Dave, I agree.
The result of an exhaust riser failure, at least at the nipple, was included in my February 2004 Tech notes report, here for C34IA members:
http://www.c34.org/mainsheet/pdf/Feb_2004.pdf The billowing black/brown smoke filling the cabin and pouring out of the companionway was a dead giveaway!
[Please note that the article says I didn't use hump hose - I corrected that shortly after the article was published.]
Much the same results would be expected if the inlet or outlet lip of the muffler failed catastrophically. That, however, doesn't seem to be the case, because the muffler lips tend to fail slowly over time. What we've learned from Claude's forensics is what the muffler is made of, since most of us simply get to see the white fiberglass cover.
There have been many posts here over the years on rebuilding those lips, because many of us have had leaks where the hoses join the muffler. Whether or not the steel insert has failed or just the fiberglass surrounding it at, most usually, in the inlet lip, has yet to be determined on my boat.
The very important information from Claude's presentation will be helpful for me in deciding what to do next.
As Ron reported (in the link I provided) both he and Claude decided to remove and replace the muffler, and explained, very well, just how to do it. Ron also did a presentation on how to replace the exhaust hose from the muffler to the transom.
With all this information, I think all of you now can best assess and determine your own next steps when it comes to that system.
Like folks who still have the old trailer connections and ammeters in their wiring harnesses, I find it interesting that many still have those old solid hoses on the inlets to the muffler instead of the far superior hump hose. But note, I've had a hump hose on mine since 1998 and have still found major deterioration of the inlet lip.
"Your boat, your muffler"
