Operational Guide · Registers & Logbooks

# 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.

AFS Convention TBT cybutryne antifouling

## 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.

## Regulatory Reference

AFS Convention (2001, in force since 2008), Annex I: ban on organotin compounds as biocides; 2021 amendments on cybutryne controls, 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

Every ship subject to the AFS Convention, for the anti-fouling coating system applied below the waterline.

## Procedure / How to Complete It

1. 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.
2. Verify the absence of organotin biocide compounds in the applied system, per the Convention's historical ban.
3. 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.
4. Document every anti-fouling system renewal in the relevant onboard log, referencing the composition of the product applied.
5. Check the paint supplier's documentation for compliance against currently prohibited or restricted substances.

## Practical Example

Example management case: a ship with a cybutryne-containing anti-fouling system applied in 2021 plans removal or sealer coating at the next scheduled dry-docking in 2025, still respecting the absolute 60-month limit from the last application even if the dry-docking were to slip.

## Real Cases

The evolution of the AFS Convention, from the historical TBT ban to the more recent cybutryne controls, reflects a recurring pattern in maritime environmental regulation: substances initially considered safe are progressively banned as scientific evidence of their impact on the marine ecosystem emerges, requiring companies to keep constant watch on regulatory developments even for systems already applied.

## 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

## PSC Observations

PSCOs check the validity of the International Anti-fouling System Certificate and may request documentary evidence of the composition of the applied system, especially for ships with applications predating the cybutryne restrictions.

## 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.

## Checklist

- 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

What does the AFS Convention historically ban?
The application or reapplication of organotin compounds, such as tributyltin (TBT), as biocides in anti-fouling systems, due to their documented harmful impact on the marine ecosystem.
What do the 2021 cybutryne amendments change?
They ban the application or reapplication of anti-fouling systems containing cybutryne from 1 January 2023, requiring removal or sealer coating by the system's next renewal, in any case no later than 60 months after the last application.
What are the modern alternatives to the banned biocides?
Modern anti-fouling technologies based on copper or advanced biocide blends, silicone or fluoropolymer foul-release systems, or hybrid approaches, still evolving ahead of the future binding biofouling framework under discussion since 2025.
🎬 Additional photos, videos and interactive diagrams for this topic will be available in a future version of the platform.

## Related Topics

Biofouling Management (IT)Coating and PSPC (IT)

### Leave feedback

Help us improve the platform during the beta -- it takes thirty seconds.

How useful do you find the platform so far?
Comment (optional)
Sign me up for the newsletter
Role