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.

Foretriangle area (m²)

Foretriangle area I * J / 2.

Jib area (m²)

Measured area of the jib.

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. 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]

Overlap percentage (%)

Jib-to-foretriangle area percentage; 100 percent means equal areas.

• 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.

• Jib Aspect Ratio

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

• Winch Power Ratio Calculator

  Compute ideal winch mechanical advantage as the handle-to-drum radius ratio multiplied by the dimensionless gear ratio. Real handle force is higher because this ideal model excludes friction.

• Comfort Ratio Calculator

  Compute Ted Brewer's motion-comfort ratio from displacement, waterline length, and length overall. When LOA is omitted, it is assumed equal to LWL.