Quote:
Originally Posted by RichH
Once you arrive/calculate (or do this 'graphically') all further dimensions will be directly proportional (ratio'd). Eg. a 120% LP will have is 'foot dimension' at ~120% of the 'J' dimension.

Hm... this is essentially saying, "If x is an altitude of a triangle, then an adjacent side is also x." That's only true if that side is perpendicular to the side that the altitude is perpendicular to. I think the angle at the tack of a jib is usually less than perpendicular.
There is a proportionality, but only in the component of the measurement perpendicular to the luff.
Okay, to anybody still confused about LP, it's just the width of the sail. Just imagine stretching the sail out with the luff along the ground and the clew held up off the ground so the sail is flat. The LP is now the height of the clew off the ground.