Winch, snatch blocks and things that go bump in the night

[scootertrs]

OK, I did a little research and almost understand how you can multiply the capacity of a winch by using snatch blocks. I can make the connection between the multiplication of load capacity by the number of snatch blocks, but I am still in awe about how that final strand of cable ... or initial strand for that matter, is going to handle the pull of the total weight... I know it sounds easy enough, but the pull of 18 tons is still a pull of 18 tons at the end of the cable... or is it?

in addition, I am not even going to begin to figure out how... you can pull a truck backwards with a front mounted winch... saw that post about a week ago and have been losing sleep ever since...

Luckily, for now, this is just a mental excercise, even though I know that soon enough, I will put the info to good use if uncle Murphy has his way.

Thanking you in advance

Raul

Oh yeah, BTW, Gotta love the deuce!

 

[area52]

Well, if you have one block then you are actually using "two" strands of cable, one to the block and one from the block right?

and never run enough cable out to the last layer on the winch, bad things will happen!

Edit: thats if you bring the cable back to the winch truck itself.

 

[scootertrs]

Thanks for the response... I read the TM, I read most if not all of the posts on the subject... it still is not clear to me... maybe I am not the brightest bulb, but I was always taught to not be afraid to ask... the way I look at it is that the actual pull by the final strand is what it is. Appreciate the help

 

[m16ty]

Even though you can multiply the pull of the winch the load on the cable never goes up. If you use a block and double the pull to 20,000lbs there is still only 10,000lbs on the winch and cable. There will be some loss due to friction but it wouldn't be much. The only way to increase pull is to decrease speed of pull. It's kind of like changing to a lower gear in a transmission. The engine's power didn't increase but you have more available power in 1st than you do 5th, you just won't move as fast. When you use a block to double pull if your winch winches in 10' of cable the load will only move 5'.

 

[scootertrs]

I hate to say this, but as I see it, it is damn close to a miracle!

 

[rizzo]

think of it as gears. when you put a block in you are now pulling at half the speed. just like shifting in to a lower gear.

as far as the fact that you get twice the pull power you now have twice as many cables. the winch is NOT pulling double it is still pulling the same. now that you have a block in there it is like your in a lower gear. understand?

 

[m16ty]

It's really just simple physics. Check out this link to better understand it.

HowStuffWorks "How a Block and Tackle Works"

 

[scootertrs]

the link... HowStuffWorks "How a Block and Tackle Works" really clears up a lot of misteries . Thanks again

 

[docfarmall]

the first block dose not double the pull it dosent double till the second block is put in from then on it doubles up

 

[atankersdad]

I teach the theory and practical application of pulleys in Confined Space Rescue class. We use a 4:1 system for pulling individuals out of tanks and vessels. The total energy exerted (work) is the same. Ok, here goes. Using a 4:1 pulley it takes 50 pounds force to move 200 pounds of load. The trade off is that to move the load 1 foot, you must move the rope that you are pulling upon, 4 feet. When you use a pulley to get mechanical advantage, be prepared to use a lot more cable, or be able to get very close. Most uf us will only use a 2:1 block so we cut our distance in half. Did that help???

 

[scootertrs]

Thanks all for the help. I think I have it.

 

[Mt Doom Field Owner]

You learn something new every day

I am going to lock in on that "How Stuff Works" website... I can see me using it a LOT! Wonder if it will explain in layman's terms the physics of a black hole?!!!

 

[scootertrs]

Well ... I guess a little knowledge is a bad thing.... I was testing snatch blocks and pulleys and... darn if I did not get the cable bound up on the spool... any tricks to getting this sucker loose? I am nudging it with an excavator... but would really not want to break anything... cable is not kinked... Darn....

 

[Scarecrow1]

Don't feel bad still have a hard time figureing out how the picture gets on my TV LOL

 

[m16ty]

Well ... I guess a little knowledge is a bad thing.... I was testing snatch blocks and pulleys and... darn if I did not get the cable bound up on the spool... any tricks to getting this sucker loose? I am nudging it with an excavator... but would really not want to break anything... cable is not kinked... Darn....

If the cable gets loose and crossed up really bad and one layer gets over another layer it can get stuck pretty good. Make sure it's just bound up on itself and not something else, hook the end to a tree, and back the truck up with the winch dog disengaged and drum lock out. You should be able to pull it free.