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post #12 of Old 07-04-2013
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Re: Spade rudders vs blue water passage making

Originally Posted by capecodda View Post
RichH...that's interesting. I don't think I've ever met anyone who dropped their rudder and did the inspection you describe. Sounds like a good idea before taking a long offshore trip on a less than new boat.

My recollection isn't perfect, but I think this rudder shaft was around 4" in diameter solid stainless. LH did lots of work in Taiwan, so I wonder about the quality of stainless.

I know Fontaine Yacht design has also done some of these shafts in carbon fiber. In talking with them, it was not only weight but also less bend, which reportedly made the bearing work better.
Solid shafting will not merit anything as essentially all or most of the bending stress is carried in the first few % of depth along the surface of the material. Crevice corrosion AND bending stresses which promote fatigue (cracks) because the endurance limit was exceeded .... once it penetrates into the macrostructure will cut even 'solid' metal like a knife through butter; same as how a puny little girl could rip apart an old fashioned thick phone book. When it comes to 'cantilevers' you want 'good' not 'solid'.

The reason pintle/hinge hung rudders are preferred for 'blue water' is they are less subject to bending stress because of their inherent (hinge) 'support'. Cantilevers are always 'bending'.
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