What to check on a Antifouling Coating.
Antifouling coating is the outermost layer of the underwater hull coating system, applied specifically to prevent barnacles, algae and other marine organisms from attaching and growing on the hull. Unlike the anticorrosive coats beneath it, whose job is to keep water off the steel, the antifouling coat's whole purpose is to interact with the water around it, either by releasing a controlled dose of biocide as it wears (self-polishing copolymer, SPC) or by presenting a low-friction silicone surface organisms cannot grip (foul-release). The choice between these two mechanisms shapes everything…
What makes this type
Antifouling coating is the outermost layer of the underwater hull coating system, applied specifically to prevent barnacles, algae and other marine organisms from attaching and growing on the hull. Unlike the anticorrosive coats beneath it, whose job is to keep water off the steel, the antifouling coat's whole purpose is to interact with the water around it, either by releasing a controlled dose of biocide as it wears (self-polishing copolymer, SPC) or by presenting a low-friction silicone surface organisms cannot grip (foul-release). The choice between these two mechanisms shapes everything from application method to expected in-service performance.
Main components
Self-polishing copolymer systems
A binder that erodes slowly in seawater, continuously exposing fresh biocide at the surface and shedding a thin layer of paint over time, which also keeps the hull relatively smooth as it wears.
Biocide-free foul-release systems
Silicone or fluoropolymer coatings that rely on surface energy and elasticity rather than biocide release; organisms that do attach are removed by the shear forces of water flow once the vessel is underway at speed.
Tie coat
An intermediate coat that bonds the antifouling layer to the anticorrosive system beneath it, particularly important with foul-release systems where adhesion between dissimilar coating chemistries is otherwise poor.
Selection / Sizing
- Vessel speed and activity profile, since foul-release coatings depend on regular underway speed to stay effective, while SPC systems work at anchor and in port as well.
- Trading pattern, as vessels with long idle periods in warm, biologically active ports need a formulation matched to that exposure.
- Intended drydocking interval, since the coating's biocide reserve or surface life must cover the full period between dockings.
- Compatibility with the existing anticorrosive system and tie coat if the coating is being changed at the next docking.
Regulations / Class
The IMO International Convention on the Control of Harmful Anti-fouling Systems on Ships (AFS Convention) bans the use of organotin compounds such as TBT in antifouling systems, a restriction that reshaped the market toward copper-based SPC and biocide-free alternatives. Class societies do not typically approve antifouling products directly, but performance and drydocking planning are reviewed as part of the vessel's hull condition and the owner's biofouling management plan, which some flag states and port states now expect to see documented.
Typical faults
| Fault | Consequence |
|---|---|
| Coating applied over an incompatible or poorly prepared tie coat | Delamination, patches of bare anticorrosive exposed early |
| SPC system on a vessel with long idle periods and low speed | Insufficient polishing rate, biocide release falls off before drydocking |
| Foul-release coating on a slow or frequently idle vessel | Fouling settles and is never sheared off by flow |
| Under-thickness application at the waterline and boot top | Premature fouling exactly where drag has the largest effect on fuel consumption |
What to look for in a supplier
- A documented performance guarantee tied to the vessel's actual speed and idle profile, not a generic drydocking interval.
- Confirmed compatibility with the coating already on the hull if this is not a full strip to bare steel.
- Application specification including dry film thickness at the waterline and boot top, the areas most exposed to wear.
Match the coating type to how the ship is actually operated, not how it was designed to operate; a foul-release hull spending months laid up will foul just as badly as an unpainted one.