buoy

A buoy is a floating device anchored to the seabed or attached to the water’s surface, used to mark locations, warn of hazards, guide vessels, or collect oceanographic data. Modern buoys are typically made of hollow plastic or fiberglass with a buoyant core, sometimes steel or concrete, and are equipped with moorings, ballast, and sometimes lights, radar reflectors, or research instruments. They can be moored in fixed positions or function as drifting devices.

There are several broad types. Navigation buoys mark channels or hazards and are typically anchored; weather and oceanographic buoys collect data such as wind speed, air and water temperature, salinity, waves, and currents. Drifting or surface drifters carry instruments to track ocean circulation and dispersion. Fishing buoys and marker buoys denote gear locations, traps, or nets. Life buoys or ring buoys are flotation devices used for rescue.

Moorings secure buoys to the seabed with anchors and chains or synthetic lines; drifting buoys rely on surface currents and drogues to maintain a rough transmission of their position. Data buoys often transmit collected information via satellite or radio to shore facilities.

Buoyage systems use color and shape to convey information. International conventions, such as the IALA system, regulate buoy design and markings to indicate safe water, hazards, and channels, though specifics vary by region.

The term buoy comes from the Old French bouée. Buoys have been used for centuries and remain essential for safe navigation, meteorology, and ocean research.