Join Date: Feb 2003
Location: New England USA
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That is what a zinc should do, wear out! They are "sacrificials" and give up their life in the valiant defence of much more expensive items, like props, shafts, struts, and the like. If you feel you are going through them too fast, you might look at your electrics. Stray currents from an un-isolated shore power connection could be eating them up. Just be happy you are just replacing zincs instead of the more costly items.
I now go through two "bullets" a year on my prop shaft, four a year before I put the galvanic isolator on line. I was having to dive over and replace them underwater halfway though the season. But you should give them a monthly "look-see" just to make sure they are fine anyway.