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Quieting noise on airboats

rick

rick

Administrator
Published September 29, 2005

Bill Daniel put his foot on the gas pedal of the 19-foot airboat and....

...As such, "Big Iron" is the only airboat to pass Seminole County's airboat noise ordinance.

The law calls for 90 decibels (dBs) at a distance of 50 feet. Daniel's produced 87 dB....

...He spent $4,000 on a quieter four-bladed carbon-fiber prop, $2,500 replacing a noisy prop drive-gear with a silent belt drive and $250 on a pair of mufflers and exhaust pipes.

"His was the only one that passed our sound meter test," Seminole County sheriff's investigator John Locklin said. "And I probably tested 30 to 50 boats."...

Here's the rest: http://www.orlandosentinel.com/sports/orl-outdoors29_105sep29,0,2275381.column
 
Silent belt drive what marketing! When you run a gear box you can slow the prop down more and make it quieter.
 
Cool,

Someone stepped up to the plate.

87db is 1/2 the sound energy of 90db. He did good and proved it!!

Jim
 
I don't know about y'all, but $33,000 seems like A LOT of buckaroos to me! What about those of us that can't dish out thousands to be so quiet? I spend every extra dollar just trying to keep my boat reliable and noisy-side-up. Guess I'll just have to be VERY courteous near houses and people. (Of course, I always am anyway) :wink:
 
Rick,

Good article!

Gotta wonder who did the testing?

I'm thinking that I can "tweak" my meter to read what we want it to! To be completely accurate, the required calibration tool is twice the expense of even the best meters!

Basketcase
 
In my opinion getting rid of warp drive props and IVO's should be more important than getting mufflers in order to help cut down noise.
I have never heard a quiet warp drive while on plane. God forbid W.O.T.

I run large mufflers on all my boats but I do understand that people with Aircraft engines don't want to add mufflers but if they could run a more efficient prop they wouldn't be looking for your mufflers in the first place.

(not trying to pick a fight) I know the big props are expensive, just wish we had some type of alternative.
 
Check out http://www.ivoprop.com

It is similar to a warp drive. I hate the noise and I think the thrust is poor on every set up I have run it on.

But back in the day, there weren't as many choices like we have today. But like I said before the cost of these big blades gets rough on the old wallet. Once you have one though you will never look back and your ears will thank you.
 
Fact the quietest airboat I have ever seen without a doubt was a Classic with counter rotating warpdrives with the tip's rounded off. No other airboat that I have seen even comes close! I was talking to my wife in a standard voice and we had a conversation while riding down the St.Johns even at WOT it was quiet.
 
friend of mine joker was running stacked five blade warp drives and were very quiet till a expansion tank wen't through them boat builder replaced them with a 3 blade power shift .he can,t stand the noise lost performance turning the same rpm 5000 rpm with a 2.37 gear box. has ordered ten blades from warp drive to replace the powershift. go figure
 
I think it depends what prop he had.

Every prop has a sweet spot and should be run at the correct speed to have the designed output.

For your Friend running the 2.37 gear box he would need a wide blade Sirius or the new 2.3 Master Blaster prop with the pitch cranked down to not let it turn over 4800 rpm's in order to get the performance and noise level the prop was designed for. In order to get props quieter you have to turn them slower. In order to turn them slower you have to change your reduction unit ratio. In order to get the same push you need a bigger prop.

The Engine, reduction, prop prop have to be all matched up together in the correct order to get the sound and performance that you are trying to achieve.

*now if we can figure a new way that is cheaper, then we will have something great!
 
Dont worry guys ,I got my order in for one of them 2.3 blasters already !It will be hush! !Stay tune same fat channel same fat time!
 
Couple of misconceptions voiced here. Every airplane except experimentals have mufflers. Aircraft engines run better with back pressure. Aircraft engines run better with mufflers.

The sound study picked out prop speed as the likely next target for airboat sound reduction. Many aircraft and auto engine airboaters believe "you have to get on top of the cam" and run a motor designed to operate at 2,750 - 2,900 rpm / at 3K plus - and that a car motor needs to turn 5 - 6 K to be "right".

When the tip speed gets close to 3K, it gets close to breaking the sound barrier and they all get LOUD at that speed. IVOs and old style Warps are loud by design. The new stacked and staggered application of 8 or 10 blade Warp Drives are said to be the quietest props available. Crank up the pitch and crank down the rpms.

I run an aircraft engine and I take no pleasure in a loud airboat. On my old hull and rigging, I had solid exhaust piping with Magna Flow mufflers and my boat was quiet. On this new one, I have ordered and been waiting on Dixon Super Traps now for almost 3 months with no results yet. Guess I'll have to go to plan "B" before Saturday.
 
Big Daddy, that was a great post. Every airplane has a muffler, and even jet aircraft are muffled ...... it's called an attenuation nozzle!! Go figure.

Many years ago I was employed in the exhaust industry, and I remember the upset that occured
when Hot Rod Magazine released the results of a dyno test on staight pipes vs. a system with
the CH60 Maremont muffler that was originally designed for the turbocharged Chevy Corvair. The muffled system made more horsepower AND torque, and it threw all the notions about straight pipes right out the window.

Any internal combustion engine thrives on a little bit of back pressure so that the shock waves in the exhaust have time to prevent over- scavenging the cylinders. All that means is that the explosion that happens in a cylider needs a little bit of time to be allowed to do all of it's work before it's sucked out the tail pipe.

The $20 mufflers are too restictive. But if you spend just a little more I think you will be surprised at not only how much more torque you have, but also how much smoother your engine is, because the carburetion will be a lot more accurate.

BF
 
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