How to attach a zinc to a cast iron keel?

[wsmurdoch]

Adding to my earlier post....

I have owned a Tanzer 22, Canary, #1949, since 1981. The boat has been in both salt and now in fresh water since I bought her. The stub keel is cast iron with a cast iron centerboard that withdraws into a slot in the bottom of a stub keel. The centerboard is raised by a stainless steel pennant. The wetted iron parts of the boat have been painted with POR epoxy and bottom paint, earlier Micron 22 (a now illegal tributyl tin paint) and more recently VC-17M. Adding a pair of of (first in both salt and later fresh water) zinc and (now in fresh water) magnesium rudder anodes attached to the sides of the keel made a significant reduction in the rust that appears at the front lower corner of the keel and on the bottom of the centerboard where the epoxy paint gets scraped off when we bump the bottom. I re-learn this every time I fail to replace the anodes.

I have never seen any corrosion of the stainless steel bolts holding the anodes to the keel. I partially fill the tapped holes in the keel with dielectric grease before inserting the bolts. I have measured the resistance between an anode and a keel bolt; it is less than one ohm -- I can't measure lower. I have not seen any corrosion in my stainless centerboard pennant, although I did break it once (in 31 years) dropping the centerboard off its winch and having it come up short on the pennant after the fall.

Anyway, that is my experience.