One thing led to another and soon I learned something pertinent to
boats.
I had read something in our local paper about very old engines called
"Hit or miss" engines and that led me to "hot bulb" engines, an early
variation of compression ignition and then I was wondering about
various fuels for modern diesels so looked up diesels on Wiki where
there is a good article.
Anyway, the article discusses emissions from diesels and why thye
smoke under load. Apparently, they smoke because they are operating
out of their range so the fuel cannot be burned completely. The black
smoke is what results. This is why a fouled prop causes a sailboat
diesel to smoke and why diesel trucks to smoke under heavy load..
They also smoke when cold which explains why my small sailboat engine
smokes initially but when warm does not.