Protecting Our Investment: Solving Fast Response Cutter Corrosion

Abstract

The USCG Fast Response Cutter (FRC) fleet is experiencing corrosion at an alarming rate in the propulsion shaft tunnels. An investigation into this problem was conducted from the perspectives of “root cause” and “prevention.” Root causes for the corrosion stem from an interaction in a complex, two-stage galvanic protection system on-board the ship that uses both passive zinc protection and impressed current cathodic protection (ICCP) from an active, feedback-controlled power supply. By using custom measuring instruments and applying them on an in service FRC in order to better understand the complications with galvanic protection on the FRC, crucial insights were discovered. The ICCP power supply unit is intended to prevent corrosion by actively injecting current through anodes in order to raise the magnitude of the voltage measured between the reference electrode and the hull. When designing the FRC, it was expected that a combination of ICCP and passive zincs would protect the hull steel in tandem; however, this has not been the case along the entirety of the ship. The ICCP system is unable to accurately determine the reference potential, a useful indicator for whether the hull steel is adequately protected from corrosion, in every area of the ship, allowing some areas to corrode at an accelerated rate. This report details a full summary of analysis and results, along with a review of laboratory experiments and field experiments with several FRCs in the USCG fleet concluding with specific, actionable suggestions for mitigating corrosion in the FRC stern tube. Additionally, this report outlines how non-intrusive load monitoring, which has a proven track record for preemptively recognizing faults in shipboard equipment, analyzed the ICCP system and how this relates to shipboard microgrids.