Military


Paint

"Haze gray and underway" is a common saying in the fleet Navy community. A ships camouflage concealment ability is enhanced and the probability of detection and targeting is reduced by the use of an overall haze gray appearance. For ship color schemes, this reduces the average contrast of the ship to the horizon through the elimination of black and white on vertical or near vertical surfaces above the upper boottopping limit.

  • Letters/hull numbers - replace white with light gray and black with ocean gray silicone alkyd enamel.
  • Ships name/draft marks -- replace white with light gray and black with ocean gray silicone alkyd enamel,
  • Stacks - the inner surface of the stack shall be painted with two coats of heat resistant over bare metal. Exterior surfaces of stacks, bliss caps and diesel uptakes shall be painted with high temp haze gray paint.
  • PCM tiles &adjacent areas of superstructure - PCM tiles shall be painted with haze gray water based acrylic latex paint. Vertical topside areas of superstructure to be preserved with haze gray topcoat silicone alkyd enamel.
  • Ship & boat canopies - ship canopies stowed in a vertical or near vertical position shall be painted haze gray vinyl over canvas. Replacement canopies should be specified in haze gray, boat canopies shall be painted on the outside with haze gray canvas preservative, and the undersides should not be painted.

The boot-topping is defined as the black area from minimum load waterline at which the ship is expected to operate to 12 inches above the maximum load waterline. The black paint is an anti-fouling paint conforming. Haze gray is carried to the black anti-fouling paint which marks the upper boottop paint.

Antifouling paints are required first and foremost to protect the boat bottom from attachment of fouling organisms present in marine and freshwater, such as barnacles, encrusting bryozoa, and zebra mussels, as well as vegetable fouling such as algae and sea-grass. Most antifouling paints contain copper compounds as the active ingredient in preventing fouling attachment. The difference between most antifouling paints is not the active ingredient, or toxicant, but the method in which the active ingredient is delivered. Leaching antifoulings function by the slow dissolution of water soluble portions of the paint film, releasing (leaching) the cuprous oxide into the water. Ablative antifoulings also function by leaching the toxicant into the water. But ablative antifoulings also function by the controlled erosion, or ablation, of the paint film, which results in a continuously renewed surface, with fresh toxicant always available for the prevention of fouling attachment.

Biofouling is a major problem for the shipping industry. The growth of marine fouling organisms on a ship's hull increases friction and drag as a ship moves through the water, resulting in reduced speed, higher fuel consumption, and more frequent hull cleaning.

Green weed can grow up to 15cm long in a band a few meters wide at the waterline. It grows rapidly and scrubbing it off triggers an even more vigorous growth within a few weeks. Shell fouling may consist of barnacles, mussels, polyzoans, and tubeworms. Weed and shell fouling decrease the ship's performance drastically.

Ships with clean bottoms sail faster, deliver more timely cargoes and outmaneuver adversaries in combat. As power-driven vessels were introduced and speed and operation costs rose, the concept of drag became better understood and it was quickly perceived that wetted surface (the actual area of bottom in contact with the water layer) was directly related to the power needed to drive a ship. A thick layer of barnacles or other critters, each a little pyramid of roughness, adds a lot to the surface area of a clean bottom, dramatically slowing a ship's progress.

Fouling is not a new problem. The danger of shipworm and of wood-boring crustaceans, generically called "gribble," have plagued mariners since antiquity. The Phoenicians, seafarers who occupied the Western Mediterranean around 1250 B.C., used copper strips to inhibit fouling. British naval vessels in the 18th and 19th centuries copper-sheathed their entire bottoms for protection, a very expensive proposition.

Athenians around 500 B.C. and centuries later, the Venetians, used to roll their galleys out of the water between uses, both to dry out a waterlogged ship, and to remove the threat of worm and fouling. Well-made Greek galleys therefore lasted 20 years, and in one case, more than 25, while the better Venetian ships lasted an average 13 years. Poorly built ships survived hardly half that time.

From the 15th century on, large trading vessels and naval ships became too large to be easily hauled. Bottoms were painted with tar or pitch, a byproduct of the charcoaling process. Vessels still had to periodically be taken into a dry dock, though, to be scraped of their prodigious load of accumulated barnacles and other growth, where they were also checked for the worm.

Ships away from such facilities were taken into a quiet backwater, and "careened." In this process, the ship's contents, much ballast and most of her rig were backbreakingly removed to float her as high as possible. Tackles to anchors or other solid supports ashore were then used to haul her down - roll her on her side - to expose half of her bottom for cleaning.

In the old days of wooden sailing ships, antifouling methods include use of arsenic, lime and mercurial compounds to prevent shipworms and barnacles from destroying the hull. By 1865 more than 300 such 'patent paints' were registered. All of them were quite ineffective.

In 1860, James Mclnness used copper sulphate as antifoulant in a metallic soap composition. This 'hot plastic paint' was very similar to the 'Italian Moravian' paint, which was a rosin and copper compound developed at the same time in Italy. This was the best paint at the time. In 1863, James Tarr and Augustus Wonson were given a US patent for antifouling paint using copper oxide and tar. At the end of the 19th century, 'Italian Moravian' and McInness' hot plastic paint were widely used, but these paint were expensive and their life-span short.

In 1906, the US Navy tested hot plastic and other antifouling paints at Norfolk Navy Yard. From 1911 to 1921 many more experiments were performed. From 1908 to 1926 ceramic-type paints were tested but they lasted only 9 months. In 1926, the US Navy developed hot plastic paint, using tar or rosin as binder and copper or mercuric oxides as toxics. Hot plastic paint required some heating facility for the paint at the ship's site which made application difficult. So 'cold plastic paints' were developed which were easier to apply. These paints already effectively decreased fouling and the periods between dry-dock times (for re-painting) was extended to 18 months.

Antifouling paint is to help in preventing the fouling of the ship's bottom by barnacles and moss and the consequent loss of speed and increased fuel consumption. The antifouling paint should not come in contact with the steel plating of the ship's bottom, as it is not designed to prevent corrosion, and pitting may occur if it is so applied. The antifouling paint is intended for use over the anticorrosive paint only; it covers the same areas as prescribed for the anticorrosive paint.

The routine during docking periods consists of cleaning the bottom and preparing the surfaces for paint; when properly clean and dry, touch up all bare spots on the under-water body (including those surfaces in way of the painted water line) with a coat of the zinc primer; after the primer has dried sufficiently, apply single coats of anticorrosive and antifouling paint from the keel up to the lower edge of the boot topping, allowing the prescribed drying time between the coats of paint and between the antifouling paint and the time of undocking.

Although organotin compounds were synthesized almost 150 years ago, it was not until the 1960's when tributyl tin (TBT) first appeared in marine paint formulations. A major breakthrough in antifouling technology occured in the 70's when paint companies began to use TBT as a toxicant. The development of self-polishing paints that continously released TBT revolutionised the ship coatings industry and permitted longer intervals between dry-docking. The shipping industry relied heavily on the use of TBT impregnated marine coatings that disperse into the sea at damaging rates. Such marine paints are cheap, very effective and preferred by the industry. Biofouling organisms are killed upon contact with such painted surfaces, thereby preventing fouling for periods ranging from 6 months to 5 years depending upon the composition of the paint and the amount of heavy metals present.

The International Maritime Organization (IMO), an Agency of the United Nations, acted on the increasing reports of toxicity to non-target organisms by adopting a resolution in 1990 recommending measures to eliminate antifouling paints containing TBT. It took eight more years (1998) before a resolution was passed for a global prohibition on the application of organotin compounds which function as biocides in antifouling marine paints. In 2002, an international treaty was signed that bans the application of paint containing tin on all ships beginning 1 January 2003 and the complete prohibition on the presence of organotin on all ships by 1 January 2008.




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