that seems a little fast to lose an entire anode.
I agree!
Either wrong weight/size
zinc or you have other abnormal problems.
I recently had a big pounding to my rudder. I had diver clean bottom, check rudder and since it have been 5 months since my last
zinc change, I was going to changed my $10
zincs , I thought go ahead and change him. He has a Go Cam under water.
Reported back...
1) clean bottom (Slim Resistant paint works0, a few barnacles on prop and thru hull bronze ferrules.
2) Rudder good
3)
Zincs looked brand new on the shaft.
(so your 4 months hmmmm?) No change!
One good reason to use the same diver, he knows your boat, and mine keeps before and after pictures in his files.
Jim...