Extensive Zinc Corrosion caused by Fish Finder

Purchased my PT last December and cruised her back to Annapolis from Norfolk (had unseasonably good weather for Dec). Between the time of the survey in Norfolk and being hauled for winter back in Annapolis, I noticed significant corrosion of the all zincs during what was essentially a week long cruise.

I replaced all zincs before Spring launch and purchased a reference electrode to investigate the cause. Tuned out to be the installed Furuno fish finder. I have not used the fish finder all season because I can't seem to isolate the problem and my zincs have shown normal corrosion. Anyone had a similar problem?

Mike

How do you know it was the fish finder? Was it wired incorrectly?

sounds like a stray current corrosion issue internal to the ducer....especially that it was that quick and you isolated it to what I gather is a bronze thru hull ducer?