Inputs
P and E define the mainsail triangle. I and J define the foretriangle. LP replaces J in the simplified headsail-area calculation. Roach allowance is an optional estimate only.
Rig geometry
Mainsail and headsail area calculator
Use this for early comparisons only. Finished sail area depends on real edge curves, roach, hollow, clew height and design shape.
Worked example
Example: preliminary inventory comparison
P 13.2 m and E 4.5 m gives 29.7 m² triangular mainsail area; a 5% allowance gives 31.2 m². I 14 m, J 4.2 m and LP 5.04 m gives about 35.3 m² headsail area.
Tool guide
How to use and interpret this tool
It creates comparable preliminary areas for a mainsail triangle, foretriangle and headsail.
Decision logic
Mainsail triangle = ½ × P × E. Foretriangle = ½ × I × J. Headsail ≈ ½ × I × LP. Optional roach percentage is applied to the mainsail triangle.
Read the result
Use the figures to compare scale and check quote consistency. A sailmaker's finished area will differ because real sails have edge curves, roach, hollow, clew height and design shape.
Worked example
P 13.2 m and E 4.5 m gives 29.7 m². A 5% estimate becomes 31.2 m². I 14 m and LP 5.04 m gives about 35.3 m².
Common mistakes to avoid
- Presenting simplified area as certified area
- Adding roach twice when comparing a quoted finished area
- Entering maximum rig limits as guaranteed finished dimensions
Professional verification
This tool supports briefing and comparison. It does not replace measurement on the boat, structural engineering, class or safety rules, or a sailmaker's final design.
Continue the decision