Thread: Hand vs electric winch: solo travelling

Originally Posted by bob10

This bloke seems to have winching backwards worked out.

https://youtu.be/_4tI3HtgdCY

Bob the bloke with the jeep got it right, except he said he used a Snatch Strap for a tree protector. bad blue, otherwise good.
The bloke with the Toyota was wrong, he claimed that the first block attached to the tree in front gave him a MA of 2, WRONG. If that was the case the next block (2nd.) in the line would have also given him a MA of 2, which it didn't, it merely changed direction of the rope.
But the angle that the 2nd. block was set at had an angle of the rope at over 90 degrees, doubling the load on the rope and the tree protector.
The 3rd. block attached to the tree was also redirecting the rope/pull and had NO MA,
the 4th block attached to the Toyota (which was overkill) is the only moving block and as it was Supported by 2 parts of rope it has a MA of 2.
The simplest way requires 2 snatch blocks (Sb), one SB in front, cable (only) through and back under your car or beside, whichever is the most convenient to a SB attached to a tree behind your vehicle and then attached to the back of your vehicle.
In the video with the Toyota the angle of the rope between the 1st. and 2nd. block and onto the third block was excessive and puts undue strain on ropes/cables/SB and tree protectors.
I seen the result of a person using a Snatch Strap(SS) as a tree protector/SB anchor rope. He had to wrap it a number of times around the tree with layers overlapping one another.
After some really tough winching the SS had stretched so tight tat it had melted itself together into one messy lump, one more good pull and it would have failed and god knows where that SB would've ended up. Don't ever use a SS as part of rigging up a Winch recovery, ever, and just for Dave, even easier is to run your cable down over the bottom fairlead roller and underneath the car and hook up to an anchor point and drag backwards, not recommended or approved but it works when you're in a pinch and bereft of 2000m of rope/cable and half a dozen SB's, Regards Frank.

Yeah, I thought the snatch strap was a bad idea, but for the reason it would be springy, and not give you a solid pull. But, if I was stuck on my own, I would use what I had. I'd even wrap a chain around a tree, if that was all I had. You do what you have to do.

Haha i loved it when i saw this thread was still going. Thanks for the videos bob, id never seen that before - hopefully I'll never need it!

Originally Posted by Tank

The 3rd. block attached to the tree was also redirecting the rope/pull and had NO MA,
the 4th block attached to the Toyota (which was overkill) is the only moving block and as it was Supported by 2 parts of rope it has a MA of 2.

Heya frank,

As you say, that 4th block was the one giving the mechanical advantage, and hence allowed the car to be pulled backwards. Im not sure what you mean when you say it was overkill? Without it the truck wouldnt have moved. Can you please clarify? (Not having a go, just wanting to know what you mean).

Cheers

Dan

Originally Posted by bob10

This bloke seems to have winching backwards worked out.

https://youtu.be/_4tI3HtgdCY

Originally Posted by bob10

This, perhaps is a better example, and better explanation. You need to enhance the sound.

https://youtu.be/P0j_9mRB5g8

Hey, I see what they did there....

Originally Posted by Blknight.aus

nope, 3 snatch blocks

Originally Posted by Tank

Bob the bloke with the jeep got it right, except he said he used a Snatch Strap for a tree protector. bad blue, otherwise good.
The bloke with the Toyota was wrong, he claimed that the first block attached to the tree in front gave him a MA of 2, WRONG. If that was the case the next block (2nd.) in the line would have also given him a MA of 2, which it didn't, it merely changed direction of the rope.
But the angle that the 2nd. block was set at had an angle of the rope at over 90 degrees, doubling the load on the rope and the tree protector.
The 3rd. block attached to the tree was also redirecting the rope/pull and had NO MA,
the 4th block attached to the Toyota (which was overkill) is the only moving block and as it was Supported by 2 parts of rope it has a MA of 2.
The simplest way requires 2 snatch blocks (Sb), one SB in front, cable (only) through and back under your car or beside, whichever is the most convenient to a SB attached to a tree behind your vehicle and then attached to the back of your vehicle.
In the video with the Toyota the angle of the rope between the 1st. and 2nd. block and onto the third block was excessive and puts undue strain on ropes/cables/SB and tree protectors.
I seen the result of a person using a Snatch Strap(SS) as a tree protector/SB anchor rope. He had to wrap it a number of times around the tree with layers overlapping one another.
After some really tough winching the SS had stretched so tight tat it had melted itself together into one messy lump, one more good pull and it would have failed and god knows where that SB would've ended up. Don't ever use a SS as part of rigging up a Winch recovery, ever, and just for Dave, even easier is to run your cable down over the bottom fairlead roller and underneath the car and hook up to an anchor point and drag backwards, not recommended or approved but it works when you're in a pinch and bereft of 2000m of rope/cable and half a dozen SB's, Regards Frank.

Just to be really picky, in the video of the toyota, counting from the winch its the second pully that is the redundant one its the only one providing a non essential redirection that makes the whole system work. I dont have a top down layout of exactly how it was done but I can easily envision it being done to get the rope clear of the side of the vehicle.

Also agree with the snatch strap round trees thing and if you do have to do it you very carefully lay the strap on the tree so it doesnt cross over itself and if you can you dont just wind the strap around the tree but you pass it through shackles so each "turn" around the tree helps support the load.

Originally Posted by Disco-tastic

Haha i loved it when i saw this thread was still going. Thanks for the videos bob, id never seen that before - hopefully I'll never need it!



Heya frank,

As you say, that 4th block was the one giving the mechanical advantage, and hence allowed the car to be pulled backwards. Im not sure what you mean when you say it was overkill? Without it the truck wouldnt have moved. Can you please clarify? (Not having a go, just wanting to know what you mean).

Cheers

Dan

What I mean by overkill was that he could have just hooked directly to the rear of the toyota, for the demo, unless he was bogged to the chassis there is no need for the last block, who carries all that gear, maybe if you are with a bunch of people who you could borrow a couple of blocks off, but if you're on your own you're not likely to have several snatch blocks.
Bob10 the only reason I don't use a chain around a tree is the damage it will do, but in an emergency, use what you got, except a snatch strap, Regards Frank.

Originally Posted by Tank

What I mean by overkill was that he could have just hooked directly to the rear of the toyota, for the demo, unless he was bogged to the chassis there is no need for the last block,

You're taking the mick right.

if your not.. when you flip your rigging ticket over does it have some fancy fonted text on it that says something like coco pops, cornflakes, wheat bix or kellogs?

without the final block on the back of the vehicle providing at least a 2:1 the system cant work. you'd just wind up stretching the vehicle, stalling the winch or snapping something.

Hi



Cheers

I just thought of another way to try to explain why a single snatch block attached to a tree can give a MA of 2.

I think we all accept the calculations associated with this diagram if we ignore frictional losses for the sake of simplicity.

I believe that we all also accept that the mounts for that green pulley have a load of 20 kg.

I think everyone accepts this one too.


Now for the fun part! Does anyone dispute the calculations in this diagram?


How about now? Still accept the calculations?


How about now? Still happy with the calculations?


Still accept the calculations?


I could add a couple more pictures, but you can probably see where all this is heading. The top pulley is now effectively the winch drum and the 5 kg force in red is being applied by the drum on the winch. Since the drum is round, surely that 5 kg force applies regardless of the angle at which I rotate the arrow.

So if you aren't happy with all the calculations, why not? Feel free to add 10% or 20% for friction, but it is still roughly a MA of 2.

I know others have tried to explain the situation in similar terms before, but I thought the series of pictures might make things clearer.

There is another way of looking at it that I don't think has been mentioned. MA is usually calculated by counting the number of ropes supporting the moving pulley and as far as I know, everyone accept that.

I read an article recently that said that the MA was equal to the number of ropes that are getting shorter. Can anyone show a situation where that description is not correct? If people are prepared to accept that it is always true that the MA is the same as the number of ropes getting shorter, then that might be an easy way to explain why a single snatch block on a tree would give a MA of 2 if the end of the cable is attached to the same vehicle as the winch.