I would not rely on just resin and Cabosil to fill a hole in my hull, especially below the water line. Cabosil offers no structural benefit. Basically, you are creating Bondo. Though I have seen it many times, I do not actually believe in the existence of Structural Bondo. With a lot of flexing and pounding that boats take, improper repairs will crack quickly.
The following diagrams describe the method that I would use to fill holes drilled in stringers. The first illustrates the existing hole drilled through a wood stringer laminated into a hull.
Drill existing hole slightly oversize to achieve a good bond between dowel and good wood in stringer.
Install dowel with wood glue that has good water resistance like Titebond 3. Allow the wood glue to fully cure before glassing it over. Sealing over uncured wood glue could prevent the glue from fully curing and the uncured glue could contaminate the composite laminations.
Feather the glass back evenly all around the repair approximately one inch per layer of glass up to final thickness. Use a coarse grinding disk to achieve as rough a surface as possible to promote mechanical adhesion between new laminations and existing glass. Blow off the grinding dust with clean dry compressed air. Any grinding dust remaining on this surface can create a boundary layer that prevents proper adhesion of the new laminations to the existing glass. Any moisture or oil from an air compressor can act as a release agent that will lead to delaminations.
Finish the new laminations down flush with the existing glass. Seal over the repair with gel coat or flow coat to seal the repair and to prevent water from wicking down the fiber stands and degrading the resin as well as providing UV resistance.
To fill a hole in the hull, feather and laminate both sides as described above.
