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doughickey

Motor Box Insulation

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doughickey

Last year, a bunch of us insulated our motor boxes. Did it work. Answers were yes, no, maybe, depends. The last answer is the most correct = "depends". It depends on how much of a drop in sound you're looking for... and at what speed. The two double kits from Overton cost about $150 total if I recall.

Here's the post I made on MBO with the dB results "before/after". I'm a geeky guy sometimes. Rather than opinions, I want data. Then the data is what helps form/validate an opinion.

Data: The data says there is an INCREDIBLE difference at slowspeeds. 10-12 dB is a HUGE drop in sound. (Slow = exhaust tips underwater and motor is idling.) At speed, (speed = exhaust tips above water and boat is moving fast enough for wind noise to add to the reacket), there is negligible difference.

Opinion: Worth the effort to install... although a bit of a PITA. If I was ordering a new boat from the factory, I would absolutely have them do the job.

***********************************************

Finally have some BEFORE and AFTER sound measurements. Did the Overton's installation, did NOT cover up the drink holders; left the small gap (for ventilation) in the motor box at the rear.(1998 RLX; 310 carb)

My apologies.... I only took "C" scale ratings BEFORE.

I took "A" (human range) and "C" measurements afterwards.

NET SUMMARY: Makes a TREMENDOUS difference at slow speeds....ie, when the exhaust outlets are UNDER water. At planing speed, not much difference. Am I glad I did the PITA project.... YES! What an incredible difference for slow speed travel with the family. At speed.... who cares... I love that throughty rumble.

The results: A drop of 10-12 DB in the front area at slow speed!!! A slight drop (1-3 DB at 36 mph. At speed, it seems like ALL the noise is coming from the exhaust outlets..... NOT the motor box area.... and wind.

BEFORE: "C" Scale Only;

At Idle: Driver Seat 82-85 DB

Passenger Seat: 82-85 DB

Rear Seat 82 - 85 DB

At 36 MPH: Drivers Seat 98 - 101 DB

Passenger 98 - 101 DB

Rear Seat 103 - 104

AFTER: "C" Scale

At Idle: Driver Seat 71-74 DB

Passenger Seat: 71-73 DB

Rear Seat 72-74 DB

At 36 MPH: Drivers Seat 98 - 102 DB

Passenger Not taken

Rear Seat Not Taken

AFTER: "A" Scale

At Idle: Driver Seat 60-62 DB

Passenger Seat: 58-61 DB

Rear Seat 60-62 DB

At 36 MPH: Drivers Seat 87 - 89 DB

Passenger 87 - 89 DB

Rear Seat 100-102 DB

NET NET NET: YES, it's worth doing this project !!!

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CarveItUp

Thanks, Doug, for posting your research.

For those that want to go forward without a kit, McMaster-Carr carries some foil-faced foam insulation that has been reported to be similar to the Overtons kit. I believe it is p/n 5692T35 on this page, but I could be wrong...does anyone know for sure?

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Wkerat

I always wondered the true difference it made. I wonder what the msst adds to this.

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rkgallagher
Thanks, Doug, for posting your research.

For those that want to go forward without a kit, McMaster-Carr carries some foil-faced foam insulation that has been reported to be similar to the Overtons kit. I believe it is p/n 5692T35 on this page, but I could be wrong...does anyone know for sure?

Wakegirl can probably confirm this one since she insulated her engine cover.

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Jimmy Buffett
p/n 5692T35

That's the part #. It comes 54" wide, I got 8' and had a little left over but not much. Get 3M spray adhesive and some aluminum tape from home depot and have at it!

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MARiley

hey everyone, i'm back from the dead and bringing this thread with me. i am now an adult(25) with a steady income, so i'm looking to throw down the cash to insulate my motorbox.

questions:

-what is the difference between the "A" and "C" scales?

-what materials did you use?

-where'd you buy them?

-total cost?

-will this stuff stay stuck to the motor box in 115F heat when i'm at the river this summer?

thanks everyone.

EDIT: nevermind. i found this: http://www.themalibucrew.com/forums/index.php?/page/articles/motorbox_insulation

Edited by madchild

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MalibuTime

hey everyone, i'm back from the dead and bringing this thread with me. i am now an adult(25) with a steady income, so i'm looking to throw down the cash to insulate my motorbox.

questions:

-what is the difference between the "A" and "C" scales?-what materials did you use?

-where'd you buy them?

-total cost?

-will this stuff stay stuck to the motor box in 115F heat when i'm at the river this summer?

thanks everyone.

EDIT: nevermind. i found this: http://www.themalibucrew.com/forums/index.php?/page/articles/motorbox_insulation

B? :unsure:

As doughickey says, A closer approximates human hearing, or read more here...

http://en.wikipedia.org/wiki/A-Scale_Sound_Level

Edited by MalibuTime

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MARiley

ah, i sort of got it. it's basically beyond me, or maybe just my interest level, haha. i'll just take y'alls word for it.

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Deke

I can't give actual numbers but my head feels a lot better now. BTW, I used a very thick 1 3/8" composite called Quiet Barrier from MarineFoam.com. This stuff has a decoupler, barrier, and absorber. If you call them they'll point you to the right product. Mine was actually slightly damaged, surplus stock sold at a discount. Does it work better than the Overton's? Once again, I can't say, but it's what is in my boat!

I think for the ultimate you have to install exhaust system mufflers as well.

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