The type of coating system used on the underwater ship hull makes an enormous difference to the integrity and safety of that hull, to the lifecycle cost of running the ship, particularly with regard to fuel efficiency and hull maintenance costs, and to the ship's environmental impact. The most basic consideration for any hull coating is the protection of the hull against corrosion. This includes, to an increasing degree, passenger ships sailing in ice and polar regions. Fuel economy is an environmental concern as well as a financial one, because greater fuel efficiency equates to reduction of GHG and other atmospheric emissions. It is also an economic concern with bunker prices high and rising. The fuel efficiency of the hull depends on its being smooth over the life of the ship and on its being kept free of fouling. Choice of hull coatings must consider the environmental effect of the emission of toxic substances such as heavy metals, biocides, silicone oils or other chemicals into the water column and sediment, and also directly onto ice in icebound regions. There is also the matter of hull-borne aquatic invasive species and their threat to biodiversity, which is of increasing concern internationally. This paper compares the various options for underwater hull coatings for passenger ships and focuses on an innovative, environmentally-friendly, economically-viable alternative to the hull coating systems in general use on the world fleet today, highlighting the specific application of a surface treated composite (STC). The paper discusses the advantages and disadvantages of each coating type, specifically on passenger ships, featuring as a case study a major cruise line which successfully converted from a biocidal antifouling coating to an STC which has been in use on all of its ships for the last eight years.
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