There are some lightships in Copenhagen. Some are private residences and change their look in time. This lightship has moored in Juni 2017 opposite the " Little mermaid". I suppose , it could be lightship ARLHS ENG-316.
Last time i've seen most of them, opposite mermaid is ARLHS ENG-316
Try to search by keyword Copenhagen lightship - it will give you more-less full list and geolocations you can find on each photos. Lucky that they are not moving to often from place to place :)