How long should my zincs last?

Depending on the electrical current in and around the boat, expect to change your zincs as frequently as every two weeks or seldom up to two years.  When you see 45% wastage it is time to replace the zinc.  Check them regularly and replace them at least every year. Check them after a change of location or new boats arrive near you.  A new neighbor in the marina or a deteriorating ground on your boat could dramatically change the speed at which your anodes erode.