foghorns

Foghorns are acoustic signaling devices used to indicate the presence of ships, coastlines, or hazards in fog, mist, or other restricted visibility. They produce loud tones that can propagate over long distances, providing a warning to vessels and aiding navigation where visual cues are limited.

Foghorns have appeared in several configurations. On ships, they have historically used steam- or electric-powered horn systems, while fixed coastal and lighthouse installations employ stationary horns or diaphragm units powered by electric or pneumatic systems. Modern shore and offshore installations often use electronically synthesized tones or low-frequency horn units designed to maximize range in fog, sometimes exploiting the greater atmospheric sound propagation at certain frequencies. The choice of horn, its mounting, and its power source affect its tone, range, and reliability in harsh weather.

In practice, sound signals are regulated by international and national navigation rules. In restricted visibility, vessels may be required to sound standard signals to indicate presence or maneuvers, and fixed fog signals warn of coastlines, shoals, or landmarks. Operators are responsible for maintaining equipment and ensuring audible operation.

Historically, foghorns played a crucial role in maritime safety starting in the 19th century with steam-driven or compressed-air devices. Although advances in radar, GPS, and other navigation aids have reduced reliance on traditional fog signals in some regions, fixed foghorns remain in service at many coastal locations and lighthouses, particularly where weather conditions are conducive to sound propagation.