keep it simple.... say anything 8 ft or less can race.... two strokes 35cc, 4 strokes 50cc or twin 20's when they come online.
two classes that run together ... stock/piped ... and run what you brung
maybe run small cards like they do in Europe white for stock class, black for Modded making it easy for ppl on the shore to id boats and close races.
i think what your after is a gentlemans class, much like the Thunderboat's race under today
a group of offshore boats runnin close, lookin scale. sounds like a neat idea
for the starter boat you could rig up a smoke system from a plane easy enuff.
when you see smoke..... you form up behind that boat NOW!!!