Sorry to hear about your misfortune on both counts.

RM auto paint produced a product called "wax and silicone remover" for years, and I believe they still do, I just can't recall the product number. if you find a local supplier of RM (which is now owned by BASF) they will be able to help you.

It will work to a degree with due diligence, but the hardened silicone must be removed first, and I assume you will have to do it mechanically by whatever means is required.

When you think that all the silicone is gone, and you can't feel any evidence of it with your fingers, then is the time to use the RM solvent to clean it up. You will need several applications of this product; the procedure is to apply liberal amount of solved and then dry with a clean cloth or towel. Then repeat the procedure with new cloth for each application.

If it was me, I would isolate the area by masking off the rest of the boat, leaving only a small area around the silicone, and when you are finished with removal and solvent washing I would remove the masking and wash the whole boat with solvent (RM) just to be sure the boat is decontaminated.

I have recently retired from a 41 year career as an automotive painter and know the perils of silicone contamination.