Re: Rudder damage - urgent advice needed
The conditions that cause corrosion problems for almost any metal seem to be so variable as to make predicting what might be weakened almost unpredictable. One thing for sure is that once any current is present, different potentials will cause electrolysis. That is interesting about the aluminum shaft. Aluminum really disintigrates quickly once any current gets to it near other metals.
I replaced the bronze rods that hold my old wood rudder together last year with the same. They have been there since 1967 and had some surface scaling but were still solid underneath after 45 years. I was able to unthread the nuts and disassemble the rudder pretty easily. IMO silicone bronze is still the toughest material over the long term in a marine environment. The large 1-1/2" SB thru-hull that was used for the head, with a little wire brush work, looks like new as well with no sign of any corrosion.
Alberg 35: With a philosophical flourish Cato throws himself upon his sword; I quietly take to the ship.