Outboard Soundproofing

[jsserene]

Has anyone added soundproofing material to their outboard cover? I saw this kit at Defender and was wondering if it helps cut some of the noise. I have a Tohatsu 50 HP 2 stroke.

[Don T]

Hello:
I have considered doing something like this however, I would use Owens Corning foil backed 703 rather than foam. It's the stuff motorhomes use to insulate their gensets. It comes in 1" and 2" thicknesses. The 703 absorbtion coefficient is -3db at 150 hz increasing to -25db at 15 khz. 1/2" High density foam comes in at -3db @ 1khz increasing to -10db at 15 khz. Unfortunately the biggest noise from the Tohatsu is the intake pulses which will have to remain open to the air unless a cover was devised to fit over the existing one with a labyrinth intake passage to mute the carb noise. Also, I have considered a reflector mounted to the back of the Captain's seat to send the sound out over the water instead of into my bimini to bounce around the cockpit. Having the back of the cockpit closed in under the seat helps a lot too.

[Chip Hindes]

I have the same motor so I sympathize fully with the noise complaint.

However, it's my feeling that most of the noise is not mechanical top end but combustion/exhaust, so that I don't believe the kit will achieve a significant reduction.

You might try an experiment to find out. Get a couple of old blankets or quilts, wrap them around the top end with some rope and duct tape and see what happens. If you get positive results, it might be worth trying a $40 kit.

I might be concerned that the insulation will also hold in the heat and elevate the temp inside the cover. Don't know if this would be significant in a water cooled engine.

I also have to point out: It's no big news to a major two stroke motor manufacturer that their motors are noisy. If they knew they could reduce one of the major complaints with a few bucks worth of bubble wrap, without adverse affect, why wouldn't they do it themselves?

[Don T]

Hello:
If you try the blanket idea you probably won't hear much difference. Blankets do not have a high absorbtion coefficient. Also, be aware that you may plug off the air intakes so the motor won't run good anyway.
You only have 2 choices, absorbtion and/or reflection, hence the idea to reflect it out over the water.
Of course there is noise transmitted by the fiberglass but I think a 50% reduction is possible at the captains seat although there will be no reduction in the cabin.
For example: we know how loud it is at the pilot position but it gets quiet fast as you go forward. By the time you are at the forward hatch you can barely hear it.

[baldbaby2000]

How about a set of 35 cent foam earplugs?

[Robert]

The thin hull of the Mac26 is easy to vibrate like a drum, so the transmitted noise will be amplified by the acoustically efficent hull.

[Moe]

Perhaps storing the companionway hatchboard under the helm seat would block some of the noise.

--
Moe

[Pouw Geuzebroek]

I have that Moe, works OK, reduces the noise some what. I was expecting more though. I have a 99X and the standard hatch fitted in almost without adjusting it. I only had to sanddust some off of the top corners. At the bottom it leaves some small space on both sides, just enough to get the petrol fuse through.

[Rich Smith]

I often thought about trying the Bose "Noise Cancelling" headphones...they're supposed to work wonders at removing low frequency noise like aircraft engines...I bet they would help quite a bit with the outboard engine sounds...however, they're not available in Canada and I'd want to be able to take them back if they didn't do the trick...



http://www.bose.com/controller;jsession ... photos.jsp

[Sloop John B]

Yeah, my Dad's practically deaf so I figure I'm next. I use the Mickey Mouse ears for shop vac, chainsaw, bush wacker, Beethoven, and even the Deere. It's a big relief.

These were essential on the bridge of carriers during launch and recovery. The jets would go to full military power when they caught the wire, in case they didn't catch the wire. The high pitched scream would dissolve the little hairs down in your ears somewhere and you'd walk around the rest of your life saying, "Huh?"

But, I think the idea here is to quiet the motor so you can hear the music and chat with the Mate. I concur that if there was a way to quiet them, the manufacturers would have done so. I use the hatch under the seat method described above. Otherwise, at certain rpms, there's a rumbling evil vibration that comes back at us from the open cabin. Weird.

Man, I gotta get a bigger wide screen monitor.

[Mark Prouty]

I don't think them rascally 2 strokes will let you off that easy.

When the exhaust port first cracks open toward the end of the combustion stroke, the burnt (burning) products of combustion escape at the speed of sound. Ever wonder why engines are so noisy? You have a miniature sonic-boom every time the exhaust port opens.

Tuned-Exhaust Systems for 2-Stroke Engines



humm

[Catigale]

The thin hull of the Mac26 is easy to vibrate like a drum

..and blue hulls have higher frequency than white noise hulls....

(Sorry)

I have a 4 stroke Mercury BF EFI and I put the companionway door behind the helm seat - it does help.

I fly a lot (Platinum on two airlines) and never leave without my Bose earphones - I lalways chew out the pilots (especially the young good looking ones) for not protecting their ears from that high turbine whine - that is nasty on your eardrums, but you dont find out how nasty until you have grandkids and cant hear them..

Cant get them Bose's in Canada?? Strange......

[TampaMac]

Well, I have a 4-stroke Mercury 60.

I insulated the cover to the tune of two hundred dollars or more in stuff.

I bought special sound insulation stuff they sell at car stereo install shops. I think the brand name is Dynamat.

I also used high density foam rubberlike stuff and ended up applying a huge coat of automobile undercoating.

It was easy to do after I bought all the junk. AND IT WORKED LIKE A CHARM.

I have no soundmeter to check the improvement but it was substantial.

I would do it again in a heartbeat.

Manufacturers do everything to a price point. I bought a new Cadillac CTS that was pretty quiet. Then I took it to a place that sprays that goop on the bottom to quiet things up. The car was infinitely more refined and quieter as I drove away leaving the place. It made a big difference.

That a $40K car could be vastly improved with a $150 undercoating... well you would think that they would do it at the factory, but they don't.

Same with the outboards. I saw a review of some outboard models in a magazine once. It showed that the exact same motor sold under different manufacturers had a big difference in sound. They were the same motors in everything except for the cover which was in tune with the particular manufacturers product line. The difference was big... only due to the covers.

[Rich Smith]

Hey Catigale - Have you ever tried the Bose headphones on the boat? Does it make a big difference???

[baldbaby2000]

Noise cancelling headphones do a fair job at cancelling out low frequencies. Voice frequencies are higher than most noise cancelling headphones will eliminate so you should be able to still carry on a conversation. I have a pair from Radio Shack 33-1218. Great for airplanes.