RE: Airboat plans?
I have built quite a few airboats in my days, but unfortunately, have never really drawn up plans for them. I am starting to change that though.
The only plans I have seen published are from a while ago. Flying Models magazine published the 'FM AIRBOAT' and you can still get 'GATOR BAIT' from rcstore.com. These plans are gridded to allow easy upscaling to almost any size you want. It is a basic, no frills flatbottom.
It is also easy to design your own. Using a basic formula of 2:1. Length is 2x the width...12 x 24, 14 x 28 etc. But this can be played with quite a bit and still function very well. Height of the hull is typically around 2". This is enough to get any design started.
Look at some of the pics that are posted in some of these threads, they would be easy to copy just by looking and keep the 2:1 in mind.