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Glossary Term

Antifouling Convention (TBT Ban)

The AFS Convention is an IMO treaty that controls the types of coating systems ships may apply below the waterline. It was adopted in 2001 and entered into force in 2008. From that date, Parties to the Convention prohibited applying organotin compounds that act as biocides, and they required ships to either remove legacy TBT or over-coat it with a sealer barrier that prevents leaching.

Certification and documentation, in yacht terms

For yachts on international voyages, compliance is checked through surveys and paperwork that scale with size:

  • Ships of 400 gross tonnage and above must be surveyed and carry an International Anti-Fouling System Certificate, the IAFS Certificate.

  • Yachts of 24 meters or more in length but under 400 GT carry a Declaration on Anti-Fouling Systems, signed by the owner or an authorized agent, supported by evidence such as paint invoices and technical datasheets.

  • Small craft below 24 meters are generally outside the certificate or declaration regime, but the ban on TBT still applies through national implementation. This matters if you plan cross-border dry docking or visits to foreign ports.

Surveyors may verify compliance by reviewing records, examining coating logs, and, if needed, taking brief samples of the applied system. The IMO has issued guidance for such sampling so that inspections are standardized and minimally invasive.

Not just TBT anymore, the cybutryne update

Regulation evolves. In 2021 the IMO adopted amendments to extend controls to cybutryne, another antifouling biocide. Those amendments entered into force on 1 January 2023. In practice, yachts must ensure cybutryne is not applied after that date and address any existing cybutryne-containing coatings at the next renewal of the antifouling system, which also drives an update of the IAFS Certificate format.

Why this matters to captains, crews, and management companies

  • Performance and fuel, a fouled hull can add double-digit percentage penalties to fuel consumption. Antifouling choices affect range planning, engine loading, and the calendar for maintenance periods.

  • Port State Control risk, non-compliance can result in detention or orders to rectify before departure, which disrupts itineraries and charter commitments. The paperwork is not a formality, it is your proof that the underwater system meets today’s rules.

  • Yard planning, whether you plan a light touch or a full refit, the AFS framework shapes blast scope, barrier choices, and the sequencing of your paint system application. Good records and product selection simplify future surveys.

Practical playbook for your next yard period

  1. Confirm legacy layers. Ask your shipyard to review historic coating reports. If there is any doubt, plan for targeted coating analysis so you do not accidentally over-coat prohibited systems without a compliant sealer. Sampling is recognized by IMO guidance.

  2. Choose a compliant system. Modern antifouling technologies use copper or advanced biocide blends, silicone or fluoropolymer foul-release, or hybrid approaches. Match the chemistry to your operating profile, idle times, and cleaning strategy.

  3. Document everything. Keep product TDS, SDS, batch numbers, film thickness logs, sealer declarations, and yard invoices with the vessel’s technical file. That is what underpins the IAFS Certificate or Declaration at survey.

  4. Think lifecycle, schedule in-water cleanings and align the coating warranty window with cruising plans and class or flag surveys. A well-timed dry docking reduces downtime and often lowers total coat thickness over the life of the yacht by avoiding unnecessary recoats.

A quick disambiguation, AFS vs MARPOL

AFS sits alongside but separate from MARPOL. MARPOL addresses pollution from operations and discharges, while AFS governs what can be on the hull in the first place. Both are administered by the IMO, and both are relevant during yard periods and inspections.

The Antifouling Convention proves that high-performance marine technology can coexist with environmental stewardship when the industry commits to better chemistry and better records. For yacht teams, the TBT story is a reminder that what lives under the waterline is as strategic as any topside upgrade. As you plan the next coating cycle, ask how your choices will impact speed, fuel, survey outcomes, and the waters you cruise. The right system, correctly applied and documented, keeps you compliant and fast, and it protects the seas that make yachting possible.

FAQ: Antifouling Convention (TBT Ban)

How do I find out if my yacht still has legacy TBT or cybutryne under newer coats?

Start with your coating history, invoices, and technical datasheets. If records are incomplete, ask the yard for targeted coating analysis, either spot sampling or non-destructive screening, to confirm whether a barrier sealer or full removal is required. This can be planned during dry docking to avoid extra haul-outs.

Do private yachts under 24 m need an antifouling certificate?

They usually do not carry the International Anti-Fouling System Certificate. However, the substance bans still apply through national law, so owners should keep product datasheets, yard invoices, and application logs handy as proof of compliance. Good records help avoid delays at marinas or during resale surveys.

Can I legally overcoat old TBT paint instead of blasting to bare substrate?

Yes, if a compliant sealer barrier is applied that prevents leaching, and the system is documented in your technical file. Full removal may still be chosen when coatings are heavily built up, damaged, or incompatible with the new paint system application plan. Your survey schedule and hull condition should guide the decision.

Which antifouling works best if my yacht sits idle for long periods?

Silicone or fluoropolymer foul-release systems excel when speed is high but may underperform during long idle periods without periodic movement. Copper-based self-polishing copolymers tolerate marina time better but rely on gradual polishing and may need more frequent in-water checks. Match the chemistry to your use pattern, cleaning plan, and warranty terms.

What happens during an AFS compliance check in port or at survey?

Inspectors review your IAFS Certificate or Declaration, then verify product types and dates against yard records. A visual hull check is common, and targeted sampling may occur if there is doubt about the underlying layers. Clear documentation is usually enough to keep the process quick.

Is in-water hull cleaning allowed under the AFS rules?

AFS does not directly regulate cleaning methods, but local port and flag rules do, and they can be strict. Confirm that your coating manufacturer approves the cleaning technique and tools, and check port permits in advance. A compliant maintenance plan reduces biofouling risk and avoids costly schedule changes.

What documents should I keep onboard to avoid antifouling delays?

Maintain product TDS and SDS, batch numbers, film thickness and stripe-coat logs, yard invoices, and any sealer declarations for legacy layers. Add your IAFS Certificate or the owner’s Declaration, as applicable. Store everything with the vessel’s technical file so the crew can retrieve it fast during inspections.

What are the real-world consequences of AFS non-compliance for a yacht program?

Expect detention, orders to rectify before departure, and itinerary disruption that can impact charters and crew rotations. You may also face unplanned yard costs if blasting and recoating are mandated on short notice. Proactive planning with your shipyard keeps risk low and protects performance.

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