Generator noise level ms390

[tiz]

Wondering if anyone has successfully reduced the generator noise on a ms390 trawler? I tried better gaskets on the cockpit hatches as well as lining those lids with soundproofing. Not really much difference.

85 db in the cockpit. Awfully loud.

--kevin

 

[Comodave]

Get a decibel app on your phone if you don’t already have one. Then move the phone around looking for noise leaks. A small hole can leak a lot of noise. Fix each one as you go. What sound insulation did you put on the underside of the deck?

 

[tiz]

I have a db app on my phone, which is how i know the spl of 85db(c). Moving around the cockpit is useless given that it's the space under which is the problem.

There is no sound shield for the generator and precious little space to add anything there.

So my question toward other owners of the same boat is, has anyone succeeded at this? Id rather go with something proven than do more experiments.

The soundproofing is 1.25" soundown insulation with the lead layer. It made essentially no difference. Maybe 0.5db less noise in the cockpit. It's clearly not enough closure of the machinery to drop the noise level.

--kevin

 

[Comodave]

I still say close up all the holes you can and then see what happens. The Soundown insulation is good but there are probably dozens of leaks around the area.

 

[rslifkin]

Is the space the generator is installed in open to the area between the cockpit sides and the hull sides? If so, that's probably the source of a lot of the noise.

 

[Comodave]

Sundown actually uses loaded vinyl not lead. Lead is hazardous so they use minerals in the vinyl to give it weight.

 

[tiz]

Yes in open space under the cockpit floor. That's why there is noise. I understand that is the problem. What im hoping for is someone who has solved the noise issue.

Its a very tight space -about 1" clearance under deck, water tanks 2-3 inches on either side. About 18" aft and 2-3ft fwd.

 

[tiz]

Lead is only hazardous in dust form or if you chew on it. I don't expect to do either but I appreciate the health concerns.

 

[diver dave]

My genset guy said an effective thing to do with small diesels is to put in an airbox. I am thinking of doing so. You can try a length of vacuum hose and do some experiments.

one story here:
https://www.boatdesign.net/threads/diesel-intake-noise-reduction.62358/

 

[tiz]

My genset guy said an effective thing to do with small diesels is to put in an airbox. I am thinking of doing so. You can try a length of vacuum hose and do some experiments.

Interesting. Ill have to see how to connect hose to the intake.

--kevin

 

[guy with a boat]

Yes in open space under the cockpit floor. That's why there is noise. I understand that is the problem. What im hoping for is someone who has solved the noise issue.

Its a very tight space -about 1" clearance under deck, water tanks 2-3 inches on either side. About 18" aft and 2-3ft fwd.

Lots of people have solved (or improved) the noise issue, and they have done it by the methods recommended here. There is almost never one magic solution to the problem, or the builder would have done it that way. Instead, you likely have multiple sources of the sound traveling from where it is generated to where you are hearing it.
It will take a little effort, and the fix will likely be multiple small measures. Comodave has given you great advice, which is to start by tracking down the path(s) that are allowing the noise to escape.

Maybe someone with the same boat will show up and help speed your path, but your answers will not be indentical to theirs, even with the same model boat.

 

[Keysdisease]

There are several good suggestions above. What stops noise is mass, or getting away from the source. Can't get away, so putting mass between you and the source is the common approach.

As mentioned, the inner panels of the cockpit sides are open to the lazarette, and those relatively thin panels let noise right through. Sometimes there are stereo speakers in those panels as well, which really exaggerate the noise.

Just putting noise insulation on the hatches, and not the entire overhead of the cockpit deck, won't help. The noise will just flank the insulation, so not surprised you had no improvement there.

I know on the 390 space is too tight to do much, but there is something that can be very effective, if it's something you care to do.

Carpet the cockpit from wall to wall, and use a Soundown acoustic carpet underlayment between the deck and the carpet. This is very effective in these situations, and has worked well on MS Pilots to reduce their noise. The Mass Loaded Vinyl (MLV) mentioned previously as the lead replacement of choice can also be used alone. It's readily available and relatively inexpensive for the small space we are talking about, you could buy that first, put it down in the cockpit, and take some readings to see how effective it might be, but the decoupled carpet underlayment will provide much better performance.

If you do this cut for the hatches outside the outline of the hatch, so the product and the carpet act as a flap seal. Lining up the cuts with the hatch would be counterproductive.

$00.02

 

[Comodave]

Lead is only hazardous in dust form or if you chew on it. I don't expect to do either but I appreciate the health concerns.

I don’t know of any manufacturers for recreational boats using lead anymore, the liability must be tremendous. So they use loaded vinyl which isn’t hazardous. Simple solution. And why would you want to use lead??? I have used lead for ballast but fully encapsulated it with fiberglass so it couldn’t get out.

 

[Keysdisease]

Intake stroke noise from a diesel can be very powerful, but only on naturally aspirated engines. On turbo engines this is not a concern.

You can tell quite easily if this is an issue with your installation. Just give it a listen with the air filter on and off, this will give you the tone the intake makes. Now go on deck and listen for that tone.

Engines make all kinds of noise, one kind is dominant. Mechanical, exhaust, intake stroke, structure borne, are some of the common types of noise that can make it on deck.

My genset guy said an effective thing to do with small diesels is to put in an airbox. I am thinking of doing so. You can try a length of vacuum hose and do some experiments.

one story here:
https://www.boatdesign.net/threads/diesel-intake-noise-reduction.62358/

 

[Comodave]

There are lots of things that you can do to help fix the problem. Find the noise leaks is the first place I would start. Then line the sides and top of the compartment with a quality loaded vinyl insulation like you have in the one area. Another way for noise to transmit is through the structure of the boat. In a previous boat I lifted the generator a bit and put isolation feet under the generator to help stop the structural vibration. I also put PSA insulation on the bottom of the drip pan to help stop oil canning of the drip pan. That insulation was pretty thin, maybe 1/8”. When I was done you almost couldn’t hear the generator when it was running. But it was a lot of time and work finding the noise leaks and plugging them, not a quick fix at all. That generator was not in a sound enclosure so it was more challenging to do.

 

[Keysdisease]

Great answer Comodave, structure borne noise from a genset can be considerable, especially when the unit is 2 feet under where you are sitting.

However:

Then line the sides and top of the compartment with a quality loaded vinyl insulation like you have in the one area.

It is not generally recommended to insulate the sides of a machinery compartment, unless there is a accommodation space on the other side of the panel to be insulated. In the case of the 390 the hull sides and "transom" abut outboard, and stopping noise from going through them would not provide reduction in or on the boat except in specific conditions. Using a acoustic absorption foam on the hull sides and "transom" would be appropriate for a few % of reduction by reducing reverberation off the hard surfaces, but a vinyl barrier product would probably be wasted.

 

[tiz]

Keysdisease-

Thanks for that. But it seems if the inner liner sides of the cockpit are what is radiating the noise (and it seems that way) then anything i do to the floor wont make much difference, based on your example. Sound proof under or over without blocking the sound travel out to and up the sides won't be enough. I can test with moving blankets so it helps to have that idea to work on.

--kevin

 

[fgarriso]

You are not going to find one thing that is the magic bullet. It will be a combination of multiple items that will be the fix. Do anything and everything they will all have an effect.

 

[Hippocampus]

Excellent posts and advice above. Had this issue with the engine in a PSC34. Replaced the engine mounts and sound gone. If engine vibration is communicated to the main structural frames they act as a sounding board. Sound may emanate at some distance from the source. Use a cellphone or fiber optics and take peak at your mounts with engine off and on if possible. I was surprised increased noise wasn’t a rattle but sounded like engine noise. Only one mount was bad but replaced them all as engine was up anyway.

 

[johnma]

Check your gen set. On the very early 350's Mainship used a 3600 rpm generator that was extremely noisy. They then switched to an 1800 rpm unit that helped some. That said, its still pretty noisy. I think part of the problem stems from the shape of the cockpit overhead. The sound seems to bounce back and forth from the deck to the overhead. The 400's have their genset located in the same position and have a similar overhead. Any 400 owners want to chime in with their noise experience?

 

[Mako]

85dB is dangerous for long exposure. Tough situation. The structure of the boat in the lazarette/cockpit is transmitting noise as well. Vibration can be reduced with a 2nd set of isolation feet, since the factory feet are generally mediocre in quality. However with your 1" of clearance above, that might not work.

Long term best solution is to relocate the generator into the engine room where it belongs, where the room is well sound-insulated as well.

Do you use your genset often enough to consider removing it and purchasing a newer, smaller, quieter unit?

 

[tiz]

85dB is dangerous for long exposure. Tough situation. The structure of the boat in the lazarette/cockpit is transmitting noise as well. Vibration can be reduced with a 2nd set of isolation feet, since the factory feet are generally mediocre in quality. However with your 1" of clearance above, that might not work.

Long term best solution is to relocate the generator into the engine room where it belongs, where the room is well sound-insulated as well.

Do you use your genset often enough to consider removing it and purchasing a newer, smaller, quieter unit?

No chance to move the generator. You've probably never seen a mainship engine room. I would if i could.

Cost prohibits a replacement. We don't use it enough yet to matter. At some point we might.

--kevin

 

[Comodave]

Soundown made some vibration absorbing pad that was about 1/4” thick. I used it as a secondary absorbing foot. The only problem was that I could only use small squares, maybe 1”x1” due to loading the pad properly. The generator wasn’t heavy enough to load the pad if I just used a solid piece under the generator. They had specs on weight loading so I was able to cut 4 pieces small enough to load it correctly.

 

[Mako]

How about make some square panels, say 2 layers of 2lb MLV glued to a piece of foam, and cover your genset loosely? A poor man’s sound enclosure.

If you can knock the sound levels down by 10dB then it may be satisfactory.

I did this years ago with a portable construction generator.

 

[Shrew]

I had a soft-sided sound shield fabricated by this company:

Custom Sound Shields | Great Southern Insulation

I used the 'heavy-duty' sound shielding option. I have a friend who has the same sound shield.

You can also stick sound shielding to block the cavity in the stairs to the upper bridge and along the underside of the cockpit deck.

 

[Mako]

Shrew, did you take any sound level difference measurements?

 

[Keysdisease]

I have a friend with one of these enclosures, works very well

I had a soft-sided sound shield fabricated by this company:

Custom Sound Shields | Great Southern Insulation

I used the 'heavy-duty' sound shielding option. I have a friend who has the same sound shield.

You can also stick sound shielding to block the cavity in the stairs to the upper bridge and along the underside of the cockpit deck.

 

[CSJ]

Try the custom sound shields from Great Southern Insulation. (https://stopthesound.com/contact-us/). It did the trick for me on my Mainship 350/390. I’ve had it now for about 4 years and it significantly reduces the noise.

 

[CSJ]

Sound shield photo

Photo attached.

 

[BBS]

Something to consider with the "soft" sound shield, at least on my 390, it retained moisture/humidity, leading to rust. Also made routine checks and maintenance unnecessarily difficult. I permanently removed mine for those reasons....rather have a bit more noise. YMMV.