Noise suppression

Doug Sick · Jul 3, 2016

I am heading to Haarlem in the Netherlands for the IMBRA race in August. I have been working on new muffling but am having trouble getting the db under 82. The exhaust is quiet on the bench so the intake is beginning to dominate the sound level. My meter shows a drop of 4 db between the engine compartment and the exhaust area when it's on the bench.

My fellow Euro boaters, any ideas on how to dampen the intake noise. I've lined the cowl with a layer of foam rubber but I still have an open top which may be allowing the sound to escape. I also wonder if the standard Eagle motor mounts are too stiff and are allowing sound to resonate from the hull.

As an interesting sideline, I've been finding the engine works better with the added mufflers. The higher exhaust pressure is making fueling more consistent and the engine stays on pipe better. At 3700 ft we need to push fuel into the carb as the normal draw of a big bore carb does not work in our thinner air.

ALLAN YUEN · Jul 3, 2016

Contact to Roman Agafonov ( Russia) He build good custom muffled long pipe and he has use A/A 45 so He will help you Good Luck!

SayMikey · Jul 3, 2016

The quietest scale boat I ever heard had a silicone isolated stuffing tube

julianconde · Jul 3, 2016

Believe me or not some guys in Germany are using the deodorant can they glue it some

How to the pipe and put the holes at the end. I seen it done at the Brandon race here in Florida.

They did not have nothing towards the from of the engine

charles siler · Jul 3, 2016

Like julian said JB Weld a can to it. Check out pics from winter nationals.

Steven Bryant · Jul 3, 2016

In Europe we have very strict sound/noise regulations, in a public area the noise has to be 82db or less at 10 meters(from memory) to get around this most people use standard muffled pipes from CMB or Dave Miles. But for those who want to run a different pipes we have to improvise, and a deodorant can has come in very handy more than once. We also use high temp insulating tape to wrap the pipe with especially with the gas engines.

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Doug Sick · Jul 4, 2016

I think my exhaust is adequate. I've built two exhaust cans, one looking like a standard available aftermarket (on the end of an AA 45 muffled pipe) and a bigger/longer one (about 5 inches by 1.25 inch) made from plastic conduit (to reduce radiated noise). As I said in my original missive, my db meter is showing the noise emanating from the intake are appears to be higher than the exhaust area.

I don't see any quick fixes, just a lot of trial and error to find the right combination.

The spec I've seen on the NAVIGA site is 80 db at the waters edge. Pretty tight. 85 is easy, the remaining 5 is the hard part.

Steven Bryant · Jul 4, 2016

Just make sure your in lane one and all will be good. How far away from the intake are you when you take the reading?

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Phil Fowler · Jul 4, 2016

Try a Baffle between the carb and the open top. Sound doesn't like to travel around corners.

rctinman · Jul 4, 2016

Hi Doug..

As you know, I'm in the same boat as you. (pun intended, LOL) I've added a muffler to the end of a 45 Parabolic pipe, and ended up around 82-83 db. Next, I'm going to try wrapping the pipe and muffler to see what happens. I'll keep you posted with results, I'll also keep an eye on this thread.

Thanks,

Steve Ball

Doug Sick said:
I am heading to Haarlem in the Netherlands for the IMBRA race in August. I have been working on new muffling but am having trouble getting the db under 82. The exhaust is quiet on the bench so the intake is beginning to dominate the sound level. My meter shows a drop of 4 db between the engine compartment and the exhaust area when it's on the bench.

My fellow Euro boaters, any ideas on how to dampen the intake noise. I've lined the cowl with a layer of foam rubber but I still have an open top which may be allowing the sound to escape. I also wonder if the standard Eagle motor mounts are too stiff and are allowing sound to resonate from the hull.

As an interesting sideline, I've been finding the engine works better with the added mufflers. The higher exhaust pressure is making fueling more consistent and the engine stays on pipe better. At 3700 ft we need to push fuel into the carb as the normal draw of a big bore carb does not work in our thinner air.

Kez · Jul 4, 2016

I remember when Octura first introduced the Humdinger mount, they talked about reducing the intake noise by adding a Bru-line air filter. The kind meant for airplane. They said there was no loss in power but the foam filter muffled the intake noise.

Rudy Formanek · Jul 4, 2016

European (and Japanese) boaters have been forced for so long to deal with very strict noise regulations. It seems in the US we would rather lose a site than comply with noise restrictions. FAI noise regulations doomed two-cycles in pattern. Muffling nitro boat engines to international standards is not an easy task. Look to the Japanese or the Europeans for solutions, it has been a long and difficult path.

the german · Jul 4, 2016

Doug

Contact Niklas Edlund here on IW .He can probably help you out and also check out the website of Niklas !

Here is the deodorant spray can idea ( scroll down to his KEP's T2-45 prototype pics )

http://www.ne-stuff.net/search?updated-max=2015-07-01T16:00:00%2B02:00&max-results=10&start=10&by-date=false

By the way ........ at the '86 NAVIGA world championship in Italy we stole the teaspoons from the hotel and mounted them on the exhaust outlet to redirect the noise away from the shore

Alex

NITROSNIFER · Jul 4, 2016

Steve, Doug and I have been trying several different ways to get them under 80db, I have my AA45 pipe wrapped with a second muffler and still can get it under. THe funny thing is that it's not the exhaust that's loud now. You can easily hear the air change from half to wide open etc. I know we are close real close but we both want to make sure that they don't pull us off due to being to loud. In lane 1/2 we are under with ease, so I guess lane one it will have to be

rctinman · Jul 5, 2016

Doug and Kevin, I'm going to try the deodorant can over the pipe and muffler. Am also going to look for an R/C car aircleaner to put on my carb, see what that will do. Won't have a chance to find out till this Sun.

Thanks,

Steve

DickJones · Jul 8, 2016

rctinman said:
Doug and Kevin, I'm going to try the deodorant can over the pipe and muffler. Am also going to look for an R/C car aircleaner to put on my carb, see what that will do. Won't have a chance to find out till this Sun.

Thanks,

Steve

Steve, If U turn the stinger exhaust wave 180 degrees 3 times before the wave exits the stinger U will be low enough to meet the 80 db's for the race.

Mobydickk

rctinman · Jul 9, 2016

Thanks Dick! Here's what I've come up with this time. Things went well till it came to put the louvers in. Not the best looking, but I think it will work

dick jones said:
rctinman said:

Doug and Kevin, I'm going to try the deodorant can over the pipe and muffler. Am also going to look for an R/C car aircleaner to put on my carb, see what that will do. Won't have a chance to find out till this Sun.

Thanks,
Steve

Click to expand...

Steve, If U turn the stinger exhaust wave 180 degrees 3 times before the wave exits the stinger U will be low enough to meet the 80 db's for the race.
Mobydickk

Don Ferrette · Jul 9, 2016

rctinman said:
Thanks Dick! Here's what I've come up with this time. Things went well till it came to put the louvers in. Not the best looking, but I think it will work

dick jones said:

rctinman said:

Doug and Kevin, I'm going to try the deodorant can over the pipe and muffler. Am also going to look for an R/C car aircleaner to put on my carb, see what that will do. Won't have a chance to find out till this Sun.

Thanks,

Steve

Click to expand...

Steve, If U turn the stinger exhaust wave 180 degrees 3 times before the wave exits the stinger U will be low enough to meet the 80 db's for the race.

Mobydickk

Click to expand...

Nice!

Andy Brown · Jul 9, 2016

One extra muffler can added to any of my muffled pipes worked for me and Al for many years. Al got called in one year, but he was running a single muffler can on a 15cc boat. We did not do anything to reduce carb noise.

When you are on the course with other boats there is sound wave cancellation going on.

Just don't run full bore near the meter when you are alone on the course.

rctinman · Jul 9, 2016

Thanks for the info Andy! I'm hoping what I have will do the trick. Will find out tomorrow. Just don't want to make the trip only to get tossed. LOL

Steve Ball

Andy Brown said:
One extra muffler can added to any of my muffled pipes worked for me and Al for many years. Al got called in one year, but he was running a single muffler can on a 15cc boat. We did not do anything to reduce carb noise.

When you are on the course with other boats there is sound wave cancellation going on.

Just don't run full bore near the meter when you are alone on the course.

Noise suppression

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