Antifoul and Racing Bottom Coatings Compared: International, Hempel and Jotun

This is an independent, objective comparison — we have no partner in this category. Figures below are the makers' own published specifications, not our measurements.

On a grand-prix boat the coating question is really a binder-and-biocide question decided by how the boat is stored — and for a dry-sailed Melges 40 the fastest answer carries no antifoul at all. Where a biocidal film is needed, International, Hempel and Jotun each lead a different chemistry, so the honest comparison is not "who is best" but "which system, for which storage regime". Start with the surface underneath — see the bottom and foils — because none of this paint improves an unfair hull.

At a glance

The genuine "winner" is a faired, correctly built, burnished bottom — dry-sailed and biocide-free where hauling allows. The brand only decides which chemistry delivers it.

The three axes that actually matter

Forget the badge for a moment. A racing bottom is defined by three engineering choices, and each house is strong in a different corner:

1. Binder system — insoluble hard matrix (vinyl/epoxy) vs self-polishing copolymer (SPC) vs biocide-free foul-release. This is set by storage.
2. Biocide package — cuprous-oxide loading plus boosters (zineb, pyrithiones, tralopyril, Selektope) — set by local fouling pressure.
3. Surface finish — build thickness, wet-sanding grit, burnishing medium, and how the film ages. This is where boats are actually won or lost, and it is largely brand-agnostic.

Binder 1 — hard, burnishable films (the classic racing surface)

A hard "racing" antifoul is an insoluble matrix — a vinyl or epoxy binder — packed with cuprous oxide. Copper leaches out through seawater-filled pores (the leached layer) while the binder stays put, so the film can be wet-sanded and burnished to a mirror and holds that finish. The trade is well understood: as the leached layer thickens the surface goes chalky, micro-rough and draggy, and it must be scrubbed back or repainted before that roughness costs speed.

International owns this niche in one-design fleets, and the two Interlux products are usefully different:

• VC Offshore — a hard vinyl film, published at 42.5% cuprous oxide and 40% solids by volume, carrying a PTFE additive for lubricity. The maker's own routine is to lay the final coat, wet-sand with 400-grit, then burnish with fine bronze wool to a super-smooth, durable surface. Thinned with Special Thinner 216; brush/roller/pressure-pot spray.
• Baltoplate (VC Offshore Regatta) — the key point of difference is the low-friction chemistry: it uses molybdenum disulfide (MoS₂) rather than PTFE as the super-lubricant, at 41.2% cuprous oxide and 38% solids. It dries dull grey/white and transforms to a gleaming metallic surface when sanded and polished — a genuinely different burnish behaviour from the PTFE films, and a fleet favourite where a hard, ultra-slick metallic bottom is wanted.

Hempel's answer is Hard Racing TecCel — a hard matrix with copper compounds and TecCel anti-adhesion technology (a PTFE-family additive) for a smoother, lower-friction, polishable film than a conventional hard antifoul. Jotun's Racing / SeaForce Racing is a hard, polishable, non-chalking copper-oxide film explicitly aimed at high-speed and regatta boats, with a white variant mandated on aluminium hulls (copper-oxide films on bare aluminium invite galvanic attack — a real constraint for alloy-hulled campaigns, and a reason primer/barrier discipline matters).

For a boat kept wet but hauled and scrubbed often, this class is the right starting point — only for a boat that actually stays in the water.

Binder 2 — self-polishing copolymers (SPC) for wet-kept boats

If the boat sits on a mooring and moves less, a hard film's leached layer thickens faster than scrubbing can manage. The answer is an SPC, and the chemistry is the whole story. SPC binders carry hydrolysable side groups — copper acrylate, zinc acrylate, or a silyl (organosilicon) acrylate — that cleave on contact with seawater, turning the outer film from hydrophobic to hydrophilic so it erodes at a controlled, predictable rate. That continuously exposes fresh biocide, sheds slime and weed, and self-fairs micro-roughness. The trade-off is that an SPC will not hold a burnished mirror the way a hard film does — it is designed to give itself up.

This is where Hempel and Jotun genuinely lead:

• Hempel Mille NCT — an SPC using NewCopperTechnology and nanocapsule biocide delivery, engineered to balance polishing rate against an even biocide release for continuous, controlled protection across fresh, brackish and salt water.
• Jotun SeaQuantum — a silyl acrylate / silyl methacrylate hydrolysing SPC. This is the technology that matters at the top end: the biocide package sits in a hydrolysing organosilyl polymer binder that dissolves at a rate giving continuous fresh-surface exposure, with a quoted ~3.5% speed loss over the docking cycle and heavy commercial-shipping validation behind it. SeaForce Active is the acrylic hydrolysing (Hydractive / ion-exchange) tier below it.
• International Micron — the Interlux copper CDP/SPC family covers the same wet-kept ground; International's deepest SPC engineering, though, now sits in foul-release (below) rather than biocide.

A note on the cheaper cousin: rosin-based CDP (controlled-depletion polymer) erodes by dissolution of a rosin binder rather than true hydrolysis — softer, less predictable, and not a racing surface. Do not confuse "ablative" (CDP) with "self-polishing" (true SPC); the mechanisms and the smoothness they hold are different.

Binder 3 — biocide-free foul-release (the modern high-end)

The most interesting development for clean-bottom campaigns is biocide-free foul-release, which changes the mechanism entirely: instead of poisoning fouling, it makes the surface one that fouling cannot key to, and lets water flow strip what does settle.

• International Intersleek 1100SR — a fluoropolymer coating with patented slime-release technology. The maker's published figures are the ones to know: 1.2% speed loss over the docking cycle and up to 9% fuel saving / CO₂ reduction versus conventional antifoul, with slime shed by movement through the water at far lower speeds than earlier foul-release generations. Entirely biocide-free and REACH-compliant. The catch for a race boat is that the ultra-low-surface-energy film is soft and cannot be burnished — its smoothness is intrinsic, not sanded in — so it needs a spray application and careful handling.
• Hempel Silic One — a silicone + hydrogel system: polymers react with water to form an invisible hydrogel that microorganisms read as a liquid, so they will not attach; anything that does settle sheds when the boat moves or is wiped. It topped the independent Chalmers foul-release study, cures fast (touch-dry ~30 min at 10 °C) but demands strict tie-coat and immersion-window discipline, and is renewed roughly every second season.

Foul-release rewards a boat that moves regularly and sits at a berth between events — it holds a genuinely low-drag, no-copper surface without hauling. It is a real third option a professional now weighs alongside hard film and SPC.

The biocide package — matching to warm-water fouling

Cuprous oxide is the workhorse against hard fouling, but copper alone is weak on slime and modern formulations boost it. The boosters a captain in warm Australian water should recognise:

• Zineb — strong on soft/weed fouling, works well beside copper, but degrades quickly in seawater (short-lived contribution).
• Zinc and copper pyrithione, tralopyril — extend slime and algae control; pyrithione is often paired with tralopyril for broad soft-fouling cover.
• Selektope (medetomidine) — a barnacle-and-tubeworm–selective repellent that works non-lethally (it over-stimulates the larva's swimming reflex so it will not settle) and is roughly a thousand times more effective gram-for-gram than conventional biocides. It is a commercial-shipping technology, but it is the sharpest tool against the barnacle pressure that defines warm-water fouling.

The engineering point: in high-fouling water a bare copper film is often under-gunned on slime, and the booster chemistry — not the copper number — separates products. All three houses formulate boosted ranges; the correct call is the locally proven package, confirmed with the supplier.

Surface finish — where the boat is actually won

This axis is largely brand-agnostic and dwarfs the badge:

• Fairing first. A true, faired substrate (see the bottom and foils) is the foundation — paint cannot fix a hull that is not fair, and a burnished film only reproduces the shape under it.
• Build to spec. Coat number, wet/dry film thickness and recoat windows are on every data sheet for a reason: too thin and the biocide (or the sacrificial burnish depth) is gone early; too thick and you carry needless weight and orange-peel. VC Offshore's 3–4 coats and its 400-grit-then-bronze-wool routine are typical of the discipline required.
• System compatibility. Primer, tie-coat and topcoat must be one manufacturer's compatible stack — the single strongest reason to stay inside one house's range rather than mix brands, and it is non-negotiable for foul-release, where the tie-coat is the adhesion mechanism.
• Ageing behaviour. A hard film is fastest fresh and degrades as its leached layer thickens; an SPC self-renews but never mirrors; a foul-release holds its intrinsic smoothness but is fragile to abrasion. Which curve you want is set by the race calendar and haul-out access.

A mediocre product applied superbly beats a superb product applied poorly — every time.

The dry-sail answer — no antifoul at all

The choice that reframes the category: a dry-sailed Melges 40 lifted between races never sits long enough to foul, so it needs no biocide — it carries a faired, biocide-free racing finish that is the lowest-drag surface available. The archetype is International's VC Performance Epoxy: a two-part, fluoro-microadditive epoxy with a hard, abrasion-resistant film that is burnished or wet-sanded to a racing-smooth white, with no antifouling or foul-release function — it is purely a low-drag skin for rack-stored, trailered or dry-sailed boats. Where a film is wanted only for the odd wet spell, VC 17m Extra — a thin-film paint marketed at up to eight times thinner than conventional antifoul, ~20% metallic copper with a fluoro-microadditive and Biolux slime-blocking — is the light, low-drag launch coat, though it is a freshwater/low-fouling/cold-salt film, not a warm-water workhorse.

The trade is logistics — hauling, cradling and launching — against pure speed. Where it is feasible it usually wins outright, which is why it is standard at grand-prix level (see what makes the Melges 40 fast).

Environmental and regulatory reality

These are biocidal products in a tightening regulatory landscape; approved biocides and permitted application/disposal vary by jurisdiction and change over time. That regulatory pressure is precisely what is pushing the high end toward biocide-free foul-release (Intersleek 1100SR, Silic One) and toward highly targeted actives like Selektope that do their job at a fraction of the loading. We will not state specific approvals here — confirm the current, locally legal product with the supplier and any class or venue rules before painting.

Our take

With no partner in this category, the objective read is that the "best brand" question is mis-framed — each house leads a different binder class, and the boat's storage regime picks the class before the badge:

• Dry-sailed (the Melges 40 default): a biocide-free faired finish wins on drag. International's VC Performance Epoxy is the reference dry-sail skin; nothing here beats a well-burnished, copper-free bottom.
• Wet-kept, hauled and scrubbed often: a hard burnishable film — International VC Offshore / Baltoplate (note the PTFE-vs-MoS₂ distinction) or Hempel Hard Racing TecCel — holds the smoothest polished surface.
• Wet-kept on a mooring: a true SPC — Hempel Mille NCT (nanocapsule copper) or Jotun SeaQuantum (silyl acrylate, commercial-grade, ~3.5% quoted speed loss) — self-renews and sheds weed.
• Berth-kept but moved regularly, copper-free wanted: foul-release — Intersleek 1100SR (1.2% published speed loss) or Hempel Silic One.

Our pick: for a dry-sailed grand-prix boat, a faired, burnished biocide-free finish (International's VC Performance Epoxy the archetype) is the fastest bottom and the right default — copper is a compromise you only accept when the boat must stay wet. If it stays wet, choose a hard PTFE/MoS₂ vinyl (VC Offshore or Baltoplate) for a hauled-and-scrubbed boat, a copper SPC (Hempel Mille NCT) or a silyl-acrylate SPC (Jotun SeaQuantum) for a moored one, and a fluoropolymer or silicone foul-release (Intersleek 1100SR or Silic One) where a copper-free, low-maintenance wet finish is the goal. Then let fairing, film build and burnish — not the badge — decide the last tenth of a knot. See the bottom and foils.

Specific product approvals, biocide rules and any class requirements change by market and over time — confirm the current, locally legal choice with your supplier and class before painting.