I'm not sure if there is an official measurement recorded in the J/30 records. I did look on the US Sailing ORR page and extracted the following data listed for stability index.
Cert # Yachtname Sail # Class Design Stab Index Disp Flotation VPPDate Offsets Dat Name
40458 AWESOME USA-243 J-30 JOHNSTONE, ROD 98.3 7056 1985-6-25 4/18/12 11:05 am US9190.OFF US40458.dat
41435 CIRCUS USA-26219 J-30 JOHNSTONE, ROD 97.0 6704 Sistership or Class Avg Inclining 4/18/12 11:10 am US9190.OFF US41435.dat
40855 FALCON USA-6019 J-30 JOHNSTONE, ROD 101.5 6994 1984-6-21 4/18/12 11:08 am US9190.OFF US40855.dat
40777 INNISFREE USA-145 J-30 JOHNSTONE, ROD 98.3 7056 1985-6-25 3/1/12 10:44 pm US9190.OFF US40777.dat
41054 MADCAP USA-358 J-30 JOHNSTONE, ROD 97.7 6980 Sistership or Class Avg Inclining 4/18/12 11:09 am us9190.off US41054.dat
41054 MADCAP USA-358 J-30 JOHNSTONE, ROD 97.7 6980 Sistership or Class Avg Inclining 4/18/12 11:09 am us9190.off US41054D.dat
42185 RAFIKI USA-6019 J-30 JOHNSTONE, ROD 101.3 7008 1985-6-25 4/18/12 11:15 am US9190.OFF US42185.dat
41020 SALACIOUS USA-30510 J-30 JOHNSTONE, ROD 98.3 7056 Sistership or Class Avg Inclining 4/18/12 11:08 am US41020.dat

Bill Kneller
Past Owner - Rhapsody J/30 #348
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