Race signals

Sail races are governed with flags and sound signals to indicate flag changes. The flags used are taken from the International maritime signal flag set. During a race and for any signal concerning the race, these flags are defined in the ISAF Racing Rules of Sailing but the signal can be modified by the Sailing Instructions.
The raising (hoisting) or removing of a visual signal is accompanied by the emission of a sound signal to draw attention to the new signal. The type of the sound signal (one short sound, two short sounds, one long sound, etc.) is described by the rule according to the type of signal. The usual meanings of these flags are as follows:

Postponement signal

The Answering Pennant (AP) with or without a numerical pennant is used to indicate a postponed race. A numerical pennant below the AP denotes the time, in hours, of the race postponement.

Flag signal		Number of sound signals when raised	Number of sound signals when lowered	Description
	AP			Races not yet started are postponed.
	AP 1			Races not yet started are postponed 1 hour.
	AP 2			Races not yet started are postponed 2 hours.
	AP 3			Races not yet started are postponed 3 hours.
	AP A			Races not yet started are postponed. No more racing today.
	AP H			Races not yet started are postponed. More information ashore.

Preparatory signal

These signal flags are used before a race start and most commonly as part of a start sequence/procedure.

Flag signal		Number of sound signals when raised	Number of sound signals when lowered	Description
	P			Normal preparatory signal - no starting penalties are in effect. A boat over the line at the start can return through the line or round an ends but must keep clear of boats not returning.If they fail to return through the line however they will be scored OCS
	I			The Round-an-End Rule 30.1 will be in effect. A boat over the line during the minute before the start must sail to the pre-start side of the line around either end before starting. If they fail to do this they will be scored OCS
	Z			The 20% Penalty Rule 30.2 will be in effect. A boat within the triangle formed by the ends of the line and the first mark during the minute before the start will receive a 20% scoring penalty
	I Z			Both the I flag rule and the Z flag Rule will be in effect during the minute before the start. If they fail to round and end then they will be scored OCS
				The Black Flag Rule 30.3 will be in effect. A boat within the triangle formed by the ends of the line and the first mark during the minute before the start will be disqualified without a hearing

Start signal

These signal flags are used in the pre-start procedure. Class flags can be numeral pennants 1 , 2 , and 3 however they can be substituted to avoid confusion with the postponement signals relating to a particular class.

Flag signal		Number of sound signals when raised	Number of sound signals when lowered	Description
,	1 ↑			Warning Signal. 5 minutes to race start when class flag raised.
	1 P ↑			Preparatory signal. 4 minutes to start when P flag raised. Flag P used or if a starting penalty applies I, Z, Black flag or I over Z is used in place of P.
	1 P ↓		Long sound	Preparatory signal. P flag removed 1 minute before start. Flag P used or if a starting penalty applies I, Z, Black flag or I over Z is used in place of P.
	1 ↓			Start Signal. Race start when class flag removed.

Recall signal

Flag signal		Number of sound signals when raised	Number of sound signals when lowered	Description
	X			Individual recall. One or more boats did not start correctly and must return and do a proper start. The X flag is displayed until the earliest of the following: all boats over the line early have returned correctly, 4 minutes from the start or until one minute before the next start. (The sound signal is in addition to the start sound signal)
	1st Sub			General recall. All boats are to return and then a new start sequence will begin. Signaled when there are unidentified boats over the line or subject to one of the starting penalties, or there has been an error in the starting procedure. The new warning signal for the recalled class will be made 1 minute after the 1st substitute is removed. (The two sound signals when the first substitute is displayed are in addition to the start sound signal)

Course change signal

Flag signal		Number of sound signals when raised	Number of sound signals when lowered	Description
	S			Shortened Course. When displayed at a rounding mark the finish is between the nearby mark and the mast displaying the S flag. When displayed at a line that boats are required to cross at the end of each lap the finish is that line. When displayed at a gate the finish is between the gate marks.
	C	...		Course Change. When displayed at a rounding mark, the position of the next mark has been changed. If the direction to the mark has changed it shall be indicated by displaying the new compass bearing or a green triangular flag (or board) for a change to starboard or a red rectangular flag (or board) for a change to port. If the length of the leg has changed then this shall be signalled by displaying a "-" if the leg will shorter or a "+" if the leg will be longer. Repeated sound signals should be made to draw attention to the signal.

Abandonment signal

Flag signal		Number of sound signals when raised	Number of sound signals when lowered	Description
	N			All races that have started are abandoned. Return to starting area for a new start. The first warning signal will be made 1 minute after N is removed.
	N A			All races are abandoned. No more racing today.
	N H			All races are abandoned. More information ashore.

Other signals

Flag signal		Number of sound signals when raised	Number of sound signals when lowered	Description
	L			When displayed afloat means: Come within hail or follow this boat. When displayed ashore means: A notice to competitors has been posted.
	M	...		Indicates a boat or an object displaying this signal replaces a missing mark. Repeated sound signals should be made to draw attention to the signal.
	Y			All people on board should wear a personal life jacket or personal buoyancy.
	BLUE			When displayed the race committee boat is in position at the finishing line.