Marine bio-fouling of submerged surfaces has been a problem encountered by ship builders, fishermen, seamen and shipping company operators for centuries. Marine organisms attach themselves to ship hulls, anchor chains, fishing equipment and the like with remarkable rapidity once the object is placed in the water. The fouling phenomenon is particularly troublesome in salt water environments where marine organisms such as barnacles can attach themselves to submerged objects in successive layers to the point that the original object becomes virtually unrecognizable over time.
The growth of marine organisms on the submerged portion of a ship's hull, by way of example, significantly increases the drag on the hull as it moves through the water, thus increasing fuel consumption and reducing the overall efficiency of the ship's operation. In the past, ships were routinely placed in dry dock for scraping and painting. Various coatings designed to prevent and/or slow the rate of growth of marine organisms have been developed over the years. Some of these coatings include copper-based paints, silicone coatings, gradually dissolving coatings, and the use of certain toxins designed to kill the marine organisms before they can adhere to a submerged object. Examples of such prior art systems may be found in U.S. Pat. No. 3,497,990 issued to F. A. Jeffries on Mar. 3, 1970 for “Cellular Antifouling Covering for Submerged Marine Objects” and in U.S. Pat. No. 3,505,758 issued to L. H. Willisford on Apr. 14, 1970 for “Antifouling Covering for Submerged Marine Objects”.
A more recent approach to the bio-fouling problem may be found in an article authored by Efimenko et al. entitled “Development and Testing of Hierarchically Wrinkled Coatings for Marine Antifouling”, American Chemical Society, Applied Materials & Interfaces, vol. 1, No. 5, pp. 1031-1040, April, 2009. This article explores the application of hierarchically wrinkled surface topographies (HWST) to prevent marine bio-fouling and is based upon the premise that smaller surface topological features present fewer points of attachment for marine bio-organisms. However, this work is in its early stages and conclusive results as to its long-term effectiveness in a sea water environment are, as yet, unavailable.
Most notable of the anti-bio-fouling toxins is the antifouling coating tributylin, which has now been banned from use in most areas due to the severe toxicity to marine mammals and other marine life forms. With respect to the silicone and other types of coatings, a certain shear force was required to release the bio-foulants, and it has been found that at speeds of less than approximately three knots, shear forces acting on the layers are too weak to cause removal of the fouling material. In particular, in littoral areas where the water is relatively stagnant, stationary sensor arrays placed along sea coasts to detect potentially hostile submarine threats are particularly vulnerable to bio-fouling. Prior art anti-fouling coatings have been found to be ineffective in addressing bio-fouling of such sensors, and, as in the case of towed sensors and sensor-equipped unmanned underwater vehicles (UUV's) and autonomous underwater vehicles (AUV's), such coatings cannot be applied to the sensor cover without severely reducing or completely destroying its effectiveness.
Hence a need exists for a material system which eliminates or materially reduces the bio-fouling of underwater structures without introducing toxic chemicals into the environment. More specifically, a need exists for a material system which eliminates or materially reduces bio-fouling of sensor-equipped UUV's and AUV's without inhibiting the effectiveness of the electronic sensor systems with which such devices are equipped.