Zinc's
 

How often do you change the zinc's on your outdrives? Our marine just told us every two years, previously we had gone much longer than that.

Observation
 

Look at them. If they are showing signs of deteriorating, replace them. I think I had 3 on my Mariah. When one was looking a little worse for wear, I had all replaced.

Dave

Zincs
 

Zincs last a long time in fresh water. Actually, I think its something else in fresh water and zinc for salt. Somebody will chime in with better info. If your boat is on a trailer or valet, change may be rare.

Magnesium anodes

Yup
 

Yeah this if you only boat on/in fresh washer. New boats don’t usually come with magnesium so you should check. If your boat has been in the water for a few years and they still look new they probably are not magnesium