Alarming Rudder Stock Corrosion on a Sun Odyssey 349 under 8 years old! 

Jeanneau have immediately responded by offering me new rudders and bearing FOC. They advise that they have identified a crevice corrosion problem affecting some 349s and have modified the rudder to prevent it. The speed of their response suggests that they have a policy in place relating to this issue.

You appear to have isolated galvanic corrosion & electrolysis thru investigation/ testing from being a cause. The depletion of the oxygen theory along with the film evidence reflecting an intense localized circumference of corrosion above the bushing does support this school of thought. The pitting within the bushing may or may not. Had a similar situation experienced with 416 SS utilized for underground natural gas piping addition for a hospital addition in San Diego, CA. The line was bedded with sand and above the crown, with the trench remainder backfilled with a cement/ sand slurry. This created an oxygen seal, where the line started to corrode and leak under the high operating gas pressure. The lines were replaced after 4-5 years with industry standard yellow polyethylene piping. Being a marine environment only assists the advancement of this corrosion. The depletion of oxygen theory is applicable, but there's always a 4th option which someone more knowledgeable may suggest.

SV Hilma had an issue when their rudder fell off their SO in the Pacific. On their series of videos I recall them saying there was a loose wire in the binnacle which had promoted electrolysis. Jeanneau gave them a replacement rudder which they fitted at sea.

I would really be interesting what the manufacturer has to say.

That’s pretty bad crevice corrosion. I would agree that oxygen depletion is a likely cause. Do you know what grade stainless it is? Is the shaft attracted to a magnet? My question would be even if the manufacturer accepts so,e responsibility and helps you out with replacement, what is to prevent it happening again? I doubt you are the first owner who has experienced this problem, so it might be worth asking if any changes were made to the design since your boat was built.