BOAT-COMPARATOR Guide

Antifouling and Hull Cleaning: What Your Rental Boat's Paint Leaves Behind in the Water

Copper, biocides, paint particles: how the antifouling that protects rental boats' hulls also pollutes harbours and the seabed around them, and what that means for renters.

Below the waterline of most rental boats sits a special paint, antifouling, that keeps algae and shellfish from colonising the hull. It works well — but it is not neutral for harbour water or the seabed around it, a topic marine ecotoxicology research has documented for almost forty years.

Why a hull needs antifouling

Left unprotected, a submerged hull gets covered within weeks in algae, barnacles and shellfish that increase drag, fuel consumption and weight. Antifouling paint continuously releases low doses of biocides that prevent this colonisation — regular hull maintenance (scraping, sanding, repainting) is part of routine upkeep for any professional rental fleet.

The tributyltin precedent

For decades, the reference biocide was tributyltin (TBT) — extremely effective, and extremely toxic. A now-classic series of studies in marine ecotoxicology, led notably by British researchers Gibbs and Bryan, showed as early as the 1980s that TBT leaching from antifouling paint caused a condition called "imposex" in the dog-whelk Nucella lapillus: the development of male sexual characteristics in females, at vanishingly small concentrations in the water, to the point of sterilising entire populations near harbours and marinas (Gibbs & Bryan, Journal of the Marine Biological Association of the UK, 1986). That research contributed heavily to the phased ban on TBT for recreational hulls, in force across Europe since the mid-2000s and made global through an International Maritime Organization convention.

Copper and paint particles: the newer concerns

TBT has mostly been replaced by copper-based biocides, less persistent but still toxic to filter-feeding species at high concentrations, particularly in harbours and marinas with limited water exchange. More recently, researchers have also turned to the paint particles themselves, worn off during hull maintenance or normal use, which turn out to be a long-underestimated source of microplastics and metals in harbour areas (Turner, review on marine paint particles, 2021).

What this means for a renter, in practice

There is nothing to do about the antifouling itself — that is on the operator — but a few habits limit your own impact: anchor on sand rather than on posidonia seagrass meadows, which accumulate these pollutants and shelter the most sensitive wildlife (our guide to anchoring and posidonia meadows covers the rules), and avoid washing or scraping the hull yourself at the dock, which disperses biocides directly into water that is not well flushed. Newer professional fleets increasingly use controlled-release copper paints or even biocide-free solutions (silicone, ultrasound) — a perfectly fair question to ask an operator if it matters to you.

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