Ships – Implements – Hull cleaning
Reexamination Certificate
1998-11-09
2001-04-03
Swinehart, Ed (Department: 3617)
Ships
Implements
Hull cleaning
C205S729000
Reexamination Certificate
active
06209472
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is generally related to an anti-fouling apparatus for marine components and, more particularly, to a device that creates an electric current in the region proximate an underwater surface in order to inhibit the growth of marine life on an underwater surface such as a boat hull.
2. Description of the Prior Art
For over a thousand years, it has been known that a ship's hull is subject to fouling by marine growth. Copper cladding had been used successfully for many years until the introduction of vessels with iron hulls which prevented its use because of the potential for galvanic action. By 1850, various paints containing copper salts had been developed. Over the past few centuries, the pace of the development of anti-fouling techniques has been influenced by warfare, and several naval encounters have been decided by the greater speed of a naval vessel that resulted because of superior anti-fouling technology.
Currently, copper salts are used in the majority of anti-fouling paints, although the most effective modem anti-foulings contain tributyltin (TBT) as well as copper salts. Recent restrictions on the use of TBT and anti-fouling paints has led to renewed interest in developing novel, environmentally acceptable anti-fouling techniques.
Throughout the description of the present invention, the unwanted growth on a ship's hull or other underwater surface will be referred to as fouling. Although fouling is primarily a biological phenomenon, its implication relate to engineering Due to an increase in the resistance to movement of the hull through water, fouling of the hulls of ships results in a reduction in speed, an increase in the cost of fuel, and losses in both time and money in the application of remedial measures.
Underwater surfaces rapidly absorb organic material, referred to as conditioning films, which may influence the subsequent settlement of microorganisms. Bacteria and diatoms are soon present after immersion in water, resulting in a slime that covers the submerged surface. Following the establishment of the micro fouling slime layer, macro fouling rapidly develops. The macro fouling community is often described as either soft fouling or hard fouling. Soft fouling comprises algae and invertebrates such as soft corals, sponges, anemones, tunicates, and hydroids while hard fouling comprises invertebrates such as barnacles, mussels, and tubeworms.
Mariners from ancient times were aware of the problems resulting from both is boring and fouling organisms. Various treatments were employed, and some of these techniques have been retried many times in many forms over more than 2,000 years. The ancient Phoenicians and Carthaginians addressed this problem over 400 years BC. The Greeks and Romans both independently used lead sheathing which the Romans secured by copper nails. In the early 16th century, Spain officially adopted lead sheathing and its use soon spread to France and England. Although it actually offered little in the way of protection against fouling, lead was the material most frequently used prior to the eighteenth century. However, its corrosive effect on iron ships was soon noticed and the British Admiralty abandoned the use of lead in 1682 for that reason.
Other treatments to prevent worms from penetrating the planking relied on a wooden sheath placed over a layer of animal hair and tar. The wooden sheathing was sometimes filled with iron or cooper nails that had large heads. This, in effect, created an outer metallic cladding. Paints were also used that had mixtures of tar, brimstone and grease. The first successful anti-fouling device was copper sheathing and the first documented evidence for the use of copper as an anti-fouling method dates back to 1625. Copper was used in 1758 on the hull of the HMS Alarm, and by 1780 copper was in general use by the British Navy. Sir Humphry Davy showed that it was actually the dissolution of the copper in sea water that prevented fouling.
In the nineteenth century, with the growing importance of iron ship building, the use of copper sheathing on the boats was discontinued. As a result, the weight of fouling quickly made the ships unmaneuverable and unseaworthy. Various alternatives were tried including sheathings of zinc, lead, nickel, galvanized iron and alloys of antimony, zinc and tin, followed by wooden sheathing which was then layered with copper.
By 1960, metallic soap was applied hot and contained copper sulfate. From these early attempts at coatings, anti-fouling paints incorporating cuprous oxide, mercuric oxide, or arsenic in shellac varnish or a resin matrix with turpentine, naphtha or benzene as solvents developed. From these formulations, modern anti-fouling paints were developed. Anti-fouling paints are currently in wide use on yachts and pleasure crafts as well as deep sea vehicles. The presence of tributyltin (TBT) in estuaries and in the sea is thought to result from the increased use of tributyltin-containing paints on these types of vessels.
Another technique for inhibiting fouling is to reduce the ease with which bacteria and algae adhere to the surfaces. The main type of low energy non-biocidal coatings are fluoro-polymers and silicones. Fluoropolymers have been under development in the United States during the past several decades. They are based on fluoro-polyurethane paints, either pigmented with PTFE or containing silicone for fluoro-epoxy additives. Although the surfaces do accumulate fouling organisms, their attachment is weak. Coatings developed to date require twice yearly cleaning with bristled brushes to remove fouling growth and can therefore only be useful as coatings on small boats.
Various other non-toxic techniques have been attempted. Both ultrasonic (e.g. 14 kHz) and low frequency (e.g. 30 Hz) sound waves inhibit barnacle settlement and may have application to fouling control in certain circumstances. These and many other anti-fouling techniques are described in an article written by Maureen Callow in the publication titled “Chemistry and Industry” at Section 5, pg. 123, on Mar. 5, 1990.
As described in the Baltimore Business Journal, Vol. 10, No. 47, Section 1, pg. 3 on Apr. 23, 1993, McCormick & Company has discovered that its red pepper extracts are natural repellents of barnacles and zebra mussels. A coating of this type has been tested, and it has been determined that it repels both barnacles and zebra mussels which have become costly nuisances in the Great Lake Region by clogging intake pipes for power plants and water treatment plants. It is estimated that several billion dollars in damage will be caused by zebra mussels before the turn of the century.
U.S. Pat. No. 5,532,980, which issued to Zarate, et. al. on Jul. 2, 1996, discloses a vibrational anti-fouling system. The system produces vibrations in an underwater structure for the purpose of inhibiting the attachment of aquatic life forms to the structure. The system includes a controller which drives one or more transducers. The transducer comprises a housing, one end of which i s closed by a resilient diaphragm. An electromagnet with soft magnetic core is contained in the housing spaced from the unsupported portion of the diaphragm. The unsupported portion of the diaphragm is mounted over an underwater structure. In operation, the electromagnet is excited with a current pulse, which deforms the diaphragm so that the housing moves towards the structure. As the current drops off, the diaphragm is restored to its original shape and the housing moves away from the structure imparting a vibrational force to the structure. The transducer includes an elastic membrane to compensate the changes in temperature and pressure commonly found when working underwater. The magnetic cores positioned in the transducers are saturated by current pulses generated by the controller to eliminate the effects of component variations and allow multiple units to be connected to the controller without changes in sound levels. The system is highly resistant to elec
Brunswick Corporation
Lanyi William D.
Swinehart Ed
LandOfFree
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