Dark coasts and shifting channels need fixed signals. A beacon is a fixed or floating aid to navigation that marks a position, hazard, or channel by means of light, shape, color, or radio signal.

Lighthouses, lighted beacons on piles, and radar beacons all fall under the term. Mariners identify them by characteristic flash patterns, color, and charted position. Modern beacons may also transmit AIS messages so they appear on electronic displays even in poor visibility.

Beacons fail through storm damage, power loss, or vandalism. Notices to mariners report outages so navigators can adjust. Despite satellite navigation, visual and radar beacons remain essential backups and primary guides in confined waters.

• Fixed or floating navigational signal marker
• Uses light, shape, color, or radio identification
• Charted and described by characteristic patterns
• Serves as backup and primary guide in narrow waters