lightship weight

A lightship is a marine navigation beacon stationed where lighthouse construction is impractical. These vessels are equipped with fog signals and radio beacons, and their names are marked in large letters for easy daytime recognition. The primary advantage of lightships is their mobility, making them useful for marking shifting hazards and traffic lanes.123

In ship design, "lightship weight" refers to the weight of the ship's structure, propulsion machinery, and outfit. This is added to the deadweight (cargo and supplies) to determine the total displacement, which is the weight of water the ship must displace to float, according to Archimedes' principle. Lightships could be up to 150 feet long and weigh around 500 tons, typically being towed into position and moored. While once common, most lightships have been replaced by automated buoys.43