Anti-Fouling Paint

Definition - What does Anti-Fouling Paint mean?

Anti-fouling paint is a special coating that is applied to the hull and propellers of a marine craft. The coating is used to slow down the growth of marine organisms such as barnacles, slime, algae and mossy weed.

In addition to anti-fouling, the coating prevents corrosion on metal hulls and propellers. It also improves water flow past the hull of the vessel.

Anti-fouling paint is also known as bottom paint.

Corrosionpedia explains Anti-Fouling Paint

Anti-fouling paint serves two purposes when applied on metal hulls: it prevents corrosion and also prevents the settling and growth of microscopic marine animals and plants on the hull. Corrosion and fouling are interrelated in that poor corrosion resistance leads to the disruption of the paint film, hence the loss of anti-fouling properties. Poor fouling resistance also leads to corrosion due to barnacles cutting their way to the substrate and disrupting the film.

Typical anti-fouling paint contains a biocide or a toxin in the paint, which is released into the area surrounding the hull to poison any attached organisms and prevent others from adhering to the paint.

The four basic ingredients of an anti-fouling paint are:

  • Biocide
  • Resin
  • Solvent
  • Pigment

The three main categories of the anti-fouling paints are:

  • Soft bottom paint - A moderately effective copper-based coating used in cooler waters in which growth potential is lower compared to the warmer climates. It is the cheapest coating.
  • Hard bottom paint - The hard anti-fouling paint has more biocide (cuprous oxide), making it more effective but more expensive. It offers a tough surface and provides good finishes for the bottoms of racing boats.
  • Ablative anti-fouling paint - Designed to wear off the outer surface and still retain amounts of biocide in the remaining layers. It is suitable for many environments and has options of either a single season or multiple seasons.

Factors to consider when choosing anti-fouling paint include:

  • Whether boat operates in fresh, salty, cold or warm water
  • Whether the hull material is steel, wood or fiberglass
  • Whether boat will operate at a fast or slow speed
  • Compatibility with the paint already on the hull

Preventing fouling and corrosion extends the vessel's life, increases efficiency, reduces operational costs and avoids marine accidents and expensive repairs.

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