Sound insulation in the engine bay

[Capt Ahab]

I have been looking at the options to add some sound insulation to the engine bay under our cruiser stern (cabin bulkhead and under the deck). I have seen some multi layer options on the web which look great, but are eye wateringly expensive. We run a Beta 38 which isnt very noisy so I am wondering if I am looking at a Rolls Royce solution when a Mondeo option will be good enough.

Has any one else gone down this route and got and suggestions?

Andy

 

[Nickhlx]

We have a Semi-trad with a Beta 43 and running with a hospital silencer. Quite early on I was wanting to be able to hear what was being said, even from quite close by, so eventually did get some sound insulation and fit some.

 

I have really only done the underside of the flooring above the engine. The product I got was from another forum member who had overbought for his needs and was selling on, so I bought the rest of what he had. I do remember it being expensive, but still cheaper than if I had been buying new, and the boxes of 4 sheets, ( each about 4 feet by 2 feet ) were each about as heavy as I could comfortably manage ( very heavy).

 

Anyway, I cut bits up and stuck to the underside of the flooring boards, cutting quite closely to minimise air gaps. The reduction in noise it gave was nothing short of utterly astounding, and demonstrated regularly when the engine is running by lifting one of the panels ( briefly !) It is so good that I would highly recommend doing something similar to anyone wondering what improvement it might make. I had intended doing a lot more of the area, and am sure I will in months to come, but the problem has been shunted to low down on the list of things to do, as already the noise level is "tolerable".

 

The material I used is about 30mm thick, silver foil on one side, a solid plastic layer about 3 mm thick near one surface and the rest is a dense black heavy foam. I don't know what it is called, although it might say on the box - I'll have a look next time I get to it and edit this post if anything is there.

 

Hope that helps,

 

Nick

Edited February 19, 2014 by Nickhlx

[john6767]

I used this stuff. A pack of 4 sheets should do you depending on how many of the surfaces you want to cover. ASAP also do thicker material, but I bet that is quite hard to get fixed to the underside of deck boards. The delivery was quite expensive though as it is big and heavy.

[NB Lola]

The "this stuff" is good. Possibly not what you want to hear ( excuse the pun), we bought and had fitted a hospital silencer, works really well, btw we have a canaline 42 under a cruiser stern

[Neil2]

If you consider that cutting down sound transmission is more important than reducing resonance (sound absorption) on a narrowboat, all you need to do is increase the mass of the partitions through which sound is escaping.

 

With deck boards for instance, you could just screw steel plate to the underside and it would have the same effect as a heavy insulation board. For example 3mm thick mild steel is about the same mass as another two deck boards.

 

The boat I have has the deck and the bulkhead lined with steel plate and you can hardly hear the engine - it's a trad as well. You can comfortably sit in the cockpit with the engine running and have a normal conversation. Mind you it has an aquadrive as well which I reckon makes a huge difference.

 

Whatever you use it just has to be heavy, it's all about increasing mass.

[Staarek]

I want to do the same thing. I was initially thinking about 18 mm mdf painted with fire retardant paint but doing the numbers i don't think it's going to be much cheaper than using something like "this stuff"

 

Here's an alternative:

 

http://www.soundcontrolservices.co.uk/index.php?main_page=product_info&cPath=28_36&products_id=58

 

• Meets the recreational craft directive - Might be important for some.

[Nickhlx]

The problem with simply "adding mass", which I acknowledge will reduce the magnitude of the vibrating surfaces, is that hard surfaces reflect sound to a far greater extent than flexible and absorbent surfaces. Additionally, it is very hard to work wood and metal accurately enough to fill small holes - compare small microphones and the pinhole of an aperture they use to receive the air movement they need.

 

Mass AND absorption ( damping) of the acoustic energy, AND isolation ( block those pin holes) between the noisy zone and the quiet zone is what is needed for an effective reduction in sound transfer...

 

... which is how the experts have evolved the successful sound absorbing ( and heavy) mats, although they still need great attention to detail in their fitting to achieve their best

 

Nick

Edited February 20, 2014 by Nickhlx

[Bullfrog]

If this material is as heavy as you say, how do you attach to the underside of decks, hatch-covers etc. without it sagging off?

[Nickhlx]

I have used a strong impact adhesive, but additionally they may be secured with "penny" washers, secured by screws, screwed through the mat into the underside of decking boards - You need to ensure that the screws are not too long though ! I haven't found the need to use the additional mechanical fixings

 

Nick

[Machpoint005]

If the deck boards don't fit snugly the results might be disappointing. Make sure the edges form good seals with the supporting frame all around, and have a look for ventilation holes/grilles (don't block these!).

 

Otherwise any addition of mass with an absorptive layer facing down will work.The mass does the work of increasing the sound transmission loss of the deck panels, but the absorption prevents reverberant build-up, ie reduces (slightly) the noise level in the engine 'ole.

[john6767]

If this material is as heavy as you say, how do you attach to the underside of decks, hatch-covers etc. without it sagging off?

For the "this stuff" (sorry I was being lazy with the link) I posted about, I bought the spray adhesive that goes with it, however the 2 piece on the deck boards directly about the engine fell off after a couple of months. I stuck them back with Evo Stick contact adhesive and they are still there (I hope). I does get surprisingly hot directly above the engine and I suspect the heat was to blame. If they fall off again I will use mechanical fixings as well as adhesive.

[Androo]

 

 

Here's an alternative:

 

http://www.soundcontrolservices.co.uk/index.php?main_page=product_info&cPath=28_36&products_id=58

 

 

What do they mean by : (+ £88,87) that can't be for P & P.....can it! ?

 

What a price just for the 'Noise of Silence'

Edited February 20, 2014 by Androo

[alan_fincher]

Unless things have changed, this stuff is very much more heavy duty than what at first sight looks like a similar product from Aquafax / Midland Chandlers.

 

It has a denser tighter foam, and the "lead like" layer is a lot more substantial.

 

However it probably doesn't meet the spec of anyone looking for a cheap solution - I have not re-checked current pricing, but when I bought it, it was certainly pricier.

 

If you use lots of Evo Stick contact adhesive to bond to board surfaces, I can pretty well guarantee it will stay put come what may, but I wouldn't skimp on the amount.

 

After I put ours together, though, I think I was floating on the ceilings for about the next three days!

 

(From what I have seen of the "self adhesive" types, I wouldn't dream of hoping they would stay stuck - use something like Evo Stck, and lots of it).

[Robbo]

What do they mean by : (+ £88,87) that can't be for P & P.....can it! ?

 

What a price just for the 'Noise of Silence'

That's the price per unit, postage is free

What do they mean by : (+ £88,87) that can't be for P & P.....can it! ?

 

What a price just for the 'Noise of Silence'

That's the price per unit, postage is free

[Capt Ahab]

Thanks for the guidance - looks like I will buy a couple of packs of "this stuff" and go from there. I have learned a lot about sound absorbtion from this research.

[Charly]

Has anyone used this instead of spray foam/polystyrene/rock wool in a trad engine room? Be interested in your thoughts :-)

[james13]

I was toying with the idea of going to the scrap yard and getting some car carpets or the felt stuff that is stuck to the underside of some bonnets and putting this under the boards on my trad to damp the sound a bit as i would have thought that in this day and age that car carpets/felt etc would be flame proof what do people think?

[Machpoint005]

NO -- those materials are to dampen the lightweight metal panel of a car bonnet, which is very thin. They won't make any difference at all to the sound insulation performance of a deck board, and won't provide any airborne sound absorption either. Don't waste your time.