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  1. #1
    Join Date
    Aug 2008
    Location
    Long Island - north shore
    Posts
    22

    Default Dynamat sound insulation under motor box?

    Hi everyone,

    I was wondering: Has anyone experimented with quieting down the motor box and or inspection floorboard plate above the mufflers/tranny/driveline? I just re-packed my stuffing box and decided to leave off the inpsection floor board while doing a quick inspection of my work. When I cranked the boat over (in water at the dock), it sounded like my mufflers were shot! It wasn't until my son reminded me the aluminum floorboard was not in place that I realized what was wrong. The floor does an admirable job of sound deadening (while everything's buttoned up), but is there room for simple improvement?

    I was thinking that this boat could be made considerably quieter with a simple treatment of some Dynamat? They make everything from door skin stuff to under-hood accoustical deadening (with lead no less). Based on the product they would recommend, I could do the underside of the motorbox (assuming clearance isn't an issue) and do the underside of the floor inspection plate. In addition, why not wrap the stuff around the top half of the mufflers! Based on what I heard with the inspection plate off, there's got to be room for sound/vibe dampening.

    Only downside? The stuff aint cheap.

    Your thoughts???

    Chris G.

  2. #2
    Join Date
    Jan 2008
    Location
    Tallahassee, FL
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    10,662

    Default

    I don't know this stuff well enough to comment but I can raise some questions. Will it absorb water? Will it stay wet and get moldy/smelly? If so, can it be removed and cleaned or at least treated with something before it goes in? I love the idea. To me, quieter is always better.
    My Mom said I'm not allowed to get wet!
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  3. #3
    Join Date
    Jan 2008
    Location
    Pensacola, FL
    Posts
    1,522

    Default

    If you go to a marine supply store, you will find motor box insulation. It is a thin foam with a reflective finish on one side and adhesive on the other side.

    http://www.cyber-bridge-marine.com/e...dproofing.html

    http://www.wakeoutlaws.com/insulateenginebox.php

    Look on Overtons for the product used in the above link.

    Good luck

    I can tell you that FAE (fresh air exhaust) really made my boat quiet.
    1997 MasterCraft 205

    2008 Moomba Outback
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    1999 Malibu Response LX
    1987 Marlin Magnum Skier

  4. #4
    Join Date
    Feb 2009
    Location
    Wausau, WI
    Posts
    436

    Default

    I have an 03 Outback I thought mine would have been louder than it is with the all fiberglass/plastic motorcover. My brothers boat is vinyl covered. I had thought about the same idea you had. I just didn't feel it was worth the work in my case. I like to ski and barefoot. At those speeds wind and water sound is more than the motor. I like the sound of a v-8 hummin along at 4600rpm though.

    I think that Dyamat is a good choice. If i remember it does not absorb water. It is a soft rubber type of material with a reflective coating on one side and adhesive on the other.

    If you give it a try, share your results!
    Matt

    2003 Outback, Assault EFI, (6) Polk Audio DB651s, JL Audio M6600 amp, JL Audio M1700 amp, JL Audio 10w6v2 subwoofer

  5. #5
    Join Date
    Aug 2008
    Location
    Long Island - north shore
    Posts
    22

    Default

    Thanks guys,

    I have an email to Dynamat's tech dept. Let's see what they say. My guess is that it's probably good enough to use (they do make several variants of the stuff). Heck, if it doesn't work out, you could always rip it out, clean off the glue and you'd probably be back to square one.

    Keep in mind, my real concern was the muffler area. I looked at the underside of that floor pan, and said to myself "this thing is begging for some good sound absorbtion type insulation".

    Assuming they get back to me with positive feedback, I'll take one for the team and let you guys know how it works out

    Thanks for your support.

    Chris
    Last edited by cgriebs; 06-22-2009 at 12:17 PM.

  6. #6
    Join Date
    May 2009
    Location
    Carlton Oregon
    Posts
    5,643

    Default

    Quote Originally Posted by Hoopskier View Post
    I have an 03 Outback I thought mine would have been louder than it is with the all fiberglass/plastic motorcover. My brothers boat is vinyl covered. I had thought about the same idea you had. I just didn't feel it was worth the work in my case. I like to ski and barefoot. At those speeds wind and water sound is more than the motor. I like the sound of a v-8 hummin along at 4600rpm though.

    I think that Dyamat is a good choice. If i remember it does not absorb water. It is a soft rubber type of material with a reflective coating on one side and adhesive on the other.

    If you give it a try, share your results!
    Im with you here. It really wouldn't do me any good to try to make my boat quiter. My truck with its Flow Master duels and 4inch exit pipes are way louder then my boat. I enjoy the rumble of my 2 V8s while the throttle is 1/2 way open and the gas gauge is moving to the big E lol.
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  7. #7
    Join Date
    Aug 2008
    Location
    Long Island - north shore
    Posts
    22

    Default

    Here's what Dynamat had to say (if anyone's interested):

    Dear Chris,

    Thank you for your interest in Dynamat. To quiet the engine noise on your
    boat, first install Dynamat Xtreme to the inside of the clamshell followed
    by the Hoodliner. To treat the floor panel for noise, install Dynamat Xtreme
    to the surface. Note that Xtreme is not recommended for areas where heat
    will exceed 300F. This may be the case in areas of such close proximity to
    your exhaust system.

    Regards,

    Technical Solutions
    International Sales Coordinator
    Dynamic Control of North America, Inc.
    (513) 860-5094
    www.dynamat.com

  8. #8
    Join Date
    Aug 2007
    Location
    Nashville, TN
    Posts
    254

    Default

    You might also look into installing the Fresh Air Exhaust system. They advertise that it results in 75% reduction in noise, and that's the side benefit. The main purpose is reduction of carbon monoxide emissions (they are redirected into the water) for safer water sports and idling - no wake situations. I don't have it and can't attest to it, but lots of people on here have it and they really seem to like it. I don't know how it would compare to noise dampening to the dynamat project you are considering, but it might be even better, just as easy, and have other benefits the dynamat does not.

  9. #9
    Join Date
    Mar 2008
    Location
    Calgary, AB, Canada
    Posts
    71

    Default

    I can offer some feedback on the FAE. Yes, without a doubt it does reduce the noise significantly. I have heard many people refer to it as the best stereo upgrade they every made. It also does an amazing job of reducing the CO exposure behind the boat for surfing etc. However, the noise reduction is on the exhaust side and does nothing to reduce the noise you hear coming from your engine box. I have an 07 Mobius LS (DD) so I likely hear more engine noise than all the V-drivers. When skiing or full open throttle, there is still a lot of noice from under that clamshell. I am very interested in how well you Dynamat reduces it.
    I have seen demonstrations of this stuff in stereo shops etc. and it sure makes sense that it will make a big difference. Can't wait to hear the results if you pull the trigger!

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