First off, this first pic was taken in 2011---

The boat's been out a couple of weeks now. The hull has several thru holes surrounding corroded areas. Only one of the holes was the leak, the others opened up easily with my finger or the pressure washer.

The first 2 pics show the difference between March 2011 and now.

Note the circled areas, and some small spots down the length of the hull. These areas were just starting to show missing metal back then, very little, like .01" or so. I treated and primed painted these and a few other areas.

Also note the tracking fin, specifically that it's bottom edge is still all there...




this is now I've circled the same area I fixed in the first pic. Notice the bad area didn't spread out. None of the areas I fixed in '11 got larger. But they got deeper. And a whole slew of other areas have cropped up.




and compare the tracking fin, this pic is in the same area as the first pic...




--this pretty much explains the whole story: Rust didn't do this, this is purely an electrolysis issue. Rust is just a by-product...