05/13/2026
The main international regulation on ship anti-fouling systems is the International Convention on the Control of Harmful Anti-fouling Systems on Ships, 2001, usually called the AFS Convention. It was adopted by IMO on 5 October 2001 and entered into force on 17 September 2008. Its purpose is to reduce or eliminate harmful effects on the marine environment and human health caused by toxic anti-fouling systems used on ships. IMO explains that the Convention prohibits harmful organotin compounds in anti-fouling paints and creates a legal mechanism to control other harmful substances in future.
Anti-fouling paints are applied to hulls and other underwater surfaces to prevent algae, barnacles, molluscs, and other marine organisms from attaching to the ship. This is operationally important because fouling increases hull resistance, fuel consumption, emissions, and voyage costs. However, older biocidal coatings can leach toxic substances into seawater. The Convention therefore tries to balance two objectives: maintaining efficient ship operation and preventing long-term harm to marine ecosystems and seafood chains. The Convention text itself recognises both sides: harmful systems must be controlled, but effective and environmentally safer anti-fouling alternatives should continue to be developed.
Scope of the AFS Convention
The AFS Convention applies broadly to ships operating in the marine environment. In the Convention, “ship” includes ordinary vessels as well as hydrofoil boats, air-cushion vehicles, submersibles, floating craft, fixed or floating platforms, FSUs, and FPSOs. “Anti-fouling system” is defined broadly as any coating, paint, surface treatment, surface, or device used on a ship to control or prevent the attachment of unwanted organisms.
The Convention applies to ships flying the flag of a Party, ships operating under the authority of a Party, and ships entering a port, shipyard, or offshore terminal of a Party. Warships and government non-commercial ships are excluded, although Parties must ensure that such ships act consistently with the Convention as far as reasonable and practicable. The Convention also applies the principle of no more favourable treatment to ships of non-Parties.
Original Control: Organotin / TBT Anti-Fouling Systems
The first major target of the AFS Convention was organotin compounds acting as biocides, especially tributyltin, or TBT. TBT was once highly effective as an anti-fouling biocide, but it caused severe ecological effects, including deformities in oysters and reproductive disruption in marine snails. IMO’s public summary specifically notes that TBT was proven to cause deformities in oysters and sex changes in whelks.
Under Annex 1 of the Convention, ships were prohibited from applying or re-applying organotin compounds acting as biocides from 1 January 2003. From 1 January 2008, ships were required either not to bear such compounds on their hulls or external parts, or to have a coating that forms a barrier preventing organotin leaching from the underlying non-compliant system.
This remains the foundation of the Convention: ships should not use harmful biocidal organotin systems, and older coatings must be removed or sealed so they cannot leach into the marine environment.
Major Recent Update: Cybutryne Ban
The most important recent update is the control of cybutryne, also known commercially in some contexts as Irgarol 1051. Cybutryne is a biocidal substance used in some anti-fouling systems. Through Resolution MEPC.331(76), adopted on 17 June 2021, IMO amended Annexes 1 and 4 of the AFS Convention to add controls on cybutryne and to update the model form of the International Anti-fouling System Certificate.
The cybutryne amendments were deemed accepted on 1 July 2022 and entered into force on 1 January 2023. From that date, ships must not apply or re-apply anti-fouling systems containing cybutryne. IMO’s public Convention page confirms the same regulatory position: from 1 January 2023, ships may not apply or re-apply anti-fouling systems containing cybutryne, and existing systems containing cybutryne must be removed or sealed at the next scheduled renewal, subject to the maximum time limit.
For ships that already had cybutryne in the external coating layer of the hull or external parts/surfaces on 1 January 2023, the Convention requires one of two actions:
The ship must either remove the anti-fouling system containing cybutryne, or apply a barrier coating/sealer coat that prevents cybutryne from leaching from the underlying non-compliant anti-fouling system. This must be done at the next scheduled renewal of the anti-fouling system after 1 January 2023, but no later than 60 months after the last application of a cybutryne-containing anti-fouling system.
There are limited exceptions. The cybutryne removal/sealing requirement does not apply in the same way to fixed and floating platforms, FSUs, and FPSOs constructed before 1 January 2023 that have not been in dry dock on or after that date; ships not engaged in international voyages; and ships under 400 GT engaged in international voyages if accepted by the relevant coastal State.
Certification Update After the Cybutryne Amendment
Resolution MEPC.331(76) also updated Annex 4 of the Convention, especially the model form of the International Anti-fouling System Certificate. The revised certificate form now includes compliance options not only for organotin compounds but also for cybutryne. The certificate must show whether cybutryne has not been applied, has been removed, has been covered with a sealer coat, is not in the external coating layer, or was applied before 1 January 2023 but must be removed or sealed before a specified date.
For ships affected by a newly controlled anti-fouling system, the Administration must issue the certificate not later than two years after entry into force of the relevant control. For the cybutryne amendment, this means affected ships should have appropriate certification within the post-entry-into-force transition period while still complying with Annex 1 requirements.
2022 Guidelines: Survey and Certification
Following the cybutryne amendments, IMO adopted updated guidelines at MEPC 78. Resolution MEPC.358(78), adopted on 10 June 2022, contains the 2022 Guidelines for Survey and Certification of Anti-fouling Systems on Ships. These guidelines replaced the earlier 2010 guidelines because the Convention had been updated to include cybutryne.
The 2022 survey and certification guidelines apply to ships of 400 GT and above engaged in international voyages, excluding fixed or floating platforms, FSUs, and FPSOs as specified in Annex 4. They explain how Administrations and recognized organizations should verify compliance and issue or endorse the International Anti-fouling System Certificate.
For an initial survey, the surveyor should verify that the anti-fouling system complies with the Convention and that the system actually applied is the same as the system identified in the documentation. The company should submit ship details and supporting information from the anti-fouling system manufacturer, including the type of anti-fouling system, manufacturer name, product name and colour, active ingredients, and CAS numbers.
When an anti-fouling system is changed or replaced, the survey should verify the new system and, where applicable, confirm that the old controlled system has been removed or properly covered by a sealer coat. If documentation is insufficient, verification may be based on sampling, testing, MSDS, manufacturer declarations, shipyard invoices, or other reliable documentation.
2022 Guidelines: Brief Sampling
IMO also adopted Resolution MEPC.356(78), the 2022 Guidelines for Brief Sampling of Anti-fouling Systems on Ships. These guidelines support port State control, flag State inspection, and survey verification. They are directly linked to Article 11 of the AFS Convention, which allows inspection of ships in ports, shipyards, or offshore terminals of a Party.
The guidelines clarify that sampling is not always required. The purpose of sampling is only to verify compliance with the Convention; it is not intended to assess coating quality, workmanship, or general anti-fouling performance.
The brief sampling guidelines set practical threshold values. Compliance is assumed if organotin compounds are not present above 2,500 mg organotin, measured as Sn, per kg of dry paint, and cybutryne is not present above 1,000 mg cybutryne per kg of dry paint. In borderline cases, a compound-specific tolerance may be applied, but the tolerance range should not exceed 30%.
For practical enforcement, the 2022 brief sampling guidelines describe three analytical cases: organotin only, cybutryne only, or a simplified approach covering both organotin and cybutryne. For cybutryne-only analysis, compliance is assumed where the average value is below the threshold plus tolerance, meaning 1,250 mg/kg dry paint. If the average is above that value, it indicates non-compliance.
Latest 2025 Update: IHM Threshold Clarification for Cybutryne
The newest update connected to anti-fouling regulation is not a new ban under the AFS Convention itself, but a 2025 amendment to the IMO Guidelines for the Inventory of Hazardous Materials, or IHM, adopted through Resolution MEPC.405(83) on 11 April 2025. This is important because the Hong Kong Convention on ship recycling entered into practical relevance with IHM obligations, and anti-fouling substances such as organotin and cybutryne must be correctly recorded in the IHM.
MEPC.405(83) amended the 2023 IHM Guidelines to clarify cybutryne threshold values depending on the sample source. For anti-fouling systems containing cybutryne, the IHM table now refers to 1,000 mg/kg or 200 mg/kg, depending on whether samples are taken from the hull or from wet paint containers.
This clarification aligns with the 2022 survey and certification guidelines. Those guidelines state that when samples are taken directly from the hull, average cybutryne values should not exceed 1,000 mg/kg dry paint; when samples are taken from wet paint containers, cybutryne should not exceed 200 mg/kg dry paint.
In practical terms, this 2025 update matters for shipowners, yards, recycling facilities, class societies, and IHM experts. It means cybutryne must be considered not only as an operational anti-fouling compliance issue under the AFS Convention, but also as a hazardous-material documentation issue for the ship’s IHM. The 2025 IMO resolution invites Member Governments to apply the amended IHM Guidelines as soon as possible and no later than 26 June 2025.
Inspection and Port State Control
Under Article 11 of the AFS Convention, a ship may be inspected in any port, shipyard, or offshore terminal of a Party. If there are no clear grounds for suspecting a violation, the inspection is normally limited to checking the International Anti-fouling System Certificate or Declaration, and/or conducting brief sampling that does not affect the integrity, structure, or operation of the anti-fouling system. The Convention also states that the time required to process sampling results should not be used as a basis for preventing the movement or departure of the ship.
If there are clear grounds to believe that the ship is violating the Convention, a more thorough inspection may be carried out. If a violation is detected, the port State may warn, detain, dismiss, or exclude the ship from its ports, while informing the ship’s Administration.
Practical Implications for Ships, Companies, and Cadets
For shipowners and managers, the key compliance message is clear: anti-fouling records, coating declarations, MSDS, shipyard documentation, and IAFS certificates must be kept consistent and updated. Any coating renewal after 1 January 2023 must avoid cybutryne-containing systems, and any remaining cybutryne system must be removed or sealed within the Convention’s transition rules.
For shipyards, the main obligations are safe application, removal, collection, handling, treatment, and disposal of wastes from controlled anti-fouling systems. Article 5 of the Convention requires Parties to ensure that wastes from application or removal of controlled anti-fouling systems are handled in a safe and environmentally sound manner.
For cadets and junior officers, the most important point is that anti-fouling is not only a “paint issue.” It is linked to marine pollution prevention, port State control, certification, ship recycling documentation, hull performance, fuel consumption, and environmental protection. A ship may be operationally efficient because of anti-fouling paint, but that paint must not contain controlled harmful substances above accepted thresholds.
Summary of the Most Recent Regulatory Position
As of the latest available IMO updates, the AFS Convention controls two main categories in Annex 1: organotin compounds acting as biocides and cybutryne. Organotin/TBT systems have been prohibited for application since 2003 and effectively eliminated or sealed from ship hulls since 2008. Cybutryne has been prohibited for application or re-application since 1 January 2023, and existing cybutryne systems must be removed or sealed at the next scheduled anti-fouling renewal, but no later than 60 months after the last application. The most recent 2025 development is the clarification of cybutryne thresholds in the IHM Guidelines: 1,000 mg/kg for hull samples and 200 mg/kg for wet paint container samples.