Reducing Outboard Engine Noise by Acoustic Treatment Inside Cowling

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Author Topic:   Reducing Outboard Engine Noise by Acoustic Treatment Inside Cowling

gmoulder posted 03-30-2014 08:20 PM ET (US)
[On my Boston Whaler OUTRAGE 18 there] are 1996 70-HP Johnson [twin engines]. [I] like [the] sound of engines, but would like there to be less of it. Has anyone installed a product called [Dynamat] inside the cowling with success? Thanks, Glen
jimh posted 03-30-2014 10:38 PM ET (US)
I believe you are asking about Dynamat products, as in
http://www.dynamat.com/brands/dynamat-xtreme/
Looking at their literature in http://www.dynamat.com/download/3019/ a comparison of sound level with and without the product Dynamat Extreme is shown in a graph that plots sound level as a function of frequency. At low frequency, 40-Hz, the product appears to cause a reduction in sound level of about 6-dB. That is a noticeable difference. At other frequencies the material produces no difference or only a difference of 2-dB.
Generally to cut down on transmission of low frequency sound you need a heavy material. I don't see any specification of the weight of Dynamat. Also, I do not see any mention of its cost.
For any material to be used inside the cowling of an outboard engine there must be concern about the temperature and the material's tolerance of water, gasoline, and oil. The temperature inside an engine cowling can become very warm, and there is often water, gasoline, or oil either in liquid form or in a mist.
macfam posted 03-31-2014 07:12 AM ET (US)
Glen,
You may want to this outfit a call.
http://www.soundown.com/Section%201%20PDFs/Products.pdf
They manufacture a complete line of products. Perhaps they could give some options.

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Author	Topic: Reducing Outboard Engine Noise by Acoustic Treatment Inside Cowling
gmoulder	posted 03-30-2014 08:20 PM ET (US) [On my Boston Whaler OUTRAGE 18 there] are 1996 70-HP Johnson [twin engines]. [I] like [the] sound of engines, but would like there to be less of it. Has anyone installed a product called [Dynamat] inside the cowling with success? Thanks, Glen
jimh	posted 03-30-2014 10:38 PM ET (US) I believe you are asking about Dynamat products, as in http://www.dynamat.com/brands/dynamat-xtreme/ Looking at their literature in http://www.dynamat.com/download/3019/ a comparison of sound level with and without the product Dynamat Extreme is shown in a graph that plots sound level as a function of frequency. At low frequency, 40-Hz, the product appears to cause a reduction in sound level of about 6-dB. That is a noticeable difference. At other frequencies the material produces no difference or only a difference of 2-dB. Generally to cut down on transmission of low frequency sound you need a heavy material. I don't see any specification of the weight of Dynamat. Also, I do not see any mention of its cost. For any material to be used inside the cowling of an outboard engine there must be concern about the temperature and the material's tolerance of water, gasoline, and oil. The temperature inside an engine cowling can become very warm, and there is often water, gasoline, or oil either in liquid form or in a mist.
macfam	posted 03-31-2014 07:12 AM ET (US) Glen, You may want to this outfit a call. http://www.soundown.com/Section%201%20PDFs/Products.pdf They manufacture a complete line of products. Perhaps they could give some options.