that add up to 500 lbs of stress on the line?
 
I've read this thread and my brain hurts. I think people are making this too complicated.

1) Rope/wire caries tension. That's it. Neglecting friction, which we can because tension is much much greater the pulley friction, tension is constant throughout an length of rope/wire. Just because you loop a rope around something and pull on both sides with X, doesn't mean at some point the rope will experience 2X.

2) Applying that fact that tension is constant over a length of rope/wire, it is very easy to calculate force applied to any part of a system. Count the number of lines.


800px-Four_pulleys.svg.png


In our application of winching, the only thing creating tension is the winch. Therefore, the max tension on your winch line is the max winch capability.

Now, for the case most common in winching. You wrap a tree saver around a tree, attach a snatch block, route the line from your winch, back to your bumper. This is case 1 shown above.

Winch = Fz
Recovery point = FL
Snatch block = pulley on the top

Using the common winch numbers:
Pull on winch = 8k lbs
Cable tension = 8k lbs
Pull on recovery point = 8k lbs
Pull on truck = 16k lbs (2 lines, 2x tension)
Pull on snatch block = 16k lbs


Now if you want to go crazy with pulleys/snatch blocks, the tension in the wire will still never exceed what the winch can provide. It would look a different than example 4, but it can be achieved with 4 snatch blocks.

Pull on winch = 8k lbs
Cable tension = 8k lbs
Pull on recovery point = 32k lbs (4 lines, 4x tension)
Pull on truck = 40k lbs

Now, if you do try this, my bet is that your bumper rips off as generally the winch and recovery point are both attached to you bumper.
 

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