Also if you run the cable out and attach the block to your anchor and then run it back to the truck you have a fixed block and have gained nothing on the pulling power of the winch. The ratio with fixed block is 1:1
Uhmmm, that is only half true
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Think of it this way: If your snatch blocks are frictionless, the cable has a tension "T" in it, no matter how many times it passes through the blocks.
If you pass the cable from the winch, to a fixed block on a tree, and back to the bumper anchor, you have two cables, each with tension "T" in them, pulling on the tree, and on your bumper. That is you have 2 times the winches force pulling on your bumper.
If instead of attaching the cable to your bumper, you attach a second snatch block to the bumper, and run the cable back to the tree, you then have three cables, each with tension "T" in them, pulling on the tree, and your bumper.
The process continues no matter how many snatch blocks you use.
The executive summary is: When using snatch blocks for straight pulls, count the number of times a cable goes between the two objects you are pulling together, and that is the force multiplier for your winch.
-Chuck
Note: The above is assuming the winch is mounted to the bumper of the truck being pulled.