Originally Posted by Jim Cate
So, if you are fabricating rudders from scratch, why must they be so thin in cross section?
Good question, Jim. Mainly it's the practicalities of fabrication here in Phuket, Thailand
, combined with my lack of knowledge (& thank you, everyone, for attempting to remedy that somewhat - up-hill battle, I know
Basically, most rudders (including the first stab at ours by our machinist) have airfoil-shaped sections welded to the rudder stock & then a skin placed over those "stringers" (if you will). The problem with this design is that it requires welding around
the shaft. Weld material is brittle & penetrates the shaft somewhat. My shafts are perhaps a bit small (1.5"), so I didn't want to weaken them at all if possible (we actually lost
in 1986 because the previous owner had welded across a cap-shroud chain-plate, so I'm a bit sensitive here).
I don't want welding around the shaft, I want all welding to be longitudinally along the shaft. I also feel that butt-welding plate(s) perpendicular to the shaft puts those plate(s) in bending, which is inherantly weak (even though this is fairly standard for rudders these days).
So I was exploring the possibility of welding the skins of the rudder blade to the outer edges of the shaft, which would make the blade only slightly wider than the shaft. But now I realize why we need a thicker chord.
Now the problem will be to find a way to attach the (wider) skins to the shaft in such a way that it's mechanically strong as well as practically doable. I've got an appointment with my machinist tomorrow, so I'll discuss the matter with him then. Except that I don't speak Thai & he doesn't speak English
Ah, the joys of cruising!
Osiris, thanks for the many links. Some good info in there! (but 1 & 5 actually go to the same place).