Originally Posted by Stout
Had our NT42 hauled this week for maintenance. Bottom paint, prop pulled for ding repair. Also, had the rudder shoe pulled to check the bolts for corrosion that secure it to the keel. The bolts look brand new! While off, we pulled the rudder to examine the rudder shaft because the Tides marine shaft seal keeps leaking shortly after replacement. Found crevice corrosion on the shaft with bad spots where the seal makes contact. Will have to be replaced. Waiting for a quote to cut off bad shaft, weld a flange onto the rudder side and build a new flanged shaft to go through the hull bearing and seal. This will make it easier to fix “next time”. (Sorry about sideways pix, did this on the iPad and do not know how to rotate in Apple)
Had a somewhat related issue on my previous Pacific Trawler 40, which already had a two-piece rudder shaft, with attendant flange immediately below the hull. When diagnosing a leaking Tides Marine seal, I discovered not shaft crevice corrosion (as you show in your photos), but a misalignment between the bearing surfaces of the upper shaft, and the rudder. This misalignment ensured subsequent leakage of the Tides seal, even after replacement.
The fix was to send both the stub shaft and the rudder to a machine shop capable of not only measuring the straightness of the assembly, but capable of measuring the straightness of the shafts, and machining the flanges dead square to make sure the ASSEMBLY has a runout of less than 0.001 in. INCLUDING the lower stub shaft at the bottom of my rudder.
I don't know how Nordic Tugs designed your rudder installation. But if your boat ends up with three bearing locations (upper rudder bearing, seal, and lower rudder bearing), as did my Pacific Trawler, you need to do your due diligence that any modifications to your rudder shaft ends up with a straight ASSEMBLY. And that's post-welding, for sure. It's not easy to ensure shaft alignment on multi-part flanged shaft assemblies.
And I'm not so sure that your proposed "fix" is much of a fix, in as much as you can easily remove your rudder shoe should your seal leak again. Remember, the flanged approach to your "fix" only means you can remove the rudder without removing the shoe. You still have to haul the boat to unbolt the flange to service the shaft seal. Six to one, half-a-dozen the other.
And I would also suggest that there are several welding-related "fixes" for stainless shaft corrosion that don't involve changing the rudder design. But I would again caution you to have your shaft measured for runout and straightness between however many bearing surfaces your boat has, again AFTER any heat process that's applied to your shafting.