The most common cause of lots of smoke is poor compression.
If not protected in some way the moisture in the wet exhaust and in the air will cause rust spots on the cylinder walls when the engine is not used for a while.
AS this rust is scraped off with each start , eventually the cylinders will not hold compression very well.
This is when it takes 140F + coolant temp to stop the smoke.
The next problem on many trawlers is a constant under load , which carbons the rings , sometimes to sticking .
Add in the oil dilution from the fuel passing the rings,at low load , and SURPRISE ! a smoker.