This, by the way, is a piece on various types of rudder construction.
http://www.sailfeed.com/2012/09/fiberglass-boatbuilding-rudder-construction/
Some high tech rudderless have machined cores closed cell cores. In those the carbon fiber post actually is tied to the skin without an integral framework.
http://www.fastcomposites.ca/publications/WhitePapers/BetterSpadeRudder.pdf