I will echo what others have said. An oil change is quite cheap when compared to other MX items on a boat. Are you sure you are not getting in over your head?
I have a pair of the exact same engines. The info on this thread is right on. BUT...there are certain little idiosyncracies to this engine when installed in a marine application. My first suggestion would be to go to and subscribe to
www.boatdiesel.com. It is relatively cheap in the grand scheme of things. While these engines do hold about 4 gallons of oil, it is recommended by many to only put 13 quarts in...basically the bottom line on the dipstick.
More info here:
http://www.sbmar.com/Maintenance/PDF...Dip-Sticks.pdf
And I would highly recommend you spend some time on "Tony's Tips" to get to know those engines a bit better.