Use this sailing calculation as a planning or educational cross-check for navigation, wind and current, rig loads, stability, anchoring, tides, visibility, performance, or recovery under explicitly stated conditions.

Length (m)

Waterline length of the vessel.

Speed (m/s)

Speed of the vessel through the water.

Compute the Froude number using froudeNumber = speedMs / sqrt(9.80665 * lengthMeters). The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

Froude number

Dimensionless ratio of speed to hull-wave speed.

• Actual conditions change with vessel design and loading, sea state, wind, current, tide datum, weather, chart accuracy, equipment, crew, regulations, and safety margins. Simplified formulas do not replace seamanship, approved stability data, or current navigation information.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Cross-check official charts, tide and weather services, instrument data, vessel manuals, and collision regulations; maintain conservative margins and a safe alternative plan.

• Forestay Sag Calculator

  Compute forestay sag with the parabolic approximation sagMeters = transverseLoadPerMeterKg * 9.80665 * stayLengthMeters^2 / (8 * tensionNewtons).

• Gybe Loss Distance

  Estimate the distance lost to gybing from the number of gybes, boat length, and boat lengths lost per gybe.

• Frictional Resistance

  Compute frictional hull resistance using frictionalResistanceNewtons = 0.5 * 1025 * speedMs^2 * wettedAreaM2 * frictionCoefficient with a default coefficient of 0.004.