The baby airboats fit into a unique place in our sport. Sometimes they're nearly as expensive as a full sized 4 cyl. Lycoming boat and the answer as to why that is, is that it takes almost as much time and attention to detail to build a small airboat as it does a full grown one. Time = money.
Jeff Leserra's little boat that ran in the Quiet Demo in May is a perfect example. His hull is a Diamondback. Yes, it's only 10' 6" long, but it's a Diamondback. Bobby had to put almost as many manhours, and within 2' of the material into building Jeff's hull as he would have to build a hull for somebody that was going to power one with a 180 Lycoming.
Second, the engine/gearbox on Jeff's boat is a brand new (not rebuilt) German made Hirth ultralight AC engine. They're as good as it gets in the ultralight engine market .... highest quality, precision, and reliable. You can buy a 4 cyl. Lycoming from Jurnigan for the same kind of money.
The baby boats are around because they fit your intended use. If you'd like to be able to run all day on 10 gal. of gas, run quiet, and have a boat light enough that you can tow it with a Toyota Corolla then one of the new baby boats is right up your alley, but don't look at them just because you think that smaller should cost a lot less.
I have a couple of 24hp Zenoah ultralight engines. This Fall I want to build a little one man airboat that I can slide into the back of my pickup. Will it be safe in rough water? Nope, but I won't have to trailer it down to Black Creek for a couple of hours of flyfishing and it should run all day on 3 gals. or less. It will be what it is, and for it's purpose it should work just fine, but I'll still probably have close to $5000 in it.
I'm guessing that one of the first things Waterthunder asks you when you call him about having an engine built is "How do you run .... what do you want to be able to do"? There probably won't be a lot of dollars difference in any of your options because you'll still be paying the man for his ability to build exactly the engine you need.
Thunder, I hope this didn't offend you ..... I used you for an example because of the high respect I have for your ability.
Olf
