“Lightships, an identification mark at sea”. A lightship can be described as a floating lighthouse and its purpose is to allow seamen to pinpoint their position at sea at unseasonable hours, during mist and when visibility is poor.

Willem Wilmink’s poem captures the purpose of a lightship: lv pos

How do you know how to find your way at sea, captain?
How do you know where you should be?
Nowhere is a house to be found
Nowhere a city street where you should be tomorrow
How do you know where to go, captain?

At dusk, this characteristic beacon of light is visible from a distance. A nautophone (fog horn) sends penetrating sound signals during mist and when visibility is poor. A radio beacon sends a radio signal in Morse code which allows ships equipped with a direction finder to determine the position of the lightship. On board ships are nautical charts which show where lightships, lighthouses and other identification marks can be found, such as buoys and cairns, each with their own specific characteristics.