Re: Sound proofing 2 stroke cover.
I've tried a couple of methods to lessen the sound. I even bought an "outboard kit" from a soundproofing materials company.
One of the basic principles of soundproofing is - use the correct material to dampen the frequency/type of sound waves. Many designed soundproofing materials are foam for general sound proofing and an inner, sandwitched layer of something denser to absorb low frequency sounds. This can be as dense as a thin lead sheet, or often, heavy vinyl or similar. So, while plain generic foam materials might work a little, they aren't the best or most effective.
Another is completely block off the sound. Example: if you gradually close a door, the sound coming out of the room of course depends on how much the door remains open. But the difference between the last crack open and completely closed is very large. It's that last little bit that makes the most difference, relatively speaking. Unfortunately, you can't do this with an outboard because you need to keep the air vents open.
In addition, the great majority of the noise comes out the exhaust which although it is in the water, still puts out a lot of noise. You can't do anything about that at all. If you think of the sound that comes out of a Harley's straight exhaust pipes compared to the sound of the engine itself, you see what I mean. The only way to meaningfully deaden the sound is to put a muffler on the tail pipe.
Therefore, even the most careful, well designed soundproofing won't do very much for you. It might cut it a little, but it won't be night and day.
After trying (fairly) expensive outboard-specific material on a large V6 and a 10 hp kicker, I decided it's not worth it and will just use generic foam in the future and accept that outboards are loud.
