Inputs
J is the horizontal foretriangle base. LP is measured perpendicular from the clew to the luff. I is the vertical foretriangle height used for the area estimate.
Rig geometry
Genoa LP and overlap calculator
Use verified J and LP measurements in the same unit. Add I for an approximate sail-area estimate.
Worked example
Example: 120% furling genoa
With J of 4.20 m and LP of 5.04 m, overlap is 120%. With I of 14.0 m, approximate area is 35.3 m² before design refinements.
Tool guide
How to use and interpret this tool
It identifies the conventional overlap percentage of a headsail and, when I is supplied, estimates its simplified triangular area.
Decision logic
Overlap = LP ÷ J × 100. Approximate headsail area = ½ × I × LP. Keep every input in the same unit.
Read the result
Around 100% indicates a non-overlapping sail; higher values indicate increasing overlap. Percentage alone does not prove fit because clew height, track, shrouds and luff length still matter.
Worked example
J 4.20 m and LP 5.04 m produces 120%. With I 14.0 m, simplified area is 35.3 m².
Common mistakes to avoid
- Measuring LP along the foot instead of perpendicular to the luff
- Assuming equal percentages produce equal handling on different rigs
- Ignoring sheet-track and shroud clearance
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