Noordzee, the first one in 1964, broadcasted from the REM island and was part of TV Noordzee (CH E 11)
Radio Noordzee was on 1403 kHz, 214 meters, with only 1 kW!! The 75 mast helped a bit.
The REM was based on an sort of oil platform (copy of the Lago di Maracaibo, Venezuela oil platforms, one of the owners was Heerema offshore who was active in the Caribean)
The TV station obviuosly was a pain in the as for the Government and its politcal parties who were linked to the public broadcasting organsations in Hilversum.
A new law prohibited transmitting from fixed structures based on the bottom of the sea. In this way Veronica was saved, since this was a floating ship.

Two more facts were vital for the end of the radio ships:
1) Political the PvdA, Labour had won the elections and was the largest party in the coalition. They were much against commercial radio and were linked to the socialist VARA in Hilversum.
2) The frequency allocation of Geneva was at hand, and Holland was warned that they would get less channels when they continued to house pirate stations off the coast. So the pirates had to go, Holland got many AM channels in Geneva 1975, many of them used only decades later by commercial stations.