lightvessel

A lightvessel, or lightship, is a conventional ship which acts as a lighthouse, usually anchored permanently and having no means of propulsion. Lightvessels are used in waters that are too deep for a lighthouse. Instead of marking coastlines, they usually mark marine traffic routes. They are superior to a buoy for this purpose because its navigational aids are more visible. They also usually carry data recorders used in research oceanography, such as wave recorders, and may also function as weather stations.
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