World Sailing classes carry the class insignia on the mainsail, national letters at international events (unless the boats are supplied), and a sail number of up to four digits allotted by the national authority or class. Letters and numbers are also required on spinnakers and headsails in some cases. Other boats follow their national authority's or class's rules.
Key points
G1 World Sailing class boats
What must appear, minimum character sizes, colours, and placement on each side of the sail.
G3 Chartered or loaned boats
The notice of race or sailing instructions may let a chartered boat carry letters or numbers that break her class rules.
G4 Warnings and penalties
The protest committee may warn a boat and give her time to comply before penalizing.