More winching ops questions

[IHASFIP]

That video was kinda hard to see. Did you have a snatch block on the back bumper? And does it not hurt the cable and/or axles with them all rubbing against each other under that much tension?

D

 

[rosco]

Your drum may start full, but as you use the winch for recoveries, the most used end, can become frayed or kinked. Sometimes, that is just the "cost of doing business". The line is down to about 175' on one of my trucks. I have cut bad spots off, several times now. Those drums you see, where the line is wound back perfectly, are often un-used lines. Even in text book style situations, hard pulls on snatch blocks can put a permanent bend in the line.

Lee in Alaska

 

[g102]

I had a old gas 5 ton wrecker back in the 80's. I had snach blocks to 4 part the rear winch cble.
I needed everything on the full spool back then to pull out a 80 ft plus tree that had a diameter as wide as a truck.

Oh ya i needed all the cable on the front winch also. I had to tie a tire on a neighbors tree across the intersection to keep the wrecker from sliding backwards.

The moral to the story , you can never have to much cable
and by the way-----the tree lost:-d

 

[jrou111]

I had a old gas 5 ton wrecker back in the 80's. I had snach blocks to 4 part the rear winch cble.
I needed everything on the full spool back then to pull out a 80 ft plus tree that had a diameter as wide as a truck.

Oh ya i needed all the cable on the front winch also. I had to tie a tire on a neighbors tree across the intersection to keep the wrecker from sliding backwards.

The moral to the story , you can never have to much cable
and by the way-----the tree lost:-d

PICS!

 

[tennmogger]

Try this for rearwards pulling, should use all the cable you got.

I don't get it. This defies logic to me so maybe someone can explain it. I believe this is a good way to 'make the truck longer'. We are close to April 1 though!

One of my Unimogs is set up with a mid-mount winch from which the cable can run backwards, u-turn around a sheave, runs back through the truck (equivalent to that line running to the side past a tree with sheave), then out the front, around another sheave, and back to the front tow hook. This setup with a double line front and rear will NOT pull the truck along but provides a way to drive the truck along a tensioned cable, as to be safe and secured across a steep slope.

The setup in the above diagram takes up cable and after the slack is out, IMHO, there will be no more movement available except to break something. Sure the winching force on the rear is higher than the force on the front but it does not matter if the front cannot move! The cable is being shortened while attached to 3 immovable objects (not counting the truck) in a triangle.

Someone please enlighten me!!!

Bob

 

[IHASFIP]

You know thats what I thought when I looked at the diagram. I suck at geometry and physics, but my "mathologically" smarter friend assured me it would work. I don't see it.

D

Edit* After staring at the picture I think I see it now.

 

[jrou111]

There's a 3:1 pull on the rear due to the pulleys vs the front.

 

[tennmogger]

There's one way it could work: the front "immovable object" not to be immovable. If that front tie point were the rear of another truck, for example, then there'd be a way to take up more slack out of the triangle (front truck moves backwards), then the stuck truck could move backwards due to the higher mechanical advantage (3 sheaves) in the rear. [but then, of course, there'd be no need for such an elaborate self-recovery]

 

[chicklin]

Confused me at first, too. But I think the key is the double snatch block in the rear. That double loop is basically getting cinched up, with the winch taking up the slack. Kind of hard to envision unless you see it.

 

[tennmogger]

Ok, but: the cable around those multiple blocks is getting shorter, right? And the cable is still being sucked into the winch, right? So where is the slack coming from that the winch is pulling in, with three immovable objects in a triangle?

Another way to look at it: the leg of the triangle that includes the truck is going to get shorter as the winch pulls in. There's no slack being generated around the three trees or the two other sides of the triangle.

edit: ok, you guys are going to get tired of my analogies, but, let's say there are no additional sheaves in the rear. The cable runs around the trees and back to the rear of the truck. Everyone would agree that the truck is not going to move, right? The cable just gets tight and the trees don't move.

So, if having those extra sheaves in the rear makes a difference, allowing harder pull in the rear, let's say we replace those 3 sheaves and their harder pull with a 30 ton winch. Would this scenario work then? Nope. Once the loop got tight there'd be nothing moving.

I will just have to go out and try it Hope you all are enjoying this as much as I am.

 

[det45]

The "slack" is coming from between the double snatch block in the rear and the snatch block attached to the pintle hook. The trick is all at the back of the truck. The setup has to be done exactly as shown. Just hooking the end of the cable to the back of the truck, without the snatch block on the pintle hook, would just try to pull the truck apart. As you pull cable onto the winch drum, the distance between the double snatch block and the pintle snatch block are shortend, taking up slack onl all three lengths of cable on the back of the truck.

I hope that helps, it is a bit difficult to explain.

 

[MikeON]

Every foot that the truck moves rearward generates 3 feet of slack in the cable because there are 3 lines between the double block and the truck. Each of the three lines gets one foot shorter.

The winch will have taken up 2 feet of cable to move the truck rearward that one foot - the 3 feet mentioned above minus the 1 foot increase in cable between the truck and first single block.

 

[tennmogger]

You are right!! I know when to admit defeat

And here's the proof:

My model had a little extra friction but when given the opportunity from a little outside force, the 'truck' moves backwards and more cable slack is created. Worst part of all this, my daughter told me I was wrong too

 

[Recovry4x4]

Bjorn, where did you get that image? Must be PS. I don't remember seeing it in any of the 4 different series of FM 20-22 that I have.

Tennmogger, I give you great credit to go and simulate the situation. Guess that's why they call it physics, I have to physically see it to believe it. I know it didn't work in my mind for a while either.

 

[KsM715]

If I had a winch on the front of my Jeep Id go straight to the ORV today and start making bets with that one. I wouldnt believe it if someone pulled up and just said it was possible.

 

[Jones]

Disclaimer: For all you wire rope purists, stop reading here.

After watching all the utility companies and several recovery outfits using synthetic line on their winchs, I think I'm gonna go the same route on mine.
Synthetic line (Not to be confused with nylon line) doesn't rust, stretch or whip back if it snaps, and will pull some pretty amazing loads.
The down side is that it's larger in diameter than cable.

I'll agree that no matter how prepared you go out, sometime in your winching career you'll find that the closest tree, rock, immovable object is about 4 1/2 feet past your absolute maximum line length.

I'm gonna run a spool full of synthetic and not worry 'cause I recently scored a ground anchor (one of the BII of the HEMTT wreckers); and although it needs a small pick-up to haul it around-- when this baby digs in... IT'S DEFINATELY SET.

Maybe someone needs to scale one down to deuce-size and start putting them out.

 

[Jake0147]

That particular recovery does take a bit of "thinking" to follow the logic in it, but it does work very well. I've never done it with a Deuce winch, but I have with civvy towing equipment that the cowboys at work overestimated the capabilitys of. If you think that looks bad, try it with a short winch cable and four extension cables of slightly varying lengths. That'll keep you hopping for a bit. It does burn up cable fast.

The easiest way to "visualize" how it works is not to try to "see" it dynamically at first, but rather move through it one step at a time. Just picture the cable being strung up and tight-
Then, move the truck backwards one inch... (The front cable won't allow this, but overlook that just for the moment...)
In the picture that Cranetruck posted, start at the left rear shackle of the truck. There is one inch of free cable in that line because the truck moved back one inch. Pull that one inch around the first sheave wheel at the double block. Now on the next line, there is that extra inch of cable you just pulled through, plus one additional inch from the truck's one inch of rearward movement. Pull that two inches of cable around the sheave at the pintle. On the next line, you have those two inches of cable, plus the one more inch of free cable due to that one inch movement of the truck towards the double sheave. Now from that one inch of truck movement and the two you "moved along the system" you have three inches of free cable headed around the second sheave at the double block towards the sheave that is anchored at the side of the truck. There is no movement between these two blocks, and likewise no movement of the sheave anchored at the front of the truck, so that three inches of cable will simply be pulled right around all three sheaves, and be directed back towards the winch. So you have three inches of cable coming out of the sheave in front of the truck, towards the winch. So now, you have three inches of "extra" cable in the line between the winch and the sheave at the front of the truck. The truck has moved rearwards one inch, requiring additional cable in that "leg" of the rigging. (That is the additional inch that was disregarded at the beginning so that this would work "one step at a time" instead of all at once). With that inch now accounted for and removed from the total, there are still two inches of cable remaining in that secton of line between the winch and the front sheave. As the winch spools in, those two inches are wrapped onto the winch drum. Two inches of cable on the drum for every inch of rearward movement. I think that's the hard part for people to see, is that while the winch is realing in cable, it's coming out of the front sheave three times as fast as what the truck is moving backwards.
In simplified theory, that means that this gives you not only rearward pull, but at a two to one advantage. Realistically due to frictional losses at the sheaves, that's not going to happen. In lieu of determining which snatch blocks are being used, how they're constructed, how they're maintained, what cable is being used and all that fun stuff, a good "rough guess" as to the recovery power of this method is that the force available to unstick the truck will be about the same as a single line pull directly to where the front sheave is anchored. Speed will be halved, as that always goes with the "theoretical" mechanical advantage,

As for stretching the truck out... it depends how stuck you are. "Action" members like a winch only exert as many pounds of force as what is available from the "reactioin" member at the other end of the line.
Let's say 10,000 pounds of force is exerted on the cable at the winch drum. That's 10,000 pounds pulling against the truck frame in a forwards direction. At the front sheave, 10,000 in and likewise, 10,000 out on the same line. (Frictional losses aside for now). For argument's sake, let's say there's a twenty degree difference between the two parts at that block. That's 19,700 pounds applied to the block hook and anchor chain/strap/tree, For all intents and purposes, the angle is acute enough that it may be considered "straight". The block to the side of the truck is another story. The angle there is more like (I'm estimating again) 140 degrees. That means the block's hook only sees a load of roughly 6800 pounds. (120 degrees is where the two lines and the hook all see an equal load). At the rear of the truck, in the double block, there is a slight angle of two of the lines, however just like the front, it is very acute and in this case negligable, and should be considered "straight". 10,000 pounds on the line into the double block, 10,000 pounds on the line to the pintle mounted shieve, 10,000 pounds on the line from the pintle mounted shieve to the double block, and 10,000 pounds from the double block to the left shackle. Added up, that's 30,000 pounds applied to the rear of the truck, and 40,000 pounds applied to the anchor for the double sheave block.
With 30,000 pounds applied to the "rear bumper" and 10,000 pounds applied to the front bumper but in the wrong direction, the net result is 20,000 pounds of pull in the correct direction.

Frictional losses abound in this system... While theoretically the pull will be 20K pounds, realistically I'd expect ten. Twelve to 15 is probably attainable with reasonable equipment, but I wouldn't count on it.

 

[cranetruck]

Made a model too, kinda crude, but it shows that it works.
Kenny, the picture comes from PS mag issue #137 (1964). Find all the pages in the "Recovery section" already uploaded (PS magazines, old site).

Edit: Jake, you put a lot of good thinking into this and yes, there is a lot of friction judging from how the model moved. I had to relieve tension in the individual legs to make the "truck" move over and over....probably best to have the truck in gear when using this method to help things along.

 

[chicklin]

Think of it like this. The rear of the truck and that rear double-snatch block are getting closer together, right? So, where does all that slack go? Into the winch. The fact that the force is 3:1 in the back is the reason it moves backwards instead of forwards.

It hurts my brain and I've never actually attempted what's in the drawing, I'm just trying to explain something that must work or they wouldn't have printed it. I wish I had enough little pulleys to test it out.

 

[KsM715]

Each time I look at this thread I get more curious. Now. I have to go to home depot and get some rope and a few small pulleys and the double pulleys (block and tackle?) and try this out with the kids wagon.