Engine room sound insulation

Our Formula 41PC with 450 Cummins was in need of some better sound insulation than the inadequate sound insulation that was installed by Formula. They put in 1/2” foam with a vinyl cover. It looked nice but didn’t do much for diesel noise. We are putting in 2” 2 pound per square foot insulation. It is comprised of 1” foam with PSA bonded to a mineral loaded vinyl layer with another 1” of foam bonded to that and topped by a white mylar. We used the old foam as a template to layout the new insulation. Took a jigsaw with a laminate cutting blade (downward cutting teeth) and easily cut out the new insulation. We then drilled holes in the new insulation. Reverse the drill to drill the foam, then forward to drill the loaded vinyl layer and then reverse to drill the bottom layer of foam. We spaced the brackets to hold up the insulation about 9” apart. After drilling the holes for the pin brackets we inserted the pins through the insulation from the PSA side. Then put a spoonful of thickened epoxy on each pin bracket. Then the fun part, carefully position the piece of insulation in place. You only get one chance as the PSA will quickly grab onto the substrate. We then used a variety of things to prop the insulation in place overnight. Soundown said the PSA will gain in strength in the first 24 hours so we wanted it held firmly in place for that time. Also the epoxy will take 4 to 6 hours to setup. We had a couple of racheting poles used in pickup beds to hold stuff from sliding around. They turned out to be the perfect thing to hold the insulation in place. We used plywood and 2x4s against the insulation and the rachet poles to put pressure up on the wood. So far it has worked very well. After the PSA and epoxy have setup we removed the supports and cut the pins to lenght. Then put on the one way washers and caps onto the pins.

Most foam I know of puts out toxic fumes in a fire. It's usually placed outside of enginerooms so there's a barrier between it and any engineroom fire.

Lepke said:

Most foam I know of puts out toxic fumes in a fire. It's usually placed outside of enginerooms so there's a barrier between it and any engineroom fire.

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It's probably no worse than the fiberglass hatch above it though

It is designed for engine room sound attenuation and is fire retardant.

SoundDown Inc makes a lead foam for sound abatement. It comes in 1"- 4" and they also have sound absorbent underlayment for the cabin soles.

Please share your sound measurements before/after. I recently insulated the cowling of my 2-stroke outboard with 2 lb MLV and realized an 18 db noise reduction.

Nice work

Thanks but it’s still too noise for me on long runs. I find the best way to silence the motor is to turn it off [emoji4]

Keysdisease said:

Nice work

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Agreed. Handy guy to have around

If you don't mind me asking how much was this 2"/2lb product from Soundown? Did you buy directly from them? Thanks

fgarriso said:

SoundDown Inc makes a lead foam for sound abatement. It comes in 1"- 4" and they also have sound absorbent underlayment for the cabin soles.

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They don’t use lead but rather a mineral loaded vinyl in the middle since lead is a hazardous material.

thedeltaskipper said:

If you don't mind me asking how much was this 2"/2lb product from Soundown? Did you buy directly from them? Thanks

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I bought 2 sheets 4.5’x6’ and a roll of the mylar edge tape to finish the cut edges. Total was 547.50 plus shipping. I ordered it directly from Soundown.

Mako said:

Please share your sound measurements before/after. I recently insulated the cowling of my 2-stroke outboard with 2 lb MLV and realized an 18 db noise reduction.

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Unfortunately I didn’t measure the before sound levels. Dumb…. When we hauled we didn’t plan on doing the sound insulation because of all the other work we planned, but after the boat was in the barn we decided to go ahead with it this year.

Honestly I didn’t even look for other sources since we had insulated 4 previous boats with Soundown and had great success with it and was very satisfied with their customer support.

I was posting this reply while the one previous to this was being deleted so this one may not make a lot of sense.

Comodave said:

Honestly I didn’t even look for other sources since we had insulated 4 previous boats with Soundown and had great success with it and was very satisfied with their customer support.

I was posting this reply while the one previous to this was being deleted so this one may not make a lot of sense.

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That was my post Dave which I deleted. I posted from soundproofcow.com where I bought it before but realized it wasn't flame retardant foam so although cheaper probably not recommended, at least for engine rooms.

lwarden said:

That was my post Dave which I deleted. I posted from soundproofcow.com where I bought it before but realized it wasn't flame retardant foam so although cheaper probably not recommended, at least for engine rooms.

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No problem we were both working at the same time.

What stops noise is Mass. Foams and Fiberglass and other "soft" insulations "absorb" noise, but are not noise "barriers."

Lead has significant mass, and is an excellent noise barrier. Mass Loaded Vinyl (MLV,) which Comodave used in the Soundown product, when used in the same weight, presents the same "mass" as lead. Noise doesn't care what the mass is, 2lb sq ft of Lead or 2lb sq ft of MLV reduce noise the same. Lead is more expensive, and as noted, is toxic, so there is no good reason to use lead instead of MLV on these type boats.

When a mass layer is incorporated into a composite with a decoupler layer of foam against the structure (hatch/bulkhead) and an absorption layer exposed to the noise source, the mass layer's performance as a noise barrier is significantly increased.

Lead is still used is some specific applications like Coast Guard inspected vessels and large class yachts, but these are the exceptions, not the rule.





Originally Posted by fgarriso
SoundDown Inc makes a lead foam for sound abatement. It comes in 1"- 4" and they also have sound absorbent underlayment for the cabin soles.

Comodave said:

They don’t use lead but rather a mineral loaded vinyl in the middle since lead is a hazardous material.

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We put the last piece in today on the access hatch in the middle of the cockpit. Will not be back to the boat until day after tomorrow since my wife has some family function tomorrow, apparently she has her priorities all wrong. Took a photo today before we put the last piece on. So far we are quite happy with how it is going.

This is and always will be an interesting topic. I looked at this years ago. My boat came with a good amount of sound suppression in the engine room, however on long trips the engine noise does get to us. As explained to me, because the vibration from the engines causes the entire boat to be a sounding board (like a guitar body), suppressing the sound is not all about the engine room. Ceiling cloth, curtains, carpet underlying, etc. all help. Of course so do good engine mounts.

I own a music school in Brooklyn and we came up with the same problem in our drum practice rooms. Just impossible to stop the vibration causing the duct work to transmit the sound to the tenants above us (caused a few complaints to the landlord). We already had 2 feet of foam installed above the ceiling when we built the rooms. After some research, I found the best option was "sound absorption", not sound proofing or suppression. We ending up buying specially made floor to ceiling sound absorbing mats.
In the drum room we actually doubled them. This caused an absorbing affect and it worked. Not soundproof, but deadened the sound by absorption.

With the above in mind, I would suggest following the same mindset and use sound absorbing materials both in and around the engine room.

Enjoy!

IntoTheBlue said:

This is and always will be an interesting topic. I looked at this years ago. My boat came with a good amount of sound suppression in the engine room, however on long trips the engine noise does get to us. As explained to me, because the vibration from the engines causes the entire boat to be a sounding board (like a guitar body), suppressing the sound is not all about the engine room. Ceiling cloth, curtains, carpet underlying, etc. all help. Of course so do good engine mounts.

I own a music school in Brooklyn and we came up with the same problem in our drum practice rooms. Just impossible to stop the vibration causing the duct work to transmit the sound to the tenants above us (caused a few complaints to the landlord). We already had 2 feet of foam installed above the ceiling when we built the rooms. After some research, I found the best option was "sound absorption", not sound proofing or suppression. We ending up buying specially made floor to ceiling sound absorbing mats.
In the drum room we actually doubled them. This caused an absorbing affect and it worked. Not soundproof, but deadened the sound by absorption.

With the above in mind, I would suggest following the same mindset and use sound absorbing materials both in and around the engine room.

Enjoy!

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The issue is sound is just waves that cause vibrations. Unless you decouple walls , ceilings, floors or duct works the vibrations will just transfer until enough mass or air weakens them. You need staggered decoupled walls or green glue etc.

I believe that is the function of the loaded vinyl layer in the middle. The foam acts as a decoupler and the loaded vinyl absorbs the sound (vibrations).

Comodave said:

I believe that is the function of the loaded vinyl layer in the middle. The foam acts as a decoupler and the loaded vinyl absorbs the sound (vibrations).

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I was replying more to the drum room scenario.

In my understanding you are correct in your main point, I believe the foam can act as a decoupler. However, MLV itself won’t absorb sound but rather redirects them. Sound absorption materials turn the waves into heat. Sound proofing like MLV redirects the waves (which decay over distance, hence why airspace between barriers is useful).

For an engine room walls from the cabin interior or other noise sensitive area , I think sound proofing would be great (with green glue or something that decouples it so it just doesn’t transfer to the fiberglass ) from the cabin, and absorbstive materials elsewhere in the engine room to try to absorb it.

It’s been said that even a small gap in soundproofing material will still pass half the noise through!

I’ve been immersed in this stuff lately, not for a boat but a house. Had six 15’ rolls of 2lb per sq ft MLV installed last week!

Yes the little holes can let out a bunch of noise but they are also the most difficult to close up. I am starting with the big obvious area, the engine room hatch which is pretty much the size of the cockpit. We finished that area and will see how much different the sound will be in the spring after we launch. Then if we still need to do more we will.

Staggered studs and green glue type treatments are great for land based installations. A staggered stud wall with MLV laced between and green glue attached drywall is probably as good as it gets without getting extreme. A "floated" floor stops transmission through the floor. These treatments are for when you have space, every inch on a boat on the other hand is precious.

Drum risers are sometimes floated or decoupled for the reasons stated. Low frequency noise has power, that's why if you're at a stop light and a car 2 lanes over has a bass bazooka in the trunk you feel the bass but can't hear any singing or other instruments. The mid and high frequency sounds are stopped easily by safety glass (which is decoupled) and a steel car. High frequency finds its way through the smallest cracks, why gaskets are important. Turbo whine will squeeze through a very crack.

There are only 2 ways to reduce noise, put mass between you and the noise, or get further away from it. Decoupling kind of fakes out noise into thinking its further away because it interrupts the wave path. Foam on either side of a mass layer increase the performance of noise reduction considerably.

Following best practice for boats is a sure way to get good performance. Some land based treatments will crossover to boats (MLV is used for both) but usually boat products perform better for the space they take.

1lb sq ft MLV = STC 28
2lb sq ft MLV = STC 32

Vibration is noise. Secondary isolation of generators and care to be sure exhaust components are not transmitting exhaust pulses into overheads and bulkheads makes for a quieter boat at anchor.

Engine mounts also have a performance lifespan, and because they deteriorate so slowly they are seldom noted as a source for noise.

So it seems that anyone with a four stroke diesel (especially a four cylinder) should consider the investment in flexible mounts.

I didn’t need them with my 6-71, but they are smooth by nature. However my V-6 will make your teeth chatter in a certain rpm band.

My Vicem had two sweet 1,100hp V10s. The engine room was directly beneath the main salon and near helm. It had quite a bit of decoupling systems and baffles/ screens/ foam for deadening sound in the ER. Lower frequency diesel grumble was not a problem. The whine of both turbos boosting up when I’d change from no wake idle to 22kt cruise speed was thrilling, like a jet getting ready to takeoff. But after a while its mid and higher frequency pitch was tiring, plus it interfered with speech normal speaking level.

Steve Moyer of Soundown was supremely helpful and talked me through the process of finding the worst noise leaks using a sound meter on my iPhone (it was $2 I think). Before I took the time to investigate with the sound meter I had planned giant carpet underlayment, assuming that all the noise was just coming through the floor from the ceiling below. This plan was less than perfect because the salon has beautiful inlaid teak and Holly with custom cut area rugs.

With the iphone app I discovered that the most offensive mid and high frequency noise was leaking through wire chases, holes near the engine air exchanges, and resonating in the lockers under the salon seating, just like a guitar body will amplify the strings.

Steve advised me to get simple foam to tightly stuff in and around the wiring and conduit in the chases, this was good for an immediate 10dB cut of the objectionable high frequency whine. Then I measured out the square footage needed to lay MLV at the bottom of every locker and wooden void. We translated that to the appropriate size roll and I had it truck shipped to my marina. I found a carpet layer who was also a boater. He and I made templates then he cut the MLV to exactly conform to those resonating spaces. That was good for another 10 dB in midrange.

My wife and I could converse at a normal level while also running music even though we were blasting along at 20 kn and more. I did not need to buy any new carpet. And we did not need to cover the beautiful salon sole.

Soundown MLV. NIOSH Sound Level meter.

Very happy that worked out well for you.

Symphony said:

Steve Moyer of Soundown was supremely helpful and talked me through the process of finding the worst noise leaks using a sound meter on my iPhone (it was $2 I think)

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I installed Sound down on all my hatches with their perferarated aluminum shield. Works incredibly well. I have a sheet of 2" left over. How much do you need?

If somebody in the next room is making too much noise, what's the first effective remedy (besides yelling at them)? Close the door. Likewise, the most bang for the buck is to close off any openings from the engine room, no matter how tiny they seem to be. Electrical wires, throttle cables, plumbing, etc. are generally not sealed. Even placing new soundproofing around those openings will prove difficult. Spray foam to the rescue. Get a gun like this one and get good at using it. Even a little foam will make a big difference and, with things like a bundle of electrical wiring passing through a bulkhead, it will be easy to rip out and redo should you need to add or subtract from the bundle. Other items, like plumbing penetrations for the head, can be made more permanent by using more foam. $50 in foam can do what $1,500 in mass loaded vinyl can't.

Marco Flamingo said:

If somebody in the next room is making too much noise, what's the first effective remedy (besides yelling at them)? Close the door. Likewise, the most bang for the buck is to close off any openings from the engine room, no matter how tiny they seem to be. Electrical wires, throttle cables, plumbing, etc. are generally not sealed. Even placing new soundproofing around those openings will prove difficult. Spray foam to the rescue. Get a gun like this one and get good at using it. Even a little foam will make a big difference and, with things like a bundle of electrical wiring passing through a bulkhead, it will be easy to rip out and redo should you need to add or subtract from the bundle. Other items, like plumbing penetrations for the head, can be made more permanent by using more foam. $50 in foam can do what $1,500 in mass loaded vinyl can't.

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I agree that sealing small holes is beneficial but not before you insulate the main surfaces first. Start with the big areas and finish with the small ones.