Tuesday, August 19, 2014

Checking the Zincs

One of the many things we have had to learn with Breeze On is to check the underwater metal parts for corrosion, specifically galvanic corrosion. As I have mentioned before, anything that has to do with electronics is Greek to me so I hope that my writing about it will help me to understand it.

Whenever two dissimilar metals are in contact with each other in seawater they become a battery and an electric current can pass between them. So, for example, a bronze propeller on a stainless steel shaft can cause an electric current to form when they are under water. The current is formed by electrons coming off of the metal. If enough electrons come off of the metal it will eventually be destroyed. The process is called galvanic corrosion. To protect these metal parts something called a sacrificial anode is attached to the metal. These are very often made of zinc, which gives off its electrons more readily than bronze or stainless steel. Many boat owners call them "zincs". Don Casey wrote a brief article explaining zincs for BoatU.S.

Stray electrical current which may be present in the water, perhaps from another boat, will hasten the deterioration of the zincs. Once the zincs have lost about 50% of their size they should be replaced. They should be checked at least once a year, but possible more often than that.

Our boat has been in the water just three months but we have been wanting to check our zincs for a few reasons. We heard that another boat owner in our marina said his zincs deteriorated much more quickly there than in other marinas. I heard from another Hanse owner on Women Who Sail that they had to replace their sail drive because the zinc had failed.

Last week we had the marina pull the boat for a short haul to check the zincs and clean the bottom. Much to our relief the zincs looked great and the bottom was pretty clean, too. Phew!

One possible reason our zincs looked good and the other boat in the marina had zincs that were deteriorating is that Breeze On has a galvanic isolator in the electrical system. When a boat is plugged into the shore power at a marina the grounding wire connects all the boats connected to shore power with each other. So, if the boat parked next to us has no zincs, the zincs on Breeze On will do the work of protecting both boats and deteriorate much faster. A galvanic isolator prevents this from happening. So I am guessing that the boat that had quickly deteriorating zincs had no galvanic isolator. In any case, I am grateful that everything looked good with Breeze On.


The rounded gray part in front of the propeller protects the propeller. The gray part behind the propeller protects the sail drive.


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