No chemical will help.
My own process for removing silicone is:
1) using a chisel on the largest amounts
2) using a knife (I have an old kitchen "steak" type knife with a relatively flexible blade) on what remains
3) using sandpaper on the surface to remove the "residue" (check by wiping some water on it - if water no longer "beads" or "pools" - silicone is finally gone).
While doing that, I keep cursing the PO and whoever was the first dumass that thought up the idea of using silicone as a sealant on a boat.
(Just had to rebed the dorade boxes and, you guessed it, more silicone)