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.

Centroid distance (m)

Signed horizontal distance from the foretriangle centroid reference to the lead point.

Waterline length (m)

Length of the design waterline.

Compute sail lead as leadPercent = centroidDistanceMeters / waterlineLengthMeters * 100; signed distances allow the centroid to fall aft of the reference. 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]

Lead percentage (%)

Lead expressed as a percentage of the waterline length.

• 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.

• Helm Balance Ratio

  Express the signed longitudinal separation between sail-plan center of effort and center of lateral resistance as a percentage of length overall.

• 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.

• Roach Area Calculator

  Estimate the mainsail roach area as roachAreaM2 = 0.5 * luffLengthMeters * footLengthMeters * roachPercentage / 100 of the triangular sail area.