TrueWind

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Revision as of 13:16, 1 November 2018 by Kannix (talk | contribs) (vessel's Movement and Orientation)
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see also

Terms

vessel's Movement and Orientation

  • 'OG' movement over ground
    • SOG Speed Over Ground (magnitude) navigation.speedOverGround
    • COG Course Over Ground (direction)
      • 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)
      • 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

  • GPS receiver

STW

AWS and AWA