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Old 10-21-2020, 01:39 AM   #1
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Noise deadening and insulation

I've just completed a 160nm cruise home in a new to me 45t steel trawler fitted with an old 200hp Mercedes OM 355 engine.

All went well. However, one area I would like to investigate is sound deadening and insulation. Ideally, I would insulate the engine room but on one full of engines, tanks, plumbing, auxiliaries etc effective retrofitting would be impossible.

I'm considering sound deadening, mass loaded vinal, sound insulating floor underlay and coverings and general weighty fabric furnishings, curtains etc.

Has anyone had any success with these or any other suggestions?

As a sense of the scale of the issue, the vessel is 85db at a fast cruise of 8 knots (1500rpm). Low frequency vibrations seem to be the main issue. I can literally find where the engine room bulkhead is by walking the length of the cabin above in bare feet and feel the vibrations change either side of the bulk head. Also touching the walls, ceilings and cabinetry I can also feel vibrations.

Many thanks.
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Old 10-21-2020, 02:11 AM   #2
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I put Soundown 2 pounds per square foot underlayment in a previous boat. Not sure if you can source that brand down there. It is a mineral loaded vinyl for the sound barrier with some foam for decoupling. Worked well for me but I don’t have actual decibel levels. Good luck.
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Old 10-21-2020, 05:08 AM   #3
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Pyrotek is an Australian company with an extensive line of sound mitigation products.


But if the issue is vibration, then you need to first focus on decoupling that from the hull. Padding and other coverings will reduce the drumming from other parts of the boat, but I think it will be much more fruitful to go after the source of the problem.


Is the engine hard mounted to the hull, or are their vibration damping mounts? Was anything else running, like a generator?
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Old 10-21-2020, 07:43 AM   #4
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I think chasing down sources of noise is a never ending, but worthwhile, task. Everything you that helps create modest improvement increases enjoyment.

As you know, finding and closing all the air leaks is step 1. I also had good luck with Sounddown products. If you can only put them on the engine room overhead, that should create some modest improvement. I also believe any exposed area that you can add insulation will help capture airborne noise even if you can't retrofit 100% of the engine room. I guess with steel you don't want to use the noise absorbing paint, right?

I also used mass loaded vinyl under the cabin flooring. Weight was an issue so I went with 1 pound PSF MLV. I'm sure it helped but I can't quantify how much. I also used a flooring that absorbed airborne noise and I have a number of rugs down. I believe any soft surfaces absorb airborne cabin noise.

Trying to isolate engine from the hull if it's hard mounted is a good idea. But there are some risks that you might set up sympathetic (or is it harmonic?) vibration that at certain RPM's makes it worse. I have hard mounts on my aluminum hull and that seems to work better that the soft mounts on my last (wooden) boat. I think I'm at 74db at WOT (2300 RPM) and my last boat was 85db at fast cruise of 2800 RPM. It's only 11db but a HUGE difference.

Good luck.
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Old 10-21-2020, 08:30 AM   #5
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In a boat, and especially a steel or aluminum boat, structure borne noise can be especially irritating and challenging to address. Airborne noise is much more straight forward. Best practice calls for addressing the noise or vibration as close to the source as possible. The 3 primary sources will be:

Engine vibration getting past mountings into structure
Exhaust components and plumbing hard mounted, either wet or dry stack
Propeller rate, water coming off prop and impacting the hull

If your engine mounts are over 10 years old, consider changing them. Just feeling with your hand the engine bracket above the mount and then below on the stringer will give you an indication of how well your mounts are working. You should feel a significant reduction from above to below the mounts.

Whether wet of dry stack, exhaust components should not be mounted hard to bulkheads. Again the hand/feel test is appropriate, or disconnecting from bulkhead and temporarily suspending with bungee cords will be a test of this as a source. Resilient mountings are the solution.

Prop rate is there, and in some boats difficult to address. When underway feel or stand on the hull in the bilge above the prop(s). You should be able to tell rather quickly if this is a source that maybe should be addressed. Ask around for “navy tiles” if you feel prop rate adds to your overall noise levels, especially if you have an aft cabin that used underway.

Mass Loaded Vinyl (MLV) is an excellent airborne noise barrier and it does have some damping properties for structure borne noise. For the deck above your engine room carpeting will always be the quietest. I suggest using the stiffest carpet padding you can find with a layer of mass loaded vinyl ON TOP of the padding. By “decoupling” the barrier from the deck with the foam you enhance the performance by a large factor.
Nothing wrong with putting a layer of MLV directly on the deck in addition to the treatment mentioned above. If you can find 2lb (6mm) MLV it will work better than 1lb.

Do not over look air trunks, how combustion and vent air get to your engine room. Often these airpaths pass through or are a part of cabin sides. This is an extension of the engine room now in your salon. It should be addressed aggressively as it is often the overlooked weak link in noise control.

MLV is your all purpose noise barrier. It plays nice with all adhesives, can be screwed, nailed, stapled, its durable and resists most solvents, oils, and water. Decks, bulkheads, overheads, everywhere is appropriate for MLV.

MLV is combustible. In the engine room best practice for a metal boat is to use only incombustible insulating products. Also as you noted because of the complexity of the engine room (they all are) if you can’t get a very high percentage of airborne insulation on the overhead and bulkheads, you will probably not get great results. Noise will just flank treated areas and find its way to the overhead/bulkhead in spite of less than 100% coverage.

Good luck
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Old 10-21-2020, 11:28 AM   #6
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MLV is your all purpose noise barrier. It plays nice with all adhesives, can be screwed, nailed, stapled, its durable and resists most solvents, oils, and water. Decks, bulkheads, overheads, everywhere is appropriate for MLV.
I'm just starting on my noise reduction journey and have been looking at Mass Loaded Vinyl. Some of my obvious problem areas are where prior owners have cut openings in the original ER sound proofing to run forced air heater duct work and to install a black water holding tank. Both were clumsy holes cut way larger than necessary. The tank opening was just left completely open to the forward cabin bilge (with no soundproofing).

I'm thinking of buying some MLV to cover these areas with openings as small and tight as possible. I would attach these "hanging panels" using Common Sense fastenings. That way, should I need to replace a tank or alter duct work, I could simply remove the panel. Having never worked with MLV, would Common Sense fasteners work with that material? The studs are available in a "tall" configuration for thicker material.

https://www.sailrite.com/Common-Sens...waAoGHEALw_wcB

I've downloaded a decibel meter app and have my baseline readings at various rpms already written down. Hopefully it will be sensitive enough to give me some positive feedback relative to time and money spent on the project.
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Old 10-21-2020, 12:52 PM   #7
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[QUOTE=Marco Flamingo;935291] Having never worked with MLV, would Common Sense fasteners work with that material? The studs are available in a "tall" configuration for thicker material.

MLV is durable, it can be glued, screwed, nailed, stapled. The fasteners you want to use will work if you use enough, you want a tight fit. Screws with fender washers will also work for as often as you may need to access.

MLV is commonly available in 1 Lb per SqFt (1/8" thick) or 2 Lb per SqFt (1/4") You should not need a longer fastener,

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Old 10-21-2020, 12:58 PM   #8
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I use long S/S sheet metal screws and large fender washers to attach sound proofing materials. Easy to do and cheap.
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Old 10-21-2020, 02:49 PM   #9
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Thanks guys. The engine is indeed hard mounted. I would be very reluctant to change this to add isolation mounts as this could introduce a whole range of unintended consequences

I do have very easy access to the mounts and rails so my intention was to 100% cover these areas in adhesive deadening mat similar to wheel arches in a car. Large pads will also be added to exposed areas inside the engine bay including over head and the bulkhead that separates the engine bay and living quarters.

There are 2 commercial duty aux generators and the electrical system is configured to have one running 100% while steaming and often while at rest. I'm actively investigating expanding the solar and battery system to essentially make these redundant and dramatically reduce run time and the associated noise.

MLV will be used widely as access permits. I'm already ~50T so the additional weight isnt a concern. 😁

Thanks again
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Old 10-21-2020, 02:59 PM   #10
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Whether wet of dry stack, exhaust components should not be mounted hard to bulkheads. Again the hand/feel test is appropriate, or disconnecting from bulkhead and temporarily suspending with bungee cords will be a test of this as a source. Resilient mountings are the solution.
.....

Do not over look air trunks, how combustion and vent air get to your engine room. Often these airpaths pass through or are a part of cabin sides. This is an extension of the engine room now in your salon. It should be addressed aggressively as it is often the overlooked weak link in noise control.
.....

Good luck
All exhausts are dry and suspended but with threaded rod rather than rubber isolation mounts. The actual outlets are a good 6' above the cabin roof. I'll investigate if isolation will assist

I'd agree that after the low hanging fruit is solved addressing the numerous smaller contributors will give good cumulative benefits

Thanks again
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Old 10-27-2020, 07:01 PM   #11
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IMHO, you will never get the result you are looking for w/o GOOD mounts. My friend and I built a wood downeast boat a couple years ago, it had a gasoline engine. He insisted that there would be no soft mounts b/c "they don't use them downeast" (which isn't really a reason at all) Anyway he spent two seasons trying to get it quiet enough that you didn't want to jump overboard after an hour or so.
This spring he gave in and we installed Cushyfloat mounts and made it a whole new boat of it. All that he had tried to do b/4 was useless b/c he wouldn't solve the underlying problem, structure borne noise & vibration.

Of course it would have been easier to have installed them in the beginning rather than working in limited space, having to cut the engine beds, and invent new ways to mount things to the engine that were mounted to the beds and stringers. However the end result was worth it.


When on the bridge of the Island Seeker, you can not hear the engine at all. The bow wave is the loudest noise. More restful than a sailboat.
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Old 10-27-2020, 09:04 PM   #12
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WHAT? After 6 decades of Rock and Roll, power tools, tanks, trucks, guns and airplanes I find my Hatt surprisingly quiet. Kidding aside there's quite a bit of "stuff" in the walls and ceiling of the engine rooms....
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Old 10-27-2020, 10:10 PM   #13
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IMHO, you will never get the result you are looking for w/o GOOD mounts. My friend and I built a wood downeast boat a couple years ago, it had a gasoline engine. He insisted that there would be no soft mounts b/c "they don't use them downeast" (which isn't really a reason at all) Anyway he spent two seasons trying to get it quiet enough that you didn't want to jump overboard after an hour or so.
This spring he gave in and we installed Cushyfloat mounts and made it a whole new boat of it. All that he had tried to do b/4 was useless b/c he wouldn't solve the underlying problem, structure borne noise & vibration.

Of course it would have been easier to have installed them in the beginning rather than working in limited space, having to cut the engine beds, and invent new ways to mount things to the engine that were mounted to the beds and stringers. However the end result was worth it.


When on the bridge of the Island Seeker, you can not hear the engine at all. The bow wave is the loudest noise. More restful than a sailboat.
This sounds right to me. If you have a hard mounted engine the most logical thing to do is to get some good vibration absorbing mounts. It's very easy to waste your time trying to band-aid NVH stuff; you need to address the fundamental issue first.
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Old 10-28-2020, 02:31 AM   #14
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This is probably the best read I've seen on engine room noise reduction. Perhaps it will help.

http://krogen42stout.com/engine-machinery/#/noisereduction/
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Old 10-28-2020, 11:37 AM   #15
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This is probably the best read I've seen on engine room noise reduction. Perhaps it will help.

http://krogen42stout.com/engine-machinery/#/noisereduction/
Thanks but the link appears to be broken
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Old 10-28-2020, 11:44 AM   #16
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Thanks but the link appears to be broken
STOUT - .

There you go - excellent article.

When I was looking closely at this for my 40' sailboat I found lots of good articles on the Soundown site. They are very helpful and reasonable folks - I actually ordered full insulation materials for my engine room, then sold the boat unexpectedly, and they allowed me to cancel the order for a full refund!

https://soundown.com/marine-noise-control/

and an article they link to:
Murray says 90 percent of the noise and vibration problems in boats to 60 feet are related to the engine, the prop and/or the exhaust system.

https://www.soundingsonline.com/boat...-the-machinery
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Old 10-28-2020, 12:01 PM   #17
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This sounds right to me. If you have a hard mounted engine the most logical thing to do is to get some good vibration absorbing mounts. It's very easy to waste your time trying to band-aid NVH stuff; you need to address the fundamental issue first.
I'd agree and intend to make extensive use of adhesive dampening mats at 100% coverage around the engine rails.

FWIW, I visited a local marine acoustic insulation contractor to get his views on products and costs. He is currently covid induced super busy (we have a large naval base, commercial and recreational boating fleet locally who all seem to be refitting while travel restrictions are in place) so was super helpful with DIY suggestions:

Mass Laden Vinyl is expensive but works well
Sandwiching MLV with acoustic panels works well
Acoustic paint can give slight benefits
Covering both sides of key bulkheads/plates gives very good results eg ER/cabins bulkhead, ER ceiling/salon floor etc.

He wasn't overly supportive of dampening pads but given that I'll be doing everything else I'll use them anyway.

He was not at all daunted about retrofitting around existing hardware saying that its routine and the matting can be easily cut to size pre placement. Just pull out anything that is removable or is due to be replaced anyway but no need to remove any permanent equipment just to get it out of the way

A big 👍 to Dicky from Northern Insulation Services in Cairns, Australia if anyone is looking for similar work.

Thanks for the comments to date.
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Old 10-29-2020, 07:19 AM   #18
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I'm considering sound deadening, mass loaded vinal, sound insulating floor underlay and coverings and general weighty fabric furnishings, curtains etc.

Has anyone had any success with these or any other suggestions?

We used Soundown. There are a couple threads about that around here...

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Old 10-29-2020, 09:13 AM   #19
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I had to take a few classes in sound silencing back in my USN submarine days.

On my boat I have used sound deadening paint, sound down, hose connections to hard pipe and baffles.

My worst noise now is the control cable vibration from the gear and engine to the helm and the autopilot pump. Have a plan to mount the AP pump to a lead mass base, but haven't made it yet. Tried a few that have failed.

You would really need to mount the engine on sound mounts to get any appreciable change. Everything else will be incremental.

On a sub, we could grab the Fairbanks Morse ND 8 1/8 diesel engine and shake it back and forth and make it move by hand. This engine weighed ~60,000 lbs.

Sound mounts are mass and frequency dependent. If you go this route, do the math or find someone to do it for you.
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Old 11-02-2020, 02:06 PM   #20
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I needed to reduce the upper frequency and turbo whine in my Downiest cruiser. I don't mind the low frequency of a diesel (sounds good to me), but the higher frequencies interfere with conversation and wreck your hearing, as well as getting on your nerves.

Get a decibel reader app for your phone. there are several, many free. create noise in the engine space, maybe with the engine or with a pink noise generator (low static from a mistuned radio). Walk around your helm area, galley, bunk, etc and read the noise levels. Finding the hot spots I noticed wire/ cable chases from ER to the helm or meters above, also open space around the fuel fill hoses on each side. back of the air trunks. flooring directly above the turbo and air intake.

I bought heavy foam and lots of 2 lb/inch MLV from Soundown. Great service and products. A carpet man helped me lay a complete barrier of MLV above the ER, and I stuffed foam in the wire chases. Also Soundown carpet underlayment under the wool rugs.

this reduced the overall noise 10dB, and rolled off the upper freqs more than that. We could run at WOT and still hold a normal conversation. This made a large improvement to enjoyment aboard and more refreshing voyages.

Good luck with your project.

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unfortunately for sale due to my health issues - if you have a dream - Go Now.
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