A government news release from Gibraltar on 21 August announced that HM Customs in Gibraltar had provided assistance in an international anti-drugs operation that has resulted in the arrest of 5 individuals and the seizure of several bales of cocaine, weighing in excess of 300 kg. The drugs were detected by the Spanish Authorities ion 19 August on board the HCH-X, a Gibraltar-registered vessel, whilst it sailed through international waters.
https://www.gibraltar.gov.gi/new/sites/default/files/press/2018/Press%20Releases/478-2018.pdf
Prensa Latina says the yacht was seized off Ibiza, the men detained were 4 Dutch and 1 German, and that the investigation began in mid 2016, when a ship was detected in Palma de Mallorca, linked to a criminal organisation dedicated to the introduction of narcotics into Europe. It says that the method used was to transport illicit cargo is known as “drop-off” [or “coopering”], which consists of using a larger ship to transport the narcotic substance to Europe, with the drugs thrown into the sea and is later collected by a smaller vessel.