Zinc Replacement

[JWT]

Our boat is in Santa Cruz CA. Curious about how often it is recommended to replace zinc. Alejuela 38 with a bronze folding prop. Just pulled the boat to repaint the bottom and replace zinc etc but now have heard that they should be replaced almost monthly? Thought that this was a semi yearly type of thing.
Thanks for your suggestions.

[Island Time O25]

My understanding is that zinc needs to be replaced for sure when it gets to about 1/2 of it's original size. I was told that if lets say it takes 6 months in your particular area and conditions for the zinc to lose 1/2 it does not mean that it will take another 6 months to lose the other half but that this will happen much sooner. Thus the need to replace. I basically leave the old zinc on and put a new zinc nearby. Next haulout I replace the older one and so on. This way I always have a back up zinc taking up any surges in electolysis, etc. Some people I know have more than 2 and/or put another one on the shaft insude the hull, which also acts as a brake in case of shaft coming out of its slot.

Another thing to consider are your neighbors and their electrical situation. I was told that the worst culprits are docked boats plugged in into shore power, marinas' own stray power, etc. A friend when docking for extended time in unfamiliar place drops a zinc "dolphin" off of his stern for added protection of the prop and the shaft.

[fstbttms]

Replace anodes when they are 50% depleted. If this occurs on a monthly basis, you have an electrical issue, either aboard your boat, a neighbor's or possibly with the shorepower system. They should last much longer.

What prop do you have?