My boat is out of the water for bottom paint, inspection and repair as necessary. The rudder was found to be cracked at the top, forward end extending down for about 6" and across the top extending back about 6". Yesterday I trimmed out all the damaged area, cut back under the fiberglas skin as far as I could. Then I refilled the area with epoxy resin, milled fiber and 1/4"chopped fiber. All this 'stuff' was retained by using a piece of stiff plastic to wrap around the front of the rudder and make a mold. My question is, the interior that I had access to appears to be a mix of resin and colloidal silica. I had assumed that the interior would be a foam core. Does anyone know how the rudder was built? My repair will be stronger that the original, but I am curious about the construction.