The new antifouling divide: copper paints face a clean, slick challenger

Copper has been the workhorse of hull protection since the global ban on tributyltin (TBT) took effect in 2008, but a new class of non-toxic, “slippery” coatings is changing the economics — and the environmental conversation. In side-by-side trials, biocide-free silicone and fluoropolymer systems have matched the antifouling performance of copper paints over several months and trimmed fuel burn by 3–8% (MDPI; MDPI). For large vessels, that first‑year efficiency — ~4–8% in a meta‑analysis — implies savings measured in millions of dollars (MDPI).

The catch: whichever chemistry you pick, longevity lives or dies with surface prep and application discipline. Near‑white metal blasting (ISO 8501‑1 Sa 2½), anchor profile in the 45–85 μm range, and tightly controlled dry film thickness (DFT) are not negotiable (Jotun).

Copper-based self-polishing systems

Traditional copper-based antifouling relies on self‑polishing copolymers (SPCs), where cuprous oxide (Cu₂O) and zinc oxides serve as active biocides in an ablative resin that erodes to release copper ions. “Self‑polishing” (ablative) means the top layer wears off in service, exposing fresh biocide while keeping the hull smooth over 1–3 years (Crimson Publishers; MDPI).

Indonesia’s practice mirrors that global standard: SPC paints with Cu₂O are used almost exclusively in the field (Crimson Publishers). After the 2008 TBT ban, copper became the main legal antifoulant (Crimson Publishers). The trade‑off is environmental: these systems leach toxic metals and require renewal — heavy fouling may force an expensive repaint every 24–36 months (MDPI; Crimson Publishers).

“Hard” antifouls — thinner, organic, often zinc‑ or alumina‑filled epoxies — can retain their matrix longer before biocide depletion but tend to underperform against barnacles. Many copper systems add organic booster biocides (for algae/soft fouling), yet these agents face tightening restrictions internationally (MDPI).

Biocide-free foul-release options

Foul‑release coatings skip toxins entirely. Built from low‑surface‑energy polymers — typically silicone elastomers or fluoropolymers — they reduce adhesion so organisms settle weakly and are shed by water flow or light grooming. There’s no toxic leaching, and surfaces are extremely smooth (MDPI).

Field trials show certain silicone/fluoropolymer systems can maintain equivalent antifouling efficacy to copper over several months; the trade‑off is a thin slime layer (bacteria/diatoms) that is easily removed by hydrodynamic shear (MDPI). The payoff: reported fuel savings of 3–8% vs. copper SPCs and ~4–8% in the first year for non‑toxic coatings, translating to millions of USD per large vessel (MDPI; MDPI). These systems generally erode minimally but perform best when ships stay in motion or commit to routine grooming (MDPI).

Hybrids are emerging — hydrophilic polymers, nanocomposites, biopolymer films — with reports of zwitterionic cellulose‑nanocrystal coatings achieving >90% fouling inhibition without leaching toxins. Market reality still favors copper, especially for slow vessels and static platforms, while biocide‑free systems are growing rapidly on fast ships and leisure craft with higher maintenance budgets, driven by environmental trends (MDPI; MDPI; FC Chemicals).

Regulatory framework: IMO AFS and beyond

The International Maritime Organization’s 2001 Anti‑Fouling Systems (AFS) Convention — in force since 2008 — is the core rulebook. It bans organotins like TBT and any “harmful anti‑fouling system,” empowers Parties to add substances to Annex I, and requires ships ≥400 GT on international voyages to carry an International Anti‑Fouling System Certificate confirming compliance (e.g., TBT‑free) (IMO; IMO).

Other regimes are tightening. The EU’s Biocidal Products Regulation (BPR 528/2012) authorizes only specific antifouling agents; policy advice urges avoiding copper in sensitive waters like the Baltic Sea, where shipping contributes an estimated ~1,560 tonnes of copper annually (European Commission; European Commission). In the U.S., antifouling paints are registered as pesticides under EPA’s FIFRA, and some states cap copper discharges at marinas.

Marine garbage rules matter operationally. MARPOL Annex V prohibits the discharge of hull cleaning wastes unless filtered to fine particles, with extra restrictions in special areas. As shipyards and service providers interpret those thresholds, the conversation often overlaps with physical separation and screening approaches categorized under waste-water-physical-separation and fine particle capture (for example, an automatic screen), without altering what Annex V requires (IMO). The IMO’s non‑binding Biofouling Management Guidelines, revised in 2023, also ask owners to log coating and cleaning practices to reduce invasive species transfer (IMO).

Indonesia compliance context

Indonesia ratified the AFS Convention via Presidential Regulation No. 66/2014, making TBT‑free compliance mandatory for Indonesian‑flag vessels and foreign ships calling its ports (BPK; IMO). Enforcement often runs through classification: Biro Klasifikasi Indonesia (BKI) requires an Anti‑Fouling System Declaration from the paint maker — including a TBT‑free certificate — before issuing compliance certificates (BKI).

Beyond AFS, Indonesia has few antifouling‑specific mandates. There is a national industrial standard, SNI 502:2016, for ship hull antifouling paints (BSN), but industry voices point to “belum ada regulasi keamanan cat terhadap lingkungan di Indonesia” (no dedicated environmental safety regulations for coating chemicals) (Bioindustries). In practice, compliance hinges on the IMO AFS framework (Perpres 66/2014) and port/classification oversight rather than a statute specifically banning copper or other biocides (BPK).

Surface preparation standards (ISO 8501‑1 Sa 2½)

Antifouling performance starts with removing old coatings, rust, salts, and oils. Best practice calls for degreasing or steam‑cleaning, then abrasive blasting to ISO 8501‑1 Sa 2½ “near‑white metal” (about 98% visually clean). The target anchor profile is 45–85 μm peak‑to‑valley, verified by replication tape (Testex) or a surface profile gauge (Jotun).

Substrate condition is checked with hygrometry and chloride tests (ISO 8502‑6) — soluble salts must be below 50 mg/m² before coating — and welds/edges are ground to ISO 8501‑3 grade P2 to remove spatter. Crews often spend 1–2 days per ship section on preparation for each coat. With proper prep, pull‑off adhesion (ASTM D4541) is high; skimping (leaving mill scale or salt) invites early peeling or underfilm corrosion on immersion (Jotun).

Application parameters and layering

On bare steel, an anticorrosive primer (epoxy or vinyl‑ester) goes down first, often as a tie‑coat, followed by the antifouling topcoats. Primer thickness is typically 100–150 µm DFT, with each layer fully cured — often 24 h at 20 °C — before overcoating. Commercial practice is 2–3 antifouling coats for ~150–200 µm total DFT. Too thin, and the copper or resin depletes early; too thick, and mud‑cracking or sagging can trap moisture (Jotun).

Conditions count: 10–30 °C, relative humidity below 80%, and substrate temperature at least 3 °C above the dew point to avoid condensation. Paint must be mixed uniformly and applied by trained crews with airless spray for consistent coverage; brush/roller is rarely used on commercial hulls. Wet‑film thickness is measured in real time to hit target DFT; each layer needs to be “touch dry” before the next, and crews often add a light St 3 dry‑blast between coats to promote intercoat adhesion (Jotun).

Service life and fuel penalties

Get the preparation and application right, and coatings reach design life: a well‑applied copper SPC typically lasts 30–36 months before renewal. Miss the mark — for example, only hand‑tool clean to St 2 — and the active layer may wash away in 12–18 months. Empirically, every 10% shortfall in cut‑in thickness from substandard prep can slice service life by ~10–20%. Operators often quip that “99% of coating failures are due to surface issues” (MDPI).

The physics shows up at the fuel meter: even light fouling can increase total resistance by 20–35% (Monty et al., as cited), and fleets that rigorously blast and coat report lower fuel bills (MDPI). Where hull grooming generates residues, compliance with Annex V’s fine‑particle rule has practical implications for capture and separation steps, including the use of oil-removal stages where free oil is present and dedicated water-treatment-ancillaries to handle collection and storage, within the limits set by the regulation (IMO).

Bottom line: copper paints still dominate on cost and familiarity, particularly for slow vessels and static platforms, while biocide‑free foul‑release is gaining fast on higher‑speed ships and leisure craft. Under either strategy, meticulous prep, correct film builds, and adherence to AFS/MARPOL rules are the keystones to longevity and compliance (IMO; FC Chemicals).

Sources include IMO regulatory documents (AFS Convention) (IMO; IMO), industry guidance (Jotun specifications) (Jotun), peer‑reviewed studies and reviews (MDPI; MDPI; FC Chemicals), and Indonesian context from research and standards (Crimson Publishers; Crimson Publishers; BSN; BKI; Bioindustries).