Engine room noise insulation

[harvey38]

I'm installing a new cabin sole, 12mm ply with a 1.5mm holly and teak HD veneer that will sit above a pair of 250hp Ford Sabres, the total area being around 6m2. Any recommendations for acoustic insulation? The existing insulation is the original from the mid eighties so in need of replacing. There is plenty on Google but first hand recommendations would be appreciated rather than marketing speak.

Cheers
Rob

 

[PaulRainbow]

My engine room is done with stuff like this : Acoustic Class “O” Insulation - Silver Faced Box of 4

Horribly expensive, but noise in the saloon is minimal, even running both engines at 2000 RPM

This looks like a cheaper alternative, but can't vouch for its effectiveness.

 

[Sandy]

ASAP have a good range. Consider the frequency of sound you are trying to block and go for a high dB rating.

 

[Tranona]

I also used the ASAP supplied sheets. As important as the material is sealing paths for noise. You should be able to get a close fit on your hatches and use as thick as sheet as possible. It will end up heavy though if the hatches are large.

 

[rogerthebodger]

Generally sound insulation for boats has 3 layers of material the outer layers are sound absorbing foan and the middle layer is a high density barrier layer to stop the sound transmission

The best high density barrier layer id lead but expensive the cheaper alternative is High density plastic.

You pay your money and take your choise

 

[harvey38]

I hadn't realised how heavy it can be, 7KG a m2, I may need to rethink the size of the new hatches

 

[SvenH]

Make sure all seams are air tight. If not you are wasting time and money. (Exagerated explanation)

 

[Halo]

I am not a mobo man so please forgive my ignorance.
If you seal up the engine room and have two large engines how do they get air ?
Is there a piped air inlet?

 

[harvey38]

I am not a mobo man so please forgive my ignorance.
If you seal up the engine room and have two large engines how do they get air ?
Is there a piped air inlet?

Two large intakes either side of the hull but others do have ducts

 

[rogerthebodger]

Make sure all seams are air tight. If not you are wasting time and money. (Exagerated explanation)

You don't need it airtight what you need is no straight air gaps to allow sound waves to pass through so there is no straight exit for sound

 

[harvey38]

You don't need it airtight what you need is no straight air gaps to allow sound waves to pass through so there is no straight exit for sound

Straight air gaps? Please clarify for me as I only want to do this once The holly and teak wasn't cheap

 

[rogerthebodger]

My engine cover is a teat and holly on top of 19 mm ply that sits on the wheel house supports on the underside is a sound deadening layer that is surrounded by a wood frame with sound deadening layer inside

https://flic.kr/p/WYNt2v

https://flic.kr/p/WYNtvr

https://flic.kr/p/WVhyow

https://flic.kr/p/VGBmK7

In this pic you can see the insulation and the sloping frame that the engine front cover rets on then create a area that any sound coming from the engine then ha to turn 90 degrees thn andther 90 degrees before it can enter the saloon

This can bee seen on the aft end of the engine in the upper pics

The same on the top cover which is the wheel house floor

 

[Boater Sam]

90% of the noise gets out through 10% of the space

Air inlets and outlets need a labrinth lined with sound adsorbing material.

Is that 4 hole self aligning bearing really just loose on the shaft?

 

[rogerthebodger]

90% of the noise gets out through 10% of the space

Air inlets and outlets need a labrinth lined with sound adsorbing material.

Is that 4 hole self aligning bearing really just loose on the shaft?

The self aligning beating is a bearing to take the thrust of the prop which is located outside th sound proof box.

The only way for any sound is through the hold the propshaft passes through the sound proof box and that section is in 2 halfs upper and lower boath or removable with a rotation cover to try to limit an noise that can escape like a labyrinth seal

This setup reduces the noise in the cockpit very low and even in the wheel house is at an acceptable level

 

[Boater Sam]

The self aligning beating is a bearing to take the thrust of the prop which is located outside th sound proof box.

The only way for any sound is through the hold the propshaft passes through the sound proof box and that section is in 2 halfs upper and lower boath or removable with a rotation cover to try to limit an noise that can escape like a labyrinth seal

This setup reduces the noise in the cockpit very low and even in the wheel house is at an acceptable level

Ah, so. Its an unfinished installation.

 

[rogerthebodger]

Ah, so. Its an unfinished installation.

Yes that was taken may be 2007 / 8 during building

I launched her in August 2009

You may notice no exhaust fitted when the pic was taken

 

[PaulRainbow]

Ah, so. Its an unfinished installation.

I think the disconnected water hoses and missing exhaust were clues.

 

[LittleSister]

Don't forget that you can use different materials and/or different thicknesses. So you may want to use heavier and/or thicker material on bulkheads where weight and thickness is less of an issue, and thinner/lighter material on hatches etc. where it is more so.

You are trying to do several different things with sound proofing, including:
- absorbing sounds so that they are not reflected and bouncing back and forth around the engine compartment;
- sealing potential air paths where possible, so that sound has little or no opportunity to travel directly through air to your ears, and where there are inevitable paths (air supply to the engine, for instance), those paths are made into 'silencers' (inevitably only partially) by means of a path as long and convoluted as practicable, and lined with material (bearing in mind its thickness will limit airflow) to deaden reflections; and
- limiting the transmission of sound and vibration through solid materials (such as bulkheads, hull, hatches), by deadening their resonance (which is one reason why weight comes into it).

Note that different sound frequencies have markedly different characteristics. High frequencies are very directional, don't go much round corners (except by reflection), have less energy and relatively easy to absorb (whether by deadening material or the rigidity of e.g. bullhead/hatch material); while low frequencies are much less directional, harder to absorb and more prone to being transmitting through solid materials and setting them moving, especially at their own resonant frequency.

Imagine someone is thrashing a drum kit in the adjacent room, the easiest thing to do is to stand such that you don't have direct line of sight to the drummer, and this will immediately sound a little quieter and much less harsh. If you put curtains and carpets in especially the drummer's room but also yours this will make the sound much less harsh and noticeably quieter; shutting the door and windows to reduce the direct airpaths will make a big difference. The tough one is eliminating the transmission of low frequencies, especially, through the wall, floors and ceilings, and ideally requires the room to be in separate structures.

 

[harvey38]

Thanks all, it seems to me then that having four large panels will have significantly less edge length than the current, badly sealed twelve hatches. With some reasonable acoustic matting, the edges butting up to each other quite snugly and sitting on some thin rubber foam, the engine noise shouldn't be too intrusive

 

[oldgit]

Some while ago had to insulate a pair of M130 Sabres from scratch on a Broom hulled Transocean 37.

Large amounts of insulation was required, trawled through all the usual suspects ie. Chandleries selling basically exactly the same stuff at slightly different prices.
Basically three different layers of various thicknesses and foam densities, some with foil facing.
It then occurred that the insulation all seemed to be of identical sizes of very similar construction but sold under different brand names.
A seach of the internet (including Ebay) produced a couple of companies who look to either actually make the stuff or sell it wholesale.
The construction in various thicknesses and weights appeared to be very similar to the branded stuff as did the claimed insulation properties.
Purchased a number of sheets via Ebay and it did make a noticable dent in the racket produced by the engines and confirm that sealing up gaps can make as much difference as big areas covered with insulation, other racket reducer was fitting a pair of waterlock silencers.
Biggest pain, securing sheets of insulation to non flat engine room surfaces especially under the floor or hatches, a combination of screws/washers/ batons and adhesive required plus using up offcuts to plug nooks and crannies.

The only advertising involved was a picture of a forklift piled high with sheets of insulation, at the time the non branded insulation was considerably cheaper plus delivered right to your door.