ASA and PSIA Instructor
Join Date: Apr 2000
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Re: Reefing a headsail???
529 ft² sounds big for a 100% jib on a 27-foot boat. Isn't P just for the mainsail?
I would think jib area is LP * Luff / 2. If Luff = forestay length, then for that boat it's
100% * 11.00 ft * sqrt((34.75 ft)² + (11 ft)²) / 2 = 200.5 ft².
So much for the back of the envelop. You are right, the correct the formula for adjusting the foretriangle area is stated as "(square root of (I squared plus J
squared)/I) times the foretriangle area".
I used the correct formula in calculating the 1.05 adjustment for a 100% jib. If you calculate the foretriangle area of I*J/2 to
191, adjust by the 1.05 and you get the 200.5 that you calculated directly...
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