The International Maritime Organization’s Marine Environment Protection Committee has adopted an amendment to the International Convention on the Control of Harmful Anti-fouling Systems on Ships (AFS Convention). From 1 January 2023, the ingredient cybutryne will be prohibited. DNV explains the implications.

Cybutryne joins the already prohibited organotin compounds which act as biocides in anti-fouling systems. The changes were adopted in July 2021, but entry into force is now fewer than six months away. So what does this mean for shipyards, coating manufacturers, ship owners and managers?

The affected ship types and effective dates are listed in the table below:

Anti-fouling systemControl measuresApplicationEffective date
Cybutryne CAS No. 28159-98-0Ships shall not apply or re-apply anti-fouling systems containing this substance. All ships 1 January 2023
Cybutryne CAS No. 28159-98-0Ships bearing an anti-fouling system that contains this substance in the external coating layer of their hulls or external parts or surfaces on 1 January 2023 shall either: (1) remove the anti-fouling system; or (2) apply a coating that forms a barrier to this substance leaching from the underlying non-compliant anti-fouling system.All ships except: (1) fixed and floating platforms, FSUs and FPSOs that have been constructed prior to 1 January 2023 and that have not been in dry-dock on or after 1 January 2023; (2) ships not engaged in international voyages; and (3) ships of less than 400 gross tonnage engaged in international voyages, if accepted by the coastal state(s).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 an anti-fouling system containing cybutryne.

The International AFS certificate will change as of 1 January 2023 to include extra cybutryne tick boxes for the compliance options on controlled anti-fouling systems.

Also read: DNV: New technology may pose threat to safety at sea

Implications for existing and new ships

Ships in operation will need to comply with the requirement within the first anti-fouling renewal survey after 1 January 2023 and will be issued a new International AFS certificate, which includes cybutryne-free compliance.

Ships under construction, which will be delivered after 1 January 2023, will need to be delivered as both try butyl tin (TBT) and cybutryne-free, and will be issued with an AFS certificate at the initial survey.


Classification society DNV advises shipowners to remain aware of vessel and fleet survey and docking schedules for both newbuildings and fleets in service for anti-fouling purchases. These should be accompanied by cybutryne-free statements from the manufacturers in order to obtain an AFS certificate from the attending surveyor.

Source: DNV.

Also read: DNV gives approval in principle to new 12 MW floating offshore concept