Sound insulation for motor room

[skipperpete]

Osprey877, sometimes the bilge and propshaft tunnel acts as a conduit for the sound, a bit like a stethoscope.

[osprey877]

Originally Posted by skipperpete

Osprey877, sometimes the bilge and propshaft tunnel acts as a conduit for the sound, a bit like a stethoscope.

Good suggestion. I also wonder if the prop wash against the hull and/or rudder is a contributor?

[Kd9truck]

Originally Posted by osprey877

My 40 ft sailboat wit 4cyl diesel and direct drive is noisy. I insulated the entire engine compartment wit expensive 2 inch lead core foam marine sound insulation. There was some improvement but not much. I think most of the noise i hear in the cockpit is vibration from the drive train. Revving the engine in neutral is much quieter than underway in gear and sail drives seem to be much quieter than direct drives, which suggests vibration is problem. Shaft alignment is good and i can't feel any vibration in shaft when underway but something is causing the noise. Anyways, don't assume insulating engine compartment will make a big improvement.

Agreed, I am replacing because of the condition of the current insulation is delaminating.

[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!

[Rotten Ricky]

I will soon be insulating my engine compartment to try to reduce noise and I am gong to follow the following advice.

A key part of transmission of sound is that if you use mechanical means of attachment, the sound will be transmitted through those fasteners to the hull, deck etc., so the best way to avoid that transmission is to not have fasteners go from one side to the other.

Before the first layer of insulation (say 1"/25mm) of Rockwool is attached by glue or screws, I will make up a number of approx. 2" by 2"/50x50mm) sheet aluminum pieces through which a 2.5"(60mm)-long, flat-head, light gauge machine-screw (say 8-32/3mm) will be inserted and locked firmly underneath with a lock-washer and nut. I will use a drill size to make the hole large enough that the screw head will protrude only a minimal amount. The 4 corners of the plate are bent down to provide teeth to dig into the first level of insulation and stop the plate later turning.

These screws with plates are then pushed into the insulation from what will be the hull/deck side, and this first layer is attached to the hull/deck. This will leave the screws protruding about 1.5"/40mm and ready for the second layer. Make sure that the nuts can spin easily onto the threads.

The second layer (say another 1"/25mm) is pushed into them so the screws now protrude through the second layer where panel washers and nuts can be used to hold the second layer in place. However the 2x2"/50x50mm plates must be drawn down later so it and the screw head does not contact the hull/deck.

Clearly there is no direct path for sound to travel directly through the fastener from the engine compartment to the outside.

In my case I will also try to install a layer of sheet plastic (say 1/4"/8mm) or a thin layer of lead or other material to install between the insulating layers to further reduce sound transmission. Commercially available materials have this feature.

I will also try to install some kind of metal or other fire-resistant material on the side exposed to that potential danger. I will find a way to remove the danger of the protruding screws with acorn nuts or similar.

Off to the boat!

Cheers, RR.

[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.

[Kd9truck]

Originally Posted by Rotten Ricky

I will soon be insulating my engine compartment to try to reduce noise and I am gong to follow the following advice.

A key part of transmission of sound is that if you use mechanical means of attachment, the sound will be transmitted through those fasteners to the hull, deck etc., so the best way to avoid that transmission is to not have fasteners go from one side to the other.

Before the first layer of insulation (say 1"/25mm) of Rockwool is attached by glue or screws, I will make up a number of approx. 2" by 2"/50x50mm) sheet aluminum pieces through which a 2.5"(60mm)-long, flat-head, light gauge machine-screw (say 8-32/3mm) will be inserted and locked firmly underneath with a lock-washer and nut. I will use a drill size to make the hole large enough that the screw head will protrude only a minimal amount. The 4 corners of the plate are bent down to provide teeth to dig into the first level of insulation and stop the plate later turning.

These screws with plates are then pushed into the insulation from what will be the hull/deck side, and this first layer is attached to the hull/deck. This will leave the screws protruding about 1.5"/40mm and ready for the second layer. Make sure that the nuts can spin easily onto the threads.

The second layer (say another 1"/25mm) is pushed into them so the screws now protrude through the second layer where panel washers and nuts can be used to hold the second layer in place. However the 2x2"/50x50mm plates must be drawn down later so it and the screw head does not contact the hull/deck.

Clearly there is no direct path for sound to travel directly through the fastener from the engine compartment to the outside.

In my case I will also try to install a layer of sheet plastic (say 1/4"/8mm) or a thin layer of lead or other material to install between the insulating layers to further reduce sound transmission. Commercially available materials have this feature.

I will also try to install some kind of metal or other fire-resistant material on the side exposed to that potential danger. I will find a way to remove the danger of the protruding screws with acorn nuts or similar.

Off to the boat!

Cheers, RR.

Hey Rotten,

https://defender.com/assets/pdf/soun...72_install.pdf

This is a great pdf of the level you are installing too, I will be following these procedures.

Also “Step flashing” is good sheet metal “plate” as you called them, the step flashing can be found in the roofing section of most construction material supply businesses like Home Depot.

[capt jgw]

My one and only engine room fire was when a small section of Sounddown-like insulation came unglued and fell on the hot section of exhaust pipe between the engine and mixing elbow. So yes, mechanical fasteners, not just the glue.
I have to admit this was due to my cutting a hatch in the cockpit sole to access the top of the engine, the valves needed adjustment and there wasn't room to get the valve cover off without the hatch. That left a 2" wide section with a seam in the middle that fell down. The insulation doesn't really burn but it did make a lot of smoke.

[Rotten Ricky]

Originally Posted by Kd9truck

Hey Rotten,

https://defender.com/assets/pdf/soun...72_install.pdf

This is a great pdf of the level you are installing too, I will be following these procedures.

Also “Step flashing” is good sheet metal “plate” as you called them, the step flashing can be found in the roofing section of most construction material supply businesses like Home Depot.

Kd9truck,

Unfortunately, because the method described is of fasteners that are connected directly from the engine side to the hull/deck, they will still transmit sound through the outside. There has to be a complete mechanical separation or else you have a similar case of when we were kids and spoke into a tin can that was connected to a recipient's can by a metal wire. It transmits sound!

Incidentally I believe that Rockwool is fairly inexpensive and, being processed rock, is virtually non-combustible. It has one side with a bright aluminum facing that should face the engine.

I proposed screws rather than the nails because I wanted some means of protection from the sharp nails protruding through, such as with acorn nuts. As well the initial nuts can be varied and even easily removed for refinement.

I would appreciate it if any expert in acoustic transmission could comment.

RR.

[skipperpete]

Well, we went ahead and bought 4 rolls of “Soundown”, not as heavy as the failed insulation but still has the deadlead layer... just very thin instead of the 2.5mm of the original. I’ll be using screws and pennywashers on the overhead sections but the access shell doors are too thin for screws so I’m considering AstroTurf adhesive, it’s easier to use than contact cement and sticks like barnacle bases.

[merrydolphin]

As has been said, mass matters. Particularly for the lower frequency’s.
Often a layer of sheet lead is used. Higher end sounds are much easier to stop.
Ever have a car pull up near you with sounds that could vibrate the inside of YOUR car. That’s low frequency. The car pull up near and ALL you hear is the bass. Though to stop. As far as I know, most good enginroom insulation includes a layer of lead or something very dense.

[Bowdrie]

Originally Posted by merrydolphin

As far as I know, most good enginroom insulation includes a layer of lead or something very dense.

I don't know the name of the product, but years ago I got a few square Ft. of a multi-layer product that was intended for lining the cabs/firewalls of large diesel trucks, (I used it to line musical instrument speaker cabinets).
I obtained it at a hose/hydraulic/rubber products shop .
It was about an inch thick.
First was a thin layer of Vinyl that was perforated, second layer was ~3/4in. of a fairly soft Neoprene foam, third layer was a thin sheet of lead foil, 4th. layer was ~1/4in. of dense Neoprene foam.
It was not cheap, and I can't speak directly to its effectiveness for an engine, but it did what I needed it for.