Replacing sound proofing diesel engines

[Hudson Force]

Earlier in this thread there was mention of the choice between the sound proof box close to the engine or the sound proof ling of the engine room. At one time I had a soundproofing cover around my generator, but the enclosure limited access and kept excessive moisture in some areas that promoted corrosion. There are variations in design and "engine room" space, but when dealing with an engine room space that a person can enter, even if it's one small crouched position like mine, I rather sound insulate the walls instead of box the engine.

Even with my automotive firewall insulation, while seated in my cockpit at idle speed or up to about 1500 rpm, my engine room exhaust fan is louder than my engine.

[Lepke]

Lead sheet is the best. Most foam works well, but gives off toxic smoke when burning. Lead on the inside walls and foam outside works well. I have two Detroit Diesels under my main cabin and can hold a regular conversation or hear tv/radio.

When soundproofing, make sure engine has enough intake air. I have seen several poor running diesels starved of air by soundproofing.

[Hudson Force]

Originally Posted by Lepke

........................
.............. I have two Detroit Diesels under my main cabin and can hold a regular conversation or hear tv/radio. .......

Lepke brings up an important issue here that we need to consider according to our propulsion systems. My plan allows me to hold a regular conversation or hear tv/radio too, but with my 56hp Yanmar 4JH3E I could pretty much do this with no insulation at all!

We are not all starting at the same place!

[Cheechako]

The old stuff had a layer of lead sheet in it. Very effective. I doubt you can buy that anymore. There is some black dense foam/rubber product with a tough layer of some type of hard rubber in it. About 3/4-1" thick. I forget what it's called, not cheap but effective. Has foil face one side.

[leftbrainstuff]

Originally Posted by trest1

Hi,
Does anyone have any recommendations regarding products available for soundproofing diesel engines. Our current sound proofing is 12 years old and breaking down quite rapidly.
thank you for any assistance
Teresa

Soundproofing has two main components. The first is airborne noise and the second is structure borne.

Airborne noise is created by the intake and to a lesser extent by the exhaust. Blowers also cause issues here. Airborne noise also leaks out of gaps around the engine room. Sealing these gaps will make a noticeable difference. This is step one.

The majority of your powertrain noise will be structure borne. If you have any misalignment in your prop shaft, engine unbalance, collapsed or bound engine mounts or worn tailcase bearings this will transfer through the mounts.

Structure borne noise will travel and breakout wherever there is large unsupported structure. The sole, vertical panels etc. Step two is to check for and fix any of the above issues.

Step 3 is to work out which frequencies are resonant for the rotating elements. Check alternators are not misaligned. You can also note at which engine revs the noise is worst. You might also find other parts of the boat resonate. To change these resonances you can change the stiffness or mass. Stiffness is typically what we tune because mass of most things is fixed.

Step 4 is to apply constrained layer damping, aka soundproofing. The key here is to choose the soundproofing to change the resonance of the panel you attach it to. Ideally this resonance should by at a higher frequency than the source will be.

I applied the above 4 steps to our generator which was exciting the aft bulkhead. I found that the engine mounts were misaligned and there were several gaps around vents and water pipes.

I reduced the noise (sound pressure) by 9 Db and eliminated the bulkhead resonance completely. Much quieter now.

Note that soundproofing would have had no impact for the above use case. You choose sound proofing based on noise attentuation at specific frequencies. This no such thing as universal soundproofing. Also note that there is no correlation between thickness and noise reduction.

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[TheThunderbird]

Outer Alu film
Covering a thin lead (!!!) film + foam, some close to 1" thick.

Without lead, it is a toy.

4'x5' plate was some 140eur and 16#.

It was fixed with long all-star and quite large washers (100?)
.
It must be worked out all around, no holes unfilled

[kentobin]

As a side issue you take an engine and seal it in a box to contain sound. It's generating heat that has no where to escape. Sure you have a heat exchanger to keep the engine block cool but what other issues are there? Alternator is the first thing I think of at risk.

Anyone with any practical experience or issues with this?

Thanks in advance for any insights.

Also old motor mounts are commonly mentioned as a problem with vibration and sound generation as well as causing out of spec engine alignment which can cause sound issues. May want to check them as well as the alignment.

[Rustic Charm]

Originally Posted by MarkSF

I used the stuff made by Soundown, which is sandwiched mass loaded vinyl. It was very effective. Used the 1" thick stuff mostly. I focused on noise in the cockpit, and used two layers under the cockpit sole and inside the access doors behind the companionway steps, one layer elsewhere.

The noise reduction in the cockpit is very noticeable, to the extent that most noise is from the exhaust now.

To the OP : where is your engine located?

Yes, that's the stuff. It's a pity it doesn't come in various thicknesses. I'd like to put two sheets on the front of the engine bay into the gally but there's not enough room to double or it would be too fidly to keep it there.

[reed1v]

There are leaded, noise absorbing liners made for high temperature settings like engine rooms. Make sure its fire retardant or better yet fire proof. Skip the home made stuff. If you can afford professional installation, go for it. If not, be sure all surfaces are covered, right down to the turn of the bilge. Also there are noise proofing tapes for manifolds, etc.

[notiesbob]

Blachford - Acoustical Products

[David kline]

Can you build panels with sound board filled with Rozall, it,s sound deadening and fire proof. Sound board and roxsall available at Home Depot, let me know, email. David.klineco@gmail.com tks.

[DumnMad]

My engine was pretty noisy when I first got the boat, but not so bad now.

My fix was;
Firstly run the motor at 25% less revs once it is warmed up.
Secondly I told myself a nicely running engine is a symphony.

[IdoraKeeper]

Currently refitting a new cockpit tub to Idora. When installed there will need to be new sound proofing/noise reduction. The engine space is not the same as it was before, I am considering a degree of baffling or dead air space between the sound reduction product and the bulkhead and overhead. Fire resistance and moisture rejection are mandatory. It' going to be interesting to fabricate.

[reed1v]

Originally Posted by Rustic Charm

Yes, that's the stuff. It's a pity it doesn't come in various thicknesses. I'd like to put two sheets on the front of the engine bay into the gally but there's not enough room to double or it would be too fidly to keep it there.

I thought Soundown did come in varying thicknesses? Or at least use to up to 2 inches thick. If you do not have room inside, can apply outside and face with a veneer.

[jhulmer]

I am in the middle of a refit and had the same question. After a lot of research and shopping I found this website that had what appears to be the same material sold by the marine stores but it is in a larger size, so easier to install in larger pieces and a little cheaper.
It is marketed for insulating semi truck cowling, engine rooms etc. and is fire retardant, and foil faced.

I talked to the vender and they said they sell a lot to boat owners and repair shops. when I received my order I was very pleased with the material. I think the foil face is thicker than what have seen on other material. I cut a piece of the foam and set it on fire. It burned for a second and then went out. I tried this several time and got the same results. I bought the 1" material with the center dense plastic sheet. I am looking forward to seeing how much it decreases the engine room noise.

hope this helps.

website: Cab Insulation - Engine Compartment