Noise levels

[Flathead]

Hi all! First, let me introduce myself. I've been casually interested in airboats for as long as I can remember but have never owned one. Always liked fishing the rivers (hence the username) and have thought an airboat would be perfect to get into those shallow areas I cannot reach by conventional boat. Last year, over the Christmas holidays our family vacationed in Florida and we went to the everglades for an airboat ride and ever since, I cannot get the idea of having an airboat off my mind. Unfortunaly, I live in Minnesota where we have a 82db sound limit on all watercraft. Anybody have any input on the subject? Would a mini be quiet enough to fall under the legal limit, and if so, would it have enough giddyup to make it worthwhile to use?( a highly subjective question, I know)

Thanks,

Flathead

[buster]

Hi Flathead,

Welcome to the forum. Where about in Minnesota are you located? I'm near Wyoming (just north of Forest Lake). Airboats are few and far between in MN., except for the fire and rescue units, but you probably know that.

I was unaware of the noise limit. I doubt an occasional airboat will have much trouble, but when there are lots of them in any one area is when a problem may arise.

I have not started up my engine yet, but I expect to very shortly, and then we will find out how noisey it is. I am running an 084, and they say it does real well power wise.

Keep in touch, Dave

[Flathead]

Hi Buster,

Thanks for the reply, I'm in St. Francis, not far from Wyoming. Ha! what a small world. I contacted the DNR about noise regulations and that's where I got the info on the noise restrictions. There is also a requirement about having some type of muffler or below the waterline exhaust. I gotta imagine running an airboat is gonna attract some attention. I talked to a guy in little falls who has an airboat and said the DNR almost took his away. Of course he was also running a 501ci V8 with straight pipes and had also had a few warnings.....I think the boat is for sale now.

Bruce

[Duane Scarborough]

Flathead,

Welcome aboard.

One of my objectives is for my boat to be as quiet as reasonable. A 4A084 with decent mufflers is fairly quiet. Or for that matter, any engine can be made quiet.

Its the prop that's going to be the problem. By nature they are noisy, but there are ways to reduce the noise level. One way is to use a reduction drive. This lets you use a longer, higher pitch prop, and lowers the tip speed. Another thing that is supposed to help is to use a wide chord 3 bladed prop.

Whether you can keep it below 82 Db will depend a lot on how the test is done. For example, you might easily pass a 50 foot drive by at 50% cruise speed, but fail under other conditions. Did your DNR contact explain how they test for noise level?

Duane

[Flathead]

Hi Duane,

Nice to meet ya, Here's a portion of the reply I received from the DNR.

3) Airboats, depending on how they are operated and the propeller on the craft, will likely exceed the limits Minnesota (and other states) have on motorboat noise. In Minnesota, the limit under the law for boats and engines built since 1982 is 82 dBA at 50 feet or an equivalent reading at other distances on pass-by test. That information can also be found in our Minnesota Boating Guide on page 22.

In addition, I discovered the state allows a 84db. max measured at idle 4 ft. from behind the motor. Interesting point about the use of a reduction drive to reduce noise. I did not know that......thanks fot the great info! My quest for an airboat is still alive!

Bruce

[buster]

Flathead,

Well things are looking up. Duane and myself were just talking about the lack of other airboats in our areas. I bet you are less than ten miles west of me. I live a half mile north of the Lynnwood fire station on 85.

We should maybe get together and talk airboats, ar somethin'. Of course, then you might give Duane all my secrets

You can check out my build in the "Rebuilding an Aircat: topic if you like.


Dave

[Duane Scarborough]

Hi Duane,

Nice to meet ya, Here's a portion of the reply I received from the DNR.

3) Airboats, depending on how they are operated and the propeller on the craft, will likely exceed the limits Minnesota (and other states) have on motorboat noise. In Minnesota, the limit under the law for boats and engines built since 1982 is 82 dBA at 50 feet or an equivalent reading at other distances on pass-by test. That information can also be found in our Minnesota Boating Guide on page 22.

In addition, I discovered the state allows a 84db. max measured at idle 4 ft. from behind the motor. Interesting point about the use of a reduction drive to reduce noise. I did not know that......thanks fot the great info! My quest for an airboat is still alive!

Bruce

Flathead,

Both the 82 db pass by test at 50 feet, and the 84 db idle test at 4 feet should be easy to pass. A properly muffled engine will be well below 84 db at idle speed, and at idle speed the prop makes almost NO noise.

So, you need to get hooked up with Buster, learn ALL of his secrets, and pass them on to ME.

But remember this: Just passing a mandated sound test doesn't mean that you'll be welcomed every where if you drive like an A$$Hole. I've ridden Harleys for a long time, and I've heard everything from "Wow, I like that sound" to "You need better mufflers", depending on how I was riding at the time.

Duane

[Sandman]

Hola Flathead!
Welcome to the Mini Forums.
I'm a new guy.. but because of you.. I'm not "THE" new guy!!
Drive fast take chances!! Prop side up!! whoohooo!!
but keep it quiet! >grins<

[chuckitt]

Hey Flathead, We will try tomorrow to do the idle at 4 ft test on an 084 and a 35 Briggs boat. Will let you know what the outcome is.
Thanks, Chuck
In Florida, we have started using the word SOUND instead of NOISE. It sounds so much better.

[Duane Scarborough]

Chuck,

Yeah, NOISE is a very negative word. Let's call it SOUND.

Duane

[buster]

Chuck and Duane

Could we get by calling it music, or the tunes, somethin' like that

Dave

[chuckitt]

We done sound test on 2 boats today.
The 084 boat, 4 ft from the side. 80 db 4 ft from the rear, 82 db
The 35 Briggs boat, 4 ft from side, 72 db 4 ft from the rear 76 db
These were both taken at idle.
Thanks, Chuck
They didn't make any noise, just sound.

[Duane Scarborough]

Chuck,

I'm very glad you did those tests.

I told you that I was amazed at how quiet Scorpy was back in April when you were running it on the trailer at the shop with no mufflers, just flexpipe. It was also pretty darn quiet on the river at WOT. I didn't really hear the exhaust as much as the prop.

Now, about those tests you did today:

What kind of mufflers did each boat, the 084 and the Briggs have?

Thanks,

Duane

[chuckitt]

The 084 had the IH1 mufflers from Tractors supply.
The 35 Briggs had the SS mufflers I make here at the shop.
Chuck

[Flathead]

Point taken on the noise vs. sound topic. Looks like building an airboat still has some potential. Woo Hoo! Thanks for the great feedback and Chuck, thanks for those sound levels. I'm not really familiar with the 35 briggs though. Would that be a 35hp briggs & stratton? (spelling). You all have been great..!

Bruce

[Duane Scarborough]

Flathead,

Knowing Chuck, that was probably not a normal 35 HP Briggs and Stratton engine.

Most likely it was a very highly souped up 35 HP Briggs and Stratton engine.

JMHO....

Duane

P.S. I've seen and heard some of Chucks custom made SS mufflers. They produce no NOISE at all, but they do SOUND nice.

[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

[chuckitt]

OH, I forgot, the 084 had a 2 blade 63 inch Whirl Wind Prop and the Briggs had a 3 blade 60 inch IVO Prop.
Chuck

[River Rat]

OH, I forgot, the 084 had a 2 blade 63 inch Whirl Wind Prop and the Briggs had a 3 blade 60 inch IVO Prop.
Chuck

Chuck, Did that 084 have a reduction unit turning that 63" Whirl Wind?

[David]

084 had a reduction on it