Sound Insulation, Different Approach, Harmonics off swim deck and water box noise

[dan144k]

I had some else drive the boat and walked arounf trying to isolate and identify potential noise points.
1. Well I could sense a lot of harmonics from my swim deck area.
2. When on plane boat would get louder as exhaust discharge would come out of the water.
3. Thicker engine hatch bubble gasket (done in the past 5/8") now 3/4"
4. Fuel hatch
5. Hollow corner areas of boat rear
6. Engine compartment area holes/ seams

I had all my exhaust system removed during the summer to install a ballast pumps (another post) and did all these items at once. It would have been nice to to do each step and record results indivually, but I was unable to. And I did not use any electronic sound recording instruments either. Good old ear and conversation testing.

1a. I installed KnoKnoise (thin membrane material with self adheasive) on all flat and curved surfaces, focusing on fiberglass at swim deck area. Where it transitions from large exhaust area and goes to narrow swim platform area. Amazon $60 KnuKonceptz Kno Knoise Kolossus Sound Deadener 100Mil Thick 14sq ft Door Kit, product similar to dynamat.

1b. 2nd sound product applied was 1" Sounddown (1/2" thick foam-1/8" membrane-1/2" thick foam, self adheasive on side and foam face on other side) I installed the sounddown on top of the knoknoise al over the exhaust compartment. Soundown kit from Jetboatpilot.com

2. Exhaust water box. I foil taped the edge of the Sounddown and wrapped around the waterbox, I did not use the adheasive, left the backing on the sounddown. Measured, cut, and positioned it. Held in place using large zip tie and then the rubber straps which hold the waterbox in place. Did not insulate the ends on waterbox on purpose, my theory was water could drain out this way.

3. Removed 5/8" bulb gasket and installed 3/4" from mcmaster carr item# 93085K82 Weather-Resistant EPDM Foam Rubber Bulb Seal Adhesive Back, 3/4" Overall Width, 3/4" Overall HT. , 50 ft. Length.
Used the extra around the fuel hatch cover.

4. Fuel hatch installed the KnoKnoise membrane and 3" sound absorbing foam from Mcmaster Carr
9710T66 Sound Absorber Sheet, Plain-Back Egg Crate, 3" Thickness, 54" X 54". Use the extra in the engine compartment to absorb random noise. Rolled it up about 12" round with 4 large zip ties and just lay on top of the engines. Also have in engine are 2 large foam wedges.

5. Rear area of boat outer corners are hollow. Unable to push entire foam sound wedge bass trap into corner so I cut up the 24" wedges into 6" length and shoved them into the corners behind the exhaust systems.
Wedges from Amazon $80 4 Corner Bass Trap - 12" x 12" x 24" Acoustic Sound Foam Kit - SoundProofing and Deadening

6. Found some white low expansion foam for windows and went around the engine compartment. Found many large seam with 1" gap.

7. Also found a harmonic vibrabrating panel on front of the boat, seat side of anchor locker. Large panel at front of boat was humming from vibration. Installed the KnoKnoise on inside of anchor locker.

From discussing with my wife and friends if it made a difference. Everybody says YES it does. Boat can run down the river at 30 mph and you can have a conversation and hear the radio easily. Prior you had to yell at each other basically. So money well spent for use.
But of note taking the rubber hoses off exhaust sytem was an awful difficult to do. Just a very tight area with minimal leverage.

 

[swatski]

@dan144k Looks fantastic! How you managed to wrap up around these water boxes! I went ahead and pulled mine out last summer, what a pain, used a bunch of hushmat butyl mat (similar to dynamat extreme) - only to find out I couldn't fit it back under the swim deck! It was very disheartening. I ended up with a partially covered project and felt defeated, albeit I have made big improvements in sound reduction overall.

You just gave me inspiration to tackle this again!

I never posted anything about my results, but did a lot of things along the same lines as you... Even used wedges of sound absorbing foam in the rear areas and the gunwales... heck, also went with 4lbs rated memory foam in the voids beside rear bulkheads.

Thank you for posting, looks great!

 

[dan144k]

@swatski Thanks for reminding me.

The waterbox's barely fit out the fiberglass opening on the swim deck. I prefabbed the insulation wrap out of the boat, and put it in place where the waterbox's mount. Then pulled the soundown insulation around the waterbox's once inside the boat. Basically cut it to go around waterbox with a precut hole in it for the exhaust outlet.

Waterbox is same thing as muffler if anyone is wondering. Just runs water through it with the exhaust gas's.

 

[njmr2fan]

Thanks for the link to this. After doing the same walk around under power last summer I came to the same conclusion, that the entire rear deck and exhaust is the main culprit for noise and vibration.

 

[Scottintexas]

thanks for the write up and pictures, added to the FAQ

 

[dan144k]

@Trevor Shipman here is pics

 

[Marvin willis]

How hot does the water box get?

 

[Ryan Cassidy]

For the larger voids (the hollow areas you cut up foam) Any thoughts on using Roxul? just saw it at the store and its got all the properties I think we'd want. Was also considering using it behind all the speakers when I do my install with those soon.

basically for the places you'd never ever see once you put the boat back together. The egg crate gives a nice finished look overall though. I'm ordering a sheet of that, but hate to waste it everywhere.

 

[Jettboatmn]

Great thread! Any updates on others who have tried this? Have you had similar success or found other ways to further reduce noise? It's Dec in MN, but I'm already thinking about upgrades I want to make in the spring. Reducing noise is on my list.

 

[adrianp89]

Nice work - my '17 is already insulated but I would like to get it a lot quieter eventually.

 

[gmtech16450yz]

The throttle/shifter Yamaha SHOULD have put on our boats...

^^^^^ pics of my insulated water boxes in that link. In the last pics you can see the foam mattress insulation I put on the front panel of the rear cleanout compartment.


Also, hints from a tightwad...

Find and buy a cheap memory foam mattress from like Ikea or someplace. A twin sized mattress will give you enough foam to insulate a lot of one of these boats and will be way cheaper than buying the same stuff as "sound insulating" foam.

Buy, or secretly use your wife's electric knife to cut the foam with. (lol) Electric knives work great for slicing up foam, even making thinner pieces from thick sheets.

Buy some good quality spray adhesive (3m 90 or 77) to attach the foam, spray both the foam and the panel you're putting it on and let it set up for a couple minutes before putting the piece in place.

Take panels like the fuel tank compartment lid off and cover the entire underside of the panel with a layer of foam. Put layers of foam in the rear cleanout compartment, but I'd try to keep them above potential water levels even with closed cell foam. Put chunks of foam in the corners to absorb bouncing sound waves. Think of the foam as sound sponges, they will stop the sound from bouncing around and propagating.

Use (a cheap version) of dynamat to stop panel vibrations only. Dynamat is more of a vibration canceling approach, it's not going to "absorb" the sound like foam will. Two different solutions for two different situations. Sometimes I'll use dynamat on the actual panel, and foam on top of the dynamat. Absorb the sound waves and dampen the vibrations at the same time. It's really an interesting science, read up on what works best in each particular situation and you'll have better success with less time and money spent.

Marvin- The water boxes don't get super hot since they have water going through the exhaust too. They do get warm though, and I'd be careful using anything that will melt on them. That's why I used fiberglass insulation and aluminum tape on mine. The fiberglass may be a little overkill as far as it's ability to take higher heats, but at least I don't have to worry if they do get hot. It also meant I could make the layers pretty thin. It doesn't take much to cancel the "tinny" sound of an aluminum can muffler as long as the layers are tightly wrapped to the can. The thickness of the insulating layer I put on my water boxes is no more than 1/2 or maybe 3/4 of an inch thick.

 

[d_coyne1984]

Last summer I also tackled this, but I just used open cell, 2" thick foam sheeting and some scrap egg crate foam that was going to be tossed from the shipping dept. at my work. For adhesive I just used a can of 3M spray. My theory is that the rear of the boat is acting like a bass drum. You may have noticed many drummers will stick a pillow inside the kick drum and this is to dampen the resonances to give the kick drum a very flat thud rather than a booming echoing one. I do believe it made a noticeable difference. I plan to add more this year to take up as much space in the back as possible to choke the "drum effect." Just be sure if you go this route you use something that is flame retardant. At this point it is more of just a half-assed experiment but I think the results warrant further/cleaner effort. My only concern is that the foam will be prone to mold, but I rarely ever see any water from the back of my boat when I pull the plugs and I have had a sheet of 2" foam under my fuel hatch for about 3 years now without issue (which I think has also helped)
.

 

[njmr2fan]

After spending a week on the water on a boat powered by a Yamaha 300 outboard, I'm wondering how it can be SO silent, and my boat is SO loud. My wife even commented that maybe we should get a quieter boat.....

 

[granpachuck]

Old thread, but just what I am looking for. I have a question about the cleanout panel that has to be removed? @swatski , @dan144k , @gmtech16450yz I am not sure what it is called, but it has a dozen screws or so that have to removed for better access to this area. Does that have to be caulked/sealed when replacing? If so, is there a recommended product for this, and possibly ok to use for sealing around ride plate and impeller area? Thank you !

 

[njmr2fan]

Last summer I also tackled this, but I just used open cell, 2" thick foam sheeting and some scrap egg crate foam that was going to be tossed from the shipping dept. at my work. For adhesive I just used a can of 3M spray. My theory is that the rear of the boat is acting like a bass drum. You may have noticed many drummers will stick a pillow inside the kick drum and this is to dampen the resonances to give the kick drum a very flat thud rather than a booming echoing one. I do believe it made a noticeable difference. I plan to add more this year to take up as much space in the back as possible to choke the "drum effect." Just be sure if you go this route you use something that is flame retardant. At this point it is more of just a half-assed experiment but I think the results warrant further/cleaner effort. My only concern is that the foam will be prone to mold, but I rarely ever see any water from the back of my boat when I pull the plugs and I have had a sheet of 2" foam under my fuel hatch for about 3 years now without issue (which I think has also helped)
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After years of listening and boating, I'm more convinced than ever that soundproofing the swim deck area and maybe even partitioning it in half with soundproofing would be one of the biggest noise reduction projects. Not only is the exhaust resonating there, but the prop is also vibrating and resonating in there. It is a bit speaker box of noise, or like you said a bass drum. I have been debating soundproofing the engine compartment and the swim deck.

 

[dan144k]

@njmr2fan
Hi, Yes it is siliconed down, I do not clean and re-silicone it every time, I have cleaned it and re-caulked. However the old caulk and many screws seal it pretty well. I think last time I did it was used a home repair bathroom white caulk, less aggressive easier to remove than marine grade silicone.
.....
fyi, also when removing the panel, you need to loosen 3 hose clamps, clean out ports and deck drain.

 

[granpachuck]

@njmr2fan
Hi, Yes it is siliconed down, I do not clean and re-silicone it every time, I have cleaned it and re-caulked. However the old caulk and many screws seal it pretty well. I think last time I did it was used a home repair bathroom white caulk, less aggressive easier to remove than marine grade silicone.
.....
fyi, also when removing the panel, you need to loosen 3 hose clamps, clean out ports and deck drain.

Thank you, I am already worried this is too much for me. The 1st water box I am loosening up looks like its going to be rough getting connected back up to the engine side. I am afraid if I pull it out,it may be too tough for me to shove back into the hose. I am not a young dude, and work on the boat usually by myself. If I dont take the boxes out, I think I am wasting my time trying to do this job. Will it likely be harder getting it out or back in ?

 

[Neutron]

My only concern with doing foam sound insulation is the retention on moisture and the lack of being able to clean those areas once foam is added.
I dont find my boat to be annoyingly loud anyway.
Part of the jet boat charm!

 

[granpachuck]

My only concern with doing foam sound insulation is the retention on moisture and the lack of being able to clean those areas once foam is added.
I dont find my boat to be annoyingly loud anyway.
Part of the jet boat charm!

That is a good point. I did notice that this area of the boat was very clean considering its the first time I looked there, and I am sure the previous owner didn't. There is some factory foam there now that is falling down, which was part of the reason I am interested in this. I don't plan on using foam at the very bottom of this area.
Also surprised the water box had water in it, since I thought revving the engine on the trailer is supposed to push this water out ?

 

[dan144k]

@granpachuck
It has been a few years. But from Memory the difficult part is disassembling. Not much room for movement and all hoses are kinda stuck. Reassembly went much easier. Disassembly was rough