Quiet Motor - Cowl Foam Options

[gbeardmore]

I read the previous post with interest! Got me thinking, my Lark III is missing a bunch of foam in the cowl. Any hands on experience or suggestions about what specific stuff to use for replacement material? Or what to avoid? Thanks!

 

[samo_ott]

Re: Quiet Motor - Cowl Foam Options

I dont know what to replace it with but if the foam is loose and falling off like it usually is, I'd remove it all before it gets sucked into the carb.

 

[d.boat]

Re: Quiet Motor - Cowl Foam Options

To be honest, there's not a lot you can do about noise w/ an outboard. MOst of he noise comes out of the exhaust. You can buy an "outboard kit" from a company that sells sound deadening materials. I bought one. It's foil backed foam with a layer of heavyweight vinyl in it to deaden certain range of frequencies. It looks very similar to the foil backed foam you can buy for vry cheap at Home Depot, etc, but it is very different because of the lamination.

Did it make my outboard a little quieter? Maybe, but it's not a night and day difference.

If you read anything about sound deadening, you will see the principles involve using mass to stop the sound waves (designed for the target frequencies) and physically blocking the sound and completely. Little cracks in the barrier make a big difference - like a 99% closed door isn't nearly as sound proof as one that's completely shut. Tough to do w/ an engine cowling.

Here's a couple of articles to read.
http://www.boatingworldonline.com/Articles/print.html_1922397039.html

http://www.thehulltruth.com/boating-forum/216480-outboard-noise-can-reduced.html

 

[ryendube]

Re: Quiet Motor - Cowl Foam Options

i myself was thinking of trying one of the spray sound deadenors on my bigtwin. let you now how it goes unless someone else can chime in

 

[tmcalavy]

Re: Quiet Motor - Cowl Foam Options

I for one would like to know if a Big Twin can digest spray on foam...record this experiment on video for posterity. Seriously, test it on a similar surface/metal before you commit to spraying it under your cowls.

 

[ryendube]

Re: Quiet Motor - Cowl Foam Options

I for one would like to know if a Big Twin can digest spray on foam...record this experiment on video for posterity. Seriously, test it on a similar surface/metal before you commit to spraying it under your cowls.

I think maybe your are thinking of the expanding foam stuff, sound deadener resembles more rocker gaurd. it would be like painting your cowl with a thick paint. it could flake off I imagine, guess ill see.

 

[tmcalavy]

Re: Quiet Motor - Cowl Foam Options

Yep it has to A.) stick well to the inside of the cowl, B.) tolerate heat, and C.) be impervious to gas/oil and fumes. If it goes on like paint and isn't expandable, how does it deaden any noise? Let us know how it goes...think I'd try it on a smaller motor first...less hp is less expensive to replace.

 

[lowkee]

Re: Quiet Motor - Cowl Foam Options

Here are a couple of options for a cheap, decently working sound barrier:

For an easy(ish) to remove $12 sound deadening barrier, line the inside of the cowling with tape, then spray over the tape with rubberized undercoating. The rubber stops nearly all high frequencies and not only does it conform really well, it also doesn't weight very much. 2-3 cans will cover an entire cowling with a couple of layers, and the rubber particles provide just enough random angles to keep the sound bouncing around before it gets a chance to exit.

If you want to go super-quiet for $20, replace the tape with 1/2" grey foam (the grey foam is heat and chemical resistant) and spray glue it is place, then spray with undercoating. Now any lower frequency sounds which make it beyond the rubber will be deadened by the air pockets in the foam.

 

[ryendube]

Re: Quiet Motor - Cowl Foam Options

Yep it has to A.) stick well to the inside of the cowl, B.) tolerate heat, and C.) be impervious to gas/oil and fumes. If it goes on like paint and isn't expandable, how does it deaden any noise? Let us know how it goes...think I'd try it on a smaller motor first...less hp is less expensive to replace.

http://www.secondskinaudio.com/sound-deadener/spectrum.php

http://www.quietcoat.com/html/products.html


Ive havent read up fully on these products resistance to fuel etc but have heard of people using bed liner spray like rhino gaurd as a sound deadner, it is fuel oil etc resistant

 

[tmcalavy]

Re: Quiet Motor - Cowl Foam Options

Heard about a guy cutting up an old wetsuit and cutting/applying pieces to fit inside the cowl...but he didn't ever say how it worked out. My Johnson 18 hp cowl keeps the noise in to a growl, but both Big Twins are pretty noisy...would be nice to see pix and trial run of something like what lowkee describes. I was told the Big Twin noise comes from the reeds rattling/working, so I guess they are heavy breathers!

 

[ryendube]

Re: Quiet Motor - Cowl Foam Options

Heard about a guy cutting up an old wetsuit and cutting/applying pieces to fit inside the cowl...but he didn't ever say how it worked out. My Johnson 18 hp cowl keeps the noise in to a growl, but both Big Twins are pretty noisy...would be nice to see pix and trial run of something like what lowkee describes. I was told the Big Twin noise comes from the reeds rattling/working, so I guess they are heavy breathers!

not this weekend but next im gunna try it guess best way would be to get a decibel meter, seein as its hard to compare something well from a few hours to the next. my issue is only at idle, moving from hole to hole while fisjing its loud, when wide open i could not care less.

 

[Mandrake35]

Re: Quiet Motor - Cowl Foam Options

I used an exercise mat from Canadian Tire. It's 1'2 inch grey foam. I cut it into pieces as large as I could that still fit the cowl, and used double sided super tack tape from my work to secure it. I only have a 1965 9.5 hp, that doesn't run very hot, but I'm keeping an eye on it for heat issues. I have to say it's made a BIG difference in the noise.....it used to be pretty abraisive, but now its only a much lower pitch hum. I have two cowls, so I'm just experimenting.