Use this sailing calculation for planning or education when the vessel, units, reference directions, environmental conditions, and assumptions are explicitly known.

Significant wave height (m)

Required number in m. Significant wave height used to classify the Douglas sea state.

The cited overview of Wind wave supplies background for the terminology and domain context used by this tool.^[1]

Look up the Douglas sea state from zero to nine for a significant wave height in meters using standard inclusive upper bounds. Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

Douglas sea state

Returned integer. Douglas sea state from zero (calm, glassy) through nine (phenomenal).

• Vessel design and loading, sea state, wind, current, tide datum, weather, chart accuracy, equipment, crew, and safety margins can make real conditions differ from a simplified result.
• Significant wave height must be at least 0.
• Use finite inputs in the displayed units, preserve source measurements and assumptions, and independently verify consequential decisions.

Cross-check current charts, tide and weather services, instrument data, vessel manuals, and applicable navigation rules, and retain a conservative alternative plan.

• Beaufort Scale Lookup

  Look up the Beaufort wind force from zero to twelve for a wind speed in knots using standard inclusive upper bounds.

• Fully Developed Wave Height

  Estimate deep-water significant wave height for a fully developed sea as 0.21 U²/g, converting the supplied wind speed from knots to meters per second.

• Code Zero Wind Angle

  Estimate the true wind angle for a code zero using codeZeroTwaDeg = round(50 + apparentWindKt * 0.3), clamped to 40 through 70 degrees.