It is is as deep as stated iot is clearly through the gelcoat, gel coat is maybe the thickness of construction paper, beyond that you are into glass or core. If you do not see foam, you have solid glass which first needs glass work, it can be done yourself but I highly advise having someone with this experience do it with you, not just you alone. You will need to first gring out the damaged area to get it smooth, no gaps ir rough spots, if you leave them you will have air pockets where the resin and glass will not adhere well. Once flat you need to first coat the damaged hull area with good resin on a brush, make sure it coats every part of the surface, this will keep the hull watertight and is important, then roll the glass with resin to soak it through evenly, lay it on the damaged area and then roll it in using a fiberglass rollers tool, get ALL air pockets out, having a smooth surface to work with makes this easier. Then, once done put a layer of wax paper over the hull, and then use a foam block above a wood base and hammer it in to form to the hole and keep the glass from falling off. Typically you will put more hardener in the resin when working with a boat sitting ona trailer and not upside down, the glass mat will want to fall off from gravity. Once it drys pull wax paper off and grind area flat, any air bubbles present grind out, then clean out with acetone and redo steps again until you build the area outward to fill the hole. Once slightly protruding from the hull grind flat, or a paper size below. Once this is done you can roll on a color matched gel coat repair kit from Grady dealer, they will match your hull color very closely and be the way to go. As you see it is not an easy job and to do right is time consuming, having someone with experience in this is needed to do it right. Leaving it to a pro is best but not a necessity. Best of luck to you and hope it works out well for you.