Snatch Blocks: A Better Way to Winch
By Paul Ederer, AW Direct Technical Product Support
Snatch blocks are a common tool on almost every tow truck for good reason. Snatch blocks can increase a winch’s line pull and provide several options in difficult recovery operations.
Basically, a snatch block is a pulley block with a swing-open plate and is intended for relatively short cable runs and intermittent service.
When selecting snatch blocks for your truck, verify that the Working Load Limit (WLL) of the winch line and snatch block are compatible. The snatch block must be at least as strong as your cable. You also need to verify that the groove in the snatch block’s sheave wheel is sized for the diameter of your cable. A groove that’s too large won’t fully support the winch line and could cause damaging flat spots while a cable that’s too large can crack the block. To determine the proper size wheel, use a 12:1 ratio. For example, a 3/8" cable dia. multiplied by 12 yields 4.5, which is the ideal sheave diameter for a 3/8" wire rope.
Changing Directions
The primary use of a snatch block is to change the direction of pull. Because blocks are anchored in a fixed position, the wider angle at the block, the less force the anchor point has to withstand. One of the most common direction changes is attaching a snatch block on your bed to feed the wire rope straight into the winch so it winds properly on the drum, and not to one side.
Snatch blocks are also used as anchor points to change the winch line direction from the disabled vehicle or tow truck to increase pulling power. Multiple snatch blocks can even be used for self-extraction by routing the winch line from the back of the tow truck to several anchored blocks to the front of the tow truck.
Increased Pulling Power
CSnatch Blocks can increasing pulling power by having a moving vs. fixed snatch block. In this situation, attach a snatch block to the load so it moves with the load as the winch is operated. The amount of line angle at the moving block determines how much mechanical advantage is gained. Maximum gain is when the input wire rope is parallel, or zero degrees, to the output wire rope. This is called a double line pull. It comes in handy when your winch is not rated for the amount of weight of your casualty. This setup doubles the capacity of your winch and cuts the line speed in half.
Another situation is when the casualty is heavier than your recovery vehicle. In this instance, the tow truck’s wire rope goes through the snatch block attached to the casualty and back to another fixed snatch block and back to the load. This is a triple line pull and gains a 3:1 advantage. The more lines run between the tow truck and the casualty the more the pulling power increases
Artwork provided by WreckMaster
Lubrication
When lubricating snatch blocks, use either sodium- or lithium-based grease. Bronze bushed blocks and sheaves generally need to be lubricated after 8 hours of continuous usage, or at least every 14 days with intermittent use. Roller bearing blocks and sheaves can handle 24 hours of continuous use before needing lubrication, but the same guideline of 14 days with intermittent use applies. Swivels follow the roller bearing lubrication schedule. Always follow your particular manufacturer’s lubrication timeline.
Inspection
Wear is a fact of life and will eventually affect the load a snatch block can handle. This means that regular and frequent inspection is needed. During inspection, keep the following in mind:
Deformation of any part is an indication of overload and the snatch block must be replaced immediately.
Swivel end-play of more than 1/16" is a danger sign. Replace the snatch block immediately.
Spreading side plates are caused by overload and must be repaired or replaced.
Looseness in the side plates are a sign of loose retaining nuts.
Sheave alignment issues such as wobbly sheaves are caused by bearing wear.
Groove wear in the sheave is caused by cable wear and can prematurely reduce wire rope life. Replace grooved sheaves immediately.
Hook latches are designed to hold loose rigging under slack conditions. Replace any damaged latches.
Any hook deformation, crack, gouge or distortion needs to be replaced immediately.
Having several snatch blocks on your tow truck can provide options when faced with challenging recoveries. Keeping them in proper working order will ensure they are ready when you need them most.
For more information, contact AW Direct’s Technical Service Specialists Monday through Friday at 1-800-243-3194.
AW Direct | Answering the Call™ 1-800-243-3194 | awdirect.com
Before using any equipment described, be sure to read, understand and follow all manufacturers instructions and guidelines.
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