bertram31.com

When I bought Amberjack 25 years ago it had two zinc collars on each shaft. Next year at haul out I just went ahead and replaced them with two more per shaft. In those days Amberjack was a "hot" boat and the zincs were obviously being worked hard. Since then I've pulled out 2-300 feet of unused, unattached wires including one in the bilge that sparked when I clipped it. So over time the boat has become more electrically stable and the zincs aren't working nearly as hard. I wonder now if the shafts really need two zincs each and would be interested to hear input from other B31 owners. All boats are different, especially ones as old and heavily modified as Bertram 31's, but there must be similarities.

Boat particulars: 5 months saltwater-7 months freshwater
1 3/4" shafts -- the collars are massive, much larger than my original 1 1/4" collars

Yes, I tried aluminum anodes one year and didn't like them, mostly because I don't really understand them and have gone back to zinc anodes.

I have been told by Pros- you can't over zinc.

That said...one on a shaft should be enough provided it is changed when 1/2 eaten away.

I went to aluminum zincs last year and only put one on. I used to put two regular zincs on and at the end of the season they were eaten but not bad. Last year when we pulled the boat in October, and I went in late, it was July before I got in, the zincs were shot.

I think I am going back to zinc collars.

One thing you need to consider, 7 months in fresh water. A regular zinc might not work. You might need aluminum.