True Wind Tool Apparent Wind, Vessel Motion & True Wind Direction

True Wind • Apparent / Relative Wind • Ship Heading • COG / SOG • STW + Current Reconstruction • Sensor Offset • Vector Averaging • Wind Components

True Wind Tool Apparent Wind, Vessel Motion & True Wind Direction

Convert ship-measured apparent wind into meteorological true wind using the vessel’s heading to orient the wind sensor and COG/SOG to remove Earth-fixed vessel motion. Simple mode returns true wind speed, true wind direction, true-wind angle to the bow and vector components. Advanced adds sensor calibration, alternate vessel-motion reconstruction from STW/current, multi-sample vector averaging, scatter/outlier diagnostics, motion-source comparison and sensitivity to apparent-angle and vessel-speed error.

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Need sensor calibration, STW/current reconstruction or multiple wind samples? Click Advanced above.Simple follows NOAA’s ship-wind vector method: heading orients the relative-wind sensor, while COG/SOG supplies vessel motion over the fixed Earth.

Fast6 primary inputs

Wind conventionDirection wind comes from

Motion basisHeading + COG/SOG separated

Apparent Wind → True Wind

Apparent / relative wind speedknots.

Apparent wind direction from bowdegrees clockwise: 000° from ahead, 090° from starboard beam, 180° from astern, 270° from port beam.

Ship heading°T. Used to orient the ship-relative wind sensor.

Course over ground°T.

Speed over groundknots.

Wind-sensor zero-reference offsetdegrees clockwise/starboard from bow positive.

Wind Sensor & Primary Vessel Motion

Raw apparent wind speed

Raw apparent wind from bow

Sensor zero-reference offsetClockwise/starboard positive.

Anemometer speed factor% multiplier applied to raw AWS.

Additional direction correctiondegrees clockwise positive after zero-reference offset.

Sensor heightm above sea. Recorded for context; no automatic height normalization.

True ship heading

Primary COG

Primary SOG

Alternate Vessel-Motion Reconstruction

This diagnostic reconstructs ground motion from a water-referenced vessel vector plus current. It does not replace GPS COG/SOG for meteorological true-wind correction when reliable ground motion is available.

Water-motion course basis

Course through water°T, used if selected above.

Speed through waterknots.

Leeway / lateral water-motion angledegrees clockwise/starboard positive, added to selected water-motion course.

Current set°T toward.

Current driftknots.

True-wind vessel-motion source

COG discrepancy review thresholddegrees.

SOG discrepancy review thresholdknots.

Multi-Sample Wind Observation Register

Each row independently converts raw ship-relative wind to true wind using that sample’s heading, COG and SOG. The Advanced result vector-averages the true-wind flow components rather than arithmetically averaging compass directions.

AWS kn	AWA from bow	Heading °T	COG °T	SOG kn	Weight

Wind / Sensor Quality Checks

Heading source verifiedTrue heading is used to orient the ship-relative sensor. COG/SOG source verifiedGround velocity represents the same observation interval as the wind measurement. Wind-vane zero reference verifiedBow or entered sensor reference offset is correct. Sensor airflow exposure reviewedMast/superstructure flow distortion is understood. Speed calibration reviewedAnemometer factor is supported by instrument/calibration information. Observation interval synchronizedWind, heading and ground motion refer to the same period. Multiple samples reviewedRapid manoeuvres/gusts are not silently mixed into one steady-wind result. Wind convention labeledDisplayed wind direction is meteorological “from” direction.

Wind-calculation limitation: this tool solves horizontal 2-D wind and vessel-motion vectors. It does not automatically correct for mast flow distortion, heel/pitch/roll, sensor dynamics, vertical wind, gust response, height normalization or ship-specific airflow effects. True wind for meteorological use should be based on synchronized heading and Earth-fixed vessel velocity, with sensor geometry/calibration verified.

Method basis: WMO/NOAA ship-observation guidance computes true wind from platform-relative wind plus the ship’s Earth-fixed motion. The ship’s heading is required to orient relative wind measured from the bow, while COG/SOG provide the vessel’s ground velocity. Wind direction is reported meteorologically as the direction from which the wind blows. NOAA ship datasets likewise derive true-wind north/east components using ship heading plus GPS course/speed and recommend sensor locations that minimize superstructure flow distortion.

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