Is there enough room for a 12" (I assume you're American?) square
"expansion" box just inside the transom?
In broad terms it is the expansion or release of the compressed gas that
makes most of the noise.
eg. If you have a 4" pipe off the manifold & half way to the transom you
enter that into a "pong box" of say 14" long by 6"dia & then go back to the
4". Then again immediately before the transom & once again back to 4" for
the exit. If it is a wet exhaust then construct it so that the bottoms of
all pipes & boxes are lined up level.
If you are in Aussie let me know as I know a chap who designs & installs
these in boats from 18' ski jobs right up to trawlers.
BruceM


"Gary Warner" wrote in message
...
Our boat (1958 Chris Craft) has a straight-6 inboard that
is raw water cooled. The exhaust exits just at the water line.
It's not too loud for me, but some of my guests seem to
find it loud. ~ What options do I have for muffling it?

I'm thinking along the lines of an elbow that could be
mounted on the transom to pipe the exhaust under
water. This would not look original and I have to
wrestle with whether I care about that or not. But
assuming I feel it's worth the noise-reduction,
would that work?

Thoughts?

Thanks,
Gary