ONSC Chat (7 Viewers)

[weejub]

Great - - I have hours of study ahead of me and will not "get" any of this stuff . . thanks a lot engineers, scientists . . .whatever you guys are!!

Edit: Better than cleaning gutters or working-out or doing work-work, though!

 

[Rice]

Is it necessary that the bottom left pulley is positioning closer to the vehicle than the anchor point?

And is it true that the pulley attached to the rear of the vehicle is going to be pulled towards the bottom left pulley?

Everything important has already been said. The issue is I'm winding down the school year, have no exam to give today, and am coming out of my skull looking for something to occupy my time. (Warning .... excessive postings possible today)

So I decided to draw another picture!

Cable length has no effect on the pull force being produced. Short or long obviously limits the range of your pull but that is all. On the other hand, angle has a huge (in fact, exponential) effect on the force being applied to the vehicle. Having cables in line with the direction of the desired direction of pull is ideal. As angles deviate away from where you wish to go effective pulling force is lost. Small angles are not a big deal. The exaggerated image below would be a big deal. By the time the angle reaches 45 degrees your effective pull is only 71% of what it would be in a direct line. At 60 degrees it is down to 50%.

 

[NCFJ]

Perhaps we should do some basic rigging demonstrations at some of the club meetings.

I have done my fair share of winching, and then some. Being the one guy with a winch among a bunch of newbies in an FJC club with folks that want to push limits will keep you busy

My two favorite pulls were in the same spot. My buddy James was stuck and his winch was dead. we were headed up hill and he was up hill from my rig. Ran a line to a block uphill to change line direction, from there to a block uphill of James' rig and then down to his rig. Pulled him up hill from a down hill position.

Our rig was stuck between trees on a 15° side slope while going up hill. Could not move forward or back without sliding farther into the trees. cable out to a block about 20' forward and 10' up the side slope, back to another block in similar position behind rig to rear of rig. Rig paralleled line (planned that) then pulled sideways up about 5-6' and out of the trees. Heather was in the cab keeping the RPMs up with a HUGE grin on her face.

 

[Rice]

Almost. If the tree saver wraps around the tree and BOTH ends are connected to the shackle then load on the tree saver is 10,000# (Something to think about when hooking up the tree saver). The shackle at the snatch block = 20,000#, but the shackle connected to the vehicle is 10,000# (the pull on the vehicle is 20,000# but it is coming from 2 different connect points). The snatch block and the tree = 20,000#.

BTW .... if there is ever a concern of shackles being the weak link, say the shackle at the block, just use 2. One shackle for each end of the tree saver. Now all shackles in the rigging are at our made-up value of 10,000#.

 

[GLTHFJ60]

BTW .... if there is ever a concern of shackles being the weak link, say the shackle at the block, just use 2. One shackle for each end of the tree saver. Now all shackles in the rigging are at our made-up value of 10,000#.

There might be an issue with this. Snatch blocks have two "ears" that slide apart to allow you to insert the winch rope, but then they're supposed to be closed and a d-ring put through them. There's only enough space for a single d-ring. If you open the snatch block and mount it with two d-rings, and the wire rope pull isn't perfectly parallel with the two ends of the tree saver, I could easily see the ears of the snatch block get bent out of shape.

For example, if you hooked up one d-ring to each of these ears and pulled just like that, do you think it could screw up the snatch block? The problem would be worse when using a tree-saver around a larger tree, because the ears would be at a larger angle to each other. Instead of ~30* in this pic, they might be offset by 90* or more.

Furthermore, the snatch block seems to be the limiting factor. The snatch block I've got is only rated for 17,600#. I remember looking into 20k# or more snatch blocks when I put together my kit before GSMTR and didn't find much IIRC:

Snatch Block - 17.6K - Smittybilt

 

[Rice]

There might be an issue with this. Snatch blocks have two "ears" that slide apart to allow you to insert the winch rope, but then they're supposed to be closed and a d-ring put through them. There's only enough space for a single d-ring. If you open the snatch block and mount it with two d-rings, and the wire rope pull isn't perfectly parallel with the two ends of the tree saver, I could easily see the ears of the snatch block get bent out of shape.

For example, if you hooked up one d-ring to each of these ears and pulled just like that, do you think it could screw up the snatch block? The problem would be worse when using a tree-saver around a larger tree, because the ears would be at a larger angle to each other. Instead of ~30* in this pic, they might be offset by 90* or more.

Furthermore, the snatch block seems to be the limiting factor. The snatch block I've got is only rated for 17,600#. I remember looking into 20k# or more snatch blocks when I put together my kit before GSMTR and didn't find much IIRC:

Snatch Block - 17.6K - Smittybilt

Solid point. We're often going to be limited by what's in the recovery box and sometimes be forced to try less than ideal rigging (with the goal still focused on safety). And I agree, I would never want to place separate shackles into separate block ears. It ain't cheap but ARB and some others do have 30K blocks on the market. Now, whether 2 shackles will fit in that eye remains to be seen. Looks like maybe.

EDIT for clarification .... 30,000# is the block rating, 15,000# is the line rating.

 

[RedHeadedStepChild]

@tgadd , I think @ rice touched upon this, but IDEALLY, you would want the pull as straight as possible at both ends of the vehicle otherwise you will induce a moment (twisting force) into the pull. His drawing was in no way inaccurate, but you might want to add another tree saver and snatch block (b) to the scenario.
He also touched upon the fact that it is preferable to have the rear rigging as close to parallel as possible. The lower portion of this graphic shows how the vectors sum. In this case I assumed 30* between the lines (each 15* from parallel) and the resultant force is:
2*pull force*Cos(angle from parallel).
If we have maxed otu our winch, then we're at 9,318 lbf rearward.

As for why the vehicle moves backward (vs just being pulled in two direction and going nowhere till something breaks) I think @GLTHFJ60 was getting at it, but I've tried to make it easy to see with the diagram below.

 

[jamesurq]

Don't get that thing stuck in the snatch block.....

That's my contribution to this in depth discussion.... you're welcome.

 

[RedHeadedStepChild]

A 17,500 snatch block is designed to par with an 8,500 pound (or less) winch. Snatch block should always be rated for AT LEAST 2x your winch capacity. Same with BOW shackles. You DO NOT want D-shackles. Ds are for only straight-line pulls that arise during standard rigging situations. They are NOT designed nor are they rated for any off axis pulling.
Some people use the terms interchangeably, but there is a difference between bows and Ds and that difference can be a life.

This = GOOD

This = BAD

 

[JohnVee]

Some good info here. I'm gonna cut out the images for James using my scissors.

 

[GLTHFJ60]

You know what, maybe it was some other reason I went with a 17.6k# snatch block. Now I'm having no trouble finding 30k models:

Amazon.com: 30,000 snatch block

Time to upgrade!

 

[SeanLX]

You know what, maybe it was some other reason I went with a 17.6k# snatch block. Now I'm having no trouble finding 30k models:

Amazon.com: 30,000 snatch block

Time to upgrade!

That first one on the list (Rugged Ridge) is the one I went with a while back. I feel better about picking the 30k now.

Good info in this thread.

 

[Rice]

Don't get that thing stuck in the snatch block.....
View attachment 1268193

That's my contribution to this in depth discussion.... you're welcome.

In the middle of a discussion about how NOT to go over a cliff James gives it a push over the edge.

And what do you get when you put it all together?

 

[RedHeadedStepChild]

In the middle of a discussion about how NOT to go over a cliff James gives it a push over the edge.

And what do you get when you put it all together?

View attachment 1268235

 

[Trollhole]

It will be a cold day in hell before you see anything like that using recovery gear.

 

[RedHeadedStepChild]

Kim Jong Un? You'r eprobably right. I'd imagine his hands are too soft.

 

[lt1fire]

Not actually an uncommon sight on the trails I grew up on.

No i'm not talking about the supreme dictator LOL

 

[Rice]

Don't get that thing stuck in the snatch block.....
View attachment 1268193

That's my contribution to this in depth discussion.... you're welcome.

From the looks of it Land Cruiser folks are more interested in translational energy.

 

[tgadd]

@GLTHFJ60 - want to do a crazy project?

http://thegarage.jalopnik.com/im-giving-away-a-car-and-heres-how-you-can-get-it-1779781028

 

[lt1fire]

@GLTHFJ60 - want to do a crazy project?

http://thegarage.jalopnik.com/im-giving-away-a-car-and-heres-how-you-can-get-it-1779781028

Wonder if he will accept, set it on fire and drag it through the pismo dunes and out into the ocean as a good project.

I'm going to enter that and see if I win