© Adolf Thies GmbH & Co. KG · Hauptstraße 76 · 37083 Göttingen · Germany 021408/04/21
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The individual calculation steps are as follows:
• Break the vectors down into orthogonal components, if necessary.
• Subtract the appropriate components,
• convert into polar coordinates.
The calculation result is the sum of true wind velocity and relative wind direction (TWDS). The
true wind direction in reference to north (TWDE) is calculated by adding the heading (HDG):
TWDE = TWDS + HDG
Approximations
The vector of speed over ground (SOG) is made up of the two vectors speed over water (SOW)
and water movement (WM):
SOG = SOW + WM
The vector of speed over ground (SOG) is specified in telegram VBW with the components
longitudinal and transversal speed over ground.
• If vector SOG is invalid (or lacking), the True Wind is calculated by approximation by
replacing SOG with SOW. This procedure is permissible, if the water movement WM is
marginal in consideration of the speed over water SOW. However, this condition cannot be
verified.
The vector of speed over water (SOW) is specified in telegram VBW with the components
longitudinal and transversal speed over ground.
• If vector SOW is invalid (or lacking), the True Wind is calculated by approximation by
replacing SOG with the longitudinal component of SOW or SOG and disregarding the
transversal components of SOW or SOG. This procedure is permissible, if the water
movement WM is marginal in consideration of the speed over water SOW and the
transversal components are marginal in consideration of the longitudinal components.
However, this condition cannot be verified.
• The longitudinal component of vector SOW is specified in telegram VHV with the
longitudinal speed over water (Log). The longitudinal component of vector SOG is specified
in telegram VTG with the longitudinal speed over ground.
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