How DO they do that

[Andy Greene]

Not looking for a noise debate, quite the opposite. Im looking for answers on how the guys across the pond can achieve 80db reading and still have competative boats?? The question has been tossed around in the locked thread several times , but the answers never came- anyone ???

 

[tnrcboatracer]

Some of the topic is being discussed on the RCBoat.com thread. THere has been some discussion on how thay achieve it, but more details have been requested.

 

[Andy Greene]

Some of the topic is being discussed on the RCBoat.com thread. THere has been some discussion on how thay achieve it, but more details have been requested.

I know I posed the question - hence the reason for asking here. Still no answers....

 

[HendricX]

Maybe you'll find some answers in a article I wrote for MGB ?

 

[Andy Greene]

Maybe you'll find some answers in a article I wrote for MGB ?

For some reason I cant access the article , I am a member of the site, just doesnt load properly.

Can you share some insight on how you guys go about being SO much lower on DB ? and what (if any) are the performance losses .

Thanks

 

[tnrcboatracer]

Ironically, that muffler can concept is exactly what I designed back in 1996. The one exception is that I run an internal stinger to the fat portion of the pipe for further reduction. I'll try to post a pic of the cad file. One additional baffle to break up the wave forms can be added at the stinger plug by making hte plug a disk with the same OD as the can ID. This plate has many holes drilled in it that total 150% of the stinger area. As I stated before the purpose of this baffle is to break up the wave fronts to multiple small waves.

I have since modified the design to eliminate the outlet stinger. I have several alternating baffle plates with the exit angled 45 degrees to the pipe axis. The outlet is pointed dpwn and to the right to direct the sound away from the meter. And yes, I am pursuing a patent on this design.

 

[tnrcboatracer]

Andy, once you log into the site, look select the how-to articles. It is on the list. I was able to access it. It is a simple cross flow perforated baffle tube design similar to my attachment. The inlet baffle area is 150% of the stinger area, and the outlet side is 130% area.

 

[Andy Greene]

Andy, once you log into the site, look select the how-to articles. It is on the list. I was able to access it. It is a simple cross flow perforated baffle tube design similar to my attachment. The inlet baffle area is 150% of the stinger area, and the outlet side is 130% area.

Thanks Jon.

 

[ozzy2]

Andy, once you log into the site, look select the how-to articles. It is on the list. I was able to access it. It is a simple cross flow perforated baffle tube design similar to my attachment. The inlet baffle area is 150% of the stinger area, and the outlet side is 130% area.

Hi Drew2

What tnrcboatrace has shown you in the drawing is almost the same method that i used to get my 21 and 45 pipes down to the 80db range for the WC last year and still have very good power i use the same pipes hear in Australia unfortunately there isn't a commercially available pipe that is quiet enough and still make great power yet. So we have to make our own pipes.

 

[DaveMarles]

If I'm allowed to mention Naviga, I've used the silencing system below in my tuned pipes since about 1985.

silencer

Its not rocket science and it does not lose any performance on a matched tuned pipe. The extended stinger with a plug in it and holes either side of the plug is another common, simple silencing method that can be made to work but the exhaust outlet noise is only a small part of the noise problem and I can't emphasise that enough. Some of the fastest boats in Naviga are also the some of the quietest because the guys who are good at making a boat perform will also apply effort to reducing the noise level of their boats.

In Naviga I run monos only but the principles remain the same for all boats. Engine noise, radiated pipe noise and induction roar are all factors that need to be addressed. Pipes should be enclosed wherever possible, and engines should be completely cowled. 90's and gas boats in particular have a lot of induction noise and on my own boats I have a thin layer of sound deadening material inside the sides of the hull and the cowl and soon I will also use an airbox on the gasboats because they are still a problem as rpm gets higher.

I see the comments that in Naviga we are using low nitro and the boats are not so fast. Thats not the reality. High rpms are a major noise factor and high rpms are the norm in Naviga with 3.5's running ca 35,000, 45's 29 to 30,000 and .90's 23,000 plus and gas engines 19,000 plus.

 

[just for fun]

If I'm allowed to mention Naviga, I've used the silencing system below in my tuned pipes since about 1985.
silencer

Its not rocket science and it does not lose any performance on a matched tuned pipe. The extended stinger with a plug in it and holes either side of the plug is another common, simple silencing method that can be made to work but the exhaust outlet noise is only a small part of the noise problem and I can't emphasise that enough. Some of the fastest boats in Naviga are also the some of the quietest because the guys who are good at making a boat perform will also apply effort to reducing the noise level of their boats.

In Naviga I run monos only but the principles remain the same for all boats. Engine noise, radiated pipe noise and induction roar are all factors that need to be addressed. Pipes should be enclosed wherever possible, and engines should be completely cowled. 90's and gas boats in particular have a lot of induction noise and on my own boats I have a thin layer of sound deadening material inside the sides of the hull and the cowl and soon I will also use an airbox on the gasboats because they are still a problem as rpm gets higher.

I see the comments that in Naviga we are using low nitro and the boats are not so fast. Thats not the reality. High rpms are a major noise factor and high rpms are the norm in Naviga with 3.5's running ca 35,000, 45's 29 to 30,000 and .90's 23,000 plus and gas engines 19,000 plus.

 

[just for fun]

For those who have been around a while, K&B brought out a .45 pipe used on their engines. It had a tube that was the same size as the largest diameter of the pipe. It extended from the join inthe two cones to about 1.5 inches past the end of the stinger. It then had a flat plate that fitted across this tube. There was five or six louver slots cut into the side of the tube about a third of the way from the start of the tube. They were about .75" to 1.0" in width across the tube. there was no other baffling. there wasn't anything in the expansion aera.

Sound(noise) doesn't go around corners well. Ever notice that when someone is mowing the lawn behind the an object (ie house,solid fence etc ) then comes out from behind the object how much louder the mower sounds. If you can make the exhaust gases go aroung corners and still allow the motor to breathe easily the noise level drops. Sound travels (yes in waves) but effectively in straight lines. Make it go around corners and it beats itself to death.

 

[bzubee]

THose used to be called the potato masher pipes I still have 2 of them. I got them after I saw Steve Ball run his 45 hydro and was so fast and very quiet over 10 years ago.

For those who have been around a while, K&B brought out a .45 pipe used on their engines. It had a tube that was the same size as the largest diameter of the pipe. It extended from the join inthe two cones to about 1.5 inches past the end of the stinger. It then had a flat plate that fitted across this tube. There was five or six louver slots cut into the side of the tube about a third of the way from the start of the tube. They were about .75" to 1.0" in width across the tube. there was no other baffling. there wasn't anything in the expansion aera. Sound(noise) doesn't go around corners well. Ever notice that when someone is mowing the lawn behind the an object (ie house,solid fence etc ) then comes out from behind the object how much louder the mower sounds. If you can make the exhaust gases go aroung corners and still allow the motor to breathe easily the noise level drops. Sound travels (yes in waves) but effectively in straight lines. Make it go around corners and it beats itself to death.

 

[Ian Folkson]

What Dave Marles says is totaly true and his pipes are some of the very best performance pipes made and the quietest as well.

I was disqualified with a mono some years ago at a Naviga champs and the boat sounded to the ear quiet but the resonance from the hull and the engine bay being open it was too loud and i was out of the Final. I have since used only covered in boats and experimented with different grades of rubber mounts and carbon fibre engine mount all of which reduce the noise. As Dave says many gas boats sound quiet but are way over the limit due to the resonances and induction noise from that big carb sucking.

Low noise can be achieved just ask Andy Brown who won the Naviga champs at 80DB.

Even naviga has problems with noise and slowly all the racers start to creep higher but at the next champs it will be run at a venue we will be testing this year and the naviga officers including myself will set the limits for next years champs this will take into account background noise including up to 12 boats running at a time. This may mean that our 80 limit is adjusted up possibly due to the venue by up to 5db according to the class and if you know anything about noise it is a logarithmic scale so 85 is a lot louder than 80.

It can be done even the Naviga tethered hydros run at 80db plus the tollerance at around 130mph they are wood and fully cowled motors and fully enclosed pipes.

Ian folkson Naviga FSRV leader

 

[Andy Greene]

Thanks for the input so far guys . A lot of good thoughts on getting boats quieter. In my opinion THIS is the direction we should be chasing instead of were and how to set the meter. Just my .02 -

 

[Jack ODonnell]

What Dave Marles says is totaly true and his pipes are some of the very best performance pipes made and the quietest as well.

I was disqualified with a mono some years ago at a Naviga champs and the boat sounded to the ear quiet but the resonance from the hull and the engine bay being open it was too loud and i was out of the Final. I have since used only covered in boats and experimented with different grades of rubber mounts and carbon fibre engine mount all of which reduce the noise. As Dave says many gas boats sound quiet but are way over the limit due to the resonances and induction noise from that big carb sucking.

Low noise can be achieved just ask Andy Brown who won the Naviga champs at 80DB.

Even naviga has problems with noise and slowly all the racers start to creep higher but at the next champs it will be run at a venue we will be testing this year and the naviga officers including myself will set the limits for next years champs this will take into account background noise including up to 12 boats running at a time. This may mean that our 80 limit is adjusted up possibly due to the venue by up to 5db according to the class and if you know anything about noise it is a logarithmic scale so 85 is a lot louder than 80.

It can be done even the Naviga tethered hydros run at 80db plus the tollerance at around 130mph they are wood and fully cowled motors and fully enclosed pipes.

Ian folkson Naviga FSRV leader

[/quote Ian You have a P/M