lightship

lightship, marine navigation and warning beacon stationed where lighthouse construction is impractical. The first lightship was the Nore (1732), stationed in the estuary of the River Thames in England. Modern lightships are small, unattended vessels equipped with fog signals, radio beacons, and gimbal devices for keeping the navigational light beam horizontal in rough weather. Their names are marked in large letters for easy daytime recognition.

The chief advantage of lightships is their mobility, which makes them valuable in marking shifting hazards and traffic lanes in coastal waters and harbour approaches.