Many yachtsmen today consider “Flag Etiquette” to be a form of snobbery only observed by Members of elite Yacht Clubs like the Royal Yacht Squadron and their
like and of no real importance to normal yachtsmen in this modern era and may be disregarded.

Others however, consider that it is a tradition worth maintaining and thus are interested in the rules.

The flag of the homeland of the boat on the back in large format. The flag of the country visited on forepart in a smaller size. On smaller boats some inventiveness will be needed, but: Never one above the other on one stick. Each nationality flag deserves its own flagpole and an antenna is not a flagpole.

http://en.wikipedia.org/wiki/Maritime_flag 

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