Mainsail planning
Mainsail reefing-area calculator
This simplified geometric estimate cannot determine safe reef locations, loads, balance or hardware engineering.
Worked example
Example: two slab reefs
With P 13.2 m and E 4.5 m, the triangular base area is 29.7 m². Reducing effective luff to 11.4 m gives about 25.7 m² before leech geometry; 9.8 m gives about 22.1 m².
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