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

Fetch (nm)

Required number in nm. Unobstructed fetch over which waves build.

Wind speed (kt)

Required number in kt. Sustained wind speed over the fetch.

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

Estimate the peak period of fetch-limited deep-water waves from wind speed and unobstructed fetch using the dimensionless SMB growth relation. Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

Wave period (s)

Returned number in s. Estimated dominant wave period.

• 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.
• Fetch must be at least 0.
• Wind speed 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.

• 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.

• Crew Drift Estimate

  Estimate how far an overboard crew member drifts as current speed times time in the water plus wind speed times time scaled by a one percent windage coefficient.

• Sail Load Calculator

  Estimate the aerodynamic load on a sail from wind speed and sail area using a flat-plate drag model.