I use a snatch block I picked up at the local tractor supply. Any snatch block that is rated at 2x the winch pulling strength or better is sufficient. You can use one that has a higher rating if you want but you shouldn't have one with a lower rating.
I just posted this in another thread, I'll cut & paste here. There is a lot to know about recovery and tensile strengths. (technically they are fixed pulleys instead of moveable, and moveable instead of compound - but for the sake of arguement...)
Originally Posted by BlueRidgeYJ
Yes, all blocks, shackles, and tree straps must be 2x the winch rating if using a snatch block(s). They are subjected (potentially) to 2x the stall pull of your winch. The line itself is still subjected to 1x the force. This is basically a movable pulley system, and doesn't offer very good mechanical advantage, physics wise. Much better would be to use 2 blocks (tree & bumper), which would essentially form a compound pulley on the jeep, giving significant mechanical advantage (3x rating vs 2x rating). The rigging used then would still need to be 2x the pulling strength. You would need a very complicated block & tackle to need more than 2x SB ratings, I am not sure off hand how / if it could be done with common off road rigging. The trade is distance for force, but the work remains the same (Work = Force ● Distance). So given this thought, your 8K (for instance) winch could easily put 24k pounds of "move-it" with a couple pulleys on your stuck jeep. That is a lot of pressure and force, and you want no part of its failure. The highest load bearing parts are the rigging points. If you use the same anchor, it needs to have strength for each leg (two legs x 16kea = 32k total + safety margin). So don't do that. Poor trees.
If you are buying at maximum load strength or break rating, factor in an aggressive saftey factor, like 3:1 or more. Dynamic loads can be much, much more than the load weight itself. Some equipment factors this in already, particularly real "rigging" equipment (for vertical suspension). You're pulling up a hill, think you can get it, roll it up a little then slide back - when the line catches you can put 5x the weight of the jeep on the line, not a good scenario, especially if the rigging gives way.
The Army recovery manual is a great resource for calculating stuck loads. A 4k lb jeep in the mud up to the frame on a 15% slope can require something like 13k lbs to move. Snatch blocks make it all possible, if rigged properly. If not, they are missles.
This is a good example of the 2x principal - the rear reveives 2x the force of the winch output. If it stalled, that'd be 2x stall pull, less frictional losses which are minimal.
Originally Posted by greentrib
Thought this was interesting. Its how to winch your self out to the rear when your winch is on your front bumper. It takes 3 snatch blocks and tree savers.
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Just as a little aside, if you're ever pulling anything with winch&/or blocks do it at an angle if at all possible or at least make sure you're standing out of the direct line of pull. If anything should break away and you're in line with the cables you'll get a mouthful of cable plus anything else it carries with it. If you can, place a coat/blanket/sleeping bag over the lines so if a line should breakaway the coat/blanket/bag absorb most of the impact.