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Thread: Engine noise abatement

  1. #1
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    Default Engine noise abatement

    Using a pretty good directional decibel meter, I confirmed what Ive suspected for a while. The highest readings are near the pilothouse overhead. The engine is beneath the pilothouse floor and the floor has 2 sound insulated under and lead/foam pad and carpet over. The overhead is cambered beams with planking over and 1/4 plywood, glass and epoxy over that. The engine is hard mounted to the beds and evidently the vibration is transferred to the cambered overhead which acts as a diaphragm or drum head.

    The problem is I dont know what to do about it. I suppose I could try putting a ceiling mounted on isolator clips under the overhead deck beams, but headroom is precious plus I wouldnt be fond of the look. Acoustic material between the beams would look even worse, plus Im not sure absorbing is the right solution. Any other ideas?

  2. #2
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    Default Re: Engine noise abatement

    Replace the Jimmie with a modern engine? Mount it in rubber? Joking aside, on my boat the engine is under the pilothouse as well (though being sail, it's part of the cabin & below the cockpit). With the old 4-107 Perkins, a conversation in that part of the cabin required shouting & no way could you hear someone up in the cockpit. With a newer Yanmar, not only can we carry on a conversation, but hearing someone from the cockpit is pretty easy.

    I can't think of a way to isolate the cabin from the beds - though if it were supported by deck beams instead of beams going to the bed it might be better - though that may already be the case? I realize you don't want to reduce headroom or look at sound absorbent material - but you might test absorbing by tacking some carpet between the beams of the pilothouse & see what difference it makes?
    "If it ain't broke, you're not trying." - Red Green

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    Default Re: Engine noise abatement

    Yes, I think experimenting with material between the beams might be a simple test. Then if that helps, maybe I could come up with a better looking solution.

    On further thinking, I’m wondering if the overhead is actually vibrating like a drum head and creating the sound, or if the ambient sound in the pilothouse is just collecting up high.

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    Default Re: Engine noise abatement

    IIRC it's curved - which would make for a great reflector. If it is reflecting, then something absorbent should help a great deal.
    "If it ain't broke, you're not trying." - Red Green

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    Default Re: Engine noise abatement

    My first though was to spray closed cell PU foam on the underside of the overhead between the beams. You would have to cover that with wood ceiling for looks, but the ceiling could be pretty thin, or you could not fill the frame bays and apply ceiling between the beams.

    Then when I read that you don't want to lose headroom I thought that perhaps the foam could be applied to the upper side between new (laminated?) beams which could then be covered with new decking, but that would probably be a real pain due to various penetrations.

    Not much help, I know, but maybe it will suggest something to somebody.

    Photos of the overhead might help.

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    Default Re: Engine noise abatement

    Ron, here's what's probably a far fetched thought..... What about an electronic sound dampening system? Something like noise reducing ear muffs have. I think I've read where factories have successfully incorporated such devices to quiet their environment.

    Jeff

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    Default Re: Engine noise abatement

    Quote Originally Posted by Gib Etheridge View Post
    My first though was to spray closed cell PU foam on the underside of the overhead between the beams. You would have to cover that with wood ceiling for looks, but the ceiling could be pretty thin, or you could not fill the frame bays and apply ceiling between the beams.

    Then when I read that you don't want to lose headroom I thought that perhaps the foam could be applied to the upper side between new (laminated?) beams which could then be covered with new decking, but that would probably be a real pain due to various penetrations.

    Not much help, I know, but maybe it will suggest something to somebody.

    Photos of the overhead might help.
    Actually, I was surprised to find that the headroom is not the issue I thought. There’s a good 3” from my head to the bottom of the beams. But just for appearance sake, I think something between the beams would be better anyway. Don’t have a pic right now, maybe later.

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    Default Re: Engine noise abatement

    Does the resonance of the overhead is worse at some engine speed, perhaps changing its resonant frequency would help.
    See whether the resonance is damped by putting some weight on the overhead- a sandbag or a person. If the noise is reduced, the adding weight or stiffness to the overhead might help.

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    Default Re: Engine noise abatement

    Quote Originally Posted by jpatrick View Post
    Ron, here's what's probably a far fetched thought..... What about an electronic sound dampening system? Something like noise reducing ear muffs have. I think I've read where factories have successfully incorporated such devices to quiet their environment.

    Jeff
    Thats an interesting idea. No doubt the noise canceling headphones help, never thought about broadcasting an inverse wave tho, but why not?

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    Default Re: Engine noise abatement

    Try simple first before spending a lot of money and effort that may be ineffective. If the roof is resonating, change its resonance frequency. Temporarily put something flat and heavy on the roof top, such as lead/foam mat or heavy rubber doormats and see if that reduces the resonance. If yes, then we can talk about how to make it permanent and unobtrusive; if not, your not out much for trying.
    Hope for the best, but plan for the worst.

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    Default Re: Engine noise abatement

    Thanks Michael. And yes it’s a good idea to do cheap trial and error testing before anything permanent.
    Beginning to think it is not resonance because it didn’t really change when a couple of years ago I added epoxied 1/4” plywood, glass and epoxy over the roof planking. Seems like that would have changed the resonance by stiffening it a lot. So if we assume it is reflectance, what would be the best absorbent material for low frequency engine noise?

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    Default Re: Engine noise abatement

    Are vibration isolation engine mounts are out of the picture? Sort of stop it where it starts.

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    Default Re: Engine noise abatement

    Quote Originally Posted by Tom Robb View Post
    Are vibration isolation engine mounts are out of the picture? Sort of stop it where it starts.
    Yes, out of the picture. No room, would have had to be designed in from the start.

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    Default Re: Engine noise abatement

    Ron, given the complexities of the noise challenge aboard Snoose that you have outlined in the past I wonder if it's not time for a belt-and-suspenders approach. Meaning just throw a bunch of sound deadening at the problem until you see some sort of change, and then refine from there.

    I was pretty impressed with the stable stall mat that forum member Favorite used aboard his eponymous boat (Favorite the tug has a 6-71 right underneath the pilothouse, and similar sound issues to Snoose). The stable stall mat has two big advantages as a sound deadening materal. It's seriously heavy, and it's incredibly cheap.

    https://www.greatmats.com/horse-stal...ack-humane.php

    You could lay down a layer over the pilothouse sole, run it up the sides, stuff it up between the overhead beams, make a box out of it to go around the dry stack and line the inside of the door to the trunk cabin all for a couple hundred dollars or less. It's not the most attractive or efficient material but using it you could quickly determine what actions have the greatest effect on the noise and then design a more elegant solution if necessary.

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    Default

    Put a bright light in the engine space at night. Close all doors; dog all hatches.

    Plug up the holes wherever you see light coming through. Engine vents excepted.

    Kevin


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    There are two kinds of boaters: those who have run aground, and those who lie about it.

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    Default Re: Engine noise abatement

    Thanks Chris and Kevin. I already have the pilot house floor pretty well attacked; 2” lead lined foam under, 1/4” lead foam pad and carpet on top. I went down today with a meter to try to track down leaks as Kevin mentions doing with light. To my surprise, I found a few leaks at joints in the floor, but my highest readings were at the overhead and about ear level when standing in the pilot house. So my current approach will be to experiment with absorbing materials between the overhead beams. As Garret and Michael suggested, this could be trial and error with carpet or foam or something. If it works then it would be a matter of finding a material that is aesthetically appropriate.

    In researching a bit, the approach may depend on the frequencies I’m trying to absorb. My first thought is that they are low frequencies, but the sound of a Detroit is complex involving many different sources. I might go to the boat with a spectrum analyzer to see which frequencies seem to be the most annoying.

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    Default Re: Engine noise abatement

    Look at Aquadrive. It puts a constant velocity joint between the transmission and the shaft coupling, and has a thrust bearing mounted to the hull to take the thrust of the prop. This setup allows very flexible engine mounts to be installed since they no longer have to take the thrust of the prop, allowing the engine to float and helping decouple its vibrations from the hull structure. Somehow the vibration of the engine is resonating with you cabintop.

    If the vibration source was coming from further aft, I would suspect the prop. Depending on the hull shape, going to a four or five blade prop could help, or switching to a prop whose blades are skewed aft to reduce hull resonance. Structure borne sound and vibration can be maddening to locate.

    It sounds like the engine room is fairly well sound isolated. Basically, visualizing the engine room full of water and locating any place that water could escape and plugging those hole is how to finish that job, after the major surfaces have had sound isolation applied.

    if your engine is hard mounted to the stringers, than looking at welding up new feet to allow soft mounts might be the way to go.

  18. #18
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    Default Re: Engine noise abatement

    i would probably start buy tacking pieces of moving blankets onto the overhead to see (hear?) what happens..
    then maybe even move to more permanent but easy to remove fasteners like grommets or tenax type.

    i once helped with a project in a problem room with a smooth-surfaced and gently arced ceiling;
    the noise from voices and chatter was deafening...
    the solution was a pretty cheap+easy application of spray on acoustic foam.
    gave the place a popcorn ceiling look, but not very noticeable.
    the difference in sound, though, is striking...

  19. #19
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    Default Re: Engine noise abatement

    I'm not an expert on this at all but I certainly have looked into it ... you would too if you had a 6-71 in your living room

    I have a paper done by the Navy, "Evaluation of an Inclined Mounting System for Diesel Engines". They did the study with a 6-71 so it's applicable.

    There are two problems - structure-borne noise and airborne noise. Airborne you can deal with by using absorptive materials. Best is rubber and Persian carpets (but there is a vast difference in price !) Next would be mundane carpet. Then THICK (as in 1" or more) cork. Foam is worthless. Your lead is good but it's possible my 3/4" of stable matting is better. 16" of concrete is good also, but maybe a bit impractical ...

    The second problem is structure-borne. In the music studio groups they call this a short circuit. This is one that's difficult to get around, because your wheelhouse is pretty firmly attached to the engine room and it transmits sound directly.

    The Navy lowered structure-borne noise by many decibels by mounting the engine on soft inclined rubber the same way that car engines have been done for the past forty years. The engine mounts are pretty simple but the trouble then is, you need a thrust bearing because the engine is now free to wallow around. I believe the Aquadrive has all the right components but it's expensive. You could do the same thing for a lot less. Even the US Navy did, and they are not famous for thrift.

    PDF's are not attachable or I'd add it here. Maybe a search is easier than me trying to send a big pdf over t-mobile but if all else fails, shoot me a pm and I'll try.

    Meanwhile, I just bought another stable mat I don't mind the sound of a jeemy but want to cut it back some. Some more, now. Doing the sole was a big help, if I can achieve that much reduction one more time I'll be happy.

    (I can actually talk on the phone now at 1600 rpm, a huge improvement. Not that I want to talk on the phone but still, much better. )

    edit : Just did a quick look, at 1 Khz they were getting between 19 and 24 decibels reduction in sound levels, depending on where they measured. If'n I wuz younger and more ambitious, that'd be what I would do for sure.

    Meanwhile, back at reality, hard reflective surfaces is bad. Bad bad bad

    Oh. One other thing to look into - won't help structure-borne but there are a few places making sound-absorbing engine blankies. They are not very cheap but might help in your case, capture some engine noise at the source. I've got a box, lining that next, hope that takes me another step forward.

    p.s. Cna someone do something about this stupid website that times out in 3.7 seconds ? This is truly annoying.

    You probably don't want to hear this but :

    Quote Originally Posted by David Taylor Research Center
    Table 1 lists the sound levels that were measured during various stages of acoustical treatment. As previously reported, when the engine was hard mounted there was no significant difference in cabin sound levels with or without the acoustical blankets around the engine even though engine compartment levels were changed appreciably. When the engine was soft mounted the forward cabin was 12 dB quieter whereas the aft cabin was only 1- 4 dB quieter. When the engine was soft mounted the sound levels in the forward cabin increased as the acoustical blankets were removed; in the aft cabin no significant change was measured at 2100 RPM. At slower speeds the levels in both !abins were found to be related to the acoustical treatment of the bulkheads and engine. These observations point to propeller noise as dominating the sound in the aft cabin at 2100 RPM.
    Last edited by Favorite; 04-07-2019 at 01:51 AM.

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    Default Re: Engine noise abatement

    What Favorite said. Structure borne noise is hard to eliminate. Some kind of rubber mount would do a lot of good.

    Thanks Favorite, I didn't want to type that much. Google found your paper: https://apps.dtic.mil/dtic/tr/fulltext/u2/a200001.pdf

    An engine stethoscope might be handy to confirm that the cabin top is vibrating. It helps to find the place(s) that is vibrating. If you don't have an engine stethoscope a wood dowel or long screwdriver works well. This video should start at 73 seconds https://youtu.be/6mpNRJ7m-c8?t=73 I thought it would have been easier to find a better description. I was taught to put my thumb over the end of the dowel and press the back of the thumb to the tragus, which closes off the external auditory meatus (hole). I had to look up ear anatomy to name them. You can easily find noisy components on an engine and it should work on other vibrating surfaces as well.

    Some years ago I reviewed an SBIR for tuned mass dampers for a diesel engine compartment. Just a thought, there might be something along those lines that will work.
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

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    Default Re: Engine noise abatement

    @ Favorite: Site timing out? I haven't seen that - when & where & while doing what?

    @ Ron - Might sound silly - but have you tried any curtains? My dad had a lot of acoustical training & I remember him saying that one way to cut noise is to break it up. I'd asked him about pieces of cloth hanging from a high ceiling & he said that they'd help cut noise levels.
    "If it ain't broke, you're not trying." - Red Green

  22. #22
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    Default Re: Engine noise abatement

    "engine is hard mounted"

    I think this is where you need to put your effort. Can you fit in a CV / thrust bearing unit ?

    Cheers,
    Mark

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    Default Re: Engine noise abatement

    If soft engine mounts are all too difficult, invest in noise cancelling headphones.

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    Default Re: Engine noise abatement

    I agree with others that it's worth spending some time staring at the engine beds to see if there isn't some way to add soft mounts as well. But I'm also curious about noise from the dry stack given the sound levels at head-height. I'd still be inclined to add more sound proofing around the stack and on top of or underneath the overhead itself to see if that helps. If nothing else, adding some really heavy sound mats to the overhead might change the frequency of the resonance so that the noise is less annoying?

    I'll acknowledge that none of these suggestions are very aesthetic but I'm thinking find a way to solve the noise problem first, then design a good looking installation...

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    Default Re: Engine noise abatement

    Lots of good info here, thanks all. I seriously doubt that I will tackle the mammoth task of remounting the engine. At that point I would almost rather repower. I have used the stethoscope method, as well as a decibel meter and it seems most is coming from the overhead and is probably reflective more than resonant. The dry stack doesn’t really seem to be a large problem. Research indicates that absorbing low frequencies is much harder than high. The best method seems to be lots of thickness of soft material. Owens Corning fg acoustic panels seem to have the best specs and come in 2’x4’x2” panels which can be attached between the overhead beams. They can be covered with a loose weave cloth. I’ll experiment with carpet first. I also like Favorites idea of stable mats on the floor. As headroom is not the problem I thought, another 1-1/2” of cheap rubber might be good.

    None of this will be done overnight but I’ll try to report on the progress.

  26. #26
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    Default Re: Engine noise abatement

    I have had great luck with this product. Used it in the motor well of my Handy Billy/Ninegret build. Seems unlikely that "paint" would do more than all the other acoustic material, but it did.
    https://www.soundproofcow.com/produc...SAAEgKjkPD_BwE

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    Default Re: Engine noise abatement


  28. #28
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    Default Re: Engine noise abatement

    Quote Originally Posted by Oldad View Post
    I have had great luck with this product. Used it in the motor well of my Handy Billy/Ninegret build. Seems unlikely that "paint" would do more than all the other acoustic material, but it did.
    https://www.soundproofcow.com/produc...SAAEgKjkPD_BwE
    We used this product on the San Juan 30’s where we had to build a removable cabinet to gain access to the outboard side of the diesels. Because the cabinet had to slide in and out we did not put the sound insulation on it like the rest of the engine room, but applied this coating which acted as a decoupled and turned to sound energy into heat.
    We never had one of these models without this coating, so hard to say how effective this was. But as I mentioned before, any small passageway out of the engine room can let an amazing amount of sound energy escape.
    We also used the Soundown decoupling tiles beneath the generator on larger San Juan models to help with structure borne vibration and sound, every little bit helps. It is quite possible to have the surrounding living spaces “library quiet”, but the amount of money chasing that spec can be astronomical.
    I have to believe that a GM 6-71 hard mounted to the engine stringers is the culprit here, the very soft Aquadrive mounts are maybe 3” tall, and if you have any access to the sides of the engine it seems like fabricating New steel mounting legs, perhaps using different tapped holes in the block could gain you the clearance for a soft mount. You will have to fabricate a floor timber to install the required thrust bearing, and the shaft will need to be shortened, so it’s not a small task. but living with high decibels is very debilitating.

  29. #29
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    Default Re: Engine noise abatement

    Some of the suggested solutions involve putting heavy sound-deadening mats on the overhead. Is that weight up high going to affect stability?
    I will beg you for advice, your reply will be concise, and I will listen very nicely and then go out and do exactly what I want! (Apologies to Lerner and Lowe.)

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    Default Re: Engine noise abatement

    I think a good portion of the jimmy's noise is the roots blower, maybe if you were to move the air intake to out side the wheelhouse this might help?

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    Default Re: Engine noise abatement

    The results of the first test, not encouraging. I ran 3 tests at 1250 rpm as is, and 3 tests after putting carpet on the overhead. The meter averages the levels, and then I further averaged the averages of each three tests. Without the carpet, the average was 95.87. After tacking up the carpet, the average was 94.57. So a reduction of about 1.3 decibels. Not very significant a reduction at those levels. But carpet is just a test, a permanent application there would be 2” acoustic fiberglass panels, which should improve the results over carpet, but not sure if it would be enough to suffer the ugly factor.

    Yes, I agree the biggest culprit is the hard mounting of the engine as Paul and others point out. Maybe it’s time to really study the soft mounts. It’s overwhelming and beyond my personal abilities, but maybe I should price the task by others.

  32. #32
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    Default Re: Engine noise abatement

    Quote Originally Posted by Penta2 View Post
    I think a good portion of the jimmy's noise is the roots blower, maybe if you were to move the air intake to out side the wheelhouse this might help?
    That might be worth considering, tho not sure where I could move it to. The sound of the engine is very complex and it is difficult to decipher what part is making the most noise. I think I have the exhaust pretty well silenced, and someone said the valve train makes a lot of noise so I replaced the sheet metal valve cover with a cast aluminum one; didn’t seem to help much. I’ve heard others say the the blower and intake can be a problem, maybe it’s time to look at that more seriously.

  33. #33
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    Default Re: Engine noise abatement

    A lot of the unbearable noice in the cab of my tractor was found to come from the metal roof acting as a loudspeaker membrane with the vibrations that found their way up there via the cab frame. It is impossible to put soft mounts on the engine of a Massey-Ferguson 165 so I had to come up with a second best solution.
    I added a thick layer of bathroom mois proofing membarane to the inside of the metal roof. That changed the frequency and stopped it from acting as a loudspeaker membrane. Then I added 30 mm soft sound insulation on top of that to absorb at least some of the sound there is inside the cab.
    I still need earmuffs when I drive the tractor but I can stick my head in there to fetch the earmuffs or start or stop the power take off without having tinnitus afterwards. When driving with the earmuffs on the sound level is okay.
    A huge improvement.

    I suppose your hard motor mount creates the same sort of vibrations in the frame of your cabin and you may have something of a similar problem....... soft motor mounts would be a reasonable first step if my assumption is correct.
    Amateur living on the western coast of Finland

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    Default Re: Engine noise abatement

    Has anyone had experience with sound-deadening paint? It is said to transform vibration into heat. It may not be effective for your noise levels. https://aquietrefuge.com/does-soundproofing-paint-work/

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    Default Re: Engine noise abatement

    Quote Originally Posted by rbgarr View Post
    Has anyone had experience with sound-deadening paint?
    Check out post #28.
    There is nothing quite as permanent as a good temporary repair.

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