I had my rudder on a Jeanneau
43DS snap right off at the hull
join while at sea as well. I contacted Jeanneau
directly and it took a bit over 3 weeks to get a rudder to me using expedited shipping
(I was in the British Virgin Islands
, there are worse places to spend time).
I know that sinking feeling when the wheel
suddenly goes loose, the boat turns sharply into the wind
and in my case I could see the rudder bobbing away in the waves so I knew that I was in trouble. At least there was no water ingression but it did take a day before I got a tow; I tried everything short of ripping out an inside door to use as a true star-board side rudder but combination of heavy seas and variable winds and a fin-keel made that a difficult task.
In my case the reason that the rudder broke off at the hull join was not directly possible to determine, but was most likely due to a hairline fracture due to a grounding before I bought the boat, coupled with crevice corrosion
in a position where it could not be easily seen and the boat was kept in an electrically active spot so there might have been a year's worth of electrolysis
to help the chemical and mechanical process along.
If you drop the remaining stock early enough a metallurgist should easily be able to do some forensic work.