Sound Proofing

[lans0012]

Gang,

I've had my Cal 27 with a Yanmar 1gm for a couple of years and am now thinking about trying to reduce the engine noise. There is some foam stuck to one side in some spots but the majority of the engine compartment has no insulation. There was a piece of insulation with like a tinfoil outer layer behind the companion way step that has fallen off and been discarded. There is no insulation above, infront, or behind the motor.

I googled the subject and saw some product websites, but does anyone have any experience with this? Will it reduce engine noise? Could there be a reason why there is so little sound proofing? Could it be because of heat or some other reason, or was it just a cost saving measure?

What are the different types and advantages/disadvantages?

I tried searching on the forums but didn't find much. I always get good responses on here.

Thanks in advance.

[MarkSF]

I was reading this article the other day.

Noise Insulation for Engine Rooms - Inside Practical Sailor Blog Article

Seems like you want 2" thick composite material that's rated for engine room use. Now what would have been REALLY useful is if they told you where to buy it

[IslanderGuy]

We have a 32 foot boat with an Atomic 4 which was bolted right on the engine bed rails, without engine mounts. It is under the stairs, open to the space under the cockpit.

I added sound insulation from here...

LED lighting, soundproof, Sailor's Solutions Inc.

around the three sides of the engine, but it is still open under the cockpit. I used a decibel meter to check the difference. I do not remember the actual numbers, but the drop on the meter was not as much as I had hoped. I was pleasantly surprised however at how the actual pitch and tone changed, and made the noise much less intrusive and much more bearable on long motoring days. A lot of the noise was from the vibrations though, not actual engine noise as evidenced by the fact the V birth was likely the loudest part of the boat!

Since then I have replaced the engine with another Atomic 4 I rebuilt, and added real engine mounts with rubber isolators. This drastically reduced the over all noise as it cut down on the vibrations immensely. Now that the vibration noise is reduced, I'm curious to know how much of a difference the foam is making, but I'm not about to pull it out to check!

Someday I want to add a rear wall to the engine compartment to cut down on noise reverberating through the space under the cockpit and thundering in the quarter births, but that's low on the list now.

So I guess overall I would say if the cost is not much to you, go ahead and give it a try, it will likely at least change the tone and make a difference that way, and might reduce the overall noise as well, especially if your engine has rubber mounts on it.

[JRA1968]

We use fat-mat , or dynamat its about 3/16 thick and has a heatshield built in fool proof goes on easily and in our opinion there is no substitute, no glue needed cut it with scissors, the only thing it needs to go one warm surface can be cool but marerial needs to be warmed up . Put it in floor of car blast heat use space heater whatever. Cheers and strong wind

[lans0012]

There is really good engine access from the giant lazerette in the cockpit. It's big enough to fit me at 6' 230 down in there with no problem with the entire port side of the motor exposed. This is good for access but probably bad for noise.

When I open the lazerette with the motor running it gets a lot louder, maybe I can start small with the lazerette door and exposed flat surfaces in the locker and see if that makes any difference before I go crazy and stick this stuff everywhere. It's not cheap stuff it seems.

I'll also see how well it sticks upside down in this small area. I hate drilling holes in a miraculously solid 25 year old cored cockpit floor more than I hate engine noise.

[lans0012]

I checked out the fatmat website and it seems like it's easy to put on and it's definitely cheaper than some of the other stuff. Thinner though. I might have to let this one stew a little.

Anybody else have any recommendations?

[Waltthesalt]

You shold be able to find a supplier in your area as it's commonly used on commercial boats. Sound insulation comes in various weights. Normally heavier thicker insulation isolates best. You can google insulation instructions. I think an important aspect is to avoid gaps or holes as the sound will channel thru there.

[jrd22]

I've sound proofed several engine compartments and have used a foam/barrier product (Barrier 104) from Hamilton Jet. You need the barrier to absorb or block the diesel knock and the foam to absorb sound in general. While the thin materials might help a bit with a gas engines noise you won't get much reduction in decibels with a diesel. The stuff isn't cheap but does an excellent job. I didn't have a decibel meter to check before and after but it was a dramatic difference, try to seal it completely (except for your combustion air supply of course). To install use the 3M spray adhesive, there are a couple of different strengths (77 and 90 IIRC), only use the stronger one.
Link to Hamilton

Noise & Vibration Control Products

[Faster]

The engine compartments doesn't really get all that hot... unless you have a long stretch of uninsulated dry exhaust there's no reason to suspect that the space gets any hotter than the operating temperature of the motor.

We've used the foil-backed leaded foam pads (about an inch thick) to good effect, using a spray contact cement to attach it to the engine box panels. In a previous boat we used thinner, lead lined rubber curtains that we had at work around air compressor installations - that might be hard to track down.

But the best thing we ever did for engine noise was to drape a dental X-ray blanket over the block itself.. just make sure to avoid moving parts and the air intake. If you can find a dentist with a 'dirty' or old tired one you may get it for nothing.

One other comment: It's truly amazing how much of the 'engine noise' can be traced to vibrating doors, ladders, panels, etc. If you put a concentrated effort into damping out those vibrations (rubber pads, gaskets, etc) you'll be amazed at the improvement - leaving mostly just the low frequency engine noise which really isn't all that bothersome - but that too can be dealt with...

[SloopJonB]

Originally Posted by Faster

The engine compartments doesn't really get all that hot... unless you have a long stretch of uninsulated dry exhaust there's no reason to suspect that the space gets any hotter than the operating temperature of the motor.

We've used the foil-backed leaded foam pads (about an inch thick) to good effect, using a spray contact cement to attach it to the engine box panels. In a previous boat we used thinner, lead lined rubber curtains that we had at work around air compressor installations - that might be hard to track down.

But the best thing we ever did for engine noise was to drape a dental X-ray blanket over the block itself.. just make sure to avoid moving parts and the air intake. If you can find a dentist with a 'dirty' or old tired one you may get it for nothing.

One other comment: It's truly amazing how much of the 'engine noise' can be traced to vibrating doors, ladders, panels, etc. If you put a concentrated effort into damping out those vibrations (rubber pads, gaskets, etc) you'll be amazed at the improvement - leaving mostly just the low frequency engine noise which really isn't all that bothersome - but that too can be dealt with...

I saw a demo setup for that lead/foam barrier once at a boat show. They had a typical plywood engine box carefully and neatly covered with it and an UNMUFFLED Chevy engine under it. When the box was down it was a very low drone, when open it was an unmuffled Chevy engine - we all know what THAT sounds like.

It was quite remarkable. It is very expensive though. I have seen sheets of it at consignment shops on occasion.