Zincs are an important part of a boat. They are attached to metal parts of the boat below the waterline and corrode away over time instead of the metal they’re connected to. On Astraea they’re on the rudder post and on the propellor shaft. Don Casey has a great writeup about boat zincs at the Boat U.S. website.
Last week I changed the zincs on Astraea. The standard ZHC-6 rectangular zincs don’t properly fit the rudder post and needed to be cut down.

The day before, I used an electric hacksaw at a local machine shop to cut the excess zinc away. Then I put on my dive gear and dove under the boat. I used a 1/2 inch socket to remove the old zinc. Astraea has had the same zincs installed since she was launched here in San Diego last spring. Nine months in the water and the old zinc didn’t look too corroded. I estimate that 90% remained.

I inspected the “Electro Guard D” round zinc on the propeller shaft and found it was still tight and in very good condition so I didn’t replace it. After New Years I’ll dive the boat again and inspect the zincs again.