Snatch block recovery (1 Viewer)

[stuckinnz]

Quote
If (for example) you're going to use your winch to pull something into a tree to hang it (I dunno....maybe a moose). The force on the pulley and branch in the tree will actually be double whatever the weight is what's hanging. So...the moose weighs 300lbs, you hook your winch up, pass the cable up through the pulley and back down to the moose and start winching. The winch pulls with 300lbs force (pulling down), and the moose weighs 300lbs (also pulling down), hence the doubling of weight and the pulley gets 600lbs of weight hanging on it.


I've been trying to follow this thread and I thought I new what I was doing.

Now I'm completly confused are we supposed to be using fish scales or moose scales cos I keep looking but I can't find any over here!!!!!!!!!!



As mentioned before

 

[yycranger4x4]

Remember....whatever forces are on one side of the pulley, have to be equal on the other side. What goes in, must come out (this is physics, and cannot be defeated!). If you have the pulley a tree, and a 300lb moose hanging from a line (passed through the pulley), and back to the winch then you will have the forces on the following picture.

This is also why you can use a pulley block to double the effective power of a winch.

 

[yycranger4x4]

In this example, you've hooked your winch up through a re-direct to pull out a stuck vehicle. The winch line makes a 90* re-direct through the pulley and to the stuck vehicle. The load on your re-direct anchor is 1.41 times whatever the winch load is.

The greater the angle between the winch lines, the less the load will be on the winch lines. If you get to 180* (a straight pull), then obviously the load on a re-direct will be 0 times the load on the winch. At 120* between the winch lines, the load will be 1 time what the winch load is (it will be exactly what the winch is being loaded with). At 0* between the winch line (like in the diagram I uploaded above), the load on the re-direct will be 2 times what the load on the winch is.

This can be explained through the use of some simple algebra. If you remember resultant forces at all from high school math, then this is where it comes into play. I use this kind of rigging all the time with work. This is why I try to stress why it is important to know the forces you're dealing with when it comes to winching.

I hope these drawings help....

PS...I love Google SketchUp

 

[yycranger4x4]

Here is a straight line pull....let's say the winch is putting a 6000lb load on the tree (using a tree saver and a shackle).

 

[yycranger4x4]

By simply adding a pulley into the equation, you effectively double the pulling power of the winch. If the winch is still putting a 6000lb load on the winch line, then the 6000lb is transmitted to the pulley, back out, and back to the anchor point on the bumper.

Because 6000lb is going into, and out of the pulley block, then there is a total of 12,000lb on the vehicle side of the pulley, hence there is 12,000lb of load on the anchor side of the pulley as well. This is where the doubling of the load comes from. Any load on one side of a pulley (or pulley system) must be even, hence any load that goes in, must come out.

The confusion in this setup is often that the pulley is not moving. This is technically true, I can't argue with that. The pulley does actually move in relation to the winch though, in that it gets closer to the winch and bumper anchor.

The tree can be changed with a vehicle. The same is still true.

 

[CruisinGA]

I thought everyone had to take physics in high school?