Haloing around thru hull sensors

[silverback]

Anybody have a good explanation as to the cause of "haloing" of paint around thru hull sensors, such as a depth sounder sender?

 

[Boatsb]

Galvanic reactions

 

[Captain Ralph]

Sometimes pretty patterns around thru hull plumbing and hardware, I've always assumed (without a lot of thought) it is galvanic erosion involving the metals in the paint and the boats hardware.

 

[SEVEN]

You are correct