I can''t recall precisely how the Rhodes 19 centerboard is constructed but you can''t repair it while its still in the boat. It sounds like the centerboard is waterlogged and the fairing material is delaminated. Leaving the centerboard in the water will continue this delamination process and if the centerboard has a metal core continued exposure may push the centerboard past being restorable.
I guess the first task to planning a repair would be to determine how the centerboard was constructed in the first place. My recollection is that they had a fiberglass covered metal core (but that could be wrong).
The first step would be to remove the fiberglass sheathing where it has delaminted and to dry out the centerboard. Small delaminations can be injected with epoxy if the area can be throughly dried out. It will probably be easier to just remove the glass skin, fair up the core,and reglass the whole centerboard. You won''t know the real answer until you know how the centerboard was built and what condition the core is in.