Anti-Fouling Systems (AFS Convention)
From TBT to cybutryne: the AFS Convention keeps narrowing the list of permitted biocides in anti-fouling paints, with precise removal deadlines to meet.
Operational Explanation
The AFS Convention (International Convention on the Control of Harmful Anti-fouling Systems on Ships), adopted by the IMO in 2001 and in force since 2008, governs the anti-fouling coating systems ships may apply below the waterline, banning the biocidal substances most harmful to the marine environment.
The first major ban concerned organotin compounds such as tributyltin (TBT), developed in the 1960s and shown to cause deformities in oysters and sex changes in whelks: the Convention prohibits the application or reapplication of such compounds as biocides in anti-fouling systems.
In 2021 the MEPC adopted amendments introducing controls on the biocide cybutryne, in force since 1 January 2023: ships may not apply or reapply anti-fouling systems containing this substance from that date, and must remove it or apply a sealer coat at the next scheduled renewal of the anti-fouling system, in any case no later than 60 months after the last application. The second obligation has exceptions; the first has none. The adopted table excludes from removal or coating, under the conditions it states: ships that have not been in dry-dock on or after 1 January 2023; ships not engaged in international voyages; and ships of less than 400 gross tonnage engaged in international voyages, if accepted by the coastal State(s) concerned. None of these exceptions permits applying or reapplying cybutryne after 1 January 2023.
Regulatory Reference
AFS Convention (2001, in force since 2008), Annex I: ban on organotin compounds as biocides; 2021 amendments on cybutryne controls, adopted by resolution MEPC.331(76) of 17 June 2021, in force since 1 January 2023, with removal or sealer coating required by the next renewal, no later than 60 months after the last application.
Scope of Application
The AFS Convention applies under two distinct thresholds: ships of 400 GT and above on international voyages must hold an International Anti-fouling System Certificate (IAFS); ships of 24 metres or more in length but below 400 GT, likewise engaged in international voyages, must carry a Declaration on Anti-fouling System signed by the owner or authorised agent. The international-voyage condition applies to both thresholds: it is the scope of the Convention, not a requirement of the first band alone. The technical perimeter is the anti-fouling coating system applied below the waterline.
Procedure / How to Complete It
- Verify that the International Anti-fouling System Certificate (or the Declaration on Anti-fouling System for ships below the size threshold) is valid and consistent with the system actually applied.
- Verify the absence of organotin biocide compounds in the applied system, per the Convention's historical ban.
- For ships with cybutryne-containing systems applied before 2023, schedule removal or sealer coating by the next renewal, no later than 60 months after the last application.
- Document every anti-fouling system renewal in the relevant onboard log, referencing the composition of the product applied.
- Check the paint supplier's documentation for compliance against currently prohibited or restricted substances.
Practical Example
A ship with a cybutryne-containing anti-fouling system applied in March 2021 has a final date of March 2026: sixty months from the last application. The next scheduled docking is autumn 2025, so within the window. The operational decision is not “we dock and the limit is met anyway”: it is to fix March 2026 as a constraint independent of the docking and to treat any slippage as an event to be managed beforehand, not justified afterwards. If the yard moves the date to June 2026, there are two roads: bring the work forward elsewhere, or agree a course with the flag Administration before the deadline. Arriving at June 2026 with the original coating is the non-conformity, not a case of force majeure.
What Typically Goes Wrong
Common Mistakes Mistake Library
| Mistake | Consequence | How to avoid it |
|---|---|---|
| No monitoring of the chemical composition of previously applied anti-fouling systems | Late discovery of substances that have since been banned or restricted | Periodically check the composition of applied systems against the evolution of the AFS Convention |
| Cybutryne removal postponed beyond the 60-month limit from the last application | Non-compliance with the maximum deadline set by the 2021 amendments | Schedule removal or sealer coating by the next renewal, while still monitoring the absolute 60-month limit |
| Paint supplier documentation not kept or not checked for compliance | Unable to demonstrate compliance of the composition applied in the event of a check | Always keep and check the supplier's technical documentation for every application |
What the PSCO Checks
Operational Tips
- Periodically check the composition of applied anti-fouling systems against the evolution of the AFS Convention, not only at the time of initial application.
- Schedule cybutryne removal by the next renewal, while still monitoring the absolute 60-month limit from the last application.
- Always keep the paint supplier's technical documentation for every application, to support a demonstration of compliance.
Preparation checklist
Educational checklist. This summary supports learning and preparation only. It does not replace the vessel’s approved procedures, manuals, statutory documents, company SMS, or applicable official requirements. Completing it demonstrates neither compliance nor readiness for an inspection: it shows that a list has been read, not that the ship is in order. Always verify the current documents carried on board.
- International Anti-fouling System Certificate verified as valid
- Absence of organotin biocide compounds confirmed
- Any cybutryne presence verified and removal/coating scheduled within the required limits
- Paint supplier documentation kept and verified
- Onboard log updated at every anti-fouling system renewal
FAQ
Related Topics
Last substantive revision of this page: 28 August 2026 · page fingerprint 16dcd29ea06a