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Old 23-10-2020, 09:38   #1
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Sound Insulation

The prior owner installed a white plastic/vinyl backed foam insulation in the engine room. The foam has disintegrated (from heat, vibration, and time). I saw a boat with something called “navy board” or “bulkhead board” in its engine room that was very effective, but I cannot find it. It is a stiff board, with multiple 1” OC holes, white surface. It can be cut to fit and glued/screwed in place. Does anyone know where to find such a material? Can anyone recommend a good (preferably non foam) sound deadening material?
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Old 25-10-2020, 05:52   #2
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Re: Sound Insulation

I'm stuggling with this. The board that you saw is both stiff and has holes in it. Both speak to it's not being a very good sound insulator. Sound insulating materials are "soft" by acoustical standards, such as foam or lead foil. The vibrations move one side of the material, but the other side just sits there, the vibration having been turned into heat within. Ergo, lead ship's bells have a poor reputation for signaling qualities, and stiff fiberglass transmits vibrations including sound very well. As for the holes, letting the air-borne vibrations sneak through a gap or hole defeats the whole process. Sound insulation needs to be sealed around the edges, not just be target panels.

Here's a manufacturer with various options:

https://www.soundproofcow.com/soundp...20applications.

Most options use foam one way or another. Asphalt paint deadens steel wheel wells and the like, largely protecting against sympathetic vibrations (drumming). You need to keep all frequencies of vibration away from the fiberglass of your boat, so rather expensive foam and/or lead foil is going to work best.

I'm sorry I can't do any better. Good luck with it.
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Old 25-10-2020, 06:08   #3
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Re: Sound Insulation

Sound down is the best commercially available product. For engine room. 2-inch thick can be ordered direct from OEM.

https://www.defender.com/product.jsp?id=3018333

The perforated board you mention is similar to old ceiling tiles. Was used in the 70s and 80s on Taiwan built boats. It's marginal at best.

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Old 25-10-2020, 06:10   #4
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Re: Sound Insulation

“Navy Board Facing” is used primarily for fireproofing. I don’t know if it has any practical use in soundproofing.
Navy Board Facing - BGF Industries, Inc. - BGF Industries, Inc.

Johns Manville fiberglass “Hullboard” is used in soundproofing.
https://www.generalinsulation.com/pr...le-hull-boards

Diesel engines generally emit higher sound pressures in the lower frequencies, typically 125Hz to 2,000Hz.
In addition, there is low frequency structure vibration related noise.

Dow “Quash” Sound Management (acoustic) Foam is a low-density closed-cell, non cross-linked, extruded polyethylene foam; which makes it inherently resistant to water absorption. Quash is particularly efficacious toward absorbing the lower frequency noise energies.

The ratings for classifying and comparing the various sound-proofing (attenuation) materials are:


- NRC, the noise reduction coefficient, which is for absorbers. The NRC rating is between 0 and 1 and its an average of how absorptive a material can be at these four frequencies - 250, 500, 1000 and 2000. NRC measures how well materials stop sound from reflecting, as a percentage of sound that a surface absorbs.
and
- STC, the sound transmission class, which is for blockers. STC is a measure of how well a material blocks sound. The higher the rating the better. You can improve the STC of a wall by building it from a more dense material (sound insulation improves by about 5 decibels for every doubling of mass), by adding an air gap, or by adding sound absorbing material.
In countries outside the North America, SRI (Sound Reduction Index), describing an improvement of so many decibels (dB) sound reduction, is a more common measurement.
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Old 25-10-2020, 06:15   #5
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Re: Sound Insulation

"The perforated board you mention is similar to old ceiling tiles."

Oooh, so that's what the OP is talking about! No wonder it crumbled....
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Old 25-10-2020, 07:19   #6
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Re: Sound Insulation

Noise is 80% structure borne and only 20% airborne in an enclosed space, so you need something with deadening absorbtion mass like a combination of dense Rubber, sandwiched inside Foam to change the harmonics of the structure.

The perforated cover (pegboard) is more of a cladding over the heavy mass insulation and helps a bit to diffuse the airborne sound.

I used the Sound down perforated aluminium sheets to clad the insulation QuieTech and it is far more durable than a wooden, plastic or fiber type for machinery spaces
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Old 25-10-2020, 07:51   #7
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Re: Sound Insulation

Thank you to all who replied. To be clear, what crumbled was NOT the Navy Board I am looking for, but the foam type insulation installed by the prior owner. I will look into the several helpful suggestions and see what I can learn. I prefer not to have the “aluminum” backed materials because I want to make the engine room as bright and light as I can, so those products that are paintable (maybe even with a sound absorbing paint, which I understand can work) would be a good option.
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Old 25-10-2020, 08:44   #8
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Re: Sound Insulation

Just a note of caution, if the ceiling tile looking acoustic material is what you have, there is a good chance it contains friable asbestos. Wear a mask and clean the crap out of everything when you’re done. Also consider as a base a self adhering membrane (SAM) like blue skin (basically a poly backed rubber butyl tape). If absolutely has to be covered with a fore retardant acoustic material but the SAM acts like lead in that it deadens vibration and is a dense soft layer and will allow good adhesion to the poly backing. I used to use it in competition car stereos on the backside of door panels and throughout vehicles to dampen vibration. You can buy it cheap at any hardware store and comes in rolls of tape or large sheet rolls but the tape will probably be plenty. Outside the engine bay but nearby use it everywhere to really cut down on vibration which as mentioned above is the bulk of noise transfer.
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