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03-31-2013 08:52 PM
Re: Acoustic Insulation for engine room?

Keep in mind, these photos were taken before I finished the installation, I had not finished taping and sealing all the areas, which I Have done now. I did not close the engine in, I left the aft section open for good air circulation, combined with a new bilge blower and engine I believe it will be much cooler and quieter...or so I hope. I painted everything while I was at it, why not

Hopefully I will be launching soon, and will post if it made any significant reduction in noise and/or heat.

03-31-2013 08:23 PM
Re: Acoustic Insulation for engine room?

Originally Posted by SloopJonB View Post
Flyby, Is that lead foil in the middle between TWO layers of foam? Can you make this up yourself in the engine room or does it have to be pre-manufactured sheet goods?
Sure if you have the lead foil and a good pressure sensitive adhesive that is compatible with the foam you use.
The really good high end foam is rubber.
03-31-2013 12:04 PM
Re: Acoustic Insulation for engine room?

I installed soundown (salem ma) 25 yrs ago around the engine box on my Apache 37 when I replaced the gas engine with a Volvo diesel (much louder). Made huge difference...can hardly hear the engine running. The only disadvantage is the weight of the wall that has to be occasionally removed for winterization. But, a great solution. Hope that helps. Soundown - peace and quiet for architectural, marine, & industrial applications

03-30-2013 01:47 PM
Re: Acoustic Insulation for engine room?

Originally Posted by miatapaul View Post

By the way Dynamat is really just asphalt, so there are adhesive roofing materials that work the same, again really just the mass of the heavy coating. The stuff does smell pretty bad though. I have used it successfully in car installations.
What are we talking about specifically by "adhesive roofing material". do you mean the brush or roll on stuff you put over felt or use for roof repairs etc. If so I could just coat the plywood that encloses the engine compartment and then add foam to the outside to add "dead air space"
03-30-2013 10:18 AM
Re: Acoustic Insulation for engine room?

Jon, I suspect the lead that is mounted against the engine compartment walls will still transmit some sound. You might try using "Dynamat" against the walls, that's what it is designed for. Not cheap but supposed to be effective.
03-30-2013 01:36 AM
Re: Acoustic Insulation for engine room?

Sounds like a trade off and a function of how much money do you want to spend, although I have noticed that my sound-proofing is entirely efficient when I shut off the motor.
03-30-2013 01:30 AM
Re: Acoustic Insulation for engine room?

I've seen a commercial lead/foam sheet that has a fairly dense black "polyfoam" type of foam with a sheet of lead sandwiched to it and a foil backing on the lead side. How does the group think this might work if you first lined your engine compartment with sheet lead then attached the foam product with the lead side "in" - this way you'd have the foam creating the dead air space between two skins of sheet lead.

It would cost several $hundred but the theory seems to fit well with the comments in this thread.
03-29-2013 11:14 PM
Re: Acoustic Insulation for engine room?

voyager, my understanding is that the closed cell foam, if it is high density, will stop high frequency noise, much as ear stopples will. If you've ever used these you may note the effectiveness differs greatly from one brand (foam type) to another.

If you want to stop low frequency noise, you do that by converting the energy into heat, and that requires mass. That's what lead sheeting is for. The high mass of lead absorbs large amounts of vibrational (acoustic) energy and converts it into heat. You can't do that with anything unless it is DENSE which is why they still use lead.

Physics rules, there's no other magic solution. There are some high density plastics like "sorbothane" and others but you will find them as pricey as lead. Bottom line, you can pay the piper, or listen to the the pipes.

Or get some of those expensive Bose active headphones.
03-29-2013 10:26 PM
Re: Acoustic Insulation for engine room?

I am in the same situation, I am in the middle of a repowering project and asked the forum for input on lining the inside of my engine compartment to reduce the engine sound.
Here is a link to the thread http://

I am going to use 1 inch sound absorbing foam I purchased form McMaster Carr. I can not give good reference as to how good it works because I never heard the engine run before I bought the boat. All I can compare it to is how loud is with the engine compartment door open or closed and how loud the engines sound on similar boats. just my .02

The compartment was originally lined with foam that has deteriorated over the 30 years.
03-29-2013 10:12 PM
Re: Acoustic Insulation for engine room?

So, would something like this have a max. temp. that's too low?

At the recommendation of some of the guys on another forum I used to frequent, I used that on a car to help acoustically insulate the passenger compartment. I realize the inside of an inboard's engine compartment will likely get warmer than my old car, but I can't help but wonder if this might not help. I mean, the inside of the engine compartment is largely made of wood; what's the max. temp. there?

Just a thought...
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