Generator vibration and noise

Was running the generator the other day and started wondering why it was so damn loud.

First of all, the generator is mounted directly below the pilot house in its own little "room", and it has a full enclosure. The generator is only about 4" from the floor of the pilothouse however, and the wooden floor has no insulation, so I'm guessing that is part of my problem. I thought about putting carpet and a sound absorbing barrier but I really don't want to cover up the pretty wood sole.

Other problem is vibration. The gen seems to vibrate the entire boat. The engine is isolated from the drip pan with traditional rubber mounts but the stainless steel pan is then directly mounted to the floor of the "generator room". Looks like this:

I saw on sundown some various bushings that maybe I could use to isolate the pan mounts to the boat? Think that would help much?

I will be at the boat later today for actual gen pics as it's mounted. Can't remember what the floor is made of where it's mounted so don't know if I can install a fancy bushing system-- I think it's just lag bolted into the floor but could be wrong.

Maybe just use a fat rubber washer?

When I installed a generator in our sailboat, I read every manual Fischer Panda had on the the model we chose.
One thing that became clear was that everything counts when it comes to sound attenuation. They cautioned against mounting on a platform that might vibrate and thus broadcast that noise.
The other suggestion was to use a second set of motor mounts between the generator enclosure and the beds.
Here is a picture of my installation. It was not silent but it was far better than other 3600 rpm small generators I have experienced in sailboats. With the door to the aft cabin closed and the air conditioning on the air was louder than the generator...
Bruce

What you are describing - so called double isolation - is pretty common on boats. I think it would help, but I have no guidelines on how to select the best mounts. They come in all sorts of capacities and stiffness. Your generator manufacturer might be able to make a recommendations.

Bruce B said:

When I installed a generator in our sailboat, I read every manual Fischer Panda had on the the model we chose.

One thing that became clear was that everything counts when it comes to sound attenuation. They cautioned against mounting on a platform that might vibrate and thus broadcast that noise.

The other suggestion was to use a second set of motor mounts between the generator enclosure and the beds.

Here is a picture of my installation. It was not silent but it was far better than other 3600 rpm small generators I have experienced in sailboats. With the door to the aft cabin closed and the air conditioning on the air was louder than the generator...

Bruce

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Very nice. I was thinking about something like this 4 series bushing if I can get to the underside of the mounting floor. Guess I could install some channel to bolt the bushing to.

http://www.soundown.com/TECHSHEETS/Ring bushings 2010.1.A.pdf

Not sure it's worth all the trouble of lifting up the generator and everything however.

cardude01 said:

Was running the generator the other day and started wondering why it was so damn loud.

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Was it louder than it had been previously?

BandB said:

Was it louder than it had been previously?

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I obviously can't speak for anyone else but I know that at times, I become aware of noises and once conscious of them I fixate on them. It then seems as though they are MUCH louder.
Bruce

Vibration - Typically with isolation mounted machinery look for any spot however small where there is an opportunity for transmission. Often a small thing like something touching the housing, something laying on the hull with little or no isolation from the platform to the hull. I have seen exhaust hoses or just the clamps 'drumming' on the hull, throttle cables, electrical wiring , water hoses, fuel lines and even covers that vibrate in sympathy.


Noise - Always very hard to hunt down unless you have a reasonably directional sound meter, mine is old but was about $40 at radio shack when I got it. You will likely find that the noise is 'leaking' out where you least expected it and often is reflecting off of another surface or two. Once found the sound leaks are often pretty easy to rectify with either direct sound proofing or by removing the reflected path. I have used Sounddown material often and likely have a large amount at home at this time but finding the source is most of the task at hand.

BandB said:

Was it louder than it had been previously?

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It's always been loud, I'm just more annoyed by it now.

do you have a muffler? Sudden increase in exhaust noise can indicate low raw water flow.

Intake noise can be loud as well.

Many times you can tell how the noise is being transmitted by touch and holding things like exhaust hose, mounting boards, etc.

The more you can isolate and insulate around the unit the better.

Sound Down should be able to tell you which mounts to get based on the specs of your genset.

And yes, carpet and padding can be a big help. Also check the condition of any gasket around the edges of the floor panel/hatche access to the genset area.

CD, be careful just jamming some bushings in there. Right now, the weight of the generator is spread across that whole pan and is supported by the floor/sole of the engine space. If you jam some bushing in there, not you take the support of the floor away and now the pan will be supporting the generator. At least that is the way I see it based on the pics.

Maybe you could put some adding support/bushings under the engine mounts in the pan?

This is how the pan is mounted. Can't tell what's on the underside.

Edit: found a panel. It's just lag bolts going down into some wood. There is a fiberglass tank right under the generator so no room to put bolts and get a nut on the bolt.

What about a thick, like 1" thick, rubber strips to run under the generator pan? Wonder if that would isolate some vibration?

Baker said:

CD, be careful just jamming some bushings in there. Right now, the weight of the generator is spread across that whole pan and is supported by the floor/sole of the engine space. If you jam some bushing in there, not you take the support of the floor away and now the pan will be supporting the generator. At least that is the way I see it based on the pics.

Maybe you could put some adding support/bushings under the engine mounts in the pan?

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Yeah that's true. Then the entire weight of the generator would be on the little tabs. Would need to put some square tubing going across under the generator pan from tab to tab I guess.

Problem is not much room between the generator and the floor to work with, so it can't be a very tubing. Maybe 1"?

While you could remount the generator and reduce the issue, as said earlier, try to figure out the source of the sound. If you deem it not to be a mechanical issue you can then fix the source issue (likely costly) of build your own sound shield through materials like carpeting, padding, insulating materials, rubber. You could either just shield by padding existing areas or could copy sound shields as sold with most of today's generators.

Look for "sound shorts". Gennie should be floating on its mounts, and any connections to outside stuff should be flexible. Anything rigid between gennie and boat is a sound short and can really increase noise and vibe transmission.

Also, is it a 3cyl 1800rpm machine? Those can usually be made fairly social. Others can be inherently noisy.

Got an open air intake to engine? It should have a silencer. LOTS of noise comes out air intake to engine. Sometimes installers forget to install the silencer.

How old is the generator? I ask becuase ours seemed loud and had some vibration when we bought our boat. At the time, the genny was approx. 10 years old with around 600 hours on it (northern lights 6KW). I wasn't sure if it was normal, as this is our first boat with a diesel generator. After doing some research on Boatdiesel, I determined that our mounts/isolators were likely worn. Replaced them last year and now you can barely tell it is running - all vibrations are gone. It also has an underwater exhaust/hushbox, but that only deals with exhaust sound.

If your genset is the MasPower one that you posted a pic of, then it is a 3 cylinder, 1,800 rpm unit.

Those Soundown bushings look like a pretty good solution. If installed properly they would isolated the whole stainless steel pan and look like they are much more flexible than the ones that support the engine.

But those mounting clips on the side only hold the unit in position horizontally. I wouldn't attempt to put the Soundown bushings under those clips and expect it to hold. The clips and probably the pan will bend.

But from the pic it looks like the heat exchanger is welded to the pan and the generator end and the engine are mounted on rubber mounts that are supported by a U shaped bracket thatis also welded to the pan.. If you could put the upper part of the Soundown bushing underneath those U brackets that support the engine/generator mounts then that would probably hold up ok. But I doubt if there is enough room for that. You probably would need to weld a bracket to the side of those to carry the engine loads over to the Soundown bushing.

David

Ski in NC said:

Look for "sound shorts". Gennie should be floating on its mounts, and any connections to outside stuff should be flexible. Anything rigid between gennie and boat is a sound short and can really increase noise and vibe transmission.

Also, is it a 3cyl 1800rpm machine? Those can usually be made fairly social. Others can be inherently noisy.

Got an open air intake to engine? It should have a silencer. LOTS of noise comes out air intake to engine. Sometimes installers forget to install the silencer.

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The generator has rubber mounts from the gen to the pan but then the pan is mounted to the boat with no isolation.


It's a 3cy Yanmar engine. 1800 rpm.

What's an air silencer look like ?

djmarchand said:

If your genset is the MasPower one that you posted a pic of, then it is a 3 cylinder, 1,800 rpm unit.

Those Soundown bushings look like a pretty good solution. If installed properly they would isolated the whole stainless steel pan and look like they are much more flexible than the ones that support the engine.

But those mounting clips on the side only hold the unit in position horizontally. I wouldn't attempt to put the Soundown bushings under those clips and expect it to hold. The clips and probably the pan will bend.

But from the pic it looks like some components- the heat exchanger are welded to the pan and the generator end and engine are mounted on rubber mounts. If you could put the upper part of the Soundown bushing underneath those U brackets that support the engine/generator mounts then that would probably hold up ok. But I doubt if there is enough room for that. You probably would need to weld a bracket to the side of those to carry the engine loads over to the Soundown bushing.

David

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Thought about running some square tube across the tabs under the pan then mounting the bushings to that, but now I realize there is no access to the bottom of the panel where the current tabs are mounted. They just used what look like lag bolts.

Is there such a thing as a big thick sheet of rubber I could slide under this pan then use some longer lag bolts on the same tabs?

Carolena said:

How old is the generator? I ask becuase ours seemed loud and had some vibration when we bought our boat. At the time, the genny was approx. 10 years old with around 600 hours on it (northern lights 6KW). I wasn't sure if it was normal, as this is our first boat with a diesel generator. After doing some research on Boatdiesel, I determined that our mounts/isolators were likely worn. Replaced them last year and now you can barely tell it is running - all vibrations are gone. It also has an underwater exhaust/hushbox, but that only deals with exhaust sound.

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It's about 8 years old. 800 hours.

Is this a silencer?

From the pilothouse.

So I was thinking, maybe I can just jack up the generator somehow (weighs around 500 lbs I think) and slide these 1/2" rubber strips under the pan where the tabs are. Think that type of rubber will hold up and provide some isolation? 60A is supposed to be like car tire hardness.

here is one web site of several to get you started searching

https://acousticalsolutions.com/product/vibration-isolation-pad/

Ted

cardude01 said:

View attachment 58637

So I was thinking, maybe I can just jack up the generator somehow (weighs around 500 lbs I think) and slide these 1/2" rubber strips under the pan where the tabs are. Think that type of rubber will hold up and provide some isolation? 60A is supposed to be like car tire hardness.

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Can't hurt. But I'd slip 4-5 of them under the pan to spread the load.

Capt.Bill11 said:

Can't hurt. But I'd slip 4-5 of them under the pan to spread the load.

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Good idea. Thanks.

Does 88-90db with the genny running seem loud to you? Maybe I'm just easily annoyed.

cardude01 said:

Good idea. Thanks.

Does 88-90db with the genny running seem loud to you? Maybe I'm just easily annoyed.

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88-90 decibels sounds loud to me with the generator and engines running. Anything over 80 is too loud to me, so I share your noise annoyance. Actually I prefer to stay under 75.

BandB said:

88-90 decibels sounds loud to me with the generator and engines running. Anything over 80 is too loud to me, so I share your noise annoyance. Actually I prefer to stay under 75.

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You know it's funny, I am driving home now in my Tahoe, which I don't consider to be very loud, and using the same decibel meter on my iPhone going 70 miles an hour my Tahoe registers the same 88 to 90 dB.

Something about that generator noise just bothers me I guess. It's a much deeper noise than a normal road noise in the car.