View Full Version : Engine sound attenuation

12-16-1999, 08:40 AM
I see in the catalouges stuff made to line the sides of engine compartments to attenuate the sound. I'm wondering if it is something I should install in the 20' gaff rigged cutter I'm building. The engine is a 9hp Yanmar diesel which resides under the cockpit but the front and sides of the engine compartment shared with the cabin. See http://home.att.net/n.messinger (http://home.att.net/~n.messinger) for pictures of the engine installation.

I'd appreciate your thoughts on this matter.

Thanks. --Norm

[This message has been edited by NormMessinger (edited 12-16-1999).]

[This message has been edited by NormMessinger (edited 12-16-1999).]

[ 03-07-2004, 06:46 PM: Message edited by: NormMessinger ]

Ian McColgin
12-16-1999, 08:53 AM
Yeah, & pricey as the stuff is, it's worth it. Best is the heavey foam/lead/foam/lead/foam laminate. You want to plan ahead so that fuel & electrical lines run neatly and visibly. At the minimum get it on the enginroom overhead, hatches and bulkead foreward. Putting it against the hull or sides of the enginroom is good. If you have a good oil catch pan, you can get the stuff down to just above the bilge.

Remember that a diesel needs lots of air. Especially when you soundproof, there's a tendency to reduce free air. You may want to increase the vent size and add a fan to the exhaust. If you baffel the air vents (amazing how much sound comes out there, you might even get to the point where only your tachemeter knows for sure when the mill is running. Think of it - the loudest sound is the water splashing out the exhaust . . .

Scott D. Rosen
12-16-1999, 09:17 AM
Ian's right. But some engines are louder than others. Yanmars are reputed to be quiet. I would start with using the stuff on the hatches and sides. If it's still too loud, you can add more stuff as needed.

Dale Harvey
12-16-1999, 09:53 AM
I like hearing and feeling my engines run. All the little thunks clunks squeeks and chatters mean something. Often detecting a change in sound has made the difference between a minor tweak and a major repair. Also, it sounds so nice when you do shut it off that your more likely to throw an extra tack or two, or just drifting in a light breeze, to avoid starting it up.

Ian McColgin
12-16-1999, 10:52 AM
Dale's remarks make me need to come clean. I've installed soundproofing on several boats but not on Granuaile because I'm too cheap & lazy and because when I rebuild her in a couple years I can do it then. So I have a really loud air cooled Deutz & there are plenty of times when the person at the helm can't hear the person fooling around with the anchor.

One boat I did is probably too quiet - it's easy to forget whether it's on or not. At one point the throttle was adjusted wrongly & she'd stall out in the middle of a landing without the owner knowing. I fixed the throttle and added (what every boat should have anyway) an audible low oil pressure alarm. Fixed that problem twice.

Scott D. Rosen
12-16-1999, 11:36 AM
I'd like to have the problem of my engine being too quiet. LOL Mine is loud even with the insulating material. Dale's comment reminds me of the guy who likes banging his head against the wall because it feels so good when he stops. Loud engines are a safety hazard in fog or low visibility, if you can't hear other vessels or aids to navigation over the roar of your engine.

Jamie Hascall
12-16-1999, 12:30 PM
Check out the recent issues of Practical Sailor. They just did a good test session on sound reducing insulations. I know I land somewhere in wanting the old Volvo to be quieter but still able to be heard.

Good Luck

Bob Cleek
12-16-1999, 12:55 PM
I'll weigh in along with everybody else. Soundproofing is nice, but on a sailboat, your engine isn't running so often that it's oppressive. On a powerboat, especially if you have a generator running while on the hook, it's a must. One thing about the material, besides the cost, is that it does limit access to your hull and so on. For it to be really effective, it has to be all over. Then you have to worry about ventilation behind it to prevent rot, which is already hard enough in the stern quarters of a small boat! One old sea fahrt I know once observed that the level of maintence an engine gets is directly proportional to the amount of access you have to it. If you have to look at it each time you start up, for instance, you are going to notice that frayed belt a lot sooner than when your batteries turn up dead! I'd do a wait and see on this one. Your engine may not be that oppressive. Lots of diesel Yanmars around here in fibreglass boats, which are a lot noisier than wood... without any soundproofing, and they seem to be fine.

Ian Wright
12-16-1999, 01:26 PM
Norm, if you have room then do by all means fit the stuff. On a small boat, and both our boats qualify as small, you need all the help you can get,,,
If Mrs Norm will ever, and I mean EVER, shelter in the cabin while you motor home in the rain, she will never come again if you don't do all you can to minimise the noise.
Insulate the hell out of it!

12-17-1999, 09:40 AM
Thank you all. I should have asked the question months ago. What ever I do will be a retrofit of sorts, no harder later as now. Sound proofing will be on my to do list with the hope that the Yanmar will not require it.

Ian, you underestimate MrsNorm. She is not one to shelter herself when someone else is exposed, irrational as that would be in this case when only one is needed to hold the tiller. However, I understand what you are advising and will treat her accordingly.

Again, thanks everyone.


Ian McColgin
12-17-1999, 10:43 AM
Norm, you'll get a lot of value out of just insulating the overhead and foreward bulkhead. Worth doing now. With the little engine, it may be enough forever.

Bo Curtis
12-17-1999, 06:36 PM
I'm surprised that everyone endorses sound insulation so much, without any mention of sound containment (except Ian's reference to the sound that escapes from air vents). Bill Garden mentioned in his book that a quiet engine is as much a question of containment as insulation, and what this means is that you can build a super-insulated, baffled box around your engine, and yet if the box has as much as a quarter-inch gap somewhere, the engine will be right in your ears.
I used to be a lightkeeper on the B.C. Coast, and we had a radio room adjacent to an engine room. When the engine room was renovated with newer, louder engines, a "soundproof" door was put in, yet we could hardly hear ourselves talk on the radio in the next room. It turned out there was a small gap at the bottom of the 2" thick door. A towel laid across the door threshold made everything quiet.
My boat has a tightly-fitting box around the engine, and when the glue holding the insulation gave up during a cruise, I pulled it out before it fell into a generator belt or something. It hasn't made a bit of difference in the noise level.

06-19-2001, 07:36 PM
Bo, which light(s) were you on? Cape Beale, with that haunting diaphone? Pine Island? I have had some good vhf chats with lightkeepers on that coast

[This message has been edited by pwilling (edited 06-19-2001).]

Phil Young
06-19-2001, 08:46 PM
I'm inclined to agree that a well sealed engine box is more important than insulation. Just bunging some insulation on the sides and top of a box with a whole lot of gaps won't achieve much at all. On my steel boat the engine room is well sealed, but the engine was still noisy. I put in a heap of insulation with no appreciable difference. Now I realise the most likely problem is that the engine is hard mounted to steel bearers, welded to the hull structure, so the whole boat vibrates in tune with the engine, which isn't much, but enough to be LOUD when down below. I guess flexible bearers and a flexi join in the shaft is the next step!

Ed Harrow
06-19-2001, 09:42 PM
Call Dr Bose and order up a set (or two) of his headphones. You can take them with you when flying, doing the lawn, cutting firewood, or riding with Brian C...

Scott, what did you do this time to get yourself unregistered?

Tom Lathrop
06-20-2001, 08:43 AM

Sound insulation is good the foam/lead/foam (most expensive, of course) is the only kind worthy to put on a diesel. Closing off as many sound paths as possible is good too. There are some canvas covers with included soundproofing material available for some engines. Check with Yanmar.

Still, there is the vibration (noise) transmission through the motor mounts and shaft to deal with. On a small lightweight boat, there is not a lot you can do about that. I was recently out on a small steel Dutch built boat with a new 9hp Yamaha installed and it was very quiet with the insulation advised above. Of course, it was very heavy with huge motor mounts. Perhaps, the main thing that made it so quiet was that it used a saildrive which allowed the prop thrust to be isolated so the engine was probably mounted on vibration isolation mounts.

My own light weight pilothouse cruiser is powered by a Yamaha 50hp four stroke that is fairly quiet. I put a motor cover on it with the foam/lead/foam stuff. The noise level is just as loud 12 feet forward in the pilothouse as in the seats on either side of the engine at the stern. This is due to vibration through the light hull and would be hard to reduce very much. Of course, I don't get to shut down the engine and sail.

I think some of the early Yanmar singles were recycled from paint shakers. They would have been very good for that anyway. In still water you could see the ripples on the water generated by the little mixmasters.

06-20-2001, 11:52 AM
There are only three practical ways to deal with unwanted sound: containment, absorption, and reflection. Sound propogates by vibrating what it touches. Heavy things are harder to vibrate, things that are farther away are harder to vibrate, things not aligned with the sound are harder to vibrate.

The towel in the gap in the door (and the doors and walls) are an example of the first; this prevents the propogation of the sound waves. Flex bearings, anti-vibration engine mounts, ... are likewise.

Various surface coatings (lead foam, ceiling tile, carpet, ...) are the second (they convert the sound energy into heat, mostly; those engine mounts do some of this, too.)

Reflection is mostly in how to shape the enclosure so that the sound is reflected to an absorbing layer, and prevented from being transmitted to a parallel enclosure. When you build the enclosing box, don't make its walls parallel to the surrounding walls. The angle doesn't have to be great, three to five degrees is fine. We tilted 4' x 8' glass panes 1/2" outwards (both, at the top) and got fine accustic insulation from them in radio stations.

An enclosing box should have as few attachments as necessary to the surroundings; ideally, there would be none. Don't add bracing between the outside of the containment and the inside of containing enclosure; it becomes a sound conduit.

I'd start by being sure there was a good gasket to the hatch (soft rubber), and lining the insides with carpet or accustic ceiling tiles, tacking it in place with hotmelt glue. If that didn't work, then go on to more expensive things.

And since it's an after-fit, wait and see how much of a problem you have. I've seen lots of sound problems (although not in boats) caused by people trying to prevent them before they appeared.

bill hersey
06-20-2001, 02:24 PM
It's absolutely true about the cracks -- floorboard hatches if the engine sits under the cabin sole, whatever. Sound will seep like water, only faster.

We discovered, quite by accident, something that REALLY works. On a 57' Buchanen teak ketch I had ten years ago, the 160 horse Perkins lurked directly beneath the pilothouse cabin sole. There was lead/foam everywhere and it was still loud. The cabin sole was teak, the overhead had beams and wood. Because she was very traditional, we threw an oriental throw rug (with no-slip backing across the pilot house sole. We did it for appearance, but it cut the noise by at least one-third. We went further and installed fine grained sheet cork between the deck beams and painted it. That cut the noise down to a very comfortable level.

I recently did the same thing on AMANTE, the Calkins 50. Same deal -- a Ford Lehman engine under the salon sole, hard surfaces everywhere. Two traditional throw rugs covering the hatch seams and cork on the overhead and it was unbelievable how the sound was reduced. The interior is all teak and white enamel, with a newly refinished teak and holly sole. The cabin sole is actually highlighted because of the rugs.

And they feel really good on bare feet on a cold morning.

This really works.

Adam C
06-20-2001, 02:56 PM
The $2 Million dollar Nordhavn 62 powerboat we make is an exceptionally quiet boat. She is lined with the best insulation....but to get that extra quietness we recommend a large carpet in the salon, which is directly above the engine room.

Underneath this is a product called SounDown, an acoustic decoupler. It really looks like 1/2" rubber. It fits under the carpet.

You would be amazed at how much quieter a little carpet and a rubber mat make inside the boat - noticeable difference.

Terry Etapa
03-07-2004, 02:22 PM
I'm currently putting in acoustic insulation in my engine room, and damping my fuel tanks. I really want a wood sole in my pilot house and galley. However, I find the sound of my DD 4-71 too loud and fatiguing. With all the above said, I'm thinking about carpet in the pilot house and galley. Does anyone have any information on using carpet in a boat? Any brands to look into? Avoid? How about the above mentioned acoustic decoupler, any comments on it, or other brands?

Bob Smalser
03-07-2004, 03:08 PM
I don't have a good answer for you....only that it could be worse....

...it could have been a 6-71 down there.

03-07-2004, 04:25 PM
Seems most DDs are noisy - but to different levels. My 2 x Detroit Diesel 4-53s - are very early ones with the noisier 2-blade superchargers. The day we started these after their rebuilds we also started a turbo 4-53 - which was an order of magnitude quieter. Mine were painfully noisy with hands over your ears / earmuffs.

Then again my STW2 Lister genset isn't exactly quiet or vibration free either.

With a 12' x 12.5' engineroom - I'm concentrating on containment and it is starting to pay dividends. I recently ran a pipe through the forward bulkhead to the Lister for cool air intake / noise reduction and could not believe the difference. Much quieter in the cabin above the Lister - much noisier in the galley above the air intake. Next step is a baffled intake for the Lister and a ducted intake system (to remote aircleaners) for the DDs. I'm baffling all vents as we build them too.

I've heard bad things about foam insulations degrading over time and causing major problems with bilge pumps. I've had foam turn to mush in my old (top quality) Bell motorcycle helmet, a rifle carry case, etc.

I like the thought posted above of fixing carpet to the underside of the cabin sole. I would only use 100% wool carpet, however (due to flammability issues).


03-07-2004, 05:40 PM
Hey Norm, your link wouldn't open for me.
If the engine's a two cylinder, I concur with what's been said.
But if the 12s are single cylinder, I expect Yanmar 9 is the same, no? I've had the YSV 12 and the YSB 12 and found that while the engine noise was pleasant the infernal chirping of every hatch and rattle of every door (plus the warble of the rigging)was a bit much. Sure the shaft's counter balanced, and that helps I'm sure, but I've considered ripping my bed logs in half and sandwiching in something like the SounDown Adam C mentioned. In a moment of calm I decided instead to move on to a two cylinder Yanmar GM. Good luck, Cleek's right, the engine's auxilliary anyway.

03-07-2004, 06:11 PM
There aughta be a law against pulling up five year old threads! My AT&T web page has even faded from memory but I doubt if what ever I put there in the last century would be of much help to the present question. I found that the sound of the little yanmar is not objectionable at reasonable rpm's and that sealing the engine compartments stops a lot of sound from getting out.

03-07-2004, 06:39 PM
Whoa, asleep at the switch there. Sorry Norm, didn't mean to stir anything up for ya.

03-07-2004, 07:04 PM
No sweat. I should use smilies but it's again my religon. There are a lot of pictures many of us put in PhotoPoint (I think it was) that are also extinct. So far ImageStation has been reliable but there are pessimists among us.

03-07-2004, 10:54 PM
Terry Etapa - sound propagation into accomodation areas is by two mediums: transmission through air and transmission through structure. Vibrations traved through structure much more efficiently than through air, so that's where I'd start. Mount the engine on quality anit-vibration feet and connect the shaft to the gearbox output shaft with a flexible coupling. All belt or shaft driven off-engine auxiliary machinery (pumps, hydraulics, etc.) should be soft-mounted, and all connecting metal pipes should be fitted with soft couplers (either hoses or flexible metal connectors. Once the engine is isolated, then you can contain the air-born sound. It is usually easier to construct a sound box around the engine than it is to retro-fit sound insulation on the existant hull. Build the sound box with adequate space around the engine for air circulation, adequately sized and located hatches for regular servicing, and provide generous air intake and venting. The latter is often best achieved via a dedicated intake fan mounted inside the sound box. Check the major manufacturer's websites for ideas on soundproof boxes - their gensets are often fitted with these items. Northern Lights is a good example. Rigid sound insulation panels of rockwool and lead are best used due to their fire resistance.

Check out the 1" thick 3M brand Thinsulate Acoustic Insulation MA 4720 M-Series insulation.

Terry Etapa
03-08-2004, 09:50 AM
mmd - A box around my engine isn't really practical. It's a salmon troller. I've got a 5' x 10' x 12' engine room. I'm putting in leaded hull board on the overhead, forward, and aft bulkheadof the engine room. The dry exhaust is wrapped with thermal insulation. I plan on adding something to my 2 - 250 gallon fuel tanks to dampen vibration. The ventilation is up through the cabin sides. I will be lining it with something yet to be determined. The engine is mounted on isolators, the shaft is hard coupled. In the future, I will be changing that. See the project here: http://www.home.earthlink.net/~tetapa. I haven't updated the site in over a year. So, there is a bit more completed than shown.

Now, on to my thoughts on carpet and underlayment. If the above doesn't lower the db level to something I can live with, I'm thinking about carpet with underlayment in the area directly above the engine room. In the saloon, I am considering some type of overhead headliner. I want a wood cabin sole in the saloon.

Just as I asked about carpet and underlayment, I'm interested in headliner.

Billy Bones
03-08-2004, 10:52 AM
Some time way back I posted about a boat I worked on which had white shag carpet in the engine room. It matched the (two) mains and two gensets (Cummins IIRC) and was without a spot or stain. This is the same yacht which had two elevators.

Sorry this is of no help whatsoever to the discussion at hand--just a funny recollection.

03-08-2004, 11:42 AM
Sound dampening is a fussy science. A couple of years ago I was very fortunate to have worked on a project with a very experienced acoustic engineering company. The senior engineer told me this story to exemplify the principle that ALL paths for sound propgation need to be sealed if you want good sound dampening:

The firm was hired to consult to Hilton International on how to retrofit hotel rooms to keep sounds from passing into adjacent rooms. After sealing off the "usual suspects" - electrical outlet boxes, vent ducts, etc. - on the common wall between rooms, they were still getting unacceptable sound transferance. After days of fine-tooth-combing of the room, they found the culprit. In the bathroom above the washbasin there was a mirror unit of stainless steel built into the wall, complete with a 2" x 1/8" slot with a small catch-cup for disposing of razor blades. When they insulated this, the sound transmission problems went away. Hard to imagine that a hole one-quarter of a square inch in area could allow enough sound to be transmitted to be measured, much less be a problem.

The object of the morality tale is that is you want a really quiet boat, you have to be enough of a fanatic to discover holes in your sound insulation as small as fractions of square inches. But then, that level of fanaticism is what makes luxury yachts luxury yachts, no? ;)