Bang for buck with Noise reduction

Discussion in 'Downeast Engine Room' started by denali2460, Apr 15, 2019 at 12:38 PM.

  1. denali2460

    denali2460 Member

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    I'm considering a DE Cruiser that would need an investment to get the sound down in the house. This will be my first DE and I already know a "loud" house will be a non starter with the admiral on long cruises.

    The current wet exhaust is an 8" exit from Turbo going to a Y with 4" out the back on either side (no mufflers). No current Sound Down under the floor although appears to be plenty of room.

    Questions from the experts (i know some of this is real subjective).

    * What is an "acceptable" Decibel level in the house at cruise to have a conversation with the admiral without shouting ?

    * Would a conversion from two 4" to one 8" custom exhaust with muffler help a lot ? Beyond sound I think this setup in this boat would provide more margin for error to protect the turbo from having a drink. Seriously considering this investment with this boat just want thoughts how much this might help with sound.

    * OR would just investing in Sound down, plugging all holes with foam etc. give more "bang for the buck" in terms of DB sound reduction ?

    Investing in both options for this candidate is on the table.

    thanks in advance for your opinions.
     
  2. denali2460

    denali2460 Member

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    Not 100% sure on the exit from the Turbo @ 8" (just guessing on that)
     
  3. Brooksie

    Brooksie Captain

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    Usually the turbo itself does quite a good job as a muffler so I would start with a complete 2" foam/lead soundproofing job on the entire overhead of the engine space & hatch/s as well as the bulkheads fore & aft of the engine. Don't forget to be sure these bulkheads are extended completely into the keel. Every hole in the space needs to be closed up. The air intake/s should be baffled b/4 they emerge in the cockpit or through the hull sides.
    You don't mention engine box so I am assuming none.
     
  4. ARC

    ARC Senior Member

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    I have full 2” all around and the hatches are tight. I still see 76db at the helm. You can converse ok but I would love to lower it a bit.
     
    ARC,
  5. Brooksie

    Brooksie Captain

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    What about the bulkheads, are they extended right down into the bilge water? The air intakes, are they baffled? Holes in the bulkheads? Maybe some kind of a rudder or shaft vibration causing something else to vibrate like the transom deck?
     
  6. chortle

    chortle Captain

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    Some good advice already given here. Do you have current sound levels with a reasonable meter? It would be good to get a baseline to see how much you need go.

    An Apple I-phone app isn't a bad start and the apps are free, older samsung models are limited by the microphone, an inexpensive meter online is better and you can get one online for less than $20.
    https://www.amazon.com/Meterk-Measuring-Instrument-Self-Calibrated-Monitoring/dp/B07558DPKN

    85 dB is the high end limit for an acceptable sound level. There are industrial and marine standards that use this limit for long term exposure to reduce the chance of long term hearing loss. 10dB less is twice as quiet but difficult to get as noise from the hull moving through the water makes quite a racket. If you are completely inside a well built boat with good vibration and sound isolation you can get lower but not much. Very difficult to retro fit that kind of noise reduction.

    85 dB is loud enough that you have to raise your voice to talk. Not quite yelling but uncomfortable for any length of time, more than an hour. I was able to get from 100+ down to 85 with quite a bit of effort on an old Jarvis Newman 36. Changing the engine from a naturally aspirated mechanically controlled engine to a modern electronically controlled engine made a big difference. So did LARGE and expensive soundown silencers in the exhaust. I have a 5" single exhaust splitting into two 4" going through two large silencers and it is very effective at reducing noise at the transom but at speed most of the noise is behind you.

    The least expensive sound reduction is closed cell foam gasketing and sealing of ALL air gaps. Sound will travel through a small gap really well. Soundown foam overhead also helps reduce reflective noise.

    Baffling air intakes and adding muffler(s) is also very effective. 2" 2# Soundown is also very effective but the cost starts going up to do it well but it is a lot cheaper than $5000 hearing aids that don't work well.

    Vibration also transmits a lot of noise. Good vibration mounts under the engine helps.

    Call Soundown and talk to their technical staff, they will walk you through this one step at a time and recommend the most cost effective solutions. They will also recommend the correct size of material to use for your application. The more technical data you can give them the better they can do the help.
     
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  7. denali2460

    denali2460 Member

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    I do not have current DB measurements as I've yet to sea trial the boat. Just doing some due diligence and all this feedback is very helpful. I plan to give sound down a call for an estimate with decent photos in hand. Need to get some measurements as the engine and genset are pretty close to the forward bulkhead so it's not clear from photo's how much clearance is there to allow for a full 2" solution. Thanks for the tip on the iphone Iapp sounds like a reasonable starting point given it's FREE.
     

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