How to Use a Snatch Block with a Winch for Off-road Recovery
Learning how to use a snatch block, also know as a pulley block, is an essential vehicle recovery skill for off-roading and overlanding. A snatch block is a heavy-duty pulley inside a metal casing that is used with a winch to recover a stuck vehicle.
Snatch blocks can serve two purposes in off-road vehicle recovery: 1) increasing the pulling force of a winch and 2) redirecting the force of the winch cable to pull the stuck vehicle from a variety of angles. This versatility extends the capabilities of your winch, allowing for recovery of heavier or seriously stuck vehicles or rescues in challenging circumstances.
This article and the video below are focused on undetstanding and using snatch blocks. For guidance on choosing the right snatch block for your vehicle and winch set up, see our guide to the best snatch blocks for overlanding and off-roading.
This article is intended for informational purposes only and is not a replacement for formal, hands-on training. Off-road recovery of vehicles can be dangerous. Check out your local off-roading club or other training programs for basic instruction on off-road recovery techniques.
What is a Snatch Block?
Modern snatch blocks used for vehicle recovery in overlanding and off-roading are fairly simple devices, comprising a pulley (also known as a sheave) sandwiched between two metal side plates and held together with a pin. The side plates can be twisted apart to wrap the winch line around the pulley. When the side plates are lined up, the two holes form an eye that is used to attach the snatch block to an anchor or vehicle using shackles and (in some cases) tree savers or other recovery straps.
How to Use a Snatch Block
Snatch Blocks can be used in a number of different scenarios and configurations in off-road recovery. Here, we’ll cover several common techniques. The physics of using winch snatch blocks can be a bit counterintuitive, but we’ll try to explain where it’s easy to make errors in these common scenarios.
Using a Snatch Block to Increase Winch Pulling Force
A snatch block bolsters the pulling force of the winch by providing mechanical advantage, a function of passing the winch cable around the snatch block’s pulley and back to the vehicle. In the case below (Technique #1), the snatch block is used to roughly double the pulling force exerted by the winch in a self-recovery situation where a tree is used as an anchor. It’s not quite double the force, because of friction added by the snatch block itself.
The winch cable extends from the winch on the vehicle through the snatch block and back to a secure recovery point on the vehicle. While the snatch block reduces the pulling force required by the winch in this configuration, note that the anchor (the tree in this case) is still bearing the entire load of the vehicle. This is one of the most common recovery techniques with a winch and snatch block. You could anchor directly to the tree-saver with a recovery shackle instead of a snatch block, but using the snatch block has the advantage of reducing the strain on your winch.
Here’s a tricky nuance to the physics. If the end of the winch cable attached back to a tree instead of the vehicle, as pictured below, the snatch block provides no mechanical advantage. Since the line is static between the trees, the winch would be required to pull the full load of the vehicle. This is basically the same as attaching directly to the tree-saver with no snatch block involved.
Another common technique involves two vehicles, depicted below, where one vehicle is stuck and the other uses its winch to rescue it. The snatch block is connected to the stuck vehicle with a shackle at a sturdy recovery point. The winch cable runs from the recovery vehicle through the shackle on the stuck vehicle, then connects back to the recovery vehicle with a shackle at a recovery point.
Multiple snatch blocks can be used in a winching and pulley configuration to further increase the pulling power of the winch. Such is the case below, where a second snatch block is attached to the rescue vehicle and the cable passes through it and back to the stuck vehicle. This roughly triples the pulling power of the winch.
This technique can be helpful when the stuck vehicle’s weight exceeds the capacity of the winch or extra force is needed to pull a very stuck vehicle loose.
Using a Snatch Block to Redirect the Winch Cable
Sometimes it is difficult or impossible to use a rescue vehicle winch to pull directly on a stuck vehicle. In such cases, a snatch block can redirect the force coming from the rescue vehicle to pull the stuck vehicle in the ideal direction.
In the situation depicted above, a tree is used as an anchor so that the rescue vehicle can exert pulling force on the stuck vehicle at a 90-degree angle. In this winching configuration, the snatch block is attached to a tree saver strap with a shackle to prevent damage to the tree. In place of the tree, another large object, could be used, such as a secure boulder. In this case, the snatch block doesn’t reduce the force required by the winch to pull the stuck vehicle – there is no mechanical advantage.
How to Connect a Snatch Block to a Tree Saver Strap
As we explained above, you should always use a tree saver to connect your winch line to a tree or rock to prevent damage to both your anchor and your winch line.
When you are using a snatch block to gain a mechanical advantage or redirect the winch line, use a shackle to connect the snatch block to the tree saver. Thread the winch line around the snatch block sheave before connecting it to the shackle.
Only use rated shackles, the manufacture lists the working load limit (WLL) of the shackle. On metal shackles, the WLL on rated will be embossed on the side. If you are using a synthetic shackle, make sure you know its load limit.
The working load limit is the maximum weight that a particular piece of rigging should be used to handle under normal conditions. The breaking strength rating (different from the WLL) is the weight at which a shackle can be expected to fail. The breaking strength is typically three times the WLL.
Don’t sideload your D-ring shackle (see image), as this is not how it is designed to be used and weakens it.
Also, make sure your shackle pin is screwed all the way end. It only needs to be lightly hand tightened but should be all the way in.
How do you increase the pulling power of a winch?
A snatch block allows you to multiple the pulling power of a winch by providing mechanical advantage. If used in the correct winching pulley configuration, a single winch can nearly double a winch’s pulling power. Winch configurations that use two or three pulleys (snatch blocks) can triple or quadruple the pulling power, when set up correctly.
What are the best snatch blocks for off-roading?
There are a number of companies that make snatch blocks for off-roading and overlanding. A few to consider when buying a snatch block are Warn, Rhino USA, Rugged Ridge, Smittybilt, and GearAmerica. For more info, check out our guide to different snatch blocks on the market.
Can you use a snatch block with synthetic cable?
Many snatch blocks can be used with synthetic cables. Ideally, a synthetic winch line should be used with a 8:1 sheave diameter, meaning the diameter of the pulley (sheave) should be 8 times the thickness of the rope. Use snatch blocks where the groove in the sheave where the line sits is U-shaped and not V-shaped, as a V-shaped grove will pinch the line, putting it under unnecessary stress. Check that the grove is free of burrs, which can snag and damage the rope.
Four-Wheeler’s Bible, 2nd Edition by Jim Allen.
Off-Road Driving Manual by Vince Cobley & Dave Phillips