I—distance between top of forestay and the foredeck
J—distance from forestay chainplate to mast
P—distance from boom to top of mast
E—length of boom
Mainsail area is approximately (P * E)/2. This is only approximate, since most main sails are cut with some roach.
Jib area is approximately (I * J)/2. This is also only an approximate because some
jibs are cut with a high clew, to help the helmsman see under the sail or other slight modifications.
Here's JRP's Link :
LINK
JRP... the forum autolinking keyword software is screwing you up.

__________________
Sailingdog
Telstar 28
New England
You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.
—Cpt. Mal Reynolds, Serenity (edited)
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