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.

Foot length E (m)

Foot length E along the boom.

Luff length P (m)

Luff length P along the mast.

Roach percentage (%)

Roach depth as a percentage of the triangular area.

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

Roach area (m²)

Additional area contributed by the roach.

• 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.

• Mainsail Area Calculator

  Compute the triangular mainsail area using mainsailAreaM2 = 0.5 * luffLengthMeters * footLengthMeters.

• Sail Area Calculator

  Compute the triangular mainsail area from the luff (P) and foot (E) measurements.

• Reef Percentage Calculator

  Compute the percentage of sail area reduced when sailing on a reefed headsail or mainsail.