Oxidation

[barkleydave]

I have seen the white oxidation in other aluminum boats. Most often I find it hiding under fittings. Most common source is salt oxidation.
I boat that has been in salt water and salt water gets trapped under the undercoating it will oxidize the aluminum.

Other chemicals can also cause the same condition. Use of various bilge cleaners or home brew cleaners can also cause the same.

Galvanic corrosion is most common seen on hard exposed edges. (Rudder edges, chines, etc;)

Clean the area look for pitting in the aluminum.

Use ONLY a stainless steel brush on hull and aluminum oxide sandpaper.
Clean, Etch, If it is an areas which often holds water I would also put several epoxy barrier coats just to protect it.

Like Rodger explained it is pretty common and often not a major concern if your electrical is solid and anodes are well maintained.

You will also see serious oxidation around a strut bearing if a metallic bearing was installed!

safe boating,