Somebody had a great evening leading you on the believe that the 18 sq. had 324 sq.ft of sail area !

It truly is 18 sq. mtr. see http://www.watersportverbond.nl/data/5Z2_numdet1_3-7-2006.pdf

Look for nacra 18m2, the m2 stands for meters-squared.

The nacra 16 square is just above it under the name nacra 16vm, vm here stands for "vierkante meter" which in Dutch means "squared meters"

Interestingly enough the true sail area is a little less then 16 sq. mtr. but then again the hulls are longer then 16 feet either. Halve the time I don't understand what Nacra is doing with their models.

But anyway the 18sq truly refers to the mainsail area.

Wouter