RE: Official Airboat classes!
No, 12"long by 10 inches wide. A speed 400 motor is very common, I believe they are 28mm can motors. Direct drive you can make them scream pretty good with a 4.75x4.75 prop. This is what is commonly used in speed 400 pylon racing in airplanes. I'll build up a fff hull this weekend and give it a try, see what I can come up with.