© Adolf Thies GmbH & Co. KG · Hauptstraße 76 · 37083 Göttingen · Germany
021408/04/21
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Page 12 of 13
4 Operational Characteristics
Definitions:
The „Relative Wind“, the heading and the ship’s speed must be available for calculation of
the „True Wind“. The “Relative Wind” is measured by means of a wind transmitter installed
on the ship’s bow. Heading and ship’s speed are received via the following NMEA telegrams:
NMEA
telegram
Interface
Heading*
GYRO
Ship’s speed *
LOG
Remark
VBW
COM 3
---
2
SOG > SOW **
VHW
COM 3
2
3
---
VTG
COM 3
---
1
---
HDT
COM 2
1
---
---
VTG
COM 3
X
X
only with
4.3251.0x.902
*: Priority (Top: 1)
** With the VBW telegrams the SOG values („speed over ground“) have priority before the
SOW values („speed over water“).
•
True Wind
Reference direction of the
True Wind
is geographic North. Zero degrees corresponds to
wind from the north with an increasing angle in a clockwise direction.
•
Relative Wind
Reference direction of the
Relativen Wind
is the ship’s longitudinal axis. Zero degrees is
indicated in direction of the ship’s bow and corresponds to wind from the front. The angle
of
relative wind direction
increases in a clockwise direction.
Conversion of the parameters at hand into „True Wind“ takes place as follows:
Calculation of True Wind
The vector
Relative Wind Velocity
(RWV) is made up of the two vectors S
peed Over Ground
(SOG) and
True Wind Velocity
(TWV).
RWV = SOG + TWV
The relative wind velocity (RWV) is hereby measured by means of an anemometer and a vane
on the ship, the
Speed Over Ground
is transmitted via a serial interface and the
True Wind
Velocity
is calculated:
TWS = RWS - SOG
This vector subtraction is carried out in an orthogonal coordinate system, which is connected
to the ship.
