An antifouling coating is the only paint on a ship that is regulated for what it releases rather than what it protects. Twice now, a product the industry considered settled has been banned outright, and both times the compliance burden landed on owners who had bought in good faith.
A Convention About Release, Not Protection
Every other coating on a vessel is judged by how well it keeps the environment out of the steel. An antifouling system is judged by what it puts into the water, which is why it sits under an international convention rather than a specification. The International Convention on the Control of Harmful Anti-fouling Systems on Ships was done at London on 5 October 2001 and entered into force on 17 September 2008.
The structure is worth understanding before the substances, because the structure is what persists. The convention does not list approved products. It lists controlled substances in an annex, and that annex can be amended. A coating that is compliant today is compliant until the annex says otherwise, and the annex has already been amended once in a way that caught a widely used product.
That distinction matters commercially. Owners and yards tend to treat antifouling selection as a performance decision about fouling resistance, speed loss and docking interval. It is also a regulatory exposure, and the exposure sits with the ship rather than with whoever sold the paint.
The convention controls substances, not products. Nothing about buying a compliant coating today protects the owner from the annex changing during its service life.
What Happened With Organotin
The first controlled entry was organotin compounds acting as biocides, tributyltin above all. The convention handled the transition in two stages, and the two-stage shape is the precedent for everything that followed.
From 1 January 2003, ships were prohibited from applying or re-applying organotin compounds acting as biocides in anti-fouling systems. From 1 January 2008, ships were required either not to bear such compounds on their hulls or external parts and surfaces, or to bear a coating forming a barrier to those compounds leaching from the underlying non-compliant system. Because the convention itself only entered into force on 17 September 2008, that second obligation took practical effect from entry into force rather than from the calendar date in the annex, and flag administration guidance commonly cites the September date for that reason.
Read the two stages together and the logic becomes clear. The first stage stops the flow of new material. The second deals with what is already on the fleet, and it offers a choice between removal and containment. That choice is the single most important feature of the framework for anyone costing a drydocking, because removal and overcoating are very different jobs.
Cybutryne Followed the Same Path
In June 2021 the Marine Environment Protection Committee adopted resolution MEPC.331(76), amending the convention to add controls on cybutryne and to revise the form of the International Anti-fouling System Certificate. The amendments entered into force on 1 January 2023.
From 1 January 2023: no ship may apply or re-apply an anti-fouling system containing cybutryne. The substance carries CAS number 28159-98-0, which is the number to look for on a product’s documentation rather than a trade name.
Ships already bearing it: a ship with cybutryne in the external coating layer on 1 January 2023 shall either remove the anti-fouling system, or apply a coating that forms a barrier to the substance leaching from the underlying non-compliant system.
The timing: at the next scheduled renewal of the anti-fouling system after 1 January 2023, but no later than 60 months following the last application to the ship of a system containing cybutryne.
Certification: affected ships were to hold a valid IAFS Certificate in the amended form no later than 24 months after entry into force, and existing certificates were to be reissued in the new format within that window.
Exemptions: fixed and floating platforms, FSUs and FPSOs built before 1 January 2023 that have not been in drydock on or after that date, ships not engaged in international voyages, and ships below 400 gross tonnage on international voyages where the coastal State accepts it.
The 60-month outer limit deserves attention because it is the provision most often misread. The obligation is triggered at the next scheduled renewal, which for a vessel on a long docking cycle might be several years away, but the 60-month clock runs from the last application of a cybutryne-containing system, not from 1 January 2023. A ship coated in 2020 therefore reached its limit in 2025 regardless of its docking plan, and the renewal and the deadline are not the same date.
Two clocks run at once. One starts at the next renewal, the other started when the paint went on, and compliance is governed by whichever arrives first.
The Paperwork Is the Enforcement
A port State control officer cannot assay a hull coating at the gangway. What they can do is read the documents, which is why the certification regime is where this convention is actually enforced.
The second and fourth items are where owners are most often let down, and the cause is almost always the same. The information that has to appear on the record originates at the application facility: which product, applied when, by whom, with which active ingredients. If the yard does not hand it over in usable form, nobody can reconstruct it later, and the certificate then rests on a record that cannot be substantiated.
Specifying that output as a deliverable in the painting contract costs nothing at tender stage and is close to impossible to recover afterwards. It is the cheapest piece of regulatory insurance available in a drydocking.
Preparing for the Next Amendment
Two substances have now followed the same route from standard practice to prohibition, with the second wave arriving roughly fifteen years after the first. Treating the current annex as permanent is a position the history does not support.
What an owner can usefully do is modest but genuine. Know the active ingredients in the system currently on the hull, by CAS number rather than trade name, since that is how controls are written. Know the date of last application, because transition provisions have twice been written as a period running from application. Keep the record and its supporting documents complete enough to prove both. And when selecting a system, ask what regulatory review the active ingredients are currently under, which is a question a serious supplier can answer and a reseller usually cannot.
There is also a distinction worth keeping clear. The AFS Convention governs what is in the coating. Managing what grows on the hull, and the invasive species risk that carries, is a separate strand of work with its own guidance and in some jurisdictions its own inspection regime. A coating can be entirely compliant and the hull still unacceptable to a port, and the two questions are answered by different documents.
Where removal is the chosen route, the work is a surface preparation and containment problem rather than a painting one, with waste classification and water management that need resolving before the vessel docks. Our industrial painting and coating work covers that preparation and the documentation that has to come out of it, which is the part the certificate ultimately depends on.
Frequently Asked Questions
What does the AFS Convention actually prohibit?
It controls substances listed in its Annex 1 rather than approving products. Organotin compounds acting as biocides came first: no application or re-application from 1 January 2003, and from 1 January 2008 ships were either not to bear them or to bear a barrier coating over a non-compliant system. Cybutryne was added by resolution MEPC.331(76), in force 1 January 2023. Because the annex can be amended, compliance is a condition that can change during a coating’s service life.
What must a ship with cybutryne on its hull do?
A ship bearing cybutryne in the external coating layer on 1 January 2023 must either remove the anti-fouling system or apply a coating forming a barrier to the substance leaching from it. The timing is the next scheduled renewal of the system after 1 January 2023, but no later than 60 months after the last application of a cybutryne-containing system to that ship. The 60-month limit runs from application, so it can fall before the next planned docking.
Which ships need an IAFS Certificate and which need a declaration?
Ships of 400 gross tonnage and above engaged in international voyages require survey and an International Anti-fouling System Certificate, with fixed and floating platforms, FSUs and FPSOs excluded. Ships of 24 metres or more in length but below 400 gross tonnage on international voyages carry a Declaration on Anti-fouling System signed by the owner or authorised agent, supported by documentation such as a paint receipt or contractor invoice.
Is overcoating an acceptable alternative to removal?
Yes. Both the organotin and cybutryne provisions offer a coating that forms a barrier to the substance leaching from the underlying non-compliant system as an alternative to removal. The sealer has to be suitable for that purpose, specified in consultation with the coating manufacturer, and acceptable to the body carrying out the survey. The details belong in the Record of Anti-fouling Systems, since that record is what the compliance case rests on.
Sources: International Convention on the Control of Harmful Anti-fouling Systems on Ships, done at London 5 October 2001, entered into force 17 September 2008, Annex 1 controls on organotin compounds acting as biocides with effective dates of 1 January 2003 for application and re-application and 1 January 2008 for ships bearing such compounds or a barrier coating, and Annex 4 survey, certification and declaration requirements covering ships of 400 gross tonnage and above on international voyages and ships of 24 metres or more in length below 400 gross tonnage · IMO resolution MEPC.331(76), Amendments to the AFS Convention, controls on cybutryne and form of the International Anti-fouling System Certificate, adopted 17 June 2021, entered into force 1 January 2023, prohibiting application and re-application of anti-fouling systems containing cybutryne, CAS 28159-98-0, and requiring removal or a barrier coating at the next scheduled renewal after that date but no later than 60 months following the last application, with the amended certificate required within 24 months of entry into force and exemptions for platforms, FSUs and FPSOs built before 1 January 2023 not drydocked on or after that date, ships not on international voyages, and ships below 400 gross tonnage where the coastal State accepts · Flag administration and classification society circulars implementing MEPC.331(76), covering the Record of Anti-fouling Systems permanently attached to the certificate and its required content, the supporting documentation for declarations, and sealer coat selection in consultation with the coating manufacturer
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