Sound insulation for motor room

[Kd9truck]

Hi all,

I am looking for recommendations on effective sound insulation For my diesel motor room.

As am contemplating re-sound proofing my Yanmar 4jh5e motor room
The outer coating is flaking off the open cell foam that was installed during commission. Right now this insulation is 2 inches thick (I would add more if it would be more effective and space allowed. I have contained this flaking outer coat with tyvec house wrap, it works well and holds up to the occasional rubbing when I need to use the access options to inspect and work on motor.

As an aside the motor mounts are in great shape and the room has an aggressive exaust fan.

To the install point has anyone made their insulation removable for when work needs to be done?

Sadly my hearing has paid the price from a career around horn sirens and loud diesel hydraulic engines.

Thanks in advance.

[GordMay]

Acoustic insulation materials work by two processes:
Absorption of sound energy, which dissipates sound as heat energy,
and
Reflection, which reflects noise away from a location where quieting is desired.

Acoustic Insulation operates on only the absorptive principle, while Vinyl Foam Composite utilizes both absorptive & Reflective processes.

Diesel engines generally emit higher sound pressures, in the lower frequencies.

Marine engine noise level tends to concentrate in the low to mid frequency range, typically 125Hz to 2,000Hz. In addition, there is low frequency structure vibration related noise.


Some earlier CF discussions:
Pay particular attention to any contributions by Alan Wheeler
➥ 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

[rwidman]

Whatever you decide, make sure the product is designed for marine use, is fireproof and fasten it with mechanical fasteners so it cannot come loose and fall onto the engine.

Understand that much of the sound you hear from the engine is actually transmitted by vibration through the structure of the boat. You can possibly reduce airborne sound with insulation, but not the sound transmitted to the structure.

[Kd9truck]

Yes on both the lower DB frequencies and sound thru vibration ie the motor mounts being isolators not unlike HVAC units and their respective isolators.

Thank you for those links Gord.

I have installed sound proofing and sound proofing tech in residential construction but that was 25 years ago. I was wondering/hoping there has been advancements in foam and velum densities since then.
We were using 1.5 in open cell foam glued to a 3/8 in high density velum, that did a good job at dropping the DBs esp in the lower frequencies.

Rwidman yes sir, will try to use the “marine grade” option but not sure why it would need to be, this is a question I ask my self a lot. I can buy the same 316 SS SCREW from a marine vendor 12.99$ Home Depot 8.99$ and 6 in Harbor Freight for 3.99$
as for the fire proof I am willing to bypass this as it is diesel and their should never be a possibility of open flames in this room, and if there is I have bigger problems as everything on a boat is flammable. If it were gas I would be 100% with you.

[Schapera]

Originally Posted by Kd9truck

Yes on both the lower DB frequencies and sound thru vibration ie the motor mounts being isolators not unlike HVAC units and their respective isolators.

Thank you for those links Gord.

I have installed sound proofing and sound proofing tech in residential construction but that was 25 years ago. I was wondering/hoping there has been advancements in foam and velum densities since then.
We were using 1.5 in open cell foam glued to a 3/8 in high density velum, that did a good job at dropping the DBs esp in the lower frequencies.

Rwidman yes sir, will try to use the “marine grade” option but not sure why it would need to be, this is a question I ask my self a lot. I can buy the same 316 SS SCREW from a marine vendor 12.99$ Home Depot 8.99$ and 6 in Harbor Freight for 3.99$
as for the fire proof I am willing to bypass this as it is diesel and their should never be a possibility of open flames in this room, and if there is I have bigger problems as everything on a boat is flammable. If it were gas I would be 100% with you.

Any sailor not worried about a fire in the(diesel) engine area has obviously never seen a fire in the engine area! This is a SERIOUS risk and many diesel-engined vessels have auto fire extinguisher systems costing many $thousands for just this reason. Please familiarise yourself with this danger!

[Kd9truck]

[QUOTE=Schapera;3853304]Any sailor not worried about a fire in the(diesel) engine area has obviously never seen a fire in the engine area! This is a SERIOUS risk and many diesel-engined vessels have auto fire extinguisher systems costing many $thousands for just this reason. Please familiarise yourself with this danger![/QUOTE



Hi Schapera,
If you read a wee bit further you would have read my retraction. That being said I am very familiar with fire and environments that create them. I stand by the frequency of occurrence, I am a retired captain on the FDNY I have been to thousands of fires in more places and with more things than you could imagine , I’ve put several hundred gas motor vehicle fires out (not an exaggeration) and only 1 diesel fire, and that was arson, gas was the accelerant. Clean properly wired, well vented, well maintained, motors should not be a concern.
Thank you for your concern.

[Cheechako]

If your current material is really 2" thick, maybe you should investigate a new thick coating to hold what you have together from flaking etc? Some sort of rubbery paint product? 2" of foam may be pretty good already.

I insulated one boat with some expensive 1" thick multi product stuff. It was shiny on one side to reflect heat, rubbery foam, a thin layer of heavy dense material (decoupler/absorbtion), more foam. (Lead sheet used to be used as decoupler and was great at sound suppression, but for this more modern liner they used some sort of heavyweight non lead in this material due to modern lead standards.) It was pretty good but difficult to install.

Part of the noise problem is the engine still sends vibrations and noise via the output shaft end etc to resonate on the hull and under the cockpit.

I guess I'm saying there is a real limit to how much you can get rid of the noise.


Maybe you should cover what you have and spend your $ and time adding material aft under the cockpit etc also?

[Kd9truck]

Yes, my thoughts as well, I just ordered some of a similar multi-layer/density insulation for auto use. My plan is to build a sound box for my portable compressor as a test.

[skipperpete]

Having recently seen 2 small engine room electrical fires I suggest that using flammable insulation would be a really, really bad idea and had this engine room been soundproofed with flammable soundproofing the outcomes could have been much worse. In the first incident the starter motor failed to disengage because the solenoid stayed active and burnt the main +ve from the solenoid to the master switch....under the insulation. No major fire occurred due to the speedy competent response by the owner and crew but if the insulation had not been fireproof they could have easily lost control of the fire.
The second fire incident in the last 2 weeks was only discovered during renewal of the failed original insulation due to age. It was the laminated type, foam, lead, foam and some sort of fireproof fabric inside a removable soundproof engine cover..... glued on originally but the weight of the lead composite sheet had pulled the insulation down and the foam was disintegrating to black powder. The owner was very surprised when we uncovered a large burnt patch where the alternator came to within millimeters of the insulation, this had been a serious alternator fire during the previous owners time with the boat and was unrecorded or noticed by the surveyor. The resin had been burnt out of the fibreglass...... under the insulation leaving a fuzzy mat of shiny glass fibres in a 10” diameter area and it would appear that the fireproof insulation had contained and probably extinguished the fire.... we’ll never know the circumstances.... the current owner has had the boat for over 10 years and the PO is deceased. At the moment we’re trying to decide which insulation to re install and since it’s a catamaran the lead composite type is a bit too heavy to use 2nd time around. We’ll be doing a test run with whatever the owner chooses..... blowlamp, to see ....A. If it burns and... B. How much smoke it emits.
This is a non commercial vessel but for those in survey, fireproofing in engine rooms is required.... often rockwool or a similar fibreglass product with a “skin” to stop it fragmenting and stop it absorbing water and oil.

[Kd9truck]

Originally Posted by skipperpete

Having recently seen 2 small engine room electrical fires I suggest that using flammable insulation would be a really, really bad idea and had this engine room been soundproofed with flammable soundproofing the outcomes could have been much worse. In the first incident the starter motor failed to disengage because the solenoid stayed active and burnt the main +ve from the solenoid to the master switch....under the insulation. No major fire occurred due to the speedy competent response by the owner and crew but if the insulation had not been fireproof they could have easily lost control of the fire.
The second fire incident in the last 2 weeks was only discovered during renewal of the failed original insulation due to age. It was the laminated type, foam, lead, foam and some sort of fireproof fabric inside a removable soundproof engine cover..... glued on originally but the weight of the lead composite sheet had pulled the insulation down and the foam was disintegrating to black powder. The owner was very surprised when we uncovered a large burnt patch where the alternator came to within millimeters of the insulation, this had been a serious alternator fire during the previous owners time with the boat and was unrecorded or noticed by the surveyor. The resin had been burnt out of the fibreglass...... under the insulation leaving a fuzzy mat of shiny glass fibres in a 10” diameter area and it would appear that the fireproof insulation had contained and probably extinguished the fire.... we’ll never know the circumstances.... the current owner has had the boat for over 10 years and the PO is deceased. At the moment we’re trying to decide which insulation to re install and since it’s a catamaran the lead composite type is a bit too heavy to use 2nd time around. We’ll be doing a test run with whatever the owner chooses..... blowlamp, to see ....A. If it burns and... B. How much smoke it emits.
This is a non commercial vessel but for those in survey, fireproofing in engine rooms is required.... often rockwool or a similar fibreglass product with a “skin” to stop it fragmenting and stop it absorbing water and oil.

You are right!

Sorry I was off gassing, I was able to find a product with a fire resistance rating that I will be testing (stated in a previous reply). I will be testing its fire resistance after the sound test. I keep a clean tight boat, I put a thermal imaging camera on the beast and its components regularly, and there is a CO detector along side the extinguisher hole. But things happen.

My comment was more of a protest on the price gouge with everything related to boating. Fire resistance can and does drive the price up on a great many products especially if there’s a regulation driving it.

Thank you for your thoughtful reply.
Cheers

[GordMay]

Practical Sailor magazine [March, 2022] had a good article, “Reducing Engine Room Noise”, ~ by Darrell Nicholson
➥ https://www.practical-sailor.com/blo...ing-boat-noise

See also, their [old] Tests of 10 sound-attenuation products:
➥ https://www.practical-sailor.com/sys...n-engine-noise

[Chotu]

there are really just a couple concepts. First, mass. Whatever you use has to be heavy. Mass is what makes things soundproof. That's how you stop airborne sounds from passing through.

Second, and probably most important, are the motor mounts. Can you find any updated ones that are better? In my own experience when I upgraded my motor mounts turned a really bad situation with loud motors that you could barely speak above into something that was a quiet hum in the background. nearly all of my problem with too much noise from my motors came from it being transmitted to bulkhead through my mounts.

try to analyze what kind of sound you are getting that is bothering you. If it is being transmitted through the boat or if it is being transmitted through the air.

Also, in addition to the standard motor mounts it is possible to fabricate some that will be better.

[NorthCoastJoe]

Look into a Aqua drive. They use soft mounts so no vibration goes to the hull and the thrust bearing takes the force not the transmission. I am happy with mine.

[Kd9truck]

The start of my motivation for this thread is that the current sound proofing has seen better days. But also my hearing is slowly declining and I figured I should try to preserve it in every way possible.

Yes to the need for density and vibration isolation
Chotu, NorthCoastJoe, I will look into the aftermarket mounts, my current ones are in great shape but there may be room in the winter maintenance budget to upgrade.
Aqua Drive will be my first stop.

[skipperpete]

Originally Posted by Kd9truck

The start of my motivation for this thread is that the current sound proofing has seen better days. But also my hearing is slowly declining and I figured I should try to preserve it in every way possible.

Yes to the need for density and vibration isolation
Chotu, NorthCoastJoe, I will look into the aftermarket mounts, my current ones are in great shape but there may be room in the winter maintenance budget to upgrade.
Aqua Drive will be my first stop.

Your yanmar 4JH5 is a very well behaved engine, low on vibration and not as noisy as just about all the other engines in its weight and power class. The original Yanmar mounts were pretty good at vibration absorption and the only reason to replace em with softer mounts would be if you opted for the Python, vetus or Aquadrive shaft and thrust bearing…. but ONLY with with the CV and thrust block, not the mounts alone.