A floating lighthouse.

Largely replaced by buoys in the modern era, this was once a permanently anchored vessel performing the functions of a lighthouse, typically in a location where construction of the latter is impractic [..]

Vessel, having its own means of propulsion, moored in a particular position and exhibiting a light and daymark to mark a navigational danger and to be a navigational aid.

The vessel condition without any form of deadweight aboard (incl.fuel and ballast).

A stationary vessel carrying a light used for navigation, serving the same purpose as a lighthouse.

An anchored ship acting as a floating lighthouse where building a lighthouse was not possible or impractical. Lightships would display a light at the top of a mast and in case of fog would sound a fog [..]

A stationary vessel carrying a light used for navigation, serving the same purpose as a lighthouse.

small ship equipped with a distinctive light and anchored near an obstruction to navigation or in shallow water to warn shipping.

a distinctively marked vessel anchored or moored at a charted point to serve as an aid to navigation. It has a characteristic light or lights, and usually other aids. View a downloadable and printable [..]

A stationary vessel carrying a light used for navigation, serving the same purpose as a lighthouse.

A vessel used to mark a hazardous area and/or guide shipping traffic, anchored in position with a mast mounted beacon and equipped with a steam whistle for fog warning. 

A ship equipped with a very large lamp; it can be positioned to warn off other ships from dangerous locations, as a sort of portable lighthouse.