Handbook of Winching Techniques

THE THEORY OF WINCHING
If we combine the weight of the vehicle, the type of surface to be transited and the gradient to be overcome we get the
calculation.
Weight of vehicle + Gradient x Weight of Vehicle
Surface to be transited 60
Therefore the winching formulae is
W + (G x W) = Effort Required
S 60
Where W = Weight of vehicle
S = Surface to be transited
G = Angle of gradient (in degrees)
i.e. Vehicle weighing 4,500 lbs is to be winched up a sand dune of dry loose sand with a slope of 15 degrees.
Using the winching formula above.
Where W = 4500 lbs (Vehicle Weight)
S = 1/4 (co-efficient for soft sand)
G = 15 (Slope in degrees)
We have
4500 + (15 x 4500) = 1125 + (1 x 4500)
4 60 4
= 1125 + 1125
= 2250 lbs effort requried to recover vehicle in these circumstances.
If we substitute clinging clay for the surface (co-efficient of 1/2) and 35 for the gradient (slope) in the above equation we
get:
4500 + 35 x 4500 = 4875 lbs Effort Required
2 60
The effort required may be outside the capacity of the winch, (the rating of a winch usually refers to the first layer of wire
rope on the drum). In this case, one solution may be to run out most of the winch cable to enable the winch to be used
at or near its rated capacity, or introduce a pulley block pulley in the winch line to create a mechanical advantage, thus
practically halving the effort required by the winch.