9.9 is pretty big for most small (8-9') inflatables. We have an air floor 10+' with an 8hp two stroke and it's almost too fast. I tried a 9.8 on it and it's scary. Most small inflatables that would be sized right for your 30' boat would only need 3-6hp IMO.
SV Laurie Anne
1988 Brewer 40 Pilothouse