Dump Truck Live

RECOVERY SCENARIO

Apparently had a commercial vehicle garbage truck that’s backed off of a ditch and needs to be recovered. It’s unclear from the photograph whether it was overturned prior to the recovery effort, but regardless, we will take an opportunity to look at some of the aspects of this particular recovery.

The first question you may ask yourself is, ’what is the mechanical advantage of the layup?’. You’re going to observe that multiple lines are connected to the load. You could apply the Golden Rule to Winching and begin counting starting from the rear. 

There’s one snatch block, a second snatch block, maybe even a 3rd or 4th. We know now from our conversations about Angle Factor Multiplier, there are large angles included at each block. Therefore, we know that we don’t have true 2:1 mechanical advantage at each snatch block.

Additionally, note that the wire ropes exit the wrecker boom and then terminate immediately at the tailboard or another anchor point on the tow truck. With multiple snatch blocks connected to the load all trying to overcome the same resistance, it’s impossible to establish line load, nor is it possible to calculate the true mechanical advantage. 

Consider that maybe the commercial vehicle had been overturned onto its side. What would the mechanical advantage lay up and look like at that time? The angles would have been much smaller. The attempt would have been made to create lift on the casualty, to help it roll over to its wheels. If we begin with the end in mind, have a look at the angles created once the casualty is on its wheels. The large angles at each snatch block are terribly inefficient with how they transmit line mode through the snatch block to the casualty. We can create a much better scenario to generate lift and transmit full line load and more efficiently through the snatch block by terminating those lines at the boom. That would generate more lift, lower that angle at the snatch block, and improve efficiency of transmitting line load to the casualty through the snatch block. 

When your goal is to transmit as much energy to the casualty as possible while keeping line loads low, an informed operator would consider creating a layup that has lower block angles and truck positioning plays a very important role in this. Boom height and distance from the casualty, all the things are going to affect the ability to lower line load and increase mechanical advantage at the casualty.