4BT Cummins sound insulation

[nick5446]

I've got a 4BT Cummins in my lobster boat that's going to make me deaf if I don't do something about it. It's not exhaust noise - I can't even hear the exhaust over the sound of the engine. I've been doing research on the boat forums and it's honestly a little overwhelming, so a smaller audience seems like it might help. Here's what I'm working with, and what I'm planning to do. Please chime in if you have any experience or ideas.

What I'm starting with:
The engine box is shitty particle board with fiberglass over it. The space around it is tight, so I don't really have any room to get bigger in any dimension. Because of that, it's a pain in the ass to get on and off. Also, the holes around where the exhaust and water discharge exit are very oversized.

Phase 1: Modify the box - cheap and best ROI
I am planning on insulating it using cheap Pink Panther board insulation from Home Depot. I know they make special marine stuff for exactly this purpose, but it's really expensive and I imagine not really worth the 10x difference in price. I'll then fill the gaps using the spray in foam insulation (Great Stuff).

Next, I need to tighten up the holes around the exhaust and water hose. Any suggestions here? Otherwise it'll be wood and glass.

Next, I'm thinking I might cut it in half to make it easier to get on and off, and use some latches to connect the two halves. The oil dipstick and coolant are accessible through the cabin at the front of the engine, so in theory I shouldn't have to remove it that often anyway. Plus, there's already an access panel in the box to get to the oil fill.

Lastly, foam gaskets all around.

Phase 2: Close off the front of the engine
Like I said, the front is exposed to the cabin, which I believe is acting as a giant speaker box. I believe I can make a relatively simple box out of plywood and insulation to seal this off. Need to spend more time looking at it.

Phase 3: Engine blankets
A few companies make special blankets/covers/koozies for valve covers, turbos, etc. that deaden sound. They're pretty expensive, so I'm saving them for last. But if anyone has glowing reviews, maybe I'll get some first.



Anything jumping out as a terrible idea? I'm totally open to suggestions, but am looking to start work this weekend.

[nhbubba]

So far out of my element here. Feel free to ignore me if this is way off base.

I've been kicking around the idea of throwing up some partition walls in my basement to build myself an enclosed workshop. There is a child on the loose in my home now and I'd like to be able to lock the sharp killy bits away from little hands. Even considering a keyed electrical feed for all the equipment. Also want to contain the dust. Coworker is highly recommending I insulate the space for comfort and to keep the sound down. He used a product called Rockwool (previously known as Roxul). Supposedly very sound AND fire resistant.

Maybe a thought for your use too?

Another thing I've looked at is people making vented enclosures for air compressors. They make their own baffles out of cardboard tubes with angled cuts/sheets in it to baffle the sound. Supposedly works really well.

[nick5446]

Haha, I was wondering where you were going with that. Let me check out Rockwool!

[TheIglu]

I think he was going for "kids are way loud, so if you have a kid, the diesel will seem quiet".

[Paul_E_D]

I think he was going for "kids are way loud, so if you have a kid, the diesel will seem quiet".

I thought he built himself a soundproof room.

[loudbeard]

I'm just chuckling at the notion of somehow bringing the noise of a 4BT down to a reasonable level.

[nick5446]

I'm just chuckling at the notion of somehow bringing the noise of a 4BT down to a reasonable level.

I can't adequately put into words how loud this thing is. The first time I started it my wife came running out like something was going to blow up. I wouldn't be shocked if she had already dialed 911.


Check these things out: DodgeRam

Obviously not the right application, but people seem to be raving about them.

[jasnmar]

Urethane foam is a much better bet than either pink foam board or great stuff. Less expensive as well.

[nick5446]

Urethane foam is a much better bet than either pink foam board or great stuff. Less expensive as well.

I don't have much experience working with those foams, but it seems like it might be difficult to use in my scenario. I don't think I've ever seen it used in hot environments. Do you really think it's better at deadening sound than pink foam board? My plan was to use that for 90% of the box, and then fill the gaps with great stuff.

[jasnmar]

I don't have any idea what your engine compartment looks like, but I'm imagining the difference in trying to "drywall" the inside of an engine compartment vs. "paint" the inside of an engine compartment.

I know you aren't drywalling. I know this isn't paint.

Also the 2LB foam is intended for Marine use and is USCG approved as such.

[nick5446]

Here's my engine, no picture of the box, but it's just a box (with a vent near the intake). I think the drywall/paint comparison is accurate.

Most of what I've read about these foams (granted, in the last 10 minutes) is the USCG rating is for buoyancy.

Attachment 48895

[stoinkythepig]

Aeroflex Aerocel sheets are the way to go. The air intake will still be a source of noise though, Can you add one elsewhere and close the one on the box?

[Tricky Mike]

Three things to keep in mind:

1. High frequencies are much more directional than low frequencies and can be dealt with by relatively low mass air barriers between you and the noise. Something like an air tight box would block them fairly effectively.
2. Low frequencies are much less directional and require different mitigation tactics (think about standing on the street next to a dance club. You hear the low frequencies but not the high frequencies until you walk past an open door). Low frequencies transmit their energy through solid objects with some ease. If your air tight box from #1 above were 1/2" plywood it would do little to block the transmission of low frequencies. You need something with significant mass like mass loaded vinyl (MLV) in addition to your air tight box.
3. Any mechanical decoupling you can manage will make a big difference. If the sound has enough energy it will pass through your MLV into your plywood and out into the cabin/etc. If you had a way of constructing the walls in such a way that the high-mass interior wall can vibrate without touching the exterior wall you'll kill a significant portion of the transmitted sound. Recording studios employ floating floors and "room within a room" construction for a reason. The real bitch in your case is that the motor is mechanically coupled to the boat and there ain't a lot you can do about that.

Each of the three makes a difference, but the only way to really make a big dent in dB is to employ all three.

[nick5446]

Aeroflex Aerocel sheets are the way to go. The air intake will still be a source of noise though, Can you add one elsewhere and close the one the box?

Thanks - looking at Aerocel now! I could potentially make it so it sucks air from the cabin...I'll have to look into that.

[nick5446]

Three things to keep in mind:

1. High frequencies are much more directional than low frequencies and can be dealt with by relatively low mass air barriers between you and the noise. Something like an air tight box would block them fairly effectively.
2. Low frequencies are much less directional and require different mitigation tactics (think about standing on the street next to a dance club. You hear the low frequencies but not the high frequencies until you walk past an open door). Low frequencies transmit their energy through solid objects with some ease. If your air tight box from #1 above were 1/2" plywood it would do little to block the transmission of low frequencies. You need something with significant mass like mass loaded vinyl (MLV) in addition to your air tight box.
3. Any mechanical decoupling you can manage will make a big difference. If the sound has enough energy it will pass through your MLV into your plywood and out into the cabin/etc. If you had a way of constructing the walls in such a way that the high-mass interior wall can vibrate without touching the exterior wall you'll kill a significant portion of the transmitted sound. Recording studios employ floating floors and "room within a room" construction for a reason. The real bitch in your case is that the motor is mechanically coupled to the boat and there ain't a lot you can do about that.

Each of the three makes a difference, but the only way to really make a big dent in dB is to employ all three.

You sound like you know what you're talking about...wanna earn some pizza and beer?? Just kidding. 1 & 2 make sense and seem to be a better way of explaining what I plan to do. #3 is a little harder to follow, but like you said, I don't think I have a ton of room for improvement here since the engine is effectively bolted to the hull and mostly open on the bottom and front.