Bob,
I think the issue is the definition you use for LP%. There are different definitions, and you used a different one than I used. I used the ratio of LP on the sail being rated to a right triangle that is the LP of a 100% sail. You used the ratio of LP/J. Both seem to be accepted standards.
The definition I used is extracted from Wiki at this link:
http://en.wikipedia.org/wiki/Genoa_Jib Genoas are categorized by the percentage of overlap. This is calculated by looking at the distance along a perpendicular line from the luff of the genoa to the clew, called the LP (for "luff perpendicular"). A 150% genoa would have an LP 50% larger than the foretriangle length.
Below are the definitions with J/30 parameters in parenthesis, followed by the calculations I used:
I= Height of foretriangle. Measured from deck sheer line abeam the mast to the point of masthead/forestay intersection. (34 Ft = 10363mm)
J= Distance from foreside of mast to the point of intersection of the forestay with the deck. (11.5 Ft = 3505mm)
LP= Shortest distance between the clew and the luff of the genoa. (distance of line perpendicular from luff to clew).
A 100% LP sail is a right triangle that fills the area defined by I and J resulting in the base LP as follows (using math for right triangles)
LP(base) = I*J/Sqrt(I^2 + J^2) = 3320.2mm
Thus using values from class rules for max and min:
LP% max = 5665 / 3320.2 = 158.1%
LP% min = 5250 / 3320.2 = 170.2%
The new lower value would be:
LP% min = 5000 / 3320.2 = 150.6% (I had a typo above and said 151.6%)
I believe the class rules infer this definition because 163% is in the mid range of the specified parameters.
[This message has been edited by Rhapsody #348 (edited 10-21-2008).]