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Sailing Windward VMG Record Check

Compare a signed true-wind-angle and through-water-speed record with an independent water-relative windward-VMG reference.

Use this result well

Inputs that matter
Aligned calibrated boat speed through water, signed port/starboard true-wind angle over the same averaging interval and an independent water-relative windward-VMG reference
Output to expect
Signed calculated windward VMG and signed/absolute difference from the entered reference
How it works
Projects STW onto the windward axis; positive means windward and negative means leeward, so downwind records are not silently excluded
  • Align true versus apparent wind, water versus ground speed, port/starboard sign, windward/leeward axis and averaging; compare only with a reference using the same conventions.
  • Use vessel-specific polars/trials and account for sea state, current, leeway, trim, sails, fouling and steering; this is not an optimum-angle, sail, reef, route or race-tactic recommendation.

Choose your path

Built around the job you need to finish

Reconcile a signed true-wind-angle and through-water-speed record with an independent windward-VMG reference while preserving leeward negative output.

Sailor checking one instrument record

Align STW, signed TWA, windward axis and averaging interval.

Enter the record plus a same-frame independent VMG reference.

Sees signed scalar projection and difference without losing downwind/leeward meaning.

Coach comparing a polar or trial point

Avoid treating one cosine as an optimum sailing angle.

Use vessel-specific polar/trial evidence and compare like conditions.

Can identify record mismatch without a universal performance grade.

Skipper choosing sail, reef or route

Keep sea state, current, leeway, trim and warnings above arithmetic.

Use qualified sailing judgment and current official marine products externally.

Does not use the worksheet as a sail or route recommendation.

Authoritative checks for this tool

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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Reference & details

How it works

Signed Windward Projection

Entered STW is multiplied by the cosine of signed true-wind angle. Positive output is windward; angles beyond plus or minus 90 degrees remain visible as negative leeward VMG.

Reference Frames Must Match

STW, true rather than apparent wind, port/starboard sign, windward axis and averaging interval must align with the entered reference VMG.

One Record, Not a Polar

The result checks one scalar projection only. Sea state, current, leeway, trim, sails, fouling and steering remain outside the arithmetic.

Updated: August 2026

Example Scenarios

Enter aligned STW and signed TWA, then compare the calculated windward projection with the independent record.

Compare only the same wind definition, axis, vessel condition and averaging method; retain negative leeward values.

Use vessel-specific polars, current forecasts and qualified sailing judgment for optimum angle, sail, reef and route decisions.

Common Mistakes to Avoid

Mixing apparent wind with true-wind angle

This contract expects signed true-wind angle and STW over the same interval. Do not compare with an apparent-wind or ground-relative reference.

Dropping the sign on downwind VMG

Relative to the windward axis, leeward progress is negative. Preserve that sign instead of relabeling every result as toward wind.

FAQ

The axis is windward. A record moving leeward has a negative projection rather than positive progress toward wind.

Equal-magnitude port and starboard angles have the same cosine, but the signed angle preserves the original tack-side record.

No for this contract. It uses STW and a water-relative wind axis; SOG introduces current and changes the reference frame.

No. One entered record is not a polar or tactical model. Use vessel-specific data and actual conditions.

Use the US Sailing speed-guide, NGA vector reference and current NWS marine products linked in the authority panel.

About Sailing Windward VMG Record Check

This tool reconciles one water-relative windward-VMG record. It is not a vessel polar, optimum-angle finder, sail or reef recommendation, race tactic, forecast, route decision or performance guarantee.