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The International Convention on the Control of Harmful Anti-fouling Systems on Ships (AFS 2001) entered force 17 September 2008 after a five-year phase-in. It prohibits organotin compounds (TBT) as biocides in anti-fouling systems and establishes the framework under which further biocides can be prohibited by IMO Marine Environment Protection Committee (MEPC) Resolution. AFS is the smaller cousin of MARPOL but touches every dry-docking planning cycle: the hull-coating specification must comply with the current AFS regime plus any port-state add-ons (California SLC, Australia AMSA hull-cleaning framework, etc.).
Article 4.1 prohibited the application of TBT-based coatings from 1 January 2003; Article 4.2 prohibited the presence of active TBT coatings on the hull from 1 January 2008. Vessels with pre-2008 TBT coatings must either strip the coating during dry-dock or apply a sealer coat that prevents leaching. Every vessel is required to carry an International Anti-fouling System Certificate (IAFS Certificate) issued by the flag state or Recognised Organisation.
MEPC.334(76) (adopted June 2021) added cybutryne to Annex 1 of the AFS Convention. The prohibition entered force 1 January 2023 for new applications; existing vessels must remove or overcoat cybutryne-containing coatings at the next scheduled dry-docking after 1 January 2023. Cybutryne (marketed as Irgarol) was widely used as a booster biocide in copper-based systems throughout the 2000s and 2010s. Vessels with pre-2023 coatings need to verify the exact formulation from the coating manufacturer to determine cybutryne content — many pre-2023 anti-foulings did not contain it, but many did.
Biofouling management (as distinct from biocide prohibition) is being extended through Resolution MEPC.207(62) — the 2011 Biofouling Guidelines. Australia + New Zealand + California operate mandatory biofouling declaration + hull-cleaning verification regimes; the EU is progressing similar measures. Watch for MEPC.378(80) guidance revision and the ongoing discussion of a possible legally-binding biofouling instrument post-2025.