I have been writing a lot recently. Because the date of departure or rather moving to the boat is getting closer. This time I have two questions. One is about engine soundproofing and the otheris transom mounted depth gauges(transducers.)
I wonder whether anyone can suggest a material for the engine cover. I am also thinking about getting a small backup depth gauge. One of those fish-finder combos. If you have used one please let me know what you think…


Clear of the dock and out of the channel in clean air I can turn off the engine. I love the new quiet. But until then I want to hear the engine. In my opinion no sound proofing is your best option.

I built a sports car once. It was a loud Cobra and for noise insulation there was a product sold by Summit Racing that was like neoprene and had a sticky back on one side and shiny foil on the other with neoprene in between. It did a good job of softening and muffling. Try a few auto sites.

----- Original Message -----
From: “BCC Forums”
Sent: Monday, April 15, 2013 8:24:58 PM
Subject: [BCC Forum Post] milhan: SOUND PROOFING

Author: milhan
Username: milhan
Forum: BCC Forum

I have been writing a lot recently. Because the date of departure or rather moving to the boat is getting closer. This time I have two questions. One is about engine soundproofing and the otheris transom mounted depth gauges(transducers.)
I wonder whether anyone can suggest a material for the engine cover. I am also thinking about getting a small backup depth gauge. One of those fish-finder combos. If you have used one please let me know what you think…


I used the foam backed with a heat reflective surface (West Marine?) on the panel to the engine compartment and on the engine bay side of the quarterberth. I also lined the inside of the built-in trash can (if you have one).

It reduced the noise a fair amount…I can sleep below when motoring… I didn’t bother with the underside of the cockpit as the noise level up there is not bothersome to me. It has been 12 years and is still intact.

Thank you guys…
Here is an article from Practical Sailor. As usual you have to be a subscriber to learn the test results… I am not…

Taming Engine Room Noise
Posted by Darrell Nicholson at 11:07AM - Comments: (1)

January 25, 2012

Practical Sailor reader Duncan Hood wrote us last week, asking about engine room noise insulation and prompting me to dive into our files to find our last test. It?s been over a decade, so we?re due for another round of testing, but much of the information in our last report is still helpful. Many of the players are the same, and one of the most prominent players in our last test, Soundown, is still regarded as a leader in the field.

For those like Hood who are contemplating ways to silence the engine, the following excerpt from that article offers some general guidance. (Subscribers can access the complete insulation test of 10 different insulation products online.)

Some engine rooms allow little space for added insulation.

Engines make noise. Crew?especially when they?re trying to hold a conversation, sleep, or just relax?don?t like noise. The solution? Isolate the crew from the engine noise and vibration.

Noise and vibration are inseparable. Noise exists because vibration causes variations in the air pressure that reaches the ear. This is perceived as sound. An effective control deals with both the vibration and the airborne noise.

Noise levels are measured in decibel units, usually referred to as dBA (the A denoting that the measurement is adjusted for the frequency response of the human ear, rather than the total sound level energy). Everyday sounds fall into a range from roughly 25 dBA (a suburban bedroom at night) to 100 dBA (a chainsaw at a distance of 3 feet).

A sensitive ear can distinguish differences of 1 dBA, but it takes a 5-dBA difference to be noticeable. On a boat, an unshielded diesel genset will produce sound levels of 100 dBA at 3 feet; an inboard typically raises the noise in the engine room to about 110 dBA. The object is to drop those levels to approximately 75 dBA for more-or-less normal conversation, and another 20 dBA for comfortable sleeping with the engine running.

There are three basic approaches to making your boat quieter. The first step is to use flexible mounts to isolate the vibrating machinery from the hull. These help prevent the transmission of vibration through the solid structure of the boat, and the consequent reverberation of hull sections that can act like amplifiers. Correcting any engine-shaft misalignment will certainly help.

The next step is to surround the noise-producing machinery in a tight, insulated enclosure to reduce air-transmitted noise.

The final step is to line enclosed living quarters, such as cabins, with sound-absorbent materials.

Once you?ve reduced vibration?and the associated structure-transmitted noise?you?re ready to deal with airborne noise. The first step is to enclose the noise-generating components?the engine?in some sort of box or compartment. Almost any sort of enclosure will reduce noise levels by 5 to 10 dBA, but improving on that takes an understanding of the nature of noise.

There are only three things that can be done with the air vibrations that we regard as noise. They can be reflected, transmitted or absorbed. Transmission doesn?t do us any good in terms of noise reduction. The 5-10 dBA reduction that comes from putting the engine in a box is due almost entirely to the sound energy absorbed by the box; most of the noise is transmitted right through the box?s walls. Reflection may have some value in some situations, but reflecting sound waves back into an enclosure simply makes it noisier inside the enclosure. A reflective material works when there?s somewhere to reflect the sound.

Sound, after all, is a form of energy, and you can?t just make it vanish. You can, however, convert sound energy into another form of energy?heat. The energy dissipates when the absorbent material becomes displaced or compressed.

The amount of energy absorbed depends upon the mass (or weight) of the material, how far it?s displaced or compressed, and the material?s damping capability. Materials like lightweight foams and fiberglass wool have good damping but not enough mass to be effective by themselves. They have a role in dealing with noise, insofar as they can reduce reflection. More specialized sound-absorbers are more effective. These are composite materials with a high-mass layer, one or more damping layers, and (usually) a thin plastic film at each face to protect the damping layer(s) from mechanical damage and moisture.

The high-mass layer should be heavy, limp, and nonporous. It should also be as thin as possible, simply because space aboard is usually at a premium. A sheet of lead works best, but a lead-filled sheet of plastic can be used where a physically tougher material is required. Mass layers of lead typically weigh 1-2 lbs. per square foot; lead-filled plastic weighs about half that for an equivalent thickness.

On either side of the mass layer is a layer of foam or fiberglass mat. The layer facing the noise source is called the absorption layer; its function is to damp out the vibrations caused by the movement of the mass layer. On the other side of the mass layer is an outer layer of foam or fiberglass: the decoupling layer. It isolates the heavy layer from the engine?s enclosure.

The range of frequencies that a sound-isolation material can deal with effectively varies with the product of the square root of the weight of the mass layer and the thickness of the decoupling layer. Thus, a 1-lb. per sq. ft. barrier on a 1/4-inch decoupler might only be effective in dealing with high-pitched sounds (500 Hz and higher); doubling both the weight and the thickness extends the useful frequency range to 125 Hz.

Reductions in dB are additive. Let?s say an unshielded engine produces a noise level of 110 dBA. If we build a box from 5/8-inch plywood around the engine, we?d lower the sound level (measured at 1 foot) to roughly 100 dBA, assuming that the box doesn?t leak and that all openings are taped. If the vent openings to the box lead overboard rather than into the cabin, you can reduce noise by another 15 dBA or so. Make sure that your vent ducts are baffled, or make up a labyrinth with several 90-degree turns.

If you line the box and the vent ducting with a simple absorption layer of fiberglass or foam, you?d only lower the noise level outside the box by 5 dBA or so, even if you used a thick layer of sound-absorber. If you lined the box with a composite material (1-lb./sq. ft. mass layer, 2" thick overall), you?d get the noise level 2’ from the box down to a bearable 76-78 dB, or 61-63 dBA if the engine?s air vents are ducted overboard.

The actual noise level in the cabin will depend on the distance between the engine box and the cabin; sound levels drop by 6 dBA each time you double the distance from the source. If the berths are close to the engine, you can also apply absorbent material to the cabin ceiling and walls (1/2 to 1-inch foam-backed fabric and perforated vinyl headliners are popular choices). If you find that noise is coming up through the floor, try noise-absorbing carpet. As a bonus, these materials are also good thermal insulators.

Sound proofing is great and decreases the racket a lot. I did our engine compartment 25 yrs ago after removing the Volvo and before installing the Yanmar–which made the job a lot easier. I used the composite material with the dense thick layer, a foam layer, with an aluminized mylar layer facing out. Contact cement stuck it down although screwed down battens were needed in some places. It was not a fun job, and if you are taking off soon, you might want to postphone it.

Fishfinders are great! We replaced our digital readout depthsounder about 15 yrs ago after having to have it repaired twice. Fishfinders are not expensive and so we bought a backup, still unused. I mounted the transducer in the engine compartment on a big blob of silicon sealant.

Several yrs ago we bought a Huminbird portable fishfinder for the dinghy for fishing. The transducer’s suction cup attaches to the fatty knee’s transom. It runs on a small 12V rechargable battery. I don’t think the suction cup would stick well to Shaula’s antifouling, but it could be lashed to a stick that is lashed to the boomkin. I tried that out with our first fishfinder.
Dan Shaula

Thanks Dan,
As always you are great. I am glad that you are not charging money for all this advice!.. $$$$$$



Ps. Yesterday just by chance I found myself face to face with “SADIE.” I couldn’t believe my eyes. Less than 300 hundred yards from my own boat. Incredible… I did not know that she spent the winter months in Deale, MD.
What a pleasant surprise…

my boat had the silver sided foam soundproof when i purchased the boat. i am not a big fan of the material. i don’t find it very effective and a when it degrades,it is a mess to remove.

i removed the old foam and replaced with a marine plywood with a rubber core. i attached photos to you to see

good luck!

soundproof finished .jpg

soundproof wood panels.jpg

One of my unfulfilled projects is soundproofing the engine as much as possible. What I have not been able to resolve is this: everything I have read about soundproofing suggests that sound is like water - any opening will allow sound to escape, so the solution seems to be to completely seal the engine compartment. If one completely seals the engine compartment, however, how does the engine get the air/oxygen it needs to operate?


Sam told me that the engine gets enough air from the forward bilges. Soundproofing the engine only REDUCES the noise, hopefully to a more tolerable level. Insulating the engine compartment’s sides, overhead and forward side makes a huge difference.

I tried a insulating curtain hung from the aft mounted fuel tank. It helped with the noise but about 15 yrs ago I removed it as it made access to the port aft outboard area of the compartment difficult. The insulation has lasted 23 years OK, although the contact cement has had to be replaced with screwed on battens in some places.

Hey Dan, I’d be interested in a little detail about your curtain. I’ve insulated the other surfaces in the engine compartment but don’t understand what you’ve done here. Any pics? Ray

Hi Ray,
I don’t have any pics, but I’ll try and describe it. I used the grey, heavy sound insulating sheet that’s about .25" thick to make the curtain. An L shaped wooden piece was fastened to the top of the sheet and hooked over the top of the tank. A line from the ends of the L piece went around the tank and held it in place. The curtain extended to starboard and fastened to side plywood.

Shaula doesn’t have a locker opening from the cockpit so the access to the area to port side of the engine is by crawling past the engine. I needed to be able to move the curtain aside for access. A batten fastened to the outboard vertical edge of the curtain let me fasten the curtain to the port side plywood, and unfasten it when I needed to crawl past and access the storage area to port.

It was a bit of a Rube Goldberg job and I got tired of dealing with the port side curtain setup. I probably should have kept it and improved it. I can’t remember for sure but I think the idea of working on it in the hot and humid tropics was not appealing.
Hope this helps. Dan

Got it. You are soooooo much more limber than I am. Not sure I could get across our motor without a big investment in creative, colorful, crass language. Thanks for the info, I’m in year 2 of approx. 3 year refit and I live in fear of finding a great idea 6 months after I’ve finished. Cheers, Ray

Old thread but useful. My friend was a Soundown dealer and instructed me about boat noise.

  1. Get a sound meter on your phone. Many are free. Measure dB and maybe freq spectrum present
  2. Enable your noise maker which could be the engine, or wind generator or fridge compressor etc. I used a primitive white and pink noise generator- AM radio tuned to static. Gave a great freq range.
  3. Move noise meter to every space and area imaginable. You seek especially the paths of small noise leaks, the size of a window open only a small crack, as these are the EASY targets. You will find many instances of these in every boat.
  4. These easy leaks are fixed with bits of foam packing, cloth gasket, newspaper. Areas around wire chases or plumbing voids are usual sources of transmitted sound which can cheaply be filled with spray foam. For any of these type of leaks, it is important that you fill every crack, slit, and opening where the sound can get through even in the tiniest dimension.
  5. After you have exhausted, fixing all of these easy leaks, you will be left with larger problems, usually low frequency noises which can only be attenuated with mass-loaded surfaces. These are expensive to purchase and a problem to install. They are also an impediment to engine maintenance and airflow.
  6. Hopefully you will find after eliminating all the mid and high frequency noises from air leaks, you won’t need to do the expensive low frequency attenuation.