Hull coating systems during dry dock

Sa 2½ is the ISO 8501-1 grade for very thorough abrasive blast cleaning. Mill scale, rust, old paint and foreign matter are removed so that any remaining traces show only as slight stains or shades on a uniform metallic surface. It is the usual minimum for immersed ship hull coatings and most high-performance epoxy systems.

Sa 3 is blast cleaning to white metal: all mill scale, rust and foreign matter are removed, leaving a uniform metallic colour. Sa 2½ is one step lower, allowing faint shadows or slight discoloration. Sa 3 costs more time and abrasive and is specified for demanding linings; Sa 2½ is the common hull and tank specification.

St 2 and St 3 are ISO 8501-1 grades for hand and power tool cleaning, used where blasting is not possible. St 2 is thorough scraping, wire brushing or disc sanding that removes loose scale and rust. St 3 is the same, but very thorough, leaving a pronounced metallic sheen.

Yes. The IMO International Convention on the Control of Harmful Anti-fouling Systems on Ships entered into force on 17 September 2008. It prohibits organotin (TBT) biocides in antifouling systems, and ships may not carry them on the hull unless covered by a barrier coat that stops leaching.

Cybutryne was added to the AFS Convention's banned list by amendments adopted in June 2021, in force from 1 January 2023. From that date ships may not apply cybutryne antifouling. Ships already carrying it must remove it or seal it with a barrier coat at the next scheduled renewal, or within 60 months of last application.

Under the AFS Convention, ships of 400 gross tonnage and above on international voyages must hold an International Anti-fouling System Certificate after survey. Ships of 24 metres length or more but under 400 GT on international voyages carry a Declaration on Anti-fouling Systems signed by the owner or agent instead.