What does the acronym OC signify when noted on a chart next to a light?

The acronym OC, when noted on a chart next to a light, signifies Occulting Flash. This terminology is used in maritime navigation to describe a specific type of light characteristic. An Occulting light is one that has a period of illumination followed by a period of darkness, with the duration of darkness being equal to or longer than that of the illumination. This pattern helps mariners differentiate various navigational aids and can be crucial for safe navigation, particularly in congested or hazardous waters where precise identification of lights is essential.

The Occulting Flash characteristic is utilized in various buoy and lighthouse signaling systems to ensure effective communication of position and navigation aids to vessels. Recognizing this distinction allows officers to make informed decisions regarding navigation and route planning.

Understanding this terminology is critical for navigating safely and effectively, especially in coastal and offshore operations.