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Day shapes are black in color and their sizes are determined by the ColRegs; for example, the size of the ball is not less than 0.6 metres (2.0 ft). The vertical distance between shapes is at least 1.5 metres (4.9 ft). Vessels of less than 20 metres (66 ft) length may use shapes of smaller size commensurate with the size of the vessel. [2]
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 ...
An example of a complete light characteristic is "Gp Oc(3) W 10s 15m 10M". This indicates that the light is a group occulting light in which a group of three eclipses repeat every 10 seconds; the light is white; the light is 15 metres above the chart datum and the nominal range is 10 nautical miles.
Before electricity, light below a vessel's deck was provided by candles, oil and kerosene lamps—all dangerous aboard a wooden ship. The deck prism laid flush into the deck, the glass prism refracted and dispersed natural light into the space below from a small deck opening without weakening the planks or becoming a fire hazard.
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.
In that sense, a daymark conveys to the mariner during daylight hours the same significance as the aid's light or reflector does at night. [3] Standard signboard shapes are square, triangular, and rectangular, while the standard colours are red, green, orange, yellow, and black.
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Leading lights, also known as range lights in the United States, are a pair of light beacons used in navigation [2] to indicate a safe passage for vessels entering a shallow or dangerous channel; they may also be used for position fixing. At night, the lights are a form of leading line that can be used for safe navigation. The beacons consist ...