Nautical flags are specially designed flags in distinct colors which can be used to signal from ship to ship, or ship to shore. In addition to an internationally recognized signaling code, many nations have specific nautical flags of their own, but ships are able to communicate through the international code with ships from other nations. These communications are used to exchange information such as news, information about hazards, or requests for assistance. Nautical flags are also known as signaling flags, because of their use in signaling information.
In addition to being used for communications, nautical flags are also used to dress the ship for special occasions. Typically, the flags are hung in a pattern which spells out a message, for those who can read it. Some ships also utilize semaphore signaling for communications. Semaphores work very differently from nautical flags.In semaphore, a message is spelled out with flags held in certain positions relative to a human body.
To increase visibility, nautical flags are made in red, blue, yellow, black, or white, because these colors can be clearly seen and distinguished. Colors which might be confusing together, such as blue and black, will not appear in the same flag. The bold block patterns combined with the high color visibility make nautical flags readily visible, even at great distance.
A set of nautical flags includes 26 flags which represent the 26 letters of the Roman alphabet, along with 10 numerals, one answer flag, and three substitute or repeater flags. One flag can be used to signal an urgent or basic message, two flags are used to communicate about navigation or distress, three can indicate points on a compass along with basic, short words, and four are used to indicate the name of a ship, its bearings, or to signal information about geography. For time and position indicators, five flags are used, while six can indicate direction, latitude, and longitude. If the longitude is over 100 degrees, seven flags are used.
In addition to spelling out the letters of the alphabet, the 26 square alphabet flags also contain shorthand messages. For example, the letter G/Golf hung alone indicates that the ship wants a pilot, while F/Foxtrot means that the ship is disabled, and Z/Zulu means that a tugboat is needed. The answer flag is used to indicate that a message was received or understood, and also as a decimal point, and the repeater flags are used as substitutes, asking the reader, for example, to read the third flag in the signal in place of the repeater flag. There are also a number of two letter codes, such as PP, for keep clear, and CD, indicating a need for immediate assistance.