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The appropriate lights may also be displayed during the day at times of restricted visibility or other necessary circumstances. [3] Vessels under 7 meters are generally not required to display day shapes even if they are required to display lights at night. [4] A square black flag displayed over the ball may be used as a distress signal. [5]
International maritime signal flags are various flags used to communicate with ships. The principal system of flags and associated codes is the International Code of Signals . [ 1 ] Various navies have flag systems with additional flags and codes, and other flags are used in special uses, or have historical significance.
The International Code of Signals was preceded by a variety of naval signals and private signals, most notably Marryat's Code, the most widely used code flags prior to 1857. What is now the International Code of Signals was drafted in 1855 by the British Board of Trade and published in 1857 as the Commercial Code. It came in two parts: the ...
Diagram of cardinal marks as seen during the day, with their light patterns. The lights shown here are configured as "Quick". A cardinal mark is a sea mark (a buoy or other floating or fixed structure) commonly used in maritime pilotage to indicate the position of a hazard and the direction of safe water.
Some signal lamps are mounted on the mastheads of ships while some small hand-held versions are also used. Other more powerful versions are mounted on pedestals. These larger ones use a carbon arc lamp as their light source, with a diameter of 20 inches (510 mm). These can be used to signal to the horizon, even in conditions of bright sunlight.
Watercraft navigation lights must permit other vessels to determine the type and relative angle of a vessel, and thus decide if there is a danger of collision. In general, sailing vessels are required to carry a green light that shines from dead ahead to 2 points (22 + 1 ⁄ 2 °) abaft [note 1] the beam on the starboard side (the right side from the perspective of someone on board facing ...
Customarily, the upper mark is up-hill from the lower (forward) mark. The mariner will know the geometry of the marks/lights from the navigational chart and can understand that when "open" (not one above the other) the ship needs to be navigated to "close" the marks (so one is above the other) and be in the preferred line of the channel.
A ship's message had to be approved by the officer of the watch, and his system was augmented and changed in various ways over the following century. In 1790, Admiral Lord Howe issued a new signal book for a numerary system, using numeral flags to signal a number; the number indicated the message, not the mast from which the flags flew.