Fouling and Biofouling

Biofouling of ships increases fuel consumption, increases drag resistance, decreases maximum attainable speed and promotes corrosion. Fouling of power plant intake bays necessitates frequent shut downs and measures such as chlorination. Fouling by calcareous organisms contributes the greatest penalty because of their profile, and their tenacious adhesion to surfaces. Each of the calcareous organisms attaches in a slightly different way using different glues.

Ships were historically constructed by wood. The decay from bacteriological and animal attacks was in general mitigated by using hard tight wood, and by treating the wood with “poisoned” tar or oil paint. Later the ships was constructed from steel other forms of “decay” became dominating, and other solutions to prevent such decay (rust) was employed. (reference)

Ships were historically constructed by wood.

Fouling was first reported on a papyrus dated around 412 BC in which is mentioned they used arsenic and sulfur mixed with Chian oil to help mitigate the problem. Christopher Columbus wrote “All ships were covered with a mixture of tallow and pitch in hope of discouraging barnacles and teredo, and every few months a vessel had to be hoed down and graven on some convenient beach.”

In 1625, William Beale filed the first patent for an antifouling recipe, that was based on iron powder, copper and cement. Fouling was reported to be up to ½ m long, and giving off odorous and aggressive gases, turning the white lead oxide pigmented paint on the topside darker on a sailing ship anchored in the Indian Ocean. Lord Nelson reportedly employed copper plates attached to the ship’s hull to prevent fouling, greatly increasing his ships maneuverability in combat. Steel ships cannot use copperplates due to the galvanic corrosion induced by such bi-metallic couples.

The most common method of prevention of fouling on ship hulls and other underwater structures uses copper or organotin containing paints. Although organotin containing coatings are highly effective, they are also dangerous to the marine environment in which they are used because the tin leachates can poison non-target organisms such as fish, vegetation, and marine mammals. Because of the increased evidence of ecosystem damage in areas close to concentrated use of tin-containing paints, application of these antifouling paints is being restricted and in some cases prohibited. Fouling release coating technologies are currently under development in response to the need for a nontoxic coating alternative to antifouling paints.

Fouling organisms may grow on the surfaces of these coatings but adhere poorly and can be removed by light brushing, water spray or by hydrodynamic self-cleaning. Silicone polymers have show better fouling release capability than fluoropolymers and other coatings. This has been attributed to their being within an optimum range of critical surface tension, which is related (but not equal) to surface energy. Other factors thought to contribute to silicones' superior fouling release ability are their surface structure, extremely low glass transition temperature and low modulus. All of the current coating technology employs condensation cure chemistry. The coatings are prepared by the reaction of a crosslinker with a silanol polymer in the presence of a condensation cure catalyst such as dibutyltindiacetate. We and others have previously shown that oil incorporation may benefit fouling release properties.