What does a yellow flag mean on a boat?
Short answer
A plain yellow Quebec flag means the vessel is healthy and requests free pratique.
In the International Code of Signals, Quebec is a single plain yellow flag. It is commonly associated with quarantine/pratique: the vessel declares itself healthy and requests clearance. Do not confuse it with yellow special marks in buoyage, which are navigation marks rather than signal flags.
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What does a yellow flag mean on a boat?