I've seen .21 powered cats raced in B hydro here in D12. Were they competitive? Definitely not when the riggers are running right. Can they come home with some wood? Sure, if they finish all their heats and enough of the riggers don't.

I think Paul's point is that spending $300+ on a $300 boat is probably overkill. CMB, Novarossi, MAC, and the OS VZ-M engines are all designed for racing. Because of this they are harder to setup and are less forgiving of abuse (intentional or unintentional). To run one well and have it last, you need to have your "stuff" together. Dropping down a price point, to the now discontinued OS .21 RG-M or the side exhaust OPS .21 will put you at a more reasonable price point and in an engine that still runs pretty well. If you decide to race, you're still in the B class (.21) for IMPBA. And then dropping down one more price point, you can go with one of the .28s, .32s, or whatever, but with the caveat that's already been mentioned, they aren't at all competitive in the classes they would be put in...

Moving on to boats. If you're going to invest in a top of the line engine, why not put it in a boat that's capable of handling the power and will be competitive if you decide to race? You could build something yourself, the Wild thing mono is a good first build and is competitive in B Mono. Plans are available from R/C Boat Modeler. If you want to go with a pre-built hull, there are many choices out there for monos, sport hydros, and tunnels. These are usually fiberglass hulls to which you would install the necessary hardware and do your own painting. There are also a few wood kits out there such as Brian Blazer's Whiplash sport hydro.