Exhaust Noise

[Pete]

Wondering if anyone has tried to reduce the exhaust noise on DD natural engines by injecting additional sea water into the muffler?

My thinking is that turbo engines produce less exhaust noise, particularily the higher frequency harmonics, because noise is simply pressure pulsations, and as the pulses of air pressure go through the turbo blades the interference of the blades "smooth out" the pulses. If you buy this thinking then something that does a similar "smoothing" on a natural engine would probably help. Just have to be sure not to create excess back pressure in the exhaust system.

One way to do this would be to inject a "sheet" of sea water at the engine end of the muffler that the exhaust must go through. It is probably very important that the "sheet" of water be complete such that the sound can go around it.

Anyone tried something like this or had success with toning down the exhaust noise on naturals in another way. Again, I am OK with the low frequency noise, it is the harmonics that produce the "ringing" sound that I would like to eliminate.

Pete

 

[MikeP]

It's true that turboed engines produce much less exhaust noise at the same RPM than non-turboed engines because of the "work" done in spinning the impellor blades. Cars with turbos frequently have/need much smaller mufflers than non-turbo cars for that reason.

However, before I tried to invent something that is inherently an added complication, I'd look at the various mufflers already offered that claim to do the same thing. There are some water-lift types that claim to reduce the noise and be suitable for these DDs. I have no personal experience at all with them but it would certainly be worth a look.

I wouldn't mind having the DDs a bit quiter at cruise myself...

 

[luckydave215]

Unless you're wiling to convert to turbos, better mufflers are the answer. You must keep in mind, our mufflers are the "glass pack" type, and the packing doesn't last forever. Now that our mufflers are old, guess what? The other thing about glass pack muflers is that they only work when the glass packing is free to resonate with the exaust pulses, absorbing the energy and releasing it as heat. Because in use at least half of the glass is saturated with cooling water, they are only half effective at best. Think about it, all the glass packing (what's left of it, anyway) is now saturated with water, oil, carbon, bottom paint, and marine life.
A labryinth design would have been better in the first place.
Bottom line, look for new ones.

 

[REBrueckner]

Exhaust backpressure is a critical engine operating characteristic. Injecting addtional water runs the risk of increasing backpressure so beware. A new muffler, as suggested already, is the far safer way to go....be sure its properly sized for your HP, exhaust diameter and length,etc...

Also, the fiberglass exhaust piping transmits more noise and vibration than exhaust hose which is more flexible, thicker, less sound conductive,etc. It's possible replacing fiberglass pipe with hose could reduce your sound levels. Also, have you looked to see your fiberglass exhaust pipe is not resting against bulkheads or floorboards...that could also be a source of vibrational noise...

Finally, I wonder if an exhaust extension, as under a swim platform ,would conduct noise in a different way than the standard stubby outlet fittings...I've seen both glass and hose extensions...

 

[SKYCHENEY]

When I look through my exhaust from the exit end, I see little more than a straight pipe with a slight drop off area at the muffler. This little drop collects water and diverts the exhaust up slightly. I can still shine a flashlight and see straight through to the 45 degree monel elbow where the exhaust tube enters the engine room. This is obviously designed for almost zero back pressure. The only pressure that could result is if there were quite a bit of water going through the system(and I think there is).

Pete, If my exhaust was as loud as yours seems to be, I think I would first check to make sure that you are getting enough water though the entire system. Check your raw water pumps for play and the cover plates for wear. Also make sure you have the right impellors in there and that they are servicable. Next, make sure your water path is clean. You may want to clean your heat exchangers and coolers if they have not been done in a while. My thinking is that you may not be overheating because of a loss of flow since you have smaller N/A engines, but you may still have enough restriction to limit the muffling effect of having sufficient water in the exhaust.

After you eliminate the water issue as a possible cause, then move on to other alternatives. Just a thought.

 

[REBrueckner]

Is yours a 48 LRC? are those 4-71's....whatever, the idea about low water flow is a good one...The few 48's I've heard, admitedlly at harbor speeds have been pretty quiet...Can you compare exhaust water and noise level with a sistership??

 

[egaito]

Is yours a 48 LRC? are those 4-71's....whatever, the idea about low water flow is a good one...The few 48's I've heard, admitedlly at harbor speeds have been pretty quiet...Can you compare exhaust water and noise level with a sistership??

4-71's are 4 cylinder, right? I wonder if it's 2nd order boom he's experiencing.....does this phenomenon occur in diesel engines as it does in gas?

 

[Pete]

I appreciate all the responses and ideas. Let me answer a few of the questions that have been included.

My boat is a 1976 48 foot Long Range Cruiser. It does have 453 DD, rated at 120 HP Gross, 112 HP Net. These are 4 cylinder, 53 cubic inch per cylinder, in line engines. DD made 3,4,6, and 8 cylinder versions. The LRC series used the 453 in the 42 and 48 versions. The 58 had 471 standard, with an option of 671. The 65 version came with 671. All are Natural Aspiration derated for continuous operation. Mine have N45 injectors. Excuse the rambling, I just wanted to impress everyone with my HIGH power engines.

I too have the traditional fiberglass Veratone muffler that you can see through with a flashlight. Nothing in there except for some rigid fiberglass baffles. I also assume that the noise supression is achieved through splashing the exhaust water across the center passage to dampen the sound pulsation.

As for water flow, I think I am OK. The sound of the exhaust has been the same for 5+ years we have owned the boat. During that period, all the steps suggested have been done, plus a down to the block rebuild. Before anyone asks, no the engines did not need to be rebuilt for any know reason, other than I decided 25 years was enough and needed something to do over the winter. There is not another 48 in the area, but we do have two 42 LRC's and their exhaust sounds the same. I have passed (going the opposite way) a couple of 48's in the ICW and I would also call them the same. So what I am looking for is improvement to the original design.

So, why now, well a buddy that we cruise with bought a 43 MY with 671TI. I have been on the boat underway, and am often present when he starts his engines before getting underway. It just sounds so much better. I am trying to figure out how I might achieve a similar level of noise in my exhaust. BTW, my boat while underway is extremely quite, normal conversation levels are just fine standing above the engines at 1800 RPM in the salon.

Finally, there has been a couple of comments about water lift mufflers. Does anyone have some names that I can used to get started on this approach?

Thanks again to all.

Pete

 

[jim rosenthal]

Pete, welll-known makers of waterlift mufflers would be Centek, Vernatone, and Vetus (who sell them, anyway, but don't make them). With small engines like 4-53s, you may indeed be able to do something about the noise.

I would imagine that the seawater pump of a 4-53 doesn't put out much cooling water- this engine doesn't generate a lot of waste heat, since it doesn't burn much fuel in the first place- so you may not have much additional water flow to work with. You might consider putting more effective mufflers in, if you can get to the area that they are installed inside.

Broken record time: the most experienced person on Hatteras refits is Tom Slane at Slane Marine. However, I don't know how many LRCs have passed through their shop. You might consider calling Washburn's, which is a yard up here in the Chesapeake Bay, in Solomons. MD. They are not a Hatteras dealer, but they specialize in trawlers and they have probably worked on as many Hatteras LRCs as any independent yard. They are well known for their expertise, and I suspect not the cheapest game in town by a long shot. They may have some suggestions that would be of value.

I would also suggest that you look at the Passagemaker Magazine web site, and find their forum. There are a lot of Hatteras LRC owners who hang out there from time to time and may be able to advise you. This seems to me to be a solvable problem, that is, without having to reengineer the entire boat.

 

[ljcrain]

Please keep this thread posted on what you find out. I have a 1966 34DC with the same engines you have. Mine are obviously not original and therefore are not a Hatteras installation.

For one thing, mine don't have any mufflers. I didn't know there was such a thing for a 4-53. Mine have straight pipes out the back and at cruising RPM are LOUD! Of course I don't have as much cabin or altitude between my engines and flybridge as you do and most of the noise is just the scream of these engines.

BTW I've always admired the lines of the 48 LRC and wish I could afford one.
Thanks

 

[dastahl]

Pete,
I have a 42 LRC with the 4-53s. These smaller motors have a higher pitched noise and what I call a loud hum. The noise is the only thing I don;t like about my boat. My marina mates joke about the noise.

I wish I had an answer for you, but I will be happy to help you search. I have talked to the muffler folks at a few boat shows. Most say that you can get a better muffler if there is room.

Skooch
42LRC401
Worton Creek MD

 

[dastahl]

Soundown and Centek Inds. both make horizontal mufflers similar in size to the mufflers on my 42 LRC. Soundown wants $1100 each, Centek is half that. Niether company has made any claims as to how much of a sound reduction I might expect. Does anyone know if new mufflers are better than 27 year old ones?
I'm going to measure to make sure I can get the old ones out and the new ones in without a chain saw. Then I may just try a set.

David Stahl
Skooch
42LRC401