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Old 16-06-2021, 18:02   #1
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1" versus 2" Engine Room Insulation


I need to replace the insulation in my engine compartment. currently it has some old 2" black foam insulation. It is kinda like a big sponge and is crumbling apart. I have been looking at hard reflective insulation with a foam backing. The one I like is on "Sailor Solutions". Here is the link (1 inch x 1 foot x 1 foot).

I am thinking the hard reflective surface will gain me some noise cancelation and make things easier to clean. However, I am moving from 2" down to 1" which is kinda a big change.... Just curious if anyone has done this and how did it go?
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Old 18-06-2021, 06:41   #2
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Re: 1" versus 2" Engine Room Insulation

Kind of hard to say, because they advertise "90% reduction" rather than number of decibels at this or that frequency. I don't know what sound characteristics their particular polymer layer has - tradition has been to use lead foil, which is expensive, because it won't resonate at any frequency you can hear.

Probably more important than thickness is completeness. Cover everything, into the corners and including the hull under the engine. Sound is damned sneaky when it comes to getting through a crack and then setting your fuel tanks to resonating.
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Old 18-06-2021, 07:00   #3
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Re: 1" versus 2" Engine Room Insulation

If you can fit 2" why wouldn't you? This wouldn't even be a question in my mind. When it comes to insulation and sound proofing, get the best and thickest that can reasonably be installed.
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Old 18-06-2021, 07:19   #4
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Re: 1" versus 2" Engine Room Insulation

I used those in my engine compartment. They work great, and provided a much improved and quieter area. The prior crumbling insulation had certainly lost all of its insulating properties, so the switch from 2 inches to 1 inch was not noticed.

I did 2 things not from the instructions:

I taped all joints and raw edges with aluminum tape.

I used some screws and fender washers to provide backup holding in the event the stick backing failed to adhere at some point in time.
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Old 18-06-2021, 08:45   #5
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Re: 1" versus 2" Engine Room Insulation

Marine engine noise level tends to concentrate in the low to mid frequency range, typically 125Hz to 2,000Hz. In addition, there is low frequency structure vibration related noise.
The ratings for classifying and comparing the various sound-proofing 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.
- 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.
- IIC: In addition to the STC rating, which concerns airborne sound, floor and ceiling assemblies are also rated for impact sound resistance. Impact sound is structure-borne sound transmitted, when one body strikes another, such as in the case of footsteps and falling objects.
SRI: 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.

See also “Taming Engine Room Noise” ~ By Darrell Nicholson in ‘Practical Sailor’
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Old 18-06-2021, 22:40   #6
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Re: 1" versus 2" Engine Room Insulation

There are two main types of materials used to reduce engine noise.
To reduce noise transmitted through a bulkhead to an adjacent compartment you need transmission loss material which is a spring eg foam, mass eg lead or other heavy membrane. You need to cover as near as possible 100% of the bulkhead to be effective.
To reduce the noise within the engine compartment, an acoustic absorption material which is an open cell foam or fibre material usually covered with a lightweight membrane or coating to prevent soaking up water, oil etc. Absorption materials only work at high frequencies (>1 kHz) unless stupidly thick and will only have a small but useful reduction in noise in adjacent compartments. Increasing such material from say 1" to 2" will lower the frequencies of absorption a little but probably marginal overall effect
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