Simon,
INTER 18 sailors that have change to a NACRA F18 in Europe have mentioned some real difference in boat speed. The overall performance of the NACRA F18 is said to be better, whereas the INTER 18 is said to be not so bad in light air. The hull disign, and that I can state myself, makes the hulls slamm more in chop and waves thus slowing the boat down. But there are more xperts out here who can better decribe it themselves.

Fritz