Marine Generator Sound Proofing 3

[ebbtide]

Hi,
Here's my problem which is not unusual in the yachting world.
I'm the engineer onboard a megayacht which has a John Deere 35Kw Generator installed in the Lazerette. The deck overhead is fiberglass with the standard Teak decking on top of it.
The Lazerette was not sound-proofed at the time of build and now everything is installed and it is not coming out.
The sound of the generator running is more than annoying.

My options are to build a box around the generator, which is the last thing I want to do in any case.
There is also the acoustical foam that is used in many engine rooms,(1/4" foam base-a layer of heavy vinyl-a top layer 3/4" of foam with a Mylar covering on it.) This works to some degree, but it is not perfect.

I have seen a product called "SilentRunning 1000" on the website "

http://www.silentrunning.us".

It is hyped as being the solution to noise and it is a "paint on" product. (Being able to paint on a coating will simplify my life greatly!)
I am not familar with this technology and want to know if anyone has any experience using an absorber like this product and if there are any products better than this or are they all pretty much the same under different brand names?
Are there any alternatives to reducing the noise aside from not running the generator?
The reason we use this one is that it is the smallest of three and consumes the least amount of diesel.
The other two generators, a 65Kw and a 100Kw are installed in the engine room along with the 3 CAT 3412's of 1300 hp.
The engine room is sound proofed and this room is not a sound problem at all. (the owner did this part right!)

I would appreciate any info if someone has time to spare in replying. You guys have more knowledge than I do in the book-learning and what products are out there...I'm too busy running around after the 11 toilets onboard!

Thanks for your help.
Regards,
Steve M.

 

[GregLocock]

When I worked in vehicle noise and vibration in the UK we were regularly plagued by sound-deadening-paint salesmen.

We never found any effect worth talking about. On a plain steel sheet they did help a bit, roughly proportional to the mass of paint applied. They didn't even seem to do much damping.

We use spray-on black goop under cars, mainly to reduce stone chipping noise, I've never seen it used for engine noise. It has to be thick.

I would suggest that you (a) mount the thing on rubber mounts (b) make sure the exhaust and intake are effective and structurally isolated and (c) build a box round it that is isolated both from the floor and engine.

Alternatively copy the details from the engine room.

AFAIK there are no shortcuts with engine noise.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[MikeHalloran]

If the noise is mostly transmitted by structure, then vibration isolators under the genset engine mounts would help. The softer the better; elastic mounts with more than an inch of static deflection would be appropriate. Most regular motor mounts are way too hard for this. As an experiment, support the genset on plywood, put some truck inner tubes under the plywood, and inflate them just enough to keep it 'airborne'.

If the noise is mostly transmitted by air, i.e. the _noise_ is exciting the boat structure, then a really big muffler, on the engine's _air_intake_, should help. I assume it's already got a muffler on the exhaust.

Of course you've got long hoses with gentle bends in them, or multiple flex sections, on all the fluid and other conduits connected to the genset already, right? Exhaust, seawater, fuel, etc.

As Greg said, forget paint.

Start shopping for fuel cells.










Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[ebbtide]

Greg,
Thank you for your input on the paint salesmen. This exactly what happened to the Owner! Now I have the job of proving/disproving the facts of this "new" paint technology.
I also used the spray on rubber undercoating in the past on my cars...also in England! This new paint sounded interesting in their concept, but I have yet to try it and need more proof than the manufacturer's claims before spending the money on it.
Steve M.

 

[ebbtide]

Mike,
First off Mike - dam good work coming out of your shop! I've seen and used DeAngelo Marine Exhaust before on previous yachts and have not been disappointed by the craftsmanship.
I am familar with the sound canceling effects of properly mounting a generator...it unfortunately was learned through the experience of a lowlife neighbor who would not pay his electric bill and had to use a generator when his power was cut-off. Believe me when I say digging a hole and putting the generator in it does nothing for the acoustical and vibration properties at 3am!
This generator is properly mounted with good flexible mounts. It just seems to be the case of an engine with a noisey motor block.The exhaust manifold is also noisey and I am looking to see if there is another design available for this. The associated hoses are well thought out in their layout so there is nothing in looking there for the problem.
The air intake is also not loud at this point.
Our 65Kw generator is not as loud as this generator, but the surrounding area adjacent to the 65Kw is more open to dissapate the sound rather than letting it be confined inside the Lazerette.
If I cannot get away from building the box, McMaster-Carr has some acoustical insulation with two layers of lead as opposed to a single layer of heavy vinyl that I would use.
Thank you for your input.
Next time we're back in town and I can throw some business your way I'll make use of DeAngelo's again.
Steve M.

 

[MikeHalloran]

Thank you very much for the kind words.

<shameless plug>
No need to wait until you're in town. We do business all over the world, and work from cad files, samples, drawings, napkin sketches, pvc pipe mockups, plywood templates, whatever it takes.

My favorite was a beautifully made plywood box, complete with rope handles, with holes where the pipe had to connect, and blocks of wood fixed in odd places inside to represent parts of the boat, with instructions: "It has to fit in _this_".
</shameless plug>

I have taken the liberty of copying this thread to someone inside Deere. Perhaps they will have something to offer.



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[MikeHalloran]

Here is Deere's reply:

<<<
As stated many times below [referring to a copy of the thread, omitted here mh]...the structure should be checked to make
sure that the engine is completely isolated from the structure (no solid
connections). Also, the entire exhaust system should be checked to make
sure that the pipe isn't vibrating somewhere down the line from the
engine. If the structure is sound then it could be intake noise. This
can be a common problem on naturally aspirated engines. There are a
couple of ways to address this. One would be to duct the intake to
another location further away. Another would be to install a resonator
on the intake. It still may be necessary to "soundproof" the room.
Fiberglass insulation and acoustical tile could be used to construct a
sound barrier between the engine and the floor above. The important
thing is to make sure that the sound can't go around the barrier.
Hopefully this helps.

>>>
I.e., nothing new. I was kind of hoping they would come up with part numbers for a retrofit kit. Apparently no such thing is offered.

It's not like you have another choice; buy a marine generator between 30 and 70 kW from anybody, and it has a Deere engine.

How about a half dozen of those Fischer Panda 'generator in a suitcase' things?



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[ebbtide]

Hi Mike,
As you say, nothing new that we didn't already know!
I'd really like to take it out and use the space for storage for my spare parts, but there is no way the owner is going to do that one.
It looks as if I'll be doing the foam insulation on the overhead...but I'm also going to try making a partial box/shield over the Exhaust manifold. I do not think this will work to any great degree, but I'd like to see if I can deflect the noise from going directly into the overhead. It is still going to echo off the bottom of the hull over the center prop, but I'm going to foam that as well to see if the prop noise can be reduced too. Since the owner wants to try working on the prop noise anyway...I've really got nothing to loose since it his idea in the first place!
Of course,the owner want to use everything from a local source so that is going to kill all my contacts in Fort Lauderdale. He is just not going to pay shipping if he can avoid it.
Okay, thanks for your help in getting to Deere. I thought about them as well, but thought they would give the standard answer you got from them.
Regards, Steve M.

 

[SomeYahoo]

I am guessing that this guy has a couple of dollars to spare; do you think that an active noise cancellation system would work? They seem to be coming down in price lately. Of course, this wouldn't help if the hull vibrating is causing the problem, it would only cancel the airborne noise.

Just another option (from left field).

 

[Rob45]

Steve:
I tend to echo what Mr. Locock said, with a couple additional points:
First, concerning shielding - your noise source is in a big box, so deflecting the noise still leaves it in the box. Therefore, I'd recommend completely shielding the genset, either building an enclosure for it or shieldiing the entire room it's in.
This will require barrier material, towards the wall, with absorber inside that. You want to contain the noise, and then dissipate it. Lead is an excellent barrier, but as long as the surface weight is at least 1.5 - 2.0 lb per sq ft, other materials will work well. Steel, aluminum, plywood, etc. The absorber should be acoustical-grade fiberglas or open-cell foam. See for example Soundcoat for foams.
Second, do take a look at the intake. I'm guessing the generator runs at a constant speed? If so, it's the ideal situation for a quarter-wave or a Helmholtz tuner on the intake duct, tuned to reduce firing frequency noise.
Third, take another long hard look at the exhaust system structure: does it contact the boat at any point? Does it have resilient mounts? Do you have bellows-type flexible piping where the exhaust manifold connects to the rigid exhaust piping? How about control cables? Are they properly isolated?
And now, for the first thing I should have suggested: make a recording and get a frequency spectrum of the noise escaping the generator room. If it's occurring at engine rotational speed (unlikely), you have a structure isolation problem. If it's occurring at engine firing frequency, look first at intake and exhaust air-borne sources. If it's much higher orders of engine firing, then you likely have noise radiated from the surfaces of the crankcase, manifold, oilpan, or valve-cover. Deadeners can be applied to all these surfaces except the exhaust manifold, and that can be treated with a metal shield lined with a ceramic-fiber insulator, at some risk to the durability of the manifold.

Hope some of this helps.

BTW, there's a freeware FFT software on the web called "Cool Edit 97" or something similar that's actually quite versatile.

- R

 

[Wicsteve]

Just a word of caution:
If you're going to look at insulation material be certain to check it's flammibility properties. Foam on walls is especially hazardous. Check with the manufacturer if the product has been used in marine applications or in engine compartments.

 

[Rob45]

And I've just learned of some new products that might be of interest, if they're as good as claimed: they're both recommended for marine applications:
first, there's a micro-perforated sheetmetal that provides noise absorption while being totally fireproof;
then there's a plywood that incorporates a viscous damping layer, thus reducing or eliminating the coincidence dip found in most homogeneous barrier materials;
finally, there's a damping sheet meant to be added to fibreglas in the lay-up stage that greatly increases the damping of the fibreglas structure, further improving its barrier properties.
Just saw these at the SAE Noise & Vibration Conference in Traverse City, Michigan. Can't find the supplier's name at the moment, but a web search might turn them up, and of course I expect I'll be getting an e-mail from the salesman at any moment...

- R

 

[Rob45]

That micro-apertured metal is called Millennium Metal, and it's from American Acoustical Products, as is the damping sheet for fibreglas, which I believe they call "PDP."

With 2" melamine foam behind it, the Millennium Metal shield results in absorption coefficients of 90% or more from 250 Hz to 8 KHz. The MM can be steel, aluminum, or stainless, bare or pre-painted.

 

[MikeHalloran]

If I couldn't find a kit, and didn't want to build a box, I'd start suppressing the noise at the source. For example, make paper templates of all the flat surfaces on the engine, make some mass dampers to fit, and glue them on with silicone adhesive.

I've used 1/8" aluminum plates for that purpose, adhered with a 1..2 mm thick layer of RTV and secured with duct tape until the RTV set. They were noticeably more effective for the first week, because that's how long it took for the ETV to cure through.





Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[Rob45]

Hey, Mike!
Those mass-dampers stuck to the engine surfaces are a great idea!
Certain parts of the engine are far better noise radiators than others: for example:
The oilpan, the valve cover, and the front timing cover are all usually light rigid structures covering noisy parts. Engine noise can often be much reduced by either structurally isolating or damping the vibraiton of these parts, or both. For example, valve covers sealed with large rubber seal/isolators, and attached via grommets, so there's no metal-metal contact between the cover and the engine structure. Adding mass to the surface of these covers is another good way to reduce the noise transmission, or better yet, isolated mass, e.g., a layer of foam separating a steel cover over the oilpan.

 

[GregLocock]

We used to use rockwool and lead sheet to encase engines, then remove a section at a time to determine the noise contribution from each component.

We also had many oil fires

Those two paragraphs are related!

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[ccw]

Why are we not using Micro-Turbine-Generators (MTG's) in these applications? For the same KWH, the boxes are smaller, and the MTG's are very-very quiet compared to diesel. Two downside is slightly less efficient than dieselgen., and higher exhaust temp. Maybe you could stick a couple of these in the corners of the lazerette space and keep the diesel in reserve for added system reliability. I don't know of these being used in mobile power. Maybe there is a "g" limit?

 

[amorrison]

Be careful with fiberglass and rockwool . . .

A story

Hardware store fiberglass was used to insulate a large industrial chimmney between the layers of steel.

On the test firing everything went OK - ie. no steam condensation so the system was accepted.

Later a big problem with condensation occured.

When the chimney was checked the insulation had disappeared! All the fiberglass FIBERS were found at the chimmney bottom.

Waa happened?

Hardware store fiberglass FIBERS are held in place with a glue that melts at a low temperature so all the fibers seperated and fell to the bottom.

A industrial use fiberglass that has a high temperature adhesive to bind the fibers should have been specified.

Live and learn.

 

[Rob45]

I've another glass-fiber story:
Once upon a time, the Blue Oval company was studying ways to quiet their big trucks, in anticipation of tightening federal noise law.
They ordered a huge remote muffler to completely eliminate the exhaust contribution - 4' in diameter and about 8' long. It came in a large wooden open-sided crate, and was installed crate and all on the rear frame of the truck. Exhaust was piped to it, it was wrapped in fibreglas, then the fibreglass was covered with lead sheets.

The noise testing began, and after several runs, the wood frame caught fire, and began to burn merrily. This led to melting of the lead, which dripped all over the test site, much to the consternation of the heavy truckers, who seemed to be very specialized in their areas of expertise. That is, the noise guy(s) never considered heat...