I have to admit...
I've been the one writing recently about flag protocol and practices that have been established over the years for recreational boats in our newsletter. There are no rules for recreational boats other than courtesy flag rules imposed by some countries (under penalty of fine or even arrest). For example, it's officially considered an act of war to fly the Cuban courtesy flag upside down. Check out the flag and realize how easy it is to fly upside down - the star should be pointing up.
The accepted practice in the US for your ensign is 1" of flag length per 1' of boat length (rounded up to an available flag size).
That said, we're picking up our new-to-us boat in another week. She's 65' and the length of the flag I'm bringing is 96". I want a big friggin flag on the boat as we cross New York harbor and I don't care about the "rules"...