Quieting Boats down

[Brian_Nelsen]

I started this thread after reading some stuff in the DB meter debate thread. Lets hear what works for you. Please provide as much data as possible and even DB reading from your site if you have them (Please don't turn this into a debate about how its measured) that way we can start to see what might and might not help. I posted the following in another thread but this may be a good example as to how we should post to this thread. LEts look at this whole thing to see what we can do. Mike Grimracer Z. had a thread about pipe testing that may be usfull as well. I am working on some new data for this years boats as they are all new ones. So lets here what you have thats works and even what did not. Pipes, engine mounts, stuffing tubes or what ever else we can do to reduce overall noise in our boats.

I run both the Stamped and quiet pipes from Irwins performance products. I have the set ups for all of my tunnels. At the pond testing with the only change being the pipe and header I have found that there is no real difference in the speed on radar.

My stamped pipes have a reverse stinger in them to take away some of the Bark. So here is how my last round of testing went. Remeber that I set up each pipe to get the max performance before the testing day. The boats are a Hopper 290 and a 360. The 290 is set up with a CMB.21 Green head outboard with a 7.5 K&B lower unit. The 360 is set up with one of my own 7.5 outboards (VisionTech). The .21 is using a 1440 prop back cut 10 degrees with 3.46 cup. the 7.5 is a cupped 230 prather prop. This testing was done last august at our pond in minnesota. Both boats where running Byron's 60% fuel

First the .21 boat

Irwin Stamped no reverse stinger 46.3 mph 92db

Irwin Stamped with reverse stinger 46.1 mph 89db

Irwin quiet 46.5 mph and 84db

.45 boat

Irwin Stamped no reverse stinger 56.5 mph 93db

Irwin Stamped with reverse stinger 56.3 mph 88db

Irwin quiet 56.6 mph and 85db

Remeber all I did was bring the boat in and change the pipe and header. All of the set ups for pipe length where done ahead of time. I found not to much difference in speed as you can see.

I hope this thread works out.

Brian

 

[Don Ferrette]

Thanks for starting this thread Brian, hopefully I will have good news on the big block 90 pipes I'll be testing this Sunday. And people should take note- the fastest pipes were also the quietest ones on both boats Brian ran.

 

[Brian_Nelsen]

Don

I look forward to your report on the new pipes. I will be running my big block rigger in the coming weeks. Its pretty quiet but has a real old Muck muffled pipe on it. I will also be testing my .21 and .45 mono's soon as well.

Brian

 

[bzubee]

Brian a couple of questions did you use the set up stated in the Noise rule? Also did you have your DB meter calibrated? If so what was the price to have it calibrated? I'm trying to get ours done at the Cal Lab here on the Arsenal. How far from the shore is your coruse set? Was the meter on a tri pod or table and foam? Just tryuing to get some answers from the other posts.

 

[10/Tenths]

I have not tried this on one of my boats, but it works in auto racing. We use a diverter pipe off of the exhaust pointing it either up or the opposite direction of the meter which ususally makes the difference of legal vs. illegal readings. While doing some testing you may want to give it a try just to see what it might offer. It would only take a 45 to 90 deg bend of pipe to add on the back. Anxious to hear any of your results with your testing program.

 

[waltr]

Just a little something to add.

Yesterday I called Jerry over @ Seaducer to question Cowl availability for all of his boats.

Unfortunatly,there are no cowls available for the 21 and 45 boats,but they are available for 60 & 80 boats.

Just might have to do my own molds for those 2 unless someone already is.

It was mentioned that a cowl was good for 3db.That's quite a bit.

Thanks for the ob pipe info.

So much for the quieter the pipe the slower the boat theory.

I have a 21 and a 45 Cooper quiet pipes here also.

When my db meter finally shows up,I would like to test them against SPP pipes too.

I guess at this point,db meter calibration really isn't necessary if your just checking differences.

But I do hope eventually we all can have them calibrated at the same place.

And Brian, thanks for the thread seperation.

Hopefully this one won't turn into a pissin match also.

 

[Brian_Nelsen]

Bill

I used the noise rull as a set up guide for testing. I have a friend who is a sound tech that calibrated mine for me. My new one does it for itself. there are units available in the 250.00 that self calibrate and calabration devices range around 500.00 as far as I have found. I did modify the rule book proceedure the last time a tested a few weeks ago. Here is the exact setup I used a few weeks ago. Last august it was by the rule book exactly, mounted on tripod 25 feet from shore between 6 and the start line (Closer to the start line).

The last testing went as follows.

Meter set up on a tripod 25 feet from the bank 4 feet above the ground (which at our pond puts it about 7 feet above the water) just before the starting bouy. What I did differently was an Idea I got from Kevin the gas director. I took a piece of ply wood 4 x 8 feet and put some acustic foam on it. I placed it 2 feet to the right of the meter and just behind the front of the meter. This was to prevent the reading from being taken after the boat had passed by. To hold the board up I used stakes with thick foam between them and the ply wood. I placed the meter in a place where there was mowed grass all the way down to the ponds edge.

the radar gun was mount well after the starting line close to the #1 bouy. There is a slight issue with the angle variable so the MPH is likely a little faster than posted.

The pond is as follows.

Our course is around 30 feet from shore and is a 1/3 mile course. We have a large bank about 70 feet from the waters edge that goes up to the freeway above the pond. This means that my boats are running around 25 feet from shore.

What I tested

HTB 290 tunnel CMB.21 RS engine mounted on a K&B 7.5 lower unit. It had a silverbullet pipe with a reverse stinger on it pointed away from shore. Can't tell you about the prop cause I did not make it and its real wierd but the engine rev extremely high when I run it. 60% byrons fuel was also used.

The other boat was my HTB 360 with the Vision Tech .45 outboard and Irwin quiet pipe. Prather 230 pro, Byrons 60% fuel.

The results

HTB 290: 10 passes at full throttle 25 feet from shore 86 to 87db 51 to 53 mph

Heres something interesting one the back straight with the exhaust pointing toward shore at speed and on the course the readings where 87 db.

HTB 360: 5 passes (boat had fuel tank problems) 25 feet from shore at full throttle 82 to 83 db and 62 to 64 mph. Reading on the back straight where 82 db. This was a boat that tested with the rule book method going slightly slower at 85 db last fall. so the plywood made some kind of difference.

I want to do some additional testing soon to see if the board actually makes a difference or not.

I think the reverse stinger works well to quiet some pipes down but quiet pipes get it down even farther

Hope that helps some.

Brian

 

[gil sonsino]

I remember years ago when people here used to run their .21/45 out's using " Magic muffler's" very quiet with no loss of power..ist this product still available?

I've been running a gas cat equipped with a G26/.90 Mac 1"belly nitro pipe plus a Mike Tyson muffler not very loud.After water injet the muffler noise reduced drastically (havent measured yet) but it was a good fix for this issue and the boat is more pleasurable to drive now.I also agree cowls help a lot to minimize this problem.

Gill

 

[Brian_Nelsen]

Gil

Magic pipes are no longer available. I do see them at times when I go to races. They where quiet and they seemed to work. We have a local guy who runs one and is very fast with it.

I agree Cowls help alot in reducing noise in an inboard boat. Threy can be a pain to install after the engine is running but they work.

Has anyone seen problems with air flow to the engine when running fully cowled?

Brian

 

[Don Ferrette]

I agree Cowls help alot in reducing noise in an inboard boat. Threy can be a pain to install after the engine is running but they work.

Has anyone seen problems with air flow to the engine when running fully cowled?

I run FULL cowls on all my boats. All it takes is one or two well placed air inlets & good water cooling & you will be fine for both airflow & engine temps. I personally prefer an opening shaped like a NACA duct opening with a piece of window screening glassed in underneath over the opening. Keep in mind you need to be sure you have as much if not more open area for air to exit the cowl as well. One thing people seen to be forgetting is that exhaust noise is only part of the equation, induction noise is also a source of alot of noise. Ever wonder why an air compressor is so noisy when you're pumping air into sealed tank?? Also a cowl can help reduce reflected interior hull noise considerably, especially on monos. B)

 

[piper_chuck]

I have not tried this on one of my boats, but it works in auto racing. We use a diverter pipe off of the exhaust pointing it either up or the opposite direction of the meter which ususally makes the difference of legal vs. illegal readings. While doing some testing you may want to give it a try just to see what it might offer. It would only take a 45 to 90 deg bend of pipe to add on the back. Anxious to hear any of your results with your testing program.

The whole point of the noise rule is to reduce noise. Tricks to skirt the rules should be forbidden. However, pointing the exhaust outlet up might be viable since it does send (some of) the sound away from anyone who might find it objectional.

 

[bzubee]

Thanks Brian I plan on doiing some testing too and will post results this is a much more constructive thread than the other complaint line. Hope it stays this way.

 

[Brian_Nelsen]

Don

I agree induction noise has a whole different set of issues. I think we need to look at all aspects of noise in this thread. Isolation engine mounts help with some of the resonance noise as will isolating the stuffing tube.

Does anyone have experience with isolating a stuffing tube? I am building two new mono's and would love to give it a try.

I wonder if mounting some kind of light weight material to a mono hulls bottom would reduce the hull noise?

Just some thoughts.

Brian

I have not tried this on one of my boats, but it works in auto racing. We use a diverter pipe off of the exhaust pointing it either up or the opposite direction of the meter which ususally makes the difference of legal vs. illegal readings. While doing some testing you may want to give it a try just to see what it might offer. It would only take a 45 to 90 deg bend of pipe to add on the back. Anxious to hear any of your results with your testing program.

The whole point of the noise rule is to reduce noise. Tricks to skirt the rules should be forbidden. However, pointing the exhaust outlet up might be viable since it does send (some of) the sound away from anyone who might find it objectional.

Chuck

Good point I think pointing it up would help. If you look at my post about testing a few weeks ago you will see that I took reading in the back straight with the pipe opening pointing toward shore. The results where somewhat interesting.

I should try to check the level with the boat going backwards down the front straight to see what the actuall difference would be.

Thanks

Brian

 

[Bob Finn]

I installed two of Steve Coopers add on mufflers on my twin 90 boat at the Internats. This boat was VERY loud even with the homemade cans I made for 2004 and 2005. The Cooper mufflers brought the DB readings down to 86 - 88. Although the boat wasn't running at peak performance, the mufflers worked great.

 

[lohring]

Attached is a picture of a spreadsheet page with the results of a day's testing on a Lazer 45. As you can see, quieter was faster. I have the entire spreadsheet with construction details if anyone is interested. The sound was measured pretty much like the IMPBA standard with the meter on a tripod at right angles to the course and about 50 feet from the boat.

Lohring Miller

 

[Mike Larson]

Now we're moving in a good direction..... Spent the morning reading Jennings section on internal stingers, anyone with testing results/measurements, theyd care to share? Terry? A DB meter is out of reach for me at this point, but, I can sure attempt and try stinger ideas... Thanks...

 

[Brian_Nelsen]

I installed two of Steve Coopers add on mufflers on my twin 90 boat at the Internats. This boat was VERY loud even with the homemade cans I made for 2004 and 2005. The Cooper mufflers brought the DB readings down to 86 - 88. Although the boat wasn't running at peak performance, the mufflers worked great.

Bob

What are your thoughts on getting it up to speed? Can you do it with the mufflers? What you posted is a significant change in DB so if you can keep it there and get it back up to speed we all would like to know.

Also what besides exhaust makes allot of noise on a twin rigger?

Lohring thanks for the post, thats some very good data.

Thanks to all, so far we are actually posting ideas that work or could work with more testing. I like this.

Brian

 

[Don Ferrette]

Also what besides exhaust makes allot of noise on a twin rigger?

Induction noise! There is a distinct audible drop in sound when the cowl goes on my twin 90 SGX. While I have not measured the exact dB change the mere fact that's it's detectible to the ear tells me it's worth noting.

 

[AWaddle322]

Brian,

What is a reverse stinger?

Allen

 

[Brian_Nelsen]

Brian,

What is a reverse stinger?

Allen

Sorry Allen

Its an internal stinger, I usually call it reverse.

My bad

Brian