From wiki.bastelbude.grade.de
see also
Terms
vessel's Movement and Orientation
- 'OG' movement over ground
- SOG Speed Over Ground (magnitude) navigation.speedOverGround
- COG Course Over Ground (direction) [0-360°]
- COGt Course Over Ground (relative to true north) navigation.courseOverGroundTrue
- COGm Course Over Ground (relative to magnetic north) navigation.courseOverGroundMagnetic
- 'SH'
- STW Speed Trough Water (magnitude) navigation.speedThroughWater
- HDG Heading (direction) [0-360°]
- HDT Heading (relative to true north) navigation.headingTrue
- HDM Heading (relative to magnetic north) navigation.headingMagnetic
- Course (CRS) – Compass direction that the boat is moving through the water (HDG + Leeway). Note that the difference between CRS and COG is Current. CRS does not include the effect of current.
- Leeway – Leeway is the angle between the HDG and the CRS and results from the lateral movement experienced by the boat as she moves forward through the water
Wind
- AW Apparent Wind (relative to vessel)
- AWS Apparent Wind Speed (magnitude) environment.wind.speedApparent
- AWD Apparent Wind Direction (direction)
- AWDt Apparent Wind Direction (relative to true north) environment.wind.
directionTrue directionApparantTrue
- AWDm Apparent Wind Direction (relative to magnetic north) environment.wind.
directionMagnetic directionApparantMagnetic
- AWA Apparent Wind Angle (relative to HDG) environment.wind.angleApparent
- TW True Wind (relative to surface of the water)
- TWS True Wind Speed (magnitude) environment.wind.
speedTrue speedWater
- TWD True Wind Direction (direction)
- TWDt True Wind Direction (relative to true north) add: environment.wind.directionWaterTrue
- TWDm True Wind Direction (relative to magnetic north) add: environment.wind.directionWaterMagnetic
- TWA True Wind Angle (relative to HDG) environment.wind.
angleTrueWater angleWater
- GW Ground Wind (relative to ground)
- GWS Ground Wind Speed (magnitude) environment.wind.speedOverGround
- GWD Ground Wind Direction (direction)
- GWDt Ground Wind Direction (relative to true north) add: environment.wind.directionOverGroundTrue
- GWDm Ground Wind Direction (relative to magnetic north) add: environment.wind.directionOverGroundMagnetic
- GWA Ground Wind Angle (relative to HDG) environment.wind.
angleTrueGround angleOverGround
use
- AW one can measure onboard a vessel
- TW derived from AW + SH
- historic as OG only became available by GPS
- of interest at performance sailing
- GW derived from AW + OG
- used in weather forecasts and reports
- usefull to plan a route
- denote weather changes
other
- 'CUrrent' movement of water by current, tide, river flows etc. (relative to ground)
- DFT Drift (speed, magnitude) environment.current.drift
- SETt Set (direction)
- SETt Set (direction relative to true north) environment.current.setTrue
- SETm Set (direction relative to magnetic north) environment.current.setMagnetic
calculate Ground Wind from Apparent Wind
- AWS Apparent Wind Speed
- COG Course Over Ground
- SOG Speed Over Ground
- GWS Ground Wind Speed
GWx = OGx - AWx = SOG * Sin (COG) - AWS * Sin (AWD)GWy = OGy - AWy = SOG * Cos (COG) - AWS * Cos (AWD)GWS= SQRT (GWx*GWx + GWy*GWy)- GWD Ground Wind Direction (relative to true north)
GWD = ATAN ( GWx / GWy )
(calculate current)
- COG Course Over Ground
- SOG Speed Over Ground
- HDT Heading (relative to true north)
- STW Speed Trough Water in direction of HDG
- DFT Drift (current speed relative to ground)
DFTx = OGx - SHx = SOG * Sin (COG) - STW * Sin (HDT)DFTy = OGy - SHy = SOG * Cos (COG) - STW * Cos (HDT)DFT= SQRT (DFTx*DFTx + DFTy*DFTy)- SET Set (current direction relative to true north)
SET = ATAN ( DFTx / DFTy )
signalk-derived-data groundWind.js
- https://github.com/SignalK/signalk-derived-data/blob/master/calcs/groundWind.js
- SOG Speed Over Ground navigation.speedOverGround
- AWA Apparent Wind Angle (relative to HDG) environment.wind.angleApparent
- AWS Apparent Wind Speed environment.wind.speedApparent
AWx = AWS * Cos (AWA)AWy = AWS * Sin (AWA)- GWA Ground Wind Angle (relative to HDG) environment.wind.angleTrueGround
GWA = ATAN2(AWy, -SOG + AWx)- GWS Ground Wind Speed (relative to ground) environment.wind.speedOverGround
GWS = SQRT (POWER(AWy,2) POWER(-SOG + AWx,2))
signalk-derived-data windDirection.js
- https://github.com/SignalK/signalk-derived-data/blob/master/calcs/windDirection.js
- HDG Heading
- HDT Heading (relative to true north) navigation.headingTrue
- HDM Heading (relative to magnetic north) navigation.headingMagnetic
- AWA Apparent Wind Angle (relative to HDG) environment.wind.angleApparent
- AWD Apparent Wind Direction
- environment.wind.directionTrue
- environment.wind.directionMagnetic
AWD = HDG + AWA
if (AWD > Math.PI * 2) AWD -= Math.PI * 2
else if (AWD < 0) AWD += Math.PI * 2
Sensors
Heading
SOG and COG
STW
AWS and AWA
