Sound proofing is tough. I went thru a week long symposium some 25 years
ago, so I won't mention materials, but:

Sound is vibration. If you rigidly bolt the generator to the boat's
structure, you'll make the hull/enclosure into the speaker diaphragm. Sure,
you can add mass to the panels to make them into poor diaphragms, but it
might be easier/cheaper to use better isolation mounts. To do a proper job
one has to consider the frequencies being generated and make sure there are
no resonators around to amplify the noise. I'd guess Honda spent a lot of
man-hours getting their units tamed.

I'd guess that most of the sound is generated by the engine exhaust. Can
you beef up the muffler? Also, make sure the entire exhaust system is not
rigidly bolted to any structure and that it's pointed away from people.

Aircraft builder/designers fight this problem all the time. There are
various materials one can glue to panels to change their resonant frequency
and damp the sound by absorbing the energy, but they all add weight (and
cost). (And absorbed energy equals heat.)

Roger

http://home.insightbb.com/~derbyrm

"GBM" wrote in message
...
Ian,

I have only read about this product, but it is very thin and claims to
reduce sound as well as lead does. I have also heard of waterproof
(closed
cell) carpet underlays that are designed to reduce sound.
http://www.acoustiblok.com/marine.html

Perforated aluminum on it's own is usually just a cosmetic covering for a
more fragile soundproofing. But perhaps someone has a product that has
soundproofing and perforated aluminum combined?

I looked up a supplier we used to use and they have just such a product
called Quietech:

http://www.soundown.com/

On my own boat, I just used 3/4" polycyanurate insulation (aluminum foil)
finish both sides and covered it with aluminum. It reduced the noise
level,
but hard to say how much because engine room is open on one side. For the
cost of a sheet of this 3/4" material, you could try this at home!

BTW - Make sure you provide good ventilation for the engine for engine
breathing air and cooling.

Another thought - What does Honda use - those units are really quiet!

GBM

"ian" wrote in message
ups.com...
I want to soundproof a genset located in the bow storage locker of a
catamaran. The genset, which does not have a sound enclosure is
located on a shelf between the hulls with a bulkhead aft and I'll make
a door which will make the enclosed area approximately 3' x 3'x 3'
Cats are weight sensitive anyway and being in the bow the location is
particularly weight sensitive. I have done some preliminary research
on the subject and it seems a sandwich of foam and a dense material,
normally lead or mass loaded vinyl (MLV), is the best sound deadening
combination however the dense material weighs a lot (duh....). 2 lbs
per sq foot for 1/4" seems typical.
I am wondering if anyone has experience with other sound proofing
strategies, techniques or materials that might be lighter? For example
would performated aluminium panels work in this application and be any
lighter?
Does anyone know the effectiveness of MLV, if I halved the thickness
how much increase in sound would I get?

Thanks for you help

Ian