Noise levels

**Duane Scarborough** · 07-09-2009, 07:45 PM

Originally Posted by chuckitt

Yes, It was a stock 35 HP Briggs & Stratton Vanguard. I may get a chance to test the Stage 3 Extreme V Twin sound tomorrow. It does have smaller Mufflers.

Chuck

Chuck,

I figured for sure that you'd have used one of those Stage 3 Extreme V Twins for the first test.

But since this is a 4 foot idle test, I'm guessing that it won't matter a lot. Same with the different props and reduction drives. At least not at idle speed.

Duane

**Flathead** · 07-09-2009, 09:00 PM

So, I'm kinda beginning to get into this sound thing. Always enjoyed a good challenge. I've read information about x pipes, shrouds, lots of tailpipe and where to point them and even about channeling the exhaust into the prop. It appears a lot of the effort seems to be going toward lowering prop sound and keeping the tip speed under .5 mach. Am I getting this right? The faster the prop tip speed the more sound it will produce?

Ignoring for the moment the issue of cost, how about the idea of running multiple smaller props. Each with a tip speed well under .5 mach, yet producing respectable thrust? I'm not referring to counter rotating props, but maybe 2, 3 or 4 mounted on the same plane all powered be the same motor?.... Or would, let's say two props, individually producing 50db each. produce 100db combined? I can't imagine I'm the first to ever consider this so there must be a good reason for not trying it. If the technical issues could be ironed out, is there any potential with this idea?

Bruce

**chuckitt** · 07-09-2009, 09:59 PM

Hey Flathead, you are on the right tract. Many combinations have been tried, even 12 blades with all the same pitch. For drag racing, we stagger the pitch, example: 4 blades at 9 degrees, every 4 th blade; 4 blades a 10 degrees, every 4 th blade; 4 blades at 11 degrees, every 4 th blade: In order they would be 9,10,11,9,10,11,9,10,11,9,10,11. This does not work good at idle so it frees up the motor. The faster the prop turns, the more the blades start working together to form the equivalent of a paddle blade that is 60 degrees wide. Set up this way, it had more snap and developed more thrust than 12 blades set at 15 degrees each. It also developed less sound. There is to many configurations to post them all here. You will have to wait until i finish writeing my book.
Chuck

**buster** · 07-09-2009, 10:09 PM

Bruce,

I am not experienced enough answer your noise questions, however if you want to visit Southern Airboat Forum, They have a subject - Airboat Sound. It is mostly aimed towards bigger boats, but there is probably a lot that may pertain to us.

I see Chuck posted while I was typing. If you need any answers about anything Airboat related, he is the best one to ask. He will give it to you straight

Dave

**Wildfowl** · 07-10-2009, 09:33 AM

Originally Posted by chuckitt

You will have to wait until i finish writeing my book.

Book Huhhhh....Now your holding out on us Chuck. More like an encyclopedia with 3 or 4 volumes dedicated to props.

Vol. 5 Prop theory and application
Vol. 6 Wood Props
Vol. 7 Composites
Vol. 8 Yeah and all that other prop stuff.

Flathead...while there may be a lot of variance in the blades and designs and how they perform what you see currently used is the cream of the cream in efficiency and design. Eveyone is just wringing the towl dry on performance for what is there. That's why there appears to be so much unrest on the issue. Tough to beat a single two or three blade for performance with a modest power plant. If there were any better designs the DOD would have figured it out and our knowlege universe would look completely different than it does today.

Multi drive set-ups are common in hovercraft and you can hold one of them with a rope (running wot) while enjoying a beverage of your choice. If that gives you an idea on thrust from multiple smaller units.

Than again nothing wrong with thinking out side the square.

**chuckitt** · 07-10-2009, 01:32 PM

No, not holding out, just don't have time to write a book on the forum. There is too many different prop configerations to explain in short order. All of these configerations can be seen on airboats in florida and all of them will run the hill. The 2 blade, 3 blade, 4 blade, 4 blade Bowtie, 5 blade, 6 blade, 6 blade bowtie, 6 blade stagger, 8 blade, 8 blade stagger, 9 blade, 10 blade, 10 blade stagger, 12 blade, 12 blade stagger, stacked 2 blade wood props, stacked 6 blades, and stacked turbo props. All of these are sucsessful props when matched to the right power, reduction combination. It mostly depends on the engine power and what you want your boat to do. If you have over 500 hp with a 2.68 gear reduction, don't expect a 3 blade prop made for airboats to have enough pitch to stop the engine from turning more than 5000 RPM. You would need to add another blade, and these blades are 15 inches wide.
Thanks, Chuck

**Wildfowl** · 07-11-2009, 08:25 AM

No doubt Chuck! The concept of the "Encyclopedia Chuckit" is a compliment to your knowlege base. No way you could put what you know in a traditional single volume book. (thats just the librarian in me talkling)

Unless.........you included the bonus book "home made two wheel carts for fun and function" so folks would have something to haul your book around with.

**chuckitt** · 07-13-2009, 09:55 PM

Thanks Wildfowl, without the info i get from you guys posting i wouldn't know where to start. I get what i have learned from building airboats thru trial and error plus what i learn from everyone on the net. When it comes to formating the book, i will need lots of help. I'am not a writer.

Now , why did Diane ask me to build that dang 2 wheel cart?

Thanks, Chuck