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Author Topic:   Cowl lining to deaden sound

cohasett73 posted 03-06-2014 07:18 PM ET (US)
Forumites one and all lend me your ear,
The problem to be solved;
What type of material is the best for lining the engine cowl to minimize engine sound? Cite sources, and best method of attaching the material to the cowl interior. Let be noted that I have a product from Overland’s, that is a ½” of something like fiberglass with an over coating of aluminum foil. The engine in this case is a 1966 Homelite Gran Prix.
It just seems that with all older engines I have encountered, adhesives failed and the sound deadening materials were discarded.
Help me out brothers.
Tom from Rubicon

ALAN G posted 03-07-2014 02:45 PM ET (US)
"Way back in 1985" I had just purchased a new Evinrude 150 for my 1975 Revenge 19. I found that the new engine was a bit louder than I wanted. In a Revenge with no bulkheads or barriers in the line of sight between engine and front seats, the engine noise not only radiates from behind, but also reflects off the windshield, making the front seats very noisy while seated. My wife and I could not converse except by shouting to one another. After reading several publications on noise and sound treatment, I settled on an acoustic noise barrier from a company called SOUNDOWN. (They are still in business).
The product I chose had an actual lead sheet barrier between a couple layers of foam and a thin vinyl inner surface. I did not measure the lead thickness, but would estimate it was 1/32 inch thick...enough to make the composite barrier noticeably heavy. After cutting patterns out of cardboard which were fit to the interior of the fiberglass engine cowling, I removed the thin useless foam that came with the engine, and glued in the composite foam. I can't remember the type of contact cement I used, but it likely was the best I could buy (I would guess it was 3M spray on adhesive, but not sure). I applied to the interior surface of the cowl and the surface of the foam pieces. It was not a difficult job, but I was careful not to cover any engine air vents or breathing openings. In some areas, there was interference between foam and engine ignition coils, but judicious trimming took care of that. The lead layer also made the foam easier to form, as it could be bent/curved similar to a heavy sheet of aluminum foil.
After all that, the engine was noticeably quieter. I wish I had a sound measuring device, as I could have taken before/after readings, but subjectively, my wife and I could then converse without shouting and the noise level was acceptable. I sold the outboard in 2004 and the sound insulation did not show any signs of coming off due to contact cement failure. In fact, I still have the 1985 9.9 Evinrude kicker I also did the same treatment to, and the barrier is still in place on that engine. Only downside was it made the cowl very heavy to remove relative to the cowl alone. I would have done this again, but my repower was a Honda 135 four stroke and was quiet enough without additional treatment necessary.
Al
cohasett73 posted 03-07-2014 06:56 PM ET (US)
Al, thanks for the come back. SOUNDOWN eh? I must look into it.
Tom from Rubicon,WI
JMARTIN posted 03-07-2014 07:44 PM ET (US)
Tom,
I put some type of sound suppression foil lined felt stuff on my 1992 Evinrude 200. It had some real thin foam before. It worked OK I guess until I had some work down on the cooling system. They did not seat one of the thermostat covers correctly and the felt got wet. It would never dry out and we are talking salt water so I took all of it out.
I am going to look at the Soundown also.
John
RENTER posted 03-07-2014 09:03 PM ET (US)
One of the best sound deadening materials used by some military applications in past years for recon in enemy areas is lining the inside of the cowl with lead sheets. These are similar to lead material in sheets that plumbers use in mounting toilets to tile floors, etc. Very heavy but a remarkable reduction in sound.
Ridge Runner posted 03-08-2014 09:32 AM ET (US)
I would two layers:
First Dynamat Extreme it is a lightweight elastomeric butyl and aluminum vibrational damper - very thin at 0.067”
Second add Dynamat Hoodliner it is a 3/4″ acoustic sound soaker foam with a reinforced, reflective aluminized skin.
I have seen high power racing inboards line there engine cover this way and it makes a huge difference.
http://www.jegs.com/pdfs/dynamatxtreme.pdf
http://www.dynamat.com/brands/hoodliner/
(there is a pdf down load on this page that shows the 2 step process)
cohasett73 posted 03-08-2014 10:34 AM ET (US)
The Dynamat product looks like the way to go. Lead may a great sound dampener but I have enough weight on the transom of my Cohasset as it is. Thanks for your help guys.
Tom from Rubicon,WI

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Author	Topic: Cowl lining to deaden sound
cohasett73	posted 03-06-2014 07:18 PM ET (US) Forumites one and all lend me your ear, The problem to be solved; What type of material is the best for lining the engine cowl to minimize engine sound? Cite sources, and best method of attaching the material to the cowl interior. Let be noted that I have a product from Overland’s, that is a ½” of something like fiberglass with an over coating of aluminum foil. The engine in this case is a 1966 Homelite Gran Prix. It just seems that with all older engines I have encountered, adhesives failed and the sound deadening materials were discarded. Help me out brothers. Tom from Rubicon
ALAN G	posted 03-07-2014 02:45 PM ET (US) "Way back in 1985" I had just purchased a new Evinrude 150 for my 1975 Revenge 19. I found that the new engine was a bit louder than I wanted. In a Revenge with no bulkheads or barriers in the line of sight between engine and front seats, the engine noise not only radiates from behind, but also reflects off the windshield, making the front seats very noisy while seated. My wife and I could not converse except by shouting to one another. After reading several publications on noise and sound treatment, I settled on an acoustic noise barrier from a company called SOUNDOWN. (They are still in business). The product I chose had an actual lead sheet barrier between a couple layers of foam and a thin vinyl inner surface. I did not measure the lead thickness, but would estimate it was 1/32 inch thick...enough to make the composite barrier noticeably heavy. After cutting patterns out of cardboard which were fit to the interior of the fiberglass engine cowling, I removed the thin useless foam that came with the engine, and glued in the composite foam. I can't remember the type of contact cement I used, but it likely was the best I could buy (I would guess it was 3M spray on adhesive, but not sure). I applied to the interior surface of the cowl and the surface of the foam pieces. It was not a difficult job, but I was careful not to cover any engine air vents or breathing openings. In some areas, there was interference between foam and engine ignition coils, but judicious trimming took care of that. The lead layer also made the foam easier to form, as it could be bent/curved similar to a heavy sheet of aluminum foil. After all that, the engine was noticeably quieter. I wish I had a sound measuring device, as I could have taken before/after readings, but subjectively, my wife and I could then converse without shouting and the noise level was acceptable. I sold the outboard in 2004 and the sound insulation did not show any signs of coming off due to contact cement failure. In fact, I still have the 1985 9.9 Evinrude kicker I also did the same treatment to, and the barrier is still in place on that engine. Only downside was it made the cowl very heavy to remove relative to the cowl alone. I would have done this again, but my repower was a Honda 135 four stroke and was quiet enough without additional treatment necessary. Al
cohasett73	posted 03-07-2014 06:56 PM ET (US) Al, thanks for the come back. SOUNDOWN eh? I must look into it. Tom from Rubicon,WI
JMARTIN	posted 03-07-2014 07:44 PM ET (US) Tom, I put some type of sound suppression foil lined felt stuff on my 1992 Evinrude 200. It had some real thin foam before. It worked OK I guess until I had some work down on the cooling system. They did not seat one of the thermostat covers correctly and the felt got wet. It would never dry out and we are talking salt water so I took all of it out. I am going to look at the Soundown also. John
RENTER	posted 03-07-2014 09:03 PM ET (US) One of the best sound deadening materials used by some military applications in past years for recon in enemy areas is lining the inside of the cowl with lead sheets. These are similar to lead material in sheets that plumbers use in mounting toilets to tile floors, etc. Very heavy but a remarkable reduction in sound.
Ridge Runner	posted 03-08-2014 09:32 AM ET (US) I would two layers: First Dynamat Extreme it is a lightweight elastomeric butyl and aluminum vibrational damper - very thin at 0.067” Second add Dynamat Hoodliner it is a 3/4″ acoustic sound soaker foam with a reinforced, reflective aluminized skin. I have seen high power racing inboards line there engine cover this way and it makes a huge difference. http://www.jegs.com/pdfs/dynamatxtreme.pdf http://www.dynamat.com/brands/hoodliner/ (there is a pdf down load on this page that shows the 2 step process)
cohasett73	posted 03-08-2014 10:34 AM ET (US) The Dynamat product looks like the way to go. Lead may a great sound dampener but I have enough weight on the transom of my Cohasset as it is. Thanks for your help guys. Tom from Rubicon,WI