Question about marine diesels
My two cents:
Buy a book on Marine diesels.
Learn about the prop shaft and shaft seals.
Learn how to bleed the fuel lines if you run out of fuel underway.
Learn how to change oil (oil must be pumped out, can''t just drain it in most circumstances).
Learn about water removal from fuel line.
Other things already mentioned:
Seawater cooling system, fuel contamination.