I boat in the great lakes (only fresh water) and switched to magnesium
anodes last year instead of zinc. After one season (5 months in the
water) the magnesium anodes are completely shot. They are riddled with
holes and are falling apart. The zinc anodes took years and years to
look this way.
I know that's what's supposed to happen, but is it possible something
is wrong if they deteriorate so quickly? I'm putting a new pair on
this week for this new season, but I didn't expect to have to change
them every year.
By the way, it's a 30 foot cruiser with twin Volvo duoprops so I have
to change 4 anodes total, 2 for each outdrive.

One more thing, someone told me to add a round, disc anode to each
stainless trim tab and that it would work better.

Ideas, comments?

Thanks