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

Rudder depth (m)

Required number in m. Vertical depth of the rudder blade.

Rudder area (m²)

Required number in m². Projected area of the rudder blade.

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

Compute the rudder aspect ratio as rudderAspectRatio = depthMeters^2 / rudderAreaM2; high ratio rudders are deep and narrow. Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

Rudder aspect ratio

Returned number. Aspect ratio of the rudder planform.

• 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.
• Rudder depth must be at least 0.
• Rudder area 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.

• Keel Aspect Ratio

  Compute the keel aspect ratio as keelAspectRatio = draftMeters^2 / keelAreaM2; deep fin keels have high ratios.

• Jib Aspect Ratio

  Compute the jib aspect ratio as aspectRatio = iMeasurementMeters^2 / jibAreaM2 using the forestay height I and the measured jib area.

• Main Aspect Ratio

  Compute the mainsail aspect ratio as aspectRatio = luffLengthMeters^2 / mainsailAreaM2; taller narrower sails have higher ratios.