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NST CENTER - TECHNICAL SOLUTIONS FOR U.S. NAVY UNDERWATER HULL ANTI-FOULING COATINGS

U.S. Navy Underwater Hull Anti Fouling Coating Program

Do you have a solution or an original idea the U.S. Navy can use
in its effort to solve the technical issue presented below?

If so, email us at info@nstcenter.biz

Discussion

Marine plants and animals accumulate on a ship’s underwater hull causing “fouling” or “biofouling” problems.  Heavily fouled ships experience:

  • Decreased speed due to hydrodynamic drag
  • Increased fuel consumption
  • Decreased effectiveness of acoustic sensors
  • Increased vessel weight

To prevent marine growth, specialized underwater coating systems have been developed and classified as “antifouling coatings.”

Marine fouling can be controlled by using physical or chemical techniques. 

Physical Fouling Control Techniques

  • Hull scraping  and underwater cleaning
  • The use of smooth, low-surface energy coatings creating a poor substrate for fouling growth so any organisms adhering to surfaces can be swept off of the hull when the ship gets underway.

 

Chemical Fouling Control Techniques

  • Coatings containing compounds toxic to marine fouling organisms.

Common toxic compounds include cuprous oxide, metallic copper, and, until recently, tri-butyl-tin oxide (TBT).

Commander, U.S. Fleet Forces Command (CFFC)

The Commander, U.S. Fleet Forces Command, (CFFC) is interested in antifouling coatings due to the growing need to reduce fuel and hull cleaning costs.
 
CFFC tasked NAVSEA 05P23 to assemble an Underwater Hull Working Group to improve areas of:

  • Documentation
  • Business Practices
  • Quality Assurance and control

The group concluded and addressed the following major issues:

  • Use of hand tools (SSPC-SP 11) on Underwater Hull
  • Work package preparation
  • Service life of antifouling systems
  • QA/QC

Environmental Requirements

The U.S. Navy does not use TBT-bearing antifouling coatings and is evaluating environmentally friendly antifouling coatings to comply with international, federal, state and local regulations.

The International Maritime Organization (IMO), an international body dedicated to establishing safety and pollution restrictions to completely prohibit the use of TBT-based biocides in antifouling paints by placing a worldwide prohibition of TBT-bearing coatings on ocean-going vessels as well as controlling copper emission rates from antifouling coatings.

International Environmental Regulations

The IMO has released a Treaty Banning TBT in antifouling coatings to member nations, which entered into force in January 2008.  It prohibits the application of TBT-bearing coatings and requires the removal of all TBT-bearing coatings from ocean-going ship’ hulls.
The European Union, Sweden, and Canada developed rules prohibiting use of coatings with TBT biocides to protect the natural habitat. International regulations influence coating selection in the U.S. because U.S. ships may trade or call in ports with prohibitions on the use of specific biocides.

In the U.S., coatings must comply with federal, state and local regulations and water-quality standards.

Federal Environmental Regulations

The U.S. Navy’s goal is to evaluate options for antifouling coatings using guidance provided by the Environmental Protection Agency (EPA) and select those that cause the least harm to the environment.

Federal regulations related to antifouling coatings include:

The U.S. Navy requires compliance with all these federal laws as a minimum requirement for inclusion of an antifouling coating on the MIL-PRF-24647 qualified products list.

The Uniform National Discharge Standards Program (UNDS)

The UNDS program is:

  • A joint effort between NAVSEA and the EPA to develop regulations for aqueous discharges
  • Reviewing Marine Pollution Control Devices (MPCDs) as mechanisms for controlling or preventing discharges from vessels into the waters of the United States
  • Evaluating and developing MPCDs for the hull-coating leachate from antifouling paints.

State Environmental Regulations

Many states implement regulations more restrictive than federal regulations. States can be influenced by the U.S. Navy's selection of antifouling coatings due to the location of U.S. Navy facilities.

Local environmental regulations

Water quality issues within ports and local waterways supporting military and civilian ships are spurring the passage of new regulations. Local regulatory bodies have introduced greater restrictions on areas of high concern. You can view local by state.

Performance Requirements

The U.S. Navy is striving to identify antifouling coatings offering:

  • Superior fouling control performance in all geographic areas;
  • Reduced need for hull cleaning and dry-docking while still effectively controlling fouling over a 12-year docking cycle.

Current Research and Testing Areas

Environmentally acceptable antifouling coatings of interest to the U.S. Navy can be broadly grouped in the following three types:

1. Low Copper Antifouling Coatings

  • Use a self-polishing resin system based on hydrolysable acrylate polymers and lower levels of copper than currently used by the U.S. Navy.
  • Enhance fouling-control performance by short half-life, metal-free, and co-biocides.
  • NAVSEA defines the maximum allowable copper release rate for a "low-copper" coating to be 10µg/cm2/day, as measured per ASTM D-6442 over a 90-day period.
  • NAVSEA requires coating companies register their low-copper antifouling coatings with the U.S. Environmental Protection Agency (EPA).

2. Copper-Free Antifouling Coatings

  • Eliminate the use of copper as a biocide.
  • Metal free, non-persistent, and contain short half-life (10 hrs) biocides to prevent marine fouling.
  • Once released into the water around a ship's hull, the copper-free biocides break down into benign by-products that will not harm the marine environment.
  • Copper-free coatings are typically based on advanced, self-polishing resin systems.
  • NAVSEA requires coating companies register their copper-free antifouling coatings with the EPA.

3. Foul-Release Coatings

  • Based on a silicone resin system forming a smooth, low-surface-energy film on the hull when applied giving a poor substrate for marine fouling. Hydrodynamic force dislodges any organisms growing on the hull when the ship gets underway.
  • Contains no biocides
  • EPA registration is not required since the foul-release products do not contain biocides.  NAVSEA does require EPA documentation indicating the product does not contain biocides and that it can be considered a foul-release product.
  • NAVSEA's operating experience with the foul-release coatings has shown they are vulnerable to scratches and damage from improper cleaning.  Improper cleaning limits the service life of foul-release coatings.  NAVSEA is working with the diver cleaning community to ensure only proper cleaning is conducted on foul-release coatings installed on Navy ships in the future."

Requirements Summary

Underwater hull copper free, low copper and/or biocide-free anti-fouling coating systems shall have the following characteristics:

Environmental:

  • Comply with current and future federal, state and local air emission regulations
  • Eliminate or significantly reduce copper emissions (or must show <50% of copper release rate of current ablative copper systems qualified to MIL-PRF-24647)
  • Must be EPA registered
  • Must obtain approval from the Navy and Marine Corps Public Health Center (NMCPHC)

Technical:

  • Coatings must support the U.S. Navy’s operating cycle
  • Coatings must perform for 12 years without hull cleaning.
  • Vendors must commit resources to register and sell coatings in the United States.

For additional information, please see NST Center’s Approved Exterior Coatings for Underwater Hulls

Coating Qualification Process

All coatings used by the U.S. Navy must be approved by NAVSEA and must meet environmental and performance criteria. 

This roadmap provides coating qualification and testing guidance for MIL-PRF-24647 coatings. Coatings meeting this specification include ship hull anticorrosive and antifouling systems.

For more information on this topic, please contact

Mr. Mark Ingle
1333 Isaac Hull Ave, SE
Washington Navy Yard
Washington, DC 20376
(202) 781-3665
mark.w.ingle@navy.mil