Depth readout problem with bronze thru-hull

[noelex 77]

I cannot see stray current as the cause of your problem. Is there a freshwater discharge close by? Fresh and saltwater often don't mix well and the interface between the two will reflect sound waves.
The minimum reading of most depth sounders is about 0.3m so a freshwater interface at this depth could cause the readings you describe.

[Reefmagnet]

Could it be interference from another transducer nearby, or AC plugged into the boat? Noelex, the Nexus system reads 0.3 m when depth exceeds 100 m for some odd reason as mine does the same. A bit disconcerting until you realise that is what is happening!

[powerpak]

Nexus has now tested the old transducer and confirmed the depth reading is non functioning and temperature and speed are erratic, and the old WSI box is damaged. They believe that a leak or fault somewhere in the 240V power supply is to blame, either on a nearby boat or in the marina system. That definitely raises galvanic corrosion issues.