Also keep in mind that modern
diesel vehicles have MUCH more sophisticated emissions systems than a
marine diesel. My BMW X5D has all these systems:
-Diesel Particulate filter, to catch larger particles and soot, It later heats up the
exhaust to burn this into ash.
-Diesel Emission Fluid, Urea, injected into the
exhaust stream to break down dangerous NOx emissions into harmless nitrogen and
water.
-EGR to reburn exhaust
-Intake swirl
generator to introduce Vortex swirling
-2
Noise mufflers
-catalytic converter.
-MAF air monitoring for more accurate injection.
Your
boat is the equivalent of a 1940's tractor with a (probably) mechanical
fuel injection
pump and none of the above emissions.
I commend you wanting to improve the situation. A simple 1 minute timer would probably do the job to keep the plugs hot. You should also do a compression/ leak down test and see if maybe your rings are bad.
All else you could do an EV conversion. Getting more popular and easier to do.