Head sail size in % for Precision 21

[eaglecreeksailor22]

My head sail luff measures 27'7" center of ring to ring center. Foot is 10'1" center to center of ring straight across. Will some one please figure exact size in %. 136, 143 etc. my club figures PHRF with exact %.
Thanks in advance, Rich

[tjspiel]

My head sail luff measures 27'7" center of ring to ring center. Foot is 10'1" center to center of ring straight across. Will some one please figure exact size in %. 136, 143 etc. my club figures PHRF with exact %.
Thanks in advance, Rich

This pdf explains how to calculate it:

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[Riggerdood]

Great explanation Tom. I always knew it to be a percentage of mast overlap, but not that it is calculated using J and LP.

[eaglecreeksailor22]

Thanks, will get a measurement soon and do the math. Wish geometry had been that simple in 1963, I might have done better than a "D".