Product Brochure

33
WINCHING TIPS
WINCHES AND
WINCHING TIPS
WINCH SELECTION
When selecting a vehicle mounted winch for any application there are two main
criteria to be taken into account, 1) Power, and 2) Duty Cycle.
1) Power, The winch must be powerful enough to do the job.
If the work being done requires a winch effort of 2.0 tonnes then obviously a
winch with a rating of 1.5 tonnes will not be powerful enough, however, if we
use a winch with a rating of 2.7 tonnes the winch will be powerful enough to do
the job.
NOTE: The power requirements will be similar whether the winch is
electric, mechanical or hydraulic, i.e.: is the winch powerful enough to suit the
application?
2) Duty Cycle, To exert 2.0 tonne effort at the first layer of rope on the
drum of a 2.7 tonne rated winch the winch may be exerting 75% of its available
power, on the third layer of rope on the drum the winch may be exerting 92% of
its available power.
In a typical 2.7 tonne rated electric winch, these figures may equal 300 to
400 amps, any small electric motor drawing this high current will generate an
enormous amount of heat and will have an extremely short life.
NOTE: Unlike the Power requirements, the duty cycle will vary greatly
depending whether the winch is electric, mechanical or hydraulic. An electric
winch operating at 80 or 90% of its rating will have a short life, but a mechanical
or hydraulic winch operating at 80 or 90% of its rating will have a much longer
life.
When deciding which winch will be suitable for
your application the following details should be
taken into account:
a) Load to be moved:
This will include details such as weight of
load, type of load, (vehicle, container, self
recovery etc), if a wheeled load, is the vehicle
running gear in good condition, are tyres
inflated to correct pressure, is the vehicle
being recovered a breakdown or is it accident
damaged.
If not a wheeled load, is the load on skids, if
so, what type of skids, material and position.
b) Terrain that load is to be moved
on:
Terrain details will include surface type,
metalled road, grass, mud, sand or any other
type of surface.
Gradient: (slope), that the load is to be pulled
up.
It should be noted that the surface will be included in gradient details, If the
surface is not smooth, surface irregularities can make a substantial difference to
the effort required to move the load.
Examples:
To push a vehicle weighing, say, 1.5 tonne, along a flat level surface will require
little effort, but if one wheel rolls into a 50mm deep pot hole it will be far more
difficult to push.
Likewise, a wheeled vehicle can be pushed, (or pulled), with little effort when all
tyres are inflated properly, but if one or two tyres are flat, the effort required is
much greater.
From the above, it will be seen that selecting a winch for any application is not
as simple as it may at first appear, If the winch is mechanical or hydraulic the
selection should be simple, If the winch is electric the selection may be less
simple.
A mechanical or Hydraulic winch, as far as vehicle mounted winches are
concerned may be rated on a continuous basis, an electric winch, even a “heavy
duty” electric winch should only be rated as intermittent duty.
A typical application may be general breakdown work recovering saloon cars
and occasional vans, of up to: 3.5 tonnes, duty cycle may be up to 6 operations
per day.
Assuming a ramp angle of, say, 30 degrees the effort required to recover a 3.5
tonne vehicle will be approximately: 2.0 tonne.
A typical mechanical or hydraulic winch rated at 3.6 tonnes will not pull this load
when the rope drum has 5 layers of wire rope, (the winch rating is based on first
layer of wire rope on the rope drum), as rope layers increase, winch capacity
decreases, i.e.: first layer = 3.6 tonne, fourth layer = 1.8 tonne, in this example
a mechanical or hydraulic winch of 4.5 tonne rating would be required.
In this example, if the only power available is electric, a 4.5 tonne electric winch
will pull this load, but, on the first layer of rope on the drum the winch will be
operating at 55% of its rating, on the fourth layer this figure rises to 90% of its
rating, This may be equivalent to 200 to 320 amps, because the higher loads will
only be occasional, this winch will do the job, but will have a shorter life than the
mechanical or hydraulic winch, a pulley block may be necessary to relieve the
load on the winch.
NOTE: In these examples the ramps etc are assumed to be flat, rigid and
smooth.
Whatever type or model of winch is to be used, the owners handbook should
be obtained, read and fully understood, by the operator/s, before attempting to
operate the winch.
THE THEORY OF WINCHING:
For winching purposes the resistance to motion of a wheeled vehicle is
dependent on 4 main factors:
1) The inherent resistance to movement of the vehicle.
2) The total weight of the vehicle.
3) The nature of the surface to be crossed.
4) The gradient up which the vehicle is to be moved.
The ground surface and gradient the load is to be moved over will affect the
effort required to move the load, the approximate surface resistance is as
follows: