In Dutch, the term ‘zeezwaaien’ refers to the process whereby a tanker leaves a Dutch port to head out to sea for the purpose of washing its tanks, and then returns to that port to receive its next cargo.
‘Zeezwaaien’ occurs when a ship leaves the port after unloading a chemical cargo, with the sole purpose of washing small quantities of cargo residues from the tank in the Exclusive Economic Zone (EEZ, beyond the 12-nautical-mile zone), discharging the wash water into the sea and then returning to the port. A deliberate detour may also be made ‘en route’ to the next port.
Investigation
The Dutch authorities have limited insight into the extent to which tank washing occurs in the Dutch EEZ. Aerial and satellite observations do not provide comprehensive coverage.
In 2020, the Dutch Inspectorate (ILT) identified, based on vessel movements and routes, 45 voyages by chemical tankers that could indicate ‘sea washing’. There is no reason to believe that this situation has changed significantly in recent years.
Ships are only permitted to wash tanks (‘sea washing’) under certain conditions. These rules are set out in Annex II of the International Convention for the Prevention of Pollution from Ships (MARPOL).
Ruling of the Supreme Court
In 2014, the Dutch Supreme Court issued a ruling on the interpretation of the legislation and the conditions under which wash water may be discharged into the sea. Article 29 of the Decree on the Prevention of Pollution by Seagoing Ships (a Dutch regulation) includes a prohibition on discharging substances into the sea other than in accordance with Annex II to MARPOL. This concerns a clarification of the term ‘en route’ from Annex II to MARPOL.
The Dutch Supreme Court has concluded that ‘sea washing’ falls under the term ‘en route’ and that this method of tank washing is permitted under Annex II of MARPOL. A ship may leave a port or deviate from its route for the sole purpose of discharging cargo residues, provided that the discharge requirements set out in Annex II of MARPOL are met.
No change in Dutch regulations
In recent years, the Dutch government has investigated the possibility of restricting tank washing at sea. Based on the findings, it was decided not to introduce a national ban on ‘sea washing’. This was set out in a letter from the Minister of Infrastructure and Water Management to the House of Representatives of the Dutch Parliament dated 17 June 2024.
The washing of ship’s tanks at sea is and remains subject to strict conditions in accordance with the MARPOL provisions.
The tanks must have been pre-washed. Washing water may only be discharged if the vessel has a minimum speed of 7 knots. Discharge is only permitted at a distance of at least 12 nautical miles from the coast and in an area where the sea has a minimum depth of 25 metres.
Photo: a chemical tanker, not related to this article.