Re: rudder replace
If you google it seems the standard is to make two female glass sections of the rudder itself, place a steel post with welded plates between the two sides of the rudder and fill the whole thing with two part foam. Then some glass at the edges I think.
However for a transom hung small boat like yours, esp if going kick up, a wood cored rudder may not be bad. You can use western red cedar (easy to work with into a naca profile, but not very strong so you need to beef up the glass layup) or else white oak, which is much stronger but more difficult to work with. You glue a bunch of 2x2's together, alternating the grain (to prevent warping) then shape it and glass it. Shaping it is easy if you have a router and electric plane, go on the woodenboat forum for lots of help on this process (I even have a write up of a plywood foil I did for a previous boat. Don't use ply BTW it is waaaay too heavy).
You may be able to get away with an aluminum rudder, beach cat style, but you will have no NACA profile that way.