As a current
in Fort Myers
Beach, FL I can tell you that as far as my fleet goes, our diesel boats carry 10 gal of gas and 10 gal of diesel, but our gas boats only carry 10 gal of gas.
I think in all the tows/jobs I have done over the years, I have brought diesel to a boat less then five times. In my diesel tow boat I cycle the 10 gal of diesel into my main tank every month so it does not go bad.
When you run out of diesel you have to prime your system again, but unless you are a sailboat with a relatively small tank, 10 gal of diesel will not do much in a power boat
Every franchise does things a little different.