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Sound insulation for motor and inside hull insulation


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G’day I just purchased an RL28 trailer boat with inboard motor for cruising on and to be honest all my sailing experience is opposite ends of the spectrum, we race a Nacra 5.8 beachcat and have bare boated a Jeanneau 44, both of these haven’t had motor sound to worry about. In Aus what would be the best sound insulation to put under the deck around the motor? Also how much space would you need each side of a Yanmar 10hp motor?  ie can I put panels with insulation a couple of feet away on each side of it? The noise isn’t big but we are planning a couple of thousand kilometre river trip so would like to deaden it as much as possible.

Inside the main cabin the hull has carpet stuck to it as insulation but the V berth has no insulation, what is the best insulation we can put inside the V berth and also replace the carpet with, I don’t mind the carpet but it’s been there a long time and it can do with an update.

Thanks in advance for any advice 

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Talk to these people, that's what they do:

https://www.acoustica.com.au/

Go to their marine section. I bought a couple of panels of their VyBar (20mm and 10mm thick) for my engine compartment. Works well.

(Try to cover every panel and hole in your engine compartment except for where the air gets in and out.)

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Engine mounts are supposed to limit the transmission of vibration to the hull.  Ensure all your engine mounts are operating correctly and are appropriate for the engine.  

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There are often vehicle sound proofing suppliers that can supply you with materiels.

The best is sheet fireproof  closed cell foam / lead/ closed cell foam. That's used in jet engine test bays. I was lucky in being given two 8ftx4ft by  3inch sheets, it's expensive .

This article on yachts soundproofing may help.

 

428634909_Marine-Soundproofing-YM-article(1).pdf

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Soundproofing is a challenge 

sound , vibration is transmitted thru everything that connects your engine room to the hull, structure and  interior of the boat 

 

generally the quieter you make your installation the more noise and vibration you detect

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Sound proofing a shaft drive Yanmar 1-Cylinder is not a realistic enterprise. The engine mounts are too stiff as it's the lightest engine they made and they used the same mounts. You can sound proof the engine compartment all you want but it's just going to resonate through the hull.

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My engine compartment is too tight to use any of the really good sound panels like lead/foam. I basically have near zero clearance.

Has anyone here any experience with those sheets of automotive deadeners like Dyna Mat?

I've seen claims for 10 Db reduction which I assume is predicated on a perfect installation.

Is closer to 5 Db the real world

It will cost $hundreds to line my box with them so I'm reluctant to simply experiment with it.

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I've not used dynamat , but it is highly recommended in the land rover world, for  real land rovers series, 90/110 and defender.

I went for the cheap option on my land rover, building flashing tape, that's Bitumen or butyl backed aluminium foil. Similar to, but not quite as good as dynamat. Works very well in stopping panel vibration and some noise penetration. 

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I've also used dynamat on cars - Subarus - but I have no idea how it would work on a boat. 

I had my engine box covered with Sounddown, re-build the engine pads and replaced the mount when I had my engine rebuilt, but because it's a 4-108, and because I wasn't able to do as Slug suggested and make my engine box airtight, the result was underwhelming.  I'd say don't bother for old installations with old engines. 

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These are great replies both the positive and negative experiences. I have heaps of room around my motor, like about a foot all around with no soundproofing unless you count fibreglass hull and steps that cover the front. There are big gaps around the motor. The inside of the hull is like an echo chamber, when I’m on deck standing above the motor and the wife comes up the companionway the sound is noticeably quieter. Just the reply saying small box coverings got me thinking of compartmentalizing to making a space for spares and tools that would further deaden the sound

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If you have the space - and the money, that foil faced lead/foam sound insulation is phenomenal stuff.

I first ran across it about 30 years ago at the boat show. The vendor had an unmuffled small block Chevy in a box lined with it. Open the box and you know what it sounded like. Closed it was just a hum - you could speak in normal tones right beside it.

They said it was critical to seal all gaps - even small gaps severely degraded its performance. All seams were taped with foil tape and so forth.

It's very expensive but you really get your money's worth.

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^ Been using a two part ceramic paint for insulation the last several years on ships.  Not sure how it would work but it's not super spendy.  Kind of lumpy going on so not a smooth finish, bit you can apply to pretty much any space. Can't remember the brand.

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1 hour ago, SASSAFRASS said:

Can't remember the brand.

Silent Running SR1000. 

It helps.  Easier to use in conjunction when refitting the engine rooms.  As you need to coat the hulls and bulkheads etc.  Sounddown over it is a big help as well.  No 'magic bullet' that I've found thus far (aside from turning them off and sailing :)

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9 hours ago, Ruminator said:

Silent Running SR1000. 

It helps.  Easier to use in conjunction when refitting the engine rooms.  As you need to coat the hulls and bulkheads etc.  Sounddown over it is a big help as well.  No 'magic bullet' that I've found thus far (aside from turning them off and sailing :)

Someone should try this and give us a report so I know whether to keep my money or not ;-)

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On 8/19/2021 at 10:25 AM, Ruminator said:

It helps.

I would not advocate it unless you are doing a full refit in the engine space.  'A little dab of paint here and there' is not going to help.  I rebuilt both engines and rooms back in 2013 and was able to cover everything.  The paint itself is not going to be enough on its own.  You will still need some sound attenuating materials as part of an overall sound management plan.

Also the Aircon compartment was painted.  Those larger Dometic AC units can be irritatingly noticeable.  And so the paint definitely helped with the aircon noise under the seatee.

IMG_0806.JPG

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28 minutes ago, Ruminator said:

I would not advocate it unless you are doing a full refit in the engine space.  'A little dab of paint here and there' is not going to help.  I rebuilt both engines and rooms back in 2013 and was able to cover everything.  The paint itself is not going to be enough on its own.  You will still need some sound attenuating materials as part of an overall sound management plan.

Also the Aircon compartment was painted.  Those larger Dometic AC units can be irritatingly noticeable.  And so the paint definitely helped with the aircon noise under the seatee.

IMG_0806.JPG

That looks really good. I may be pulling the motor this winter so if I do, I'll likely attempt it. Very little clearance for any other options.

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19 hours ago, Ruminator said:

I would not advocate it unless you are doing a full refit in the engine space.  'A little dab of paint here and there' is not going to help.  I rebuilt both engines and rooms back in 2013 and was able to cover everything.  The paint itself is not going to be enough on its own.  You will still need some sound attenuating materials as part of an overall sound management plan.

Also the Aircon compartment was painted.  Those larger Dometic AC units can be irritatingly noticeable.  And so the paint definitely helped with the aircon noise under the seatee.

 

What do you think about doing the surface that faces into the boat, the deck above the motor is very thick and I can paint about half  the side walls. I’m considering having a go with this paint and then putting insulation over the paint. I’m happy to do sound readings for each step to assess it accurately. I just need to find an easy ( cheap) way to measure the db’s. 

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you can put a sound meter app on your phone, it won't be hugely accurate or calibrated but it will show relative change in a somewhat quantifiable manner, better than "I think it is more quiet"...

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1 hour ago, sculpin said:

you can put a sound meter app on your phone, it won't be hugely accurate or calibrated but it will show relative change in a somewhat quantifiable manner, better than "I think it is more quiet"...

Different treatments tend to affect different frequencies. Try to find an app that gives you a spectral analysis in addition to just a dB measurement. I've used Spectroid on my Android phone and like it.

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6 hours ago, madboutcats said:

What do you think about doing the surface that faces into the boat, the deck above the motor is very thick and I can paint about half  the side walls.

Depends.  How perceivably loud is your environment now when running the engine(s)?  As stated above in other posts; any lack of deadening material or openings not dealt with may leave you disappointed.  As both airborne acoustics and material vibrations will transmit through these areas (and may be enough) to negate the effort of both paint and foam panels.

In my case I was able to cover the bulkhead (under the foil faced Sounddown material) and the entire engine compartment including: the transom steps, the aft most portion of the hull, the ceiling and the deck hatch with paint.  This amount of surface area is what probably gives us a favorable outcome for the noise issue.

Although a little finicky, the paint is simple to apply.  But as with any paint job, prep is 90% of the project.  Its been close to 10 years since this project was done and the paint is still holding up fine.  But it comes out of the supplied gun like watered-down playdoh.  And if in a temperate climate you need to make sure its heated to cure properly. 

I completed the engine rooms along with several other projects concurrently to prepare for a multi-year cruise.  As such, I did not take any readings before or after.  My wife and I simply selected the best products (we thought) at the time, did the job(s) and then went blissfully sailing.  When I buy another catamaran and I have to redo the engine rooms would I do it (paint) again - yes.

However, most learned professionals might give the following advice prior using paint or sound deadening materials:

1.  Anything that is not supposed to move in the engine room; shouldn't.  Hoses vibrating against the hull, cheap metal brackets not properly secured. transom shower hoses left dangling, etc. can be a big source of induced noise.  Zip-ties and lacing go a long way in preventing odd sounds.

2.  Make sure your engine(s) are running in spec.  No wild vibrations, cylinders and injectors working insync, valve clearance adjustments, engine mounts serviceable, etc. all will help (or hurt) with the issue.

3.  Invest in an aftermarket air intake filter.  Practical Sailor did an article (18-ish months ago) about aftermarket filters and surprise, surprise - they observed a big sound reduction with these components over the OEM types.  I'm looking at doing this for my Yanmars currently and will probably select the K&N filters.

4.  Fill any cracks, holes or opening that should not be present in the design of your boat in/and around the engine compartments to slow the spread of both airborne and material vibration energy.

5.  Then go with sheets (Sounddown, Dynamat) and paint, etc.  As it all adds weight...

 

Hope this helps, good luck!

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14 minutes ago, IStream said:

Different treatments tend to affect different frequencies. Try to find an app that gives you a spectral analysis in addition to just a dB measurement. I've used Spectroid on my Android phone and like it.

Sonic spectral analysis on your phone. :blink:

Arthur C. Clarke was right - any sufficiently advanced technology is indistinguishable from magic.

I used to pride myself on understanding how things worked but when I read that they had E-mailed a wrench to the space station I cried Uncle.

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30 minutes ago, SloopJonB said:

I used to pride myself on understanding how things worked but when I read that they had E-mailed a wrench to the space station I cried Uncle.

That sounds a bit like RFC 1437

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32 minutes ago, SloopJonB said:

Sonic spectral analysis on your phone. :blink:

Arthur C. Clarke was right - any sufficiently advanced technology is indistinguishable from magic.

I used to pride myself on understanding how things worked but when I read that they had E-mailed a wrench to the space station I cried Uncle.

Yup, now that everyone has a supercomputer in their pocket it's a whole new world.

I downloaded Spectroid to help my son program his DSP-based guitar preamp/effects box to make a cheap Fender Rumbler bass amp sound like a high-tone jazz amp. I figured it was a hopeless mission but between the supercomputer in his guitar preamp and the supercomputer in my pocket, we were able to make that cheap 10" driver do things it was never meant to do.

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How do you get air into the engine compartment if it is completely sealed off?

I’d like to do better on our engine now that we’re using the boat for more cruising and the kids like to be down below.  Last weekend we went at 4 knots vs 6 on a short leg and windless day to keep the sound down. 

I have plenty of clearance around the engine. Our boat is very open and pretty stiff which makes it a great resonance chamber — not ideal when the engine is in the center. 

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Thankyou for the replies and as far as current sound insulation goes I’m starting from about as low a base as you can go, except the engine is mounted on good rubber blocks and there is no vibration. There is a big gap on one side of the motor that is open to the rest of the boat, which I’ll make a new side panel for and do the sound treatments before installation, as I can tab it from the outside of the compartment, the moulded stairs that cover the front of the motor are just the original fibreglass again I can apply the sound treatments to that easily. I will have to give thought to the air intake. I knew there were apps for sound on the iPhone but thought they would be dodgy but now I’ll get the one mentioned, it won’t matter if it shows the exact db as long as it reasonably accurately shows any changes. It’s worth the project to me as a lot of mornings we don’t have wind here and we can make a start to a destination with the motor, as we did a couple of days ago when we had to get back to pack the boat up and head home

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8 hours ago, madboutcats said:

I’ve been trying to find SR1000 in Aus but can’t find any, it’s $160 freight from US anybody know of a place in Aus that sells it

There are several local sound deadening paints available locally; Repco sells some (for car bodies).

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Thanks for the replies, I’ve got onto someone that has some sound deadening panels left over from building a submarine  and I reckon the Navy concentrates on noise, so I’m going to use those panels, that’s a good tip about the automotive paint, I’ll look into that as well

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On 8/21/2021 at 10:29 AM, Alex W said:

How do you get air into the engine compartment if it is completely sealed off?

I’d like to do better on our engine now that we’re using the boat for more cruising and the kids like to be down below.  Last weekend we went at 4 knots vs 6 on a short leg and windless day to keep the sound down. 

I have plenty of clearance around the engine. Our boat is very open and pretty stiff which makes it a great resonance chamber — not ideal when the engine is in the center. 

This is actually really important, the best solution is forced air in and exhaust, but it's a bit spendy for the two fans install etc.  It does give you a lot of flexibility in closing up the space, on a smaller diesel 4" flex ducting should be plenty.  Usually a self draining louver or dorade type intake and exhaust box for air as high as you can get and away from spray, is the best. Starving a diesel of air is bad, leads to poor combustion and gradual fouling of the engine which just gets worse.  Restricting air flow and increasing it's velocity also can pull moisture into the space.  For a given engine I would talk to a rep and ask about min intake exhaust size without fans and see if that can work.  The fans are nice, they enable a much smaller space and or more sound insulation.  You need to pull heat out and feed adequate intake air that's about it.  In the PNW not a huge deal as in tropics, so just ducting will probably work.  Also going with softer engine mounts can make a huge difference, another one to talk to a engine rep about.

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Besides combustion air, there is also the issue of cooling air for the alternator. My 90A Balmar gets pretty warm, I have been trying to think of some way to get cooling air to it but the engine box is very tight.

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I have an opening in the engine box that is at the head of the aft berth.  Very loud if you are trying sleep.  I have been trying to think of ways to close this but get sufficient air for the engine.  I realize that positive pressure is a no no as it can push fumes into the cabin that you do not want.  I am not sure how you increase airflow without increasing positive pressure.

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17 minutes ago, Ishmael said:

Besides combustion air, there is also the issue of cooling air for the alternator. My 90A Balmar gets pretty warm, I have been trying to think of some way to get cooling air to it but the engine box is very tight.

That's one of the biggest causes of alternator failure in modern cars - they get so packed in that there's no airflow cooling.

As for combustion air - my 2GMF has an air horn with about a 1 1/2" opening so I can't see the need for big ducting and forced air for that aspect.

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