The Boatyard, St Just in Roseland, Truro, Cornwall TR2 5JD
50°10'52.64"N, 5° 1'22.22"W
T: 01326 270269

Anodes, skin-fittings and seacocks.

Tue, 01/16/2018 - 11:30 -- admin

Having now finished the lay-up servicing we thought it worth sharing some of our findings as it may help you to prevent unnecessary work and therefore keep down the cost of maintaining your boat. A galvanic anode is the main component of a galvanic cathodic protection system used to protect submerged metal components from corrosion. They are made from a metal alloy with a more "active" voltage than the metal of the structure. The difference in potential between the two metals means that the galvanic anode corrodes, so that the anode material is consumed in preference to the structure. The loss (or sacrifice) of the anode material gives rise to the alternative name of sacrificial anode. It is fairly simple to change an anode but renewing every year isn’t always necessary as the current one (or more) may have “plenty of life in it”. However if the anode has survived two seasons without corrosion it is unlikely to be doing its job and something else is “fizzing” away instead. This may be a skin-fitting, out-drive or propeller or rudder-fitting for example. Making sure your anodes are fresh and appropriately sized and positioned is the cure. This article highlights some troubles we have spotted. We suggest you have a good look, or ask the yard to have a look, to be sure a problem is identified before any damage occurs. Whilst conducting an annual seacock service to the skin fitting shown below it failed at the base with only a small amount of pressure applied the handle causing the whole lot to snap off. 

Clearly if this had happened a month earlier when the vessel was still afloat this could have resulted in a big problem. The electrolysis has caused “pinking” which has caused the bronze to change to a brittle state and become very weak. An easy test is to scratch the fitting’s surface with a knife to see if the bronze is still ‘yellow’ or has turned pink. If it is pink then changing it would be wise.  In the picture you can see the colour change around the perimeter where it has failed. Another case which is common is the deterioration of lifting centre plates where unchecked they have corroded until they jam in the up position. Galvanised steel work, be it keel bands or rudders, become affected over time if the anodes are insufficient.  

This picture shows the effect of corrosion on a rudder which after a few seasons then needed costly replacement. In conclusion, anode checking on a seasonal basis can save your vessel’s vital components and if your anodes aren’t wearing look into what is.

We hope that this information is helpful to you. If you’d like any further information on how Pasco’s Boatyard can assist you with these issues or any other aspect of boat maintenance please email us at or give us a ring on 01326 270269.