There are endless reasons for a diesel to smoke.
1800 RPM's at the dock or under load?
Is the bottom clean?
Is the smoke from both motors?
What color is the smoke?
Does performance change?
"Air cleaner is dirty, engines a little dirty and soot in engine room". Assuming this is a statement then you have potential answers in two of those, air cleaner and soot in ER (exhaust leak)
What do the fuel filters look like? How old is the fuel?