Reconcile signed apparent wind, boat speed through water, and an independent water-relative true-wind reference without losing port or starboard tack side.
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Reconcile one signed apparent-wind/through-water-speed record with an independent water-relative true-wind reference without making forecast, sailing or instrument-certification claims.
Preserve whether apparent wind is from port or starboard and use boat speed through water.
Enter the aligned apparent speed, signed wind-from angle, STW and independent reference record.
Sees a reproducible water-relative vector and signed comparison without losing tack side.
Separate vector arithmetic from sensor, alignment and averaging problems.
Inspect signed/absolute speed and angle differences, then verify calibration, heel, upwash and timing externally.
Uses the worksheet as a record diagnostic rather than a calibration certificate.
Keep official forecasts, warnings and seamanship above one onboard record.
Consult current official marine products and vessel/operator limits outside the calculator.
Does not use the calculated vector as a forecast, reef instruction or route approval.
Outputs and checklists are planning aids. Review the linked current authorities and the records, terms, instructions, and requirements that apply to your exact situation before a consequential decision.
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The calculation converts the entered apparent wind-from record to a wind-toward vector, adds the forward boat-speed-through-water vector, and converts the result back to a signed bow-relative wind-from angle.
Negative angles mean port and positive angles mean starboard. Preserving that sign avoids the old 0–180-degree ambiguity and keeps the entered and reference records comparable.
Signed and absolute speed/angle differences compare the calculated record with an independent entered reference. Sensor alignment, calibration, averaging, heel, upwash and current effects remain external checks.
Updated: August 2026
Enter an aligned apparent-wind record and boat speed through water, then compare the resulting water-relative vector with the independent log reference.
Retain port/starboard sign and inspect the signed difference before checking masthead alignment, heel, upwash, averaging window and instrument configuration.
Use the worksheet for one onboard record only; consult current official marine forecasts, warnings and qualified seamanship for routing, sail plan and reefing decisions.
Use negative degrees for port and positive degrees for starboard, both measured as wind-from relative to the bow.
This water-relative vector requires aligned STW. SOG introduces the current vector and changes the reference frame.
Use this calculator to reconcile one signed apparent-wind and through-water-speed record with an independently entered water-relative true-wind reference. It is a transparent vector check, not a forecast, sail recommendation, route decision or instrument-calibration certificate.