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

I measurement (m)

Required number in m. Height of the foretriangle on the forestay.

Jib area (m²)

Required number in m². Measured area of the jib.

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

Compute the jib aspect ratio as aspectRatio = iMeasurementMeters^2 / jibAreaM2 using the forestay height I and the measured jib area. Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

Aspect ratio

Returned number. Aspect ratio of the jib 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.
• I measurement must be at least 0.
• Jib 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.

• Main Aspect Ratio

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

• Jib Car Position Calculator

  Compute a jib-car reference position as a selected percentage of foot length, measured aft of the clew. Final trim still depends on clew height and sheeting geometry.

• Jib Overlap Percentage

  Compute jib area as a percentage of foretriangle area. This is an area-ratio proxy; formal LP overlap percentage requires the luff-perpendicular and J dimensions.