Flag etiquette for sailing holidays and clearing customs.

National flags or ensigns

The vessel's national flag – not necessarily the same nationality as the skipper or owner – should be displayed at the stern of the yacht; however on traditional yachts, placement on the main leech or gaff is historically more correct.
If the crew's nationality differs from that of the yacht, the crew's national flag can be flown under the courtesy flag at the starboard spreader. Likewise the nationality of an important guest on board is displayed this way.
Note that the European flag should not be used, since it doesn't refer to a nation.
Flag and ensign are synonymous. The name ensign is derived from the French enseigne and Latin plural insignia.

Courtesy flags

When in foreign waters the courtesy ensign, often the national flag of that country, is hoisted under the starboard spreader of the most forward mast. On a mastless powerboat, the courtesy flag replaces any flag that is normally flown at the bow.
Like the national flags or ensigns, the courtesy flag is hoisted at 08:00 local time and lowered at sunset. Yet, when manoeuvring - for example entering or leaving port - the national flags should be flown even at night until your ship is out of sight or safely at dock.

Q flag

The yellow Q flag should be flown instead of the courtesy ensign until the yacht is properly cleared by customs and immigration, after which the Q flag is replaced by the courtesy flag.

Burgee

The – often triangular – burgee from the skipper's yacht club or sailing organisation is also hoisted at the starboard spreader, but below the courtesy flag. International yacht club burgees are often hoisted above the nationality flags of crew or guests. Yet, purists will say that also crew national flags should be hoisted above any burgee. Too avoid possible insult it is therefore best to fly your burgee below all national flags!
The burgee may be flown day and night.

International code of signals

First drafted in 1855, this visual system was first published internationally in 1857 and gradually adopted by most seafaring nations. The 1932 modernisation allowed for new situations like a medical distress call involving radiation casualties (AN 2). Some other interesting examples: (IT): I am on fire; (US 4): Nothing can be done until weather moderates; (GM): I cannot save my vessel; (NC No and Yes) is used as a distress signal.

Alphabet

Numerals