Replacing Those Sacrificial Zinc Anodes

Every other year I make the trip from Juneau to Puget Sound and part of my winterization is performing basic maintenance and using North Harbor Diesel in Anacortes for dry storage. I like dry storage because not only is it less expensive than in water moorage, it is worry free. There are no frequent trips to the dock to check the lines and that the shore power is on and the heaters are operating. Before I know it , it’s April and time to get my 4-year old Nordic 42 ready for launch. This year the hull has been repainted, gel coat cleaned and buffed, hydraulic system inspected, engine room fire suppression system checked, a sticky thru hull valve replaced, interior teak wood oiled, furnace/hot water unit checked, fluids and filters changed, and the zincs replaced.

Yes, those all important sacrificial zinc anodes. If you do this yourself every time, it’s not a problem. You remember that there are pencil zincs in the cooling water system. The big hull anode is obvious as are those on the rudder and rudder shoe, but several other locations are not so obvious. Since I helped replace the zincs last April, I remembered the little collar zinc on the bow thruster. But the collar zinc on the shaft in front of the prop, I completely forgot about. Not a good thing. This is a critical location because of more galvanic action with a bronze impeller on a stainless steel shaft. Having a good checklist to go through before launching each spring is important otherwise, be sure you have a competent marine service to do these things for you.

The home port for the Nordic Quest is Juneau, Alaska and zinc anodes have to be changed twice a year rather than once. I have been curious for some time as to why prolonged exposure to sea water in Juneau results in faster zinc loss. Oceanographers who study salinity changes will tell you that the North Pacific has a higher salinity than California waters, the Gulf of Mexico or the Atlantic. SE Alaska has huge tidal exchanges, often 14 feet or more, which results in full exchange twice a day flushing out any fresh water sources. I have concluded that there is another reason. Alaskan marinas are crowded. My boat can be surrounded with old hulls used by live aboards, near derelicts, and massive steel hulls. If just a few of these guys have not kept up with zinc replacement or are improperly grounded to the shore power, there are a whole lot of stray currents making their way to my anodes under the dock. So, if I can’t get on the dry for six months, changing the zincs twice a year will be on my checklist.

About Fred Cooper

Alaska resident at the time of statehood and returns annually; professional civil engineer and for 35 years owner of an engineering company; skipper of the Nordic Quest; author, avid fisherman and world traveler. Lives with his wife and their water-loving standard schnauzer in Portland, Oregon.
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