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How does Windmeter work?
Windmeter is a composite term for anemometer and anemoscope. While anemometer
measures wind speed, anemoscope provides wind direction.
Wind-mill type is the most commonly used on ships and consists of both transmitter and
receiver. The transmitter transmits the wind direction and speed signals to the receiver. The
receiver converts these signals into wind direction and wind speed values, which are displayed
on indicators. The indicators are mounted, usually, on front bulkhead of ship’s bridge above
the windscreen. The indicators are also provided with dimmer control for adjusting the lighting
for day/night conditions.
Windmeter Indicator
The indicators provide relative wind speed and direction. True wind and direction need to be
calculated mathematically or graphically by using true wind triangle OAT. OAT consists of
three vectors namely: OA (apparent wind and direction), OT (true wind and direction) and AT
(own ship course and speed). Caution needs to be exercised to see that ship’s speed and wind
speed are in same units.
An example of wind-mill type of transmitter is shown in photograph. It is mounted high on aft
mast, free of obstructions. Propeller is attached to the leading edge of the magneto generator.
The rear end consists of tail wing (wind vane). The entire assembly is carefully balanced and
pivoted to rotate freely about vertical axis. The weight is evenly distributed on each side of the
Anemoscope Anemometer
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surface of tail wing. However, the surface area is unequally divided so that the side with the
larger surface area is blown away from the wind direction and the smaller side, where the
propeller is fitted, pivoted to face the wind direction.
Wind-mill Transmitter
Operation and Principle:
Propeller
Tail Wing
(Wind Vane)
Generator in
casing
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EMF generated, calibrated to wind speed in knots and m/s
Anemometer (wind speed measurement) works on principle of generator and anemoscope
(measurement of wind direction) employs the system of synchro motors.
The propeller of the transmitter rotates under the action of wind blowing past, which in turn
causes a small internal AC magneto generator to spin. The generated electromotive force is
proportional the revolutions of the generator, which means proportional to wind speed. The
indicator is calibrated to show the wind speed in knots and meters/second.
Wind direction measurement makes use of the property of the synchronization that can convert
mechanical changes in angles into corresponding electric signals. The anemoscope is
calibrated to show the angle which the relative wind makes with respect to ship’s port bow or
starboard bow. The synchro system works by aligning the shaft at the receiver side with the
shaft at the transmitter side. On alignment, the flow of current is nil, but when transmitter shaft
changes direction, voltage is induced and torque is produced which brings the receiver shaft in
line with that of the transmitter. This angular displacement is displayed as angle between
relative wind and ship’s bow on the indicator.
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Synchro Motor system for direction
Transmitter Receiver
