Soundproofing advice wanted??

[geoleo]

Hello all-especially benne owners. I need advice ! I was proceeding to add soundproofing to the engine area of My 1990 First Beneteau 41S5 with the perkins prima 50 diesel engine. I bought and placed over the old eggcrate foam a Mass loaded vinyl sheet of 1/4" thick 2#sf . I did about 16sf covering the back of the lower steps in the salon and the inside of the vanity cabinet s back which is in the large stateroom above the engine. Then I covered the vinyl with some inexpensive 1" thick 12x12" stick om light weight foam. When checked with a I phone---- very disapointing results so far so Im stopping to regroup. Only 1 DB less on average at our charted key locations. !!!Noise at 1500RPM at dock---- still up around 85db! Perhaps I should have removed all the old factory foam first?? What can I do now? can I add something or must remove and start over. I have unused 20sf MLV. Suggestions please.

[Lepke]

One of the best sound proofing materials is lead sheeting.

[wholybee]

Really difficult on a sailboat. I would say the first step is to make sure it is airtight. Even a small slit will let out a lot of sound. I'm not sure if mass loaded vinyl works if over top of any kind of foam. And certainly the foam won't work as intended if you cover it with anything. You should have the heavy material solidly fixed to wood or fiberglass. The idea is the weight the wood so the wood doesn't vibrate as easily. Then soundproof foam needs to be exposed to the air. It needs to be as thick as possible with lots of deep indentations and angles. Typical would be about 3-4 inches thick, with deep wedges cut into it. The sound gets trapped in the wedges.

[Bowdrie]

Doing a copy-and-paste of a post of mine from another thread.

"I don't know the name of the product, but years ago I got a few square Ft. of a multi-layer product that was intended for lining the cabs/firewalls of large diesel trucks, (I used it to line musical instrument speaker cabinets).
I obtained it at a hose/hydraulic/rubber products shop .
It was about an inch thick.
First was a thin layer of Vinyl that was perforated, second layer was ~3/4in. of a fairly soft Neoprene foam, third layer was a thin sheet of lead foil, 4th. layer was ~1/4in. of dense Neoprene foam.
It was not cheap, and I can't speak directly to its effectiveness for an engine, but it did what I needed it for."

A previous poster is correct, "Lead", you need some mass.

But you just can't make an engine enclosure airtight, the engine needs air to run and you've got to let the heat escape.
That last sentence is what makes noise containment/abatement on a sailboat an uphill battle no matter the magic material used.
A few db of sound reduction is doable and is usually about the best we can hope for without a lot of cost.

[SV Confianza]

We found the a significant amount of sound was coming from un-soundproofed exterior engine hatches on our cat. We covered in Soundown and had a significant reduction in noise. Then…noticed the noise coming from a hard to reach cavity behind the cockpit seats. Will try to cover that too eventually. Very happy with Soundown, but the chase seems like it could be endless.

[Rapanui]

The noise we hear from a boat engine/gearbox/ shaft or saildrive assembly comes to us by 2 routes

• Airborne noise from the noise sources radiated directly and which transmits through the engine enclosure and we hear directly
• Structureborne noise generated by the noisy bits as vibration and which is transmitted as vibration through the engine mounts, through any flexible or rigid connection to the hull and which is re-radiated as airborne noise by the hull, furniture or anything attached. Airborne noise from the noise sources can also excite the hull etc to be re-radiated as airbone noise to the listener.

In general for boats, the structure borne noise component is at least as important as the airborne component even when next to the engine enclosure (unless the engine bay is not well sealed and insulated) and certainly for listeners who do not have direct line of sight to the engine enclosure (e.g. on deck, forepeak etc).

The best you can do with reducing the directed radiated noise is to ensure that

1. Ensure as 100% sealing of the engine compartment.
2. Cover as near as 100% as possible of sides and top of the engine compartment have a transmission loss material comprised of a spring & mass say 25mm foam and heavy floppy mass layer of about 1lb/ft2 (5kg/m2). Lead is perfect but loaded vinyl ok.
3. Provide as much as possible acoustic absorption material usually as a top layer to reduce the reverberation noise in the engine compartment. At least 25mm is required. Warning. Acoustic absorption materials are porous and sometimes flammable and run the risk of absorbing fluids like fuel so have to be designed carefully.

The sad news is that doing all the above will probably make a small reduction in perceived noise as reported by others in this post. To do better will require addressing the structureborne noise and that is much harder to address. You will need to achieve a better performance from the engine mounts and eliminate flanking transmission through engne connections, controls, gearbox and shaft. A good start would be source higher performance engine/gearbox mounts if available.

[Shrew]

We had one of these made for our generator. It works great.

They will send a schematic, you mark exactly where you need openings for hoses. It comes with a ss tube frame. It works and fits perfectly.


Custom generator covers | Great Southern Insulation