Presently, U.S. Navy surface ships with anti-submarine warfare (ASW) responsibilities carry a bow-mounted sound navigation and ranging (SONAR) array for the detection of submerged targets. Marine biofouling of the outer surface of the SONAR dome (especially by hard-shelled organisms - barnacles, bivalves, tube-worms, etc.) is the major external factor responsible for degrading the performance of bow-mounted SONAR systems.
This project will evaluate the antifouling capability of a rubber boot coating for surface ship bow SONAR domes that contains Vinyzene-Max, an isothiazolin-based biocide that is heavy metal free and subject to rapid breakdown to nontoxic materials once released into the environment.
Approximately 5 years ago, scientists at the Naval Undersea Warfare Center (NUWC) Newport and Naval Surface Warfare Center (NSWC) Carderock began to work on a more environmentally friendly replacement for the Navy standard "no-foul" neoprene rubber. That rubber was protected from biofouling by a highly toxic, heavy-metal-based biocide, bis-tri-n-butyl tin oxide (TBTO). The researchers decided to incorporate a new biocide called Vinyzene-Max (developed by Rohm and Haas; now Dow Chemical) into different elastomers used by the Navy to see if it would protect those materials from marine biofouling. The initial experiments were successful; up to 6% Vinyzene-Max was added to neoprene, ethylene propylene diene monomer (EPDM), and polyurethane without any adverse effects on the physical properties of these elastomers. Testing of panels in area at both warm (Hawaii, Florida, Singapore) and temperate (California, Rhode Island) waters confirmed that the Vinyzene-Max retained sufficient potency and mobility within these rubbers to protect them from marine biofouling for several years without any cleaning or grooming of the exposed surfaces. By 2010, this testing had indicated that Vinyzene-Max performed similarly to TBTO, and because it was much less toxic and persistent in the environment, Vinyzene-Max could now in theory replace legacy Navy uses of TBTO and other heavy-metal-based biocides for the protection of rubbery surfaces.
During the last 10 years, the Navy was designing and prototyping a new surface ship bow dome, the Improved SONAR Acoustic Window (ISAW), and agreed to include the new antifouling rubber into the prototype ISAW that was being built and scheduled to be tested on the NSWC Port Hueneme's Self Defense Test Ship (SDTS) the ex USS Paul Foster in 2012. Portions of the ISAW boot installed on the SDTS will be inspected and photographed quarterly for 3 years to allow marine biologists to determine the efficacy of the new rubber and biocide combination in preventing unwanted biofouling. Concurrently, a series of laboratory and field experiments will be conducted to obtain critical information, such as the release rate of Vinyzene-Max from the rubber, and diffusion constants for the biocide within the rubber.
If the Vinyzene-Max-containing rubber boot on the prototype ISAW can be shown to provide adequate protection from marine biofouling during the SDTS test, then the technology can transition directly into the ISAW program. Thus, all future Navy surface ship bow domes would be TBTO-free, and the Navy's last legacy use of TBTO would be eliminated. The Vinyzene-Max technology is transferable to other Navy programs that currently use heavy-metal-based, antifouling paints to protect critical rubbery surfaces, such as submarine bow dome boots and CW-1181 SONAR domes. Not only would this remove sources of copper pollution from the environment (the paints are self-polishing and ablative), it would reduce maintenance costs for the Navy because the Vinyzene-Max would be stored throughout the volume of the rubber (a large reservoir compared to a thin paint layer); thus, repainting the rubber surface every year or two would no longer be required. (Anticipated Project Completion - 2015)