I missed this part earlier:
If there's no water and no exhaust
and your engine compartment is getting warm, then the pipe to/from your muffler, or the muffler itself, is broken/loose. Or the pipe between the mixing elbow and the radiator has come loose, and the exhaust
is coming out that. By hook or crook you've either got a loose hose, or a busted muffler, and the stuff that's supposed to be coming out your tailpipe is discharging freely in your engine compartment. That's good news, because a loose hose is free to fix, and a busted muffler is cheaper than engine parts.
From personal experiences, mufflers are a major pain in the rear to fix, and hiring someone is a great idea. It's a real simple issue, congratulate yourself on diagnosing the problem, and have a beer while someone else fixes it.
Particularly if the boat isn't where you are. But it could be something as simple as a hoseclamp come loose, so if you can't fit down to fix it, get your wife to do it. Might save you some labor.