Winching

[Robert A.M. Stephens]

A new page at Behold that may or may not be of interest.

http://behold-the-rage.com/jeep_page22.html

[Iceman]

maybe you should also address safety issues like a towel or something over a winch cable in case it breaks (never seen it myself luckily) or the use of the current hype (safety first though) -> winch rope

[mudpup]

heaviest jeep ever....box frame with 1" plate, WOW. Is grade 8 bolt not stronger in sheer than a grade 10 because of hardness?

[Robert A.M. Stephens]

Originally posted by Iceman
maybe you should also address safety issues like a towel or something over a winch cable in case it breaks (never seen it myself luckily) or the use of the current hype (safety first though) -> winch rope

I keep my cable new in condition, with a lay of factory wrap once stretched and laid-in. The first sign of a fray it goes away and replaced with new, so, no towel. I know about the breakaway for sheer failure so don't worry about it.


Thank you, however.

[Robert A.M. Stephens]

Originally posted by mudpup
heaviest jeep ever....box frame with 1" plate, WOW. Is grade 8 bolt not stronger in sheer than a grade 10 because of hardness?

Grade 10 only comes in fine-thread SAE. It is a factor of another 40% stronger than grade 8.

VEX weighs in, with fluids, at 5989 lbs. now.

[mudpup]

Originally posted by Robert A.M. Stephens
Grade 10 only comes in fine-thread SAE. It is a factor of another 40% stronger than grade 8.

VEX weighs in, with fluids, at 5989 lbs. now.

40% in tension

[mudpup]

http://behold-the-rage.com/images/VE...hdynamic-2.jpg

would that not net a total of 48k lbs...each line carrying the max 12k?

edit: spelling

[Robert A.M. Stephens]

Originally posted by mudpup
http://behold-the-rage.com/images/VE...hdynamic-2.jpg

would that not net a total of 48k lbs...each line carrying the max 12k?

edit: spelling

Uh oh............

[mudpup]

?

[Robert A.M. Stephens]

Originally posted by mudpup
?

If you can read down the page and the diagrams and it explains the rate of pull for each block installed, regardless of the size winch capacity, the pull doubles with each block. It doesn't add just 12,000 lbs of pull for each wrap on a block, it doubles it.

So, if you have a 8000 lb winch on your Jeep and you use a good block, you double the pull to 16,000 lbs., as long as the lines of departure remain parallel.

[mudpup]

Pretty sure it doesn't simply double with every snatch block added. It is that the total pull force is equal to the winch capacity + # of snatch blocks*winch capacity.

[Robert A.M. Stephens]

Originally posted by mudpup
Pretty sure it doesn't simply double with every snatch block added. It is that the total pull force is equal to the winch capacity + # of snatch blocks*winch capacity.

Well, here we go again..........

Would it be possible to call one or all those toll free numbers at the bottom of that page for the winch manufacturers so listed, and then verify with them. Call the big industrial ones like Thern or CARCO and find out from tech how it works.

I've gone through this over and over with what people think they know on this subject, but not a soul would call a toll free number so provided and take the time to find out for certain. At Jeep Forum, it was one of the reasons I left there since the level of caustic stupidiity got tiresome.

I do not want a flaming war here either over fact. If you "think" what you posted above that I've quoted, could you at least call and verify.

I do teach this stuff and I am correct: one more time: each block added doubles the pull, halves the speed of the line.

And there is no offense or truculence intended whatsoever in this response so please take my rebuttal well.

2:1 data;

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

http://www.atvconnection.com/editor/...nch/safety.htm

http://www.dodgepowerwagon.com/glovebox/snatch.html

That'll get you started a little bit if you question my facts as stated.

Does that help better?

[derf]

Originally posted by Robert A.M. Stephens
http://www.ec4wda.org/4x4score3.asp

http://www.atvconnection.com/editor/...nch/safety.htm

http://www.dodgepowerwagon.com/glovebox/snatch.html

That'll get you started a little bit if you question my facts as stated.

Does that help better?

Those only talk about using one snatch block. They don't address the question he asked about multiple snatch blocks.


*cough* *cough*

http://www.phys.unsw.edu.au/~jw/blocks.html

[Robert A.M. Stephens]

A little more, directly, and also that I've added to my page for help and application.

"So far, our winching examples have assumed a straight pull. What happens when you begin winching at angles? Simple (not) multiply FI (8,000lbs) times the Cosine of the angle to the anchor. For a 45 degree angle, that means 8,000 X .707 reducing your effective force to 5656lbs. Also, your winch mount was designed for straight pulls meaning it may not withstand the torsional forces applied when angle winching. Simply put, get as straight in line as possible with the anchor or stuck vehicle when winching."

Here is the departure angles and drop in pull away from a 0 Degree departure angle:

""Snatch block" is a specific type of block. A "block" is a "sheave", which is a wheel with a grooved edge to hold the rope or cable, combined with an axle or pin, side plates and a means of attaching it to something, typically a hook or shackle. Blocks are used in "block & tackle" combinations using multiple sheaves and two block assemblies, to increase mechanical advantage. _ A "snatch block" is a specially-designed block which is used to "snatch" loads or anchors, and is designed so that the side plate can be opened or swung away for the easy insertion of a loop of rope or cable without having to thread a bitter end through the side plates, and can thus be inserted anywhere in the cable without having to remove the load first to change the direction of the cable pull. _ Snatch blocks are one of the most mis-understood and misused items in the RV winching field, and can cause enormous harm and death if not properly rigged. _

Remember, if you overload a cable/snatch block, and the block parts from the anchor, you have a 10 or more pound missile flying at great speed, which can kill instantly. _ The most important thing to remember about snatch block winching, as used in the typical recovery sceneario, is that there is tremendous force applied to the block/anchor even when using a single-block system for a simple change of line direction.
_ _
> = vehicle
O = block
# = anchor
- |= line
_ _
1. >-----------O|
_______________ |
_______________ |
_______________ |
_______________ #
_ No mechanical advantage, 1 pound of pull required for each pound of lift/tension.
_ _
2. >----------------O|
__ >-----------------|
_ Mechanical advantage = 2/1 1 pound of pull results in 2 pounds of lift/tension. _
Now for the IMPORTANT part; The amount of force applied to the *block* is dependant upon the angle between the incoming line (to winch) and the anchor line (to tree)! The total load on a block can be as much as *2 times* the load applied. The maximum force on the block comes when the angle of the two lines is 0 degrees, or are parallel to each other as shown in #2 above. The actual load varies with the angle between the legs.
_
Here is the table from the Crosby Group catalog:
_
Angle is the measured angle between the legs of the line as they pass over the block sheave. Factor is the multiplier for the applied line load to calculate the block load.
_
Angle
Factor
0
2
10
1.99
20
1.97
30
1.93
40
1.87
50
1.81
60
1.73
70
1.64
80
1.53
90
1.41
100
1.29
110
1.15
120
1
130
0.84
135
0.76
140
0.68
150
0.52
160
0.35
170
0.17
180
0

In #1 above, the angle is 90 degrees, so the factor is 1.41. So a 10,000 pound load will place 14,100 pounds of force on the block/anchor.
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.
_
This is why using a properly rated and carefully maintained block is of the utmost importance when winching. In most RV winching situations, "double-lining" is the best method to reduce stress and strain on the lines and winch motor, at the expense of speed, but may be the *worst* thing you can do from the safety or block standpoint, if your block is not adaquately rated or is in poor condition or if you don't know the strength of the anchor or the stall-pull of your winch. The block is being subjected to twice the force of any of the other components, and consequently the winch operator may never know he is exceeding the capacity of the block until it parts and takes his head off. This is especially true when using very powerful winches.
_
Imagine the stress on a block (and it's anchor as well) when the SUV owner with the Warn 12,000 lb winch double lines to pull his vehicle over an obstacle and sticks a wheel behind a rock, locking the vehicle in place. The winch is already rated for 6 tons single line pull, and adding a traveling block doubles the pulling force to 12 tons. If your snatch block is (as many are) underrated for the winch/line combination, and you have a 6 ton rated snatch block, or even a "really big 8 ton-rated" block, which is commonly sold with RV winches, you still have the potential of block failure because you are using a 6 - 8 ton block with a system capable of exerting 12 tons of force under circumstances where you might not recognize the actual pulling force you are exerting, because you are not really stressing out the winch. _

A recipe for disaster.
_
This is *even more true* of hydraulic winches, which, unlike electric winches, usually pull until something breaks. With an electric winch, there is a built-in "safety" mechanisim which is that near the maximum-pull winch-stall load, the motor draws enormous amounts of amperage and heats up quickly. This means that the motor will usually stall due to lack of available amperage, increased electrical cable resistance due to heating, or motor overheat long before one can actually reach the rated pull, which is determined under lab conditions. _
With a hydraulic winch though, the hydraulic motor runs happily along, getting slower and slower, and exerting more and more force, until something snaps, and will *rarely* stall before reaching breaking load. _ So, one must be *extra* careful when using hydraulic winches, since the winch appears to be quite happy, and is just getting slower and slower, and the typical RV person expects it to stall, which it won't.
_
Please keep in mind that we are always talking about the "safe working load limit" here, and while the ultimate failure safety limit is typically 5 times the working load limit for commercially-rated hoisting gear, it may be less, or non-existent in cheap, uncertified blocks, *particularly* "surplus" blocks available at low price. _

NEVER, NEVER, NEVER!!!!! USE AN OFF-BRAND, UNCERTIFIED OR SURPLUS BLOCK WHEN WINCHING."

I buy mine at Logging and Industrial Supply outfits, and same for the cable. I increase my cable on a 12,000 lb. winch to 7/16" (what the light weight outfits like Warn and Ramsey put on their 16,000 lb. winches, so called.)

http://catalog.thecrosbygroup.com/BODY_314.HTM

[Robert A.M. Stephens]

Derf,

If one block doubles it, why does adding another 1/2 the increase. You realize this makes no sense, and too, is factually no true.

"cough?", you gotta cold. Sorry.

[derf]

Originally posted by Robert A.M. Stephens
Derf,

If one block doubles it, why does adding another 1/2 the increase.

With the second snatch block, you're not actually doubling the amount of line being pulled. You're only adding the distance between the two points over again. It's mere coincidence that the first block doubles the length being pulled. That's the key to the understanding of this topic.

If the points are 10 feet apart and you add one snatch block, you'll pull 20 feet of cable to move something 10 feet. Add a second block and you're not pulling 40 feet of cable to move the same 10 feet, you're only pulling 30 feet of cable. And much like gear reduction, that 3:1 line pull is how much the overall force is increased.

In all reality, adding a snatch block only adds again the single pull force to the total force.

Work = Force ? Distance

Triple the distance with the same force and you only get 3 times the work.

http://encarta.msn.com/encyclopedia_...53/Pulley.html

Here's a good site that explains how the relation of force and distance travelled equate to each other.

http://www.madsci.org/posts/archives...2615.Ph.r.html

[Jeff Weston]

Why all the arguments? Draw a free-body diagram of the forces and be done with it. Engineering 101

[mudpup]

Originally posted by Jeff Weston
Why all the arguments? Draw a free-body diagram of the forces and be done with it. Engineering 101

did that before I ever posted....my way is correct

[mudpup]

pic

there is how the forces add up...in your theory if you added another snatch block you be able to pull 192,000lbs.

[mudpup]

derf is also right on line speed. It is single line speed *(1/(1+# of blocks))

Oh yea, don't take this as flaming, just trying to get the information correct.

[derf]

Originally posted by mudpup
did that before I ever posted....my way is correct

Yup.

Back in high school, we rigged up multiple pulleys with fish scales between them and the bar it was pulling. We also had a fish scale connecting the bar to a fixed point. We were able to see the force applied at each pulley, the force applied to the end of the string and the total force applied to the bar. It was very educational.

In the cited example, if one were to put some way to measure force on all the attachment points, you would find that:

1) each snatch block applied roughly 24,000 pounds of force to the object it was attached to.

2) each end of the cable applied roughly 12,000 pounds of force to the object it was attached to.

Given that the truck had two snatch blocks on it, it would have 48,000 pounds of force applied to it.

Given that the Jeep had 2 cable ends and one snatch block, we would have the other side of that 48,000 pounds of force applied to it.

The forces equal each other so this system can exist in real life.

Q.E.D.

[Robert A.M. Stephens]

Originally posted by mudpup
derf is also right on line speed. It is single line speed *(1/(1+# of blocks))

Oh yea, don't take this as flaming, just trying to get the information correct.

Okay, okay. You are all correct. Disregard the winching post-thread. I am grossly il-informed.

Dumb me.

Sorry.

[derf]

Originally posted by mudpup
Oh yea, don't take this as flaming, just trying to get the information correct.

What he said...

[derf]

Originally posted by Robert A.M. Stephens
Okay, okay. You are all correct. Disregard the winching post-thread. I am grossly il-informed.

Dumb me.

Sorry.

It happens. The important thing is that we all learn the correct answer. That's good science.

[Joe Dillard]

Nice topic & discussion Robert.

Off topic, but we like to do that around here sometimes.

Maybe you can appreciate the rigging we do here while conducting underway replenishment.

Basically we tie/lock two ships together with cables for & aft, and use rigging to send hoses over to the recipient ship to refuel or send pallets of supplies at sea. Most of the time, we send fuel to each receiving station simultaneously.

Also, the supply ship, typically an oiler, will do two ships at the same time. One on the port side & one starboard, all while slicing through the open seas.

When you take into account the forces of the sea pushing against each ship while traveling ~14kts through open ocean, there's a lot going on with stresses.

The probes deliver both Diesel Fuel Marine (DFM), or JP5 for ships jet engines, or for the helicopter?s.

We don't seem to always take heavy seas into account either. I recall doing an unrep in the Bearing Sea while seas were easily 15-18', and winds were ~40kts.

[Robert J. Yates]

Originally posted by Robert A.M. Stephens
VEX weighs in, with fluids, at 5989 lbs. now.

I'm not an engineer and won't even begin to try and BS my way into or around the snatchblock/line pull discussion. I haven't studied a book on the subject and have pretty much learned much of my 4 wheeling techniques from old timers, magazines, internet and sheer accident.

One thing I do know from experience is that I would not want my Jeep to weigh almost 6000 lbs. There are a number of reasons why but balance and durability of componants (axles for example) come foremost to mind. Its all personal preference of course and most of my wheeling is not "expeditionary" in nature.

In my case wherein I would define what I do as recreational wheeling, I am plenty certain that my Warn 9.5TI with Masterpull 3/8ths line, my assortment of straps, D-rings, recovery points, Coyote Chain and ARB snatchblock will provide me with plenty of recovery options. At 1500 to 2000lbs less weight on my rig and typically at the most, 3 days in the outback trips, I don't see the need for for the type of gear or recovery scenarios being discussed. I do think that if I personally were to be more involved in expeditionary types of wheeling, I would want a bigger vehicle but thats another topic.

[derf]

Originally posted by Robert J. Yates
One thing I do know from experience is that I would not want my Jeep to weigh almost 6000 lbs. There are a number of reasons why but balance and durability of componants (axles for example) come foremost to mind.

Ever see a nearly 8,000 pound built up K5 Blazer wedge a rear tire and have the forces build up until something let go? Like a 14 bolt pinion gear? Releasing that much energy WILL grenade a Klune V and the 700R4 it's attached to. True story. Oh, and it did crack the rear yoke on the Atlas.

That was an ugly recovery.

I don't want that to happen to my Jeep. I'm doing what I can to keep it under 4,000 pounds.

[Robert J. Yates]

Thats exactly my point - I'm still running around on a D30/D44 with an aluminum 231 t-case. I have it all built up very nicely but there is a limit to weight and forces which this equipment will reliably handle IMO. The closer I can stay to the 4000lb mark,the more comfortable I am with my reliability factor. And of course, this opinion is based purely on personal superstition/experience with no science to be found anywhere to back it up with

[Joe Dillard]

Originally posted by Robert J. Yates
And of course, this opinion is based purely on personal superstition/experience with no science to be found anywhere to back it up with

Hehehe, can I use that phrase Robert? Or is it going through the patent pending process?

[Jeff Weston]

Originally posted by Joe Dillard

Cool pics Joe. My dad made the crossing from an oiler to his carrier in a similar matter while travelling on the open seas. He had visions of the two ships veering apart, snapping the line and him sinking to the bottom of the ocean in this steel cage. I'll have to show him these pics.