F18 too big and heavy. Yep
The real question is what rig is Nacra putting on the 17. If its an F18 rig than not a good idea for a mixed crew.
Nacra 17 will have a 2 part carbon mast with a scaled down F20 Carbon sail plan.
But as a matter of interest and argument why do you believe an F18 rig is not suitable for an Olympic mixed team? I am ready for a row about this!