Our boat could dissolve-if it weren’t for anodes!

So this is pretty complicated but I’ll try to make what I learned this week simple.

First point is our boat is steel. Most sailboats are constructed of fiberglass. One of the many benefits of a steel sailboat include safety (hard to puncture a hole if we hit something). One of the not so great things about steel in salt water has to do with chemistry. Let me see if I can get this right (I’ll need Greg to proof this before I post, to be sure I get it!).

When one type of metal is exposed to another type of metal in an electrolyte (salt water), the salt water can create an electrical circuit through the water and electrons can flow from one metal (less “noble”) to the other (more noble) metal through the saltwater.  This can essentially dissolve the less noble metal! So to prevent the steel of our hull (or prop and prop shaft) from “dissolving”, as well as corroding, there needs to be a less noble metal in contact with our hull that gives up its electrons more easily. The “other” (less noble) metal is zinc. Zinc gives up its electrons much more easily than steel (our boat). So we need to bolt about 10 anodes to the hull, rudder and propeller on our boat. We did that while it was on the hard in the boat yard. So here is a photo of the type of anode we put on our hull:

There are many different shapes and sizes of anodes. Even fiberglass boats need anodes for their metal propellers and prop shafts. Because if they didn’t, the props would corrode and dissolve!  We have a friend who lost the anode on the prop shaft, and after 3 months, the propeller was ragged where it had dissolved and the prop shaft was covered with corrosion from the brass prop dissolving (several $1000 of repairs!).

Here is a photo of an anode that has a little dissolving that has happened (and what ours kind of look like this year):

Every year, we need to inspect these after we take the boat out of the water to determine if we need to buy new anodes for next season. Rule of thumb, I think, is that it is 50% deteriorated, or you can’t read the writing “Do not paint”, then it’s time to replace the anode.

So, something I learned this year! And your chemistry lesson for today!


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