Trident
Well-known member
Bronze is close to stainless and thus considered safe from galvanic corrosion or as most sources I read state its "unlikely"
My rudder stock is held by phosphor bronze bushes in the rudder shoe. The 316L shoe I made 6 years ago is still perfect . However, the last time I lifted the boat, the stock just above it (might not be 316 though non magnetic) having lived happily for 40 years had an area eaten out of it by corrosion that I clean and welded back in . I have checked and checked for stray currents and can trace none so all I am left with is galvanic. Could the bush (which I reused what I made new shoes as it was perfect ) be an issue? It seems like something changed - the stocks were fine for years, and on one rudder still are and the zinc on that rudder corrodes slowly but surely. The zinc on the damaged rudder was perfect after a year on, and after my repair I changed it and the new one still is completely untouched . (Another thread on rudders it was suggested a stainless rudder and stock don't even need an anode )
There is no damage after a year since the repair but some surface corrosion (probably from the stainless welding rod being different quality to the main metal) but I still can't figure out what cause the initial problem... except that after covid the boat sat in Chi Harbour mud for almost 3 years with only 4 - 6 hours a day afloat (and shore power connected without isolation but again no stray current from my boat and few hours in the day when others boats might have a circuit with me) . Would the mud perhaps destroy the passive layer and then inhibit further oxygen reaching the surface? I am now afloat continually and not even connected to shore power - I just want to put to bed what might have caused this so I can stop worrying that it may happen again.
My rudder stock is held by phosphor bronze bushes in the rudder shoe. The 316L shoe I made 6 years ago is still perfect . However, the last time I lifted the boat, the stock just above it (might not be 316 though non magnetic) having lived happily for 40 years had an area eaten out of it by corrosion that I clean and welded back in . I have checked and checked for stray currents and can trace none so all I am left with is galvanic. Could the bush (which I reused what I made new shoes as it was perfect ) be an issue? It seems like something changed - the stocks were fine for years, and on one rudder still are and the zinc on that rudder corrodes slowly but surely. The zinc on the damaged rudder was perfect after a year on, and after my repair I changed it and the new one still is completely untouched . (Another thread on rudders it was suggested a stainless rudder and stock don't even need an anode )
There is no damage after a year since the repair but some surface corrosion (probably from the stainless welding rod being different quality to the main metal) but I still can't figure out what cause the initial problem... except that after covid the boat sat in Chi Harbour mud for almost 3 years with only 4 - 6 hours a day afloat (and shore power connected without isolation but again no stray current from my boat and few hours in the day when others boats might have a circuit with me) . Would the mud perhaps destroy the passive layer and then inhibit further oxygen reaching the surface? I am now afloat continually and not even connected to shore power - I just want to put to bed what might have caused this so I can stop worrying that it may happen again.
