Budget friendly engine sound insulation.

[GILow]

Hi all,

I’ve been thinking I really should get around to putting some sound insulation in my engine bay.

There are some terrific commercial products out there, but they are mostly very expensive.

So I got to thinking laterally and wondered about using old firewall insulation from car wrecks. The local wreckers sell them for a pittance. There would be a little work in recutting them and patching the holes, but my labour is free.

Has anyone tried something like this or do they have any other clever hacks that have worked for them?

Matt

[JPA Cate]

Spun fiberglass is not very good sound deadening. The expensive stuff with lead in it is.
Would the stuff from cars be worth the effort and the glue? Probably still won't be able to use a phone below decks with the engine running.

Ann

[George_SD]

Most boats don't have real sound insulation, it's only basic foam that gives minimal effect if any at all. You need a suspended mass product (like JPA Cate pointed out) with a layer of lead and foam or rubberized backing. But this stuff is indeed expensive. Another alternative could be spraying/rolling/gluing the engine bay walls with dynamat type of material, but it can be heavy.

You can try to DIY this too if you can get your hands on closed cell heat resistant rubber type of material. You can cover it (glue) with heavy aluminum foil (several layers of aluminum tape maybe), but at the end - it may not be much cheaper.

[Fore and Aft]

Gilow Bunnings has earmuffs for less than $30.
I used the foam insulation with silver foil finish. I like the foil finish as it's easy to keep clean and looks good. There is nothing worse than a scruffy looking engine room.
Cheers

[GordMay]

We’ve had several discussions about sound attenuation/deadening insulation, that would be well worth reviewing.
Including:

➥ https://www.cruisersforum.com/forums...on-241599.html

➥ https://www.cruisersforum.com/forums...ion-65506.html

➥ https://www.cruisersforum.com/forums...nt-220062.html

➥ https://www.cruisersforum.com/forums...tes-76703.html

[Hudson Force]

Originally Posted by JPA Cate

Spun fiberglass is not very good sound deadening. The expensive stuff with lead in it is.
Would the stuff from cars be worth the effort and the glue? Probably still won't be able to use a phone below decks with the engine running.

Ann

I'll agree with Ann regarding the automotive firewall matts being less effective; however, you can find this product new for as little as a dollar/square foot. Well, that's what I paid for it some years back.

I used two layers of the foil lined matting as it was cheap and I had much room to work with it. I covered the forward and aft bulkheads of my engine room as well as the doors.

My sound reduction was significant, but not impressive. For the cost, I would have done it again.

[BillKny]

Sound reduction is a bit of an art, and to do a great job even the experts need some trial and error.

There are a couple of ways to reduce sound transfer through a boat.

The first is frequently the most important, and also the hardest to retrofit. That is sound transmitted directly by hull or bulkhead vibrations. If the engine mounts are worn, improperly configured, badly designed, or badly specified for the installation, or if the engine is poorly aligned, the sound in the cabin can actually come more from the hull vibrating than as sound waves through the air. Not just engine mounts, but other parts of the drive train can be involved. This is tough to fix. Adding sound deadening products is not likely to help much.

Sound in an engine room can bounce around, back and forth, rattling the bulkheads each time it reflects. Reducing this kind of sound amplification is what the "egg crate" foams are good at by eliminating the reflections.

The suspended mass products with lead impregnated foam can be very effective at reducing the vibrations transferred through the air to large, flat panels.

One issue with most boats is that sound can "escape" from a well insulated engine room through even the tiniest holes. Doing a partial job is almost not worth the trouble.

Our boat has an engine room totally sealed from the cabin. Totally airtight, and watertight isolation from the living space. The builder sound insulated the engine room with a combination of layers of coated eggcrate foam, and lead impregnated foam pads. Since they used different products in different places I assume they optimized that based on either careful analysis or experiment. It is extremely effective.

With our propulsion diesel running the interior of the cabin is no louder than the inside of a luxury car. The genset is almost inaudible when running.

[rwidman]

As noted above, much of the sound from the engine running is transmitted to the structure of the boat and the structure transmits this sound, much like the body of a guitar or violin does. Insulation won't help with this and it's going to be very difficult and expensive to remedy this.

As far as anything else, it's critical to make sure that whatever you use is absolutely fire proof and won't give off toxic fumes if overheated or burned in a fire.

It's also very important to mechanically fasten it so it cannot fall onto the engine or contact moving parts.

I don't think your idea is practical or effective.


Ear plugs are cheap and effective.

[waterman46]

All bulkheads in our engine room are already covered in equipment, plumbing and wiring. Do people just mount sound deadening panels over existing equipment or do they remove all and replace after adding panels? A tremendous job in our case.

[captlloyd]

I know hotrodding is big in Australia, find a hot rodder and ask him. They insulate their firewalls and interiors all the time. I am sure there are speed shops over there.

[Lepke]

I've sound insulated a lot of boats. The best is lead sheeting and sprayed urethane foam. But the foam, probably any foam, needs to be outside the engine room because of fire danger, Burning foam is toxic.
But anything helps, even car insulation. Also noise can be transmitted thru the hull and bulkheads depending on how the engine, plumbing and exhaust are mounted. And the engine intake creates a lot of noise. Bigger diesels have air silencers. Just don't restrict your engineroom air intakes. Lots of people try to kill the sound by adding soundproofing to the intakes and then they forget when the diesel runs poorly.

[sailingchiro]

+1 for lead sheeting. It wasn't very expensive and I used double sided roofing tape to adhere around my generator enclosure. Then I used Kilz-Mat on top of the lead sheeting. The sound reduced so much that my air conditioner is louder than the genset.

[GILow]

Some interesting comments here. Thanks all.

[GILow]

Originally Posted by GordMay

We’ve had several discussions about sound attenuation/deadening insulation, that would be well worth reviewing.
Including:

➥ https://www.cruisersforum.com/forums...on-241599.html

➥ https://www.cruisersforum.com/forums...ion-65506.html

➥ https://www.cruisersforum.com/forums...nt-220062.html

➥ https://www.cruisersforum.com/forums...tes-76703.html

Yes, I'd already read those. Mostly they focus on commercial products though the lead sheet idea was more generic.

[BillKny]

Originally Posted by waterman46

All bulkheads in our engine room are already covered in equipment, plumbing and wiring. Do people just mount sound deadening panels over existing equipment or do they remove all and replace after adding panels? A tremendous job in our case.

Yes, everything must be removed and remounted on standoffs to avoid compressing the foam, preferably using rubber vibration isolators. It’s a LOT of work.

The amount of design and installation time, effort and cost is one of the reasons so few boat builders do this job well.