Calculating Winch Forces

By | January 18, 2015

 

Why do we need such large winches?

The new trucks will have 16,500 pound winches mounted on the front and rear of the trucks. 

Until the trucks are completed and weighed we won’t know the exact weight but we estimate the weight to be around 11,200 pounds fully loaded. 

So why do we need such a large winch for a truck that weighs 11,000 pounds? To understand why we went with the largest electric recovery winches available you have to do a little math.

 

Surface resistance

A pull of 1,100 pounds will cause these truck to move on a hard, level surface.

A pull of 3,300 pounds will cause the truck to move on a softer surface, such as grass or gravel,

 

Stuck (mire) resistance:

If the truck is stuck to a depth of the sidewall on the tires:

A pull of 100% of actual weight (11,200 pounds)  will be required. 

This can be accomplished using a straight line pull.

 

If the truck is stuck to the hubs.

A pull of 200% of actual weight (22,400 pounds) will be required.

This can be accomplished using the snatch block to effectively double the pulling power of the winch.

 

If the truck is stuck to the frame.

A pull of 300% of actual weight (33,600 pounds) will be required.

This CANNOT be accomplished using the truck mounted winch.  A HEMTT or off road wrecker or heavy equipment such as an excavator or medium-large dozer will be required to remove this rig.  Using any other method will be dangerous and destructive.

Mired in mud is actually harder to pull because of the suction effect of the mud. Pulling the truck from the highest point possible is helpful to break the suction effect of the mud.

 

 

Damage resistance:

A pull of 7,333 pounds will be required to move if the wheels cannot rotate (as if the brakes were fully applied), the pull required to overcome the resistance (drag) the truck is 2/3 or 67% of the actual truck weight.

Grade (slope) resistance:

Upgrade (vehicle has to be recovered up a slope or grade)

15 degrees – add 25% of LW (14,000 pounds) Single line pull

30 degrees – add 50% of LW (16,800 pounds) Single line pull

45 degrees – add 75% of LW (19,600 pounds) Double line pull using the snatch block