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Chlorination System reduces Bio-Fouling of Sub Equipment in Littoral Water

NAVSEA News Wire

Release Date: 4/16/2004

By Naval Sea Systems Command Public Affairs Office

Washington, DC - As the submarine force's focus turns increasingly from blue water to littoral areas, the challenges presented are not limited to operational issues. With subs increasingly deployed in warmer, shallower waters, the new environment is rich in nutrients that support varied families of marine organisms. As a result, the ship's cooling systems can clog with biological creatures -- such as sea grass, barnacles and the like-- while at sea. When this occurs, it can mean curtailing operations until the sub's seawater systems can be cleaned.

In the past, this kind of fouling of sub equipment was only a problem when subs returned to homeports, especially warm-water ports like Pearl Harbor and San Diego. But with the broader use of subs in littoral areas, NAVSEA saw the need for installed chlorination systems to prevent bio-fouling in its newer classes of submarines.

Initial designs were highly successful but at a cost, both in installation and maintenance. The first such deployment of an installed submarine electrolytic chlorine generator (ECG) was part of the Improved Propulsion Machinery Program in 1987, resulting in an expensive $3 million system including a $350,000 ECG, which needed a $200,000 overhaul every five years. During the design development of the new Virginia class subs, the chlorination system was designed to isolate the chlorinator from high seawater pressures, allowing use of a commercial off-the-shelf (COTS) ECG that costs about $3000, and reducing maintenance costs. The drawbacks were that the seawater injection system needed to integrate the low cost ECG, at $1.2 million, was still an expensive system with a greater annual operating cost and additional on-board storage requirements.

The challenge was to find a less expensive system without the large storage requirement that could be successfully back-fit on operational submarines. The justification for doing so was clear. During 2001, the Navy paid shipyards more than $5 million for cleaning seawater systems on its older, non-chlorinated subs, because of reduced propulsion capability and high equipment operating temperatures due to bio-fouling. More significantly, many submarines experienced deployment interruptions to clean heat exchangers clogged with bio-fouling.

Addressing the problem was a team effort organized by Rich Kurz of NAVSEA's Undersea Warfare Directorate.

"Using a portable kit was ruled out early on because carrying chlorine in the strength needed posed a danger to the crew," says Kurz. "So the key hurdles were to find an inexpensive chlorinator and to minimize system and installation costs."

At first, this work was approached with the idea of limiting the size of the chlorinator to that needed for operations in littoral waters. Toward that end, commercial off the shelf (COTS) units could be bought for about $3,000.

With this design concept, a design and implementation team was established. The littoral electrolytic chlorine generator (LECG) design lead was the Naval Research Lab (NRL) in Key West, Florida. NRL was a natural participant, with years of experience developing and operating pier-side chlorinators. Edward J. Lemieux, Corrosion Engineering Section Head, led NRL's effort. He found the COTS units and combined two such units to provide the needed capacity. Other participants -- David Wilson and Tim Stark -- were from the 688 Class Design/Planning Yard, Newport News Shipbuilding. They provided sound recommendations for the engineering system design and are credited with improving the piping and LECG layout to minimize cost and optimize operations.

Users were also involved throughout the design process. MMCM Jeff Helgeson, SUBPAC's Force Mechanic, had already contributed to the success of this effort by finding initial funding for it, and was a key contributor to the design concept. For his efforts, he recently received a check for $11,000 through the Navy's Beneficial Suggestions program. Participants from SUBPAC also included MMC Nick George of the Pearl Harbor Performance Monitoring Team (PMT). SUBLANT's primary representatives were MMCS Mark Moss and MMC John McLemore from Norfolk PMT, who worked to keep the design Sailor friendly.

When the Fleet decided that it wanted a LECG that could withstand deep water operations, the chlorinator electrodes proved thick enough to withstand higher pressures. With better connector seals, the unit was successfully tested to the proper hydro pressures for certifying deep water capability. With the addition of LECG housing supports, the unit passed shock and vibration tests.

On November 26, 2003, the first back-fit installation of an integral chlorination system was put into service on the USS. Louisville, home ported in Pearl Harbor, Hawaii, following installation and testing at Pearl Harbor Naval Shipyard. Subsequent tests and operational data proved that the system works well. Not only did the LECG supply chlorine levels at or even slightly above design, the system piping provided more than adequate flow under all combinations of auxiliary seawater system operations.

The next step will be to ruggedize the LECG and its power supply. Preliminary investigations indicate that sturdier, more reliable electrode connectors may be realized for an added cost of about $10,000. The power supply will be made lighter, which will lower the cost of the foundation to support it. Because the LECG system was installed under mission funding, an exact cost for installation is not available. However, estimates by Newport News Shipbuilding indicate it will run between $350,000 and $500,000 - substantially less than the installation costs on the newer-class subs.

Currently, a similar LECG system is being designed for SSGN subs. In addition, Virginia Class boats may be evaluated for a future design change to the LECG system design, based on potential savings in installation costs and annual operational costs, and reduction in stowage requirements.

Meanwhile, the surface Fleet has been looking into using chlorinators and has inquired about the LECG design. With a larger number of independent seawater cooling systems than exist on a sub, surface ships will need more ECGs and should be able to adapt the new LECG design. It is clear that the need for bio-fouling control on U.S. Navy ships is not going away. And the inexpensive LECG presents an attractive solution.