Measuring Anode and Cathode Degradation

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The anodes were cleaned, weighed, and installed on 2-foot lengths of 3/4-inch, copper pipe (type M), which were also weighed. We hung the samples between slips in the mid-Chesapeake Bay near Rockhold Creek for one year, cleaning quarterly to mimic light use. At the end of the test period, the samples were cleaned with a plastic scraper and scrub brush, and their interiors were scrubbed with a snugly fitted multi-knotted rope. Testers gave them a light acid cleaning to loosen barnacle residue and scrubbed them again before weighing them. We also measured potential driving force and current for each anode before and after exposure. Salinity at the test site varied from brackish to seawater salty. We will be testing in full-strength salt water for a followup article.

Anodes

1. For testing, we mounted a variety of anodes to plain-copper tubing. This photo shows the samples before they were suspended in brackish water for a year. From left to right, they are the Sea Shield aluminum Streamlined with nail polish, Sea Shield zinc Streamlined with nail polish, Sea Shield aluminum Streamlined with grease, zinc Camp X-2, aluminum CMP Martyr, zinc CMP Martyr, Sea Shield aluminum Streamlined, Sea Shield zinc Streamlined, and the control (no anode).

2. After a year in the water, the anodes had a fair bit of marine growth. This photo (samples in the same order as photo #1) shows the test field after slight cleaning. Note that the aluminum anodes have barnacles, but the more-toxic zinc anodes and the unprotected copper tube do not.

3. Testers weighed each anode sample before and after the year-long test to gauge degradation level. The weights and percent of weight loss are shown in the accompanying Value Guide.

Darrell Nicholson
Practical Sailor has been independently testing and reporting on sailboats and sailing gear for more than 50 years. Supported entirely by subscribers, Practical Sailor accepts no advertising. Its independent tests are carried out by experienced sailors and marine industry professionals dedicated to providing objective evaluation and reporting about boats, gear, and the skills required to cross oceans. Practical Sailor is edited by Darrell Nicholson, a long-time liveaboard sailor and trans-Pacific cruiser who has been director of Belvoir Media Group's marine division since 2005. He holds a U.S. Coast Guard 100-ton Master license, has logged tens of thousands of miles in three oceans, and has skippered everything from pilot boats to day charter cats. His weekly blog Inside Practical Sailor offers an inside look at current research and gear tests at Practical Sailor, while his award-winning column,"Rhumb Lines," tracks boating trends and reflects upon the sailing life. He sails a Sparkman & Stephens-designed Yankee 30 out of St. Petersburg, Florida. You can reach him by email at practicalsailor@belvoir.com.