I don't have a plane, think about one from time to time. Just don't think I could handle one. I have been into the airboats, that is where my question come in. I am looking for a prop to put on a HB.61, where can I find one with a small diameter and a lot of pitch? I am looking for top end speed. The ducted fan unit is in my mind, but I do not have the funds yet for one. This is for a hull I am designing to attempt to make beleivers out of some people. That it is possible for a air driven boat to be just as fast as a water prop driven.

I'd go even further... a properly designed airboat can be faster than any water prop driven boat... if you design it in such a way that it leaves the surface and in fact becomes a plane when it's cruising... this is what makes "hydroplanes" so fast too... minimise contact with the water...

Have you ever heard of vehicles that travel "in ground effect"? If not, do a web search, there's plenty of info out there.

Try this for starters:[link=http://www.du-groundeffect.com/]Designs Unlimited Ground Effect Vehicles[/link]

As for high pitch props... they can be had at any major hobby distributor, most hobby shops, ...
Check out [link=http://www.apcprop.com/]APC propellers[/link]

Thanks, the hull I am desiging is on the lines of a hydro, water contact will be bare minimun. The hulls at DU have a lot more to them than what I am working on. What would be a good prop?

When we talk high speed we are looking at 20+K rpm engines going 180-200mph in airplanes. For this you want a small high pitch prop. For your airboat you want to match the prop to the rpm and speed you are looking for. I would guess your engine would be in the 15K rpm range and your expected top speed would be no more than 70-80mph. This would mean you're looking more for a torque prop than a horsepower prop. I would try a 12X6 or 11X7 prop first and go from there. I would use a wider blade prop like a Master Airscrew to pull more wind.

I have used the MAS on the swamp style airboats, and they do work really well, with a lot of power. The engine I am planing to use is putting out 30,000 and a little over 5hp. As for the speed I have built water prop boats running in the 70 -80 mhp range, and to have a airboat do this also would be great. But my goal is much higher, the record is 122mph. 180 -200 mph in planes, that is hulling.

If you really think you'll get 30K rpm don't use any normal prop, even the sport APCs won't hold up, post the same question to the Pylon guys, they have more experience with the carbon fiber speed props...

I fly a North Star flying boat and I do high speed taxi runs(probably doing 50mph or so) and it's super cool, but 122mph???? man that's going to be something to see!!!!

What the hell did you do to that HB to make it do 30K rpm...?! Did you make a new rod for it too?

Anyway, if that engine is putting out the numbers you say it does, then I would look at the wide blade QM40 props from APC for starters... see how the engine does on that...

If you don't find the prop you need in the APC range... you will probably end up making your own, or recarving a bigger prop to the desired shape and size...

Now I'm going to sound like a dumby. the hb.61 is the engine that I have been using on the swmp style airboats, and I have gave it a thought about useing it on this new project. Then I had a change of feeling and did not post it right. After talking with you guys I realized that the HB would not be enough. The last engine I posted about is a Rossi.61 that has been mod into a .65. I am sorry for trying to get you guys to read my mind. This engine is a marine water cooled, which can run a lot leaner getting more RPM's and HP.
Guys thank you very much for your help, and please keep helping me. This has floored me, that air plane guys helping out a boat guy, this much. Thank you

Whole 'nother puzzle. The marine engine will not turn an air propeller 30K rpm. It's desined to work with a boat prop to get those rpms. If it has long enough crank threads to put an air prop on it I would go ahead and use it though, I assume a full length tuned pipe? You'll want to try to get in the 20K rpm range and a 11X7 would be a good start, use a APC sport prop to test with as the carbon APC pylon props will set you back a bunch. When you get a pix post it for us, we like speed, any speed.