Which Zincs

[Bigohshin]

I've just scraped the hull on my full keel Formosa 41 Ketch.
Diver suggested 1 1/2 collar zinc for the shaft. That seems easy to fix/replace.
Next zinc he suggested is ZHC5 zincs one for each side of rudder.
Is there a source explaining what zincs and sizes are needed per this boat and or others?
Seems like a lot, the zincs aren't cheap and quite large.
Thx

[a64pilot]

You can overzinc but it’s tough to do on a fiberglass boat.
Zincs are insurence, they may seem expensive, but can really save money in the long run.
They have to be bonded to work of course.