I
recall the same discussion when they
lost the rudders and the boat. Maybe it was on another forum that I 'owned up' to my Nautitech 40 rudder shafts being only 1 1/4" and tube, not solid. I just checked again, since I have spare rudder bearings, and you can see from the
photo the diameter is 34mm or 1 5/16".
Please don't turn this into a Nautitech bashing opportunity. They may be one of the smaller production yards but there must be detailed design calculations and a wealth of experience. My only point, I think, is that it would be wrong to knock the Alpha people on the suspicion that they cut corners and reduced factors of
safety or whatever.
I should add though, the Alpha 42 rudder blades look significantly larger than the N40. To me, they look larger than necessary (but there I go - pretending I know about yacht design..)