Soundproofing Basics

[captainwireman]

I am redoing my engine compartments with a hardwood (Santa Maria). I intend to tongue and groove, cut to shape to match the existing semi rotten plywood, and seal the edges to the hull and sole with a rubber or similar gasket. The Santa Maria is currently planned to about 1/2 inch thickness. I am not concerned with silent operation but do you think this will be insufficient for an acceptable volume​ reduction on a Yanmar 2GM20F?
Here I am in the Rio Dulce and it will not be easy to get the proper materials but I will pay if you may think this set up will not help at all.

[Meanderthal]

I don't know the layout of your boat, although I think you have a cat listed on your profile, and don't know the magnitude of reduction you need. Are your engine compartments more like the doghouse on my catalina?From my own efforts redesigning (still in progress, alas) our doghouse, and measuring the decibel difference with and without the doghouse using an android app, the 1/2" santa maria WILL help. A lot more than

[captainwireman]

The engine compartments are actually quarter births. I will use them for gear and supply storage. A very difficult question to answer but your rep!y gives me enough confidence to see what I get. I have the Android app also. Number one concern is hearing damage from too high of a decibel reading.

[DeepFrz]

Have you checked out Soundown?

[Zach]

It will help. If you have a decibel meter, before you start beefing stuff up have someone stand and watch the meter while you go bear hug parts of the boat and lean on walls.

Sometimes a thin panel close to the engine compartment are making her sing... You can 5200 stiffeners to things, with a couple dots of a hot glue to keep it there until it hardens up.

If you've ever been on a boat with a clear plastic slide panel in the head under engine power you'll know what I mean. It rattles, then starts wiggling... then starts trying to free its self, and sounds like a dolby surround speaker for an engine 20 feet away.

Other panels to look at, are any thin ones around the galley. Sometimes for weight savings 3/8's gets used on the sides of cabinets. Any wide 2 foot x 3 foot panels are big enough to get down to the low vibrations.

Back to your question:

If you have room, laminating on a 1/2 inch layer of plywood before you install the hard wood will help more as it will stiffen the panel more than tongue and groove will.

1/4 inch plywood sounds like a drum skin. 1/2 inch plywood sounds like a drum. 1 inch plywood is quieter... Lamintated 1 1/2 bulkheads you can carry on a conversation on the other side.

If you grab your bulkheads around the engine and can visibly move any of them... A full size sheet of plywood can vibrate at a low frequency and move a lot of sound. If you put an 8 quarter hard wood side to side, and case out any door openings with the same material, it takes the panel size of what can vibrate and makes it smaller so that the frequency it takes to vibrate it hard enough to transmit the sound waves through it like a speaker goes up higher. Diesels are slow, and diesels make deep vibrating booms from combustion that shake everything. Bulkheads are good at transmitting the noise that shakes everything.

Diesels also have valves that send high vibrations out the intake tract. The noise so loud that you can't hear yourself think, is intake tract noise. They make air intake mufflers, and simply having a filter or hose with a few bends in it cuts down on the sound. The rest of the noise is the diesel shaking everything else.

The rule for sounds transmission is that every time you double the weight or density of something, the sound that is transmitted through the material is halved. A lot of boats have heavy weights tied directly to the engine bed. Have an engine bed, and weld battery boxes brackets directly to it.

If you are weight sensitive, and have more room you can use Nidacore which is a polypropylene honeycomb that keeps both skins separated and cuts down on sound transmission because of the air gap between the skins and semi-flexible core absorb the energy. If you hit a hard a bare hand on a plywood panel it rings, if you hit a structural foam panel, it rings... If you hit a Nidacore panel it slaps.

Sound Down and other Lead Lined foam insulation also helps with absorption. You take the energy from the sound wave, give it heavy foam to run through and a lead sheet to bounce into and the energy tries to convert from sound to heat by moving things. This cuts down on sound bouncing from one surface back to the other which is helpful... but also cuts down the amount of transmission that makes it through the surface you are trying to insulate.

The closer you can get to insulating all surfaces around the engine compartment, the less energy makes it out of the engine compartment as sound.

The catch 22 is insulating one bulkheads helps, but all the rest of the bulkheads are reflecting and refracting inside the box. The more insulation you have on all surface the less bounces aft and comes back forward at your insulated panel.

Don't forget the cabin sole and bilge.

Sometimes the majority of the sound comes from the sole panels. Engines are tied into the hull down low, and the cabin sole is down low. If the cabin sole vibrates and your bilge access panels dance around, you can cut down sound transmission by fitting hold down bolts or 1/4 turn fasteners. Sometimes they just need to be heavier. If you standing on the floor reduces the sound level on your decibel meter, you know something else to fix.

If you have the ability, you can also glass in a solid partition less the limber hole ahead of the engine in the bilge so that the entire cabin sole has to vibrate, in order to get sound transmission through it... Rather than just having air to go through.

Cheers,

Zach

[MarkSF]

I understand you are replacing plywood with hardwood. Any sound reduction would relate to the relative mass of the two woods. Is the hardwood much denser than the plywood?

Another way to increase the sound reduction would be to add a second layer of something. Is it practical to have two layers of wood? Can you get any kind of foam wall insulation to place between them?

The commercial products like Soundown work by effectively creating a second layer of heavy material, separated from the primary layer by absorbent foam. I've used it myself, and it is very effective, so that's why I'm proposing doing the same in the locally available materials.

[DeepFrz]

MarkSF, what you are suggesting is essentially plywood, only using one layer of commercial ply and one heavy layer of wood. It will reduce sound transmission somewhat although the somewhat is really unknown and if the structure happens to resonate at a frequency produced by the engine it will actually amplify the resonant sound frequency. I didn't respond to the OP because I don't know what acceptable is.

[Terra Nova]

Originally Posted by captainwireman

...do you think this will be insufficient for an acceptable volume​ reduction...

Insufficient, yes.

[Meanderthal]

Originally Posted by DeepFrz

MarkSF, what you are suggesting is essentially plywood, only using one layer of commercial ply and one heavy layer of wood. It will reduce sound transmission somewhat although the somewhat is really unknown and if the structure happens to resonate at a frequency produced by the engine it will actually amplify the resonant sound frequency. I didn't respond to the OP because I don't know what acceptable is.

As to magnitude, you are probably riggt, but the tongue and groove should mitigate some of the 'drum' effect of a large expanse of plywood. I agree OP should at least get some epdm or foam under the t&g if he can, and before he starts test noise at all the surfaces and look for weak points/nonessential air intrusion.

Sound deadening on boats and cars is a pain in the ass. The limitations of space, weight, budget, supplier availability, diy skill level, healthy engine requirements, and human comfort--add a dose of stupid annoying false advertising car products with 1000% profit margins.

[Meanderthal]

Originally Posted by Zach

It will help. If you have a decibel meter, before you start beefing stuff up have someone stand and watch the meter while you go bear hug parts of the boat and lean on walls...

and etc etc.

Good stuff!

[wingless]

There are three basic steps to controlling noise.

1. Controlling vibration, using CLD (Constraint Layer Dampers) tiles, like Dynamat
2. Block Sound, using MLV (Mass Loaded Vinyl) in a continuous dense decoupled barrier.
3. Absorb Middle to High Frequency Sound, using HMF (Hydrophobic Melamine Foam)

When I soundproofed by car I used this radiant barrier for the (2.) decoupling under my MLV.

One important point is that the openings must be sealed so a direct sound path doesn't exist from the noise to the protected area.

[Pelagic]

I consult closely with noise and vibration specialists on new build of yachts, so here is how I would approach your project.

Noise is 80% structure borne, so first take a look at engine and pump mounts, / hose connections to boat to see if you can quieten down the vibrations.

The cheapest way to reduce the energy of machinery sound waves inside a compartment is to sandwich some basic sound foam between your wall and a pegboard finish on the inside.

Sound energy gets trapped and absorbed in the foam, once it enters the holes in the pegboard and disappates rather than to create a harmonic pulse.

For the airborne, that is easy, just make sure there are no gaps or holes in the engine compartment.

[Meanderthal]

Originally Posted by Pelagic

I consult closely with noise and vibration specialists on new build of yachts, so here is how I would approach your project.

Noise is 80% structure borne, so first take a look at engine and pump mounts, / hose connections to boat to see if you can quieten down the vibrations.

The cheapest way to reduce the energy of machinery sound waves inside a compartment is to sandwich some basic sound foam between your wall and a pegboard finish on the inside.

Sound energy gets trapped and absorbed in the foam, once it enters the holes in the pegboard and disappates rather than to create a harmonic pulse.

For the airborne, that is easy, just make sure there are no gaps or holes in the engine compartment.

Taking your advice on a project, thank you!

[belizesailor]

Originally Posted by MarkSF

I understand you are replacing plywood with hardwood. Any sound reduction would relate to the relative mass of the two woods. Is the hardwood much denser than the plywood?

...

Santa Maria is a local hardwood. I think of it as similar to oak, but here are the details:

http://www.woodworkdetails.com/knowl...od/santa-maria

[captainwireman]

Originally Posted by DeepFrz

Have you checked out Soundown?

Yes sir. I intend to utilize their products if the noise reduction is not substantial enough. As I stated, it is going to get spendy with shipping and everything else so it is kind of a last option but if I have to do the work in the jungle, well money can generally solve every yacht problem.